Endocrine and Reproductive Systems
• This artificially colored
scanning electron
micrograph shows
sperm (orange
objects) on the
uterine wall
Endocrine and Reproductive Systems
The Endocrine System
• If you had to get a message to just one or two of your
friends, what would you do?
• You might use the telephone
• Wires running from your house to theirs would carry the
message almost instantaneously
• The telephone is a good way to reach a small
number of people, but what if you wanted to get that
same message to thousands of people?
• You might decide to broadcast it on the radio,
sending the message in a way that made it possible to
contact thousands of people at once
The Endocrine System
• Your nervous system works much like the telephone: Many
impulses move swiftly over a system of wirelike neurons that
carry specific messages from one cell to another
• But another system, the endocrine system, does what the
nervous system generally cannot
• The endocrine system is made up of glands that release their
products into the bloodstream
• These products deliver messages throughout the body
• In the same way that a radio broadcast can reach thousands or
even millions of people in a large city, the chemicals released
by the endocrine system can affect almost every cell in the
body
• In fact, the chemicals released by the endocrine system affect
so many cells and tissues that the interrelationships of other
organ systems to one another cannot be understood without
taking the endocrine system into account
ENDROCINE SYSTEM
• Consist of glands that transmit chemical
messages (hormones) throughout the body
• Hormones:
– Substances that are produced in one part of the body
and specifically influence the activity of cells in
another part of the body
– Blood transports the hormones
– Each hormone affects only specific cells (target cells)
that have receptors for the specific hormone
Hormones
• The chemicals that “broadcast” messages from the
endocrine system are called hormones
• Hormones are chemicals released in one part of the
body that travel through the bloodstream and affect
the activities of cells in other parts of the body
• Hormones do this by binding to specific chemical
receptors on those cells
– Cells that have receptors for a particular hormone are called
target cells
– If a cell does not have receptors or the receptors do not respond
to a particular hormone, the hormone has no effect on it
Hormones
• In general, the body's responses to
hormones are slower and longer-lasting than
the responses to nerve impulses
• It may take several minutes, several hours, or
even several days for a hormone to have its
full effect on its target cells
• A nerve impulse, on the other hand, may take
only a fraction of a second to reach and
affect its target cells
Glands
• A gland is an organ that
produces and releases a
substance, or secretion
• Exocrine glands release their
secretions, through tubelike
structures called ducts, directly
to the organs that use them
• Exocrine glands include those
that release sweat, tears, and
digestive juices
• Unlike exocrine glands,
endocrine glands release
their secretions (hormones)
directly into the bloodstream
• The figure at right shows the
location of the major endocrine
glands in the human body
GLANDS
• The body has two types of glands
– Exocrine: glands with ducts
• Sweat glands, oil glands, salivary glands, pancreas digestive
glands
– Endocrine: ductless glands
•
•
•
•
Secrete directly into the blood
Located throughout the body
Glands: thyroid, parathyroid, adrenal, pineal, gonads, thymus
Specialized cells: hypothalamus, islets of Langerhans
(pancreas), digestive glands of stomach and intestine
EXOCRINE GLANDS
• Secretions from
glands with ducts
move through tubes
ENDROCINE GLAND
• Secretions from
endocrine glands are
released into the
bloodstream
Endocrine System
• Endocrine glands
produce hormones
that affect many parts
of the body
• What is the fuction of
the pituitary gland?
Endocrine System
HORMONES
• Two main types:
– Protein
– Lipid
Hormone Action
• Hormones may be classified
as belonging to two general
groups—steroid hormones
and nonsteroid hormones
– Steroid hormones are
produced from a lipid called
cholesterol
– Nonsteroid hormones
include proteins, small
peptides, and modified
amino acids
• The two basic patterns of
hormone action are shown in
the figure at right
Hormone Action
• The two main types of
hormones are:
– Steroid hormones
(top)
– Nonsteroid hormones
(bottom)
• How are steroid
hormones different
from nonsteroid
hormones?
Hormone Action
Steroid Hormones
• Because they are
lipids, steroid
hormones can cross
cell membranes
easily, passing
directly into the
cytoplasm and even
into the nuclei of
target cells
LIPID HORMONES
• Steroid
• Diffuse through the cell membrane into
cytoplasm
• Binds to a receptor molecule to form a receptorsteroid complex that enters the nucleus
– Stimulates genes to synthesize mRNA
– mRNA moves into cytoplasm forming proteins at the
ribosome
• Proteins functions as enzymes , promoting reactions that
bring about the changes associated with the hormones
Steroid Hormones
•
•
•
•
•
A steroid hormone enters a cell by
passing directly across its cell
membrane
Once inside, it binds to a
steroid receptor protein (found
only in its target cells) to form a
hormone-receptor complex
The hormone-receptor complex
enters the nucleus of the cell,
where it binds to a DNA control
sequence
This binding initiates the
transcription of specific genes
to messenger RNA (mRNA)
The mRNA moves into the
cytoplasm and directs protein
synthesis
Steroid Hormones
• Hormone-receptor
complexes work as
regulators of gene
expression—they can
turn on or turn off
whole sets of genes
• Because steroid
hormones affect gene
expression directly,
they can produce
dramatic changes in
cell and organism
activity
LIPID HORMONES
LIPID HORMONES
• Steroid hormones
penetrate the target
cell membrane
LIPID HORMONES
• Once inside the target
cell, the hormone
binds to a receptor
protein
LIPID HORMONES
• The newly formed
hormone-receptor
complex enters the
nucleus of the target
cell and binds to
DNA, activating
mRNA transcription
LIPID HORMONES
• Genes are activated,
mRNA is transcribed,
and new proteins are
synthesized
Nonsteroid Hormones
• Nonsteroid
hormones generally
cannot pass
through the cell
membrane of their
target cells
PROTEIN HORMONES
• Most Hormones
• Either complete proteins, polypeptides, amino
acids, or amines
• Remains outside the cell (does not enter)
• Hormone (first messenger) attaches itself to a
receptor on the membrane of the target cell
– Activates an enzyme in the cell membrane
– Enzyme converts ATP inside the cell to cyclic AMP
– AMP (second messenger) initiates changes within the
cell by activating specific enzymes
Nonsteroid Hormones
•
•
•
•
•
A nonsteroid hormone binds to
receptors on the cell membrane
The binding of the hormone
activates an enzyme on the inner
surface of the cell membrane
This enzyme activates secondary
messengers that carry the
message of the hormone inside
the cell
Calcium ions, cAMP (cyclic
adenosine monophosphate),
nucleotides, and even fatty acids
can serve as second messengers
These second messengers can
activate or inhibit a wide range of
other cell activities
PROTEIN HORMONES
PROTEIN HORMONES
• An amino acid-based
hormone acts as a
first messenger by
binding to receptor
proteins located on
the target cell
membrane.
PROTEIN HORMONES
• The hormonereceptor complex
indirectly activities an
enzyme that converts
ATP to cyclic AMP
PROTEIN HORMONES
• Cyclic AMP indirectly
activities other
enzymes that cause
changes in the target
cell
Prostaglandins
• Until recently, the glands of the endocrine system
were thought to be the only organs that produced
hormones
• However, except for red blood cells, all cells have
been shown to produce small amounts of
hormonelike substances called prostaglandins:
– Prostaglandins get their name from a gland in the male
reproductive system, the prostate, in which they were first
discovered
• Prostaglandins are modified fatty acids that are
produced by a wide range of cells:
– They generally affect only nearby cells and tissues, and
thus are known as “local hormones”
Prostaglandins
• Some prostaglandins cause smooth
muscles, such as those in the uterus,
bronchioles, and blood vessels, to contract
• One group of prostaglandins causes
the sensation of pain in most
headaches
– Aspirin helps to stop the pain of a headache
because it inhibits the synthesis of these
prostaglandins
PROSTAGLANDINS
•
•
•
•
Special group of lipids
Function as cell regulators
Not produced by specific glands
Powerful substances produced in small quantities by
virtually all cells of the body
• Act locally not through blood transport
• Effects:
–
–
–
–
Relaxation of smooth muscle of air passages and blood vessels
Contraction of uterine and intestinal walls
Regulation of blood pressure
Stimulation of inflammatory response to infection
Control of the Endocrine System
• As powerful as they are, hormones are
monitored by the body in order to keep the
functions of different organs in balance
• Even though the endocrine system is one of
the master regulators of the body, it too must
be controlled
• Like most systems of the body, the
endocrine system is regulated by feedback
mechanisms that function to maintain
homeostasis
Control of the Endocrine System
• Recall that feedback inhibition occurs when
an increase in any substance “feeds back” to
inhibit the process that produced the
substance in the first place
– Heating and cooling systems, controlled by
thermostats, are examples of mechanical
feedback systems
– The hormones of the endocrine system are
biological examples of the same type of process
FEEDBACK MECHANISM
– Self regulating system
– Mechanism in which the end products of a
series of steps controls the first step in the
series
• Positive feedback: the end product controls the
first step
• Negative feedback: end product inhibits the first
step
– Most endocrine glands have a negative
feedback mechanism which maintains
homeostasis in the body
Controlling Metabolism
• To see how an internal feedback mechanism
regulates the activity of the endocrine
system, let's look at the thyroid gland and its
principal hormone, thyroxine
• Thyroxine affects the activity of cells
throughout the body, increasing their rate of
metabolism
– Recall that metabolism is the sum of all of the
chemical reactions that occur in the body
• A drop in thyroxine decreases the metabolic activity of
cells
Controlling Metabolism
•
•
•
•
•
Does the thyroid gland determine how
much thyroxine to release on its own?
No, instead the activity of the thyroid
gland is controlled by the hypothalamus
and the anterior pituitary gland
When the hypothalamus senses that the
thyroxine level in the blood is low, it
secretes thyrotropin-releasing hormone
(TRH), a hormone which stimulates the
anterior pituitary to secrete thyroidstimulating hormone (TSH)
– TSH stimulates the release of
thyroxine by the thyroid gland
High levels of thyroxine in the blood
inhibit the secretion of TRH and TSH,
which stops the release of additional
thyroxine
This feedback mechanism, shown in the
figure, keeps the level of thyroxine in the
blood relatively constant
Feedback Mechanism
•
•
•
•
•
One way the endocrine system
is regulated by internal
feedback mechanisms is by
maintaining the rate of
metabolism
When the hypothalamus senses
that the level of thyroxine in the
blood is low, it secretes TRH
TRH stimulates the anterior
pituitary to secrete TSH
TSH stimulates the thyroid to
release thyroxine
Increased levels of TSH and
thyroxine inhibit TRH secretion
by the hypothalamus
Feedback Mechanism
Feedback Mechanism
• Recall that the hypothalamus is also sensitive to
temperature
• When the core body temperature begins to drop,
even if the level of thyroxine is normal, the
hypothalamus produces extra TRH
• The release of TRH stimulates the release of TSH,
which stimulates the release of additional thyroxine
• Thyroxine increases oxygen consumption and
cellular metabolism
• The increase in metabolic activity that results helps
the body maintain its core temperature despite lower
temperatures
Maintaining Water Balance
• Homeostatic mechanisms regulate the levels of a
wide variety of materials dissolved in the blood and
in extracellular fluids
– These include minerals such as sodium, potassium, and
calcium, and soluble proteins such as serum albumin,
which is found in blood plasma
• Most of the time, homeostatic systems operate so
smoothly that we are scarcely aware of their
existence
• However, that is not the case with one of the most
important homeostatic processes, the one that
regulates the amount of water in the body
Maintaining Water Balance
• When you exercise strenuously, you
lose water as you sweat
– If this water loss continued, your body
would soon become dehydrated
• Generally, that doesn't happen because
your body's homeostatic mechanisms
swing into action
Maintaining Water Balance
• The hypothalamus contains cells that are sensitive
to the concentration of water in the blood
– As you lose water, the concentration of dissolved materials
in the blood rises
• The hypothalamus responds in two ways:
– First, the hypothalamus signals the pituitary gland to release
a hormone called antidiuretic hormone (ADH)
• ADH molecules are carried by the bloodstream to the kidneys,
where the removal of water from the blood is quickly slowed
down
– Later, you experience a sensation of thirst, a signal that you
should take a drink to restore lost water
Maintaining Water Balance
• When you finally get around to taking that
drink, you might take in as much as 1 or 2 liters
of fluid
• Most of that water is quickly absorbed into
the bloodstream
– But this volume of water added to the blood would
dilute it so much that the equilibrium between the
blood and the cells of the body would be
disturbed
• Large amounts of water would diffuse across blood
vessel walls into the tissues
– The cells of the body would swell with the excess
water
Maintaining Water Balance
• Needless to say, this doesn't happen, because the
same homeostatic mechanism intervenes
• When the water content of the blood rises, the
pituitary releases less ADH
– In response to lower ADH levels, the kidneys remove water
from the bloodstream, restoring the blood to its original
concentration
• This homeostatic system sets both upper and lower
limits for blood water content:
– A water deficit stimulates the release of ADH, causing the
kidneys to conserve water
– An oversupply of water causes the kidneys to eliminate the
excess water as a component of urine
Complementary Hormone Action
• Sometimes two hormones with opposite effects act
to regulate part of the body's internal environment
• One way to think about how the endocrine system
functions is to think about driving a car
• A good driver might be able to control a car on an open
highway by using only the accelerator pedal
• But driving around town, even a good driver would get
into trouble using just the accelerator
• There are too many situations in which the brake is
needed to slow the car down
Complementary Hormone Action
• In the same way, many endocrine functions depend
on the complementary effects of two opposing
hormones
• Such a complementary system regulates the level of
calcium ions in the bloodstream
• The level of calcium dissolved in the bloodstream is
kept within a narrow range
• The two hormones that regulate calcium
concentration are:
– Calcitonin, from the thyroid gland:
• Decreases the level of calcium in the blood
– Parathyroid hormone (PTH), from the parathyroid glands
• Increases the level of calcium in the blood
Complementary Hormone Action
• When blood calcium levels are too
high, the thyroid secretes calcitonin
– Calcitonin signals the kidneys to reabsorb
less calcium as they form urine
– Calcitonin also reduces the amount of
calcium absorbed in the intestines and
stimulates calcium deposition in the bones
Complementary Hormone Action
• If calcium levels drop too low, PTH is
released by the parathyroids
– PTH, together with vitamin D, stimulates
the intestine to absorb more calcium from
food
– PTH also causes:
• Kidneys to retain more calcium
• Stimulates bone cells to release some of the
calcium stored in bone tissue into the
bloodstream
Complementary Hormone Action
• You may be surprised that the body
regulates calcium levels so carefully
• This adaptation has evolved because calcium
is one of the most important minerals in the
body
• If calcium levels drop below their normal
range:
– Blood cannot clot
– Muscles cannot contract
– Transport of materials across cell membranes
may fail
Human Endocrine Glands
• The endocrine glands are scattered
throughout the body
• Generally, they do not have direct connections to
one another
• Like signals that are beamed throughout the
country from a broadcast station, the
hormones released from the endocrine
glands into the bloodstream travel
throughout the body, reaching almost every
cell
Human Endocrine Glands
• The human endocrine system regulates a wide variety of
activities
• Any improper functioning of an endocrine gland may
result in a disease or a disorder
• The major glands of the endocrine system include:
–
–
–
–
–
–
–
Pituitary gland
Hypothalamus
Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Reproductive glands
PITUITARY/HYPOTHALAMUS
• Pituitary: located at the base of the brain
– Secretes hormone that control body growth and
regulate the activity of other endocrine glands
– Two portions: both adjacent to the Hypothalamus
• Anterior lobe: connected to the hypothalamus by blood
vessels
• Posterior lobe: connected to the hypothalamus by nerves
• Both form a major link between the
endocrine and nervous systems
PITUITARY/HYPOTHALAMUS
• Neurosecretory cells in
the hypothalamus
produce hormones that
affects the pituitary gland
• The hypothalamus
regulates the posterior
pituitary through axons
and the anterior pituitary
through blood vessels
• Blood vessels in the
posterior pituitary have
been omitted to show
axon projections
Pituitary Gland
• The pituitary gland is a beansized structure that dangles on
a slender stalk of tissue at the
base of the skull
• As you can see in the figure
at right, the gland is divided
into two parts:
– Anterior pituitary
– Posterior pituitary
• The pituitary gland:
– Secretes nine hormones
that directly regulate many
body functions and controls
the actions of several other
endocrine glands
Pituitary Gland
• Controls many other
endocrine glands
• Located below the
hypothalamus in the
brain
• Has two lobes:
– Anterior lobe
– Posterior lobe
Pituitary Gland
Pituitary Gland
• Normal function of the pituitary gland is essential to
good health
• For example, if the pituitary gland produces too much
growth hormone (GH) during childhood, the body
grows too quickly and a condition called gigantism
results
• Too little GH during childhood causes a condition
known as pituitary dwarfism, which can be treated
by administering growth hormone
• Growth hormone used to be in short supply
– Today, however, genetically engineered bacteria are able to
produce GH in large quantities
Hypothalamus
• The hypothalamus is the part of the brain
above and attached to the posterior pituitary
• The hypothalamus controls the secretions of
the pituitary gland
• The activity of the hypothalamus is
influenced by the levels of hormones in the
blood and by sensory information collected
by other parts of the central nervous system
• Interactions between the nervous system
and the endocrine system take place at the
hypothalamus
Hypothalamus
• The posterior pituitary is made up of axons
belonging to cells called neurosecretory
cells, whose cell bodies are in the
hypothalamus
• When these cell bodies are stimulated, the
axons in the posterior pituitary release their
hormones into the bloodstream
• In a way, the posterior pituitary is an
extension of the hypothalamus
PITUITARY/HYPOTHALAMUS
– Two additional hormones are synthesized but
released from groups of cells that extend into
the posterior pituitary gland
• Vasopressin (antidiuretic:ADH): absorption of
water back into blood in kidneys
• Oxytocin: regulates blood pressure, smooth
muscle contraction, milk production, and uterine
contractions in childbirth
Hypothalamus
• In contrast, the hypothalamus has indirect
control of the anterior pituitary
• The hypothalamus produces small amounts
of chemicals called releasing hormones,
which are secreted directly into blood
vessels
• The releasing hormones are carried by the
circulatory system to the anterior pituitary,
where they control the production and
release of hormones
PITUITARY/HYPOTHALAMUS
• Hypothalamus:
– Secrete hormones called releasing factors into the anterior lobe
of the pituitary via blood vessels
• Six releasing factor hormones: each controls the release and
level of specific hormones produced in the anterior lobe of the
pituitary:
– Growth hormone: regulates growth of bones
» Over production: gigantism
» Under production: dwarfism
• Gonadotropic hormone (luteinizing hormone:LH): stimulates
development of sex organs and hormones / controls ovulation
– Adrenocorticotropic hormone (ACTH): stimulates secretions of the
adrenal cortex hormones
– Prolactin (luteotropic hormone:LTH): controls growth of mammary
glands, milk production, maintains corpus luteum
– Thyroid-stimulating hormone (TSH): stimulates production of
thyroxine by the thyroid
– Follicle-stimulating hormone (FSH): controls gamete production
Hypothalamus
• The close connection
between the
hypothalamus and the
pituitary gland means that
the nervous and
endocrine systems can
act together to help
coordinate body activities
• Hormones released by
the pituitary gland are
listed in the figure at right
Pituitary Gland Hormones
• The hypothalamus controls the secretions of the
pituitary gland
• Notice the effect that each hormone produced by
the pituitary gland has on the body
Pituitary Gland Hormones
THYROID
•
•
•
Two lobed gland
Lower part of larynx in the neck
Secretes hormone thyroxine
–
Regulates:
•
•
•
Hyperhyroidism: over active
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–
–
–
•
High levels of thyroxine
Overactive / thin
High blood pressure / heartrate / body temperature
Treatment: medication or partial removal of gland
Hypothyroidism: under active
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–
–
–
•
protein synthesis
ATP production
Low heartrate / blood pressure / body temperature
Underactive / overweight
Treatment: supplement thyroxine
Cretinism in infant (stunted growth / mental retardation / altered physical appearance
Thyroxine contains iodine
–
–
Thyroid swells if iodine deficiency (goiter)
Treatment: iodine added to salt and water
Thyroid Gland
• If you look at the
figure, you can see
that the thyroid
gland is located at
the base of the neck
and wraps around
the upper part of the
trachea
Thyroid Gland
• The thyroid gland has the major role in regulating
the body's metabolism
• Cells in the thyroid gland produce thyroxine, which is
made up of the amino acid tyrosine and the mineral
iodine
• Remember that thyroxine affects nearly all of the
cells of the body by regulating their metabolic rates
• Thyroxine increases the rate of protein,
carbohydrate, and fat metabolism as well as the rate
of cellular respiration, which means that the cells
release more heat and energy
• Decreased levels of thyroxine can decrease the rate
of cellular respiration and the amount of heat and
energy released
THYROID
• The thyroid hormones regulate
cellular metabolic rates
through a negative feedback
mechanism
• Low concentrations of the
thyroid hormones stimulate
production and secretion of
TSH-releasing hormone from
the hypothalamus
• High concentrations of the
thyroid hormones inhibit TSHreleasing hormone but
stimulate TSH releaseinhibiting hormone
Thyroid and Parathyroid Glands
• Hormones produced
by the thyroid gland
and the parathyroid
glands maintain the
level of calcium in
the blood
• The thyroid gland
wraps around the
trachea
Thyroid and Parathyroid Glands
Thyroid Gland
• The homeostatic activities of the thyroid gland are
so well controlled that you may never become aware
of them
• However, if the thyroid gland produces too much
thyroxine, a condition called hyperthyroidism occurs
– Hyperthyroidism results in nervousness, elevated body
temperature, increased metabolic rate, increased blood
pressure, and weight loss
• Too little thyroxine causes a condition called
hypothyroidism
– Lower metabolic rates and body temperature, lack of
energy, and weight gain are characteristics of this condition
– In some cases, hypothyroidism can cause a goiter, an
enlargement of the thyroid gland
Thyroid Gland
• The importance of proper thyroid activity can be seen in
parts of the world where food lacks enough iodine for
the thyroid to produce normal amounts of thyroxine
• Unable to produce the thyroxine needed for normal
development, iodine-deficient infants suffer from a
condition called cretinism, in which neither the
skeletal system nor the nervous system develops
properly
• Two effects of cretinism are:
– Dwarfism
– Severe mental retardation
• Cretinism usually can be prevented by the addition
of small amounts of iodine to table salt or other
items in the food supply
Parathyroid Glands
• The four parathyroid
glands are found on
the back surface of
the thyroid gland
PARATHYROID
• Four glands embedded in the back of the
Thyroid (two in each lobe)
• Secrete parathyroid hormone
– Regulates:
• Levels of calcium and phosphate ions in the blood
– Essential for normal bone growth, muscle tone, and
nerve activity
Parathyroid Glands
• Hormones from the thyroid gland and the
parathyroid glands act to maintain homeostasis of
calcium levels in the blood
• Parathyroid glands secrete parathyroid hormone
(PTH)
– Recall that PTH and calcitonin have opposite effects on the
body
• PTH regulates the calcium levels in the blood by
increasing the reabsorption of calcium in the
kidneys and by increasing the uptake of calcium
from the digestive system
• Parathyroid hormone also affects other organ
systems, promoting proper nerve and muscle
function and bone structure
PARATHYROID
• The four parathyroid
glands are embedded
in the dorsal side of
the thyroid gland
• They secrete a
hormone that
regulates the
concentration of
calcium ions in the
blood
THYMUS
• Located under the sternum (breastbone)
between the lungs
• Large in young children
– Smaller as you grow older
• Hormone produced: Thymosins
– Stimulate the development of infectionfighting antibodies and bolster the child’s
immune system
Adrenal Glands
• The adrenal glands are two
pyramid-shaped structures that
sit on top of the kidneys, one
gland on each kidney, as
shown in the figure at right
• The adrenal glands release
hormones that help the body
prepare for and deal with
stress
• An adrenal gland has an outer
part called the adrenal
cortex and an inner part
called the adrenal medulla
– These parts contain
different types of tissues
An Adrenal Gland
• Release hormones
that help the body
prepare for and deal
with stress
• Each adrenal gland
is divided into two
structural parts:
– Adrenal cortex
– Adrenal medulla
ADRENAL
• Two
• Located on top of each kidney
• Two parts: function as separate glands
– Medulla: inner portion
• Produces two hormones: adrenaline (epinephrine) and
noradrenaline
– Helpful in period of stress
– Cortex: outer portion
• Produces the hormones (corticoids):
• Cortisol:
– Regulates certain phases of carbohydrate, fat, and protein metabolism
• Aldosterone:
– Stimulates the kidneys to reabsorb sodium ion which helps maintain
water and salt balance in the body
An Adrenal Gland
Adrenal Cortex
• About 80 percent of an adrenal gland is its
adrenal cortex
• The adrenal cortex produces more than two
dozen steriod hormones called
corticosteroids
• One of these hormones, aldosterone,
regulates the reabsorption of sodium ions
and the excretion of potassium ions by the
kidneys
• Another hormone, called cortisol, helps control
the rate of metabolism of carbohydrates,
fats, and proteins
Adrenal Medulla
• The release of hormones from the adrenal
medulla is regulated by the sympathetic
nervous system
• The sympathetic nervous system prepares the
body for energy-intense activities
• The two hormones released by the adrenal
medulla are epinephrine and norepinephrine
• Epinephrine, which is more powerful than
norepinephrine, makes up about 80 percent
of the total secretions of the adrenal medulla
Adrenal Medulla
•
•
•
•
•
•
•
•
•
The adrenal medulla produces the “fight or flight” response to stress
This response is the feeling you get when you are excited or frightened
Nerve impulses from the sympathetic nervous system stimulate cells
of the adrenal medulla
This stimulation causes the cells to release large amounts of
epinephrine and norepinephrine
These hormones increase heart rate, blood pressure, and blood flow to
the muscles
They cause air passageways to open wider, allowing for an increase in
the intake of oxygen
They also stimulate the release of extra glucose into the blood to help
produce a sudden burst of energy
The result of all these actions is a general increase in body activity,
which can serve as preparation for intense physical activity
If your heart rate speeds up and your hands begin to perspire when
you take a test, you are feeling the effects of your adrenal medulla!
ADRENAL
• The adrenal glands,
located above each
kidney, consist of an inner
medulla and an outer
cortex
• Epinephrine and norepinephrine are produced
in the medulla, while
cortisol and aldosterone
are produced in the
cortex
Pancreas
• The pancreas is an unusual gland that has
both exocrine and endocrine functions
– Recall that the pancreas is a digestive gland whose
enzyme secretions help to break down food
– These secretions are released into the pancreatic
duct and flow into the small intestine
– This makes the pancreas an exocrine gland
• However, different cells in the pancreas
release hormones into the blood, making the
pancreas an endocrine gland as well
Pancreas
• The hormone-producing portion of the pancreas
consists of clusters of cells that resemble islands
– These clusters of cells are called islets of Langerhans after
their discoverer, the German anatomist Paul Langerhans
• Each islet includes:
– Beta cells, which secrete a hormone called insulin
– Alpha cells, which secrete another hormone called
glucagon
• Insulin and glucagon help to keep the level of
glucose in the blood stable
– Insulin stimulates cells in the liver and muscles to remove
sugar from the blood and store it as glycogen or fat
– Glucagon stimulates the liver to break down glycogen and
release glucose back into the blood
• It also stimulates the release of fatty acids from stored fats
PANCREAS
ISLETS OF LANGERHANS
• Pancreas: primarily an exocrine gland producing
digestive enzymes
• Specialized cells (Islets of Langerhans) function as
endrocrine glands maintaining carbohydrate metabolism
– Produces two hormones: must be in balance
• Insulin: lowers blood sugar level
– Stimulates cells to absorb glucose
– Stimulates the liver and muscles to convert glucose to glycogen
– Diabetes Mellitus: high blood sugar levels
» Tpye 1: juvenile-onset diabetes (little or no insulin)
» Type 2: maturity-onset diabetes (normal levels of insulin but low
number of receptors for insulin molecules)
– Hypoglycemia: low blood sugar levels
» Too much insulin
• Glucagon: raises blood sugar level
– Stimulates the breakdown of glycogen to glucose
Maintaining Blood Sugar Levels
• When blood glucose levels rise after eating, the
pancreas releases insulin
• Insulin stimulates cells throughout the body to take
glucose out of the bloodstream
• Insulin's major target cells are found in the liver,
skeletal muscles, and fat (adipose) tissue
– Glucose taken out of circulation is stored as glycogen in the
liver and skeletal muscles
– In fat tissue, glucose molecules are converted to lipids
• Insulin prevents the level of glucose in the blood
from rising too rapidly and ensures that excess
glucose is stored for future use
Maintaining Blood Sugar Levels
• Within one or two hours after eating, when
the level of blood glucose drops, glucagon is
released from the pancreas
• Glucagon stimulates the cells of the liver and
skeletal muscles to break down glycogen
and increase glucose levels in the blood
– Glucagon also causes fat cells to break down fats
so that they can be used for the production of
carbohydrates
• These actions make more chemical energy
available to the body and help raise the
blood glucose level back to normal
PANCREAS
ISLETS OF LANGERHANS
• The islets of
Langerhans play a
crucial role in the
regulation of blood
glucose
PANCREAS
ISLETS OF LANGERHANS
• Working in opposition,
glucagon and insulin
maintain a balanced
blood glucose
concentration
• These antagonistic
hormones oppositely
affect the amount of
glucose in the blood
Diabetes Mellitus
• When the pancreas fails to produce or
properly use insulin, a condition known as
diabetes mellitus occurs
• In diabetes mellitus, the amount of glucose in
the blood may rise so high that the kidneys
actually excrete glucose in the urine
• Very high blood glucose levels can damage
almost every cell in the body, including the
coronary arteries
Diabetes Mellitus
• There are two types of diabetes mellitus
• Type I diabetes is an autoimmune disorder
that usually develops in people before the age of
15
– In this type of diabetes, there is little or no secretion
of insulin
– People with this type of diabetes must follow a strict
diet and get daily injections of insulin to keep their
blood glucose levels under control
Diabetes Mellitus
• The second type of diabetes, Type II, most
commonly develops in people after the age of 40
• People with Type II diabetes produce low to normal
amounts of insulin
• However, their cells are unable to properly respond to
the hormone because the interaction of the insulin
receptors and the insulin is inefficient
• In its early stages, Type II diabetes can often be
controlled through diet and exercise
– A diet high in complex carbohydrates and low in saturated
fat and sugar can prevent blood sugar fluctuations
Diabetes Mellitus
• Unfortunately, many people with Type II
diabetes eventually require medication, as
well
• If the body stops producing insulin, the
person will also need to have daily insulin
injections
STOMACH/SMALL INTESTINE
• Stomach:
– endocrine glands produce:
• Hormone Gastrin: stimulates other stomach cells
to produce HCl
• Small Intestine:
– Endocrien glands produce:
• Hormone Secretin: stimulates the pancreas,
stomach, and the liver
PINEAL
• Located in the forebrain
• Hormone: Melatonin
– Involved in biorhythms
– Influences maturation by inhibiting the release
of certain hormones
PINEAL
• The pineal gland,
located near the base
of the brain, secretes
the hormone
melatonin at night
GONADS
• Gamete producing organs
• Female: ovaries (eggs)
– Sex Hormones: estrogen and progesterone
• Male: testes (sperm)
– Sex Hormones: group of hormones called
Androgens
• Main hormone: Testosterone
Reproductive Glands
• The gonads are the body's reproductive
glands
• The gonads serve two important
functions:
– Production of gametes:
• The female gonads:
– Ovaries—produce eggs (ova; singular: ovum)
• The male gonads:
– Testes (singular: testis)—produce sperm
– Production and secretion of sex hormones
Reproductive Glands
• The ovaries produce the female sex
hormones, estrogen and progesterone
• Estrogen is required for the development of
eggs and for the formation of the physical
characteristics associated with the female
body
– These characteristics include the development of
the female reproductive system, widening of the
hips, and development of the breasts
• Progesterone prepares the uterus for the
arrival of a developing embryo
Reproductive Glands
• The testes produce testosterone
• Testosterone is required for:
– Normal sperm production
– Development of physical characteristics
associated with the male body
• These characteristics include the growth of
facial hair, increase in body size, and
deepening of the voice
• You will read more about these hormones
in the next section
The Reproductive System
• Reproduction is the formation of new individuals
– This makes the reproductive system unique among the
systems of the body
• If any other body system, such as the nervous or
circulatory system, failed to function, the result
would be fatal in most animals
– This is not the case for the reproductive system because an
individual can lead a healthy life without reproducing
• However, the reproductive system could be thought
of as the single most important system for the
continuation of a species—without it, no species
could produce another generation
The Reproductive System
• In humans, as in other vertebrates, the
reproductive system produces, stores,
and releases specialized sex cells
known as gametes
– These cells are released in ways that make
possible the fusion of sperm and egg to
form a zygote, the single cell from which
all cells of the human body develop
Sexual Development
• For the first six weeks of development, human male
and female embryos are identical in appearance
• Then, during the seventh week, major changes occur
– The primary reproductive organs—the testes in males and
the ovaries in females—begin to develop
• The testes begin to produce testosterone
– Tissues of the embryo respond to this hormone by developing
into the male reproductive organs
• If the embryo is female, the ovaries produce estrogen
– In response to this hormone, the tissues of the embryo develop
into the female reproductive organs
• These hormones determine whether the embryo will
develop physically into a male or female
Sexual Development
• After birth, the gonads produce small amounts of
sex hormones that continue to influence the
development of the reproductive organs
– However, neither the testes nor the ovaries are capable of
producing active reproductive cells until puberty
• Puberty is a period of rapid growth and sexual
maturation during which the reproductive system
becomes fully functional
– At the completion of puberty, the male and female
reproductive organs are fully developed
• The onset of puberty varies considerably among
individuals
– It usually occurs any time between the ages of 9 and 15,
and, on average, begins about one year earlier in females
than in males
Sexual Development
• Puberty begins when the hypothalamus
signals the pituitary to produce
increased levels of two hormones that
affect the gonads
– These hormones are follicle-stimulating
hormone (FSH) and luteinizing hormone
(LH).
The Male Reproductive System
• The release of FSH and LH stimulates cells in
the testes to produce testosterone
– FSH and testosterone stimulate the development
of sperm
• Once large numbers of sperm have been
produced in the testes, the developmental
process of puberty is completed
• The reproductive system is now functional,
meaning that the male can produce and
release active sperm
• The main function of the male reproductive
system is to produce and deliver sperm
The Male Reproductive System
• The figure at right shows
the structures of the male
reproductive system
• The primary male
reproductive organs,
the testes, develop
within the abdominal
cavity
• Just before birth (and
sometimes just after)
the testes descend
through a canal into an
external sac called the
scrotum
MALE
• Male gonads (reproductive organs)
– Testes:
• Two functions:
– Gamete production: sperm
– Hormone production: mainly testosterone
• Located in a pouch called the scrotum:
– Hangs outside the body
– Temperature inside is 1.5 Celsius degrees lower than within the
body cavity
• Before a boy is born, they develop within his abdominal
cavity:
– Several weeks before birth, they normally descend into the
scrotum
– Testes that fail to descend usually do not produce sperm
MALE
• Puberty: sexually mature but might not be
psychologically mature
– Testes begin to produce high levels of
testosterone
• Influences:
– The testes to produce sperm by the process of meiosis
» Continues throughout life, as long as, testosterone is
present
– Development of facial and pubic hair
– Voice change
The Male Reproductive System
• The testes remain in the
scrotum, outside the
body cavity, where the
temperature is about
one to three degrees
lower than the normal
temperature of the body
(37°C)
• The lower temperature
is important for proper
sperm development
The Male Reproductive System
• Within each testis are
clusters of hundreds
of tiny tubules called
seminiferous
tubules
– The seminiferous
tubules are tightly
coiled and twisted
together
– Sperm are produced
in the seminiferous
tubules
The Male Reproductive System
• The main structures
of the male
reproductive system
produce and deliver
sperm
• The main organs of
the male reproductive
system are the testes
The Male Reproductive System
Sperm Development
• Sperm are derived from specialized cells
in the testes that undergo the process of
meiosis to form the haploid nuclei of
mature sperm
• Recall that a haploid cell contains only
a single set of chromosomes
(monoploid/haploid)
SPERMATOGENESIS
• Sperm production by mitotic/meiotic cell division
– In the seminiferous tubules
• 1st Division: mitotic: Diploid sperm-producing cell
develops into a primary spermatocyte (diploid)
• 2nd Division (First Meiotic): primary spermatocyte
(diploid) divides and produces 2 secondary
spermatocytes (diploid)
• 3rd Division: (Second Meiotic): secondary spermatocytes
divide producing 4 spermatids which develop flagellum
and become sperm (haploid/monoploid)
• Sperm are into an elongated sac (epididymis) where
they mature (usually within 18 hrs) and are stored
• One Primary Spermatocyte produces four sperm
Sperm Development
• A sperm cell is illustrated
• A sperm cell consists of a
head, which contains a
highly condensed nucleus; a
midpiece, which is packed
with energy-releasing
mitochondria; and a tail, or
flagellum, which propels the
cell forward
• At the tip of the head is a
small cap that contains an
enzyme vital to the process
of fertilization
Sperm Cell
• The sperm is the
male gamete, or sex
cell
Sperm Cell
SPERM
• Head:
– Contains the haploid/monoploid nucleus
• Tail: is a flagellum
– Contains:
• Mitochondria in the anterior portion
• Absorbs fructose from the seminal fluid quickly
converting it into usable energy stored in ATP
– Needed for the journey
• Life expectancy: short but some may
survive for a few days
The Male Reproductive System
• Sperm produced in the seminiferous tubules are
moved into the epididymis
– This is the structure in which sperm fully mature
and are stored
• From the epididymis, some sperm are moved
into a tube called the vas deferens
– The vas deferens extends upward from the
scrotum into the abdominal cavity
• Eventually, the vas deferens merges with the
urethra, the tube that leads to the outside of the
body through the penis
EPIDIDYMIS
• 5% Seminal Fluid
• One in each testis
• Contains large number of twisted tubules
which receive sperm from testis
• Store sperm while they mature and until
needed for ejaculation
SEMEN
• Vas Deferens:
– Paired tube leading from epididymis into
urethra within tissue of Prostate Gland
• Part of sperm cord which also contains muscle
tissue and blood vessels
– As sperm travels from the epididymis to the
urethra (tube within the penis) they pass
through the vas deferens (sperm cord)
• Several glands add secretions to the sperm as
they pass through the vas deferens/urethra (the
fluids plus the sperm are called semen)
GLANDS
• Cowper’s Gland: (5% Seminal Fluid)
– Also called Bulbourethral Gland
– Paired (pea Size)
– Empty secretions into urethra
– Secretes alkaline fluid:
• neutralizes urine residue in urethra
GLANDS
• Seminal Vesicle: (30% Seminal Fluid)
– Paired glandular sacs
– Secretions contribute to seminal fluid
– Opens into vas deferens (as the vas deferens
enters the Prostate Gland)
– Secretions contain fructose, amino acids,
mucous, etc. for nourishment and protection
of sperm
GLANDS
• Prostate Gland: (60% Seminal Fluid)
– Unpaired (size of chestnut)
– Urethra and vas deferens join inside
– Alkaline secretions help neutralize acidic urine
residue in urethra
– During ejaculation, reflex swelling of Prostate
temporarily closes off upper portion of urethra
• Prevents mixing of urine with seminal fluid
SEMEN
• Seminal Fluid
– Contains:
• Sperm: 120 million/ml
• Gland secretions:
– Relatively high alkalinity neutralizing residual acids in
male urethra and protects sperm from vagina’s acidic
secretions
• Average Ejaculation:
– 4ml
– ½ billion (500,000,000) sperm
» Only one of which is needed for fertilization ??????
The Male Reproductive System
• Glands lining the reproductive tract: produce a nutrient-rich fluid
called seminal fluid
– Seminal vesicles
– Prostate
– Bulbourethral glands
• The seminal fluid nourishes the sperm and protects them from
the acidity of the female reproductive tract
– The combination of sperm and seminal fluid is known as
semen
• The number of sperm present in even a few drops of semen is
astonishing
– Between 50 and 130 million sperm are present in 1 milliliter of
semen
– That's about 2.5 million sperm per drop!
PENIS
•
•
•
•
Organ of urination and copulation
Prepuce: foreskin
Glans: head (sensory neurons)
Corpus Cavernosum: dorsal tissue that swells with blood
giving firmness to the penis in an erection
• Corpus Spongiosum: ventral tissue that swells with blood
giving firmness to the penis in an erection
• Erection: corpus cavernosum/ corpus spongiosum cause
arteries to dilate and veins to constrict
Sperm Release
• When the male is sexually aroused, the autonomic
nervous system prepares the male organs to deliver
sperm
– Sperm are ejected from the penis by the contractions of
smooth muscles lining the glands in the reproductive tract
• This process is called ejaculation
• Because ejaculation is regulated by the autonomic
nervous system, it is not completely voluntary
• About 2 to 6 milliliters of semen are released in an
average ejaculation
• If these sperm are released in the reproductive tract of a
female, the chances of a single sperm fertilizing an egg,
if one is available, are quite good
MALE ORGASM
• Semen is forcefully expelled from the body
by strong muscular contractions of the
sperm ducts (ejaculation)
The Female Reproductive System
• The primary reproductive organs in the
female are the ovaries
– The ovaries are located in the abdominal
cavity
• As in males, puberty in females starts
when the hypothalamus signals the
pituitary gland to release FSH and LH
– FSH stimulates cells within the ovaries to
produce estrogen
The Female Reproductive System
• The main function of the female
reproductive system is to produce ova
– In addition, the female reproductive
system prepares the female's body to
nourish a developing embryo
• In contrast to the millions of sperm
produced each day in the male
reproductive system, the ovaries usually
produce only one mature ovum (plural:
ova), or egg, each month
FEMALE
• Female gonads (reproductive organs)
– Ovary
• Two
• Produce female gametes (eggs)(ovum/ova)
– Each female is born with approximately 400,000
immature eggs
– Will not produce anymore on her lifetime
– Only about 400 eggs actually mature
• Produce hormones
FEMALE
• Puberty: Sexually mature but might not be
psychologically mature
– Development of Primary Oocytes resumes
– Breast with mammary tissue develop
– Pubic hair develops
– Menstrual cycle begins
FEMALE EXTERNAL GENITALIA
•
•
•
•
•
Labium Majora (outer)
Labium Minora (inner)
Clitoris
Urethral orifice (opening)
Vaginal opening
– Hymen
• Anal opening
INTERNAL FEMALE
REPRODUCTIVE ANATOMY
• Ovary: organ of egg production
• Fallopian Tube (Oviduct) (Uterine Tube)
– Tube connecting the ovary with the uterus
– Usually site of fertilization
• Uterus:
– Muscular organ that functions to house the developing fetus if
fertilization occurs
• Cervix:
– Lower entrance to the uterus
• Vagina:
– Tube leading from the cervix to the outside of the body
– Canal that accepts the male penis during intercourse
– Canal through which the fetus passes during childbirth
OOGENESIS
• Production of an egg (ovum)
• Even before birth egg producing cells in
the ovary have developed into primary
oocytes (diploid)
– At birth, all the primary oocytes for a lifetime
are present
• Primary oocytes (diploid) begin the first meiotic
division but do not complete it
• Ovum develop does not resume until the girl
reaches puberty
OOGENESIS
• Approximately every 28 days
• A Primary Oocyte undergoes meiosis
– Two haploid/monoploid cells produced are of unequal size
• Larger cell: Secondary Oocyte receives most of the cytoplasm
• Smaller cell: Polar Body
• Secondary Oocyte is released from the ovary as a Ovum
– Second meiotic division is not actually completed until a sperm
enters the ovum
• Division produces larger ovum (almost all the cytoplasm) with a
haploid nucleus and a second polar body
– Cytoplasm provides nourishment if the ovum is fertilized
• Polar bodies do not live long
• One Primary Oocyte produces one ovum
Egg Development
• Each ovary contains about 400,000
primary follicles, which are clusters of
cells surrounding a single egg
– The function of a follicle is to help an egg
mature for release into the reproductive
tract, where it can be fertilized
• Eggs develop within their follicles
Egg Development
• Although a female is born with thousands of
immature eggs (primary follicles), only about
400 eggs will actually be released
• Approximately every 28 days, under the
influence of FSH, a follicle gets larger and
completes the first meiotic cell division
– When meiosis is complete, a single large haploid
egg and three smaller cells called polar bodies are
produced
• The polar bodies have very little cytoplasm and soon
disintegrate
Egg Release
•
When a follicle has completely matured, its egg is released in a
process called ovulation
– The follicle breaks open, and the egg is swept from the surface of the ovary into
the opening of one of the two Fallopian tubes
•
The egg moves through the fluid-filled Fallopian tube, pushed along
by microscopic cilia lining the walls of the tube
– During its journey through the Fallopian tube, an egg can be fertilized
•
After a few days, the egg passes from the Fallopian tube into the cavity of
an organ known as the uterus
– The lining of the uterus is ready to receive a fertilized egg, if fertilization
has occurred
•
•
•
The outer end of the uterus is called the cervix
Beyond the cervix is a canal—the vagina—that leads to the outside of the
body
The structures of the female reproductive system are shown in the figure at
right
Female Reproductive System
• The main function of
the female
reproductive system
is to produce ova
• The ovaries are the
main organs of the
female reproductive
system
Female Reproductive System
The Menstrual Cycle
• After puberty, the interaction of the
reproductive system and the endocrine
system in females takes the form of a
complex series of periodic events called the
menstrual cycle
• The cycle takes an average of about 28 days
• The word menstrual comes from the Latin word
mensis, meaning “month”
• The menstrual cycle is regulated by
hormones made by the hypothalamus,
pituitary gland, and ovaries; and it is
controlled by internal feedback mechanisms
The Menstrual Cycle
• The menstrual cycle begins at puberty and
continues until a female is in her mid-forties
– At this time, the production of estrogen declines,
and ovulation and menstruation stop
• The permanent stopping of the menstrual cycle
is called menopause
• The average age for menopause is about 51,
but it can occur anytime between the late thirties
and late fifties
MENSTRUAL CYCLE
•
•
•
•
Periodic changes controlled by hormones
Each Primary Oocyte is enclosed in a structure called a Follicle
Beginning of the cycle: (Follicular Phase)
Hypothalamus produces a releasing factor that stimulates the anterior lobe of the pituitary
to release FSH:
–
Follicle-Stimulating Hormone (FSH)
•
•
•
Secreted by the Anterior Pituitary Gland
Travels through the blood
Stimulates the several follicles to grow
–
One usually grows faster and the others stop
–
Growing Follicle secretes Estrogen
–
–
Growth of the follicle and thickening of the endometrium continue for 9/10 days
Estrogen stimulates the Hypothalamus which releases a tropic hormone that stimulates the Pituitary to
secrete Luteinizing Hormone (LH)
Sudden rise of LH causes the follicle to burst: (Ovulation Phase)
•
–
•
•
–
–
Causes the endometrium of the uterus to thicker and blood supply increase in preparation for pregnancy
Ovum is released from the follicle into the oviduct (fallopian tube) (uterine tube)
Ovulation
LH converts the old follicle into the Corpus Luteum: (Luteal Phase)
Another hormone produced by the anterior pituitary , luteotropic hormone (LTH), stimulates the
corpus luteum to send out steroid hormones (estrogen and progesterone)
•
•
Continues development of the endometrium
High Progesterone levels suppressed the Pituitary from secreting FSH
The Menstrual Cycle
• During the menstrual cycle,
an egg develops and is
released from an ovary
• In addition, the uterus is
prepared to receive a fertilized
egg
• If the egg is fertilized, it is
implanted in the uterus and
embryonic development
begins
• If an egg is not fertilized, it is
discharged, along with the
lining of the uterus
• The menstrual cycle has four
phases: follicular phase,
ovulation, luteal phase, and
menstruation
The Menstrual Cycle
• The menstrual cycle
is divided into four
phases
• Notice the changes in
hormone levels in the
blood, the
development of the
follicle, and the
changes in the uterine
lining during the
menstrual cycle
The Menstrual Cycle
Follicular Phase
• The follicular phase begins when the level of
estrogen in the blood is relatively low
• The hypothalamus reacts to low estrogen
levels by producing a releasing hormone that
stimulates the anterior pituitary to secrete
FSH and LH
• These two hormones travel through the
circulatory system to the ovaries, where they
cause a follicle to develop to maturity
• Generally, just a single follicle develops, but
sometimes two or even three mature during
the same cycle
Follicular Phase
• As the follicle develops, the cells
surrounding the egg enlarge and begin to
produce increased amounts of estrogen
• As the follicle produces more and more of
the hormone, the estrogen level in the blood
rises dramatically
• Estrogen causes the lining of the uterus to
thicken in preparation for receiving a
fertilized egg
• The development of an egg in this stage of
the cycle takes about 10 days
Ovulation
• This phase is the shortest in the cycle
• It occurs about midway through the cycle
and lasts three to four days
• During this phase, the hypothalamus sends a
large amount of releasing hormone to the
pituitary gland
• This causes the pituitary gland to produce
FSH and LH
– The release of these hormones has a dramatic
effect on the follicle: It ruptures, and a mature egg
is released into one of the Fallopian tubes
Luteal Phase
• The luteal phase begins after the egg is released
• As the egg moves through the Fallopian tube, the cells
of the ruptured follicle undergo a change
• The follicle turns yellow and is now known as the
corpus luteum, which means “yellow body” in Latin
– The corpus luteum continues to release estrogen but also
begins to release progesterone
• During the first 14 days of the cycle, rising estrogen
levels stimulate cell growth and tissue development
in the lining of the uterus
• Progesterone adds the finishing touches by
stimulating the growth and development of the blood
supply and surrounding tissue
Luteal Phase
• During the first two days of the luteal phase, immediately
following ovulation, the chances that an egg will be fertilized
are the greatest
– This is usually from 10 to 14 days after the completion of the last
menstrual cycle
• If an egg is fertilized by a sperm, the fertilized egg will start to
divide by the process of cell division known as mitosis
– After several divisions, a ball of cells will form and implant itself in
the lining of the uterus
• The embryo continues to grow by repeated mitotic divisions
• Within a few days of implantation, the uterus and the growing
embryo will release hormones that keep the corpus luteum
functioning for several weeks
– This allows the lining of the uterus to nourish and protect the
developing embryo
MENSTRUAL CYCLE WITH
FERTILIZATION
• Egg in fallopian tube has a jellylike covering and is
surrounded by a layer of cells from the follicle
– Many sperm needed to dissolve the outer covering with enzymes
– Only one will actually enter the egg and fertilize it
• Egg membrane engulfs the head of a single sperm and the sperm
nucleus breaks out of the head
• Membrane forms around the egg and prevents any other sperm
from entering
• Sperm nucleus (23 chromosomes) (1N: monoploid) fuses with egg
nucleus (23 chromosomes) (1N: monoploid) forming a zygote (46
chromosomes) (2N: diploid)
– Presence of a diploid set of chromosomes initiates embryo
development
• Corpus Luteum continues to secrete Progesterone
– Continues development of endometrium
Menstruation
• What happens if fertilization does not occur?
• Within two to three days of ovulation, the egg
will pass through the uterus without
implantation
• The corpus luteum will begin to disintegrate
• As the old follicle breaks down, it releases
less estrogen and less progesterone
– The result is a decrease in the level of these
hormones in the blood
Menstruation
• When the level of estrogen falls below a certain
point, the lining of the uterus begins to detach from
the uterine wall
• This tissue, along with blood and the unfertilized
egg, are discharged through the vagina
• This phase of the cycle is called menstruation
• Menstruation lasts about three to seven days on
average
• A new cycle begins with the first day of menstruation
Menstruation
• A few days after menstruation ends,
levels of estrogen in the blood are once
again low enough to stimulate the
hypothalamus
• The hypothalamus produces a
releasing hormone that acts on the
pituitary gland, which then starts to
secrete FSH and LH, and the menstrual
cycle begins again
MENSTRUAL CYCLE WITHOUT
FERTILIZATION
– Ovum disintegrates in a few days
– Corpus Luteum begins to breakdown
– 11 days after ovulation the Progesterone level is low causing the
endometrium to breakdown
– Blood and endometrial tissue exit the body through the vagina
• Process called Menstruation
• Last a few days
– Progesterone level falls stimulating the Pituitary to secrete FSH
– Cycle begins again
– Most women menstruate until age 50
•
•
•
•
Menstruation ceases (Menopause)
No more ovulation
No more Estrogen/Progesterone production
Pitiutray continues to secrete FSH
Sexually Transmitted Diseases
• Diseases that are spread from one
person to another during sexual
contact are known as sexually
transmitted diseases (STDs)
• STDs are a serious health problem in the
United States, infecting millions of people
each year and accounting for thousands
of deaths
Sexually Transmitted Diseases
• Unfortunately, public information about many STDs has not
kept pace with the rate of infection
• For example, one might think that the name of the most
commonly reported infectious disease in the United States
would be a household word, but it isn't
• That disease is chlamydia
• The Centers for Disease Control estimates that more than three
million cases of chlamydia occur in the United States every year
• Chlamydia is caused by a bacterium that is passed from person
to person by sexual contact
• Females between the ages of 15 and 19 show the highest
incidence of chlamydia infection of any age group
– Chlamydia puts them at risk of infertility due to the damage this
disease can cause in the reproductive system
Sexually Transmitted Diseases
• Other STDs caused by bacteria include syphilis,
which can be fatal, and gonorrhea, a serious
infection that is easily spread during intercourse
• Viruses can also cause STDs
• Viral STDs include hepatitis B, genital herpes, genital
warts, and AIDS
– AIDS, a result of human immunodeficiency virus (HIV)
infection, causes tens of thousands of deaths in the United
States alone
– Millions of deaths around the world can also be attributed to
AIDS
• Unlike the bacterial STDs, these viral infections
cannot be treated with antibiotics
Sexually Transmitted Diseases
• Like other infectious diseases, STDs can be
avoided
– Any sexual contact carries with it the chance of
infection
• The safest course to follow is to abstain from
sexual contact before marriage and for both
partners in a committed relationship to
remain faithful
• The next safest course is to use a latex
condom, but even a latex condom does not
provide 100 percent protection
Fertilization and Development
• When an egg is fertilized, the
remarkable process of human
development begins
• In this process, a single cell no larger
than the period (.) at the end of this
sentence undergoes a series of cell
divisions that results in the formation
of a new human being
Fertilization
• If an egg is to become fertilized, sperm must be
present in the female reproductive tract—usually, in
a Fallopian tube
• During sexual intercourse, sperm are released when
semen is ejaculated through the penis into the
vagina
• The penis generally enters the vagina to a point just
below the cervix, which is the opening that connects
the vagina to the uterus
• Sperm swim actively through the uterus into the
Fallopian tubes
• Hundreds of millions of sperm are released during an
ejaculation, so that if an egg is present in one of the
Fallopian tubes, its chances of being fertilized are good
CLEAVAGE AND IMPLANTATION
•
•
First Trimester: 3 months (embryo)
Cleavage: phase that follows fertilization
–
–
zygote goes through many mitotic cell divisions while still in the Fallopian Tube
A ball of cells develops called a Morula:
•
Fluid is released into the center of the sphere now called a Blastocyst
–
–
•
–
6 to 7 days after fertilization
Membrane formation:
•
Part of the trophoblast becomes the amnion: membrane which enclose the embryo/fetus
–
–
•
•
a membrane that surrounds the yolk
Nourishment during early embryo development
Allantois forms:
–
Chorion and allantois lengthens to form the umbilical cord
Placenta:forms whenthe chorionic villi embed in the endometrium
–
–
•
Forms the placenta with the mother (most of the tissue forms from the chorion)
» Placenta attaches to the umbilical cord
Yolk Sac forms:
–
–
•
Contains fluid the cushion and protects the embryo/fetus against eternal shocks
Prevents the embryo/fetus from sticking to the uterus
Another part of the trophoblast becomes the chorion: membrane outside the amnion
–
•
Outer layer of cells, called trophoblast, release enzymes which breakdown the epithelial tissue of the uterus enabling the
blastocyst to embed itself into the endometrium (Implantation)
» These cells become the membranes that protect and support the embryo
Inner group of cells becomes the embryo
» Has three primary germ layers: ectoderm, mesoderm, endoderm
A small part comes from the mother
Most of it is derived from the chorion
5 cm long / most organs established / heart beating / toes / fingers / ears formed
Fertilization
• The egg is surrounded by a protective layer that contains
binding sites to which sperm can attach
• When a sperm attaches to a binding site, a sac in the sperm
head releases powerful enzymes that break down the protective
layer of the egg
• The sperm nucleus then enters the egg, and chromosomes
from the sperm and egg are brought together
• The process of a sperm joining an egg is called fertilization
• After the two haploid (N) nuclei (one from the sperm and one
from the egg) fuse, a single diploid (2N) nucleus is formed
• A diploid cell contains a set of chromosomes from each parent
cell
• The fertilized egg is called a zygote
Fertilization
• What prevents more than one sperm from fertilizing
an egg?
• Early in the twentieth century, cell biologist Ernest
Everett Just found the answer
• The egg cell contains a series of granules just
beneath its outer surface
• When a single sperm enters the egg, the egg reacts
by releasing the contents of these granules outside
the cell
• The material in the granules coats the surface of the
egg, forming a barrier that prevents other sperm
from attaching to and entering the egg
Fertilization
• The process by which a
sperm joins an egg is
called fertilization
• Ernest Everett Just
discovered that once the
sperm nucleus enters the
egg, the egg's cell
membrane changes,
preventing other sperm
from entering
Fertilization
Early Development
• While still in the Fallopian
tube, the zygote begins to
undergo mitosis, as shown
in the figure at right
• Cell division continues
• As each cell divides, the
number of cells doubles
• Four days after fertilization,
the embryo is a solid ball of
about 64 cells called a
morula
• The stages of early
development include
implantation, gastrulation,
and neurulation
Fertilization and Implantation
• If an egg is fertilized, a zygote forms and begins to
undergo cell division (mitosis) as it travels to the uterus
• The egg in this illustration has been greatly enlarged
• How much time passes before the blastocyst is attached
to the uterine wall?
Fertilization and Implantation
Implantation
• As the morula grows, a
cavity forms in the center
• This transforms the morula
into a hollow structure with
an inner cavity called a
blastocyst
• About six or seven days after
fertilization, the blastocyst
attaches itself to the wall of
the uterus
• The embryo secretes
enzymes that digest a path
into the soft tissue
• This process is known as
implantation
FIRST TRIMESTER
• First three weeks resembles embryos of
other animals
• Third week brain, spinal cord, and nervous
system form
– Heart begins to beat
• Fifth week human features
Implantation
• At this point, cells in the blastocyst begin to
specialize as a result of the activation of genes
• This specialization process, called differentiation, is
responsible for the development of the various types
of tissue in the body
• A cluster of cells, known as the inner cell mass,
develops within the inner cavity of the blastocyst
– The embryo itself will develop from these cells, while the
other cells of the blastocyst will differentiate into the tissues
that surround the embryo
Gastrulation
•
•
•
•
The inner cell mass of the
blastocyst gradually sorts itself
into two layers, which then give
rise to a third layer
The third layer is produced by a
process of cell migration known
as gastrulation, shown in the
figure at right
The result of gastrulation is the
formation of three cell layers:
ectoderm, mesoderm, and
endoderm
These three layers are referred
to as the primary germ layers,
because all of the organs and
tissues of the embryo will be
formed from them
Gastrulation
• The ectoderm will
develop into the skin and
the nervous system
• The endoderm forms the
lining of the digestive
system and many of the
digestive organs
• Mesoderm cells
differentiate to form
many of the body's
internal tissues and
organs
Gastrulation
• Gastrulation results in the formation of three cell layers
• The diagram below shows the primitive streak, a line that
forms in the center of the blastocyst
• The movement of cells away from the primitive
streak, shown in the diagram on the right, forms the
mesoderm
Gastrulation
Neurulation
• Gastrulation is followed by an important step
in human development, neurulation
• Neurulation is the development of the nervous
system
• Shortly after gastrulation is complete, a
block of mesodermal tissue begins to
differentiate into the notochord
• Recall that all chordates possess a
notochord at some stage of development
DIFFERENTIATION
• Process in which unspecialized embryonic
cells develop into specialized cells
Neurulation
• As the notochord
develops, the neural
groove changes shape,
producing a pair of
ridges, or neural folds,
as shown in the figure
• Gradually, these folds
move together to create
a neural tube from
which the spinal cord
and the rest of the
nervous system,
including the brain,
develop
Neurulation
•
•
•
•
•
•
Neurulation is the formation of
the central nervous system
The ectoderm near the
notochord thickens and forms
the neural plate
The raised edges of the neural
plate form neural folds
The neural folds gradually move
together and fuse to form the
neural tube
One end of the neural tube will
develop into the brain; the other
end develops into the spinal
cord
Cells of the neural crest migrate
to other locations and develop
into nerves
Neurulation
Extraembryonic Membranes
• As the embryo develops, membranes form to
protect and nourish the embryo
• Two of these membranes are the:
– Amnion:
• Develops into a fluid-filled amniotic sac, which cushions and
protects the developing embryo within the uterus
– Chorion:
• By the end of the third week of development, the chorion—
the outermost of the extraembryonic membranes—has
formed:
– Small, fingerlike projections called chorionic villi form on the
outer surface of the chorion and extend into the uterine
lining
Extraembryonic Membranes
• The chorionic villi and uterine lining form a vital
organ called the placenta
– The placenta is the connection between mother and
developing embryo
• The developing embryo needs a supply of nutrients
and oxygen
• It also needs a means of eliminating carbon dioxide
and metabolic wastes
• Nutrients and oxygen in the blood of the mother diffuse
into the embryo's blood in the chorionic villi
• Wastes diffuse from the embryo's blood into the mother's
blood
Extraembryonic Membranes
• The figure shows that, in
actuality, the blood of the
mother and that of the
embryo flow past each other,
but they do not mix
• They are separated by the
placenta
• Across this thin barrier, gases
exchange, and food and waste
products diffuse
• The placenta is the embryo's
organ of respiration,
nourishment, and excretion
• The placenta allows the
embryo to make use of the
mother's organ systems while
its own are developing
The Fetus and the Placenta
• The placenta is the connection between the mother and the
developing fetus
• It is through the placenta that the fetus gets its oxygen and nutrients
and excretes its waste products
• Notice how the chorionic villi from the fetus extend into the
mother’s uterine limning (indicated by the overlapping
brackets)
The Fetus and the Placenta
Importance of Development
• This early period of development is particularly
important because a number of external factors
can disrupt development at this time
• The placenta acts as a barrier to some
harmful or disease-causing agents
• Other disease-causing agents, including the
ones that cause AIDS and German measles,
can penetrate the placenta and affect
development
• So can drugs—including alcohol,
medications, and addictive substances
Importance of Development
• After eight weeks of development, the embryo is
called a fetus
• By the end of three months of development, most of
the major organs and tissues of the fetus are fully
formed
• During this time, the umbilical cord also forms
• The umbilical cord, which contains two arteries and
one vein, connects the fetus to the placenta
• The muscular system of the fetus is by now well
developed, and the fetus may begin to move and show
signs of reflexes
• The fetus is about 8 centimeters long and has a mass of
about 28 grams
Control of Development
• As you have read, over just a few weeks of
development, a single zygote cell differentiates into the
many complex cells and tissues of a human fetus
• How does this happen?
• Is the fate of each cell in the embryo predetermined?
• Is there a master control switch that decides whether
a cell will become skin, muscle, blood, or bone?
• These are the kinds of questions that fascinate
developmental biologists, who study the processes
by which organisms grow and develop
Control of Development
• Although many of the most important questions
about development are still unanswered, researchers
have made remarkable progress in the last few years
• One of their most surprising findings is that the fates
of many cells in the early embryo are not fixed
• In mice, for example, researchers can mix cells from
the inner cell mass of two different embryos
• Rather than growing into a jumble of disorganized
tissues, a perfectly normal mouse develops
• This suggests that embryonic cells communicate
with one another to regulate development and
differentiation
Control of Development
• This finding is confirmed by experiments
showing that the inner cell mass contains
embryonic stem cells, which are capable of
differentiating into nearly any specialized cell
type
• Researchers are now working to learn the
mechanisms that control stem cell
differentiation, hoping eventually to grow
new tissue to repair the damage caused by
injury or disease to individuals after birth
Control of Development
• Stem cells are also found in adult
tissues, including the blood-forming
tissues of the bone marrow, and even
in the brain
• The developmental potential of adult stem
cells is only beginning to be understood,
but it is already clear that they also have
the ability to differentiate into a wide
variety of cell types
Later Development
• During the fourth, fifth, and sixth months after
fertilization, the tissues of the fetus become more
complex and specialized, and more tissues begin to
function
• The fetal heart becomes large enough so that it can be
heard with a stethoscope
• Bone continues to replace the cartilage that forms the
early skeleton
• A layer of soft hair grows over the fetus's skin
• As the fetus increases in size, the mother's abdomen
swells to accommodate it
• The mother can begin to feel the fetus moving
Later Development
•
•
•
•
•
During the last three months, the
organ systems mature, and the
fetus grows in size and mass
The fetus doubles in mass, and
the lungs and other organs
undergo a series of changes
that prepare them for life
outside the uterus
The fetus is now able to
regulate its body temperature
In addition, the central nervous
system and lungs complete their
development
The figure shows an embryo and
a fetus at different stages of
development
An Embryo and a Fetus at Different Stages
• At 7 weeks, most of the
organs have begun to form
• The heart—the large, dark
rounded structure—is beating
• By 14 weeks, the hands, feet,
and legs have reached their
birth proportions
• The eyes, ears, and nose are
well developed
• When the fetus is full-term, it is
fully developed and capable of
living on its own
• What significant changes do
you see from 7 weeks to 14
weeks?
An Embryo and a Fetus at Different Stages
5 WEEK OLD EMBRYO
• Visible heart
• Eyes, internal ears, nasal organs, arms,
legs, and digestive system develop
6 WEEK OLD EMBRYO
• Fingers, toes, and external ears form
7 WEEK OLD EMBRYO
• HANDS AND FEET
8 WEEKS EMBRYO
• DISTNCT FINGERS AND TOES
SECOND TRIMESTER
•
•
•
•
•
•
•
•
Middle 3 months of pregnancy
After 8th week
In beginning 5 cm
Called Fetus
Skeleton formed
Soft hair grows over the skin
Eyes open
At end is 32 cm
11-12WEEK OLD FETUS
• NOTE PLACENTA AND UMBILICAL
CORD
12 WEEK OLD FETUS
22 WEEK OLD FETUS
THIRD TRIMESTER
• Final 3 months of pregnancy
• Fetus becoming modified to survive in the
outside world
• Grows in size and weight
Later Development
• On average, it takes nine months for a fetus
to fully develop
• Babies born before eight months of
development, called premature babies, often
have severe breathing problems because of
incomplete lung development
• Premature babies also can be handicapped
because the central nervous system has not
fully developed
Childbirth
• About nine months after fertilization, the fetus is ready for birth
• A complex set of factors affects the onset of childbirth
• One factor is the release of the hormone oxytocin from the
mother's posterior pituitary gland
– Oxytocin affects a group of large involuntary muscles in the
uterine wall
– As these muscles are stimulated, they begin a series of rhythmic
contractions known as labor
• The contractions become more frequent and more powerful
• The opening of the cervix expands until it is large enough for
the head of the baby to pass through it
• At some point, the amniotic sac breaks, and the fluid it contains
rushes out of the vagina
• Contractions of the uterus force the baby, usually head first, out
through the vagina
Childbirth
• As the baby meets the outside world, he or she may
begin to cough or cry, a process that rids the lungs
of fluid
• Breathing starts almost immediately, and the blood
supply to the placenta begins to dry up
• The umbilical cord is clamped and cut, leaving a
small piece attached to the baby
• This piece will soon dry and fall off, leaving a scar known
as the navel—or in its more familiar term, the belly
button
• In a final series of uterine contractions, the placenta
itself and the now-empty amniotic sac are expelled
from the uterus as the afterbirth
BIRTH
• Approximately 270 days after fertilization
• Childbirth is intiated
–
–
–
–
Pituitary gland of the fetus activates
Prostaglandins in the fetal membranes activate
Glands in the mother activate
Estrogen level increases:
• Increasing the ability of the uterine muscles to contract
– Oxytocin:
• Hormone secreted by the posterior pituitary gland
– Causes contractions of the uterus
• Amniotic sac breaks: fluid flows out of the vagina (breaking water)
• Cervix enlarges
• Uterus begins to contract over and over
– Repeated contractions are called labor
– Contractions push the baby’s head against the cervix, through the
cervix, and eventually through the vagina and out
AFTERBIRTH
•
Baby still attached to the placenta by means of the umbilical cord
– Once tied and cut, the baby no longer obtains food and oxygen from the mother
– Navel is the spot where your umbilical cord was attached to your body
•
Lung filled with amniotic fluid
– First cries rid the lungs of fluid and fill them with air
– Newborn begins to breathe on its own
•
In the uterus most of the blood bypassed the lungs
– Right ventricle through a duct into the systemic system
– Duct closes at birth
– Right ventricle begins pumping to the lungs
•
Before birth, an opening exists between the right and left atria
– Normally this opening closes shortly after birth preventing oxygenated and
deoxygenated blood from mixing
•
The remains of the placenta and amnion are then expelled from the
mother’s body about 10 minutes after the birth of the baby (afterbirth)
Childbirth
• The baby now begins an independent
existence
• Most newborn babies are remarkably
hardy
• Their systems quickly switch over to life
outside the uterus, supplying their own
oxygen, excreting wastes on their own,
and maintaining their own body
temperatures
Childbirth
• The interaction of the mother's reproductive
and endocrine systems does not end at
childbirth
• Within a few hours after birth, the pituitary
hormone prolactin stimulates the production
of milk in the breast tissues of the mother
• The nutrients present in that milk contain
everything the baby needs for growth and
development during the first few months of
life
Multiple Births
• Sometimes more than one baby develops
during a pregnancy
• For example, if two eggs are released during the
same cycle and fertilized by two different sperm,
fraternal twins result
• Fraternal twins are not identical in appearance
because each has been formed by the fusion of
a different sperm and egg cell
• Fraternal twins may or may not be the same sex
TWINS
• Identical:
– One embryo splits into two separate embryos
• Probably during the blastocyst stage
• Fraternal:
– Two eggs are fertilized by different sperm
Multiple Births
• Sometimes a single zygote splits apart
to produce two embryos
• These two embryos are called identical
twins
• Identical siblings are formed by the fusion
of the same sperm and egg cell; therefore,
they are genetically identical
• Identical twins are always the same sex
Early Years
• Although the most spectacular changes of
the human body occur before birth,
development is a continuing process—it
lasts throughout the life of an individual
• In the first weeks of a baby's life, the
systems that developed before birth now
move into high gear, supporting rapid
growth that generally triples a baby's
birth weight within 12 months
Infancy
• The first two years of life are known as infancy
• Infancy is a period of rapid growth and development
• The nervous system develops coordinated body
movements as the infant begins to crawl and then to
walk
• A baby's first teeth appear, and the baby begins to
understand and use language
• Growth in the skeletal and muscular systems is
especially rapid, demanding good nutrition to
support proper development
Childhood
• Childhood lasts from infancy until the onset
of puberty, typically at an age of 12 or 13
• Children become more active and
independent
• Language is acquired, motor coordination is
perfected, permanent teeth begin to appear,
and the long bones of the skeletal system
reach 80 percent of their adult length
• The key elements of personality and human
social skills are developed, and reasoning
skills are developed to a high level
Adolescence
• Adolescence begins with puberty and ends
with adulthood
• The surge in sex hormones that starts at
puberty produces a growth spurt that will
conclude in mid-adolescence as the long
bones of the arms and legs stop growing and
complete their ossification
• The continuing development of intellectual skills
combines with personality changes that are
associated with adult maturity
Adulthood
• Development continues during adulthood
• By most measures, adults reach their
highest levels of physical strength and
development between the ages of 25
and 35
• During these years most individuals
assume the responsibilities of adulthood
Adulthood
• In most individuals, the first signs of physiological
aging appear in their thirties
• Joints begin to lose some of their flexibility, muscle
strength starts to decrease, and several body
systems show slight declines in efficiency
• By age 50, these changes, although generally still
minor, are apparent to most individuals
• In women, menopause greatly reduces estrogen
levels
– After menopause, follicle development no longer occurs and
ovulation stops
• At around age 65, most systems of the body become
less efficient, making homeostasis more difficult to
maintain
Adulthood
• Although there are some changes in mental functioning
during older adulthood, these changes usually have
little effect on thinking, learning, or long-term
memory
• The brain remains open to change and to learning
• In fact, evidence suggests that the aging process can
be slowed by keeping the mind active and
challenged
• Most older adults are fully capable of continuing
stimulating intellectual work
• By practicing the habits of good health and regular
exercise, every person can hope to be happy and
productive at every stage of human development