Biology 103 - Main points/Questions
1. Remember Plant Hormones?
2. What are the major human endocrine
glands?
3. What hormones do you need to know?
4. How are hormones controlled?
• In Summer plants
need to balance
root and shoot
growth - too much
of either is a waste
of resources. Do
you remember how
they do this?
shoot tip
gradient of
auxin
(high)
(low)
(high)
gradient of
cytokinin
• plants need to balance
root and shoot growth
– use AUXIN &
CYTOKININ amounts
positive phototropism – controlled by …?
AUXIN!
Light!
• In fall plants need to
respond to
changing
environmental cues
to trigger leaf
senescence (death).
Figure 24.14 The effects of ethylene
Hormone Signals in Animals
• Used for longer term signals than neurons
• Different cells respond to different hormones
• Hormones often key for homeostasis
33.02 The Timescale over
Which Chemical Messengers
Work
• CD33020.GIF
There are three big advantages to using
chemical hormones as messengers rather
than speedy electrical signals (nervous)
1. chemical molecules can spread to all
tissues via the blood
2. chemical signals can persist much longer
than electrical ones
3. many different kinds of chemicals can act
as hormones
Balancing water concentration
• The concentration of the urine is
regulated to maintain homeostasis
• Hormones are key signaling molecules in
this process.
• Negative feedback loops fight
dehydration..
Page. 626
• As you dehydrate you get thirsty (this is
Where does water
controlled by the nervous system)
get reabsorbed in
• Your body also releases a hormone
ADH that
the kidney?
signals to the kidneys.
Page. 626
The 5 steps of
urine formation
1. Pressure
Filtration
2. Reabsorption
of water
3. Selective
reabsorption
4. Secretion
5. More water
reabsorption
Further reabsorption of water
• Final step that balances water amounts
• Water can be variably reabsorbed into
blood from collecting duct
• waters ability to be reabsorbed is controlled
by a hormone called ADH – how?
Hormone signaling is a series of simple steps
1. issuing the command – release of the
hormone from a gland
• Issuing the command
Hormone signaling is a series of simple steps
1. issuing the command
2. transporting the signal
– most are transported through body by the
blood
• Transport
Hormone signaling is a series of simple steps
1. issuing the command
2. transporting the signal
3. hitting the target
– hormone binds to a receptor on the target cell
• “hit the
target”
Hormone signaling is a series of simple steps
1. issuing the command
2. transporting the signal
3. hitting the target
4. having an effect
– After binding the receptor protein changes
shape and triggers a change in cell activity
Two basic categories of hormones
• ADH is a peptide hormone (remember a
peptide bond?
– Built of amino acids
• The other class of hormones are steroid
based
– Steroids are lipids so can pass through
membranes!
• Peptide based
Fat-soluble
hormone
Watersoluble
hormone
– Bind to receptor
on membrane
• Steroid
Signal receptor
Transport
protein
TARGET
CELL
(a)
Signal
receptor
NUCLEUS
(b)
– Transported
attached to a
protein
– Bind to receptor
inside the cell
• Peptide based
Fat-soluble
hormone
Watersoluble
hormone
Transport
protein
Signal receptor
TARGET
CELL
Cytoplasmic
response
OR
(a)
• Steroid
Signal
receptor
Gene
regulation
Cytoplasmic
response
NUCLEUS
(b)
– Signals are
often more
transient (just in
the cytoplasm)
– May alter gene
expression
Gene
regulation
– Mostly alter
gene
expression
– Tend to be long
lasting effects
Hormones are
produced in
glands
throughout your
body
Coordination of Endocrine and
Nervous Systems in Vertebrates
• The hypothalamus receives information
from the nervous system and initiates
responses through the endocrine system
• Attached to the hypothalamus is the
pituitary gland composed of the
posterior pituitary and anterior pituitary
• The posterior pituitary stores and
secretes hormones that are made in the
hypothalamus
• The anterior pituitary makes and
releases hormones under regulation of the
hypothalamus
The posterior pituitary contains cells that
originate in the hypothalamus
The hypothalamus and the posterior pituitary
are connected by a tract of neurons
• hormones are made by cell bodies in the
hypothalamus & moved to posterior pituitary
– antidiuretic hormone (ADH) regulates the
kidney’s retention of water
– oxytocin initiates uterine contractions during
childbirth and milk release in mothers
The anterior pituitary is a complete gland that
produces the hormones that it secretes
The Hypothalamus and the Pituitary
The hypothalamus controls production and
secretion of the anterior pituitary hormones
by means of a family of special hormones
• neurons in the hypothalamus secrete
releasing hormones
• they travel to the anterior pituitary through a
special capillary system,
Portal system of the anterior pituitary gland
and hypothalamus
The Anterior Pituitary
Secretes seven different hormones some you
already know about…
• LH & FSH
Some that are new to you…
• TSH & GH
Pituitary hormones
• Follicle-stimulating hormone (FSH)
– in females, it triggers the maturation of egg
cells and stimulates the release of estrogen
– in males, it regulates sperm development
• Luteinizing hormone (LH)
– in females, it triggers ovulation of a mature egg
– in males, it stimulates the gonads to produce
testosterone
(a)
Control by hypothalamus
Hypothalamus
–
GnRH
+
Inhibited by combination of
estrogen and progesterone
Stimulated by high levels
of estrogen
–
Inhibited by low levels of
estrogen
Anterior pituitary
Estrogen
production
feeds back on
the signal that
drives
estrogen
release
LH
FSH
Pituitary hormones
in blood
(b)
LH
FSH
FSH and LH stimulate
follicle to grow
Ovarian cycle
(c)
Growing follicle
Days
LH surge triggers
ovulation
Follicular phase
|
|
0
5
Corpus
luteum
Maturing
follicle
|
10
Ovulation
|
|
14 15
Degenerating
corpus luteum
Luteal phase
|
20
|
25
|
28
• growth hormone (GH)
– simulates the growth of muscle and bone
throughout the body
• Thyroid stimulating hormone (TSH)
– Stimulates thyroid to produce thyroxin – a key
control of metabolism
• Negative feedback (feedback inhibition)
controls how target gland hormones in the
anterior pituitary are produced
• when enough of the target hormone has
been produced, the hormone then feeds
back to the hypothalamus and inhibits the
release of stimulating hormones from the
hypothalamus and the anterior pituitary
• Thyroxine
– Modifies
metabolic rate
– Requires iodine
• What if you
don’t have
enough iodine?
Fig. 35.11.b
Hormones are key players in
maintaining homeostasis
• Commonly used as signals in negative feedback
loops
• Remember Insulin & Glucagon?
Insulin and Glucagon: Control of
Blood Glucose
• Insulin and glucagon are antagonistic
hormones that help maintain glucose
homeostasis
• The pancreas has clusters of cells that
produce glucagon and insulin
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
rises.
Blood glucose
level declines.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Blood glucose level
falls.
Blood glucose
level rises.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Glucagon
Control of Blood Calcium
• Two antagonistic hormones regulate
calcium (Ca2+) in the blood of mammals
– Parathyroid hormone (PTH) causes blood
calcium levels to increase
– Calcitonin causes blood calcium levels to
decrease.
• PTH increases the level of blood Ca2+
– It releases Ca2+ from bone and stimulates
reabsorption of Ca2+ in the kidneys
– It also has an indirect effect, stimulating the
kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+ from food
• Calcitonin decreases level of blood Ca2+
– It stimulates Ca2+ deposition in bones and
secretion by kidneys
Draw the two negative feedback loops that
involve these two hormones
Increasing Blood
Calcium level
Blood Calcium level
(about 10mg/100ml)
Decreasing Blood
Calcium level
Calcium Regulation
• What happens when calcium levels drop?
• Parathyroid hormone (PTH) is secreted &
causes bone cells to release calcium from
the bones
• PTH also stimulates calcium reabsorption
by the kidneys and absorption by the gut
• So dropping Ca++ leads to raising Ca++
PTH
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+ level
Homeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
Fig. 45-20-2
Active
vitamin D
Increases
Ca2+ uptake
in intestines
Stimulates Ca2+
uptake in kidneys
PTH
Stimulates
Ca2+ release
from bones
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+ level
Blood Ca2+
level rises.
Homeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
Calcium Regulation
• What happens when calcium levels rise?
• Calcitonin is secreted & causes bone cells
to sequester calcium in the bones
• Calcitonin also slows calcium reabsorption
by the kidneys
• So raising Ca++ leads to falling Ca++
Hormonal control of calcium homeostasis in mammals
What do you need to know?
• Control Systems - Hormones:
• List major plant hormones and their roles.
• Explain how the two basic classes of animal
hormones have their effects on a cell.
• Describe antagonistic hormones and explain how
they work together to maintain homeostasis.
• List some major human hormones (certainly you
should know ADH, insulin, glucagon, calcitonin &
PTH and you should be familiar with FSH, LH,
estrogen, and progesterone), where they are
produced and their roles.
Non-mammal Hormones
• In insects, hormonal secretion influence both
metamorphosis and molting
• prior to molting, neurosecretory cells on the surface
of the brain secrete brain hormone
• brain hormone then stimulates a gland in the thorax
to produce molting hormone (ecdysone)
• juvenile hormone is produced in the brain and
determines the result of a particular molt
– when juvenile hormone levels are high, the molt produces
another larva
• Juvenile hormone promotes retention of
larval characteristics
• Ecdysone promotes molting (in the presence
of juvenile hormone) and development (in
the absence of juvenile hormone) of adult
characteristics
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Prothoracic
gland
Ecdysone
EARLY
LARVA
Juvenile
hormone
(JH)
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Prothoracic
gland
Ecdysone
EARLY
LARVA
Juvenile
hormone
(JH)
LATER
LARVA
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Low
JH
Prothoracic
gland
Ecdysone
EARLY
LARVA
Juvenile
hormone
(JH)
LATER
LARVA
PUPA
ADULT
The hormonal control of metamorphosis