Chapter 11
The Endocrine System
Human Anatomy & Physiology - P. Wilson
1
The nervous system & the endocrine system function
coordinately to enable body parts to communicate with each
other & to constantly adjust to changing incoming signals. (see
table on page 277)
Nervous System
Endocrine System
Cells
Neurons
Glandular epithelium
Chemical signal
Neurotransmitter
hormone
Specificity of response
Receptors on postsynaptic
cell (neuron)
Receptors on target cell
Speed of onset
Seconds
Seconds to hours
Duration of action
Very brief unless neuronal
activity continues
May be brief or may last
for days even if secretion
ceases
Human Anatomy & Physiology - P. Wilson
2
Human Anatomy & Physiology - P. Wilson
3
II. 11.1 Introduction & Clinical Example
A. Pheromones are chemical signals (messengers) sent
between individuals of the same species
• The message communicated is usually sexual in nature ( the
pheromones stimulate sexual / reproductive behavior).
• It is thought pheromones lead animals to chose mates that are
genetically dissimilar to themselves.
B. Hormones are chemicals that interact with specific target
cells & affect the functioning of that cells. (Within the
individual!!)
Human Anatomy & Physiology - P. Wilson
4
II. 11.1 Introduction & Clinical Example
C. Exocrine Glands
C. Endocrine Glands
• Secrete their products to the • Secrete their products into
outside of the body through
the internal environment;
tubes or ducts.
the hormones diffuse from
the interstitial fluid into the
• Ex: sweat & saliva glands
bloodstream.
• Ex: testes, ovaries, thyroid
Human Anatomy & Physiology - P. Wilson
5
II. 11.1 Introduction & Clinical Example
D. Paracrine gland secretions
affect only cells in their
immediate surroundings
Ex: mast cells (a type of white
blood cell secrete histimines)
D. Autocrine gland secretions affect
only the cell which secretes them
Ex: neurons secrete neurotransmitters
Human Anatomy & Physiology - P. Wilson
6
III. 11.2 General Characteristics
A. As a group, endocrine glands regulate metabolic processes.
B. To accomplish their functions endocrine glands:
•
•
•
•
control the rate of chemical reactions
aid in the transport of substances across membranes
help regulate water & electrolyte balances
also, play vital roles in reproduction, growth, & development
Human Anatomy & Physiology - P. Wilson
7
IV. 11.3 Hormone Action
A. The specific site of a hormone’s action is called a target
cell.
B. There are 2 types of hormones: steroid & nonsteroid:
• steroid hormones are synthesized from cholesterol
• all other hormones are amines, peptides, proteins, or
glycoproteins and are synthesized from amino acids
Human Anatomy & Physiology - P. Wilson
8
IV. 11.3 Hormone Action
C. Steroid hormones are soluble in lipids and lipids make up
the bulk of cell membranes, therefore steroid hormones can
diffuse into cells easily & rapidly.
• steroid hormone binds to receptor
• hormone-receptor complex binds to a particular region on the DNA and
activates the transcription of a mRNA molecule
• the mRNA molecule leaves the nucleus, links with a ribosome and directs the
synthesis of a specific protein
• the newly synthesized protein (may be an enzyme, a transport protein, or a
hormone receptor) carry out the specific effects associate with the particular
steroid hormone
Human Anatomy & Physiology - P. Wilson
9
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
11 - 10
IV. 11.3 Hormone Action
C. Nonsteroid hormones are not soluble in lipids and must
follow a more complicated path through a process called
signal conduction
• This path employs a binding site, an activity site, a first
messenger, a second messenger
D. Cyclic adenosine monophosphate (cAMP) is a second
messenger associated with one group of hormones
Human Anatomy & Physiology - P. Wilson
11
IV. 11.3 Hormone Action
E. Prostaglandins are biochemical (lipids) synthesized from a
fatty acid in cell membranes. Their effect is more localized
than hormones, usually affecting only the organ where they
are produced. Prostaglandins
• are potent & are present in very small quantities
• are not stored in cells but are synthesized just prior to release
• produce diverse & even opposite effects (some may relax smooth
muscles, others may contract smooth muscles
• stimulate secretions of other hormones, influence blood pressure &
inflammation, and have powerful effects on male & female
reproductive physiology
Human Anatomy & Physiology - P. Wilson
12
V. 11.4 Control of Hormonal Secretions
A. Hormone secretions are controlled in 3 ways, all of which
employ negative feedback:
1. The release of trophic hormones from the hypothalamus controls
secretions of the anterior pituitary.
2. The nervous system influences certain endocrine glands directly.
3. Other glands respond to changes in the composition of internal
fluids.
Human Anatomy & Physiology - P. Wilson
13
V. 11.4 Control of Hormonal Secretions
B. When the level of a
hormone in the blood rises
to a certain level (above
the set point), negative
feedback inhibits the
system & hormone release
decreases. As the hormone
levels in the blood
decrease to the set point,
inhibition is lifted &
secretion of the hormone
increases again.
Human Anatomy & Physiology - P. Wilson
14
V. 11.4 Control of Hormonal Secretions
C. The brain controls the activity of the pituitary (the master
gland) via the hypothalamus.
• The location of the hypothalamus allows it to receive a constant
flow of information about the body’s internal environment from
neural connections and the CSF.
Human Anatomy & Physiology - P. Wilson
15
VI. 11.5 Pituitary Gland
A. The pituitary gland
• is about the size of a pea and has a mass of about 0.5 gram
• it is located at the base of the brain inferior to the hypothalamus &
is surrounded by a bony cavity called the sella turcica
• it is attached to the hypothalamus by a stalk called the pituitary
stalk or the infundibulum
• it consists of an anterior lobe and a posterior lobe
Human Anatomy & Physiology - P. Wilson
16
Human Anatomy & Physiology - P. Wilson
17
Hormone
Stimulus for secretion
Actions
Growth hormone GH)
The hypothalamus releases a
GH - stimulating hormone
Stimulates cells to increase in size & to
divide more frequently. Enhances the
movement of amino acids across the cell
membrane, & speeds the rate at which
cells utilize carbohydrates & fats.
Prolactin (PRL)
The hypothalamus releases a
prolactin- stimulating hormone
Sustains milk production. Hormone release
is stimulated by the suckling of an infant.
Thyroid stimulating
hormone - TSH
The hypothalamus releases a
thyrotropin - stimulating hormone
Controls secretion of hormones from the
thyroid gland
Adenocorticotrophic
hormone - ACTH
Regulated by corticotropic releasing
hormone & by stress
Stimulates the release of hormones from
the adrenal cortex
Follicle stimulating
hormone (FSH) &
Luteinizing hormone
(LH)
The hypothalamus releases a
gonadotropin-releasing hormone (GnRH)
(these are sex hormones)
Stimulates the male & female reproductive
organs.
Anterior lobe
Human Anatomy & Physiology - P. Wilson
18
Hormone
Stimulus for secretion
Actions
Posterior lobe
Antidiuretic hormone
Stimulated by the hypothalamus in Causes the kidneys to conserve water.
response to changes in water
In high concentrations, this hormone
concentration
increases blood pressure
Oxytocin
Stimulated by the hypothalamus in Contracts the muscles in the uterine
response to stretching of the
wall in labor and contract muscles
muscles of the uterine wall and
associated with milk secreting glands
stimulation of the breast
This table can be found on
page 286 or your text book
Human Anatomy & Physiology - P. Wilson
19
VII. 11.6 Thyroid Gland
See figure 11.10 on page 287
Human Anatomy & Physiology - P. Wilson
20
VII. 11.6 Thyroid Gland
B. Thyroid hormones:
1. Iron is essential for the synthesis of triiodothyronine (T3)
and thyroxine (T4).
2. Secretions of T3 & T4 are stimulated by TSH (released by the
anterior pituitary).
• Both T3 & T4 increase the rate of energy release from carbohydrates,
increase the rate of protein synthesis, stimulate the breakdown &
mobilization of lipids,
• Both T3 & T4 are required for normal growth & development and are
essential to nervous system maturation
• but triiodothyronine is five times more potent that thyroxine
T3 & T4 are the major factors determining how many calories a
body must consume at rest in order to maintain life – the basal
metabolic rate (BMR).
Human Anatomy & Physiology - P. Wilson
21
VIII. 11.7 Parathyroid Gland
A. The
parathyroid
glands are
located on the
posterior
surface of the
thyroid gland
Human Anatomy & Physiology - P. Wilson
22
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
11 - 23
VIII. 11.7 Parathyroid Gland
B. Parathyroid hormone
(PTH) increases blood
calcium ion
concentration and
decreases phosphate
ion concentration.
C. Calcitonin increases the rate
at which calcium is stored in
bones and excreted in the
urine.
• In short: calcitonin lowers
blood calcium ion
concentration.
Calcitonin and PTH exert opposite effects in
regulating calcium ion levels in the blood.
Human Anatomy & Physiology - P. Wilson
24
IX. 11.8 Adrenal Glands
A. The adrenal glands sit like a cap on top of the kidneys and
are enclosed in a layer of fat.
B. 1. The adrenal medulla secretes 2 hormones: epinephrine
and norepinephrine.
B. 2. The effects of these hormones resemble those of the
sympathetic division neurotransmitters of the same name,
except that they last up to 10 times longer when they are
secreted as hormones.
• They are used in times of stress for “fight or flight”
Human Anatomy & Physiology - P. Wilson
25
IX. 11.8 Adrenal Glands
Human Anatomy & Physiology - P. Wilson
26
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
IX. 11.8 D.
Corticotrophinreleasing hormone
Adrenocorticotropic
hormone (from anterior
pituitary)
11 - 27
IX. 11.8 D Cortisol Release Sequence
1. Centers in the higher brain receives sensory input & sends a signal
to the hypothalamus.
2. The hypothalamus is stimulated to release CRH.
3. The pituitary is stimulated by the CRH to release ACTH which
stimulates the adrenal cortex to release cortisol.
4. Cortisol enters the bloodstream and affects the target cells.
5. When blood glucose levels reach set point, cortisol levels inhibit the
release of CRH & ACTH.
Human Anatomy & Physiology - P. Wilson
28
IX. 11.8 Adrenal Glands C. Adrenocortical Hormones
Hormone
Stimulus for
secretion
Effects of the Hormone
Mineralocorticoids
(aldosterone)
Decrease in Na
concentration or
an increase in K
concentration
Conservation of Na &excretion of K, and conservation of
water
Glucocorticoids
(cortisol)
Released by the
hypothalamus
• Increases amino acids by decreasing protein synthesis
• Increases the use of fatty acid as an energy source
• Stimulates the liver to synthesis glucose from
noncarbohydrates
The overall effect is to maintain blood glucose concentration
and in times of stress to maintain a constant supply of blood
glucose (required when a body is under stress)
Sex hormones
(adrenal androgens)
Not known
May supplement the supply of sex hormones from the gonads
and stimulate early development of sexual organs.
The hormones produced are androgens (male type
hormones) but some are converted to estrogens (female type
hormones)
in -females
Human Anatomy
& Physiology
P. Wilson
29
X. 11.9 Pancreas
The pancreas is
posterior to the
stomach
and
anterior to the
spine
Human Anatomy & Physiology - P. Wilson
30
X. 11.9 Pancreas
Hormone
Source of control
Effects of hormone
Glucagon
Low blood sugar concentrations
stimulate the alpha cells of the
pancreas to release glucagon
• Glucagon stimulates the liver to break down
glycogen & noncarbohydrates (such as amino
acids) into glucose.
• Glucagon raises blood sugar very rapidly
Insulin
High blood sugar concentrations
stimulate the beta cells of the
pancreas to release insulin
• Insulin stimulates the liver to make glycogen from
glucose and inhibits the use of amino acids to
form glucose.
• Insulin also promotes facilitated diffusion of
glucose across cell membranes that have insulin
receptors
• Insulin promotes the transport of amino acids
into cells, promotes protein synthesis, &
stimulates adipose tissue to store fat
• These actions of insulin decreases blood glucose
Human Anatomy & Physiology - P. Wilson
31
(sugar) concentration.
Human Anatomy & Physiology - P. Wilson
32
XI. 11.10 Other Endocrine Glands
A. Pineal Gland
• is located deep between the
cerebral hemispheres & is
attached to the upper portion
of the thalamus.
• Secretes melatonin in
response to light conditions
outside the body. Melatonin
acts on certain brain regions
that function as a “biological
clock” & therefore may help
regulate circadian rhythms.
Human Anatomy & Physiology - P. Wilson
33
XI. 11.10 Other Endocrine Glands
B. Thymus Gland
• is located in the mediastinum
posterior to the sternum &
between the lungs
• it is relatively large in children
but shrinks with age
• secretes a group of hormones
called thymosins that affect the
production & differentiation of
certain WBCs (lymphocytes) so
it plays an important role in
immunity
Human Anatomy & Physiology - P. Wilson
34
XII. 11.11 Stress & Health
A. A factor that can trigger the body’s physiological responses
to stress is called a stressor. A stressor can be physical or
psychological.
• Physical stressors can include exposure to extreme heat or cold,
decreased oxygen concentration, infection, injury, prolonged
exercise, or loud noises.
• Psychological stressors can include thoughts about real or imagined
dangers, personal loses, unpleasant social interactions, or feelings
of grief, anger, anxiety, depression, & guilt
Human Anatomy & Physiology - P. Wilson
35
XII. 11.11 Stress & Health
A. Physiological
responses to stress
(which are under
control of the
hypothalamus) are
referred to as
general
adaptation
syndrome. There
are 2 stages to this
response: 1) fight
or flight;
2)resistance
Human Anatomy & Physiology - P. Wilson
36
XII. 11.11 Stress & Health
C. The positive effects of
stress syndrome are
increased alertness &
endurance.
D. The negative effects of
stress syndrome are
increased risk of
hypertension,
atherosclerosis (hardening
& narrowing of the arteries
due to plaque buildup), &
gastrointestinal ulcers.
Human Anatomy & Physiology - P. Wilson
37