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Endocrine System
Martini Chapter 18
Functions of the
Endocrine System



Controls the processes involved in
movement and physiological equilibrium
Includes all tissues or glands that secrete
hormones into the blood
The number of receptors for a specific
hormone can be altered to meet the body’s
demand
2
Endocrine Glands

Secrete products (hormones) into
bloodstream


Pituitary, thyroid, parathyroid, adrenal, pineal
Other organs secrete hormones as a 2nd
function

Hypothalamus, thymus, pancreas,ovaries,testes,
kidneys, stomach, liver, small intestine, skin, heart &
placenta
3
Hormone Receptors

“Lock and Key” approach: describes the
interaction between the hormone and its
specific receptor.
 Receptors for nonsteroid hormones are
located on the cell membrane
 Receptors for steroid hormones are found
in the cell’s cytoplasm or in its nucleus
4
Classification of Hormones






Steroid Hormones
Lipid soluble
Derived from
cholesterol
Gonads: Androgens,
Estrogens, Progestins
Adrenal cortex: Corticosteroids, androgens
Kidneys: calcitriol
5
Classification of Hormones


Peptide Hormones
Water soluble Glycoproteins and short
polypeptides
 Pituitary
 Kidneys
These all secrete
 Hypothalamus
Water soluble
 Heart
Peptide Hormones
 Pancreas
 Parathyroid
6
Classification of Hormones



Amino Acid Derivatives
Thyroid Hormone: Lipid soluble
Catecholamines: Water Soluble
 Epinephrine
 Norepinephrine
 Dopamine
7
Hormone Receptors

Hormones only affect target cells with
specific membrane proteins called receptors
8
Number of Receptors



Receptors are constantly being synthesized &
broken down
Down-regulation: is the decrease of hormone
receptors which decreases the sensitivity to that
hormone
 Receptors undergo endocytosis
Up-regulation: deficiency of hormone, produces
an increase in the number of receptors
 Target tissue more sensitive to the hormone
9
Hormone Transport in Blood


Water soluble hormones circulate in free
form in the blood
Steroid (lipid) & thyroid hormones must
attach to transport proteins synthesized by
liver
10
Lipid Soluble Hormone Actions


Pass through the cell membrane and binds to a
receptors
Then enters the nucleus to bind with DNA


Activates certain genes (Direct gene activation).
mRNA is synthesized → protein synthesis for:
 Enzymes as catalysts
 Tissue growth and repair
 Regulate enzyme function
11
Lipid Soluble Hormone Actions
12
Water Soluble Hormone Actions

React with receptors outside the cell



Activates G-protein in the membrane
Leads to the formation of a second messenger (cAMP).
cAMP can produce specific intracellular functions:
 Activates cell enzymes
 Change in membrane permeability
 Promote protein synthesis
 Change in cell metabolism
 Stimulation of cell secretions
13
Nonsteroid Hormone Actions
Nonsteroid
hormone
14
Amplification of Hormone
Effects


Response to a lipid soluble hormone is directly
proportional to the number of hormone-receptor
complexes available
Response to a water soluble hormone is greatly
amplified.


Cells are highly sensitive to changes in the concentration
of nonsteroid hormones
Each target cell responds to hormone differently
 Liver cells: insulin stimulates glycogen synthesis
 Adipose: insulin stimulates triglyceride synthesis
15
Control of Hormone Secretion



Regulated by signals from nervous system,
chemical changes in the blood or by other
hormones
Negative feedback is the primary
mechanism through which the endocrine
system maintains homeostasis
Disorders involve either hyposecretion or
hypersecretion of a hormone
16
Hypothalamus




It is the master of the
Pituitary Gland
 8 different releasing &
inhibiting hormones
This is the main
interface between
the nervous system and the endocrine system
Located in the brain, this region controls most
endocrine secretions
Mainly regulatory hormones are released here.
Most control the pituitary gland
18
Pituitary Gland



Pea-shaped, 1/2 inch gland found in sella turcica
of sphenoid
Infundibulum attaches it to brain (at the
hypothalamus)
Anterior lobe


Secretes mainly regulatory hormones
Posterior lobe



Ends of axons of 10,000 neurons found in
hypothalamus
Neuroglial cells called pituicytes
Secretes hormones, but manufactures none
19
Anterior
Pituitary
Hypothalamus
Infundibulum
Posterior Pituitary
Sella Turcica
20
Flow of Blood to Anterior Pituitary



Controlling hormones from hypothalamus enter
blood
Travel through the hypophyseal portal system of
veins (2 capillary beds in series)
Enter anterior pituitary at capillaries
21
Hypothalamus
Releasing Hormones
GHRH
→
GHIH (GH-Inhibiting-H)
→
CRH(corticotropin-RH)
→
→
GnRH (gonadotropin-RH)
PRH (PRL-releasing)
PIH (PRL inhibiting)
TRH (thyrotropin-RH)
Anterior Pituitary
→
→
→
GH (growth hormone)
(AKA: somatotropin)
GH (growth hormone)
ACTH (adrenocorticotropic)
LH (luteinizing hormone)
FSH (follicle-stimulating)
PRL (prolactin)
PRL (prolactin)
TSH (thyroid stimulating)
22
23
Anterior Pituitary
Growth Hormone (GH)



The anterior pituitary releases bursts of GH
every few hours.
A major regulator is the blood glucose level
During hypoglycemia, the hypothalamus secretes
GHRH

Anterior pituitary releases more GH, more glycogen
broken down into glucose by liver cells
24
Growth Hormone
GH

Anterior Pituitary
Within target cells increases synthesis of insulinlike growth factors that act locally or enter
bloodstream
 ↑ cell growth & cell division



Remember from the skeletal system, it stimulates
cartilage and therefore bone growth in children
↑ lipolysis in adipose so fatty acids used for
ATP
↓ glucose for ATP production so blood glucose
levels remain high enough to supply brain
25
Anterior Pituitary
Growth Hormone
Effects
26
Hypothalamus
Inhibition of Growth Hormone



Growth hormone-inhibiting hormone
(GHIH) suppresses the secretion.
The hypothalamus releases this in response
to hyperglycemia
GHIH inhibits the anterior pituitary
secretion of GH

Less GH from anterior pituitary, glycogen does
not breakdown into glucose
27
Anterior Pituitary
Growth Hormone (GH) Diseases
(refer to skeletal system notes from 231 for details)



Too much GH in children leads to gigantism
Too much GH in adults leads to acromegaly
Too little GH in children leads to dwarfism
Pituitary Dwarfism
Acromegaly
28
29
Anterior Pituitary
Thyroid Stimulating Hormone:
TSH


This pituitary hormone stimulates the
thyroid gland synthesis & secretion of T3
and T4
Metabolic rate stimulated
30
Anterior Pituitary
Adrenocorticotropic Hormone
ACTH



Pituitary secretion stimulated by CRH
(corticotropin releasing hormone) from the
hypothalamus
ACTH works on the cortex of the adrenal
gland to release glucocorticoids.
Stress can increase CRH secretion which
will increase ACTH secretion
31
Anterior Pituitary
ACTH
Negative
Feedback
32
Anterior Pituitary
Follicle Stimulating Hormone:
FSH



Initiates the formation of follicles within the
ovary
Stimulates follicle cells to secrete estrogen
Stimulates sperm production in testes
33
Luteinizing Hormone
LH


Anterior Pituitary
In females, LH stimulates
 Ovulation
 Formation of corpus luteum
 Secretion of progesterone
In males, stimulates interstitial cells
to secrete testosterone
34
Anterior Pituitary
Prolactin: PRL

In females, PRL promotes lactation



Suckling reduces levels of hypothalamic
inhibition and prolactin levels rise along with
milk production
In males, PRL decreases LH secretion (note
that too much PRL would then decrease
androgen levels and cause sterility)
Controlled by both PRH and PIH from the
hypothalamus
35
Posterior Pituitary
(Neurohypophysis)



Posterior Pituitary
No hormones are made here. They are made in
the hypothalamus and just released here.
Consists of axon terminals of hypothalamic
neurons
Neurons release two neurotransmitters that enter
capillaries
 Antidiuretic hormone
 Oxytocin
36
Antidiuretic Hormone
ADH



Posterior Pituitary
AKA: Vasopressin
ADH decreases urine formation by having
kidneys conserve water
ADH release triggered by osmoreceptors
and inhibited by stretch receptors in blood
vessels
37
Posterior Pituitary
38
Posterior Pituitary
Diabetes Insipidus


Caused by a lack of ADH
Diabetes insipidus is
caused by the inability of
the kidneys to conserve
water, which leads to
frequent urination and
pronounced thirst.
39
Posterior Pituitary
Oxytocin


Two target tissues both involved in
neuroendocrine reflexes
During delivery




Baby’s head stretches cervix
Hormone release enhances
uterine muscle contraction
Baby & placenta are delivered
After delivery


Suckling & hearing baby’s cry stimulates milk ejection
Hormone causes muscle contraction & milk ejection
40
Posterior Pituitary
Oxytocin During Labor






Stimulation of uterus by baby
Hormone release from posterior pituitary
Uterine smooth muscle contracts until birth of
baby
Baby pushed into cervix increases hormone
release
More muscle contraction occurs
When baby is born, positive feedback ceases
41
(GHIH)
42
Thyroid
Thyroid Gland


Located on the
anterior surface of
the larynx (neck)
Has 2 lobes
connected by the
isthmus
43
Thyroid
Histology of the Thyroid

Follicle: sac of stored
hormone (colloid)
surrounded by follicle
cells that produced it



T3 & T4
Inactive cells are short
In between cells called
parafollicular cells

Produce calcitonin
44
Thyroid
Follicular Cells
45
Thyroid
Formation of
Thyroid Hormone
1. Iodide is actively transported into thy cytoplasm of
the follicle cells
2. Iodide diffuses to apical surface of cell and is
converted to I+ by thyroid peroxidase
3. Synthesis of thyroglobulin (TG) in the follicle cell
4. Release of TGB into colloid
5. Iodination of a tyrosine molecule on the TG in
colloid forming T3 & T4
6. T3 & T4 re-enter the follicle cell by endocytosis
7. T3 & T4 diffuse into blood and attach to transport
46
proteins TGB
47
Thyroid
Actions of Thyroid
Hormones


T3 & T4: thyroid hormones
responsible for metabolic
rate, synthesis of protein,
breakdown of fats, use of
glucose for ATP production
Calcitonin: responsible for
building of bone & stops
reabsorption of bone (lower
blood levels of Calcium)
48
Thyroid
Control of T3 & T4 Secretion




Negative feedback system
Low blood levels of hormones stimulate
hypothalamus
It stimulates pituitary to release TSH
TSH stimulates gland to raise blood levels
49
Thyroid
Thyroid
Negative
Feedback
T3 & T4
50
Thyroid Negative Feedback
Calcitonin
Thyroid
Calcitonin production is not regulated by the anterior pituitary.
It's secretion is stimulated by high calcium levels in the blood.51
Medical Example: Endemic
(Colloid) Goiter



Thyroid
Occurs in people living in
geographical areas within iodinedepleted soil, causing iodine
deficiency.
Remember: iodine is vital in the
formation of thyroid hormone.
Iodized table salt in the U.S.
prevents this deficiency; however,
it is still common in central Asia
and Central Africa.
52
53
Hyperthyroidism:
Grave’s Disease

This is an autoimmune disease




Thyroid
Immune system over stimulates the thyroid gland
Symptoms include insomnia, irritability, weight
loss, heat sensitivity, increased perspiration, fine
or brittle hair, muscular weakness, rapid heart
beat, and hand tremors.
Grave’s Disease is the only kind of
hyperthyroidism that is associated exophthalmos
Some patients will develop lumpy reddish
thickening of the skin in front of the shins called
pretibial myxedema
54
Thyroid
Grave’s Disease
Exophthalmos
Pretibial Myxedema
55
Thyroid
Hypothyroidism



Hypothyroidism during infancy results in
dwarfism & retardation called cretinism
Hypothyroidism in adult produces
sensitivity to cold, low body temp. weight
gain & mental dullness and depression
Hashimoto's Thyroiditis an autoimmune
disease in which the immune system
attacks and destroys the thyroid gland
56
Thyroid
57
Thyroid
Hypothyroidism
Endemic goiter
and cretinism
Cretinism
58
Parathyroid
Parathyroid Glands



These are 4 pea-sized glands
found on back of thyroid
gland
Principal cells produce
parathyroid hormone (PTH)
PTH function

Increases blood calcium (Ca2+)
levels and decreases blood
phosphate (PO42-) levels
59
Parathyroid
Parathyroid Hormone



Raise blood calcium levels
 ↑ activity of osteoclasts
+2 by kidney
 ↑ reabsorption of Ca
 ↓ reabsorption of phosphate
 ↑ formation of calcitriol (vitamin D3) by kidney
which increases absorption of Ca+2 and Mg+2
by intestinal tract
Opposite function of calcitonin
PTH is regulated by blood calcium levels, not by
other glands!
60
Parathyroid
↓ Serum Ca+
↑ Serum Ca+
61
Parathyroid
Hyperparathyroidism

Stimulates excessive osteoclast activity


Bones become soft and subject to
spontaneous fractures; is most often caused
by a tumor (parathyroid adenoma).
Secondary hyperparathyroidism is caused
by renal failure
62
Parathyroid
63
Parathyroid
Hypoparathyroidism


Symptoms include muscle cramps and
seizures
Most common cause is inadvertent surgical
removal or injury after thyroid surgery.
64
Adrenal
Adrenal Glands



One on top of each
kidney
Cortex produces 3
different types of
hormones from 3
zones of cortex
Medulla produces
epinephrine &
norepinephrine
65
Adipose tissue
Structure of
Adrenal Gland
Adrenal
Capsule
Zona Glomerulosa
Zona Fasciculata
Zona Reticularis
Adrenal Medulla
66
Adrenal
Adrenal Medulla


Acts very much like a part of the sympathetic
nervous system (fight or flight)
Secretes the catecholamines
 Epinephrine & norepinephrine
 Stimulated by preganglionic neurons directly,
so controlled by the hypothalamus as if part of
the autonomic nervous system, NOT by tropic
hormones
67
Adrenal
Adrenal Cortex




Secretes over 30 different steroid hormones
(corticosteroids)
Mineralocorticoids
 Aldosterone: maintains electrolyte balance
Glucocorticoids
 Cortisol
Gonadocorticoids
 Testosterone, estrogen, progesterone
68
Adrenal
Adrenal Cortex
69
Adrenal
Aldosterone



Mineralocorticoid from the Zona Glomerulosa
Functions
+
 Decreases the amount of Na ,Cl , HCO3
and water excreted by the kidney
+
+
 ↑ excretion of K and H
Hypersecretion: tumor producing
aldosteronism
 High blood pressure caused by retention of
Na+ and water in blood
70
Adrenal
Aldosterone Secretion
↑ Plasma K+
↓ Plasma Na+, blood
pressure & blood volume
↑ Aldosterone Secretion
↑ Kidney
K+ secretion
(↓ Plasma K+)
↓ Kidney Na+
Excretion
(↑ plasma Na+)
71
Adrenal
Regulation of Aldosterone



Blood plasma ion concentrations affect its
secretion directly (but not always strongly)
Kidney secretes renin in response to altered
electrolyte levels, which triggers
angiotensin activation in the blood, which
leads to aldosterone secretion
ACTH from the anterior pituitary can cause
aldosterone secretion
72
Adrenal
73
Adrenal
Cortisol




Glucocorticoid from the Zona Fasciculata
Functions to help regulate metabolism
Overall effect is to help keep blood glucose
within a normal range between meals
Anti-inflammatory effects



Decreases the permeability of capillaries
Inhibits the synthesis of prostaglandins
Stabilizes lysosomal membranes
74
Adrenal
Cortisol Functions

↓ Synthesis of protein


↑ Release of fatty acids from adipose tissue


Increases blood concentration of amino acids
Increasing the fatty acids as an energy source and
decreasing the use of glucose as an energy source
It stimulates liver cells to synthesize glucose from
noncarbohydrates (gluconeogenesis), such as
circulating amino acids and glycerol, thus
increasing blood glucose concentrations
75
Adrenal
Brain
↑
Glucose
available to
brain
76
Adrenal
Cushing Syndrome





Hypersecretion of
glucocorticoids
Redistribution of fat
(buffalo hump), spindly
arms & legs due to
muscle loss
Moon Face
Purple Striae (stretch
marks)
Wound healing is poor,
bruise easily
77
Adrenal
Addison’s Disease


Hyposecretion of
glucocorticoids
Rare: 1 in 100,000



Hypoglycemia, muscle
weakness, low BP, dehydration
due to decreased Na+ in blood
Mimics skin darkening effects of
MSH
Potential cardiac arrest
78
Adrenal
DHEA: Androgens



Hormones produced from DHEA are male
(adrenal androgens)
Some of them are converted into female
hormones (estrogens) by the skin, liver, and
adipose tissues.
These hormones may supplement the supply of
sex hormones from the gonads and stimulate
early development of the reproductive organs.
79
Congenital Adrenal
Hyperplasia (CAH)




Adrenal
Autosomal recessive disorders that have
complete or partial deficiency of an enzyme
involved in cortisol or aldosterone synthesis.
The precursors are turned into DHEA (androgen)
Male infants: present at 3-4 with salt wasting with
vomiting, diarrhea, dehydration
Female infants: present at birth
with ambiguous genitalia
because of virilization due
to excess androgens
This is a GIRL80
Pancreas
Pancreas



Organ (5 inches) consists of head, body & tail
Cells (99%) in acini produce digestive enzymes
Endocrine cells in pancreatic islets produce
hormones
81
Pancreas
82
Pancreas
Pancreas Histology
Acini produce digestive enzymes (exocrine)
83
Pancreatic Islets
(Islets of Langerhans)



Pancreas
Alpha cells (20%) produce glucagon
 Increase Glucose
Beta cells (70%) produce insulin
 Decrease Glucose
Delta cells (5%) produce somatostatin
 Inhibits Glucagon and Insulin
84
Pancreas
Glucagon

It works on the liver to cause the
production of glucose via:



It is regulated by blood glucose levels
directly:


Glycogenolysis (break down glycogen)
Gluconeogenesis (break down glucose)
Secreted when blood glucose drops (before
next meal)
Prevents hypoglycemia
85
Pancreas
Insulin

It works on the liver to remove glucose
from the blood via:





Making glycogen
Preventing gluconeogenesis
Increasing glucose transport into cells
It is also regulated by blood glucose levels
directly
Prevents hyperglycemia
86
Pancreas
Note: glucagon
and insulin work
in opposition,
and their
combined effects
control blood
glucose
87
Pancreas
Diabetes




Type 1: Insulin Dependent Diabetes
AKA: juvenile diabetes
Caused by a lack of insulin
Autoimmune disorder

Immune system destroys beta cells in the
pancreas
88
Pancreas
Diabetes



Type 2: Non-Insulin Dependent
Caused by an insensitivity of cells to insulin.
(Down regulation of receptors)
Diabetes mellitus marked by hyperglycemia



↑ urine production (polyuria)
↑ thirst (polydipsia)
↑ eating (polyphagia)
89
Pineal Gland


Secretes only one
hormone: melatonin
Involved in circadian rhythms
(Recognition of day and night times)



Day ↓ melatonin
Night ↑ melatonin
Melatonin secretion produces sleepiness
90
Other Endocrine Hormones


We will be covering these in great detail
when we study the other systems.
Reproductive system:


Renal System


LH, FSH, Estrogen, Progesterone, Testosterone
Renin, Angiotensin
Heart

Atrial natriuretic peptide
91
Stress
Stress & General Adaptation
Syndrome




Stress response is a set of bodily changes called
general adaptation syndrome (GAS)
Any stimulus that produces a stress response is
called a stressor
Stress resets the body to meet an emergency
As a result of the general response to stress, the
blood concentration of epinephrine, cortisol, and
aldosterone increase.
93
94
Alarm Phase




Immediate response to stress
Directed by the sympathetic nervous system
“Fight or Flight response”
Epinephrine plays the dominant role
95
Resistance Phase

Initiated by hypothalamic releasing
hormones (long-term reaction to stress)


Corticotropin, growth hormone & thyrotropin
releasing hormones
Allow body to continue to fight a stressor
96
Resistance Phase

Glucocorticoids are released (↑ cortisol so protein
catabolism is increased & other sources of glucose
are found)




↑ Aldosterone



Mobilize lipid and protein reserves
Conserve glucose for neural tissue
Elevate and stabilize blood glucose concentrations
Conserve salts and water
Eliminate K+ and H+.
↑ Thyroid hormone to ↑ metabolism
97
Exhaustion



Resources of the body have become depleted
Resistance stage can not be maintained
Prolonged exposure to resistance reaction
hormones




Wasting of muscle
Suppression of immune system
Ulceration of the GI tract
Failure of the pancreatic beta cells
98
The End