1. Parathyroid Hormones
Calcitonin (Thyrocalcitonin) is made by the parafollicular (C-cells) of the thyroid gland and
when secreted lowers the blood calcium level
An increase in blood calcium will stimulate the C-cells of the thyroid to secrete calcitonin
Increased calcitonin will cause a negative feedback inhibition of parathyroid hormone (PTH) which
causes a decrease in blood calcium and an increase in blood phosphate levels

2. PARATHYROID HORMONES (Interactions Animation)
Calcitonin
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3. Parathyroid Hormones
Parathyroid hormone (PTH) is made by the more numerous chief (principal) cells of the gland
PTH increases absorption
of Ca2+ from the GI tract
and stimulates osteoclastic
activity so that Ca2+ is
released from bone into
the blood

4. PARATHYROID HORMONES (Interactions Animation)
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5. Calcium Regulation 1 High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT. 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level. 3 2 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level. 2 1
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 5 1
CALCITRIOL stimulates
increased absorption of
Ca2+ from foods, which
increases blood Ca2+ level.
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 5 6

6. The Adrenal Glands
There are two adrenal glands, one superior to each kidney (also called the suprarenal glands). During embryonic development, the adrenal glands differentiate into two structurally and functionally distinct regions
the adrenal cortex
the adrenal medulla
Steroid hormones like cortisol
Catecholamines like norepinephrine

7. The Adrenal Glands

8. The Adrenal Cortex
The adrenal cortex is peripherally located and makes up 80-90% of the total weight of the gland
The cortex is subdivided into three zones, each of which secretes a different group of steroid hormones, all formed
from the cholesterol
molecule

9. Adrenocortical Hormones
Just deep to the CT capsule, the cells of the zona glomerulosa synthesize mineralocorticoid hormones
The middle zone, or zona fasciculata, secrete mainly glucocorticoid hormones,
primarily cortisol
The inner zona reticularis
is the site of synthesis
of weak androgens
(masculinizing hormones)

10. Adrenocortical Hormones
Mineralocorticoids regulate the concentrations of Na+ and K+ in the blood (affects blood volume/pressure)
Aldosterone is the major hormone in this group
Glucocorticoids influence glucose metabolism and the ability to resists the effects of stress
Cortisol is the major hormone in this group
Weak androgens (masculinizing sex hormones) have little effect in men, but play an important role in promoting libido in women

11. RAAS
The most important effects of aldosterone is seen in the renin-angiotensin-aldosterone system (RAAS)
The RAAS is stimulated by a decrease in blood volume and/or blood pressure – as in cases of dehydration or hemorrhage. Low BP stimulates juxtaglomerular cells
in the kidney to
secrete the
enzyme renin

12. RAAS
Renin converts the plasma protein angiotensinogen (produced in the liver) into angiotensin I. As angiotensin I circulates to the lungs, an enzyme called angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II
Angiotensin II stimulates the adrenal cortex to secrete aldosterone (salt and H20 resorption indirectly increases BP), and it is a
potent vasoconstrictor (which
directly increases BP)

13. RAAS

14. Glucocorticoids
Glucocorticoids (mainly cortisol) regulate metabolism by promoting the breakdown of proteins and fats to form glucose (gluconeogenesis). Increased blood sugar levels assist the body to cope with stress
Their inflammatory effects result from inhibiting white blood cells. Unfortunately they also retard tissue repair and slow wound healing
glucocorticoids are very useful in the treatment of chronic inflammatory disorders such as Lupus, though long term side-effects are severe

15. Glucocorticoids
High levels of circulating cortisol, as seen with corticosteroid drugs (prednisone), or tumors (adrenal cortex, pituitary gland) is called Cushing’s syndrome
Manifestations include hyper-
glycemia, poor wound healing,
osteoporosis, dermatitis, fat
redistribution (spindly arms and
legs, moon face, buffalo hump at
the neck), and truncal obesity

16. Glucocorticoids
In adults, hyposecretion of glucocorticoids and aldosterone, usually as a result of an autoimmune disorder, is called Addison’s disease
The physiologic effects include
hypoglycemia, Na+ loss, low BP,
dehydration, and muscle weakness
only after his death did the world
learn that President Kennedy
suffered from Addison’s disease
Many people know that U.S. President John F. Kennedy ( ) suffered from back pain most of his life and that he was assassinated in But it was not until after his death that the public learned that President Kennedy also had Addison's disease.
Addison's disease is a chronic condition that results when the adrenal glands are unable to produce enough of certain important hormones. This can lead to fatigue, low blood pressure, loss of appetite, and darkening of the skin.
It is a rare condition that results when the body fails to produce enough of certain hormones* that help regulate important body functions.
Image from

17. The Adrenal Medulla
The inner region of the adrenal gland, the adrenal medulla, is a modified sympathetic ganglion that develops from the same embryonic tissue as all other sympathetic ganglia of the ANS and is innervated by sympathetic preganglionic neurons
The catecholamines epinephrine (80%), and norepinephrine (20%), are secreted at the adrenal medulla and serve to prolong the sympathetic response

18. ADRENAL MEDULLA HORMONES (Interactions Animation)
Epinephrine/Norepinephrine
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19. The Pancreas
The pancreas is both an endocrine and an exocrine gland. It is located posterior and inferior to the stomach. We will discuss its endocrine functions here and its exocrine functions
in detail in chapter 24
The tail is contained within the splenorenal ligament but all the other parts of the pancreas are retroperitoneal.

20. The Pancreas
Most of the exocrine cells of the pancreas are arranged in clusters called acini and produce digestive enzymes which flow through ducts into the GI tract
Distributed among the acini are clusters of endocrine tissue
called pancreatic
islets (islets of
Langerhans)

21. Pancreatic Hormones
Each pancreatic islet contains four types of hormone-secreting cells: alpha (A), beta (B), delta (D), and F cells
Alpha cells secrete glucagon which increases blood glucose levels by acting
on hepatocytes to
convert glycogen
to glucose
Beta cells secrete
insulin

22. Pancreatic Hormones
Insulin is an anabolic hormone - it decreases blood glucose levels by acting on
hepatocytes to convert glucose
to glycogen and then facilitating
diffusion of glucose into the cells
Insulin and glucagon are counter-
regulatory hormones in that
their actions act to balance one
another in terms of blood glucose

23. Pancreatic Hormones
Somatostatin acts in a paracrine manner to inhibit both insulin and glucagon release from neighboring beta and alpha cells. It
also inhibits the secretion
of hGH
The interactions of the
four pancreatic hormones
are complex and not
completely understood

24. Glucose/Insulin Regulation 1 5 2 3 4 6 1 5 2 3 4 6 7 1 5 2 3 4 6 7 8 1
Insulin acts on various
body cells to:
• accelerate facilitated
diffusion of glucose
into cells
• speed conversion of
glucose into glycogen
(glycogenesis)
• increase uptake of
amino acids and increase
protein synthesis
• speed synthesis of fatty
acids (lipogenesis)
• slow glycogenolysis
• slow gluconeogenesis
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
INSULIN
GLUCAGON 1 5 2 3 4 6
Insulin acts on various
body cells to:
• accelerate facilitated
diffusion of glucose
into cells
• speed conversion of
glucose into glycogen
(glycogenesis)
• increase uptake of
amino acids and increase
protein synthesis
• speed synthesis of fatty
acids (lipogenesis)
• slow glycogenolysis
• slow gluconeogenesis
Blood glucose level falls
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
INSULIN
GLUCAGON 1 5 2 3 4 6 7
Insulin acts on various
body cells to:
• accelerate facilitated
diffusion of glucose
into cells
• speed conversion of
glucose into glycogen
(glycogenesis)
• increase uptake of
amino acids and increase
protein synthesis
• speed synthesis of fatty
acids (lipogenesis)
• slow glycogenolysis
• slow gluconeogenesis
If blood glucose continues
to fall, hypoglycemia
inhibits release of
insulin
Blood glucose level falls
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
INSULIN
GLUCAGON 1 5 2 3 4 6 7 8
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete 1
GLUCAGON
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
GLUCAGON 1 5 2 3 4
INSULIN
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON 1 2
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON 1 2 3
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON 1 2 3 4
Glucose/Insulin
Regulation

25. PANCREATIC HORMONES (Interactions Animation)
Insulin
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26. Gonadal Hormones
The ovaries are paired oval bodies located in the female pelvic cavity. They produce several steroid hormones including two estrogens (estradiol and estrone), progesterone, relaxin, and inhibin
Estrogens, along with FSH and
LH from the anterior pituitary,
regulate the menstrual cycle,
maintain pregnancy, and prepare
the mammary glands for lactation

27. Gonadal Hormones
Ovarian hormones also promote enlargement of the breasts and widening of the hips at puberty, and help maintain these female secondary sex characteristics
Progesterone prepares the uterus lining for implantation of a fertilized ovum

28. OVARIAN HORMONES (Interactions Animation)
Hormonal Regulation of Female Reproductive System
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29. Gonadal Hormones
The male gonads, the testes, are oval glands that lie in the scrotum. The main hormone produced and secreted by the testes is testosterone, an androgen (male sex hormone)
Testosterone is needed for
production of sperm and
maintenance of male
secondary sex characteristics

30. TESTICULAR HORMONES (Interactions Animation)
Hormonal Regulation of Male Reproductive Function
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31. The Pineal Gland The pineal gland is a small endocrine gland
attached to the roof of the
third ventricle – it is part of
the epithalamus
The pineal gland secretes the hormone melatonin, which contributes to maintaining the biological clock (seasonal and daily cycles)
more melatonin is secreted in darkness; the pineal gland is very developed in nocturnal animals

32. The Thymus gland
The thymus gland secretes thymosin, which promotes the proliferation and maturation of T cells
T cells are a type of white blood cell (lymphocyte) that destroys microorganisms
and foreign substances
through direct
cellular contact

33. General Adaptation Syndrome
The general adaptation syndrome (GAS) or stress response refers to the consequences of failure to respond appropriately to emotional or physical threats, whether actual or imagined
Interestingly, stressful situations can be events normally considered to be “good”, as well as bad
for instance, a marriage can be as stressful as a divorce, a birth as stressful as a death, etc.
Psychologist Hans Selye described the General Adaptation Syndrome (GAS) where initial observations about infectious reactions led to the discovery that stress can lead to infection, illness, disease and death. There are three stages that he discovered: Alarm, Resistance and Exhaustion.
Alarm
When we are surprised or threatened, we have an immediate physical reaction, often called the Fight-or-Flight reaction. This prepares the body for life-threatening situations, channeling away resources from such as the digestive and immune system to more immediate muscular and emotional needs. This leads to the immune system being depressed, making us susceptible to disease.
Resistance
As we become used to the stress levels, we initially become more resistance to disease, which leads us to believe we can easily adapt to these more stressful situations. However, this is only the immune system fighting to keep up with demands and expectations, but requires it to work at abnormally high levels.
Exhaustion
Eventually reality kicks in and our bodies give up on trying to maintain a high level of stress. Parts of the body literally start to break down and we become very unwell. If we continue to fight this situation, we may even die.

34. General Adaptation Syndrome
It is impossible to remove all of the stress from our everyday lives, and some levels of stress actually help us perform well and be productive. Regardless, the body’s homeostatic mechanisms attempt to counteract stress, and maintain a constant internal environment whenever possible
If stress is extreme, unusual, or long lasting, the normal mechanisms may not be enough, and they may elicit a series of changes called the stress response or GAS

35. General Adaptation Syndrome
There are three stages to a prolonged stress response: alarm reaction, resistance reaction, and exhaustion
The alarm reaction is the short-lived fight-or-flight response initiated by the hypothalamus and mediated by the sympathetic division of the ANS
it brings huge amounts of glucose and oxygen to the brain, the lungs, and skeletal muscles
the RAAS is also activated to maintain blood volume and BP

36. THE ALARM REACTION (Interactions Animation)
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37. General Adaptation Syndrome
The three stages to the GAS continued…
The resistance reaction is initiated in large part by hypothalamic releasing hormones and is a longer-lasting response. The release of high levels of cortisol and thyroid hormones assures that the tissues of the body can sustain necessary metabolic needs

38. General Adaptation Syndrome
The alarm reaction leads to a resistance response.

39. General Adaptation Syndrome
The three stages to the GAS continued…
Exhaustion occurs when the body’s reserves become so depleted that they cannot sustain the resistance stage
Prolonged exposure to high levels of cortisol and other hormones causes wasting of muscle, suppression of the immune system, ulceration of the GI tract, and failure of pancreatic beta cells… disease often ensues

40. THE GAS (Interactions Animation)
General Adaptation Syndrome
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41. End of Chapter 18
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