1. Faisal I. Mohammed, MD, PhD
Endocrine System L4
Faisal I. Mohammed, MD, PhD
University of Jordan

2. Parathyroid Glands Embedded in lobes of thyroid gland, usually 4.
Parathyroid hormone (PTH) or parathormone
Major regulator of calcium, magnesium, and phosphate ions in the blood
Increases number and activity of osteoclasts
Elevates bone resorption
Stimulates the conversion of 25-hydroxycholecalciferol (inactive vitamin D) into 1,25-dihydroxycholecalciferol (Active vitamin D-calcitriol) which will increase intestinal Ca++ reabsorption.
Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback
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3. Parathyroid Glands
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4. Parathyroid Glands Embedded in the lateral lobes of the thyroid gland.
Parathyroid hormone (PTH):
Only hormone secreted by the parathyroid glands.
Single most important hormone in the control of blood [Ca2+].
Stimulated by decreased blood [Ca2+].
Promotes rise in blood [Ca2+] by acting on bones, kidney and intestines.
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5. Roles of Calcitonin, Parathyroid hormone, Calcitrol in Calcium Homeostasis
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6. High level of Ca2+ in blood stimulates thyroid gland 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. 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 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
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level. 2
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7. Adrenal Glands 2 structurally and functionally distinct regions
Adrenal cortex
Mineralocorticoids affect mineral homeostasis
Glucocorticoids affect glucose homeostasis
cortisol
Androgens have masculinzing effects
Dehydroepiandrosterone (DHEA) only important in females
Adrenal medulla
Modified sympathetic ganglion of autonomic nervous system
Intensifies sympathetic responses
Epinephrine and norepinephrine
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8. Adrenal Glands
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9. Adrenal Glands Paired organs that cap the kidneys.
Each gland consists of an outer cortex and inner medulla.
Adrenal medulla:
Derived from embryonic neural crest ectoderm (same tissue that produces the sympathetic ganglia).
Synthesizes and secretes:
Catecholamines (mainly Epi but some NE).
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10. Adrenal Glands (continued)
Adrenal cortex:
Does not receive neural innervation.
Must be stimulated hormonally (ACTH).
Consists of 3 zones:
Zona glomerulosa.
Zona fasciculata.
Zona reticularis.
Secretes corticosteroids.
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11. Functions of the Adrenal Cortex
Zona glomerulosa:
Mineralcorticoids (aldosterone):
Stimulate kidneys to reabsorb Na+ and secrete K+.
Zona fasciculata:
Glucocorticoids (cortisol):
Inhibit glucose utilization and stimulate gluconeogenesis.
It is anti inflammatory (Stabilizes lysosomal membranes)
At higher conc. it has mineralocorticoid action
Zona reticularis (DHEA):
Sex steroids:
Supplement sex steroids in males and females
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12. Functions of the Adrenal Cortex (continued)
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13. University of Jordan

14. Functions of the Adrenal Medulla
Innervated by preganglionic sympathetic axons.
Increase respiratory rate.
Increase HR and cardiac output.
Vasoconstrict blood vessels, thus increasing venous return.
Stimulate glycogenolysis.
Stimulate lipolysis.
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15. Stress and the Adrenal Gland
Non-specific response to stress produces the general adaptation syndrome (GAS).
Alarm phase:
Adrenal glands activated.
Stage of resistance:
Stage of readjustment.
Stage of exhaustion:
Sickness and/or death if readjustment is not complete.
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16. University of Jordan

17. University of Jordan

18. University of Jordan

19. Pancreatic Islets Both exocrine and endocrine gland
Roughly 99% of cells produce digestive enzymes
Pancreatic islets or islets of Langerhans
Alpha or A cells secrete glucagon – raises blood sugar
Beta or B cells secrete insulin – lowers blood sugar
Delta or D cells secrete somatostatin – inhibits both insulin and glucagon
F cells secrete pancreatic polypeptide – inhibits somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes
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20. Pancreas
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21. Pancreatic Islets (Islets of Langerhans)
Alpha cells secrete glucagon.
Stimulus is decrease in blood [glucose].
Stimulates glycogenolysis and lipolysis.
Stimulates conversion of fatty acids to ketones.
Beta cells secrete insulin.
Stimulus is increase in blood [glucose].
Promotes entry of glucose into cells.
Converts glucose to glycogen and fat.
Aids entry of amino acids into cells.
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22. Negative Feedback Regulation of Glucagon and Insulin
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23. 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
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)
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
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)
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
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24. Ovaries and Testes Gonads – produce gametes and hormones
Ovaries produce 2 estrogens (estradiol and estrone) and progesterone
With FSH and LH regulate menstrual cycle, maintain pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics
Inhibin inhibits FSH
Relaxin produced during pregnancy
Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics
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25. Pineal Gland Attached to roof of 3rd ventricle of brain at midline
Masses of neuroglia and pinealocytes
Melatonin – amine hormone derived from serotonin
Appears to contribute to setting biological clock
More melatonin liberated during darkness than light
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26. Pineal Gland Secretes melatonin:
Production stimulated by the suprachiasmatic nucleus (SCN) in hypothalamus.
SCN is primary center for circadian rhythms.
Light/dark changes required to synchronize.
Melatonin secretion increases with darkness and peaks in middle of night.
May inhibit GnRH.
May function in the onset of puberty (controversial).
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27. Pineal Gland (continued)
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28. Thymus and Other Endocrine Tissues
Located behind sternum between the lungs
Produces thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin
All involved in T cell maturation
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29. Thymus
Site of production of T cells (thymus-dependent cells), which are lymphocytes.
Lymphocytes are involved in cell-mediated immunity.
Secretes hormones that are believed to stimulate T cells after leave thymus.
Thymus gland size is large in newborns and children.
Regresses after puberty and becomes infiltrated with strands of fibrous tissue.
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30. Gonads and Placenta Gonads (testes and ovaries): Placenta:
Secrete sex hormones.
Testosterone.
Estradiol 17-b.
After menopause, produces estrone.
Progesterone.
Placenta:
Secretes large amounts of estriol, progesterone, hCG, hCS.
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31. Prostaglandins Most diverse group of autocrine regulators.
Produced in almost every organ.
Wide variety of functions.
Different prostaglandins may exert antagonistic effects in some tissues.
Immune system:
Promote inflammatory process.
Reproductive system:
Play role in ovulation.
Digestive system:
Inhibit gastric secretion.
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32. Prostaglandins (continued)
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33. Prostaglandins (continued)
Respiratory system:
May bronchoconstrict or bronchodilate.
Circulatory system:
Vasoconstrictors or vasodilators.
Urinary system:
Vasodilation.
Inhibitors of prostaglandin synthesis:
Non-steroidal anti-inflammatory drugs (NSAIDS).
Aspirin, indomethacin, ibuprofen: inhibit COX1.
Celecoxib and rofecoxib: inhibit COX2.
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34. The Stress Response Eustress in helpful stress / Distress is harmful
Body’s homeostatic mechanisms attempt to counteract stress
Stressful conditions can result in stress response or general adaptation syndrome (GAS)
3 stages – initial flight-or-fight, slower resistance reaction, eventually exhaustion
Prolonged exposure to cortisol can result in wasting of muscles, suppression of immune system, ulceration of GI tract, and failure of pancreatic beta cells
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35. Stress Response
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36. Thank You
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