The document summarizes several endocrine glands and their functions. It discusses the pancreas and pancreatic islets, which secrete the hormones insulin and glucagon to regulate blood glucose levels. The pineal gland secretes melatonin and helps regulate circadian rhythms. The thymus gland helps regulate the immune system. Other glands discussed include the gonads, gastrointestinal tract, and placenta. The document also covers prostaglandins and how NSAIDs like aspirin inhibit their production to reduce inflammation.

1. Pancreas and Other
Endocrine Glands

2. Pancreas and other Endocrine
Glands
 Pancreatic Islets (Islets of
Langerhans)
 Pineal Gland
 Thymus
 Gastrointestinal Tract
 Gonads and Placenta

3. Pancreatic Islets
 These structures are most common in
the body and tail of the pancreas
 On a microscopic level, the most
conspicuous cells in the islets are the
alpha and beta cells
 Hormones secreted by the pancreatic
islets:
 Glucagon
 Insulin

4. Pancreatic Islets

5. Glucagon
 Secreted by: Alpha cells
 Produced in response to a fall in blood
glucose concentrations.
◦ Glucagon Stimulates the liver to hydrolyze
glycogen to glucose
 Stimulates the hydrolysis of stored fat
(lipolysis) and the consequent release of
free fatty acids into the blood.
◦ This effect helps provide energy substrates
during fasting when blood glucose levels
decrease

6. Insulin
 Secreted by: Beta cells
 Produced in response to a rise in
blood glucose concentrations
◦ Promotes the entry of glucose into tissue
cells and the conversion of this glucose
into glycogen and fat
 Insulin aids the entry of amino acids
into cells and the production of cellular
protein

7. The actions of Insulin and Glucagon are
antagonistic
 After a meal
◦ Insulin> Glucagon
 During times of Fasting
◦ Insulin<Glucagon

8. Pineal Gland
 Is found on the roof of the third
ventricle near the corpora
quadrigema, where it is encapsulated
by the meninges covering the brain
 The pineal gland of a child weighs
about 0.2 g and is 5-8 mm long and
9mm wide
◦ This gland begins to regress at age 7 and
in the adult appears as a thickened strand
of fibrous tissue

9. Pineal Gland

10. Pineal Gland
 It lacks direct nervous connection to
the rest of the brain but it is highly
innervated by the sympathetic nervous
system from the superior cervical
ganglion
 Secretes melatonin
◦ Production and secretion is stimulated by
activity of the Suprachiasmatic Nucleus
(SCN) in the hypothalamus of the brain

11. Circadian Rhythms
 The primary center for circadian
rhythms in the body is the SCN
 These are Rhythms of Physiological
activity that follow a 24-hour pattern
 The circadian activity of the SCN is
automatic

12. Circadian Rhythms
◦ environmental light/dark changes are
required to synchronize this activity to a
day/night cycle
 Secretion of melatonin increases with darkness
and peaks at the middle of the night
 During the day, the neural pathways from the
retina of the eyes to the hypothalamus act to
depress the activity of the SCN (decreasing
melatonin secretion)

13. Melatonin Secretion
 Excessive melatonin secretion in
humans is associated with a delay in
the onset of puberty.
 Melatonin secretion is highest in
children between the ages of 1 and 5
and decreases thereafter, reaching its
lowest levels at the end of puberty

14. Thymus
 A bilobed organ positioned in front of
the aorta and behind the manubrium
of the sternum
 It is relatively large in newborns and
children and sharply regresses in size
after puberty.
◦ The thymus in adults becomes infiltrated
with strands of fibrous and fatty
connective tissue.

15. Thymus

16. Thymus
 The Thymus secretes hormones that
help to regulate the immune system
 Site of production of T cells (thymus
dependent cells)
 In addition to providing T cells, the
thymus secretes a number of
hormones that are believed to be
stimulate T cells after they leave the
thymus

17. Gastrointestinal Tract
 The stomach and intestine secrete a
number of hormones that act on the
gastrointestinal tract itself and on the
pancreas and gallbladder.
 The effects of these hormones
coordinate the activities of different
regions of the digestive tract and the
secretions of pancreatic juice and bile.

18. Gonads
 The gonads(testis and ovary) secrete
sex steroids.
◦ Males-androgens
◦ Females- estradiol-17β and progestogens

19. Testis
 Consists of two compartments:
1. Seminiferous tubules-which produce
sperm cells
2. Interstitial tissues-contains the Leydig
cells which secrete Testosterone
◦ Testosterone- is needed for the
development and maintenance of the
male genitalia [penis and scrotum] and
the male accessory organs [prostate,
seminal vesicles ,epididymis and vas
deferens]

20. Testis

21. Ovary
 Estrogen is secreted by small structures
within the ovary called ovarian follicles
◦ The ovarian follicles contain the egg cell (or
ovum) and granulosa cells that secrete
estrogen
 By about the midcycle,one of these
follicles grows very large and ,in the
process of ovulation,extrudes its ovum.
◦ The empty follicle under the influence of the
Luteinizing hormone becomes the corpus
luteum [which secretes progesterone and
estradiol-17β]

22. Ovary

23. Placenta
 It is the organ responsible for nutrient and
waste exchange between the fetus and
the mother

24. Placenta
 It secretes:
◦ Large amounts of estrogen and
progesterone
◦ A number of polypeptide and protein
hormones
 Human Chorionic Gonadotropin (hCG)-similar
to LH
 Somatomammotropin- similar in action to both
growth hormone and prolactin

25. Autocrine and Paracrine
Regulation

26.  Autocrine regulators-if they are
produced and act within the same
organ
 Paracrine regulators-if they are
produced within one tissue and
regulate a different tissue of the same
organ

27. Examples of Paracrine
Regulation
 Nitric Oxide-can function as a
neurotransmitter in memory processes and in
other processes can be produced by the
endothelium of blood vessels
◦ Functions as the regulator previously known as
endothelium-derived relaxation factor
 Endothelins-directly promote vasoconstriction
◦ Endothelin-1 –is produced by the epithelium of
the airways
 Bradykinin-promotes vasodilation
*endothelins and bradykinin are very
important in the control of blood pressure.
These are also involved in artherosclerosis

28. Examples of Autocrine
Regulation
 Cytokines- molecules that regulate
different cells of the immune system
◦ Lymphokines- cytokines produced by
lymphocytes (interleukins are the specific
molecules involved)
 Neutrophins-including nerve growth
factor,guide regenerating peripheral
neurons that have been injured
 Growth factors- promote growth and cell
division in any organ
*cytokines may also function as growth
factors

29. Growth factors
◦ Platelet-derived growth factor
◦ Epidermal growth factor
◦ Insulin-like growth factor
*stimulate cell division and proliferation
of their target cells
 Prostaglandins

30. Prostaglandins
 The most diverse group of autocrine
regulators
 Members of a family called the
eicosanoids[molecules derived from the
precursor arachidonic acid]
◦ Upon stimulation arachidonic acid is released
from phospholipids in the cell membrane and
may enter one of the two possible metabolic
pathways
1. Arachidonic acid is converted by the enzyme
cyclo-oxygenase into other prostaglandins
2. Arachidonic acid is converted by the enzyme
lipoxygenase into leukotrienes

31. Prostaglandins
 Prostaglandins of the E series (PGE)-can cause
smooth muscle to relax in the
bladder,bronchioles intestine and unterus and the
same can cause the vascular smooth muscle to
contract
 PGF₂α -has exactly the opposite effects as PGE
 Thromboxane A₂- promotes clotting by
stimulating platelet aggregation and
vasoconstriction
 Prostacylin or PGI₂-has the opposite effects as
Thromboxane A₂
*these antagonistic effects ensure that, while
clotting is promoted, the clots will not normally
form on the walls of the intact blood vessels

32. Examples of Prostaglandin
Actions
1. Immune system-prostaglandins promote the
development of pain and fever.
2. Reproductive system- plays a role in ovulation and
corpus luteum function in the ovaries and in
contraction of the uterus.
◦ Excessive prostaglandin production leads to
dysmenorrhoea,endometriosis and premature labor
3. Digestive system-the stomach and intestines produce
prostaglandins,which are believed to inhibit gastric
secretions and influence intestinal motility and fluid
absorption
4. Respiratory system-The leukotrienes are potent
bronchoconstrictors and these compounds together
with some prostaglandins may cause respiratory
distress and contribute to bronchoconstriction in
asthma

33. Examples of Prostaglandin
Actions
5. Circulatory system- Prostacylin,a
vasodilator ,and Thromboxane A₂ ,a
vasoconstrictor play a role in blood clotting.
◦ In fetus PGE₂ is believed to promote ductus
arteriosus –a short vessel that connects the
pulmonary artery to the aorta fails to close after
birth. It can be closed by the administration of
drugs that inhibit prostaglandin sythesis
6. Urinary system- Prostaglandins produced in
the renal medulla cause vasodilation
resulting in increased blood flow and
increased excretion of water and
electrolytes in the urine

34. Inhibitors of Prostaglandin
Synthesis
 Aspirin-most widely used member of a
class of drugs known as nonsteroidal
anti-inflammatory drugs(NSAIDs)
◦ Other members of this class are
indomethacin and ibuprofen
◦ These drugs specifically inhibit the cyclo-
oxygenase enzyme that is needed for
prostaglandin sythesis
◦ Inhibit inflammation but with side effects like:
 Gastric bleeding
 Possible kidney problems
 Prolonged clotting time

35. Inhibitors of Prostaglandin
Synthesis
 2 isoenzyme forms of cyclo-
oxygenase:
1. Type I isoform(COX1)-produced in a
constant fashion by cells of the
stomach and kidneys and by blood
platelets
2. Type II isoform(COX2)-is induced in
a number of cells in response to
cytokines involved in inflammation
◦ Produces prostaglandins that promote