endo 5 red
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Pancreas and Other Endocrine Glands
Pancreas and other Endocrine GlandsPancreatic Islets (Islets of
Langerhans)Pineal GlandThymusGastrointestinal TractGonads and Placenta
Pancreatic IsletsThese 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
Pancreatic Islets
GlucagonSecreted by: Alpha cellsProduced in response to a fall in blood
glucose concentrations.◦Glucagon Stimulates the liver to hydrolyze
glycogen to glucoseStimulates 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
InsulinSecreted by: Beta cellsProduced 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
The actions of Insulin and Glucagon are antagonistic
After a meal◦Insulin> Glucagon
During times of Fasting◦Insulin<Glucagon
Pineal GlandIs 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
Pineal Gland
Pineal GlandIt 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
Circadian RhythmsThe primary center for circadian
rhythms in the body is the SCNThese are Rhythms of
Physiological activity that follow a 24-hour pattern
The circadian activity of the SCN is automatic
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)
Melatonin SecretionExcessive 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
ThymusA 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.
Thymus
ThymusThe 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
Gastrointestinal TractThe 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.
GonadsThe gonads(testis and ovary)
secrete sex steroids.◦Males-androgens◦Females- estradiol-17β and
progestogens
TestisConsists 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]
Testis
OvaryEstrogen 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]
Ovary
Placenta
It is the organ responsible for nutrient and waste exchange between the fetus and the mother
PlacentaIt 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
Autocrine and Paracrine Regulation
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
Examples of Paracrine RegulationNitric 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 factorEndothelins-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
Examples of Autocrine RegulationCytokines- 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
Growth factors
◦Platelet-derived growth factor◦Epidermal growth factor◦Insulin-like growth factor
*stimulate cell division and proliferation of their target cells
Prostaglandins
ProstaglandinsThe most diverse group of autocrine
regulatorsMembers 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 pathways1. Arachidonic acid is converted by the enzyme
cyclo-oxygenase into other prostaglandins2. Arachidonic acid is converted by the enzyme
lipoxygenase into leukotrienes
ProstaglandinsProstaglandins 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 PGEThromboxane A₂- promotes clotting by stimulating
platelet aggregation and vasoconstrictionProstacylin 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
Examples of Prostaglandin Actions1. 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
Examples of Prostaglandin Actions5. 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
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
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 the inflammatory condition