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Posterior pituitary hormones

Posterior pituitary gland

oThe posterior pituitary consists mainly of neuronal projections (axons) extending from the supraoptic and paraventricular nuclei of the hypothalamus.Hypothalamic stimulation can also be produced by other factors; o In lactating women, genital stimulation.oVasopressin receptors : oV1A ,V1B and V2 receptors

Effects of Vasopressin 1.On the kidneys : oADH increase the permeability of the collecting ducts of the kidneys , so water enter the hypertonic interstitium of the renal pyramids oSo that the urine become concentrated and its volume decrease [antidiuretic effect]

oThe overall effect is retention of water in excess of solute , so the effective osmotic pressure of the body fluids is ?.?A moderate?in the [ECF] volume stimulate these receptors -> impulses pass from them via vagi -> to the nucleus of tractus solitarius , an inhibitory pathway project from this nucleus to the caudal ventrolateral medulla , which stimulate SON -> ADH release.the number of oxytocin receptors in the uterus oOxytocin plays an important role in initiating the labor , and its secretion is increased during it , which is essential for delivery of the baby and expulsion of the placenta

[3] Sperm transport : oThe transport of sperms in the females genitals tract depends not only on the motility of the sperms but also on uterine contractions.Synthesis
oADH mainly in the SON, and oxytocin mainly in the PVN

           ADH hormone

?Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-GlyNH2 ?o Stimulates of touch receptors around the nipple, with suckling result in discharge of impulses that activate the PVN in hypothalamus, this stimulate release of stored oxytocin in the posterior pituitary .OXYTOCIN
Oxytocin: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2 Introduction; oPolypeptides 9 oSecreted mainly by the paraventricular.o When oxytocin is secreted in response to suckling or by conditional responses, it causes contraction of myoepithelial cells lining these small ducts, forcing the milk into large ducts.[2] contraction of the smooth muscles of the uterus : oOxytocin causes contraction of the smooth muscles of both the pregnant and non-pregnant uterus oThe sensitivity of the uterine muscle to oxytocin is increased by estrogen and inhibited by progesterone.o Sensory receptors in the nipple transmit impulses to the spinal cord via afferent neurons.o If suckling continues, new oxytocin is synthesized in the hypothalamic cell bodies, travels down the axons, and replenishes the oxytocin that was secreted.[4] in males :- oFunction of the oxytocin in males it may causes discharge of sperms from the seminiferous tubules and the epididymis to the vas deferens

Thank you oReferences oGuyton oConsciseo nephrogenic diabetes insipidus;

Symptoms of [DI] oPolyuria: o excretion of large amount of urine (can reach 23L/day) the urine is colorless & diluted.o Vasopressin secretion is regulated by osmoreceptors located in the anterior hypothalamus .in ECF volume , this result in. ?Reduction in Na+ concentration, & osmolarity of the[ ECF] decrease.Regulation of Oxytocin Secretion ?Several factors causes the secretion of oxytocin from the posterior pituitary, including; o suckling.o These axons release peptide hormones into the capillaries of the hypophyseal circulation.Control of vasopressin oA-Osmotic stimuli; oWhen the osmotic pressure of the plasma is increased, vasopressin secretion is increased.The high pressure receptors: ?Arterial baroreceptors in the carotid sinus and aortic arch act in a similar way as low pressure receptors .Are located in the atria , great veins and pulmonary vessels .2.

Posterior pituitary hormones

Posterior pituitary gland

•The posterior pituitary consists mainly of neuronal projections (axons) extending from the supraoptic and paraventricular nuclei of the hypothalamus.

• These axons release peptide hormones into the capillaries of the hypophyseal circulation.

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hormones
•2 hormones are released from the gland :
● antidiuretic hormone and oxytocin .
●Two are polypeptides containing 9 amino acids.
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 Synthesis  

•ADH mainly in the SON, and oxytocin mainly in the PVN

           ADH hormone

●Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-GlyNH2
● vasopressin or arginine vasopressin
●Half life : 18 min inactivated in the liver and kidneys .

•Vasopressin receptors :
•V1A ,V1B and V2 receptors

Effects of Vasopressin
1.On the kidneys :
•ADH increase the permeability of the collecting ducts of the kidneys , so water enter the hypertonic interstitium of the renal pyramids
•So that the urine become concentrated and its volume decrease [antidiuretic effect]

•The overall effect is retention of water in excess of solute , so the effective osmotic pressure of the body fluids is ↓.
•In the absence of ADH :
● the urine is hypotonic to plasma , urine volume is ↑ and there is a net water loss.
●As a result the osmolarity of the body fluids rises.
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2. On the blood vessels :
   •In large doses , ADH causes direct and powerful Vasoconstriction which ↑ both the peripheral resistance and the ABP .
   •Only large doses of ADH elevate the ABP.

Control of vasopressin
•A-Osmotic stimuli;
•When the osmotic pressure of the plasma is increased, vasopressin secretion is increased.
• Vasopressin secretion is regulated by osmoreceptors located in the anterior hypothalamus .

B. ECF volume :-
•ADH secretion is increased when the ECF volume is low , and decrease when the ECF volume is high .
•This means that changes in the ECF volume effect ADH release .

•Two types of volume receptors;
•Low pressure receptors.
•High pressure receptors.

The low pressure receptors :
● Are located in the atria , great veins and pulmonary vessels .
●A moderate↓in the [ECF] volume stimulate these receptors → impulses pass from them via vagi → to the nucleus of tractus solitarius , an inhibitory pathway project from this nucleus to the caudal ventrolateral medulla , which stimulate SON → ADH release.
●which causes water retention that increase the ECF volume to its normal level.

The high pressure receptors:
●Arterial baroreceptors in the carotid sinus and aortic arch act in a similar way as low pressure receptors .
●They regulate the release of ADH only if the changes in the ECF volume are large enough to effect the ABP .
●Haemorrhage is the most potent stimulus for ADH release .

•Hypovolemia and hypotension produced by conditions such as hemorrhage release large amounts of vasopressin.
• The result is water retention and reduced plasma osmolality.

C. other factors :
•ADH is released by pain , nausea , exercise , emotion and surgical stress.
o Nausea is associated with particularly large increases in vasopressin secretion.

• D. drugs :-
•ADH released is stimulated by morphine and nicotine .
• And[ADH] inhibited by alcohol.

Abnormality
•To type of diabetes insipidus;
•Neurogenic diabetes insipidus;
●BY disease in the supraoptic nuclei.

• nephrogenic diabetes insipidus;

Symptoms of [DI]
•Polyuria:
• excretion of large amount of urine (can reach 23L/day) the urine is colorless & diluted.
•Polydipsia:
• drinking of large amount of water as result of excessive sensation of thirst caused by dehydration due to polyuria.
•Loss of water soluble vitamin in the urine.

 Syndrome of inappropriate ADH [SIADH]  

•Hypersecretion of ADH sometimes occur in patients having :
• cerebral diseases.
• In certain pulmonary diseases.

•Effect of SIADH;
•The main effect is excessive water retention in the body which lead to;
➢Sign of water intoxication.
➢Marked ↑ in ECF volume , this result in.
●Reduction in Na+ concentration, & osmolarity of the[ ECF] decrease.
●Inhibition of secretion of aldosterone, this lead to Na+ loss in urine causing hyponatraemia .

               OXYTOCIN  

  Oxytocin: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2

Introduction;
•Polypeptides 9
•Secreted mainly by the paraventricular.
• Stored in the posterior pituitary gland.
•Its action on the target cells mediated by increasing the intracellular Ca++ content.

Regulation of Oxytocin Secretion
●Several factors causes the secretion of oxytocin from the posterior pituitary, including;
• suckling.
• the sight, sound, or smell of the infant.
• and dilation of the cervix .

Mechanism of secretion
•The major stimulus is suckling of the breast.
• Sensory receptors in the nipple transmit impulses to the spinal cord via afferent neurons.
• This information then ascends in the spinothalamic tract to the brain stem, and finally to the paraventricular nuclei of the hypothalamus.
• Within seconds of suckling, oxytocin is secreted from nerve terminals in the posterior pituitary.
• If suckling continues, new oxytocin is synthesized in the hypothalamic cell bodies, travels down the axons, and replenishes the oxytocin that was secreted.

Effects of Oxytocin
●Oxytocin functions includes;
●Milk ejection.
●Contraction of smooth muscle of the uterus.
●Sperms transport.
●Some function in male.
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milk ejection :
•Milk ejection is normally initiated by a neuroendocrine reflex.
• The receptors involved are the touch receptors, which are plentiful in the breast—especially around the nipple.
• The milk is stored in mammary alveoli and small milk duct.

• Stimulates of touch receptors around the nipple, with suckling result in discharge of impulses that activate the PVN in hypothalamus, this stimulate release of stored oxytocin in the posterior pituitary .

• When oxytocin is secreted in response to suckling or by conditional responses, it causes contraction of myoepithelial cells lining these small ducts, forcing the milk into large ducts.
• The milk collects in cisterns and then flows out through the nipple.
• The baby sucks the milk& at the same time causes more stimulation & therefore more release of oxytocin.

Hypothalamic stimulation can also be produced by other factors;
• In lactating women, genital stimulation.
• emotional stimuli also produce oxytocin secretion.

[2] contraction of the smooth muscles of the uterus :
•Oxytocin causes contraction of the smooth muscles of both the pregnant and non-pregnant uterus
•The sensitivity of the uterine muscle to oxytocin is increased by estrogen and inhibited by progesterone.

•In the late pregnancy , the blood progesterone level is ↓ and the uterus becomes very sensitive to normal blood level of oxytocin by the effect of high blood estrogen level which may ↑ the number of oxytocin receptors in the uterus
•Oxytocin plays an important role in initiating the labor , and its secretion is increased during it , which is essential for delivery of the baby and expulsion of the placenta

[3] Sperm transport :
•The transport of sperms in the females genitals tract depends not only on the motility of the sperms but also on uterine contractions.

[4] in males :-
•Function of the oxytocin in males it may causes discharge of sperms from the seminiferous tubules and the epididymis to the vas deferens

Thank you
•References
•Guyton
•Conscise