Posterior pitutary power point txt .pptx

Posterior pitutary power point txt .pptx

1. Posterior pitutary Dr. D. Shaalini 1 st year post graduate

2. Phylogenitically pitutary gland consists of 3 lobes Anterior lobe or adenohypophysis Posterior lobe or neurohypophysis Intermediate lobe or pars intermedia

3. Posterior lobe or neurohypophysis consists of 3 parts Pars posterior also called as pars nervosa or neural lobe or infundibular process forms the main bulk of neurohypophysis Infundibular stem funnel shaped extension arising from the median eminence at the floor of the 3 rd ventricle Median eminence small protrusion from the base of the hypothalamus . It is situated just beneath the 3 rd ventricle and is highly vascular.

4. Pitutary stalk Posterior pituitary maintains its neural connection to hypothalamus by this pituitary stalk.

5. Histologically it has Unmyelinated nerve fibers Pituicytes Glial cells

6. Posterior pituitary hormones Anti diuretic hormone or vasopressin Oxytocin

7. Source of secretion of hormones Actually posterior pituitary doesn’t secrete any hormones ADH and oxytocin are secreted from hypothalamus From hypothalamus they are transported to the posterior pituitary through the nerve fibers of Hypothalamo hypophyseal tract by means of axonic flow Proteins involved in the transport are neurophysins In the posterior pituitary the hormones are stored at the nerve endings

8. Whenever the impulse from hypothalamus reach the posterior pituitary Hormones are released from the nerve endings into the circulation So only these hormones are called as neurohormones There are two types of neurophysin Neurophysin 1 or oxytocin neurophysin is the binding protein for oxytocin Neurophysin 2 or ADH neurophysin is the binding protein for ADH

9. ANTI DIURETIC HORMONE Secreted from supraoptic and paraventricular nucleus of hypothalamus From here it is transported to posterior pituitary by means of axonic flow It is a polypeptide hormone containing 9 aminoacids Half life is 18 to 20 minutes ADH secretion mainly depends on Plasma osmolarity Blood volume and pressure

10. Plasma osmolarity Osmolarity above 250mosm/kg promotes and increase ADH secretion appropriate to osmolarity rise Which is sensed by osmoreceptors These receptors are located in anterior pitutary

11. Blood volume and pressure Decrease in blood volume and pressure increases ADH secretion Percentage fall in mean arterial pressure causes linear increase in ADH secretion Decreased ECF volume also increases ADH secretion

12. Factors which increase ADH secretion Increased plasma osmolarity Decreased ECF volume Pain, nausea Decreased blood pressure Increased blood temperature

13. Factors that inhibit ADH secretion Decreased plasma osmolarity Increased ECF volume Decreased temperature

14. Mechanism of action 2types of receptors V1 and V2 receptor V2 Receptor are located on kidney tubules ADH increases the permeability of tubular cells by acting on V2 receptors

15. Release of ADH from posterior pituitary Binding on receptors on collecting duct and distal convoluted tubules Activation of adenyl cyclase cAMP system Increased cAMP in cytosol Activation of protein kinase Phosphorylation of cytosolic proteins Transport of endosomes by microfilaments Incorporation of aquaporins in CD and DCT Increased water reabsorption via aquaporins

16. V1 receptors - ADH acts on V1 receptors present in smooth muscle of blood vessels causing vasoconstriction

17. Functions of ADH Increased water reabsoption Vasoconstriction Facilitates memory Contraction of smooth muscles of spermatic cord Increased corticotrophin relesing hormone Glycogenolysis in liver

18. Applied physiology ADH deficient causes DIABETES INSIPIDUS Severe dehydration Unbalanced urinary water loss (polyuria) Excessive thirst (polydipsia) 2 types Nephrogenic type - disease in kidney Nephrogenic type – disease in CNS

19. ADH excessive causes SIADH (Syndrome of inappropriate secretion of ADH) Decreased excretion of water Cellular overhydration Seen in head injury , ectopic production ADH due to carcinoma If SIADH is due to brain disease then it is called as cerebral salt wasting If SIADH is due to lung disease then it is called as pulmonary salt wasting

20. Oxytocin Secreted from paraventricular nucleus Polypeptide hormone with 9 aminoacids Half life of 6 minutes Regulation of secretion is by 2 physiological stimuli Suckling at the time of breast feding Cervical stimulation at the time of delivery

21. Functions of oxytocin Oxytocin mediates 2 physiological Milk ejection reflex Parturation reflex

22. Milk ejection reflex Suckling Stimulation of tactile receptors in the areolar regionof the breast Activates stomatoasthetic neural pathways Which transmit signal to the paraventricular nuclei in hypothalamus Reflex secretion of oxytocin into blood stream The oxytocin is carried to the mammary gland where it causes milk release following a latent period of 30 to 60 sec

23. Parturation reflex Dilatation of cervix Afferent impulses Stimulates paraventricular nucleus in the hypothalamus Oxytocin release