hypo pitutary system physiology 1.0 ppt.pptx

hypo pitutary system

1. AFFERENTS From other parts of limbic system: Ventral pathway Stria terminalis Fornix Med. hypothalamic tract From cingulate gyrus

2. II. From brain stem 1) From MB tegmentum : - massive projections of catecholamine & 5HT containing fibres to mamm . nuclei & MFB. - It is thro’ this route that ascending sensory pathways project to hypothalamus.

3. 2) Dorsal longitudinal fasciculus of Schultz : - arises from periaqueductal grey matter & spreads over dorsal & caudal region of hypothalamus. - also carry visceral impulses to hypothalamus. 3) MFB : - ascending fibres arise from MB & project to lateral hypothalamic & preoptic nuclei. - also carry visceral impulses to hypothalamus.

4. 4) Catecholaminergic pathways from Locus Coeruleus : - ascend monosynaptically to cerebrum & cerebellum. - on the way to cerebellum, they project fibres to thalamic nuclei, hypothalamus, septal area, amygdaloid body and hippocampus. - these projections modify the degree of alertness. - ascending catecholaminergic fibres are distributed to supraoptic & paraventricular nuclei & possibly regulate the output of releasing hormones of hypothalamus.

5. 5) Serotoninergic pathways : - ascending from raphe nuclei of pons & lower MB; terminate in hypothalamus, septal nuclei, amygdaloid body & neocortex . - regulate sleep-wake cycle. - total insomnia develops when serotonin levels are depleted by the use of the drug – reserpine .

6. III. From neocortex : - corticohypothalamic fibres interconnect the prefrontal & orbitofrontal regions with preoptic , paraventricular & ventromedial nucleus of hypothalamus. IV. From globus pallidus : - pallidohypothalamic fibres from globus pallidus go to diffuse area on hypothalamus.

7. V. From thalamus : - thalamohypothalamic fibres from dorsomedial & midline nucleus of thalamus go to diffuse area on hypothalamus. VI. From retina : - retinohypothalamic fibres are projected from ganglionic cells of retina to suprachiasmatic nucleus of hypothalamus, thro’ optic nerve & optic chiasma . - this pathway explains the influence of light on hormonal reg. of reproductive cycle by hypothalamus.

8. 1. 2. 3. 4. 5 6. 7 . 8.

9. EFFERENTS Autonomic centres Other parts of limbic system Thalamus Tegmentum of MB Neocortex

10. VI. Pituitary gland Hypothalamo–hypophyseal tract : Axons of large neurosecretory cells of SO & PV nuclei of hypothalamus ( unmyelinated ) Infundibular stem of hypothalamus Post. lobe of pituitary ( neurohypophysis ) Form series of dilated terminals – ‘Herring bodies’ Come in contact with cap. bed of neurohypophysis Neurosecretory cells of SO & PV nuclei secrete ADH & Oxytocin

11. 2. Tuberoinfundibular tract : Arcuate nuclei – median eminence & infundibular stem - in close contact with cap. plexus of hypophyseal portal system. Neurons synthesize releasing or inhibiting hormones – memb . bound vesicles - tuberoinfundibular tract to hypophyseal portal vessels. Hormones carried by portal vessels to ant. pituitary – regulate secretion of ant. pituitary hormones.

12. Sl. No. Function Afferents Integrating areas 1. Temp. reg. Temp. receptors in skin, deep tissues, spinal cord, hypothalamus & other parts of brain Ant. Hypo – to heat Post. Hypo – to cold 2. Neuroendocrine control a. Catecholamines Limbic areas connected with emotion Dorsal & Post. Hypo b. Vasopressin Osmoreceptors , vol. receptors, others SO & PV nuclei c. TSH via TRH Temp. receptors in infants, perhaps others PV & neighboring areas d. ACTH & β lipoprotein via CRH Limbic system, reticular form., hypo & ant. Pituitary cells sensitive to oing blood cortisol level, suprachiasmatic nuclei PV nuclei e. FSH & LH via GnRH Hypo cells sensitive to estrogen, eyes, touch receptors in skin & genitalia of reflex ovulating species Preoptic & other areas f. Prolactin via PIH & PRH Touch receptors in breast, other unknown receptors Arcuate nucleus g. GH via Somatostatin & GHRH Unknown receptors Periventricular & arcuate nucleus

13. Sl. No. Function Afferents Integrating areas 3. Reg. of ANS 4. Appetitive behavior a. Thirst Osmoreceptors , probably in OVLT, Ang II uptake in SFO Lat. Sup. Hypothalamus b. Hunger Glucostat cells sensitive to rate of glucose utilisation , leptin receptors, receptors for other polypeptides Ventromedial , arcuate , PV nuclei, lat. Hypo nuclei c. Sexual behavior Cells sensitive to oing estrogen & androgen & others In females - Ant. Ventral hypo In males – pyriform cortex 5. Defensive reactions (fear, rage) Sense organs & neocortex (path unknown) Diffuse, in limbic system & hypo 6. Control of body rhythms Retina via retinohypothalamic fibres Suprachiasmatic nuclei

14. I. AUTONOMIC FUNCTION Sherrington called hypothalamus as “Head Ganglion of ANS”. Ant. Hypo : parasymp . area Post. Hypo : symp . area

15. CVS reg.: thro CV control centres in reticular region of medulla & pons . +ion of post. & lat. nuclei : ↑HR, ↑BP & cut. Vasoconstriction. +ion of preoptic area : ↓HR, ↓BP & cut. Vasodilatation. Reg. of pupil size: +ion of post. & lat. nuclei : dilatation. +ion of ant. & med. parts of preoptic & supraoptic areas : constriction. Reg. of peristaltic & secretomotor functions of GIT: +ion of post. & lat. nuclei : ↓ secretion,↓motility of GIT ( ergotropic function). +ion of ant. & med. nuclei : ↑peristalsis & secretomotor functions of GIT ( trophotropic function).

16. II. ENDOCRINAL FUNCTION

17. Lat.hypothalamus receives aff . impulses from thalamus, reticular activating system, limbic system, eyes & neocortex ., & relays to neurosecretory cells of ant. & med. basal portions of hypothalamus. Response – release of hormones in median eminence which reach ant. pituitary thro’ portal vessels.

18. Releasing & inhibiting hormones: Growth hormone releasing hormone (GHRH) Growth hormone inhibiting hormone (GHIH); Somatostatin Corticotropin releasing hormone (CRH) Thyrotropin releasing hormone (TRH) Gonadotropin releasing hormone ( GnRH ) Prolactin releasing hormone (PRH) Prolactin inhibiting hormone (PIH)

19. Mech of action : induce effects via cAMP , Ca++ & phosphatidylinositol products as second messengers. +/– transcription, modulate translation & +/– secretion of target ant. Pituitary hormones.

20. Hypothalamus Controls metabolism by controlling thyroid gland. Thro’ its influence over adrenal cortex controls metabolism of diff. foodstuffs & maintains electrolyte balance. Keeps gonads inhibited till gonadal growth is complete; then inhibition is removed so that gonads start functioning & gametes are produced. Gonadal hormones acting on the brain bring about physiological changes for mating of male & female. Controls formation of milk by mammary glands by controlling prolactin secretion.

21. Control of post. pituitary Thro’ hypothalamo-hypophyseal tract. ADH & Oxytocin are synthesized in cell bodies of magnocellular neurons of both SO & PV nuclei but predominant secretion of SO – ADH; PV – Oxytocin Both are nonapeptides with disulphide ring at one end; bound with polypeptides – neurophysins .

22. Oxytocin causes : Contraction of uterine smooth muscles during coitus & parturition. On suckling, causes contraction of myoepithelial cells in alveoli of mammary gland – milk ejection.

23. Vasopressin Gets attached to ext. surface of sensitive renal tubules Stimulates adenylate cyclase Form. of cyclic AMP in tubular cells ↑ ed permeability of luminal side of tubular cells for absorption of water.