Physiology of Hypothalamus by Dr. Mudassar Ali Roomi

7/30/2019 Physiology of Hypothalamus by Dr. Mudassar Ali Roomi

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PHYSIOLOGY

of

HYPOTHALAMUS

BY

DR. MUDASSAR ALI ROOMI (MBBS, M. PHIL)


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HYPOTHALAUMS

it is the part ofdiencephalon which isbelow the hypothalamicsulcus.

Hypothalamus is the Major

Control Headquarters for theLimbic System

It forms the anteroinferiorwall and the floor of thethird ventricle.

It extends from optic

chiasma to mamillary body


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Nuclei of

hypothalamus

Three groups of nuclei:

1. Anteriotr or Preoptic group : lateral and

medial preoptic nuclei, suproptic nucleus,

suprachiasmatic nucleus, paraventricular

nucleus and anterior nucleus.

2. Middle or Tuberal: Ventromedial,

dorsomedial, arcuate or tuberal nucleus,posterior and lateral nuclei.

3. Posterior or Mammillary:

supramammillary, premammillary, medial

and lateral mammillary nuclei.


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AFFERENTS TO THE HYPOTHALAMUS ARE FROM

1. Amygdala

2. Hippocampus

3. Reticular formation of brainstem

4. Nucleus of tractus solitarius

5. Locus ceruleus: these secrete norepinehrine at the nerve endings

6. Raphe magnus nucleus: these secrete serotonin at their nerve endings7. Afferents from the sensory pathways

8. retina

9. Thalamic nuclei

10. Hippocampus

11. Frontal cortex12. Globus pallidus

13. Lentiform nucleus


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EFFERENTS FROM THE HYPOTHALAMUS GO TO

1. Amygdala

2. Hippocampus

3. Frontal cortex

4. Nucleus of tractus solitarius

5. mid brain

6. Reticular formation of brainstem

7. Spinal cord8. Nervous connections with posterior pituitary and vascular

connections with the anterior pituiatory:


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Nervous connections with posterior pituitary and

vascular connections with the anterior pituiatory:

Supraoptic and paraventricularnuclei of hypothalamus secreteADH and oxytocin. Thesehormones are transported alongwith their carrier proteins alongthe nerve fibers to the posterior

pituitary where they are stored.These are the hormones ofhypothalamoneurohypophysealsystem.

In the median eminence andinfundibulum of the

hypothalamus, there aresinusoids. Blood from thesesinusoids pass through thehypophyseal portal blood vesselsand these pass through the orcommunicate with the capillaryplexus in the anterior pituitary.


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FUNCTIONS OF HYPOTHALAMUS

1. Secretion of posterior pituiatry hormones (paraventricular andsupraoptic nucleus)

2. Control of anterior pituitary (discrete areas)

3. Control of adrenal cortex (paraventricular nucleus)

4. Regulation of heart rate and blood pressure (posterior, lateral and

anterior hypothalamus)5. Regulation of sleep and wakefulness (ant. Hypothalamus and mamillary

body)

6. Role in behaviour and emotional changes (ventromedial, post and lateralnuclei)

1. Reward centre: in ventromedial nucleus

2. Punishment centre: Post. And lateral nuclei3. Rage centre: Post. And lateral nuclei.

7. Regulation of response to smell (post. hypothalamus)

8. Role of circadian rhythm (supraoptic and ant. nuclei)


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9. Control of autonomic nervous system

stimulation ofposterior and lateral hypothalamus resultsinto sympathetic responses such as increase in the heart

rate and blood pressure, pupillary dilatation,

piloerection, secretion of catecholamines from adrenal

medulla and hyperglycemia. Stimulation ofanterior hypothalamus (preoptic area)

results into parasympathetic responses such as slowing

of heart rate and fall in blood pressure, papillary

constriction, contraction of urinary bladder, GIT motilityand secretions.

in addition hypothalamus is also a relay station in the

pathway of sympathetic cholinergic nerves which

produce vasodilatation in skeletal muscle and sweating.


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10. Control of water balance of the body

water balance is maintained through the control of water intakeand excretion through the kidney.

When the thirst centre in lateral hypothalamus is stimulated,

there is conscious desire to take water and fluids.

Thirst centre is stimulated when there is increased osmolarity ofECF, Hypovolemia and also by angiotensin II.

In the anterior hypothalamus, there are osmoreceptors which

are specialized neurons which respond to changes in osmolarity.

Water excretion is controlled by ADH. Stimuli which secrete ADH

may be osmotic or volume.

If there is hyperosmolarity or Hypovolemia, there is secretion of

ADH. These stimuli will act on hypothalamus and ADH is

released which acts on the distal parts of renal tubules to

reabsorb water.


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11. Control of uterine contraction and milk

ejection

oxytocin is synthesized in hypothalamus, mainly the

paraventricular nuclei.

Oxytocin causes uterine contraction to help in the child birth.

In the second stage of labor there are high levels of oxytocin.

In milk ejection (milk letdown) there is role of oxytocin. The

baby suckles breast of the mother, impulses from the receptor

around nipples go to the hypothalamus and then there is

release of oxytocin from post. pituitary. Oxytocin causes contraction of myo-epithelial cells as a result

of which milk is ejected from the breast. This is a neuro-

endocrinal reflex. Afferent part is nervous and efferent is

endocrine.


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12. Control of food intake or hunger

inthe lateral hypothalamus, there is a feedingcentre or hunger centre. When this centre isstimulated there is desire to take food and there

is hunger. Activity of the feeding centre is controlled by a

satiety centre in the ventromedial nucleus of thehypothalamus.

When satiety centre is active, feeding centre isinhibited. When satiety centre is inactive, feedingcentre is activated.


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12. Control of food intake or hunger

(cont)

Glucostat mechanism: In the satiety centre, neurons arecalled glucostat cells. Glucose uptake in the glucostat cellsdepends upon the presence of adequate concentration ofinsulin. In almost all brain cells glucose uptake dont requireinsulin except glucostat cells in satiety centre. In

uncontrolled diabetes mellitus, there is polyphagia andincreased appetite because of inactivity of satiety centrebecause there is less insulin as result of which there isoveractivity of feeding centre resulting in polyphagia.

Lipostatic mechanism: through leptin.

Mammillary bodies in the hypothalamus control feedingreflexes such as swallowing and licking of the lips.


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13. Regulation of body temperature

Heat loss centre: in the preoptic nucleus of ant.hypothalamus there is a centre which regulate thetemperature. When temperature of the body increaseswith respect to thermostat in the hypothalamus,

various temperature decreasing mechanisms areinitiated which include cutaneous vasodilatation andsweating.

Heat gain centre: When body temperature decreaseswith respect to thermostat, various temperature

increasing mechanisms are initiated and these includecutaneous vasoconstriction, shivering and later onthere is chemical thermogenesis. Shivering centre islocated in posterior hypothalamus.


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DISORDERS OF HYPOTHALAMUS:

1. Central Diabetes insipidus: may be because of

tumor or damage to hypothalamus.


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Laurence-Moon-Beidl Syndrome

moon face, obesity,

polydactylism, mental

retardation,

hypogentalism.
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Dystrophia adipogentalis (Frohlichs syndrome):

obesity, sexual infantalism, dwarfism.


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Narcolepsy: sudden uncontrollable desire for sleep

during daytime.

Cataplexy: sudden uncontroled outburts of emotions

associated with narcolepsy.

Physiology of Hypothalamus by Dr. Mudassar Ali Roomi

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