INTRODUCTION
hypothalamus is a group of nuclei located in the subcortical region regulating various body functions.
It is situated below the thalamus. It extends from the optic chiasma in the anterior part and the mamillary body in the posterior part.
forms the lateral wall of third ventricle.
NUCLEI OF HYPOTHALAMUS
The nuclei of hypothalamus can be classified based on their position.
Anterior Hypothalamus.
preoptic nucleus - stimulation causes loss of hat
paraventricular nucleus - simulation secrete oxytocin
anterior hypothalamic nucleus
supraoptic nucleus
suprachiasmatic nucleus
Medial Hypothalamus
Dorsomedial nucleus
Ventromedial nucleus
Arcuate nucleus
Lateral Hypothalamus
lateral hypothalamic nucleus
Posterior Hypothalamus
Posterior hypothalamic nucleus
Mamillary nucleus
FUNCTIONS OF HYPOTHALAMUS
Hypothalamus plays important role the following processes
Control of food intake
Feeding Center
- feeding center is present in the lateral nucleus
- produces desire to eat
- destruction of feeding center causes anorexia and death
Satiety center
- present in the ventromedial nucleus.
- gives the sense of satisfaction.
- destruction of satiety center causes overeating and hypothalamic obesity .
Mamillary bodies of the hypothalamus-
controls the feeding reflex such as licking and swallowing.
Arcuate nucleus -
it has two centers that regulate the feeding behavior and energy expenditure.
Pro-opiomelanocortin
reduces intake of food and increases expenditure of energy.
2. Neuropeptide Y neurons
increases food intake and decreases expenditure of energy.
The mechanism of intake of food can be explained through the following hypothesis:
GLUCOSTATIC HYPOTHESIS
the satiety center has glucostatic centers that detects the presence of glucose with the influence of insulin
Diabetes Meletus, where there is lack of glucose, there is lack of entry of glucose into satiety center which causes excessive hunger.
LIPOSTATIC HYPOTHESIS
signals are produces with response to the fat level in the body.
GUT PEPTIDE HYPOTHESIS
This suggests that the polypeptides secreted in the GIT prevents further intake of food.
THERMOSTATIC HYPOTHESIS
A drop in the body temperature below a certain level leads to the stimulation of hunger.
Regulation of Water balance
Hypothalamus controls the execration of water and the thirst system of the body.
It controls the water balance through Anti-diuretic Hormone or vasopressin (ADH).
The supraoptic nucleus of hypothalamus controls the renal excretion of water.
ADH enhances water reabsorption and conserves water.
Control of Anterior Pituitary
Hypothalamus controls Anterior pituitary through secretion of releasing and inhibiting factors.
These factors reach the anterior pituitary through the blood stream connecting the hypothalamus and anterior pituitary which is the hypothalamo-hypophyseal portal system.
Control of Posterior Pituitary
Hypothalamus controls the Posterior pituitary through the nerve endings of paraventricular nuclei
They regulate the secretion of oxytocin and ADH.
Regulation of Body Temperature
Stimulation of lateral hypothalamus causes vasoconstriction and shivering to increase temperature.
Stimulation of the preoptic area causes vasodilation and sweating to cause loss of heat.
Control of Autonomic Function
Hypothalamus controls contraction of smooth muscle and urinary bladder.
The stimulation of the anterior hypothalamus decreases heart rate and produces vasodilation and increases GIT secretion, due to parasympathetic stimulation.
The stimulation of the lateral and posterior hypothalamus produces vasoconstriction and increases heart rate, due to sympathetic stimulation.
Control of Sleep Wakefulness cycle
stimulation of the posterior hypothalamus produces wakefulness.
Stimulation of the anterior hypothalamus produces sleep sensations.
Control of the Circadian Rhythm
the 24 hour cycle of the body function is known as the circadian rhythm.
It is maintained by the ventromedial nucleus of the hypothalamus.
Control of Behavior
Stimulation of the lateral hypothalamus produces the flight or fight reaction
Stimulation of the periventricular nucleus produces the fear and punishment reactions.
Stimulation of the anterior and posterior hypothalamus increases sex drive.
Stimulation of ventromedial nucleus reduces sex drive.
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