Medical Lecture Notes

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Tuesday, 5 December 2017


Is a part of Diencephalon, made of a collection of nuclei below the thalamus.
Each nucleus is a collection of neurons that regulates specific  body function(s).
Regulation of water  intake & loss by:
Thirst center.
Supraoptic & paraventricular nuclei that secrete Vasopressin.
Stimuli of the thirst centre & Vasopressin secretion include :
Hyperosmolality of the plasma by hypernatraemia or  hyperglycaemia.
Hypovolaemia: Decreased blood volume after haemorrhage,diarrhoea, sweating, polyuria, vomiting.
Thirst center stimulation → ↑ water intake
Vasopressin stimulates water reabsorption from the renal collecting duct → ↓ the water loss.
2.Regulation of food intake & body weight.
Feeding center located laterally & satiety center ventromedially in hypothalamus.
Feeding centre Activation → hunger felling ↑ the appetite for food intake.
Activation of satiety centre inhibits the feeding centre → Satiety feeling ↓ the appetite for food intake.
The chemical messengers acting on the hypothalamus to ↑ the appetite for food intake, include:
Neuropeptide Y.
melanin-concentrating hormone. MCH
Chemical meseengers acting on the hypothalamus to ↓ the appetite for food:
Cocaine-& Amphetamine-regulated transcript CART.
Corticotropin-releasing hormone CRH.
Melanocytes stimulating hormone MSH.
Hypotheses controlling the food intake:
lipostatic hypothesis States that:
↑ fats in the adipose tissue → release of  a chemical messenger  Leptin .
Leptin acts on the hypothalamus to ↓ Neuropeptide Y.
Ø   → Satiety feeling ↓ing  the appetite.
II. The glucostatic hypothesis States that :
Increased glucose utilization in hypothalamus activate satiety centre →  satiety feeling.
III. Gut Peptides  Hypothesis: States that:
food entering the GIT triggers release of GIT hormones which act on the brain to cause satiety. They include:
Ø  Gastrin releasing peptide GRP.
Ø  Glucagon.
Ø  Somatostatin.
Ø  Cholecystokinin CCK.
IV. Thermostatic hypothesis: States that:
Ø  ↑in body or climatic temperature ↓ the appetite for food intake.
Ø  Cold climate↑ the appetite for  food intake
This theory is important for regulation of body temperature.
The hypothalamus is a main regulatory centre in the Autonomic nervous system.
Regulation of body temperature by two centres:
Heat sensitive area in the anterior hypothalamus. Stimulation gives responses :
Ø  Satiety feeling ↓ing  appetite for food.
Ø  Dilation of skin (cutaneous) blood vessels to  flow of the warm blood to skin surface.
Ø  Sweating. & apathy.
Ø  Assuming relax posture to ↑ exposed skin area
Cold sensitive area in the posterior hypothalamus, Stimulation leads to:
Ø  Hunger to increase food intake.
Ø  Cutaneous vasoconstricion.
Ø  Increased muscular activity (shivering).
Ø  Assuming tense posture to ↓ the exposed skin area
5.Neuroendocrine function:
The hypothalamus is connected by neural tract to the posterior lobe of the pituitary gland, & by vascular (portal) to the anterior lobe.
Cell bodies of supraoptic & paraventricular nuclei synthesize Vasopressin & Oxytocin that pass via hypothalamohypophysial tract to the posterior pituitary.
Hypothalamic releasing & inhibiting factors  are hypophysiotropic hormones that control the anterior pituitary.
6. Hypothalamic suprachiasmatic nucleus SCN control the cyclic phenomena (circadian rhythm) which are physiologic effects related to the day- night cycle.
7. Hypothalamus is a part sleep zone.
8. As a functional part of the limbic system. Its involved in the defense reactions (fear & rage), emotions & motivations (reward & punishment).

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