Hypothalamus Dr Mohammed Jeelani Specific learning outcomes Describe
Hypothalamus Dr Mohammed Jeelani
Specific learning outcomes �Describe the hypothalamus �Describe the role of hypothalamus – thermoreceptors (body temperature), glucoreceptors (hunger and food intake), osmoreceptors (volume, osmolarity, water intake and thirst) and chemoreceptors (oxygen, carbon dioxide and p. H).
Limbic system
Hypothalamus �Major Control Headquarters for the Limbic System �controls most of the vegetative and endocrine functions of the body as well as many aspects of emotional behaviour
Role of the hypothalamus Ø Control of food intake �Hypothalamus has feeding center in its lateral part and satiety center in ventromedial part �Coordinated activities of these centers determine feeding behavior
�Stimulation of feeding center – Desire to eat �Destruction of feeding center Anorexia �Stimulation of Satiety center – Sense of satisfaction �Destruction of Satiety center Excessive eating (hypothalamic obesity)
Hypothesis �Glucostatic hypothesis- Satiety center has glucostatic cells, the entry of glucose under influence of insulin stimulates these cells causing sense of satiety. �Lipostatic hypothesis- suggests that signals are generated in proportion to fat present in body, these signals influence hypothalamus to decrease food intake and increase energy output.
�Gut peptide hypothesis- proposes that polypeptides are produced in GIT by the presence of food, these polypeptides inhibit further intake of food �Thermostatic hypothesis- a drop in the body temperature below critical level stimulates desire to consume food, rise in temperature above the set point reduces appetite
Regulation of water balance �Hypothalamus has got osmoreceptors capable of detecting osmolarity of the blood. �When there is hemoconcentration, fluid moves out of the osmoreceptor into the blood �This stimulates cells to increase production of hormone ADH (antidiuretic hormone) �ADH increases permeability of the DCT and collecting ducts to water enhancing water reabsorption
Regulation of body temperature �Hypothalamus acts as thermostat to maintain normal body temperature �Stimulation of lateral and posterior hypothalamus produces vasoconstriction and shivering, which cause increase in the body temperature �Stimulation of anterior hypothalamus causes loss of heat by vasodilation and sweating
Cardiovascular Regulation � Stimulation in the posterior and lateral hypothalamus increases the arterial pressure and heart rate, �Stimulation in the preoptic area cause a decrease in both heart rate and arterial pressure. �These effects are transmitted mainly through specific cardiovascular control centers in the reticular regions of the pons and medulla.
Chemoreceptors The chemoreceptors are chemosensitive cells sensitive to �Oxygen lack �Carbon dioxide excess and �Hydrogen ion excess.
Location of chemoreceptors
�Chemoreceptors excite nerve fibers that, along with the baroreceptor fibers, pass through Hering’s (glossopharyngeal) nerves and the vagus nerves into the vasomotor center of the brain stem. �When arterial pressure falls below 80 mm Hg, the chemoreceptors are stimulated
Control of anterior pituitary �Hypothalamus produces releasing and inhibiting factors, which regulates secretion from anterior pituitary �Egs; thyroid releasing hormone causes secretion of thyroid stimulating hormone
Control of posterior pituitary �Regulates formation and release of oxytocin and ADH
Control of behavior �Stimulation of lateral hypothalamus produces fight and flight reaction, increases sex drive �Stimulation of ventromedial hypothalamus reduces rage resulting in avoidance reaction, decreases sex drive
Control of sleep and wakefulness �Posterior hypothalamus forms a part of reticular activating system, stimulation of this system produces wakefulness �Activity of anterior hypothalamus produces electrical changes in the brain similar to those seen during sleep
References �Arthur Guyton, Textbook of Medical Physiology. 13 th. Ed. Elsevier Saunders, page number 754 -759(chapter 59), page 889 -894(chapter 72), page 381 -382 (chapter 29), 915 -919 (chapter 74), page 222(chapter 18), page 542 -543(chapter 42)
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