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Functions of hypothalamus for 6 mark

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python3 -c " import pdfplumber with pdfplumber.open('/tmp/workspace/attachments/bc4ee387-8320-4797-a979-d5a70c290b30/HYPOTHALAMUS.pdf') as pdf: print(f'Total pages: {len(pdf.pages)}') for i, page in enumerate(pdf.pages): text = page.extract_text() print(f'--- PAGE {i+1} ---') print(text) print() "

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Functions of Hypothalamus

1. Regulation of Autonomic Functions

  • Hypothalamus is the "head ganglion" of the ANS.
  • Stimulation of lateral areas → diffuse sympathetic discharge + increased adrenal medullary secretion.
  • Stimulation of anterior hypothalamus → parasympathetic effects.

2. Neurosecretory Function

  • Posterior pituitary hormones:
    • Paraventricular nucleus synthesizes Oxytocin.
    • Supraoptic nucleus synthesizes Vasopressin (ADH).
    • Axons travel to posterior pituitary via the hypothalamohypophyseal tract.
  • Anterior pituitary control: Hypothalamus secretes releasing and inhibitory hormones into the hypothalamohypophyseal portal system, which regulate anterior pituitary hormone secretion.

3. Regulation of Body Temperature

  • Temperature-regulating centers are located in the hypothalamus.
  • Anterior hypothalamus = Heat loss centre → stimulates sweating and vasodilation.
  • Posterior hypothalamus = Heat gain centre → stimulates shivering and vasoconstriction.
  • Lesion of anterior hypothalamus → Hyperthermia.
  • Lesion of posterior hypothalamus → Hypothermia.

4. Regulation of Food Intake

  • Two opposing centers:
    • Feeding centre (Lateral nucleus) - chronically active; stimulation → increased food intake; destruction → anorexia.
    • Satiety centre (Ventromedial nucleus) - inhibits feeding centre; stimulation → fullness; destruction → hyperphagia.
  • Theories: Glucostatic, Lipostatic (Leptin), Gut peptide (CCK, Peptide YY), Thermostatic.
  • Key molecules: Neuropeptide Y (orexigenic), Leptin and Ghrelin (Ghrelin from stomach - stimulates appetite during fasting).

5. Regulation of Water Balance

  • Thirst regulation:
    • Osmoreceptors in anterior hypothalamus detect rise in plasma osmolality → stimulate thirst centre → water intake.
    • ECF volume decrease → renin-angiotensin system → Angiotensin II stimulates thirst via subfornical organ and OVLT.
  • ADH secretion:
    • Hyperosmolality or low blood volume → stimulation of supraoptic nucleus → ADH release → renal water reabsorption.
    • Damage to anterior hypothalamus → deficient ADH → Diabetes Insipidus.

6. Control of Circadian Rhythm

  • Suprachiasmatic nucleus (SCN) = master biological clock.
  • Receives light/dark information via retinohypothalamic fibers.
  • Controls: ACTH secretion, sleep-wake cycle, body temperature rhythm.
  • Regulates melatonin release (high at night, low during day).
  • SCN disruption causes jet lag.

7. Control of Emotional and Instinctual Behaviour

  • Hypothalamus + Limbic system interpret sensory impulses as pleasant or unpleasant.
  • Reward centre (Lateral and ventromedial nucleus) → pleasurable sensations.
  • Punishment centre (Medial hypothalamus) → pain, fear, defence, escape reactions.
  • Strong stimulation of punishment centres → Rage (violent, aggressive state).
  • Release from cortical inhibition → Sham rage (undirected, explosive, not aimed at a specific target).
Tip for 6-mark exam format: Cover any 6 of the 7 functions above - each with a 2-3 line explanation. The most commonly asked ones are: autonomic regulation, neurosecretion, temperature, food intake, water balance, and circadian rhythm.
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