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Hypothalamus

Hypothalamus

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Hypothalamus

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  1. Hypothalamus PROF. ASHRAF HUSAIN

  2. Key concept for hypothalamic function is HOMEOSTASIS • Its goal is to maintain internal homeostasis • There are both neural and hormonal inputs to and outputs from the hypothalamus.

  3. Where is the hypothalamus ? Anatomical Location: It consist of group of nuclei present in the floor of third ventricle (which lies between the two thalami) It is a very vascular structure so much so that the nuclei are floating in the blood.

  4. Vital anatomical points • It is a very small structure and comprises less than 1% of our brain volume • Lines third ventricle right above the pituitary • Divided into medial and lateral regions by fornix which is a tract of fibres that run from the hippocampus to the mamillary bodies

  5. Limited at the anterior by the optic chiasm and anterior commissure • Limited at the posterior by the mammillary bodies • Hypothalamus is intimately connected to the amygdala which controls emotion

  6. HYPOTHALAMIC NUCLEI • ANTERIOR GROUP: • ANTERIOR NUCLEUS • LATERAL HYPOTHALAMIC NUCLEI • PREOPTIC NUCLEI • PARAVENTRICULAR NUCLEI • SUPRAOPTIC NUCLEUS • SUPRACHIASMATIC NUCLEUS

  7. HYPOTHALAMIC NUCLEI • MIDDLE GROUP(INFUNDIBULAR REGION) : • MEDIAL NUCLEUS • DORSOMEDIAL NUCLEI • VENTROMEDIAL NUCLEI • LATERAL HYPOTHALAMIC NUCLEI • TUBERAL • POSTERIOR GROUP : • MAMMILLARY NUCLEUS • LATERAL HYPOTHALAMIC NUCLEI • POSTERIOR NUCLEUS

  8. HYPOTHALAMIC FUNCTION • AUTONOMIC CONTROL • TEMPERATURE REGULATION • HYPOTHALAMIC CONTROL OF PITUTARY SECRETION THROUGH RELEASING OR INHIBITORY HORMONES • HYPOTHALAMIC PITUTARY RELATIONSHIP • CONTROL OF HUNGER, FEEDING AND SATIETY • THIRST CONTROL • CONTROL OF BODY RHYTHM (CIRCADIAN) • CONTROL OF SLEEP, FEAR AND RAGE • SEXUAL BEHAVIOUR

  9. Hypothalamic control of pituitary secretion

  10. FEEDING AND SATIETY • Food intake increased by(Lateral feeding centre) • Neuropeptide Y • Orexin A and B • MCH (Melanin conc. Hormone) • Ghrelin • Food intake decreased by (Medial satiety centre • Leptin • Bombesin ,CCK • Somtostatin etc.

  11. CONTROL OF FOOD INTAKE Four hypothesis for control of food intake • Lipostatic hypothesis: adipose tissues emit humoral signals to the hypothalamus causing reduction in food intake • Gut peptide hypothesis: food in GIT causes release of one or more polypeptides these signal the hypothalamus to reduce food intake

  12. Glucostatic hypothesis: increased glucose utilization in hypothalamus produces a sensation of satiety • Thermostatic hypothesis : reduction in body temperature below a certain level leads to increased appetite and an increased in body temperature above a certain level decreases appetite • Leptin (from Adipocytes (fat cells)) this hormone acts on the hypothalamus to decrease food intake & increase energy consumption. It inhibits activity of Neropeptide Y neurons

  13. Increase food intake, decreased energy expenditure HYPOTHALAMUS Increased activation of Leptin receptors Increased plasma leptin concentration FAT DEPOTS Increased fat deposition ↓ Increased leptin synthesis Solid arrows indicate stimulation; dashed arrows indicate inhibition

  14. Control of hunger , feeding and satiety Hypothalamic regulation of appetite for food depends on the interaction of two areas • Feeding center: Site: lateral hypothalamic nucleus. Stimulation: voraciuos eating Lesion: loss of eating (fatal anorexia)

  15. 2. Satiety Center: Site: Ventromedial nucleus Stimulation: cessation of eating Lesion: Hyperphagia eg. Hypothalamic obesity. Mechanism of hunger regulation Feeding center is mostly active and is transiently inhibited by activity in the satiety center. INHIBITS SATIETY CENTER FEEDING CENTER

  16. SATIETY CENTER (GLUCOSTAT) If glucose utilization decreases If glucose utilization increases Feeding center inhibited Feeding center unchecked Loss of appetite Increase Food Intake

  17. Hypertonicity Hypovolumia Baroreceptors Angiotensin II Osmoreceptors Thirst Thirst control

  18. HYPERTONICITY STIMULATES OSMORECEPTORS SIGNALS HPOTHALAMUS STIMULATES THIRST • HYPOVOLEMIA STIMULATES BARORECEPTORS AND ANGIOTENSIN II WHICH IN TURN STIMULATES THE HYPOTHALAMUS TO PRODUCE A THIRST SENSATION

  19. Hypothalamic temperature regulating mechanism • Thermoregulatory mechanism by the hypothalamus are basically reflex or semi reflex response.

  20. BODY TEMPERATURE • INVERTEBRATES CANNOT ADJUST BODY TEMPERATURE AND IT DEPENDS ON ENVIRONMENT • VERTEBRATES BODY TEMPERATURE FLUCTUATES OVER A CONSIDERABLE RANGE DUE TO RUDIMENTARY BODY TEMPERATURE REGULATING MECHANISM POIKILOTHERMIC COLD BLOODED • MAN IS HOMEOTHERMIC AND MAINTAINS HIS BODY TEMPERATURE CONSTANT INSPITE OF WIDE VARIATIONS IN ENVIRONMENTAL TEMPERATURE WARM BLOODED

  21. NORMAL BODY TEMPERATURE • ORAL TEMPERATURE 37 DEGREES CENTIGRADE (98.6 DEGREES FAHRENHEIT) • CORE TEMPERATURE(RECTAL TEMPERATURE) 0.5 DEGREES CENTIGRADE ABOVE ORAL TEMPERATURE • SKIN TEMPERATURE LOWER THAN ORAL TEMPERATURE • SCROTAL TEMPERATURE REGULATED AT 32 DEGREES CENTIGRADE

  22. THE EXTREMITIES ARE COOLER THAN THE REST OF THE BODY • FEET IS COOLER THAN HAND • CORE TEMPERATURE VARIES LEAST WITH CHANGES IN ENVIRONMENTAL TEMPERATURE • HYPERPYREXIA IS HIGH TEMPERATURE OVER 41DEGREES CENTIGRADE (106 DEGREES FAHRENHEIT) • HYPOTHERMIA LOW BODY TEMPERATURE 3 DEGREES OR LESS

  23. FACTORS NORMALLY AFFECTING TEMPERATURE • DIURNAL VARIATION 0.5 TO 0.7° C MOSTLY • LOWEST AT ABOUT 6 AM AND DURING SLEEP • AGE INFANT IRREGULAR AGED SUBNORMAL • RISE IN BASAL TEMPERATURE AT TIME OF OVULATION IN FEMALES • EXERCISE AS HIGH AS 40 ° C HAS BEEN RECORDED AFTER EXERCISE • EMOTION TEMPERATURE RISES DUE TO UNCONCIOUS TENSING OF THE MUSCLES

  24. HYPERTHYROIDISM • BMR INCREASES AND BODY TEMPERATURE INCREASES • HYPOTHYROIDISM • BMR DECREASES AND BODY TEMPERATURE DECREASES

  25. MECHANISMS OF HEAT LOSS (% OF HEAT LOSS AT 21 DEGREE C) • RADIATION AND CONDUCTION 70% • VAPORIZATION OF SWEAT = 27% • RESPIRATION = 2% • URINATION AND DEFECATION =1% • MECHANISMS OF HEAT GAIN • BASIC METABOLIC PROCESSES • FOOD INTAKE(SDA) • MUSCULAR ACTIVITY

  26. DURING A HOT HUMID DAY • SWEAT SPREADS OVER THE SKIN • THERE IS REDUCED EVAPORATION OF SWEAT • PERSON FEELS HOT

  27. AFFERENTS FOR TEMPERATURE CONTROL SENSORY COLD RECEPTORS: • SKIN • DEEP TISSUES • SPINAL CORD • EXTRAHYPOTHALAMIC PARTS OF BRAIN • HYPOTHALAMUS

  28. THRESHOLD CORE TEMPERATURE FOR TEMPERATURE REGULATION RESPONSE THRESHOLDS (WHEN THRESHOLD IS REACHED RESPONSE BEGINS) - 35.5 DEGREES CENTIGRADE FOR SHIVERING - 36 DEGREES CENTIGRADE FOR NON SHIVERING THERMOGENESIS -36.8 DEGREES CENTIGRADE FOR VASOCONSTRICTION - 37 DEGREES CENTIGRADE FOR SWEATING & VASODILATATION

  29. HEAT GAIN • METABOLISM • FOOD(SDA) • MUSCULAR ACTIVITY HEAT LOSS • CONDUCTION • CONVECTION • RADIATION • EVAPORATION SKIN,LUNGS • URINATION DEFECATION

  30. BASAL METABOLISM • 30 TO 40 KCAL PER SQ METER PER HOUR • 1700 KCAL PER DAY MALE • 1500 KCAL PER DAY FEMALE • MODERATE ACTIVITY 2500 TO 3000 KCAL PER DAY • HEAVY WORK 6000 KCAL PER DAY • SHORT BURSTS OF SEVERE EXERCISE 10-16 TIMES BASAL LEVEL

  31. SPECIFIC HEAT OF WATER • ONE CALORIE RAISES THE TEMPERATURRE OF 1 GM WATER BY 1 DEGREE CENTIGRADE • HENCE IF NO HEAT IS LOST OUR BODY TEMPERATURE WOULD RISE BY 1 DEGREE CENTIGRADE PER HOUR

  32. HEAT LOSS BY EVAPORATION OF WATER THROUGH LUNGS AND SKIN • INSENSIBLE PERSPIRATION PASSAGE OF WATER BY DIFFUSION THROUGH SKIN INSENSIBLE BECAUSE IT CANNOT BE SEEN OR FELT • LUNGS ON AVERAGE WATER IS LOST FROM THE LUNGS IS ABOUT 300 ML/DAY AND EQUIVALENT HEAT IS NEARLY 200 KCAL

  33. HEAT LOSS • CONDUCTION HEAT LOSS BY DIRECT CONTACT • CONVECTION THE AIR IN IMMEDIATE CONTACT WITH SKIN IS WARMED THE HEATED MOLECULES MOVE AWAY AND COOLER ONES COME IN TO TAKE THEIR PLACE AND SO ON • RADIATION HOT OBJECTS EMIT INFRARED HEAT RAYS ,IT DEPENDS ON SURFACE AREA DIFFERENCE OF TEMPERATURE BETWEEN THE SKIN AND THE SURROUNDING OBJECTS

  34. SKIN LOSS • INSENSIBLE PERSPIRATION IT IS ABOUT 600 TO 800 ML PER DAY EQUIVALENT TO HEAT LOSS OF 400 KCAL SWEATING : RISE OF TEMPERATURE CAUSES SWEATING • SWEATING MAY BE UPTO 1.7 LITRES PER DAY. • IT MAY BE THERMAL,EMOTIONAL EXERCISE, SYMPATHETIC OVERACTIVITY, GUSTATORY SWEATING

  35. Posterior Hypothalamus Skin (cold receptors) • Increase Heat Production • Shivering • Hunger • Increase Voluntary activity • Increase secretion of Adrenalin, noradrenalin, TSH • Cutaneous Vascular Counter current exchange. • Decrease Heat loss • Cutaneous Vasoconstriction • Curling up – decrease body surface area Above mechanisms results in raising the body temprature

  36. Anterior Hypothalamus Skin (Heat receptors) • Increase Heat Loss • Cutaneous vasodilatation • Sweating • Increase perspiration • Decrease Heat production • Anorexia • Apathy • Inertia Above mechanisms results in decrease in the body temperature

  37. FEVER • THERMOSTAT HAS BEEN RESET TO NEW POINT ABOVE 37 DEGREES CENTIGRADE • ACTUAL BODY TEMPERATURE IS BELOW NEW SET POINT • LEADS TO INCREASED TEMPERATURE RAISING MECHANISM • CHILLY SENSATION DUE TO CUTANEOUS VASOCONSTRICTION AND SHIVERING

  38. PATHOGENESIS OF FEVER • ENDOTOXINS • CYTOKINES PRODUCTION (PGE2) • LOCAL RELEASE OF PROSTAGLANDIN IN HYPOTHALAMUS • ASPIRIN REDUCES PG SYNTHESIS

  39. PATHOGENESIS OF FEVER

  40. BENEFITS OF FEVER • BENEFICIAL RESPONSE TO INFECTION AND OTHER DISEASES eg.(ANTHRAX,PNEUMONIA) • INCREASE IN TEMPERATURE REDUCES BACTERIAL GROWTH • INCREASE IN TEMPERATURE INCREASES ANTIBODY PRODUCTION • SLOWS THE GROWTH OF SOME TUMORS) • VERY HIGH TEMPERATURE ARE HARMFUL