PROF. ASHRAF HUSAIN

Key concept for hypothalamic function is HOMEOSTASIS

Its goal is to maintain internal homeostasisThere are both neural and hormonal inputs to

and outputs from the hypothalamus.

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.

Vital anatomical pointsIt 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

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

HYPOTHALAMIC NUCLEII. ANTERIOR GROUP:

I. ANTERIOR NUCLEUSII. LATERAL HYPOTHALAMIC NUCLEIIII. PREOPTIC NUCLEIIV. PARAVENTRICULAR NUCLEIV. SUPRAOPTIC NUCLEUSVI. SUPRACHIASMATIC NUCLEUS

HYPOTHALAMIC NUCLEIII. MIDDLE GROUP (INFUNDIBULAR

REGION) :I. MEDIAL NUCLEUS

I. DORSOMEDIAL NUCLEIII. VENTROMEDIAL NUCLEI

II. LATERAL HYPOTHALAMIC NUCLEIIII. TUBERAL

III.POSTERIOR GROUP :I. MAMMILLARY NUCLEUSII. LATERAL HYPOTHALAMIC NUCLEIIII. POSTERIOR NUCLEUS

I. AUTONOMIC CONTROLII. TEMPERATURE REGULATIONIII. HYPOTHALAMIC CONTROL OF PITUTARY

SECRETION THROUGH RELEASING OR INHIBITORY HORMONES

IV. HYPOTHALAMIC PITUTARY RELATIONSHIPV. CONTROL OF HUNGER, FEEDING AND

SATIETYVI. THIRST CONTROLVII. CONTROL OF BODY RHYTHM (CIRCADIAN)VIII.CONTROL OF SLEEP, FEAR AND RAGEIX. SEXUAL BEHAVIOUR

HYPOTHALAMIC FUNCTIONHYPOTHALAMIC FUNCTION

Hypothalamic control of pituitary secretion

FEEDING AND SATIETYFood intake increased

by(Lateral feeding centre)

Neuropeptide YOrexin A and BMCH (Melanin conc.

Hormone)Ghrelin

Food intake decreased by (Medial satiety centre

LeptinBombesin ,CCKSomtostatin etc.

CONTROL OF FOOD INTAKEFour 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

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

Increase food intake ,decreased energy expenditure

FAT DEPOTSIncreased fat deposition

↓Increased leptin synthesis

Increased plasma leptin concentration

HYPOTHALAMUSIncreased activation of

Leptin receptors

Solid arrows indicate stimulation; dashed arrows indicate inhibition

Control of hunger , feeding and satiety

Hypothalamic regulation of appetite for food depends on the interaction of two areas

1. Feeding center:Site: lateral hypothalamic nucleus.Stimulation: voraciuos eatingLesion: loss of eating (fatal

anorexia)

2. Satiety Center:Site: Ventromedial nucleusStimulation: cessation of eatingLesion: Hyperphagia eg. Hypothalamic obesity.

Mechanism of hunger regulationFeeding center is mostly active and is transiently

inhibited by activity in the satiety center.

SATIETY CENTER FEEDING CENTERINHIBITS

SATIETY CENTER

(GLUCOSTAT)

If glucose utilization increases

Feeding center inhibited

Loss of appetite Increase Food Intake

Feeding center unchecked

If glucose utilization decreases

Thirst controlHypertonicity

Osmoreceptors

Hypovolumia

Baroreceptors

Angiotensin II

Thirst

HYPERTONICITY STIMULATES OSMORECEPTORS SIGNALS HPOTHALAMUS STIMULATES THIRST

HYPOVOLEMIA STIMULATES BARORECEPTORS AND ANGIOTENSIN II WHICH IN TURN STIMULATES THE HYPOTHALAMUS TO PRODUCE A THIRST SENSATION

Hypothalamic temperature regulating mechanism

Thermoregulatory mechanism by the

hypothalamus are basically reflex or semi

reflex response.

BODY TEMPERATURE1. INVERTEBRATES CANNOT ADJUST BODY

TEMPERATURE AND IT DEPENDS ON ENVIRONMENT

2. VERTEBRATES BODY TEMPERATURE FLUCTUATES OVER A CONSIDERABLE RANGE DUE TO RUDIMENTARY BODY TEMPERATURE REGULATING MECHANISM POIKILOTHERMIC COLD BLOODED

3. MAN IS HOMEOTHERMIC AND MAINTAINS HIS BODY TEMPERATURE CONSTANT INSPITE OF WIDE VARIATIONS IN ENVIRONMENTAL TEMPERATURE WARM BLOODED

NORMAL BODY TEMPERATUREORAL 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

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

FACTORS NORMALLY AFFECTING TEMPERATURE

1. DIURNAL VARIATION 0.5 TO 0.7° C MOSTLY2. LOWEST AT ABOUT 6 AM AND DURING SLEEP3. AGE INFANT IRREGULAR AGED SUBNORMAL

1. RISE IN BASAL TEMPERATURE AT TIME OF OVULATION IN FEMALES

2. EXERCISE AS HIGH AS 40 ° C HAS BEEN RECORDED AFTER EXERCISE

3. EMOTION TEMPERATURE RISES DUE TO UNCONCIOUS TENSING OF THE MUSCLES

HYPERTHYROIDISMBMR INCREASES AND BODY

TEMPERATURE INCREASES

HYPOTHYROIDISMBMR DECREASES AND BODY

TEMPERATURE DECREASES

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 GAINBASIC METABOLIC PROCESSESFOOD INTAKE(SDA)MUSCULAR ACTIVITY

DURING A HOT HUMID DAY

SWEAT SPREADS OVER THE SKIN

THERE IS REDUCED EVAPORATION OF SWEAT

PERSON FEELS HOT

AFFERENTS FOR TEMPERATURE CONTROL

SENSORY COLD RECEPTORS:

1.SKIN2.DEEP TISSUES3.SPINAL CORD4.EXTRAHYPOTHALAMIC PARTS OF

BRAIN5.HYPOTHALAMUS

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

HEAT GAIN

1.METABOLISM

2.FOOD(SDA)

3.MUSCULAR ACTIVITY

HEAT LOSS

1.CONDUCTION

2.CONVECTION

3.RADIATION

4.EVAPORATION SKIN,LUNGS

5.URINATION DEFECATION

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

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

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

HEAT LOSSCONDUCTION 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

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

Skin (cold receptors)

Increase Heat Production

•Shivering

•Hunger

•Increase Voluntary activity

•Increase secretion of Adrenalin, noradrenalin, TSH

•Cutaneous Vascular Counter current exchange.

Posterior Hypothalamus

Decrease Heat loss

•Cutaneous Vasoconstriction

•Curling up – decrease body surface area

Above mechanisms results in raising the body temprature

Skin (Heat receptors)

Increase Heat Loss

•Cutaneous vasodilatation

•Sweating

•Increase perspiration

Anterior Hypothalamus

Decrease Heat production

•Anorexia

•Apathy

•Inertia

Above mechanisms results in

decrease in the body temperature

FEVERTHERMOSTAT 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

PATHOGENESIS OF FEVERENDOTOXINS

CYTOKINES PRODUCTION (PGE2)

LOCAL RELEASE OF PROSTAGLANDIN IN HYPOTHALAMUS

ASPIRIN REDUCES PG SYNTHESIS

BENEFITS OF FEVERBENEFICIAL 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

HYPERTHERMIATEMPERATURE > 41 DEGREES

CENTIGRADE (106 ° F) FOR PROLONGED PERIODS RESULTS IN PERMANENT BRAIN DAMAGE

OVER 43 DEGREES CENTIGRADE eg. HEAT STROKE DEVELOPS & CAUSES DEATH

MALIGNANT HYPERTHERMIA

GENE MUTATION CAUSING INCREASED CALCIUM RELEASE DURING MUSCULAR CONTRACTION DUE TO STRESS

MUSCLE METABOLISM IS INCREASED IN THIS CONTRACTED STATE

THIS CAUSES AN INCREASE IN HEAT PRODUCTION IN MUSCLE AND MARKED RISE IN BODY TEMPERATURE AND MAY BE FATAL IF NOT TREATED

OTHER IMPORTANT DISORDERS OF TEMPERATURE

HEAT STROKE

HEAT EXHAUSTION (CIRCULATORY DEFICIENCY WITH DEHYDRATION AND SALT DEFICIENCY

HYPOTHERMIA

HYPOTHERMIASKIN OR BLOOD IS COOLED LEADING TO REDUCED

METABOLIC RATE AND PHYSIOLOGICAL PROCESS

HEART RATE BP AND RESPIRATORY RATE REDUCES

AS RECTAL TEMPERATURE REACHES 28 DEGREES CENTIGRADE THE ABILITY TO SPONTANEOUSLY RETURN TO NORMAL TEMP IS LOST

IF PERSON SURVIVES THEN REWARMING RETURNS TO NORMAL STATE

HUMANS TOLERATE BODY TEMPERATURE LOWS OF 21 TO 24 DEGREES CENTIGRADE

CERTAIN SURGERIES ARE DONE UNDER INDUCED HYPOTHERMIAS