HomeostasisThermoregulation & Fluid regulation

Thermoregulation

Preventing body temp from FallingCold receptors hypothalamus 5 physiological / behavioural responses1. Vasoconstriction: sympathetic NS blood vessels in skin constrict2. Adrenaline / Noradrenaline: sympathetic NS adrenal medulla adrenaline / noradrenaline in blood increase in metabolic rate (increase in heat)3. Thyroxine: A.lobe Pituitary TSH Thyroid Thyroxine in blood increase in metabolic rate (increase in heat) * slower to react but longer lasting4. Shivering: Various areas in the brain increase in skeletal muscle tone oscillating (rhythmic muscle contractions, 10 -20 / sec). Can be suppresses by cerebral cortex (voluntarily)5. Piloerection: (not effective)6. Behavioural responses.

Preventing Body Temp from RisingMain area of heat loss: Skin (some in lungs, faeces, urine)Heat receptors hypothalamus 3 physiological / behavioural responses1. Vasodialation: sympathetic NS blood vessels in skin dialate (effective up to 28 oC)2. Sweating: sympathetic NS periodic contraction of cells surrounding sweat glandsSweat consists of: water, salt, urea, lactic acid, K+

3. Decrease in Thyroxine secretion4. Behaviour Response

Temperature ToleranceIncrease in temp results in:

Nerve malfunctionProtein destructionDeath (44 - 46 oC)

Heat stroke: when body temp increases but regulatory mechanisms cease

Heat exhaustion: extreme sweating and vasodilatation low water/low resistance to blood flow low blood pressure/ low cardiac output person may collapse. (temp is usually normal)

Hypothermia: below 33C very low metabolic rate, heat producti9on can’t replace heat loss nbody temp continues to fall.

Fluid Regulation

Body FluidsHumans composed of approx 60% water (male: 65%, female: 55%)Intracellualr fluid: cytoplasm (inside cells)Extracellular Fluid: outside cells

Intercellular fluid (interstisial / tissue fluid) between cellsBlood plasma

Fluid & excretion:

IN: food (0.7)/drink (1.6) / metabolic water (0.2) (product of chem. reactions) approx 2.5LOUT: kidneys (urea, uric acid, creatinine approx 1.5 L), skin (salt, urea, lactic acid, approx 0.5 L), lungs (CO2, 0.3L), alimentary canal (bile pigments, 0.2L)

Regulation of water contentFeedback mechanism:1. Thirst (behavioural)2. ADH

Detection of changes in water level: • As water is lost from blood, plasma is more conc.• Water moves from intercellular material to plasma

(osmosis)• Water moves from cells to intercellular (osmosis)• Cell shrinks in size

Osmoreceptors hypothalamus p. pituitary or drink centre

StimulusIncreased osmotic

pressure of blood (low

water conc)

Receptor / Modulator

Osmoreceptors in

hypothalamus

EffectorP. Pituitary

gland release ADH

ResponsePermeability to water of distal convoluted tubule and collecting tubule increase

ResponseIncreased

reabsorption of water to

plasma

FeedbackDecreased

osmotic pressure of

blood

Control of water balance due to ADH

StimulusIncreased osmotic

pressure of blood

ReceptorOsmoreceptors

in hypothalamus

ModulatorNerve

impulses stimulate

drinking centre in

hypothalamus

EffectorDrinking centre in

hypothalamus activates drinking

behaviour

ResponseWater intake

increases

FeedbackDecreased

osmotic pressure of

blood

Control of water balance due to thirst mechanism

Dehydration: water loss exceeds water intake. (often caused by sweating, vomiting or diarrhoea)Symptoms: severe thirst, low blood pressure, dizziness & headaches (after approx 2% water loss) Water intoxication/poisoning: body fluids become dilute (lack of ions)Symptoms: light-headedness, headaches, vomiting & copllapse