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