Homeostasis Thermoregulation & Fluid regulation

Thermoregulation

Preventing body temp from Falling Cold receptors  hypothalamus  5 physiological / behavioural responses 1. Vasoconstriction: sympathetic NS  blood vessels in skin constrict 2. 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 lasting 4. Shivering: Various areas in the brain  increase in skeletal muscle tone  oscillating (rhythmic muscle contractions, / sec). Can be suppresses by cerebral cortex (voluntarily) 5. Piloerection: (not effective) 6. Behavioural responses.

Preventing Body Temp from Rising Main area of heat loss: Skin (some in lungs, faeces, urine) Heat receptors  hypothalamus  3 physiological / behavioural responses 1. Vasodialation: sympathetic NS  blood vessels in skin dialate (effective up to 28 o C) 2. Sweating: sympathetic NS  periodic contraction of cells surrounding sweat glands Sweat consists of: water, salt, urea, lactic acid, K + 3. Decrease in Thyroxine secretion 4. Behaviour Response

Temperature Tolerance Increase in temp results in: Nerve malfunction Protein destruction Death ( o C) 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 Fluids Humans composed of approx 60% water (male: 65%, female: 55%) Intracellualr fluid: cytoplasm (inside cells) Extracellular Fluid: outside cells Intercellular fluid (interstisial / tissue fluid) between cells Blood plasma Fluid & excretion: IN: food (0.7)/drink (1.6) / metabolic water (0.2) (product of chem. reactions) approx 2.5L OUT: kidneys (urea, uric acid, creatinine approx 1.5 L), skin (salt, urea, lactic acid, approx 0.5 L), lungs (CO 2, 0.3L), alimentary canal (bile pigments, 0.2L)

Regulation of water content Feedback 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

Stimulus Increased osmotic pressure of blood (low water conc) Receptor / Modulator Osmoreceptors in hypothalamus Effector P. Pituitary gland release ADH Response Permeability to water of distal convoluted tubule and collecting tubule increase Response Increased reabsorption of water to plasma Feedback Decreased osmotic pressure of blood Control of water balance due to ADH

Stimulus Increased osmotic pressure of blood Receptor Osmoreceptors in hypothalamus Modulator Nerve impulses stimulate drinking centre in hypothalamus Effector Drinking centre in hypothalamus activates drinking behaviour Response Water intake increases Feedback Decreased 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