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, 10 -20 / 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 (44 - 46 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.
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