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Homeostasis

Thermoregulation & Fluid regulation. Homeostasis. Thermoregulation. Preventing body temp from Falling Cold receptors  hypothalamus  5 physiological / behavioural responses 1. Vasoconstriction : sympathetic NS  blood vessels in skin constrict

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Homeostasis

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  1. Thermoregulation & Fluid regulation Homeostasis

  2. Thermoregulation

  3. 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.

  4. 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 28oC) • 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

  5. Temperature Tolerance • Increase in temp results in: • Nerve malfunction • Protein destruction • Death (44 - 46oC) • 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.

  6. Fluid Regulation

  7. Body Fluids • Humans composed of approx60% 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, creatinineapprox 1.5 L), skin (salt, urea, lactic acid, approx 0.5 L), lungs (CO2, 0.3L), alimentary canal (bile pigments, 0.2L)

  8. 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

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

  10. Stimulus Increased osmotic pressure of blood Receptor Osmoreceptors in hypothalamus Feedback Decreased osmotic pressure of blood Response Water intake increases Modulator Nerve impulses stimulate drinking centre in hypothalamus Effector Drinking centre in hypothalamus activates drinking behaviour Control of water balance due to thirst mechanism

  11. 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

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