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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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slide3

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.
slide4

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
slide5

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.
slide7

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)
slide9

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
slide10

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

slide11

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

slide12

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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