Homeostasis

• Endotherms


  • Brown adipose tissue
  • Increased number of mitochondria per cell
  • Insulation
• Fur


  Insulation against cold
• Brown adipose (fat)


  • Packed with large mitochondria to aid in hibernation transition
  • Mitochondria stores ATP
• Behavioural responses


  • Kleptothermy
  • Hibernation
  • Aestivation
  • Torpor
• Kleptothermy


  Huddling together to share body heat, reducing exposed surface area
• Torpor


  Reduced activity, physiological state of lowered metabolic rate to save energy (reduced body temperature, oxygen consumption, and energy requirements)
• Hibernation


  Prolonged torpor in endotherms e.g bears in winder
• Aestivation


  Prolonged hibernation in ectotherms e.g. insects, fish, and amphibians in hot dry weather
• Physiological responses

  • Vasomotor control
  • Evaporative heat loss
  • Counter-current heat exchange
  • Thermogenesis/metabolic activity from organs and tissues
• Vasomotor control


  Vasodilation or vasoconstriction
• Evaporative cooling


  Sweating or panting
• Counter-current heat exchange


  Blood is warmed by adjacent blood vessels flowing in the opposite direction
• Homeostatic mechanisms


  • Thyroid hormones
  • Insulin
• Thyroid hormones


  Regulate cell metabolic rate (increased rate increases heat generation (thermogenesis)
• Insulin


  Acts on temperature-sensitive neurons in the hypothalamus, which stimulates brown adipose tissue to produce heat
• Thermoregulation in humans: negative feedback loop

  1. Cold: Stimulus: body is cold

  2. The body's temperature is cooler than the hypothalamic set point

  3. Heat-promoting centre in hypothalamus is activated

  4. Vasoconstriction to minimise heat loss from skin surface, and skeletal muscles activated to shiver

  5. Body temperature increases, and heat-promoting centre is shut off

  6. Hot: Stimulus: body is hot

  7. Heat loss centre in hypothalamus is activated

  8. Vasodilation to allow heat loss from skin surface, sweat glands activated to secrete perspiration, vapourised by body heat

  9. Body temperature decreases, heat loss centre is shut off
• Three heat producing mechanisms

  • Shivering (activation of skeletal muscles)
  • Kleptothermy (huddling to share body heat)
  • Vasoconstriction (conservation of body heat by reducing heat loss on skin surface)
• Structural, physiological and behavioural adaptations of emperor penguins for survival

  • Structural: Fur to insulate against cold
  • Physiological: Counter-current blood flow in feet
  • Behavioural: Kleptothermy, huddling to keep warm
• Methods of heat exchange

  • Conduction: heat transfer through direct contact
  • Convection: movement of heat from hotter to colder region by liquid or gas
  • Radiation: heat transfer without direct contact
  • Evaporation: the loss of heat through water
• Osmoregulation


  Regulation of water balance in organisms
• Osmoregulators


  Organisms that maintain the internal osmotic concentration of bodily fluids regardless of their external concentration changes through behavioral or physiological responses
• Osmoconformers


  Animals that change their internal osmotic concentration to match that of the external environment
• Osmolality


  A measure of the concentration of solutes in the blood
• Osmoregulation in humans


  1. Osmolality monitored by hypothalamus and baroreceptors in the atria of the heart

  2. Water content of blood too low: pituitary gland releases lots of ADH, kidney secretes renin causing release of aldosterone, absorption of sodium into blood drawing water and causing potassium excretion

  3. Water content of blood too high: pituitary gland releases little ADH, low volumes of water get reabsorbed by the kidney
• Structural adaptations in plants for osmoregulation


  • Leaf surface area through shapes
  • Number of stomata
  • Sunken or protected stomata
  • Thick and waxy cuticle (reduce evaporation)
  • Extensive root systems
  • Leaves oriented away from sunlight
• Physiological adaptations in plants for osmoregulation

  • CAM photosynthesis (stomata open at night)
  • Drought tolerance (xenophytes)
  • Salinity tolerance (halophytes – salt glands shed leaves with accumulated salt, pump salt from roots)
  • Water plants (hydrophytes – thin/absent cyticle with stomata absent or on top of leaf)
  • Abscisic acid secreted by root cells, passing up xylem to leaf epidermis stimulating stomata closure
• Osmolality measures the concentrations of solutes in the blood
• ABA is abscisic acid and it is a response of plant root cells that stimulates the closing of the stomata to reduce water loss in dry environments
• Xerophytic plants are tolerant to conditions of drought, so they have small leaves to reduce surface area and therefore water loss; long roots that reach deep into the soil for water absorption, and a waxy cuticle to reduce transpiration
• There are three types of neuron - sensory (afferent), motor (efferent) and interneurons.
• Neurons are specialised cells that transmit electrical impulses to other parts of the body.