Homeostasis

• Homeostasis


  The maintenance of a relatively constant internal environment within a narrow range in an organism even when the external environment changes significantly
• Example of homeostasis


  • Blood glucose regulation

  
• Homeostasis


  • Maintenance of a constant internal environment
  • Constant (within narrow limits) eg. body temperature (37°C), body fluid water potential, body fluid blood glucose levels, body fluid pH
• Homeostasis (with Negative Feedback)


  1. Stimulus triggers a response that counteracts the initial change

  2. If the body's constant internal environment is disrupted, the body reacts to reverse the change and returns the internal environment back to normal (optimal)

  
• Negative Feedback


  A primary mechanism of homeostasis, whereby a change in a physiological variable triggers a response that counteracts the initial change

  
• Negative Feedback Process


  1. Normal/set point

  2. Stimulus (change from normal condition in internal environment)

  3. Receptors/sensors detect the stimulus

  4. Corrective mechanism brings about reverse effect of the stimulus

  
• What happens when glucose concentration rises

  1. Receptor (Islets of Langerhans in pancreas stimulated)

  2. Corrective Mechanism (Islets of Langerhans secrete more insulin, transported by blood to liver and muscles, liver and muscles convert excess glucose to glycogen)

  3. Negative feedback (blood glucose concentration decreases and insulin production falls, blood glucose concentration returns to normal)

  
• What happens when glucose concentration falls

  1. Receptor (Islets of Langerhans in pancreas stimulated)

  2. Corrective Mechanism (Islets of Langerhans secrete more glucagon, transported by blood to liver and muscles, liver and muscles convert stored glycogen back to glucose)

  3. Negative feedback (blood glucose concentration rises and glucagon production decreases, blood glucose concentration returns to normal)

  
• Fishes do have different systems in place to maintain their blood water potential
• Marine vertebrates (bony fish) lose water through gills and skin, so they drink large amounts and use active transport at gills to remove excess salt
• Freshwater organisms (fish) take in too much water and lose salt, so they produce lots of dilute urine and use active transport to take in salt at the gills
• What happens when blood water potential falls

  1. Receptor (Osmoreceptors in hypothalamus stimulated)

  2. Corrective Mechanism (Posterior pituitary gland secretes more ADH, more water reabsorbed by kidney tubules)

  3. Negative feedback (blood water potential returns to normal)

  
• What happens when blood water potential rises

  1. Receptor (Osmoreceptors in hypothalamus stimulated)

  2. Corrective Mechanism (Posterior pituitary gland secretes less ADH, less water reabsorbed by kidney tubules)

  3. Negative feedback (blood water potential returns to normal)

  
• Epidermis of mammalian skin

  • Outer cornified layer (dead, dry, flat cells)
  • Granular layer (living cells moving upwards)
  • Malpighian layer (cell division, pigment, protects from UV)
• Dermis of mammalian skin

  • Blood vessels (arterioles and capillaries for temperature regulation)
  • Hair (hair papilla, hair follicle, hair erector muscles)
  • Sweat glands (excretion, temperature regulation)
  • Sensory receptors (thermoreceptors, touch receptors, pressure receptors)
  • Adipose tissue (fat storage, insulation)

  
• Heat gain by body from aerobic (tissue) respiration
• Hair


  • Keratin proteins intertwine and harden to form hair
  • Hair follicle: hollow tube through epidermis and dermis
• Hair erector muscles


  • Attached to hair follicles
  • Muscles contract to cause hair to stand
  • Skin around hair raised to form goose bumps / pimples
• Sweat glands


  • Coiled tube (in a tight knot) in the dermis & surrounded by blood capillaries
  • Sweat flows through sweat duct to sweat pore (on skin surface)
  • Excretory organ: removal of urea
  • Sweat regulates body temperature
• Sensory receptors


  • Thermoreceptors, touch receptors & pressure receptors
  • Detect changes in the environment or detect stimuli
  • Thermoreceptors found in dermis & epidermis
  • Touch receptors just below epidermis
  • Pressure receptors deeper/lower in dermis
• Adipose tissue (sub-cutaneous fat)


  • Fats storage
  • Insulating layer
  • Prevents heat loss
• Heat gain by body

  1. Aerobic (tissue) respiration (metabolic activities)

  2. In muscles & liver

  3. Heat distributed by blood to whole body

  4. By eating

  5. By exercising

  6. From the sun's radiation

  7. From warm air on a hot day

  8. By shivering on a cold day
• Heat loss by body

  1. By radiation, convection (& conduction) from skin

  2. By evaporation of sweat from skin surface

  3. Through faeces & urine

  4. Through exhalation of air
• Radiation


  • The loss of heat down a concentration gradient to the surroundings
  • Transfer of heat from a warm body to a cooler body through air
• Convection


  • Movement of air in which warmer air is replaced by cooler air due to differences in air density
  • Air movements speed up heat loss by radiation and evaporation
• Conduction


  Transfer of heat from a hot solid to a cooler solid when they are in contact with each another
• Evaporation


  • Change of phase from a liquid to a vapour
  • Evaporation of sweat removes latent heat and is accompanied by cooling
• Hypothalamus


  • Monitors and regulates body temperature
  • Receives information from thermoreceptors on skin surface and in hypothalamus
• Regulating Body Temperature - on a Hot Day

  1. Arterioles in skin dilate

  2. More blood flows to capillaries in skin

  3. Greater heat loss

  4. Shunt vessels constrict

  5. Sweat glands more active

  6. Sweat production increases

  7. More latent heat lost as sweat evaporates

  8. Hair erector muscles in skin relax
• Regulating Body Temperature - on a Cold Day

  1. Less blood flows to capillaries in skin

  2. Arterioles in skin constrict

  3. Shunt vessels dilate

  4. Less heat loss

  5. Sweat glands less active

  6. Sweat production decreases

  7. Less latent heat lost

  8. Hair erector muscles in skin contract
• When body temperature increases

  • Vasodilation of arterioles near the skin's surface
  • Increased production of sweat
  • Decreased metabolic rate
  • Increased heat loss and reduced heat production
  • Body temperature decreases
• When body temperature decreases

  • Vasoconstriction of arterioles near the skin's surface
  • Decreased production of sweat
  • Increased metabolic rate
  • Shivering occurs
  • Decreased heat loss and increased heat production
  • Body temperature increases
• Heat stroke happens when core body temperature increases above 40 ⁰C and the body is unable to lose the extra heat
• Common symptoms of heat stroke include rapid pulse, disorientation, nausea, vomiting
• Hormones


  Chemical substances produced by endocrine glands, carried by blood, which alter the activity of more than one specific target organs and are then destroyed by the liver
• Hormones


  • Produced in minute quantities by an endocrine gland
  • Influence growth, development and activity of an organism
• Endocrine glands


  Ductless glands that secrete their products, hormones, directly into the blood rather than through a duct
• Control of hormones production

  1. Nervous system controls endocrine glands, preventing excessive hormones from being produced

  2. Endocrine glands produce hormones

  3. Hormones enter bloodstream and are transported to other parts of the body

  4. Hormones reach other parts of the body where they exert their effects

  5. Hormones are destroyed in the liver
• Glands and their hormonal secretions

  • Pituitary gland
  • Hypothalamus
  • Ovaries
  • Testes
  • Thyroid gland
  • Adrenal gland
  • Pancreas

  
• Glucagon


  Increases blood glucose concentration by stimulating the conversion of glycogen into glucose, fats and amino acids into glucose, and lactic acid into glucose