Homeostasis

• Homeostasis is the maintenance of a relatively constant internal environment within an organism even when the external environment changes significantly
• Enzymes require an optimum temperature and pH to function properly; drastic changes in pH level in the blood affect the activity of enzymes and the rate of cellular reactions
• The composition of tissue fluid must be maintained to ensure that the water potential of cells is kept constant; changes in water potential affect body cells, which can either shrink or burst in solutions with different water potentials
• Glucose in food is required for tissue respiration, which releases energy for cells to carry out their activities; drastic changes in blood glucose concentration can be dangerous
• Principles of homeostasis:

  • A stimulus is a change from normal conditions in the internal environment
  • Receptors detect the stimulus
  • A corrective mechanism brings about the reverse effect of the stimulus (negative feedback)
  • Feedback 'tells' the receptors that the condition has been restored back to the normal state
• Regulating blood glucose concentration:

  • When blood glucose increases above the norm:
  • Islets of Langerhans in the pancreas secrete more insulin, which is transported by blood to the liver and muscles
  • Liver and muscles convert excess glucose to glycogen, stored in the liver and muscles
  • Concentration of blood glucose decreases and insulin production falls
• Regulating body water potential:

  • When the water potential of blood increases above the norm:
  • Pituitary gland releases less anti-diuretic hormone (ADH)
  • More water is excreted, and urine produced is more dilute
  • Water potential of blood decreases
• Osmoregulation:

  • Marine Vertebrates (Bony Fish):
  • Ocean is hypertonic and dehydrates fish
  • Fish lose water through gills and skin
  • Solutions: little urine production, drink large amounts, active transport at gills to remove excess salt
  • Freshwater Organisms (Fish):
  • Freshwater is hypotonic to fish
  • Fish take in too much water and lose salt
  • Solutions: lots of dilute urine, use active transport to take in salt at the gills
• Structure of the Human Skin:

  • Epidermis: outermost layer consisting of cornified, granular, and Malpighian layers
  • Dermis: found directly below the Malpighian layer, with numerous blood capillaries supplying blood to the skin
• Homeostasis is the process that helps maintain stability in an organism by making small adjustments to keep the internal environment stable, even when the external environment fluctuates
• Examples of homeostatic mechanisms include sweating to cool down when the external temperature increases and shivering to warm up when the external temperature decreases
• Cells in the body can function properly when the internal environment is stable; if it becomes too hot or too cold, cells may not function properly, leading to sickness or death
• Homeostasis is crucial for life as it allows animals to maintain a stable internal environment despite constant changes in the external environment
• The skin plays a vital role in maintaining a constant body temperature in humans through processes like vasodilation, vasoconstriction, sweating, and relaxation or contraction of hair erector muscles
• A hormone is a chemical substance produced by a gland, carried by blood, altering the activity of more than one specific target organ and then destroyed by the liver
• Adrenaline's role in boosting blood glucose levels involves speeding up the breakdown of glycogen to glucose in the liver and muscles
• Signs of diabetes mellitus include increased blood glucose levels, glucose in urine; treatment involves insulin injections for Type 1 diabetes and lifestyle changes for Type 2 diabetes
• Insulin decreases blood sugar concentration by making cell membranes more permeable to glucose, stimulating the liver and muscle cells to convert glucose into glycogen for storage, and increasing the oxidation of glucose during tissue respiration
• Glucagon increases blood glucose concentration by stimulating the conversion of glycogen into glucose, fats, amino acids, and lactic acid into glucose
• The nervous system has localized effects, while the endocrine system has widespread effects affecting more than one target organ with the same hormone