BIO-MODULE 7

• Homeostasis - the physiological consistency of the body despite external fluctuations. It can also refer to stability, balance, or equilibrium. It is the body's attempt to maintain a constant internal environment.
• Homeostatic regulation


  The adjustment of physiological systems within the body
• What we need to understand about homeostasis

  • The main parts and functions of the homeostatic control system
  • The mechanism of this control system
  • How balance is re-established following a disruption

  
• Components of homeostatic control


  • A receptor (sense organ) to detect a change
  • A center of control (the brain or the spinal cord) that will process and integrate what is happening
  • An effector (muscle cells or organs/ glands) to produce a response appropriate to the change

  
• Forms of Feedback Mechanisms


  • Negative
  • Positive
• Negative feedback


  A reaction in which the system responds in such a way as to reverse the direction of change
• Examples of negative feedback


  • Thermoregulation
  • Carbon dioxide concentration
  • Blood sugar level
• Positive feedback


  A response that occurs to amplify the change in the variable. This has a destabilizing effect, so does not result in homeostasis.
• Examples of positive feedback


  • In nerves, a threshold electric potential triggers the generation of a much larger action potential
  • Blood clotting
  • Events in childbirth
• Positive feedback is less common in naturally occurring systems than negative feedback, but it has its applications.
• During the Antarctic winter, temperatures drop as low as -50°C (-58°F), but emperor penguins stay put to mate and hatch their eggs.

  
• The survival of the emperor penguin embryo inside its egg depends on a constant internal temperature; eggs not maintained above 35°C (95°F) perish.
• Temperatures inside tight penguin huddles can become tropic-like, as high as 37.5°C (99.5°F).
• Thermoregulation


  The homeostatic mechanism by which animals maintain an internal temperature within an optimal range despite variations in external temperature

  
• Types of thermoregulation in animals


  • Endothermic
  • Ectothermic
• Endothermic


  Warmed mostly by heat generated by metabolism (e.g. humans, other mammals, birds)
• Ectothermic


  Gain most of their heat from external sources (e.g. many reptiles, fishes, most invertebrates)
• Ways of heat exchange


  • Conduction
  • Radiation
  • Convection
  • Evaporation
• If you are sweating on a hot day and turn a fan on yourself, two mechanisms that contribute to your cooling are convection and evaporation.
• Categories of thermogulatory adaptations


  • Metabolic heat production
  • Insulation
  • Circulatory adaptations
  • Evaporative cooling
  • Behavioral responses

  
• Waste disposal is a crucial aspect of osmoregulation because most metabolic wastes must be dissolved in water to be removed from the body.
• Types of animals based on the osmolarity of their body fluids

  • Osmoconformers
  • Osmoregulators
• Osmoconformers


  Allow the osmolarity of their body fluids to match that of the environment, generally hyperosmotic to their surroundings, consume little or no energy in maintaining water balance

  
• Osmoregulators


  Keep the osmolarity of body fluids different from that of the environment, either discharging water in hypotonic environment or taking in water in a hypertonic environment

  
• Nitrogenous wastes excreted by animals


  • Ammonia
  • Urea
  • Uric acid
• Ammonia


  The primary nitrogenous waste for aquatic invertebrates, teleosts, and larval amphibians, readily soluble in water but highly toxic, can only be excreted in dilute solutions
• Urea

  Produced by mammals, most amphibians, some reptiles, some marine fishes, and some terrestrial invertebrates, about 100,000x less toxic than ammonia, its excretion requires only about 10% as much water compared to ammonia
• Uric acid


  Excreted by birds, insects, and terrestrial reptiles, relatively nontoxic but more energetically expensive to produce than urea, largely insoluble in water and excreted as a semisolid paste or precipitate with very little water loss
• Functions of the kidneys

  • Filter blood plasma and excrete toxic metabolic wastes
  • Regulate blood volume, pressure, and osmolarity by regulating water output
  • Regulate the electrolyte and acid-base balance of the body fluids
  • Secrete the hormone erythropoietin
  • Contribute to calcium homeostasis and bone metabolism
  • Clear hormones and drugs from the blood
  • Detoxify free radicals
  • Help support blood glucose level in conditions of extreme starvation

  
• Hormones that regulate kidney function

  • Natriuretic peptides
  • Antidiuretic hormone
• Natriuretic peptides


  Increase sodium excretion in the urine in the collecting duct
• Antidiuretic hormone


  Promotes water retention and reduces urine volume in the collecting duct
• Glomerular filtration


  Passage of fluid from the bloodstream into the nephron, carrying not only wastes but also chemicals useful to the body
• The fluid filtered from the blood is called glomerular filtrate. In contrast to the blood, it is free of cells and very low in protein. After it passes into the renal tubule, its composition is quickly modified.

  
• Gluconeogenesis


  Process of synthesizing glucose from amino acids
• State at least 4 kidney functions other than forming urine

  
• What is the most abundant nitrogenous waste in the urine? What terms describe an abnormally high level of this waste in the blood, and poisoning by this waste?
• Urine Formation


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion

  4. Water conservation

  
• Flow of fluid from glomerular capsule to where urine leaves the kidney

  • Glomerular capsule
  • Proximal convoluted tubule
  • Nephron loop
  • Distal convoluted tubule
  • Collecting duct
  • Papillary duct
  • Minor calyx
  • Major calyx
  • Renal pelvis
  • Ureter

  
• Factors influencing filtration


  • Blood enters the glomerulus under high pressure
  • Glomerular capillaries are highly "leaky" to water and small solutes
  • The volume of blood flow affects the rate of filtration