bio chp#01

• Homeostasis


  A self-regulating process by which biological systems maintain stability while adjusting to changing conditions
• Homeostasis is essential for the continuity of life as it is responsible for the stability of body functions according to the environment
• Organisms live in terrestrial and aquatic environments with variable conditions that influence their physical and physiological changes
• Organisms need to maintain their internal body environment up to suitable limits
• Body environment

  • Comprises of different components including body fluids, tissues, organs, systems
  • Physiologically well integrated and efficiently controlled and coordinated by endocrine and nervous systems
  • Ensures proper performance of homeostatic regulatory functions like osmoregulation, excretion and thermoregulation
• Feedback system


  Necessary physiological check and balance mechanism of the body functions that maintain its normal state
• Feedback system components


  • Receptors
  • Control center
  • Effectors
• Receptors


  Sensory organs neurologically connected with the nervous system that detect external or internal environmental changes and send messages to the central nervous system
• Control center


  The central nervous system that responds by concerned effector organs to bring back the normal state of the body
• Effectors


  Organs that respond to the control center to maintain homeostasis
• Positive feedback


  Concerned with the increase or initiation of change of output for any biological process
• Positive feedback


  • Platelets reaching the site of injury, recognizing the damaged area and sticking together to stop blood loss and form a clot
• Negative feedback


  Suppresses the normal physiological activities to bring the body back to normal state
• Negative feedback


  • When body temperature decreases below the set point, the body shivers to produce heat and return temperature to the normal range
• Set point


  The physiological value around which the normal range fluctuates
• Normal range


  The restricted set of values that is optimally healthful and stable
• Osmoconformers


  Organisms that have internal body solute composition equal or isotonic to the external environment
• Osmoregulators


  Organisms that maintain a constant internal osmotic environment in spite of changes in their external environment
• Osmoconformers


  • Marine organisms
  • Can survive in a wide range of salinities
• Osmoregulators


  • Live in marine, fresh water and terrestrial environments
  • Can survive in a narrow range of salinities
• Fresh water animals have an external hypotonic environment and a hypertonic internal body environment, so they face the problem of excessive water entry and need to remove it
• Marine animals have a hypertonic external environment and face the problem of severe dehydration, so they need to intake water but also need to retain salts
• Terrestrial organisms retain water in their body, but face the problem of dehydration and salt loss due to perspiration in hot environments
• Osmoregulation in fresh water habitat

  1. Minimize water influx and salt loss through gills and skin

  2. Balance water influx and salt removal through specialized kidney filtration and reabsorption

  3. Use specialized ionocytes in gills and skin to actively extract salts from external medium
• Osmoregulation in marine water habitat

  1. Drink seawater and digest its salts

  2. Extract and excrete excessive salts through specialized rectal and gill glands

  3. Reabsorb some water and salts, excrete small amounts of urine with excessive salts
• Osmoregulation in terrestrial habitat

  1. Develop waterproof external coverings to prevent water loss

  2. Produce excretory waste that requires less water like uric acid

  3. Efficiently reabsorb water and salts in kidney and intestine

  4. Obtain metabolic water from breakdown of fats and other compounds
• Excretion


  The process of removal of metabolic waste produced during biochemical reactions in the body
• Excretion is an important homeostatic activity as it involves controlling osmotic pressure, balance of inorganic ions and water, and maintaining acid-base balance
• Nitrogenous wastes


  Ammonia, urea, uric acid, creatinine
• The type of nitrogenous waste produced depends on the nature of food, availability of water, and the animal's habitat
• Ammonotelic


  Animals that generate large amounts of ammonia and need a lot of water to dissolve it
• Ureotelic


  Animals that excrete urea
• Uricotelic


  Animals that excrete uric acid
• Ammonia


  An immediate and highly toxic gaseous waste that is soluble in water and body fluids, so it needs to be present in low concentrations
• Ammonia is excreted in aquatic animals through diffusion and in small amounts through urine as urea, while in terrestrial animals it is converted to urea and excreted through urine
• Ammonotelic


  Animals that excrete ammonia
• Ammonia


  Immediate and highly toxic gaseous waste initially produced by the breakdown of nitrogenous compounds in the body
• Ammonia


  • Highly soluble in fresh water and body fluids
  • Raises the pH, therefore should be present in low concentration in the body
  • Reduces its toxicity in water and requires lot of fresh water to dissolved and generate non-toxic ammonium (NH4+) ions
  • Produced in aquatic animals in gaseous form and mostly diffused out from the body while some amount also excreted through urine as urea
  • Produced in terrestrial animals and converted in to urea and excreted through urine
  • Chemically it is alkaline, corrosive and 100,000 times more toxic than urea
• Urea


  Nitrogen containing liquid waste product produced by the breakdown of protein in mammals, amphibians, in some fishes and excreted in urine
• Urea


  • Neither acidic nor alkaline and highly soluble in water
  • Liver combines ammonia with CO2 molecule to form some intermediate compounds and then produces urea in the urea cycle or ornithine cycle
  • Not only a waste product in the body but also plays important role in the absorption of important ions and water in kidneys