Skip to main content
Back

Osmoregulation and Excretion in General Biology

Control buttons has been changed to "navigation" mode.
1/20
  • What is osmoregulation?

    Osmoregulation is the control of water and solute balance in the body to maintain homeostasis.

  • What is excretion in biological systems?

    Excretion is the secretion of metabolic wastes, especially nitrogenous wastes, from the body.

  • Why is osmoregulation especially important in terrestrial organisms?

    Terrestrial organisms need to conserve water and also excrete water-soluble toxic metabolic wastes, requiring specialized osmoregulation and excretion mechanisms.

  • What is the role of kidneys in mammals?

    Kidneys function in osmoregulation and excretion by creating an osmolarity gradient and selectively reabsorbing water and ions.

  • Define osmolarity and give typical values for freshwater, blood, and seawater.

    Osmolarity measures osmotic pressure in mOsm/L: freshwater ~0-20, blood ~300, seawater ~1000.

  • What is the difference between osmoconformers and osmoregulators?

    Osmoconformers have body fluids isoosmotic with their environment; osmoregulators actively regulate their body fluid osmolarity.

  • How do marine fish osmoregulate?

    Marine fish lose water by osmosis, drink seawater, and actively excrete ions via gills and kidneys.

  • How do freshwater fish osmoregulate?

    Freshwater fish gain water by osmosis, excrete large amounts of dilute urine, and actively uptake ions from food and kidneys.

  • What is anhydrobiosis?

    Anhydrobiosis is a dormant state allowing some animals to survive extreme dehydration by losing almost all body water.

  • What nitrogenous waste do most aquatic animals excrete and why?

    Most aquatic animals excrete ammonia (NH3) because it is highly toxic but highly soluble and can diffuse away in water.

  • What nitrogenous waste do mammals and many vertebrates excrete?

    Mammals and many vertebrates convert ammonia to urea, which is less toxic and can be concentrated to conserve water.

  • What nitrogenous waste do reptiles and birds excrete and why?

    Reptiles and birds excrete uric acid, which is non-soluble, precipitates as a solid, and requires very little water but is costly to produce.

  • What are the four general steps of urine formation?

    1. Filtration, 2. Reabsorption, 3. Secretion, 4. Excretion of urine.

  • What is the functional unit of the mammalian kidney?

    The nephron is the functional unit, consisting of Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct.

  • What happens in the proximal tubule of the nephron?

    Active reabsorption of ions and water occurs, concentrating wastes in the filtrate.

  • What is the role of the descending loop of Henle?

    It is permeable to water but not salts, allowing water reabsorption and further concentration of filtrate.

  • What is the role of the ascending loop of Henle?

    It is permeable to NaCl but not water, allowing active reabsorption of salts and dilution of filtrate.

  • How does the collecting duct contribute to urine concentration?

    The collecting duct reabsorbs water and NaCl under hormonal control, concentrating urine as it moves down the osmolarity gradient.

  • What hormone regulates water reabsorption in the kidney?

    Antidiuretic hormone (ADH) increases water permeability in distal tubules and collecting ducts, concentrating urine and lowering blood osmolarity.

  • What is the function of the renin-angiotensin-aldosterone system (RAAS)?

    RAAS maintains blood pressure by initiating vasoconstriction and increasing sodium and water reabsorption when blood pressure is low.