Water & Electrolyte Balance

Electrolytes

  • An electrolyte is a substance that dissociates into ions when dissolved in water. Examples include NaCl and HCl.

Osmosis

  • Osmosis is the movement of water down its concentration gradient across a semipermeable membrane.

Osmolarity

  • Osmolarity refers to the concentration of solutes in a solution, measured in osmoles per liter (Osmoles/liter).

Osmotic Stress

  • Osmotic stress is a condition where the concentration of dissolved substances in a cell or tissue is abnormal.

Organs Involved in Ionoregulatory Homeostasis

  • The main organs involved in ionoregulatory homeostasis in animals are:
    • Fish & crustacean gills
    • Insect Malpighian tubules
    • Maxillary glands in barnacles
    • Kidneys in mammals

Ionocytes

  • Ionocytes are mitochondrion-rich cells that actively pump ions to maintain osmotic, ionic, and acid-base levels.

Kidney Functions

  • The functions of the kidneys include:
    • Maintaining water/salt balance
    • Controlling blood volume and pH
    • Producing red blood cells (RBCs)
    • Activating Vitamin D

Nephron

  • A nephron is the functional unit of the kidney, consisting of tubules and blood vessels, and concentrates urine.

Glomerular Pressure

  • Pressure in the glomerulus is high because the afferent arteriole is wider than the efferent arteriole. This creates high pressure for filtration.

Glomerular Filtration

  • Glomerular filtration involves forcing liquid and solutes through capillary pores in the glomerulus, retaining blood cells in the blood.

Tubular Reabsorption

  • Tubular reabsorption is the process where most glomerular filtrate is reabsorbed by proximal tubule cells to prevent nutrient loss.

Aquaporins

  • Aquaporins allow water to pass through cell membranes via osmosis.

Loop of Henle

  • In the Loop of Henle:
    • Water is reabsorbed in the descending limb.
    • Na^+ and Cl^- are reabsorbed in the ascending limb (thin = passive, thick = active).

Tubular Secretion

  • Tubular secretion involves capillaries secreting substances like ammonia and drugs into the distal tubule for removal in urine.

ADH (Antidiuretic Hormone)

  • ADH signals kidney collecting ducts to open aquaporins and reabsorb water into the body.

Effects of Caffeine and Alcohol on ADH

  • Caffeine and alcohol inhibit ADH release, leading to increased water loss in urine.

Deamination

  • Deamination is the removal of an amino group from an amino acid, usually in the liver, producing ammonia.

Nitrogenous Waste Products

  • The three nitrogenous waste products and the organisms that produce them are:
    • Ammonia (fish)
    • Urea (mammals)
    • Uric acid (birds and reptiles)

Osmoregulators vs. Osmoconformers

  • Osmoregulators maintain an internal osmolarity different from their environment.
  • Osmoconformers match their internal osmolarity to their environment.

Fish Adaptation

  • Some fish switch between salt and freshwater environments by using alternative splicing to flip transport proteins in ionocytes.