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.