Osmoregulation Concepts Quiz

Osmoregulation

• Osmotic pressure is the pressure needed to keep the movement of pure solvent, like water, from crossing a semipermeable membrane.
• Hydrostatic pressure is the pressure exerted by a fluid on its surroundings.

Concepts you should recall

• Isotonic solutions: The concentration of solutes is equal inside and outside the cell, maintaining the cell's shape.
• Hypotonic solutions: The concentration of solutes is lower outside the cell than inside, causing water to flow into the cell, potentially causing it to burst.
• Hypertonic solutions: The concentration of solutes is higher outside the cell than inside, causing water to flow out of the cell, potentially causing it to shrink.

Electrolyte composition: serum ≈ ECF

• Table 14-2 shows electrolyte composition in human body fluids.
• Serum, interstitial fluid, and intracellular fluid concentrations are tabulated.
• Cations include Na⁺, K⁺, Ca²⁺, and Mg²⁺.
• Anions include Cl⁻, HCO₃⁻, HPO₄²⁻, and SO₄²⁻.

Challenges in maintaining homeostasis

• The environment affects water and ion balance.
• Different animals have different strategies to regulate water and electrolyte balance.

Adaptation of mammalian kidney to environment

• Kidney structure is adapted to the environment.
• Urine concentration reflects environmental conditions.
• The kangaroo rat is adapted to their environment.

Sources of water gain and loss by the kangaroo rat

• Kangaroo rats' water balance is critical for survival.
• Gain: 90% metabolic water, 10% free water in "dry" food, 0% drinking
• Loss: 70% evaporation/perspiration, 25% urine, 5% feces

Arid adapted birds limit (some) water loss

• Water loss varies by species and environment.
• Cutaneous water loss is lower in species from arid environments.

Metabolic water

• Water produced from the oxidation of food stuffs.
• Carbohydrates, lipids, and proteins each generate varying amounts of metabolic water.

Fat stores as a hidden source of water storage

• Migratory birds use fat energy stores.
• Fat stores release more water than some other food types.

Protein stores as a hidden source of water storage

• Protein breakdown releases bound water.
• This extra water can be important for migratory birds.

Hummingbirds: Dehydration is not the problem (during the day)

• Hummingbirds frequently drink copious amounts of dilute nectar during the day.
• They produce dilute urine and maximize glucose reabsorption.

Hummingbirds: Dehydration is not the problem (during the day) (Graph)

• Tracer data shows little urine production at night, while the GFR rates change significantly.

Carb absorption in intestine

• Intestinal cells effectively absorb carbohydrates.
• The process involves brush border enzymes and active transport.

Glucose (or amino acid) reabsorption

• Active transport, facilitated diffusion, and Na+/K+ ATPase all contribute to glucose reabsorption.

Type II diabetes

• Common symptom is hyperglycemia.
• Historical diagnosis was based on sweet tasting urine.

Blood pH regulation

• Blood pH is tightly regulated.
• Carbonic anhydrase, H⁺ pumps, and bicarbonate exchange all are important for maintaining pH balance.

Capacity for urine acidification

• The maximum pH of urine is around 4.5.
• Buffers, like ammonia, are important in forming acidic urine.
• Protein-rich diets can lead to more acidic urine.

Vasopressin (and BP regulation)

• Vasopressin (ADH) regulates water reabsorption.
• Its release is triggered by increased plasma osmolarity.
• Release is inhibited by blood pressure.

Vasopressin increases cell permeability

• Vasopressin increases the number of water channels (aquaporins) in the collecting duct.
• This increases water reabsorption.

Hypertension

• The body compensates for high sodium intake.
• Blood volume increases with water reabsorption, increasing blood pressure.

Antihypertensive drugs

• Several classes of drugs effectively treat high blood pressure.
• ACE inhibitors and angiotensin II receptor blockers are two common classes.

Renin-Angiotensin-Aldosterone (RAA) Pathway

• A hormonal cascade regulating blood pressure.
• Juxtaglomerular cells, baroreceptors, and macula densa cells all trigger renin secretion.