12-+Renal+and+Acid-Base+Physiology

Kidney Functions

Maintains constancy of ECF volume and osmolality by balancing intake/excretion of Na+ and water, adjusts excretion of H+ and HCO3-, conserves nutrients, and excretes metabolic end products.

Reabsorption

The process where the greater part of ultrafiltrate is transported across the tubule wall and reenters the blood.

Excretion

The process where the fraction that is not reabsorbed remains in the tubules and appears in the terminal urine.

Secretion

The process where some urinary solvents enter the nephron lumen from tubule cells.

Nephron

Consists of a glomerulus and renal tubule, which includes segments like proximal tubule, loop of Henle, distal tubule, and collecting ducts.

Glomerular Filtration Rate (GFR)

The volume of filtrate produced by both kidneys per minute.

Renal Clearance

Indicates the volume of plasma cleared of a substance per unit time, measured in ml/min.

Na+-Glucose Cotransport

Mechanism in the proximal tubule that reabsorbs glucose from tubular fluid into the blood.

Transport Maximum (Tm)

The reabsorptive rate at which carriers are saturated, limiting reabsorption of substances.

ADH Mechanism

ADH attaches to V2 receptors, activating a cascade to increase water permeability through aquaporins.

Corticopapillary Osmotic Gradient

Established by countercurrent multiplication and urea recycling, crucial for producing concentrated urine.

Acid Production

Involves volatile acid (CO2), produced from aerobic metabolism, which forms H2CO3 that dissociates into H+ and HCO3-.

Buffers

Prevent changes in pH by neutralizing added H+ ions; major extracellular buffer is HCO3-.

Excretion of H+ as Titratable Acid

Dependent on urinary buffer presence; involves secretion of H+ that combines with filtered HPO4-2 to form H2PO4-.

Metabolic Acidosis

Characterized by overproduction of fixed acid or loss of base, leading to increased arterial H+ and decreased HCO3-.

Metabolic Alkalosis

Characterized by loss of fixed H+ or gain of base, resulting in decreased arterial H+ and increased HCO3-.