Kidney Function and Structure

Kidney Function and Structure

• Kidneys maintain ion balance, blood pH, osmolarity, and extracellular fluid volume.
• Regulated ions include Na+, HCO3-, K+, and Ca2+.
• Urine's yellow color is from urobilinogen.
• Urine is produced by the kidneys and transported to the bladder via ureters.
• Kidneys lie behind the peritoneal membrane.
• Kidney blood flow includes a unique portal system.
• Structures in kidney blood circulation: renal corpuscle, vasa recta, and glomerulus.
• Renal corpuscle is made of Bowman's capsule and glomerulus.
• Secretion is active and energy-dependent.
• Glomerulus: a capillary "knot" in Bowman's capsule.
• Proximal tubule is closest to the renal corpuscle in the nephron.
• Distal tubule connects to the collecting duct in the nephron.
• Loop of Henle is the hairpin-shaped segment of the nephron.
• Loop of Henle descends into the medulla then returns to the cortex.
• Kidney filtration is relatively nonspecific.
• Filtrate normally contains urobilinogen, potassium, and glucose.

Glomerular Filtration

• Cysts on the kidney can raise nephron pressure, decreasing GFR and increasing blood pressure.
• Approximately 1/5 of plasma volume filters into the nephrons.
• Blood cells and plasma proteins aren't normally filtered.
• Filtration barrier consists of Bowman's capsule epithelium, basal lamina, and glomerular capillary endothelium.
• Glomerular filtration pressure is based on blood pressure in glomerular capillaries.
• The proximal tubule primarily reabsorbs ions, organic molecules, and water.
• Secretion actively transports substances from the peritubular capillaries into proximal and distal tubules.
• Glucose and amino acids are reabsorbed via Na+ symport.

Autoregulation and Feedback

• Autoregulation is a mechanism that maintains a constant GFR.
• Myogenic response: smooth muscle in afferent arterioles constricts in response to stretch.
• Tubuloglomerular feedback: macula densa cells signal the afferent arteriole in response to filtrate concentration.
• Myogenic response is paracrine signaling.
• Substances are excreted when plasma concentration exceeds renal concentration.
• Collecting duct function is affected first by renal medulla damage.
• Glomerulus obstruction affects blood flow into the efferent arteriole.
• Increased afferent arteriole blood flow triggers vasoconstriction.
• Urea is passively absorbed in the proximal tubule.
• Na+-dependent transport often involves apical symport proteins and basolateral facilitated diffusion carriers.

Urea and Filtration Pressure

• Urea diffuses freely through channels as Na+ transport creates a water gradient.
• Glomerular hydraulic pressure (69 mm Hg), Bowman's capsule fluid pressure (15 mm Hg), and plasma osmotic pressure (30 mm Hg) determine net GFR (24 mm Hg).
• Decreasing plasma protein concentration increases GFR.