All flashcards
Flashcard 1: Which segment actively reabsorbs Na+, K+, and Cl− and is impermeable to water?
Answer: Thick ascending limb (NKCC2); diluting segment. Actively transports ions out via NKCC2, creating dilute filtrate and contributing to medullary gradient.
Flashcard 2: What is the key mechanism that creates the corticomedullary osmotic gradient?
Answer: Countercurrent multiplication in the loop of Henle. Differential permeability and active transport in loop segments amplify osmotic gradient for urine concentration.
Flashcard 3: Identify the cell type in the collecting duct that secretes H+ to acidify urine.
Answer: Type A (alpha) intercalated cell. Uses H+-ATPase to excrete acid, maintaining blood pH during acidosis.
Flashcard 4: Identify the cell type in the collecting duct that secretes HCO3− during alkalosis.
Answer: Type B (beta) intercalated cell. Secretes bicarbonate via pendrin exchanger to correct alkalosis and reclaim H+.
Flashcard 5: Which blood vessel directly delivers blood into the glomerular capillaries?
Answer: Afferent arteriole. Delivers oxygenated blood under pressure to glomerulus for filtration into Bowman's capsule.
Flashcard 6: What happens to glucose in the nephron under normal plasma glucose levels?
Answer: Completely reabsorbed in the PCT (below transport maximum). Glucose is actively reabsorbed via SGLT transporters in PCT until saturation, preventing glucosuria.
Flashcard 7: What is the correct order of filtrate flow from Bowman's space to the renal pelvis?
Answer: PCT → loop of Henle → DCT → collecting duct → papillary duct → calyx → pelvis. Filtrate progresses from proximal tubule through loop for concentration, distal tubule for fine-tuning, and collecting system for final urine drainage.
Flashcard 8: What are the three major processes that determine urine composition in the nephron?
Answer: Filtration, reabsorption, secretion. These processes filter plasma at glomerulus, reclaim essentials along nephron, and add wastes to form concentrated urine.
Flashcard 9: What is the filtration barrier of the glomerulus composed of?
Answer: Fenestrated endothelium, GBM, podocyte slit diaphragms. Barrier selectively filters blood by size and charge, preventing large proteins from entering Bowman's space.
Flashcard 10: Which blood vessel directly drains blood away from the glomerulus?
Answer: Efferent arteriole. Carries filtered blood from glomerulus to peritubular capillaries for reabsorption and secretion.
Flashcard 11: What is the main function of the proximal convoluted tubule (PCT)?
Answer: Bulk reabsorption of solute and water; secretion of some wastes. Performs iso-osmotic reabsorption of most filtered solutes and water while secreting H+ and organics.
Flashcard 12: What fraction of filtered Na+ and water is reabsorbed in the PCT (approximate)?
Answer: About 65%. PCT reabsorbs majority of filtered load iso-osmotically via active transport and osmosis.
Flashcard 13: Which segment is permeable to water but not to NaCl: thin descending limb or thick ascending limb?
Answer: Thin descending limb. Allows water efflux into hyperosmotic medulla, concentrating filtrate without solute movement.
Flashcard 14: What is the primary role of the vasa recta in the kidney medulla?
Answer: Countercurrent exchange to preserve the medullary gradient. Prevents dissipation of hyperosmotic medullary interstitium by equilibrating with surrounding fluid.
Flashcard 15: Which nephron type (cortical or juxtamedullary) is most important for concentrating urine?
Answer: Juxtamedullary nephrons. Long loops extend deep into medulla, enabling greater water reabsorption via countercurrent system.
Flashcard 16: What is the main function of the distal convoluted tubule (early DCT)?
Answer: NaCl reabsorption (NCC) with low water permeability. Further dilutes urine by reabsorbing NaCl without water, regulated by thiazide-sensitive cotransporter.
Flashcard 17: Which hormone increases Na+ reabsorption and K+ secretion in principal cells?
Answer: Aldosterone. Stimulates ENaC and Na/K-ATPase for Na+ retention and ROMK for K+ excretion in late DCT/CD.
Flashcard 18: Which hormone increases water permeability in the collecting duct via aquaporin-2 insertion?
Answer: ADH (vasopressin). Binds V2 receptors to insert aquaporins, allowing water reabsorption down osmotic gradient.
Flashcard 19: What is the macula densa and what does it sense?
Answer: DCT cells sensing tubular NaCl delivery (flow-related). Specialized cells at DCT end detect NaCl levels to regulate GFR via tubuloglomerular feedback.
Flashcard 20: Which enzyme produced by juxtaglomerular cells initiates the RAAS cascade?
Answer: Renin. Released in response to low BP or Na, cleaves angiotensinogen to activate RAAS for homeostasis.
Flashcard 21: State the formula for renal clearance of a substance x.
Answer: Cx=PxUx×V. Calculates volume of plasma cleared of x per unit time, equaling GFR for freely filtered, non-reabsorbed/secreted substances.
Flashcard 22: Which conclusion follows if Cx>GFR for a solute x?
Answer: Net secretion of x. Indicates tubular secretion adds more x to urine beyond filtered amount.
Flashcard 23: Which conclusion follows if Cx<GFR for a solute x?
Answer: Net reabsorption of x. Indicates tubular reabsorption removes some filtered x, reducing excretion below filtered load.
Flashcard 24: What is the relationship between plasma osmolarity and ADH release?
Answer: Increased plasma osmolarity increases ADH release. Hypothalamic osmoreceptors detect high osmolarity, stimulating posterior pituitary to release ADH for water retention.