MCAT - Organ Systems:: Renal System Flashcards (50 Cards) — Study Online

Curriculum Overview

Comprehensive, high-yield MCAT study deck focusing on Renal System. Features 50 rigorous, curriculum-aligned flashcards designed for advanced-level mastery. Core concepts covered include High Na, key problem-solving heuristics, foundational formulas, and exam-tested application scenarios. Ideal for active recall review, spaced repetition study, and scoring in the top percentile.

Topics & Key Concepts

ENaC HCO3 Have MCAT NaCl Henle ATPase Active Bowman's Directly

Sample Flashcard Questions & Answers

Showing 8 of 50 cards

Question #1 Active Recall

Which structure is considered the functional unit of the kidney, responsible for filtration, reabsorption, and secretion?

- **A)** The renal pelvis
- **B)** The ureter
- **C)** The nephron
- **D)** The renal capsule

Answer & Explanation:

**Answer: C)**

The nephron - composed of the glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct - is the basic structural and functional unit performing all of the kidney's filtration, reabsorption, and secretion functions.

Question #2 Active Recall

Glomerular filtration is driven primarily by:

- **A)** Net filtration pressure - glomerular capillary hydrostatic pressure exceeding the opposing capsular hydrostatic and plasma oncotic pressures
- **B)** Active transport of plasma across the filtration membrane
- **C)** Osmotic pressure generated by filtered glucose
- **D)** Peristaltic contraction of the glomerular capillaries

Answer & Explanation:

**Answer: A)**

Like capillary Starling forces elsewhere in the body, glomerular filtration rate depends on net filtration pressure: glomerular capillary hydrostatic pressure (favoring filtration) minus Bowman's capsule hydrostatic pressure and plasma oncotic pressure (opposing filtration). Unlike systemic capillaries, glomerular hydrostatic pressure is high enough that net filtration occurs along the entire length of the capillary.

Question #3 Active Recall

The afferent arteriole supplies blood to the glomerulus; constriction of the afferent arteriole (with efferent unchanged) would:

- **A)** Increase glomerular capillary pressure and GFR
- **B)** Decrease glomerular capillary pressure and GFR, since less blood reaches the glomerulus
- **C)** Have no effect on GFR
- **D)** Increase renal blood flow while decreasing GFR

Answer & Explanation:

**Answer: B)**

Afferent arteriolar constriction reduces blood flow (and thus hydrostatic pressure) into the glomerular capillaries, decreasing net filtration pressure and lowering GFR - and also decreases overall renal blood flow, distinguishing it from efferent constriction.

Question #4 Active Recall

Constriction of the efferent arteriole (with afferent unchanged), within physiologic limits, would:

- **A)** Increase glomerular capillary hydrostatic pressure, initially increasing GFR despite decreased renal blood flow
- **B)** Decrease glomerular capillary pressure and GFR
- **C)** Have no effect on filtration
- **D)** Cause glomerular capillaries to rupture immediately

Answer & Explanation:

**Answer: A)**

Efferent constriction impedes outflow from the glomerulus, backing up pressure within the glomerular capillaries and increasing net filtration pressure (and thus GFR) despite an overall decrease in total renal blood flow - the mechanism exploited (and disrupted by ACE inhibitors/ARBs) in angiotensin II-mediated GFR autoregulation.

Question #5 Active Recall

The three layers of the glomerular filtration barrier, in order from blood to Bowman's space, are:

- **A)** Podocyte foot processes, basement membrane, fenestrated endothelium
- **B)** Basement membrane, fenestrated endothelium, podocyte foot processes
- **C)** Mesangial cells, basement membrane, fenestrated endothelium
- **D)** Fenestrated capillary endothelium, glomerular basement membrane, podocyte foot processes (with filtration slits)

Answer & Explanation:

**Answer: D)**

Blood first crosses the fenestrated capillary endothelium (excludes cells), then the glomerular basement membrane (a key size/charge barrier, rich in negatively charged heparan sulfate), then podocyte foot processes forming filtration slits - together restricting filtration of large and/or negatively charged molecules like most plasma proteins.

Question #6 Active Recall

Under normal conditions, plasma proteins such as albumin are largely excluded from the glomerular filtrate primarily because of:

- **A)** Active reabsorption of albumin back into the blood before filtration occurs
- **B)** Albumin's very small molecular size, which allows it to pass but then be immediately degraded
- **C)** Albumin's relatively large size combined with its negative charge, which is repelled by the negatively charged basement membrane
- **D)** Complete absence of any pores in the filtration membrane

Answer & Explanation:

**Answer: C)**

Albumin is filtered only in tiny amounts because it is both fairly large (though not enormous) and negatively charged, and the glomerular basement membrane's negatively charged heparan sulfate proteoglycans electrostatically repel similarly charged molecules - a size AND charge barrier. Loss of the charge barrier (as in some glomerular diseases) causes proteinuria even without much size-selectivity change.

Question #7 Active Recall

Glomerular filtration rate (GFR) can be estimated clinically using the clearance of which substance, considered the gold-standard marker because it is freely filtered and neither reabsorbed nor secreted?

- **A)** Glucose
- **B)** Inulin
- **C)** Urea
- **D)** Sodium

Answer & Explanation:

**Answer: B)**

Inulin is freely filtered at the glomerulus and is neither reabsorbed nor secreted by the tubules, so its clearance (urine concentration x urine flow rate / plasma concentration) exactly equals GFR - the classic research gold standard, though creatinine clearance is used more often clinically as a practical (slightly imperfect) approximation.

Question #8 Active Recall

Creatinine clearance is a commonly used clinical estimate of GFR, even though creatinine is not a perfect marker, because creatinine is:

- **A)** Completely reabsorbed by the tubules, requiring a correction factor
- **B)** Not filtered at the glomerulus at all
- **C)** Freely filtered and minimally secreted by the tubules (causing a slight overestimation of true GFR), but easy to measure from endogenous muscle metabolism without an infusion
- **D)** Actively synthesized by the kidney itself

Answer & Explanation:

**Answer: C)**

Creatinine (an endogenous byproduct of muscle creatine metabolism) is freely filtered and undergoes only slight tubular secretion (which slightly overestimates true GFR), but because it doesn't require an exogenous infusion like inulin, creatinine clearance is the practical clinical standard for estimating GFR.

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