Glomerula filtration

How is glomerular filtrate produced?

A. Active secretion of plasma into Bowman’s space

B. Bulk flow driven by glomerular capillary hydrostatic pressure

C. Osmotic movement of water due to plasma proteins

D. Transport of solutes via podocyte channels

Correct: B

Which structure provides the final size‑selective barrier to filtration?

A. Fenestrated endothelium
B. Glomerular basement membrane
C. Podocyte slit diaphragm
D. Mesangial matrix

Correct: C

A patient with nephrotic syndrome presents with heavy proteinuria. Which layer of the filtration barrier is most likely damaged?

A. Fenestrated endothelium

B. Basement membrane

C. Podocyte foot processes

D. Mesangial cells

Correct: C

Which change would increase GFR?

A. Increased plasma oncotic pressure

B. Constriction of the afferent arteriole

C. Constriction of the efferent arteriole (moderate)

D. Decreased glomerular capillary hydrostatic pressure

Correct: C

Which factor directly determines GFR?

A. Renal sympathetic nerve activity only

B. Net filtration pressure and filtration coefficient

C. Aldosterone secretion

D. Plasma sodium concentration

Correct: B

In tubuloglomerular feedback, what does the macula densa do when it detects high NaCl?

A. Dilates the afferent arteriole

B. Constricts the afferent arteriole

C. Stimulates renin release

D. Constricts the efferent arteriole

Correct: B

Which best describes the myogenic mechanism of autoregulation?

A. Macula densa senses NaCl and alters renin release

B. Afferent arteriole smooth muscle contracts when stretched

C. Podocytes adjust slit diaphragm width

D. Mesangial cells alter capillary surface area

Correct: B

Why is GFR used clinically?

A. It directly measures nephron number

B. It reflects the kidney’s ability to filter plasma

C. It measures tubular secretion

D. It measures renal blood flow

Correct: B

Which molecule is LEAST likely to cross the filtration barrier?

A. Glucose

B. Sodium

C. Albumin

D. Urea

Correct: C

A patient with renal artery stenosis has reduced GFR. Which change explains this?

A. Increased glomerular hydrostatic pressure
B. Decreased afferent arteriole pressure
C. Increased filtration coefficient
D. Increased renal perfusion

Correct: B

Which condition increases filtration coefficient (Kf)?

A. Mesangial cell contraction

B. Loss of podocytes

C. Thickening of the basement membrane

D. Increased plasma oncotic pressure

Correct: B

A patient with diabetic nephropathy has a thickened basement membrane. What effect does this have on GFR?

A. Increases GFR

B. Decreases GFR

C. No effect

D. Causes afferent dilation

Correct: B

What 3 layers make up the filtration barrier

1. glomerula capillary endothelium

2. Basement membrane

3. epithelial cells (podocytes)

Which molecules are MOST restricted by the fenestrated endothelium?

A. Large plasma proteins

B. Red blood cells

C. Glucose

D. Sodium ions

Correct: B

Why: The fenestrations allow most solutes through but prevent cellular elements like RBCs.

The negative charge of the glomerular basement membrane primarily prevents filtration of:

A. Positively charged ions

B. Negatively charged proteins

C. Water

D. Glucose

Correct: B

Why: The basement membrane is rich in negatively charged glycoproteins → repels albumin and other anionic proteins.

A patient with minimal change disease presents with massive proteinuria. Which layer is most affected?

A. Fenestrated endothelium

B. Basement membrane

C. Podocyte slit diaphragm

D. Mesangial matrix

Correct: C

Why: Podocyte foot process effacement disrupts slit diaphragms → albumin leaks through.

define GFR

GFR = the volume of filtrate formed by all nephrons in both kidneys per unit time.

WHAT IS NORMAL, a high GFR or low GFR

high GFR

name 2 determinants of GFR

1. Glomerular capillary filtration coefficient (Kf)

   • Reflects permeability and surface area of the filtration barrier.

2. Net filtration pressure (NFP)

• The balance of hydrostatic and oncotic pressures across the glomerular capillary wall.

equation for GFR

Equation = GFR = Kf * NFP ​

GFR for healthy kidney

GFR ≈ 180 L/day.

describe the direction of movement of fluid in hydrostatic pressures and oncotic pressures

• Hydrostatic pressures → drive fluid outward (favor filtration).

• Oncotic pressures → pull fluid inward (oppose filtration).

name 3 factors affecting glomerular hydrostatic pressure (PG).

Determinants of PG:

1. Systemic arterial pressure (overall blood pressure).

2. Afferent arteriole resistance (controls blood entry into glomerulus).

3. Efferent arteriole resistance (controls blood outflow from glomerulus).

in relation to arteriole constriction and dialtion what would increase GFR

Increasing GFR

Efferent arteriole constriction

• ↓ Renal plasma flow leaving the glomerulus.

• ↑ Glomerular hydrostatic pressure (P_G).

• Increases GFR.

Afferent arteriole dilation:

• ↑ Blood flow into the glomerulus.

• ↑ Glomerular hydrostatic pressure (P_G)

• Increases GFR.

in relation to arteriole constriction and dialtion what would decrease GFR

Afferent arteriole constriction

• ↓ blood flow into glomerulus

• ↓ glomerular hydrostatic pressure

• ↓ GFR.

Efferent arteriole dilation

• ↑ blood flow out of glomerulus

• ↓ glomerular hydrostatic pressure

• ↓ GFR.

name 3 humoral mediators which increase GFR and what effect they have exactly

• Angiotensin II - Constrict the EA

• Prostaglandins and ANP - vasodilate the AA

name 3 humoral mediators which decrease GFR and what effect they have exactly

• Noradrenaline, Adenosine, Endothelin

• Cause afferent arteriole vasoconstriction.

name 2 autoregulatory mechanism of GFR

1. Myogenic response – arterioles constrict or dilate in response to changes in blood pressure.

2. Tubuloglomerular feedback – the juxtaglomerular apparatus senses changes in flow/NaCl delivery and adjusts arteriole tone accordingly.

describe the myogenic response

1. Trigger: High systemic blood pressure → more blood is pushed into the kidney →increased RBF & GFR

2. Afferent arteriole wall stretches because of the increased pressure.

3. That stretch opens stretch‑activated calcium channels in the smooth muscle cells of the arteriole wall.

4. Calcium enters the cells → smooth muscle contracts.

5. Contraction narrows (constricts) the arteriole, which:

   • Increases resistance to incoming blood flow.

   • Prevents glomerular capillary pressure from rising too high.

   • Brings GFR back down toward normal.

describe the tubuloglomerula ffedback mechanism for both increasing adn decreasing GFR

Response to ↑ Arterial Pressure

1. ↑ Arterial pressure → ↑ renal blood flow & GFR.

2. ↑ GFR → more Na⁺ and Cl⁻ filtered into the nephron.

3. Macula densa senses ↑ NaCl (via NKCC2 transporter).

4. Macula densa releases adenosine (paracrine factor) → causes afferent arteriole vasoconstriction.

5. ↑ Resistance → ↓ renal blood flow & ↓ glomerular hydrostatic pressure.

6. GFR falls back to normal.

Response to ↓ Arterial Pressure

1. ↓ Arterial pressure → ↓ renal blood flow & GFR.

2. ↓ GFR → less Na⁺ and Cl⁻ delivered to macula densa.

3. ↓ Adenosine release → less vasoconstriction → afferent arteriole dilates.

4. ↑ Renal blood flow → ↑ glomerular hydrostatic pressure.

5. GFR restored to normal.

Which transporter allows the macula densa to sense increased NaCl delivery?

A. Na⁺/K⁺ ATPase

B. ENaC

C. NKCC2

D. SGLT2

Answer: C

Explanation: NKCC2 detects changes in tubular NaCl concentration.

What paracrine factor is released by the macula densa in response to increased NaCl?

A. Renin

B. Adenosine

C. Angiotensin II

D. Nitric oxide

Answer: B

Explanation: Adenosine causes afferent arteriole vasoconstriction, reducing GFR back toward normal.

What happens to the afferent arteriole when arterial pressure decreases?

A. It dilates due to reduced adenosine

B. It remains unchanged

C. It constricts due to increased renin

D. It constricts due to increased adenosine

Answer: A

Explanation: Low NaCl at the macula densa reduces adenosine release, allowing afferent dilation.

What is considered the gold‑standard method for measuring GFR?

A. Serum creatinine

B. Serum urea

C. Inulin clearance

D. eGFR equations

Answer: C

Explanation: Inulin is freely filtered and neither reabsorbed nor secreted, making it the ideal marker.

Why is inulin clearance not routinely used in clinical practice?

A. It is inaccurate

B. It requires multiple blood samples

C. It is expensive, time‑consuming, and requires infusion

D. It is affected by muscle mass

Answer: C

Explanation: Inulin measurement requires infusion and steady‑state monitoring, making it impractical.

Which endogenous marker is the least accurate for estimating GFR?

A. Serum creatinine

B. Serum urea

C. eGFR

D. Cystatin C

Answer: B

Explanation: Serum urea is influenced by hydration, diet, and liver function, reducing accuracy.

Why is serum creatinine alone an imperfect measure of GFR?

A. It is not filtered by the kidney

B. It varies with muscle mass, age, sex, and diet

C. It requires infusion

D. It is too expensive for routine use

Answer: B

Explanation: Creatinine production depends on muscle mass and other factors, making single values unreliable.

Which of the following is TRUE about eGFR?

A. It is unaffected by muscle mass

B. It is accurate for drug dosing in chemotherapy

C. It is derived from equations based on adult populations

D. It requires infusion of an exogenous marker

Answer: C

Explanation: eGFR equations are adult‑derived and less accurate in children or muscle‑mass extremes.

What is considered a normal eGFR?

1. 30 mL/min/1.73 m²

1. 60 mL/min/1.73 m²

1. 75 mL/min/1.73 m²

1. 90 mL/min/1.73 m²

Answer: D
Explanation: Normal kidney function corresponds to an eGFR above 90.