Renal Embryology and Physiology

Question 1

Define Glomerular Filtration Rate (GFR).

Answer 1

The volume of fluid filtered in the renal glomerular capillaries into the Bowman’s capsule per unit of time

Question 2

Define Filtration Fraction (FF)

Answer 2

The proportion of the fluid reaching the kidneys that passes into the renal tubules

Question 3

Define Renal Plasma Clearance (RPC)

Answer 3

The volume of plasma completely cleared of a substance by the kidneys per unit of time

Question 4

Define Renal Plasma Flow (RPF)

Answer 4

The volume of plasma delivered to the kidneys per unit of time

Question 5

Define Renal Blood Flow (RBF)

Answer 5

The volume of blood delivered to the kidneys per unit of time

Question 6

What are the functions of the kidneys?

Answer 6

A - acid-base balance
W - water balance
E - electrolyte balance
T - toxin removal
B - blood volume/pressure
E - erythropoietin production
D - Vitamin D activation

Question 7

Describe the blood flow through the kidneys, what arteries and veins are involved?

Answer 7

Renal artery > Segmental > Interlobar > Arcuate > Interlobular > Afferent arteriole > Glomerulus > Efferent arteriole > Peritubular capillaries and vasa recta > interlobular veins > arcuate > interlobar > renal

Question 8

What are the components of the nephron?

Answer 8

The nephron consists of the afferent and efferent arterioles the glomerulus, Bowman’s capsule, PCT, DCT, the Loop of Henle and the collecting tubule

Question 9

What is the function of the nephron?

Answer 9

The nephron is the functional unit of the kidney and is where the filtration, secretion and reabsorption takes place

Question 10

What are the three tissues that compose the kidneys?

Answer 10

Renal capsule, cortex and medulla

Question 11

What are the stages of urine production?

Answer 11

Filtration, Reabsorption, Secretion and Excretion

Question 12

What are the 3 layers of the filtration bed?

Answer 12

Capillary endothelium
Basement membrane
Podocytes

Question 13

Describe the components of the filtration bed and how they promote filtration

Answer 13

The endothelial cells are fenestrated and therefore some small uncharged molecules can diffuse across the filtration bed

The podocytes are negatively charged cells that have pedicels, foot-like processes that wrap around the capillaries creating thin filtration slits that prevent large molecules from crossing into the nephron

Question 14

What is the average GFR?

Answer 14

~125ml/min

Question 15

How is RPF calculated?

Answer 15

Plasma makes up 55% of the circulating blood therefore RPF is 55% of RBF

They kidneys require 20% of the total cardiac output. We have ~6L of blood in our bodies, 20% is 1200ml

55% of 1200ml is 625ml

RPF = ~625ml/min

Question 16

What is the only known substance where GFR and RPC are the same value?

Answer 16

Inulin

Question 17

What is the name of the formula that estimates creatinine clearance?

Answer 17

Cockcroft-Gault

Question 18

Why is creatinine a crude marker of GFR?

Answer 18

Creatinine is filtered in the glomerulus but it is also secreted by the tubules and it there overestimates the GFR by 15-40%

Question 19

What is rhabdomyolysis?

Answer 19

muscle breakdown releases myoglobin into the blood and blocks the filtration bed of the nephron resulting in reduced renal function and can lead to kidney damage