Glomerular Filtration and Regulation

Question 1

3 functions of each nephron

Answer 1

Glomerular filtration
Tubular reabsorption
Tubular secretion

Question 2

Glomerular filtration rate (definition, normal value, used for)

Answer 2

Volume of plasma filtered from the glomerular capillaries per unit time
Normal: 90-120 mL/min
Used to evaluate the presence and severity of kidney injury and progression of kidney disease

Question 3

How much of total body water is ICF vs ECF

Answer 3

ICF: 2/3
ECF: 1/3

Question 4

What type of cells make up the visceral vs parietal layer of Bowman’s capsule

Answer 4

Visceral: podocytes (specialized epithelial cells)
Parietal: epithelial cells

Question 5

What is the space between the interdigitated foot processes called?

Answer 5

Filtration slits

In life covered by a membrane

Question 6

2 factors that influence selective filtration in the glomeruli

Answer 6

Charge (GBM is negatively charged)

Size (not permeable to large molecules)

Question 7

Alport’s syndrome

Answer 7

Genetic defect in type 4 collagen of glomerular basement membrane
X-linked disease
See kidney failure, deafness, blindness

Question 8

Nephrotic syndrome

Answer 8

Disease of podocytes/slit diaphragm

Question 9

3 things that regulate glomerular filtration

Answer 9

Renal blood flow
Starling forces
Filtration coefficient

Question 10

What 2 forces

1. Push fluid out
2. Pull fluid in

Answer 10

1. Hydrostatic pressure in capillary, oncotic pressure in urinary space
2. Oncotic pressure in capillary, hydrostatic pressure in urinary space

Question 11

Permeability coefficient

Answer 11

Product of intrinsic permeability of the capillaries and surface area

Question 12

Autoregulation

Answer 12

The intrinsic mechanism of the kidneys by which renal blood flood and thus GFR are maintained over a range of aortic pressure

Question 13

3 factors that influence the hydrostatic pressure of glomerular capillaries

Answer 13

Systemic arterial pressure (effect is buffered by autoregulation)
Afferent arteriole resistance
Efferent arteriole resistance

Question 14

What happens if both afferent and efferent arterioles constrict?

Answer 14

Renal blood flow is reduced
GFR depends on the relative balance of the vasoconstrictors/dilators available and their strength of action (AA more, GFR falls. If EA more, GFR will remain the same or rarely increase)

Question 15

Characteristics of an ideal marker for GFR measurement

Answer 15

Small solute
Completely filtered
Non-secreted by renal tubules and GI tract
Excreted unchanged in the urine
Urinary appearance (clearance) is equal to GFR
Not expensive and easy to measure

Question 16

Formula to calculate the renal clearance

Answer 16

C = U/ P x V
C: renal clearance
U: [ ] of substance in urine
P: [ ] of substance in plasma
V: urine flow rate

Question 17

Inulin

Answer 17

Gold standard to measure GFR but expensive and cumbersome to assay
Mainly used in studies

Question 18

Creatinine

Answer 18

Most commonly used to measure GFR
More practical and less expensive
Less accurate (significant amount of tubular secretion. Increase GI excretion at lower GFR)

Question 19

Renal autoregulation works within a range of what mean arterial BPs

Answer 19

70-160 mmHg

Question 20

3 responses in renal autoregulation

Answer 20

Myogenic response
Tubuloglomerular feedback
Neuro-hormonal vasoactive response

Question 21

Myogenic response

Answer 21

Walls of afferent arterioles are made of smooth muscle cells
These blood vessels stretch when there is increased blood flow
Stretch reflex causes vasoconstriction of afferent arterioles and brings an increased GFR back to a normal range

Question 22

Tubuloglomerular feedback

Answer 22

When GFR decreases, the kidney tries to compensate
Links Na and Cl concentration of the filtrate at the macula dense with control of renal arteriolar resistance
2 components: afferent and efferent arteriolar feedback
Help renal autoregulation and tubular reabsorption
Basically activates the RAAS system, and causes dilation of AA and constriction of EA

Question 23

3 cell types in the juxtaglomerular apparatus

Answer 23

Juxtaglomerular cells in the walls of afferent arterioles
Macula dense (of DCT)
Extraglomerular mesangial cells (contractile)

Question 24

Neural regulation of GFR

Answer 24

Sympathetic nerve fibers innervate both afferent and efferent arterioles
Excessive sympathetic stimulation = renal vasoconstriction (drop GFR)
Parasympathetic = renal vasodilation (via NO)

Question 25

3 vasoconstrictors

Answer 25

Norepinephrine/epinephrine
Endothelin
Angiotensin 2 (preferentially efferent arterioles)

Question 26

3 Vasodilators

Answer 26

NO
Prostaglandin (works on AA)
Bradykinin

Question 27

Drugs that reduce GFR

Answer 27

NSAIDs (less prostaglandins, more AA constriction)
ACEIs
ARBs
SGLT2 inhibitors (more Na to macula densa)

Question 28

2 responses to decreased GFR and decreased NaCl delivery to the macula densa

Answer 28

Vasodilation of afferent arteriole (increase GFR and also NaCl - mediated by adenosine and ATP)
Vasoconstriction of efferent arteriole (also increases GFR and NaCl - mediated by RAAS)

Question 29

Does angiotensin 2 preferentially work on the afferent or efferent arterioles?

Answer 29

Efferent