13: Renal Function

Question 1

Three layers of the glomerular filtration barrier

Answer 1

1. Cap endothelium
2. Glomerular BM
3. Podocytes epithelium

Question 2

Molecules that are 1. Freely filtered, 2. Maybe filtered, and 3. Not filtered in the glomerular apparatus

Answer 2

1. Freely filtered: <20 Angstroms
2. Maybe filtered: 20-42 A
3. Not filtered: 42+ A

Question 3

Three layers of the glomerular BM

Answer 3

1. Lamina rara externa
2. Lamina densa
3. Lamina rara interna

Question 4

Composition of the lamina rara interna and externa vs lamina densa

Answer 4

Lamina rara interna/externa: made of proteoglycans, mainly heparin sulfate
Lamina densa: made of type IV collagen and laminins

Question 5

Purpose of proteoglycans in the lamina rara exerna and interna

Answer 5

Provide electronegative charges to GBM to repel proteins

Question 6

Glycocalyx of glomerular endothelium

Answer 6

Forms a sticky layer that helps filter what can get through

Question 7

What charge of particles is more likely to be filtered through the glomerular apparatus

Answer 7

Positive charge (bc of negative glycocalyx)

Question 8

Things that are freely filtered vs not freely filtered through the filtration barrier

Answer 8

Freely: water, small solutes (glucose, AAs, electrolytes)

Not freely: large molecules (most proteins), cells

Question 9

What does it mean if excretion exceeds filtration?

Answer 9

Tubular secretion must have occurred

Question 10

What two volumes are equal to arterial input to the kidney?

Answer 10

Venous output + urine output

Question 11

Quick conversion: what is 1mL/min in L/day?

Answer 11

1 mL/min -> 1.44 L/day

Question 12

How does glomerular filtrate compare to plasma?

Answer 12

Isosmotic to plasma, just without proteins and cells

Question 13

Filtered load vs filtration fraction

Answer 13

Filtered load: rate of filtration of a specific molecule

Filtration fraction: ratio of GFR to RBF

Question 14

Four conditions that must be present to assume that GFR = Clearance

Answer 14

1. Substance freely filterable
2. Substance neither absorbed nor secreted
3. Substance not synthesized or broken down by kidney
4. Substance must be physiologically inert (non-toxic, without renal effects)

Question 15

Two substances often used when using renal clearance to estimate GFR and WHY

Answer 15

Inulin, creatinine - they are not really reabsorbed or secreted, and are freely filtered

Question 16

What marker is used in clinical settings to determine GFR? Why is this not ideal?

Answer 16

Creatinine - is it actually secreted in a small amount, but is easier bc it doesn’t require an infusion like inulin does

Question 17

Adrenergic receptors present on arterial vessels, JG cells, and Na-K ATPases

Answer 17

Arterial vessels: a1
JG cells: B1
Na-K-ATPase: a1

Question 18

Starling forces that favor vs oppose filtration

Answer 18

Favor: PGC, pi BC
Oppose: PBC, pi GC

Question 19

Where does pressure drop steeply in renal vasculature

Answer 19

Across afferent and efferent arterioles

Question 20

Constricting/dilating the efferent/afferent arterioles: two ways to increase and two ways to decrease GFR

Answer 20

Increasing GFR: dilate afferent + constrict efferent

Decreasing GFR: constrict afferent + dilate efferent

Question 21

Examples of vasoconstrictor moleucles vs vasodilator molecules

Answer 21

Vasoconstrictors: catecholamines, endothelin, ATP, angiotensin II
Vasodilator: prostaglandins, bradykinin, NO, dopamine, ANP, ACE-inhibitors

Question 22

What happens in PTC with increased GFR?

Answer 22

Increased GFR -> increased PTC oncotic pressure -> increased reabsorption in tubules

Question 23

Two intrinsic and three extrinsic control mechanisms of hemodynamics

Answer 23

Intrinsic: autoregulation, tubuloglomerular feedback
Extrinsic: symps, hormones, composition of blood