Renal Physiology Refresher- Liang

Question 1

Where is the water in the body stored? What separates these compartments? What connects them?

Answer 1

2/3- Intracellular Fluid
1/3- Extracellular Fluid (25% plasma, 75% Interstitial)

Cell membrane separates intra- and extracellular fluid while capillary membrane separates plasma from interstitial.

Lymphatics connects plasma and interstitial.

Question 2

Which solutes are found in extracellular fluids and which in intracellular fluids?

Answer 2

Extracellular- Na, Cl, HCO3

Intracellular- K, Phosphate, Protein

Question 3

What is the difference between osmolarity and osmolality?

Answer 3

At dilute concentrations, nothing.

osmolarity- mosm/ LITER OF WATER
osmolality- mosm/KILOGRAM OF WATER

Question 4

What is the osmolarity of the solutions in the body?

Answer 4

280-300 mosm/liter

Question 5

What are the four steps that determine the composition of the urine?

Answer 5

1) filtration
2) absorption
3) secretion
4) excretion

Question 6

Where does filtration occur? What does the “urine” look like at this time?

Answer 6

Glomerular apparatus

“Urine” is basically acellular plasma, contains proteins, solutes, sugars, etc

Question 7

How is the filtration pressure calculated?

Answer 7

filtration pressure= glomerular hydrostatic pressure-(bowman’s capsule hydrostatic pressure+ glomerular colloid pressure)

Question 8

What is the ultrafiltration coefficient? What determines its value?

Answer 8

translates the net pressure into permeability

determined by podocyte foot structure and surface area of glomerular capillaries

Question 9

How variable is the GFR and renal perfusion?

What controls GFR and renal perfusion?

Answer 9

stable except at very low or very high pressures

myogenic response, tubuloglomerular feedback

Question 10

What is the myogenic response?

Answer 10

Intrinsic to smooth muscle cells in the arteries, when blood pressure rises, smooth muscles constrict and increase resistance.

Question 11

What is tubuloglomerular feedback?

Answer 11

With increased perfusion, more sodium enters the macula densa. At high concentrations of sodium, the macula densa causes afferent constriction and decreased renin release, leading to decreased GFR.

Question 12

What are the layers of the capillaries in the glomerular apparatus?

Answer 12

• podocyte feet
• basement membrane with negatively charged polymer proteins (collagen, laminin, etc)
• fenestrated endothelium with negatively charged glycocalyx

TLDR: charge-selective and size-selective

Question 13

What occurs in the thin descending loop of Henle?

Answer 13

Water reabsorption

Question 14

What occurs in the thin ascending loop of Henle?

Answer 14

Passive reabsorption of sodium

secretion of urea

Question 15

What occurs in the thick ascending loop of Henle?

Answer 15

Reabsorption of Na by Na/K/2 Cl transporter
passive, paracellular absorption of positive ions
secretion of H
Water impermeable

Question 16

What drug inhibits the Na/K/2Cl co-transporter?

Answer 16

Loop diuretics

Question 17

What happens in the early distal tubule?

Answer 17

Resorbs Na, Cl, Ca, and Mg
Na/Cl co transporter
Water impermeable

Question 18

What drug acts on the early distal tubule?

Answer 18

Thiazide diuretics

It inhibits the Na/Cl co-transporter

Question 19

What happens in the late distal tubule and cortical collecting tube?

Answer 19

Na resorption/K secretion- aldosterone

Water resorption- ADH

Question 20

What drug works in the late distal tubule and cortical collecting tube?

Answer 20

Potassium sparing diuretics

Aldosterone antagonists

Question 21

What happens in the medullary collecting tubes?

Answer 21

Resorbs sodium
Water resorption- ADH
Urea resorption

Question 22

What does aldosterone do? Where does it act?

Answer 22

Aldosterone upregulates ENaC channels to resorb Na and secrete K

Acts in the late distal tubule and collecting duct

Question 23

What does angiotensin II do? Where does it act?

Answer 23

Angiotensin II upregulates Na/H antiporter activity to resorb sodium, secrete H

Acts in the proximal tubule

Question 24

What does ADH do? Where does it act?

Answer 24

Inserts aquaporins to increase water absorption

Acts in late distal tubule, cortical and medullary collecting duct

Question 25

What does ANP do? Where does it act?

Answer 25

It decreases Na resorption by phosphorylating the ENaC channels to inactivate them

Acts in the distal tubule and collecting duct

Question 26

What does parathyroid hormone do? Where does it act?

Answer 26

It decreases phosphate resorption and increases calcium resorption

Phosphate effects happen in the proximal tubule, calcium happens in the ascending loop of Henle and distal tubule