Kidney Function II

Question 1

What is “clearance”

Answer 1

The volume of plasma that is cleared of a substance in given time

Question 2

Renal Clearance

Answer 2

= u v /p

u= concentration in urine
v= volume of urine / min
p= concentration in plasma
where all the values are calculated at the same point in time

Question 3

Inulin clearance rate-

Answer 3

It can be used to measure the GFR because:

it is freely filtered
it is not absorbed
Is not metabolised
easily measured

Good for experimental because it is administered intravenously

Question 4

Creatinine examples

Answer 4

used clinically to estimate the GFR-

it is an estimate because it is slightly secreted- so value calculated would be a slight overestimate

Question 5

Use of PAH

Answer 5

PAH is filtered, completely secreted, not reabsorbed

This means that all the plasm that enters the kidney per unit time is cleared of PAH

Rate of excretion = u x v

Since all the plasma that enters the kidney per unit time is cleared of PAH it is assumed that:

PAH clearance = renal plasma flow

Effective Renal Plasma flow ~ 600 ml/min
NB Effective because some is directed to perineal fat region

Question 6

Renal Plasma FLow ——> Renal Blood Flow

Answer 6

Blood flow = Plasma Flow/ ( 1- haemocrit)

whole blood contains 45% cells
blood contains 55% plasma

Renal blood flow = 600/0.55 =1100 ml/min
The importance is stressed as this is 20% of cardiac output

Blood flow = Plasma flow / ( 1- haemocrit)

Question 7

Osmalilty

Answer 7

mOSm/kg

the higher the solution osmolality the lower the water concentration

Question 8

Sodium Balance

Answer 8

The main osmotically active solute in the plasma

Sodium freely filtered at renal corpuscle

Na concentration in plasma = 140 mol/l

Amount filtered = [Na] x GFR

Question 9

Where is Sodium reabsorbed

Answer 9

Thin ascending limb (passive)

Proximal Tubule (LOTS OF REABSORPTION)

Thick ascending (LOTS OF REABSORPTION)

distal tubule

Collecting duct

Question 10

Na transport Pathways (PT)

Answer 10

The Na+/K+ pump ensures that the [Na] intraceullarly is low which allows for the

Na+/H+ exchanger and Na+/nutrient symporter to transport Na+ inside

Due to the fact that Na+ and Cl- move together and due to the electrochemical gradient, Cl- moves down in-between the epithelium cells by diffusion

Question 11

Na transport Pathways (Thick ascending limb)

Answer 11

The Na+/K+ pump ensures that the [Na] intraceullarly is low which allows for the

Na+/K+/2Cl- contransporter
to transport Na+ inside

Since there’s a buildup of K+ inside the cell, K+ can diffuse out of the epithelial cell by diffusion down its concentration gradient. This will encourage the Na+ to move inbetween the cells to IF due to there being a greater positive charge in the lumen

Question 12

Na transport Pathways (distal tubule)

Answer 12

The Na+/K+ pump ensures that the [Na] intraceullarly is low which allows for the

Na+/Cl- co transporter

The filtrate in the lumen is negatively charged so Cl- will move inbetween the cells

Question 13

Na transport Pathways (collecting duct)

Answer 13

The Na+/K+ pump ensures that the [Na] intracellulgvarly is low which allows for the

Na+ facilitated diffusion

The filtrate in the lumen is negatively charged so Cl- will move inbetween the cells

Question 14

Water Reabsorption

Answer 14

Osmosis

Sodium Reabsorption

Tubule permeability- variable since different segments will express different water channels
and different segments will have tight junctions between the cells decreasing the movement of water between the cells

Question 15

Proximal Tubule example

Answer 15

Na+ moves into the tubular epithelial cells from the tubular lumen by the symporters or the H+/Na+ anti porters. Na+ moves into the IF through Na+/K+ ATPase

The osmolarity decreases in the tubular lumen whilst increases in the IF
The osmolarity in the tubular lumen is less than the osmolarity in the IF

Water moves by osmosis through the epithelial cells to the IF or by osmosis in between the cells

BULK FLOW - due to the higher hydrostatic pressure in the iF, water will move into the plasma of the capillaries

Key–> volume of filtrate reduced and osmolarity is not changed

Question 16

How to produce concentrated urine

Answer 16

Separate the water reabsorption with the Na+

Create a renal medulla IF with high osmolarity to drive the water reabsorption- this is done in the loop of Henle

Question 17

Separating the Na+ and water reabsorption

Answer 17

Flow is said to be countercurrent- the flow in the limb is in the opposite direction

Since Henle’s loop reabsorbs more salt than water, it is implied that Na+ and water reabsorption is separated

In the ascending limb, walls are impeccable to water
Descending limb- express AQPI water channels so water an be reabsorbed. NaCl is also being secreted- moving into the filtrate passively

Question 18

Blood Supply?

Answer 18

would wash away the osmolarity gradient but the vasa recta mirrors the shape of the loop
therefore gradient not washed away

Question 19

Urea Recycling by the kidney

Answer 19

1) Urea is fully filtered at the Renal Corpuscle
2) Passive reabsorption in they the PT
3) Secreted back in the LOH
4) Reabsorbed at the CD via UT-A1 and UT-A3

Question 20

ADH action

Answer 20

causes the fusion of AQP2 with the CSM facing the filtrate

This means that the water can move from the filtrate into the epithelial cell via aquaporins and then into IF by AQP3 and 4