Review of Renal Physiology (pgs 1-17 in handout)

Question 1

In a 70kg person, what is the:
TBW?
ICF?
ECF?
Intravascular Fluid?
Extravascular Fluid?
Plasma?

Answer 1

TBW- 42L
ICF-28L (40% of weight)
ECF- 14L (20% of weight)
IVF-4.9L (7% of weight)
EVF-11L (75% of ECF)
Plasma- 3L (25% of ECF)

Question 2

How does body composition change as we age?

Answer 2

-as age increases total body fluid decreases

Question 3

How does the osmolarity of the ECF compare to that of the ICF?

Answer 3

essentially the same (solute composition differs)

Question 4

What do rapid gains and losses in body weight reflect?

Answer 4

a change in total body water

Question 5

What percentage of CO perfuses the kidneys (RBF)?

Answer 5

20% (1-1.2L)

Question 6

What percentage of renal blood flow (RBF) is renal plasma flow (RPF)?

Answer 6

55% (600-700ml)

Question 7

What percentage of renal plasma flow (RPF) is GFR?

Answer 7

20% (125ml)

Question 8

Approximately how many times per day is the ECF volume filtered through the kidney?

Answer 8

10x

Question 9

Approximately what percent of the daily GFR (180L) is excreted in urine?

Answer 9

1-2L/day (0.5-1%)

Question 10

Which solute in the ECF primarily determines ECF volume?

Answer 10

Na+ (more Na, more ECF volume)

Question 11

When ECF volume expands how does the kidney compensate?

Answer 11

increases Na output and therefore water output leading to ECF volume contraction –> compensatory decrease in Na and water output
*This does not change GFR

Question 12

Severe ECF volume contraction (dehydration) can cause a decrease in what?

Answer 12

GFR

Question 13

How is Na balance regulated?

Answer 13

by adjusting urine Na output to match Na intake

Na intake restricted–>gradually increasing Na reabsorption until lower Na output in urine is achieved

Question 14

What happens to ECF volume when Na intake is reduced?

Answer 14

ECF volume contracts in an amount equivalent to the volume of urine needed to eliminate the excess Na isosmotically

Question 15

An imbalance in hydrostatic and oncotic pressure across the capillary wall inducing a shift of fluid from intravascular space to extravascular space

Answer 15

Edema

Question 16

How does the circulating volume change in edema and what does it do physiologically?

Answer 16

• decreases

- activates the renin-angiotensin-aldosterone system–>increase in sodium retention–>maintenance of the edema

Question 17

All of the following are potential causes of what?
CHF
Liver Disease
Nephrotic Syndrome
Pulmonary Edema

Answer 17

Edema

Question 18

How do diuretics work in treating edema?

Answer 18

they force an increased elimination of Na and water–>decrease in hydrostatic pressure and increase in oncotic pressure–>absorption of edematous fluid

Question 19

Renal Handling equation

Answer 19

Excretion= Filtration - Reabsorption + Secretion

Question 20

What is produced in the glomerulus?

Answer 20

an ultrafiltrate of the blood with similar solute concentration to the plasma (-protein)

Question 21

Where is the proximal tubule located and what is its function?

Answer 21

• in the cortex
• reabsorbs 66% of filtered Na, 67% of K+ and most of filtered Bicarb
• This is a leaky epithelium so reabsorption is isosmotic and 66% of the filtered water is also reabsorbed

Question 22

Where is the loop of henle located and what is its function?

Answer 22

• thin desc. and asc. in med, thick ascend, in medulla and cortex
• 25% of filtered Na, and 20% of K+ reabsorbed in thick asc limb by the Na/K/2Cl contransporter w/o water**–>drives the counter current multiplication of interstitial solute concentration

Question 23

Where is the distal tubule located and what is its function?

Answer 23

• in the cortex
• reabsorption of 6% of filtered Na via Na/Cl cotransporter at luminal membrane and Na/K ATPase at basolateral membrane
• *Na/Cl cotransporter is target of thiazide diuretics**
• impermeable to water
• late distal tubule-last part of the nephron to control ion composition of the urine

Question 24

Which hormone regulates Na reabsorption and K+secretion in the distal tubule? Water reabsorption?

Answer 24

• aldosterone

- ADH

Question 25

Where is the collecting duct located and what is its function?

Answer 25

- outer cortex and inner medulla | - reabsorption of water induced by ADH

Question 26

What is the filtration fraction?

Answer 26

fraction of plasma flowing through the glomeruli which is ultrafiltered to form tubular fluid (GFR/RPF) ~.20 (20%)

Question 27

How is the fractional excretion of water calculated? (FEwater)

Answer 27

= urine flow rate (V)/GFR | -fraction of glomerular filtrate not reabsorbed from the tubular fluid

Question 28

How can GFR be measured?

Answer 28

=Clearance of inulin= (Urine Inulin)(urine flow rate)/(Plasma inulin)

Question 29

How can the fractional excretion of Na be calculated?

Answer 29

=(Urine Na X Plasma Cr) / (Urine Cr X Plasma Na)

Question 30

When in water and Na balance, approximately how much of the filtered water and Na is in the urine?

Answer 30

1%

Question 31

When in NEGATIVE water balance, approximately how much of the filtered water is in the urine?

Answer 31

<1%

Question 32

When in POSITIVE water balance, approximately how much of the filtered water is in the urine?

Answer 32

>1%

Question 33

In which 2 areas of the nephron is K+ reabsorbtion/secretion NOT affected by dietary K+ intake? which areas are affected by dietary K+ intake?

Answer 33

- are NOT affected-proximal tubule and thick ascending loop of henle - are affected- distal tubule and collecting duct

Question 34

What happens in negative K+ balance?

Answer 34

- it is induced by a low K+ diet | - decreased secretion and increased reabsorption of K+

Question 35

What happens in positive K+ balance?

Answer 35

- induced by normal or high K+ diet | - increased secretion and decreased reabsorprtion of K+

Question 36

What is the effect of alkalosis on K+ secretion? Acidosis? Diuretic induced increase in tubular flow?

Answer 36

- alkalosis-increases K+ secretion - acidosis- decreases K+ secretion - Diuretic induced increase in tubular flow-increases K+ secretion

Question 37

How does the level of Na+ affect the secretion of K+? ***Very important point from lecture***

Answer 37

- an increase in Na+ reabsorption in the late distal tubule and collecting duct is functionally linked to an increase in K+ secretion-->increase in K+ excretion * *This is why patients taking loop diuretics are at risk for hypokalemia and instructed to increase their K+ intake**

Question 38

What drives the Ca and Mg reabsorption across the tubular epithelium in the thick ascending loop of henle?

Answer 38

- K+ leaks back into tubule lumen after being reabsorbed by Na/K/2Cl cotransporter - Cl- efflux across basolateral membrane - ->Lumen + potential difference-->drives Ca and Mg reabsorption

Question 39

The solute reabsorption in the thick and thin ascending loop of henle without water reabsorption leads to....

Answer 39

dilution of the tubular fluid and the capacity to make a dilute hyposmotic urine

Question 40

What does the preservation of ECF volume depend on?

Answer 40

the ability of the kidney to concentrate or dilute the urine in response to ECF volume contraction or expansion

Question 41

What does a hypertonic urine indicate?

Answer 41

the kidney is responding to ECF volume contraction by retaining water in excess of solutes (free water)

Question 42

What does hypotonic urine indicate?

Answer 42

the kidney is responding to ECF volume expansion by excreting water in excess of solutes (free water clearance)

Question 43

Does ADH increase or decrease in response to an INCREASE in plasma osmolarity?

Answer 43

ADH increases with increase osmolarity-->retention of water-->hypertonic urine (- free water clearance)

Question 44

Does ADH increase or decrease in response to a DECREASE in plasma osmolarity?

Answer 44

ADH decreases with decrease in osmolarity-->elimination of free water by kidney-->hypotonic urine (+ free water clearance)

Question 45

What is free water clearance (C h2o) defined as?

Answer 45

the rate at which the kidney can retain or eliminate water free of solutes

Question 46

When C h2o (free water clearance) is equal to 0 is the urine hypotonic, isotonic, or hypertonic? >0?

Answer 46

=0-urine is isotonic | >0- urine is hypotonic

Question 47

How does Aldosterone affect the late distal tubule?

Answer 47

1) diffuses into the cell from basolateral membrane 2) binds intracellular receptor 3) enters nucleus and induces transcription of mRNA for membrane transport proteins mediating Na reabsorption 4) increased Na reabsorption