Week 3

Question 1

What are the functions of the kidney?

Answer 1

Removing metabolic waste from extracellular fluid, controlling the volume of extracellular fluid and maintaining optimal concentrations of vital solutes in the extracellular fluid.

Question 2

Where is extracellular fluid?

Answer 2

In intravascular spaces, or interstitial space

Question 3

What is extraceullar fluid composition and volume dependent on?

Answer 3

Salt intake (hunger, food availability), water intake (thirst, water availability) and salt and water losses (sweat and gut)

Question 4

What are the three basic processes of the nephron?

Answer 4

Glomerular filtration, tubular reabsorption and tubular secretion

Question 5

What is glomerular filtration?

Answer 5

Filtering of blood into tubule forming the primitive urine (glomerular filtrate)

Question 6

What is tubular reabsorption?

Answer 6

Selective absorption of substances from tubule to blood

Question 7

What is tubular secretion?

Answer 7

Secretion of substances from blood to tubular fluid

Question 8

How is selective reabsorption achieved?

Answer 8

Unique renal tubular cell membrane composition:

Question 9

What percentage of cardiac output do kidneys receive?

Answer 9

Approximately 20%

Question 10

How is selective reabsorption achieved?

Answer 10

Unique renal tubular cell membrane composition

Question 11

What percentage of total body weight is extracellular water?

Answer 11

20%

Question 12

What is the most common cation in the extracellular fluid?

Answer 12

Sodium

Question 13

What is the most common cation in the intracellular fluid?

Answer 13

Potassium

Question 14

What is the most common anion in the extracellular fluid?

Answer 14

Chloride

Question 15

What is the most common anion in the intracellular fluid?

Answer 15

Protein

Question 16

What happens in the fluid compartments of the body if one litre of water is added?

Answer 16

Number of particles in each compartment does not change, volume changes very slightly (water is distributed evenly in each compartment) and concentration in each compartment falls

Question 17

What happens in the fluid compartments of the body if 300 meq of sodium is added?

Answer 17

Particles increase the IV and the IT compartments, but not in the IC compartment. Because of water redistribution, all compartments change in size, and concentration (increases)

Question 18

What happens in the fluid compartments of the body if 300 meq of sodium, and 1 litre of water is added?

Answer 18

Isotonic addition of salt and water leads to expansion of the IV and IS compartments, but no change in the IC compartment

Question 19

Describe some of the mechanisms of selective reabsorption:

Answer 19

The basolateral surface of the tubular cells maintains a negative charge inside the cells (by Na/K ATPase), which facilitates net movement of a sodium ion, along with an anion, from the lumen of the tubule and into the interstitial space

Question 20

What features of the proximal tubule enable selective reabsorption?

Answer 20

Cellular projections into the lumen, many mitochondria at the basolateral surface and infoldings of the basolateral membrane for ATPase

Question 21

How does movement of solutes and water across membranes occur?

Answer 21

Diffusion, or by specific membrane channels (energy dependent, down a concentration gradient, down an electrical gradient, down an osmotic gradient)

Question 22

How is movement of solutes and water across membranes controlled?

Answer 22

Presence and activity of membrane channels controlled by systemic and local (paracrine) mediators e.g. angiotensin II, ADH, aldosterone, PTH

Question 23

Where is the majority of the sodium chloride reabsorbed?

Answer 23

70% is reabsorbed in the proximal tubule, as well as nearly all amino acids and glucose

Question 24

How does the loop of henle facilitate countercurrent exchange?

Answer 24

Thick ascending limb is impermeable to water, but actively transports sodium, potassium and chloride.
Thick ascending limb provided the concentration gradient to promote water reabsorption from the thin DLH
Thin descending limb is freely permeable to salt and water
Vasa recta does not wash away the gradient by using the countercurrent exchange

Question 25

What does the juxta-glomerular apparatus do?

Answer 25

Maintains GFR in face of increases or decreases in blood flow to the kidney. The macula densa senses tubular flow

Question 26

What happens when there is increased tubular flow to the kidney?

Answer 26

Sensed by the macula densa, macula densa produces adenosine, which causes afferent arteriolar constriction

Question 27

What happens when there is reduced tubular flow to the kidney?

Answer 27

Sensed by macula densa, granular cells produce renin, causing secretion of angiotensin II which increases reabsorption of sodium chloride and water

Question 28

What is the kidney response to reduced sensed volume?

Answer 28

Efferent glomerular arteriolar constriction preserves waste excretion
Avid tubular sodium and water reabsorption preserves extraceullar fluid volume