Question

Glomerular Filtration

1. What is the major force/pressure that causes filtration?

2. What is the major force/pressure that causes reabsorption?

3. What would happen to the filtration rate if glomerular capillaries were damaged to an extent to be leaky to plasma proteins?

Identifying how renal arterioles affect GFR

Complete the following table that describes how changes in the diameters of these resistance vessels affect glomerular hydrostatic pressure and GFR (assuming no change in renal arterial pressure) with no change, increase, or decrease.

Afferent Arteriole	Efferent Arteriole	Glomerular Hydrostatic Pressure and Filtration Rate
No change	No change	Normal
Constricts	No change
No change	Constricts
Dilates	No change
Dilates	Constricts

How renal arterioles respond to changes in blood pressure

Changes in mean arterial pressure (MAP) can lead to wide changes in systemic pressure, including the renal arteries. Use your understanding of the renal mechanisms identified in part and your understanding of cardiovascular physiology and blood pressure to answer the following questions.

1. In the human body, if MAP is between 80 and 160mmHg, would GFR be expected to change as MAP changes? Explain your answer, including in your answer the afferent arteriolar response, what stimulates it to do so (2 stimuli), and the purpose of this response.

1. GFR:

2. afferent arteriole response:

3. two stimuli of response:

4. purpose of response:

2. What would happen to GFR if MAP rises above 160mmHg? Explain your answer, including in your answer what each arteriole does, what stimulates their responses, and the purpose of their responses.

1. GFR:

2. afferent arteriole response:

3. efferent arteriole response:

4. stimulus for responses:

5. purpose of responses:

3. What would happen to GFR if MAP falls below 80mmHg? Explain your answer, including in your answer what each arteriole does, what stimulates their responses, and the purpose of their responses.

1. GFR:

2. afferent arteriole response:

3. efferent arteriole response:

4. stimulus for responses:

5. purpose of responses:

Answer 1

1) The major pressure that causes filtration is hydrostatic pressure in the glomerular capillaries and bowman's capsule.

2)The major force that causes reabsorption is colloid osmotic/oncotic pressure in the glomerular capillaries and bowman's capsule.

3)The filtration rate INCREASES if glomerular capillaries is damaged to an extent to be leaky to plasma proteins as proteins are lost due to leakage, it causes hypoproteinemia leading to decreased colloid osmotic pressure, so that reabsorption decreases and filtration increases causing increase in filtration rate.

4) a) afferent arteriole - CONSTRICTS, Efferent arteriole - NO CHANGE, glomerular hydrostatic pressure and filtration rate DECREASES

EXPLANATION -As afferent arteriole is constricted, less blood flows to the glomerular capillaries causing decrease in glomerular hydrostatic pressure and also decrease in filtration rate.

b) afferent arteriole - NO CHANGE, efferent arteriole - CONSTRICTS, glomerular hydrostatic pressure and filtration rate INCREASES

EXPLANATION - As efferent arteriole constricts, so less blood come out from the glomerular capillaries leading to increased in glomerular hydrostatic pressure and filtration rate.

C) afferent arteriole - DILATES, efferent arteriole - NO CHANGE, glomerular hydrostatic pressure and filtration rate INCREASES

EXPLANATION -As afferent arteriole is dilated, more the blood flows to the glomerular capillaries causing increase in both glomerular hydrostatic pressure and filtration rate.

d) afferent arteriole - DILATES, efferent arteriole -CONSTRICTS glomerular hydrostatic pressure and filtration rate INCREASES.

EXPLANATION - As afferent arteriole dilates, more blood flows to the glomerular capillaries and as efferent arteriole constricts, less blood comes out from the glomerular capillaries causing increase in glomerular hydrostatic pressure and filtration rate.

How renal arterioles respond to blood pressure -

1)Mean arterial pressure(MAP) - 80 to 160 mmhg.

GFR - remains normal.

Afferent arteriole - normal (no dilation or constriction)

2 stimuli of response -normal renal vascular resistance and normal MAP, normal capillary hydrostatic pressure

Purpose of response - To maintain the normal GRF.

2)Mean arterial pressure - above 160mmhg

GFR - increases(as capillary hydrostatic pressure increases with increase in the MAP)

Afferent arteriole response - Afferent arteriole dilates

Efferent arteriole response - constriction

Stimuli for response - increase in mean arterial pressure and increase in capillary hydrostatic pressure, decrease in renal vascular resistance

3)mean arterial pressure - below 60mmhg

GFR - decreases(as capillary hydrostatic pressure decreases with decrease in MAP)

afferent arteriole response-constriction

Efferent arteriole response - dilatation

Stimuli for response - decrease in both MAP and capillary hydrostatic pressure,increase in renal vascular resistance.