Module 5.5 Regulation of Glomerular Filtrate

Question 1

GFR is dependent on the ________\_and the ________\_

Answer 1

GFR is dependent on the filtration coefficient (Kf) and the net glomerular filtration pressure

Question 2

There are a number of unregulated pathological changes that can affect GFR, but the only regulated variable is ______________

Answer 2

There are a number of unregulated pathological changes that can affect GFR, but the only regulated variable is glomerular capillary hydrostatic pressure (P_GC)

Question 3

Unregulated pathological changes that affect GFR include changes to

• _____
• _____
• _____

Answer 3

Unregulated pathological changes that affect GFR include changes to

• glomerular capillary oncotic pressure (π_GC),
• Bowman’s capsule oncotic pressure (π_BC), and
• Bowman’s capsule hydrostatic pressure (P_BC)

Question 4

What effect would the following scenarios have on GFR?

1. “a severely burned patient loses protein-rich plasma at exposed skin surfaces”
2. “a patient suffering from dehydrating diarrhea would experience?”

Answer 4

1. Loss of protein-rich plasma would result in an overall decrease in plasma-protein concentration, thus decreasing π_GC (Glomerular Capillary Oncotic Pressure) and increasing GFR
2. an increase in plasma-protein concentrations, resulting in an increased π_GC and a decreased GFR

Question 5

How would obstructions such as kidney stones or an enlarged prostate affect GFR?

Answer 5

These would increase P_BC (Bowman’s Capsule Hydrostatic Pressure) and thus decrease GFR.

Question 6

Regulated changes to GFR occur through changes to ________\_

In response to an increase in mean arterial pressure (MAP), GFR would be predicted to ______. GFR, however, remains relatively constant

Answer 6

Regulated changes to GFR occur through changes to Glomerular Capillary Blood PressureP_GC.

In response to an increase in mean arterial pressure (MAP), GFR would be predicted to increase

Question 7

How is GFR able to withstand changes in response to changes in Mean Arterial BP?

Two Intrinsic Mechanisms:

Answer 7

1. myogenic regulation and
2. tubuloglomerular feedback.

Question 8

What is Myogenic Regulation?

What are the effects if MAP increases?

What are the effects if MAP decreases?

Answer 8

The intrinsic response to a stretching of the smooth muscle in the walls of the afferent arteriole

• Increase in MAP → Increased stretching of the walls of the afferent arteriole→ vasoconstriction → decrease vessel diameter → increase resistance → decrease P_GC = decrease GFR
• A decrease in MAP would result in a corresponding relaxation of the smooth muscle (vasodilation) and an increase in P_GC.

Question 9

What is Tubuloglomerular Feedback

Answer 9

The intrinsic response of the macula densa cells of the juxtaglomerular apparatus in response to an increase in the salt concentration of the fluid in the filtrate

Question 10

How would the Tubuloglomerular Feedback respond to an increase in MAP?

Answer 10

Increase in MAP →

in an increase in the flow of filtrate through the tubular component of the nephron →

increase in the salt concentration of the filtrate reaching the distal tubule →

the macula densa cells secrete adenosine (paracrine chemical messenger) →

acts on the neighbouring smooth muscle cells of the afferent arteriole, causing them to vasoconstrict →

Increase resistance of afferent arteriole →

Decrease Glomerular Capillary Hydrostatic Pressure (P_GC)

Question 11

GFR is also regulated by ____\_mechanisms that can override the intrinsic mechanisms. The extrinsic mechanisms allow for changes to GFR even when ____\_ is within the range of ______\_ and subject to intrinsic mechanisms of regulation

Answer 11

GFR is also regulated by extrinsic mechanisms that can override the intrinsic mechanisms. The extrinsic mechanisms allow for changes to GFR even when MAP is within the range of 80–180mmHg and subject to intrinsic mechanisms of regulation

Question 12

What is the goal of extrinsic regulation of GFR?

What part of the body is in charge of Extrinsic Regulation?

Answer 12

• To maintain MAP
• Regulated by the Sympathetic Nervous System

*THERE IS NO PARASYMPATHETIC INNERVATION OF THE KIDNEYS*

Question 13

How does the sympathetic nervous system control MAP?

Answer 13

The sympathetic NS exerts its actions through the baroreceptor reflex and through mesangial cell contraction.

Question 14

The ______\_ is involved in both the short-term and long-term regulation of MAP.

Answer 14

The baroreceptor reflex is involved in both the short-term and long-term regulation of MAP.

Question 15

What are Mesangial Cells?

How do they effect GFR?

Answer 15

Mesangial Cells are modified smooth muscle cells that surround the glomerular capillaries and are capable of contracting, thereby decreasing the surface area available for filtration across the glomerular membrane.

A decrease in surface area results in a decreased filtration coefficient (Kf) and thus a decreased GFR. Increased sympathetic innervation results in increased mesangial cell contraction.

Question 16

Mesangial Cells are _________ cells that surround the _________ and are capable of contracting, thereby decreasing the _________ available for filtration across the glomerular membrane.

A decrease in surface area results in a decreased filtration coefficient (Kf) and a _________ GFR. Increased sympathetic innervation results in _______________

Answer 16

Mesangial Cells are modified smooth muscle cells that surround the glomerular capillaries and are capable of contracting, thereby decreasing the surface area available for filtration across the glomerular membrane.

A decrease in surface area results in a decreased filtration coefficient (Kf) and a decreased GFR. Increased sympathetic innervation results in increased mesangial cell contraction.

Question 17

Fill in the blanks with either “increases” or “decreases”

Answer 17

Fill in the blanks: