Glomerular Filtration

__ and ____ of the afferent or the efferent arteriole will alter the resistance of the arterioles and will influence the pressure in both the glomerular capillaries and the peritubular capillaries

Vasoconstriction or vasodilation

Pressures promoting filtration (curve A)

1. Hydrostatic capillary pressure: (PGC) decreases slightly along the glomerulus (from 60 mm Hg to 58 mm Hg) 2. Oncotic pressure in Bowman's capsule: equal to zero. • The sum of the capillary hydrostatic pressure and the oncotic pressure in Bowman's capsule decreases slightly from the arterial side of the glomerulus to the venous side and is represented by curve A. The shaded area between lines A and B is PGC - (PBC + GC) and indicates net filtration all along the glomerulus.

Vasoconstricting the efferent arteriole will

1. Vasoconstricting the efferent arteriole will increase the pressure in the glomerulus and this in turn will increase the glomerular filtration rate (solid line). ↑ RE→ ↑ PGC→ ↑ GFR 2. Vasoconstricting the efferent arteriole will decrease blood flow through the kidney capillary beds (dotted line, similar to vasoconstriction of the afferent arteriole). A decrease in blood flow will lead to a decrease in glomerular filtration. ↑ RE→ ↓ RBF→ ↓ GFR

Vasoconstricting the afferent arteriole will

1. decrease the pressure in the glomerulus (solid line) and this in turn will decrease the glomerular filtration rate. ↑ RA→ ↓ PGC→ ↓ GFR 2. Vasoconstricting the afferent arteriole will decrease blood flow to the glomerulus (dotted line) and this in turn will decrease the glomerular filtration rate. ↑ RA→ ↓ RBF→ ↓ GFR

The glomerular filtration rate: A. depends on the balance of the four Starling forces in the glomerular capillary and in Bowman's capsule. B. is driven in large part by the low concentration of protein in the urine C. will increase upon constriction of the afferent arteriole D. will decrease upon moderate constriction of the efferent arteriole. E. A and C

A. depends on the balance of the four Starling forces in the glomerular capillary and in Bowman's capsule.

Hydrostatic pressure in which of the following locations will decrease after moderate constriction of the efferent arteriole? A. peritubular capillaries B. Bowman's capsule C. glomerular capillaries D. afferent arteriole E. all of the above

A. peritubular capillaries

Which of the following is true concerning sympathetic stimulation of kidney arterioles? A. Increased sympathetic stimulation will increase renal blood flow. B. Increased sympathetic stimulation will decrease renal blood flow. C. Decreased sympathetic stimulation will result in vasodilation of only the efferent arteriole. D. Decreased sympathetic stimulation will result in vasodilation of only the afferent arteriole. E. None of the above.

B. Increased sympathetic stimulation will decrease renal blood flow.

Where is plasma oncotic pressure highest? A. the afferent arteriole B. the efferent arteriole C. the glomerular capillary bed D. Bowman's capsule E. lumen of the proximal tubule

B. the efferent arteriole

Given the following values: Glomerular capillary hydrostatic pressure 52mm Hg Bowman's space hydrostatic pressure 21 mm Hg Protein concentration in Bowmans capsule 0 mg/ml At what value of glomerular capillary oncotic pressure would glomerular filtration stop? A. 0 mm Hg B. 52 mm Hg C. 31 mm Hg D. 21 mm Hg E. none of the above

C. 31 mm Hg

You discover a new drug that causes GFR to increase but renal blood flow to decrease. This drug does not affect arterial blood pressure. The drug causes: A. constriction of the afferent arteriole B. dilation of the afferent arteriole C. constriction of the efferent arteriole D. dilation of the efferent arteriole E. mild equal constriction of both afferent and efferent arterioles

C. constriction of the efferent arteriole

Why is the renal blood flow such a large fraction of cardiac output? A. epithelial cells in the nephron need a larger blood supply than other cells in the body. B. renal blood flow is not a large fraction of cardiac output if renal blood flow is compared to organs of similar size. C. the kidneys are the main site of filtration for body fluids D. the body has two kidneys and therefore needs a much larger supply of blood E. none of the above

C. the kidneys are the main site of filtration for body fluids

The following table shows the four Starling forces in two different parts of the kidney. All pressures are in mm Hg Vessel 1 Vessel 2 Capillary hydrostatic 45 10 Interstitial hydrostatic 18 6 Capillary osmotic 32 32 Interstitial osmotic 15 15 Based on this information which of the following is true? A. there is net filtration at both of these blood vessels. B. there is net reabsorption at both of these blood vessels. C. there is net filtration at blood vessel 1 and net reabsorption at blood vessel 2. D. blood vessel 2 is probably closer to the afferent arteriole than blood vessel 1. E. there is net reabsorption at blood vessel 1 and net filtration at blood vessel 2.

C. there is net filtration at blood vessel 1 and net reabsorption at blood vessel 2.

Filtration occurs all along the glomerular capillaries and all along the peritubular capillaries

F

Strong constriction of the efferent arteriole will increase the glomerular filtration rate

F

The glomerular capillaries and the peritubular capillaries are in parallel with one another.

F

Moderate constriction of the efferent arteriole will increase the glomerular filtration rate

T

The average hydrostatic pressure in the glomerular capillaries is higher than the average hydrostatic pressure in a muscle capillary

T

The plasma osmotic pressure in the peritubular capillaries is higher than the plasma osmotic pressure on the arterial side of the glomerulus.

T

At higher levels of efferent vasoconstriction

blood flow is eventually reduced enough to override the pressure effect and glomerular filtration will start to fall.

In the kidney the balance of the four pressures promotes

filtration at both the arterial and venous ends of the capillary.

The hydrostatic pressure at the glomerular capillaries is determined by the pressure generated by the ____ and the ___ between the aorta and the glomerular capillary bed. The relatively ___ resistance maintains a high hydrostatic pressure along the glomerular capillary. This serves to promote filtration into Bowman's capsule.

heart resistance low

basement membrane:

major constituent are structures called chords that consist of type IV collagen. These chords contain pores which restrict filtration based on size and also contain negative charges (in the form of negatively charged glycoproteins) that prevent filtration of negatively charged substances.

At lower levels of vasoconstriction of the efferent

n the pressure effect (↑PGC) dominates and vasoconstriction of the efferent arteriole increases glomerular filtration.

filtration slits or slit pores of the podocytes:

provides further restriction to large particles and macromolecules that have passed through the fenestrations and the basement membrane.

fenestrations of the capillary endothelial layer:

restricts filtration based on both size and charge. Fenestrations are 70-90 nm and thus only restrict very large particles (albumin is about 36 nm in diameter).

In a normal healthy individual the protein concentration in Bowman's capsule is

zero

Factors that promote reabsorption in the pertibuular capillaries

• Interstitial hydrostatic pressure (PISF): constant along the peritubular capillaries • Capillary oncotic pressure (πPT): because proteins are not filtered at the glomerulus, the capillary oncotic pressure increases along the glomerular capillaries, but then remains constant along the peritubular capillaries. • curve B represents the sum of the hydrostatic pressure in the interstitial space and the peritubular capillary oncotic pressure (PISF + πPT)

Glomerular filtration is determined by the:

• filtration coefficient (Ki = PA) • balance of the four Starling forces

Factors that promote filtration in the peritubular capillaries

• hydrostatic capillary pressure: (PPT) decreases along the peritubular capillaries • interstitial oncotic pressure: (OncoticISF) remains contains along the peritubular capillaries • curve A represents OnISF + PPT