Glomerular filtration

Question 1

List the three basic renal processes.

Answer 1

Filtration
Reabsorption
Secretion

Question 2

What % of the plasma volume passing through the glomerulus at any given time is filtered

Answer 2

20%

Question 3

What is the blood filtering component of a nephron

Answer 3

Renal corpuscle

Question 4

20% of the plasma volume passing through the glomerulus at any given time is filtered, what happens to the other 80%

Answer 4

passes via the efferent arterioles into the peritubular capillaries and then to the renal vein

Question 5

Plasma makes up what % of blood volume

Answer 5

55%

Question 6

Glomerular filtration rate > ?mls/min

Answer 6

> 90

Question 7

Glomerular filtration is dependant on the balance between what forces

Answer 7

Hydrostatic forces (pushing fluid out capillary, i.e. favouring filtration)

and

Oncotic forces (favouring fluid into capillary, i.e. favouring reabsorption)

Question 8

What is starling’s hypothesis

Answer 8

that the fluid movement due to filtration across the wall of a capillary is dependent on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary

Question 9

Glomeruli are permeably selective on what solutes they allow cross the glomerular filtration barrier - what are some of the things considered

Answer 9

Molecular size
Electrical charge
Molecular shape

Question 10

The fenestrated capillaries making up each glomerulus prevents filtration of what cells into the glomerulus

Answer 10

Blood cells - RBC/WBC etc

only allows plasma to get through

Question 11

Why is glomerular capillary pressure higher than most other capillaries in the body

Answer 11

because the afferent arterioles making up the glomerulus is short and wide and so little resistance to flow so blood arriving has high hydrostatic pressure

Question 12

Afferent arterioles are one of the final divisions of each segmental artery supplying the kidney, what do the afferent arterioles form

Answer 12

capillary network, i.e. the glomerulus

Question 13

Efferent arterioles of the glomerulus are unlike the afferent arterioles - how?

Answer 13

long and narrow so offers a high post-capillary resistance

Question 14

At the glomerular capillaries, the high capillary pressure means what starling’s force is favoured

Answer 14

hydrostatic pressure favouring filtration exceeds the oncotic pressure

Question 15

Explain why normally only filtration occurs at the glomerular capillaries

Answer 15

because glomerular capillary pressure always&raquo_space; colloid osmotic pressure gradient due to proteins in plasma (i.e. oncotic pressure)

so filtration always favoured

Question 16

Factors affeting GFR

Answer 16

Glomerular capillary pressure

Question 17

Glomerular capillary pressure is dependent on

Answer 17

afferent and efferent arteriolar diameter and therefore the balance of resistance between them

Question 18

Afferent and efferent arteriolar diameter is extrinsically controlled by what 3 things

Answer 18

Sympathetic nerves –> constrict them

Catecholamines –> constrict them

Angiotensin II –> constrict efferent arterioles at low conc of angiotensin II at both at high conc.

Question 19

If resistance is increased in afferent arteriole of the glomerulus, what does this mean for blood flow to other organs

Answer 19

increased blood flow to other organs

Question 20

If renal blood flow is decreased, what do the efferent arterioles do in response to this to maintain GFR

Answer 20

increase their resistance so decreasing their diameter therefore increasing hydrostatic pressure to favour filtration and increase GFR

Question 21

If resistance of afferent arterioles were decreased further (they already are low resistance), what does this mean for

• glomerular capillary pressure
• GFR

Answer 21

Glomerular capillary pressure increases so GFR increases

Question 22

GFR can be maintained over what range of mean arterial BP

Answer 22

60-160mmHg

Question 23

Below 60mmHg, what happens to GFR

Answer 23

Filtration rate decreases

Question 24

If mean arterial BP increased, what would be the intrinsic response of the glomerulus to maintain GFR

Answer 24

afferent arteriolar constriction, preventing pressure rise from being transmitted to glomerular capillaries

Question 25

Renal vasculature has an intrinsic ability to adjust its resistance (i.e. change its diameter) in response to changes in what in order to keep BF and GFR essentially constant, i.e, renal autoregulation

Answer 25

arterial BP

Question 26

If a severe haemorrhage were to happen, what implication does this have on GFR

Answer 26

systemic vasoconstriction would override autoregulation of renal blood flow and therefore GFR in order to liberate blood for more important organs in that moment

Question 27

100% plasma volume entering the afferent arteriole of the glomerulus, 20% of this filters into the PCT, how much of this is reabsorbed/excreted

Answer 27

19% reabsorbed into peritubular capillaries and returns to systemic circulation

Question 28

180 litres of plasma is filtered through the kidneys a day, how much of this is actually excreted as urine

Answer 28

1-2l

Question 29

Glomerular capillaries lie between what 2 arterioles to form a vascular network

Answer 29

afferent and efferent

Question 30

Explain why normally only reabsorption occurs at the peritubular capillaries

Answer 30

Because oncotic pressure exceeds hydrostatic pressure in the peritubular capillaries so always favours reabsorption
-since the other 80% blood not filtered into the tubule remains in the afferent arteriole and subsequently the peritubular capillary so it will have high conc. of plasma proteins than in the tubule so will exert increased oncotic pressure

Question 31

Why is the peritubular capillary pressure very low compared to capillary pressure in the glomerulus

(peritubular capillaries carry blood away from glomerulus)

Answer 31

Because there’s a large frictional resistance along the length of the peritubular capillary (ie. efferent arteriole) while glomerular capillaries always favour filtration into the tubule

Question 32

Function and afferent and efferent arterioles

Answer 32

Carry blood to and away from the glomerulus respectively

Question 33

Constriction of the afferent arterioles has two effects:

Answer 33

increases the vascular resistance which reduces renal blood flow (RBF),

and it decreases the pressure downstream from the constriction, which reduces the GFR

Question 34

Constriction of the efferent arterioles has 2 effects:

Answer 34

also increases the vascular resistance so it reduces RBF.

The pressure within the glomerular capillaries may increase so the net result is an increased filtration fraction (ratio of GFR to RBF) but GFR overall still decreases as RBF is decreased

Question 35

Filtration fraction is the ratio of

Answer 35

GFR to RBF

Question 36

If you have high resistance, does hydrostatic pressure upstream/downstream increase or decrease

Answer 36

Upstream - increase

Downstream - decrease