5. GFR And Filtration

Question 1

Describe the blood flow through the kidneys.

Answer 1

Renal artery, segmental artery, interlobar artery, arcuate artery, interlobular artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries (cortical nephrons)/vasa recta (juxtamedullary nephrons), interlobular vein, arcuate vein, lobular vein, segmental vein, renal vein.

Question 2

Give 3 differences between cortical nephrons and juxtamedullary nephrons.

Answer 2

Cortical. Juxtamedullary.
Small glomerulus. Larger glomerulus.
Loop of Henle just into Loop of Henle deep into medulla. Medulla.
AA>EA. AA=EE.
EA forms peritubular EA forms vasa recta.
capillary.
Rich sympathetics. Poor sympathetics.
High renin conc. Low renin conc.
Ratio 90%. 10%.

Question 3

What is the renal blood flow per minute and so what is the renal plasma flow?

Answer 3

Renal blood flow = 1.1L/min.

Renal plasma flow = renal blood flow - haematocrit = 0.55 x 1.1 = 605 mL/min.

Question 4

How much blood from the renal artery is filtering through the glomerulus into the Bowman’s capsule at any one time?

Answer 4

20%.

Question 5

What is the renal corpuscle?

Answer 5

Glomerulus + Bowman’s capsule.

Question 6

What type of cells form the parietal later of the Bowman’s capsule?

Answer 6

Simple squamous epithelium.

Question 7

What produces the filtration barrier in the renal corpuscle?

Answer 7

Capillary endothelium and visceral layer of Bowman’s capsule (basement membrane and podocytes).

Question 8

What is the end product of filtration?

Answer 8

Identical to plasma, without large proteins and cells.

Question 9

How does filtrate move across the capillary endothelium?

Answer 9

Filtrate moves between cells.

Question 10

What is the glomerular basement membrane formed of?

Answer 10

Is an acellular gelatinous layer of collagen/glycoproteins.

Question 11

What property of the glomerular basement membrane repels large protein movement?

Answer 11

Glycoproteins (negatively charged).

Question 12

What part of the podocyte layer of the glomerulus forms filtration slits?

Answer 12

Pseudopodia interdigitate.

Question 13

What causes proteinuria?

Answer 13

Disease process leading to the negative charge on the filtration barrier (glycoproteins in the basement membrane) being lost, so the proteins are more readily filtered.

Question 14

What 3 physical forces are involved in the filtering of plasma to form ultra filtrate?

Answer 14

Hydrostatic pressure in the capillary.
Hydrostatic pressure in the Bowman’s capsule.
Oncotic pressure difference between the capillary and tubular lumen.

Question 15

What is the net filtration pressure in the glomerulus?

Answer 15

10mmHg.

Question 16

What is the purpose of autoregulation of GFR?

Answer 16

Keep renal blood flow and GFR constant. Without autoregulation, slight changes in blood pressure would cause significant changes in GFR.

Question 17

What is the myogenic mechanism of autoregulation?

Answer 17

Arterial smooth muscle response to increases and decreases in vascular wall tension - pressure, contracts. Less pressure, relaxes.

Question 18

How long does the myogenic mechanism of autoregulation take to occur?

Answer 18

Occurs rapidly - 3-10 seconds.

Question 19

In which vessels does the myogenic response occur?

Answer 19

Predominantly preglomerular resistance vessels - accurate artery, interlobular artery and afferent arteriole.

Question 20

What happens to the myogenic response when there is an increase in blood pressure?

Answer 20

Afferent arteriole constriction, GFR unchanged.

Question 21

What happens in the myogenic response when there is a decrease in blood pressure?

Answer 21

Afferent arteriole dilation, GFR is unchanged.

Question 22

Between what limits of BP is autoregulation able to maintain GFR?

Answer 22

Physiological limits of BP = 80-180 mmHg systolic.

Question 23

What is tubuloglomerular feedback?

Answer 23

Signalling from the macula densa cells of the distal tubule in response to sodium and chloride levels, back to the glomerulus to alter filtration rate.

Question 24

Describe the tubuloglomerular feedback response to an increase in GFR.

Answer 24

Increase in tubular flow rate, increase in GFR, increase in NaCL reaching distal tubule. Juxtoglomerular cells decrease renin release, increase adenosine release to dilate EA.

Question 25

Describe the tubuloglomerular feedback response to a decrease in GFR.

Answer 25

Decrease in tubular flow rate, decrease in GFR, decrease in NaCL reaching distal tubule. Juxtoglomerular cells increase renin release, decrease adenosine release, and increase prostaglandin release to dilate AA.

Question 26

How do the macula densa cells sense distal convoluted tubule luminal [NaCl]?

Answer 26

Concentration dependant salt uptake via NaKCC co-transporter in the apical membrane of macula densa cells.

Question 27

When does the relationship between GFR and distal salt concentration only apply?

Answer 27

In acute changes.

Question 28

What conditions can stimulate the renal vessels via sympathetic stimulation, resulting in vasoconstriction, conservation of blood volume and a fall in GFR?

Answer 28

Fight or flight.
Ischaemia.
Haemorrhage.

Question 29

What division of the nervous system causes vasodilation?

Answer 29

Parasympathetic.

Question 30

What is glomerulotubular balance?

Answer 30

Changes in GFR are mirrored by changes in reabsoption. So increased GFR, more water and solute reabsorbed.

Question 31

What system is responsible for the longer term volume control in BP changes?

Answer 31

Renin-angiotensin aldosterone system.