039 Overivew of Kidney Function

Question 1

How much output do kidneys receive from the heart?

Answer 1

20-25%

Question 2

How much blood do we filter per day?

Answer 2

180L

Question 3

How long is the proximal tubule?

Answer 3

15mm in length

Question 4

What occurs in proximal tubule?

Answer 4

2/3 Water, Na+, Cl- absorption, all of glucose & amino acid absorption

Question 5

What occurs in the loop of henle?

Answer 5

This regulates whether urine is dilute

Question 6

What occurs in the distal tubule and collecting duct?

Answer 6

Fine tuning of Na+ and water under hormonal control

Question 7

How is the proximal tubule adapted for absorption?

Answer 7

Contains microvilli that increase absorption by rate of x200

Question 8

What does calcitriol (vitamin D metabolite) help absorb from intestines?

Answer 8

Ca2+ and Pi

Question 9

How does the kidney regulate Ca2+ and Pi

Answer 9

Dietary vitamin D needs to be activated by UV light on the skin. A hydroxyl group is added in the liver, and then in the kidney, the enzyme 1a-hydroxylase forms calcitriol. Calcitriol indicates to the gut to increase uptake of calcium. Parathyroid gland senses Ca2+ levels and is able to regulate 1a hydroxylase with parathyroid hormone release.

PTH has the opposing effect on phosphate – it is thought to be because calcium and phosphate can react and form a compound.

Question 10

Where is enzyme 1a-hydroxylase produced and regulated?

Answer 10

Produced in the proximal tubules and regulated by the parathyroid hormone.

Question 11

Describe the arterial vascular supply of the kidneys

Answer 11

Renal artery goes into kidney at hilum. This splits into interlobar arteries between renal pyramids. This splits into arcuate arteries at junction between cortex and medulla which lead to the afferent arterioles entering the glomerulus. Efferent arterioles are peritubular (go along the tubules of nephron)

Question 12

Describe venous drainage of the kidneys

Answer 12

After peritubular arteries, blood drains into stellate veins, and then into the cortical radial veins, and then arcuate vein, interlobar veins and finally out through the renal vein.

Question 13

How % much blood is filtered into the tubule from the the 100% input of afferent arterioles?

Answer 13

20%

Question 14

What is an important transmitter found in the proximal tubules?

Answer 14

SGLT2
In the proximal convoluted tubule, there is low affinity high capacity.
In the proximal straight tubule, there is high affinity low capacity SGLT1 to make sure all glucose is absorbed.

Question 15

How much urine do we produce per day?

Answer 15

1.2-2L (varies)

Question 16

Where are the cortical and juxtamedullary nephron located?

Answer 16

Juxtamedullary is more embedded in the medulla pyramid while cortical nephrons are mainly embedded in the cortex.

Question 17

What are the papillae of the kidney?

Answer 17

The apex of a renal pyramid which projects into the lumen of a calyx of the kidney

Question 18

Where are the renal sinuses located?

Answer 18

In between each pyramid in the cortex region. It contains the fatty parts of the kidney.

Question 19

How can differentiate the proximal from the distal tubule of the kidney on microscopic images?

Answer 19

Distal tubules have a narrower lumen and proximal tubules contain microvilli.

Question 20

What is the functional difference between juxtamedullary and cortical nephrons?

Answer 20

Juxtamedullary nephrons are able to secrete either very dilute or concentrated urine.

Question 21

How many juxtamedullary nephrons are there relative to cortical nephrons?

Answer 21

Cortical nephrons - 80%

Juxtamedullary nephrons - 20%

Question 22

What is the venous saturation oxygen of the kidney and why?

Answer 22

It is approx. 90% because of the high cardiac output that reaches the kidney for such a small surface area.

Question 23

Where do renal nerves come from?

Answer 23

Most come from the sympathetic autonomic nervous system. Most have vasomotor function which regulates blood flow. Renin secretion is also controlled sympathetically. There is parasympathetic nerve supply but function is still unknown.

Question 24

What ion homeostasis do the kidneys regulate?

Answer 24

Ca2+, Pi, K+, Na+

Question 25

How much Ca2+ and Pi do the kidneys secrete?

Answer 25

Equal amounts that are entering the body via GI tract.

Question 26

How are the kidneys oxygen sensors?

Answer 26

85% of erythropoetin is produced by interstitial fibroblasts of the kidney. This is released due to decrease in blood PO2 and acts on bone marrow stem cells to increase RBC production.

Question 27

Describe renin regulation and secretion in the kidney.

Answer 27

Angiotensinogen is released in the liver. Due to a signal of increased sympathetic activity, reduced afferent arteriole pressure, or decreased Na+ in distal tubule, Renin will be released by juxtaglomerular cells. This converts angiotensinogen into angiotensin I by ACE enzymes in capillary walls, which is then converted into angiotensin II and then aldosterone in suprarenal gland. Aldosterone causes Na+, H2O uptake and arteriole constriction. Angiotensin II has direct effects on arteriole constriction.

Question 28

Where are juxtaglomerular cells mainly found?

Answer 28

In the afferent arteriole where they mainly secrete renin.

Question 29

How much volume is reabsorbed and excreted from 100% entering the nephron?

Answer 29

99% reabsorbed

<1% excreted

Question 30

What is standard GFR rate?

Answer 30

125ml/min

Question 31

Where does blood from the descending vasa recta drain?

Answer 31

Directly into the arcuate vein

Question 32

What ion is used as a buffer in urine?

Answer 32

Phosphorus

Question 33

What 3 types of cells make up the juxtaglomerular aparatus?

Answer 33

Macula densa cells
Granular cells/ juxtaglomerular cells
Mesangial cells/ Lacis cells

Question 34

What do juxtaglomerular cells do?

Answer 34

Specialised smooth muscle cells of the arterioles

Question 35

What do macula densa cells do?

Answer 35

Columnar epithelial thickening of the distal convoluted tubule that senses Na+ concentration