Kidneys

Question 1

Kidneys functions

Answer 1

1) To filter blood to remove nitrogenous waste - urea
2) Ultrafiltration (in glomerulus and bowman’s capsule)
3) Selective reabsorption (PCT)…?
4) Osmoregulation, the homeostatic function of regulation the water and solute composition of the blood (DCT and collecting duct)

Question 2

Kidneys facts

Answer 2

They recieve 20-25% of the total output of the heart. They filter 170dm3 of filtrate a day.
They reclaim each day 1300g of NaCl, 180g glucose, almost all the water (180dm3) that is filtered each day.
They produce 1200-2000cm3 urine a day.

Question 3

Blood supply to/from kidneys

Answer 3

TO each kidney via RENAL ARTERY

FROM each kidney via RENAL VEIN

Question 4

Blood supply to/from the nephron

Answer 4

TO via an afferent arteriole, which splits into a capillary network, the glomerulus.
FROM by the efferent arteriole to two other capillary structures know as pertubular capillaries.

Question 5

Pertubular capillaries

Answer 5

A capillary network serving the PCT and DCT and another one running alongside the loop of Henle, called the vasa recta.

Question 6

Kidney nephron facts

Answer 6

the functional unit of the kidney - about 1 million in each kidney.

Question 7

Kidney nephron structure

Answer 7

A nephron begins with a cup shaped structure called a renal (Bowman’s) capsules, followed by the proximal convoluted tubule (PCT) and then the loop of Henle, which leads to the distal convoluted tubule (DCT) and finally joins to the collecting duct.

Question 8

What are the two parts of the kidney nephron?

Answer 8

Cortex (bit on outside of kidney) and medulla (bit on inside of kidney).

Question 9

Difference between PCT and DCT

Answer 9

PCT has lots of microvilli and DCT does not.

Question 10

Loop of Henle facts

Answer 10

Descending (going down part) loop has thinner walls than the ascending loop (going up part).

Question 11

PCT

Answer 11

Proximal convoluted tubule - longest part of the renal tubule. It has a simple tall cuboidal epithelium, with a brush border (of microvilli). The epithelium almost fills the lumen and the microvillli increase the SA by 30-40 fold.

Question 12

Loop of Henle

Answer 12

This has a thick descending portion (pars recta), a thin descending portion, a thin ascending portion and a thick ascending portion. The lumen is made up of simple squamous epithelium. Hard to tell apart from adjacent capillaries, except that there are no red blood cells in the lumen.

Question 13

DCT

Answer 13

Distal convoluted tubule - these tubules are less numerous than the PCTs. The epithelial cells are cuboidal, with very few microvilli. The cells stain more palely than those of the PCT.

Question 14

Collecting tubules

Answer 14

NOT PART OF THE NEPHRON - The eptihelium of these tubules consist of cuboidal or columnar cells. They empty into collecting ducts that are easy to recognise because they have large lumens, with pale staining columnar epithelium.

Question 15

Ultrafiltration

Answer 15

It is the filtration of small molecules - e.g. water, glucose, urea, amino acids, ions - from the blood plasma into the Bowman’s capsule (occurs here), when under pressure.

Question 16

Selective filtration

Answer 16

PART OF ULTRAFILTRATION - High filtration pressure in glomerulus pushes out small molecules from the capillaries into the lumen of the Bowman’s capsule, through 3 layers which together form a selective barrier. Any molecules in the blood can cross this barrier, except large plasma proteins and blood cells.

Question 17

How is there a high filtration pressure in the glomerulus?

Answer 17

High blood pressure in renal artery.

Difference in diameter of the afferent and efferent arterioles - the afferent is much wider, going into the glomerulus.

Question 18

What are the 3 layers of the selective barrier between the lumen of the capillaries and that of the Bowman’s capsule?

Answer 18

1) Endothelium of the capillaries - contains pores called fenestrae.
2) Capillary basement membrane - main part of the selective barrier, sometimes called ‘molecular sieve’. It is an extra-cellular layer of proteins that only lets very small molecules through.
3) Podocytes - kidney cells that wrap around the capillaries of the glomerulus and have large gaps between them.

Question 19

Describe the basic process of ultrafiltration

Answer 19

High filtration pressure in glomerulus pushes out small molecules from the capillaries into the lumen of the Bowman’s capsule. By the time the blood leaves the glomerulus via the efferent arteriole, it has a much lower water potential.

Question 20

Why does blood have a much lower w.p. post-ultrafiltration?

Answer 20

So much water has been lost to the filtrate, that there is now a high concentration of proteins and red blood cells in the blood. High solute concentration so low water potential.

Question 21

Middle, cloudy bit of a cross section of a kidney

Answer 21

Renal pelvis - carries urine down to ureters…?

Question 22

What happens in selective reabsorption?

Answer 22

All the important molecules that the blood plasma has lost to the filtrate (but needs to retain), i.e. glucose, amino acids, ions (like Na+ and Cl-), water and vitamins, are reabsorbed.

Question 23

Where does selective reabsorption happen?

Answer 23

PCT - that’s why it has all those microvilli! At the end of the PCT, the filtrate will be isotonic (equal w.p.s) with the blood plasma.

Question 24

Water reabsorption details in PCT

Answer 24

About 90% of water is reabsorbed by OSMOSIS. This happens because the ions are removed from the filtrate, causing the w.p. to increase compared with that of the blood. Therefore, water moves back into the blood, down a water potential gradient.

Question 25

Ion reabsorption details in PCT

Answer 25

About 70% of ions in the filtrate reabsorbed (mainly) by ACTIVE TRANSPORT.

Question 26

Urea / small proteins reabsorption details in PCT

Answer 26

About 50% of urea / small proteins are reabosrbed by DIFFUSION.

Question 27

ADH function

Answer 27

Antidiuretic hormone - ADH causes more water to be reabsorbed from the nephrons to dilute the urine, when the blood has a lower than normal solute potential / higher than normal water potential…?

Question 28

Why does alcohol ‘increase urinary output’?

Answer 28

Because alcohol inhibits ADH production and release.

Question 29

What do diuretics do?

Answer 29

Promote water loss in the urine, decrease blood volume and decrease blood pressure.

Question 30

Secretion of ADH from the _______ occcurs in response to ______ and causes ______.

Answer 30

pituitary gland…. high blood osmolarity…. increased permeability of collecting ducts to water.

Question 31

Why will a long loop of Henle retain more water?

Answer 31

It creates a much lower water potential in the medulla, which has the ability to reabsorb more water from the collecting duct.