OSMOREGULATION AND EXCRETION IN THE KIDNEYS

Question 1

Describe the process of deamination. (1)

Answer 1

To achieve the breakdown without the release of ammonia cells in the liver convert amino groups into urea, which is relatively harmless product that can be safely transported into the blood to the kidneys where it is excreted.

Question 2

Give the chemical process of deamination. (1)

Answer 2

1) proteins excess to requirements
2) hydrolysed to amino acids
3) the COOH breaks down into organic acids and is further respired via the Krebs cycle
4) NH2 is reacted with carbon dioxide to produce urea CO(NH2)

Question 3

Define deamination. (1)

Answer 3

The biochemical process of breaking down excess amino acids by removal of amino groups, ultimately producing urea

Question 4

Define urea. (1)

Answer 4

An excretory nitrogen-containing compound of low-toxicity produced by deamination of amino acids in the liver of mammals and some other animals

Question 5

Describe the conditions of the formation urea. (1)

Answer 5

This reaction cannot occur by direct reaction, instead it occurs by reactions with intermediates in a cycle of changes called the urea cycle or ornithine cycle.

Question 6

What is the role of the Ornithine molecule? (1)

Answer 6

The role of ornithine here is a ‘carrier’ molecule on which urea is built up (from two molecules of ammonia and one of carbon dioxide)

Question 7

Where does the ornithine cycle occur? (1)

Answer 7

This occurs in the liver, and the urea molecules are safely transported into bloodstream

Question 8

What is the function of the kidneys? (1)

Answer 8

Regulate the internal environment by constantly adjusting the composition of the blood, the waste products of metabolising cells by the blood circulation, removed from the blood in the kidneys, and excreted in a solution called the urine.

Question 9

What is urine? (1)

Answer 9

A solution of urea, mineral ions and some other metabolic wastes excreted by the kidneys

Question 10

Explain the structure of the kidneys. (3)

Answer 10

Each kidney is served by a renal artery and drained by a renal vein. Urine from the kidney is carried to the bladder by the ureter, and then, at intervals, to the exterior by the urethra when the bladder sphincter muscle is relaxed.

Question 11

What are the parts of the nephron? (5)

Answer 11

• Bowman’s capsule
• proximal convoluted tubule
• loop of henle
• distal convoluted tubule
• collecting duct

Question 12

What is the function of the bowman’s capsule? (1)

Answer 12

Ultrafiltration

Question 13

What is the function of the proximal convoluted tubule? (1)

Answer 13

Selective réabsorption from filtrate

Question 14

What is the function of the loop of henle? (1)

Answer 14

Water conservation

Question 15

What is the function of the distal convoluted tubule? (1)

Answer 15

PH adjustment and ion réabsorption

Question 16

What is the function of the collecting duct? (1)

Answer 16

Water reabsorption

Question 17

Describe the structure of the kidneys. (3)

Answer 17

-cortex
-medulla
-nephrons

Question 18

What is the first stage of urine formation? (1)

Answer 18

In the glomerulus, water and small molecules of the blood plasma are forced out of the capillaries along with urea, into the lumen of the capsule (ultrafiltration) it is powered by the pressure of the blood, which drives substances through an extremely fine sieve-like structure.

Question 19

Why does ultrafiltration need high blood pressure? (1)

Answer 19

Because the input capillary (afferent arteriole) is wider than the output capillary (efferent arteriole).

Question 20

Describe the structure of the ‘sieve’ in ultrafiltration. (1)

Answer 20

The sieve is made of two layers of cells (the endothelium of the capillaries of the glomerulus and the epithelium of the capsule) between which is a basement membrane.

Question 21

What is ultrafiltration? (1)

Answer 21

The process by which small molecules are forced out of the capillaries in the capsule of the kidney by high blood pressure.

Question 22

What are the cells of the capsule wall called? (1)

Answer 22

Called podocytes

Question 23

Describe the podocyte cells. (1)

Answer 23

They have a foot- like extensions that form a network with tiny slits between them (situation we call fenestrated)

Question 24

Describe the process of filtration through the podocytes. (1)

Answer 24

The entire contents of the blood are not forced out, blood cells are retained but the majority of blood proteins and polypeptides dissolved in the plasma are also retained in the circulating. This is because of the presence of the basement membrane.

Question 25

What is the second stage of urea formation? (1)

Answer 25

Selective reabsorption in the proximal convoluted tubule

Question 26

Describe the process of selective reabsorption in the proximal convoluted tubule. (2)

Answer 26

The cell membrane in contact with the filtrate has a brush border of microvilli which enormously increase the surface area for reabsorption. A large part of the filtrate is reabsorbed into the capillary network here

Question 27

What are the individual mechanisms of transport for stage 2 of the formation of urea? (5)

Answer 27

-movement of water by osmosis -active transport of glucose and amino acids across membranes -movement of mineral ions by a combination of active transport, facilitated diffusion and some exchange of ions -diffusion of urea -movement of proteins by pinocytosis

Question 28

What is stage three of formation of urea? (1)

Answer 28

Water conservation in the loop of henle

Question 29

Describe the stage of water conservation in the loop of henle. (2)

Answer 29

The role of the loop of. Henle with its descending and ascending limbs, together with a parallel blood supply, the vasa recta, is to create and maintain a high concentration of salts in the tissue fluid in the medulla of the kidney. This is bought about by the countercurrent multiplier mechanism.

Question 30

Describe the countercurrent multiplier mechanism. (1)

Answer 30

It is the building of a high concentration of salts in the tissue of the medulla that causes water to be reabsorbed from the filtrate in the collecting ducts. The collecting ducts run through the medulla.

Question 31

What are the roles of the vasa recta? (2)

Answer 31

-absorb water that has been absorbed into the medulla at the collecting ducts -remove carbon dioxide and deliver oxygen to the metabolically active cells of the loop of henle without removing the accumulated salts from the medulla.

Question 32

What occurs at the loop of henle? (1)

Answer 32

Sodium and chloride ions are pumped out into the medulla but water is retained inside the ascending limb. Opposite the descending limb is permeable here, so sodium and chloride ions diffuse in. Water passes out into the medulla tissue, due to the salt concentration in the medulla. As the filtrate flows down the descending limb, this water loss increases the salt concentration in the loop, making the filtrate more concentrated.

Question 33

What is stage 2 of the formation of urea? (1)

Answer 33

Blood pH and ion concentration regulation in the distal convoluted tubule

Question 34

Describe the regulation in the distal convoluted tubule. (2)

Answer 34

Cells role is to adjust the composition of the blood and the pH, if the blood deviates from pH 7.4, then the concentration hydrogen ions and hydroxyl ions in the blood is adjusted, along with the concentration of the hydrogen carbonate ions. Also, the selective reabsorption of ions useful in metabolism occurs from the filtrate.

Question 35

What is stage 5 of formation of urea? (1)

Answer 35

Water reabsorption in the collecting ducts run through

Question 36

Describe water reabsorption in the collecting ducts. (2)

Answer 36

Where the water content of the blood is regulated. When the water content is low, antidiuretic hormone is secreted from the posterior pituitary gland. When the water content of the blood is high, little to no ADH is secreted

Question 37

What is the function of ADH? (1)

Answer 37

Causes the walls of the collecting ducts to be fully permeable this allows water to be withdrawn from the filtrate of the tubule into the medulla due to the high concentration of sodium and chloride ions there. The water is take up and redistributed in the body by the blood circulation and on,y small amounts of concentrated urea are formed.

Question 38

What happens if no. ADH is formed? (1)

Answer 38

The walls of the collecting ducts become less permeable, large quantities of very dilute urine are formed.