Excretion M5

Question 1

Definition of excretion

Answer 1

Excretion is the removal from the body of metabolic waste products and other substances, such as water and ions, that are in excess in the body

Question 2

Role of the liver

Answer 2

plays a vital role in breaking down substances into less harmful forms which can then be excreted by other organs.

Question 3

Examples of harmful substances the liver will break down.

Answer 3

caffeine, paracetamol, alcohol, nicotine, other drugs

Question 4

the function of the hepatic artery

Answer 4

supplies oxygenated blood to the liver

Question 5

the function of the hepatic vein

Answer 5

takes deoxygenated blood away from the liver

Question 6

the function of the hepatic portal vein

Answer 6

brings blood from the duodenum and ileum to the liver. Any digested harmful substances such as alcohol are broken down straight away.

Question 7

the function of the bile duct

Answer 7

takes bile (a substance produced by the liver to emulsify fats) to the gallbladder for storage. Bile is released down bile duct to the top of the small intestine

Question 8

Describe the basic structure of the liver

Answer 8

Liver contains thousands of LIVER LOBULES that are cylindrical shapes, that contain HEPAOCYTES. There are many small capillaries connecting the inside and outside of the lobule called SINUSOIDS. These contain KUPFFER CELLS that remove bacteria and break down old red blood cells

Question 9

Deanimationa and ornithine cycle

Answer 9

1. the nitrogen-containing amino acids groups (NH2) are removed from excess amino acids, forming NH3 and organic acids (deamination)
2. Organic acids can be respired to give ATP or converted to carbohydrate and stored as glycogen.
3. Ammonia is too toxic for mammals to be excreted directly so it’s combined with CO2 in the ornithine cycle, to create urea and water - the cycle requires ATP and occurs in the mitochondria and cytoplasm.
4. The urea is released from the liver into the blood, The kidneys then filter the blood and remove the urea as urine which is excreted from the body

Question 10

How does alcohol affect the liver

Answer 10

Alcohol is toxic so can damage cells. Broken down by the liver to ethanal and the acetic acid. Excess alcohol can lead to cirrhosis of the liver, liver cells die and scar tissue blocks blood flow.

Question 11

How does paracetamol affect the liver

Answer 11

It is broken down by the liver. Excess paracetamol in the blood can lead to liver/kidney failure.

Question 12

How do hormones affect the liver

Answer 12

Hormone levels controlled by blood glucose levels. Insulin is broken down in the liver, excess insulin can cause BG problems

Question 13

Key features that occur in the kidney.

Answer 13

1. Ultrafiltration in the glomerulus in the Bowmans capsule
2. Selective reabsorption PCT
3. Countercurrent mechanism allows the generation of water potential in the medulla of the loop of Henle.
4. Osmoregulation and producing urine in the collecting duct.

Question 14

Comment on whether steroids should be used for sport.

Answer 14

1. gives an unfair advantage. 2. health risks i.e mental health like depression as well as physical health like heart and liver failure 3. The outstanding performance doesn’t really reflect the athlete’s natural abilities

Question 15

Outline how a pregnancy test works.

Answer 15

1. testing for human chorionic gonadotrophin (hCG) 2. this hormone is small so passes through Bowman’s capsule from the blood to filtrate. 3. Antibodies are on the stick, they are attached to a bead of dye. 4. The hormone binds to the antibody and dye and triggers the appearance of a colour. 4. the second line is used to validate te, two lines mean pregnancy.

Question 16

Explain how Type 1 diabetes is caused

Answer 16

1. beta cells are damaged or destroyed meaning you produce less or no insulin. 2. autoimmune disease 3. may be caused by genetics in family history

Question 17

Why is counter-current flow needed in haemodialysis?

Answer 17

Maintain steep concentration gradient to increase the rate of diffusion

Question 18

Why would a high intake of protein lead to a high concentration of urea in the urine?

Answer 18

1. high intake of protein means a large number of amino acids 2. excess amino acids cannot be stored so they are deaminated to ammonia. 3. ammonia enters the ornithine cycle to convert to urea. 4. increasing the concentration of urea in the blood. 5. high concentration of amino acids in the blood increases water absorption from urine.

Question 19

Explain how the glomerlus is able to perform its function.

Answer 19

1. the diameter of the afferent arteriole is greater than that of the efferent arteriole. 2. build up of high hydrostatic pressure. 3. endothelium walls has small pores called fenestrations. 4. these allow ultrafiltration

Question 20

Describe the features of the glomerulus and Bowman’s capsule that allows them to
perform their function effectively

Answer 20

1. Ultrafiltration, the afferent arteriole has a larger diameter than the efferent arteriole. 2. high hydrostatic pressure in the glomerulus than the Bowmans capsule. 3. basement membrane stops the removal of larger molecules like proteins.

Question 21

suggest two ways in which the structure of this aquaporin prevents the passage of ions.

Answer 21

1. positively charged channel repels the negatively charged ions. 2. the ions in the solution are too large to pass through the channel

Question 22

Suggest where ADH is removed from the blood and describe what then happens to the ADH
molecule.

Answer 22

ADH as a PROTEIN, in the HEPATOCYTES in the liver it is acted on by PROTEASE 2. deamination, the formation of ammonia. 3. ornithine cycle, the formation of urea. 4. ammino acids used for protein synthesis.
ADH as a small molecule - ultrafiltered from the blood through the glomerulus and Bowman’s capsule, because its a small molecule, urea is not reabsorbed and therefore ADH is excreted.

Question 23

Suggest why patients receiving peritoneal dialysis usually need to have the peritoneal
dialysis fluid replaced four times a day, but those receiving haemodialysis only need
treatment three times a week.

Answer 23

1. PD can remove less waste than HD. 2. HD is constantly changed and refreshed whereas PD is not. 3. HD uses counter-current flow to maintain its concentration gradient whereas in PD the concentration gradient gets lower. 4. Pd reaches equilibrium with the blood.

Question 24

Explain how the longer loop of Henle is able to assist the desert kangaroo rat in preventing
excessive water loss.

Answer 24

More sodium and chloride ions pumped out if ascending limb, into the medulla. Which builds up a GREATER water potential. This allows reabsorption of more water from the COLLECTING DUCT.

Question 25

Describe the composition of the fluid that goes through the kidney.

Answer 25

1. Larger molecules like proteins cannot enter the filtrate, smaller molecules like ions and amino acids and will. 2. The ENDOTHELIUM, FENESTRATIONS, and BASEMENT MEMBRANE prevent larger molecules reaching the Bowmans capsule. 3. All glucose is reabsorbed at the PCT. 4. All the amino acids reabsorbed at the PCT. 5. Not all the ions are reabsorbed, they move into the blood. 6. urea concentration increases because ions move in decreasing the water potential and water is lost.