EXCRETION

Question 0

What are the main substances excreted?

Answer 0

• C02 from respiration

- Nitrogen containing compounds - Urea

Question 1

Definition of Excretion

Answer 1

The removal of metabolic waste from the body.

Question 2

Where is CO2 excreted?

Answer 2

Passed from cells of respiring tissues into the bloodstream. It is then transported in the blood to the lungs. C02 diffuses out of alveoli as we breathe out

Question 3

Where is urea excreted?

Answer 3

Urea is produced by breaking down excess amino acids in the liver (deanimation). Urea is passed into the bloodstream to be transported to the kidneys. Dissolved in plasma. In kidneys, urea is removed from bloody to become urine, and excreted via the uretha.

Question 4

Why must CO2 be removed?

Answer 4

• Too much CO2 is toxic
• CO2 combines with haemoglobin to form carbaminohaemoglobin - lower affinity for oxygen
• can cause respiration acidosis - co2 dissolves in plasma and combines with water to form carbonic acid. Carbonic acid dissociates to real ease H+ ions which lower pH and make blood more acidic.

Question 5

Why must nitrogenous compounds be removed?

Answer 5

-once broken down, toxic amino acid formed, ammonia.

Question 6

How is the liver supplied with oxygenated blood?

Answer 6

Bloody travels from the aorta via hepatic artery into liver.

Question 7

How is deoxygenated bloody transported to the liver?

Answer 7

Bloody from digestive system. This enters the liver via hepatic portal vein.

Question 8

How does blood leave the liver?

Answer 8

Via the hepatic vein. This rejoins the vena cava and the bloody returns to normal circulation.

Question 9

Explain the role of the bile duct.

Answer 9

Bile is a secretion from the liver. Bile duct carries bile from the liver to the gall bladder where it is stored until required to aid digestion of days in the small intestines.

Question 10

Explain the arrangement of cells inside liver.

Answer 10

Liver is divided into lobes which are further divided into lobules.
Hepatic artery and hepatic portal vein split into vessels as they enter liver. Blood from the two blood vessels mix and pass along chamber called sinusoid.

Question 11

Give 3 roles of the liver.

Answer 11

Breakdown of hormones
Control of bloody glucose
Detoxification of alcohol/drugs

Question 12

What is deamination?

Answer 12

Process where ammonia is produced.

Question 13

Explain the Ornithine cycle.

Answer 13

Ammonia combined with CO2 to produce Urea.
Urea is less toxic than ammonia therefore can be passed back into the bloody and transported around the body to the kidneys where it is filtered.

Question 14

Explain detoxification of alcohol.

Answer 14

Alcohol depressed nerve activity. It is broken down into hepatocytes by ethanol dehydrogenase producing ethanal. Further catalysed by ethanal dehydrogenase to produce ethanoate (acetate) which is combined with coA to form acetyl coA

Question 15

Explain the role of the kidney.

Answer 15

To remove waste products from the blood and produce urine.

Question 16

Explain ultrafiltration.

Answer 16

Afferent arteriole is bigger than efferent arteriole to cause high pressure.
Endothelium has holes of fenestrations. This allows the plasma to come into direct contact with the basement membrane.
Small molecules can get through, but large molecules cannot. (Water,glucose,sodium)
Other side of basement membrane contains podocytes. Gaps in podocytes allow spaces for molecules to move quickly into bowmans capsule

Question 17

Explain selective reabsorption.

Answer 17

Sodium ions pumped from epithelial cells into blood.
Sodium ions conc. decreases in cells.
Sodium + glucose move into cells by facilitated diffusion.
Glucose conc decreases
Water moves into cells by osmosis down water potential gradient.
Glucose diffuses out of cell into blood from epithelial cell.
Water potential decreases in bloody so water moves into blood by osmosis down water potential gradient.

Question 18

Explain loop of henle.

Answer 18

Descending limb is permeable to water. Ascending limb is impermeable to water.
Water moves out of D limb down water potential gradient.
Loss of water causes Sodium conc to increase at the bottom of loop so it diffuses out into tissue fluid.
Ascending limb pumps sodium out of limb into tissue fluid by active transport to make water potential high in loop.
Counter current mechanism. Low WP at bottom, high WP at top.

Question 19

Explain water reabsorption.

Answer 19

WP of bloody is maintained by osmoreceptors in hypothalamus.
When WP is low, nerve impulse send to posterior pituarity gland where ADH is released.
ADH makes walls of collecting duct more permeable to water.
More water reabsorbed into medulla and into the blood.
Urine is produced, less water lost.