Excretion

Question 1

What is excretion?

Answer 1

The removal of metabolic waste

Question 2

What is egestion?

Answer 2

The elimination of faeces

Question 3

Which substances need to be excreted?

Answer 3

CO2
Nitrogen containing compounds (urea)
Other compounds such as bile pigments

Question 4

What are the main excretory organs?

Answer 4

Lungs - removal of CO2 & water vapour
Kidneys - removal of urea
Liver - production of bilirubin and urea

Skin - removal of salts, urea, water etc. via sweat

Question 5

How does oxygenated blood travel to the liver?

Answer 5

Oxygenated blood from the heart travels to the liver via the aorta and hepatic artery

Question 6

What does “hepatic” refer to?

Answer 6

The liver

Question 7

How is blood removed from the liver?

Answer 7

Blood leaves the liver and returns to the heart via the hepatic vein which re-joins the vena cava

Question 8

What is the role of the hepatic portal vein?

Answer 8

It carries the products of digestion to the liver, directly from the intestines

Question 9

Where is bile produced and secreted?

Answer 9

It is produced and secreted in the liver

Question 10

What does “renal” refer to?

Answer 10

The kidneys

Question 11

Where is bile stored?

Answer 11

Bile is stored in the gall bladder

Question 12

Where is bile released?

Answer 12

Bile is released by the bile duct into the small intestine where it then emulsifies fats

Question 13

What are hepatocytes?

Answer 13

Liver cells

Question 14

Features of hepatocytes

Answer 14

Large nuclei
Prominent Golgi apparatus
Lots of mitochondria

Question 15

What are sinusoids?

Answer 15

The space surrounded by hepatocytes

Question 16

Functions of the liver

Answer 16

Control blood glucose levels
Synthesis of bile, cholesterol
Breakdown of hormones
Destruction of red blood cells

Question 17

What is the role of catalase?

Answer 17

Catalase converts hydrogen peroxide to oxygen and water

Question 18

What is the role of Cytochrome p450?

Answer 18

Cytochrome p450 is a group of enzymes used to breakdown drugs

Question 19

What is the role of alcohol dehydrogenase?

Answer 19

Alcohol dehydrogenase breaks down ethanol into ethanal.

Ethanal is then converted to ethanoate

Question 20

Examples of substances broken down by the liver

Answer 20

Alcohol
Paracetamol
Insulin

Question 21

What is transamination?

Answer 21

The conversion of one amino acid to another. This is important as the diet may not always contain the required amino acids

Question 22

What are some adaptations of hepatocytes?

Answer 22

Thin/flat cells allow for short diffusion distance

Fenestrated (tiny openings/pores) increases permeability

Question 23

What is deamination?

Answer 23

Excess amino acids are harmful and can’t be stored as they are nitrogenous.
The hepatocytes remove the amino groups. This forms ammonia which is then converted to urea. Urea is then removed from the blood by the kidneys and excreted via urine

Question 24

What are the functions of the kidneys?

Answer 24

Osmoregulation
Excretion

Filter urea and waste products out of the blood and excrete them

Question 25

What is the role of the renal artery and where is it found?

Answer 25

The renal artery carries unfiltered blood into the kidney.

The renal artery branches off the abdominal aorta and are at arterial pressure

Question 26

What is the role of the renal vein?

Answer 26

The renal vein drains blood once it has circulated through the kidneys and inferior vena cava

Question 27

Describe the process of the ornithine cycle?

Answer 27

Ammonia and carbon dioxide combine with ornithine to produce citrulline and water. Citrulline is converted to arginine (removal of water). Arginine is then re-converted to ornithine by the addition of water and removal of urea.