Excretion

Question 1

What is excretion

Answer 1

The removal of waste products from the body

Question 2

What is metabolism

Answer 2

All the chemical reactions that happen in your cells. It produces waste products such as CO2 and nitrogenous waste.

Question 3

Why does excretion happen

Answer 3

The waste products of metabolism are often toxic and so if they built up they would cause damage. So it removes the waste products.

Question 4

What are the functions of the liver

Answer 4

Excess amino acids are broken down

Removal of harmful substances from the blood

Storage of glycogen

Question 5

How does the liver carry out it’s function of breaking down amino acids

Answer 5

1) The amine groups are removed from any excess amino acids forming ammonia and organic acids (deamination)
2) The organic acids can be respired to give ATP or converted to carbohydrate and stored as glycogen.
3) Ammonia is too toxic to be excreted directly so it is combined with CO2 in the ornithine cycle to create urea
4) Urea is released from the liver into the blood, the kidneys then filter the blood and remove the urea as urine

Question 6

Why does the liver carry out it’s function of breaking down amino acids

Answer 6

Amino acids contain nitrogen which can’t usually be stored in the body so excess amino acids can be damaging.

Question 7

Why does the liver carry out it’s function of removing harmful substances from the blood

Answer 7

They are broken down into less harmful compounds to be excreted called detoxification.

Question 8

What are some of the harmful products broken down in the liver

Answer 8

Alcohol (ethanol)

Paracetamol

Insulin

Question 9

How does the liver remove alcohol from the blood

Answer 9

It is broken down into ethanal which is broken into a less harmful substance called acetic acid. Excess alcohol can lead to cirrhosis of the liver and it’s cells die and scar tissue blocks blood flow.

Question 10

What does the live do with excess glucose

Answer 10

Converts it to glycogen and stores it as granules in its cells until needed

Question 11

What does the hepatic artery do

Answer 11

Supplies the liver with oxygenated blood from the heart, so the liver has a good supply of oxygen for respiration providing plenty of energy

Question 12

What does the hepatic vein do

Answer 12

Take deoxygenated blood away from the liver

Question 13

What does the hepatic portal vein do

Answer 13

Brings blood from the duodenum and ileum so it’s rich in the products of digestion. Any ingested harmful substances are filtered out and broken down straight away

Question 14

What does the bile duct do

Answer 14

Takes bile to the gall bladder to be stored

Question 15

What is the liver made up of

Answer 15

Liver lobules - cylindrical structures made of cells called hepatocytes that are arranged in rows radiating out from the centre

Question 16

What does each liver lobule contain

Answer 16

A central vein that connects to the hepatic vein. Many branches of the hepatic artery, hepatic portal vein and bile duct are also found connected to each lobule

Question 17

What are the hepatic artery and portal vein connected to

Answer 17

The central vein by capillaries called sinusoids

Question 18

How does blood run through the lobule

Answer 18

Through the sinusoids past the hepatocytes that remove harmful substances and oxygen from the blood. The harmful substances are broken down by the hepatocytes into less harmful substances that then re-enter the blood. The blood then runs to the central vein and the central veins from the lobules to form hepatic vein. Kupffer cells attached to the walls of the sinusoids remove bacteria and break down old red blood cells.

Question 19

What do hepatocytes produce

Answer 19

Bile and secrete it into tubes called bile canaliculi. These tubes drain into bile ducts from all the lobules eventually connect up and leave the liver.

Question 20

What does the central vein look like under a light microscope

Answer 20

Large white circular shape

Question 21

What does the sinusoids look like under a light microscope

Answer 21

White spaces

Question 22

What does the hepatocytes look like under a light microscope

Answer 22

Cells that radiate from the hepatocytes with red dots as nuclei

Question 23

What are the functions of the kidney

Answer 23

To excrete waste products

Regulate water potential of the blood

Question 24

How does the kidney excrete waste products

Answer 24

• Blood enters through the renal artery and passes through capillaries in the cortex
• As blood passes through substances are filtered out of the blood and into long tubules (ultrafiltration)
• Useful substances (glucose) are reabsorbed back into the blood from the tubules in the medulla and cortex (selective reabsorption)
• The remaining unwanted substances such as urea pass along the tubules, along the ureter to the bladder where they’re expelled as urine
• Filtered blood passes out through the renal vein

Question 25

What are nephrons

Answer 25

Long tubules along with the bundles of capillaries where blood filtered are called nephrons. There are around 1 million in each kidney