5 - MZH - Homeostasis 5 - Excretion and the Liver

Question 1

Define:

Excretion

Metabolic waste

Detoxification

Answer 1

Excretion = The removal of metabolic waste from the body

Metabolic waste = A substance that is produced in excess by the metabolic processes in cells

Detoxification = Breakdown of toxins into less harmful products

Question 2

why is it important to remove metabolic wastes?

Answer 2

Because if they build up they can inhibit enzyme activity or become toxic

Question 3

4 examples of extretory waste that we’ve already met?

Answer 3

1. CO₂ from the lungs in respiration
2. Nitrogen containing substances e.g. Ureafrom kidneys
3. Bile pigments removed from blood by liver and found in faeces
4. Combination of water, salts, urea, uric acid and ammonia excreted in sweat from skin

Question 4

Where is the liver found in the body?

Answer 4

It’s the biggest organ in the body and lies in the abdomen just below the diaphram

Question 5

Function of:

Hepatic artery

Hepatic vein

Hepatic portal vein

Answer 5

Hepatic artery = Delivers oxygenated blood from the aorta

Hepatic vein = Drains blood from the liver and delivers it back to the inferior vena cava

Hepatic portal vein = Delivers blood from the small intestines and is rich in absorbed nutrients

Question 6

Fill in the blanks for the strucutre of the liver

Answer 6

Question 7

Draw a more simple diagram of this and explain the parts of the liver

Answer 7

Question 8

What is the purpose of the bile duct?

Answer 8

The bile duct drains bile from the liver, this is stored in the gall bladder before being entied into the duodenum

Question 9

What type of cells is the livermade from?

Answer 9

It’s made primarity from hepatocytes which are packed together into columns called lobules

Question 10

Properties of hepatocytes/ liver cells (3)

Answer 10

• Relatively unspecialised - therefore you can have a partial liver transplant
• Cubodial in shape with many microvilli on their cell surface membrane to max SA
• Cytoplasm is very dense - contains specific organelles needed to carry out a range of functions

Question 11

Functions of the liver (5)

Answer 11

• Regulates - levels of glucose, amino acids & lipids
• Synthesises - Cholesterol, bile, plasma proteins (blood clotting proteins) and fetal RBCs
• Stores - Vitamins A,D and B₁₂ and iron and glycogen
• Removes - Hormones from the blood and ages RBCs
• Detoxifies - e.g. H₂O₂, alcohol, drugs and ammonia

Question 12

Describe the structure of a lobule

Answer 12

• Each lobule blood from the hepatic artery and hepatic portal vein mix and pass through channels called sinusoids between hepatocytes and empty into the branch of the heaptic vein.
• Hepatocytes have many mitochondria to provide ATP for all the energy requiring processes in the cells.
• The plasma membranes of the hepatocytes and lining of sinusoids have microvilli to increase SA for uptake of substances from the blood.
• Kupfer cells are specialised cells in the lining of the sinusoid and are phagocytic. They digest debris and bacteris to help defend against disease. Also break down old RBCs.
• In between the liver cells are channels called canaliculi. Tehy collect bile as it is formed in the hepatocytes and carry it towards the bile duct.

Question 13

What is bile made up of?

Answer 13

Bilirubin and biliverdin

Question 14

How does the liver breandown surplus amino acids?

Answer 14

1. It first undergoes deamination to remove an amine group
2. The Ammonia produced then gets fed into the ornithine cycle and the keto acid left over is respired

Question 15

Define deamination

Answer 15

Deamination = The removal of nitrogen-containing amino groups from surplus amino acids to form ammonia and organic acids

Question 16

Fill in the blanks for the ornithine cycle

Answer 16

Question 17

Write the general equation for the break down of surplus amino acids in the liver

Answer 17

Question 18

Why do you need to breakdown ammonia to form urea?

Answer 18

Ammonia is very soluble and very toxic and can’t be excreted directly by mammals. You’d require too much water to do so.

To eliminate this ammonia is fed into the ornithine cycle, combines with CO₂ to prduce urea.

Question 19

A summarised simple equation of the formation fo urea = ?

Why urea? How is it removed from the body?

Answer 19

Urea is both less toxic and less soluble than ammonia.

The liver releases urea into the blood and it is removed from the blood as it passes through the kidneys.

Question 20

Complete the table and give examples of animals that fall into each category of ammonia, urea and uric acid

Answer 20

Question 21

Example of a substance detoxified by the liver?

Answer 21

Alcohol (ethanol)

Question 22

Equation for the detoxification of alcohol (ethanol)?

Answer 22

Question 23

The downside of detoxification fo ethanol?

How does it cause a fatty liver?

Answer 23

It inhibits the metabolism of fatty acids, so these are converted in to facts and stored in te liver cells.

Excess fats in the liver cells causes damage leading to cirrhosis (fatty degeneration of the liver) when liver cells no longer break down toxins and other vital liver functions cannot occur.

Question 24

Apart from alcohol name 2 other substances that are detoxified by the liver

Answer 24

• Drugs - e.g. antibiotics and paracetamol
• Hormones - which themselves are not toxic but if they remain in the blood too long there effects could well continue long after they are needed. Breaking them down limits their effects