Excretion, homeostasis and the liver

Question 1

Excretion:

Answer 1

the removal of waste products of metabolism from the body

Question 2

Main metabolic waste products in mammals are:

Answer 2

• Carbon dioxide –> one of the wate products of cellular respiration which is excreted from the lungs
• Bile pigments –> formed from the breakdown of haemoglobin from old red blood cells in the liver. Excreted in the bile from the liver into the small intestine via the gall bladder and bile duct. They colour the faeces.
• Nitrogenous waste products (urea) –> formed from the breakdown of excess amino acids in the liver. All mammals produce urea as their nitrogenous waste. Fish produce ammonia, birds and insects produce uric acid. Urea is excreted by the kidneys in the urine.

Question 3

Liver - fun facts

Answer 3

• Largest internal organ
• Takes up 5% of body mass
• Major organ in homeostasis
• Damaged areas generate very quickly
• Lies below diaphragm
• Made up of several lobes

Question 4

Blood flow to the liver

Answer 4

• Hepatic artery –> to the liver
• Hepatic portal vein –> to liver
• Hepatic vein –> from the liver to heart

Question 5

Hepatic portal vein:

Answer 5

• Carries blood loaded with products of digestion straight from intestines to liver, start of many metabolic activities of the liver.
• 75% of blood flowing through liver comes from hepatic portal vein

Question 6

Structure of the liver: hepatocytes

Answer 6

Hepatocytes (liver cells) have:
- Large nuclei
- Prominent Golgi apparatus
- Lots of mitochondria
Metabolically active cells

• Divide and replicate, even if 65% of liver lost it will regenerate in months
• Secrete bile from the breakdown of blood into spaces called canaliculi .

Question 7

Structure of liver: sinusoids:

Answer 7

• Blood from hepatic artery and hepatic portal vein is mixed in sinusoids, which are surrounded by hepatocytes
• This increases oxygen content of blood from hepatic portal vein, supplying hepatocytes with enough oxygen.
• Sinusoids contain Kupffer cells

Question 8

Structure of the liver: Kupffer cells

Answer 8

• Resident macrophages of liver
• Ingest foreign particles and help protect against disease.

Question 9

Structure of the liver: canaliculi:

Answer 9

• Where bile from breakdown of blood is secreted
• From canaliculi –> bile drains into the bile ductulus, which take it to the gall bladder

Question 10

Functions of the liver:

Answer 10

• Carbohydrate metabolism
• Deamination of excess amino acids
• Detoxification

Question 11

Functions of liver: carbohydrate metabolism

Answer 11

• Hepatocytes involved in homeostatic control of glucose levels in the blood by their interaction with insulin and glucagon
• When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose into storage carbohydrate glycogen.
• When blood sugar levels fall, the hepatocytes convert the glycogen back to glucose under the influence of glucagon.

Question 12

Functions of the liver: deamination of excess amino acids

Answer 12

• The body cannot store either proteins or amino acids.
• Excess proteins would be excreted and wasted if not for hepatocytes
• Deaminate and convert amino acids into ammonia (toxic) then to urea
• Remaining amino acids are fed into cellular respiration or converted into lipids for storage

Question 13

Deamination meaning

Answer 13

The removal of an amine group from a molecule

Question 14

Urea:

Answer 14

• Toxic in high concentrations, but not in concentrations found in blood
• Urea is excreted by kidneys in excretion and water balance.

Question 15

Ornithine cycle

Answer 15

Conversion of ammonia into urea in an enzyme-controlled reaction

Question 16

Transamination:

Answer 16

• Carried out by hepatocytes
• conversion of one amino acid into another
• Diet does not always contain the required balance of amino acids but transamination can overcome the problems this might cause

Question 17

Functions of the liver: detoxification

Answer 17

• Toxin levels in body always increase –> alcohol, urea, lactic acid, hydrogen peroxide

Question 18

Breakdown of hydrogen peroxide:

Answer 18

• Liver
• Hepatocytes contain enzyme catalyse that splits hydrogen peroxide into water and oxygen.

Question 19

Breakdown of ethanol

Answer 19

• Drug from alcoholic drinks
• Hepatocytes contain enzyme alcohol dehydrogenase, breaks down ethanol into ethanal.
• Ethanal is converted into ethanoate, which many be used to build up fatty acids or used in cellular respiration

Question 20

Observing liver cells:

Answer 20

• Stain
• Light microscope –> see liver cells, blood vessels and sinusoids

High mag –> can see individual hepatocytes and details of sinusoids

Question 21

Cirrhosis in the liver: disease

Answer 21

• Normal liver tissue is replaced by fibrous scar tissue.
• Lots of different causes: genetic conditions / hepatitis C / drinking lots of alcohol

Question 22

Three stages of alcoholic liver disease:

Answer 22

Three stages:
- Alcoholic fatty liver disease
- Alcohol hepatitis
- liver cirrhosis

Question 23

How does liver disease develop:

Answer 23

• Fatty liver –> big fat-filled vesicles displace nuceli of hepatocytes and liver gets larger.
• alcoholic hepatitis –> patient has fatty liver and damaged hepatocytes and the sinusoids, hepatic veins narrow
• Alcoholic cirrhosis –> may become irreversibly damaged. Many hepatocytes no longer divide and the liver shrinks. Its ability to deal with toxins decreases.