Higher Human Biology

Chapter 23

Removal of materials from the blood

Excretion

• Excretion is the elimination of waste products from metabolism

• Carbon dioxide is a waste product produced during respiration

• Its removal from the lungs is an example of excretion.

Role of the lungs

• Cells produce carbon dioxide during aerobic respiration

• It diffuses to blood plasma• CO2 forms bicarbonate ions • These ions enter red blood cells in the pulmonary

circulation• Carbonic acid is formed• An enzyme then breaks down the acid to release

CO2

• This then diffuses out of the blood and into the lungs.

Diffusion in the alveoli

Role of the liver

• Regulates the level of glucose in the blood• De-amination of some proteins• Excess glucose stored as glycogen• Some plasma proteins are synthesised• Liver maintains a stable internal environment• Liver provides cells with optimum conditions

Detoxification of toxic materials

Detoxification

Chemical alteration Chemical breakdown Chemical attachment

Drugs

Rendered inactive

Products excreted in bile or through kidney

Alcohol

Converted by liver into Acetyl CoA

Acetyl CoA used in respiration

Food preservatives attached to a. acids by liver

Acts as molecular label

Recognised as waste by kidney and excreted

Detoxification of toxic materials

• Foreign particles for example bacterial cells are removed by macrophages which line the liver’s blood vessels

Removal & excretion of bilirubin

• When red blood cells reach the end of their 120 day life span, they are destroyed by macrophage cells in the liver, bone marrow and spleen

• Haemoglobin is broken by these cells into a yellow pigment called bilirubin which is released into the blood giving plasma its faint yellow colour.

Removal & excretion of bilirubin

• It is in this conjugated form that bilirubin is added to bile and becomes bile pigment.

• When bile pigment passes into the small intestine, bile salts aid digestion by emulsifying lipids.

• However, bile pigment (conjugated bilirubin) does not perform a useful role in digestion. Its release in bile is a form of excretion.

• In the gut, bilirubin is converted by bacteria to the brown pigment that gives faeces their characteristic colour.

Jaundice

• Accumulation of bilirubin in the bloodstream

• Liver suffers a disease which prevents its cells from absorbing bilirubin

• Bile duct becomes blocked

• Excessively high rate of red blood cells occurs

Production of urea

• De-amination of amino acids in the liver

• Amino acids broken down to form ammonia and an organic acid

• Organic acid may be pyruvic or one of Kreb’s cycle intermediates

• It can then enter the respiratory pathway.

Deamination

• De-amination needs oxygen

• It produces an organic acid

• It produces ammonia which goes to the ornithine cycle.

Urea production

• During the conversion of ammonia into urea, two molecules of ammonia and one molecule of carbon dioxide combine to form one molecule of urea and one of water. Assisting this process there is a cyclical conversion of ornithine into citrulline, arginine, and then back to ornithine again.

Ornithine cycle

• This shows how ammonia is converted to urea

• Ornithine is constantly regenerated.

Structure of the Nephron

distal convoluted tubule

proximal convoluted tubule

Loop of Henle

Role of the Kidneys

Role of the Kidneys

hypothalamus

thirst drink