13. Excretion in Humans

Question 1

Outline the structure and function of a nephron and its associated blood vessels

Answer 1

1. Ultrafiltration: Capillaries of the glomerulus are under high pressure, forcing small molecules out the blood/capillaries into the bowman’s capsule. Including water, glucose, urea and ions which form a filtrate
2. Selective reabsorption: Glucose is reabsorbed into the blood by active transport at the proximal convoluted tubule. While necessary salts are reabsorbed at the loop of henle by diffusion and active transport, followed by the reabsorption of water by osmosis
3. Formation of urine: As the fluid leaving the collecting duct contains urea, excess water and excess ions which must be excreted

Question 2

Describe the role of the liver in the assimilation of amino acids by converting them to proteins

Answer 2

• Digested amino acids absorbed into the blood from the small intestine, are carried into the liver for assimilation
• They’re used to build proteins e.g. fibrinogen, and excess amino acids are broken down during deamination as they cannot be stored
• Enzymes in the liver split up amino acid molecules: Carbon is converted into glycogen for storage. Nitrogen is turned into ammonia then converted into urea (less toxic). Dissolving in the blood, to the kidney for excretion

Question 3

Describe deamination

Answer 3

The removal of the nitrogen-containing part of amino acids to form urea

Question 4

Explain the importance of excretion, limited to toxicity of urea

Answer 4

1. Cell death
2. Reduced response to insulin, leading to diabetes
3. Deposits inside blood vessels