Excretion

Question 1

What are the excretory products of the lungs, kidneys and skin?

Answer 1

• Carbon dioxide
• Urine
• Sweat

Question 2

What are the roles of the kidney?

Answer 2

• Ultrafiltration, filtration on a molecular level between glomerulus and Bowman’s capsule
• Selective reabsorption
• Osmoregulation, regulation of concentration of water molecules in the blood

Question 3

What does urine contain?

Answer 3

Water, urea and ions

Question 4

Describe ultrafiltration in the Bowman’s capsule

Answer 4

• Blood from the renal artery enters the capillaries of the glomerulus.
• The blood is under high pressure from pumping heart but also smaller diameter of blood vessel
• The high pressure forces all s all molecules out of the holes in capillary walls, leaving larger molecules in protein

Question 5

Describe composition of glomerular filtrate

Answer 5

urea, water, vitamins, fatty acids, water, glucose, nitrogen, salts and other small molecules

Question 6

Why does selective reabsorption of glucose occur in the proximal convoluted tubule?

Answer 6

Glomerular filtrate contains essential molecules that cannot be lost in urine, so they must be reabsorbed before they reach the collecting duct. This cannot take place anywhere else as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule

Question 7

How is water reabsorbed into the blood from the collecting ducts?

Answer 7

-Water that is filtered by kidney is re-absorbed into blood by the Collecting Duct, depending on levels of ADH produced by the Pituitary Gland.
-More ADH: more water re-absorbed into Collecting Duct
-Less ADH: less water re-absorbed into Collecting Duct

Question 8

Describe the process of excretion in the nephron from the Bowman’s capsule

Answer 8

• In the proximal convoluted tubule, glucose and animo acids are reabsorbed back into the blood by active transport
• Filtrate travels to the loop of Henlé where the water is reabsorbed by osmosis
• At the distal convoluted tubule, water, mineral salts and other useful substance apps are reabsorbed into the blood
• Remain fluid passes into collecting duct
• Collecting ducts from other nephrons join up to form the ureter, which leads to the bladder
• Urine is stored in the bladder ready for excretion

Question 9

Explain how the water content of blood is regulated when sweating increases

Answer 9

1. Hypothalamus in the brain detects low water levels in the blood
2. Pituitary gland releases anti-diuretic hormone (ADH) into blood
3. ADH travels to kidneys
4. Cells of collecting ducts have receptores that respond to ADH
5. Cells become more permeable
6. More water reabsorbed into the blood