6.4.3 Control of blood water potential

Question 1

Excretion of waste

Answer 1

Blood enters kidney through renal artery and passes through capillaries in cortex. Ultrafiltration and selective reabsorption takes place, unwanted substances pass to bladder and ae excreted as urine

Question 2

Nephrons

Answer 2

Long tubules along with bundles of capillaries where blood filtered

Question 3

Ultrafiltration

Answer 3

Blood from renal artery enters smaller arterioles and the glomerulus. High pressure forces liquid and small molecules in the blood out of the capillary and into Bowman’s capsule (glomerular filtrate), large molecules cannot pass through

Question 4

Glomerular filtrate

Answer 4

Substances that enter the Bowman’s capsule

Question 5

Afferent arteriole

Answer 5

Arteriole that takes blood into each glomerulus

Question 6

Efferent arteriole

Answer 6

Arteriole that takes filtered blood away from glomerulus, smaller in diameter so higher pressure

Question 7

Selective reabsorption

Answer 7

Takes place as glomerular filtrate flows through PCT, through loop of Henle and the DCT. Useful substances reabsorbed along PCT by active transport and facilitated diffusion. Water enters by osmosis into blood

Question 8

PCT

Answer 8

Proximal convoluted tubule, has microvilli to provide a large surface area for reabsorption from glomerular filtrate

Question 9

DCT

Answer 9

Distal convoluted tubule

Question 10

Osmoregulation

Answer 10

Control of the water potential of the blood

Question 11

Water reabsorption

Answer 11

Reabsorbed along all he nephron, but regulation of water potential in loop of Henle, DCT and collecting duct. Controlled by hormones

Question 12

Loop of Henle

Answer 12

Located in medulla. Top of ascending loop, sodium actively pumped out into medulla, low water potential in medulla. Water moves out of descending limb by osmosis, glomerular filtrate more concentrated. Water reabsorbed by capillaries. Bottom of ascending limb, sodium diffuses into medulla. Water moves out of DCT and collecting duct. Water in medulla reabsorbed into blood

Question 13

Ascending loop

Answer 13

Impermeable to water

Question 14

Descending loop

Answer 14

Permeable to water, impermeable to ions

Question 15

ADH (Antidiuretic hormone)

Answer 15

Osmoreceptors in hypothalamus. Posterior pituitary gland releases ADH. ADH binds to receptors on DCT and collecting duct. Adds aquaporins to cell membrane

Question 16

Dehydrated

Answer 16

Low water potential, detected by osmoreceptors from hypothalamus, posterior pituitary gland releases more ADH into blood, DCT and collecting duct are more permeable so more water reabsorbed by osmosis

Question 17

Hydrated

Answer 17

Water potential rises, detected by osmoreceptors in hypothalamus, posterior pituitary gland releases less ADH, less ADH means DCT and collecting duct less permeable, less water reabsorbed. Large amount of dilute urine produced and more water lost