Homeostasis- Kidney

Question 1

Define osmoregulation

Answer 1

Control of water potential of the blood

Question 2

Role of hypothalamus in osmoregulation

Question 3

Water potential too low

Answer 3

More water is reabsorbed by osmosis into the blood from the tubules of the nephrons.
More ADH released
Urine more concentrated

Question 4

Water potential too high

Answer 4

Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons
Less ADH released
Urine more dilute

Question 5

Where is loop of Henle

Answer 5

Medulla of kidneys

Question 6

What is kidney medulla made up of

Answer 6

Descending and ascending limb

Question 7

Role of descending and ascending limbs

Answer 7

Control movement of sodium ions for water absorption

Question 8

Where is water reabsorbed into the blood

Answer 8

Along most of nephron
Mainly in loop of Henle, distal convoluted tubule, collecting duct

Question 9

Afferent arteriole

Answer 9

Takes blood into glomerulus
Larger diameter
Blood under less pressure

Question 10

Efferent arteriole

Answer 10

Takes filtered blood away from glomerulus
Smaller diameter
Blood under higher pressure
Forces small molecules out of capillary endothelium and into Bowman’s Capsule epithelium

Question 11

Formation of glomerular filtrate

Answer 11

High pressure in efferent arteriole forces liquid and small molecules in the blood out of the capillary and into Bowman’s Capsule- glomerular filtrate
Pass through 3 layers to do so.
Large molecules e.g. proteins stay in blood
Glomerular filtrate passes along rest of nephron + useful substances absorbed along way

Question 12

3 layers molecules pass through to get from capillary to Bowman’s Capsule

Answer 12

Pass through capillary endothelium, a membrane, epithelium of Bowman’s Capsule

Question 13

Nephron

Answer 13

Long tubules with bundles of capillaries where blood is filtered

Question 14

Selective reabsorption

Answer 14

Useful substances leave tubules of nephrons and enter capillary network around them
Useful solutes reabsorbed along proximal convoluted tubule by active transport and facilitated diffusion.
Water enters by osmosis because water potential of blood is lower than filtrate.
Water reabsorbed by PCT, loop of Henle, DCT and collecting duct
Filtrate that remains is urine

Question 15

Proximal convoluted tubule adaptations

Answer 15

Microvilli for large surface area
Increase diffusion rate

Question 16

How is the gradient of sodium ions in the medulla maintained by loop of Henle

Answer 16

Top of ascending limb- Na^+ ions actively transported into medulla (impermeable to water)
Lowers water potential in medulla
Water moves from descending limb into medulla by osmosis
Glomerular filtrate more concentrated (descending limb not permeable to ions)
Water in medulla reabsorbed into blood
Bottom of ascending limb- Na^+ ions diffuse into medulla, lower water potential in medulla
Water moves out of DCT by osmosis + reabsorbed into blood
High ion conc + low water potential in medulla
Water moves out of collecting duct by osmosis
Water reabsorbed into blood

Question 17

How is volume of water reabsorbed in capillaries controlled

Answer 17

Changing permeability of distilled convoluted tubule and collecting duct

Question 18

How is ADH released into blood

Answer 18

Osmoreceptors in hypothalamus
Detect decrease in water potential of blood
Water moves out of osmoreceptor by osmosis
Cells decrease in volume
Sends signals to other cells in hypothalamus which sends signals to posterior pituitary gland
Sends signal to release hormone ADH

Question 19

Role of ADH in osmoregulation

Answer 19

ADH molecules bind to receptors on plasma membranes of cells in DCT + collecting duct
Protein channels - aquaporins inserted into plasma membrane.
Walls more permeable to water- increased osmosis rate
More water reabsorbed from tubules to medulla and into blood
Small amount of concentrated urine produced