more homeostasis

Question 1

what is osmoregulation

Answer 1

it is the control of water and salt levels in the body

Controlled by hormones e.g. antidiuretic hormone (ADH) which affect the distal convoluted tubule and collecting duct

Question 2

how does the body respond to a decrease in water potential

Answer 2

1. the change is detected by osmoreceptors in the hypothalamus
2. the hypothalamus produces more ADH - so the posterior pituarity gland secretes more ADH into the blood
3. ADH travels in the blood to the kidney and is attached to receptors on collecting duct/ DCT of the kidney
4. ADH increases the permeability of cel walls of the DTC/ more aqaporins fuse with cell membrane to water - so more water is absorbed from the DCT

Question 3

explain ultrafiltration

Answer 3

the diameter of the efferent arteriole is smaller than the afferent arteriole
This leads to a build-up of hydrostatic pressure in the glomerulus

water, glucose, and mineral ions are squeezed our of the capillary into the Bowman;s capsule to form glomerular filtrate

through pores in capillary endothelium basement and podocytes (act as a filter)

large molecules such as protein and blood cells are unable to be pushed out as they are too large

Question 4

Reabsorption of glucose and water by the proximal convoluted tubule

Answer 4

1. sodium ions are actively transported our of the epithelium cell to the capillary
   This lowers the concentration of Na+ in the epithelial cell
2. Na+ moves via facilitated diffusion from PCT into the epithelial cell down a concentration gradient
   - co-transport of glucose increases concentration of glucose in the epithelial cells
3. glucose moves into the capillary via facilitated diffusion down a concentration gradient which lowers the water potential in the capillary
4. water moves via osmosis down a water potential gradient into the capillary ( it is reabsorbed)

Question 5

maintaining a gradient of sodium ions in the medulla by the loop of henle

Answer 5

1. the loop of henel acts as counter current multiplier - it maintains water potential gradient - water leaves collecting duct/ DCT by osmosis
2. Na+ actively transported out of ascending limb and ascending limb is impermeable to water so water remains
   This increases the concentrations of sodium ions in the medulla and lowers the water potential
3. water moves out of descending limb/ collecting duct by osmosis into the medulla
   The water is reabsorbed into the medulla and the filtrate becomes more concentrated as they move down the “hairpin”
4. Na+ diffuses into the descending limb
   so Na+ is recycled in the loop of Henle
   water potential is further reduced