Water extreme summary

What is meant by osmoregulation?

The homeostatic control of the water potential of the blood.

What carries out osmoregulation?

Nephron in the kidneys

What are the nephron?

Long tubules surrounded by capillaries

What does urine contain?

urea

water

dissolved salts

other small substances

What does urine NOT contain?

proteins, blood cells, glucose

Name the main structural elements of the nephron.

Glomerulus

Proximal convoluted tube

Loop of Henle

Distal convoluted tube

Collecting duct

Describe the Glomerulus

network of capillaries inside Bowman’s Capsule

Describe the PCT

 Series of loops surrounded by capillaries.

Describe the loop of henle.

Long loop surrounded by capillaries, has an ascending limb and descending limb.

Describe the DCT.

follows the loop of henle - a series of loops surrounded by blood capillaries

Describe the collecting duct

a tube into which a number of distal convoluted tubules from a number of nephrons empty

What is the role of the glomerulus?

ultrafiltration

What is the role of the PCT?

selective reabsorbtion

Name the 4 main roles of the nephron

Formation of glomerular filtrate

Selective reabsorption

Maintaining a gradient of sodium ions in the medulla

Reabsorption of water by the DCT and collecting ducts

Describe the Formation of glomerular filtrate.

Hydrostatic pressure causes small molecules such as glucose and water to pass through the pores in the capillaries of the basement membrane. Proteins are too large so they stay behind. Glucose in the filtrate lowers WP of cells, so less water is reabsorbed by osmosis.

Describe the process of selective reabsorbtion.

Glomerular filtrate passes into PCT. Na+ actively transported out of PCT into capillaries. Due to concentration gradient, Na+ moves by facilitating diffusion using co-transport proteins down the gradient into cells lining the PCT. The co-transporters also carry glucose. Glucose diffuses from PCT into the blood stream. Glucose has been re-absorbed.

Describe the role of the hypothalamus.

• Detect changes in water potential

• Produces ADH

Describe the role of the posterior pituitary gland.

ADH moves here after being produced

Stores and release ADH into blood

Describe the role of ADH.

• Produced in hypothalamus, released from pituitary gland, target organ is kidney

• Makes the cell membrane of the collecting duct and DCT more permeable to water

• When more ADH is released, more water is reabsorbed by tubules by osmosis, urine is more concentrated.