The Kidneys - Dec 11

what do the kidneys play a role in?

removing wastes, balancing the pH of blood and maintaining osmoregulation ( water balance )

in humans, how many L of fluid are filtered by the kidneys each day and how many L are reabsorbed into the body?

180L of fluid are filtered by the kidneys each day and 178-179L are reabsorbed into the body

2 main regions of the kidneys:

1. the outer cortex

2. inner medulla

what are the main filtering units of the kidneys called?

nephrons

how many nephrons are there per kidney?

1 000 000

3 main processess involved in the formation of urine:

1. filtration

2. reabsorption

3. secretion

filtration: the receiving area of the nephron is called..

Bowman’s capsule

what is the Bowman’s capsule?

the capillary coils itself into a lump called the glomerulus

filtration: the passage of blood is very..

slow

filtration: the passage of blood is very slow, allowing what?

allowing wastes and water to diffuse out of the blood and into the nephron

filtration: what are too large and should not leave the capillary?

blood cells, platelets, and plasma proteins

filtration : blood cells, platelets, and plasma proteins are what?

are too large and shouldnt leave the capillary

reabsorption: the fluid enters the..

proximal tubule

reabsorption: the fluid enters the proximal tubule where substances are..

are transferred back to the interstitial fluid by passive and active transport

reabsorption: which pumps move these ions out of filtrate?

K+, Na+ and Cl- pumps

reabsorption: what do the K+, Na+ and Cl- pumps do?

move these ions out of the filtrate

reabsorption: proteins in the walls of the tubule move…

amino acids, glucose and nutrients actively from the filtrate and enter the peritubular capillaries

reabsorption: causes the filtrate to be what?

hypoosomotic to the interstitial fluid, therefore water leaves the tubule by osmosis

reabsorption: causes the filtrate to be hyposomotic to the interstitial fluid, therefore what?

water leaves the tubule by osmosis

reabsorption: aquaporins are membrane proteins that act as what?

act as water channels

reabsorption: aquaporins are membrane proteins that act as water channels to allow what?

to allow more water to leave the tubule ensure that the maximum amount of water is removed from the filtrate during this process

reabsorption: in the descending loop, what happens?

additional water is reabsorbed by osmosis and thru aquaporins which concentrates the molecules and ions in the tubule

reabsorption: in the first part of the ascending loop, what happens?

Na+ and Cl- ions are reabsorbed into the interstitial fluid by passive transport

reabsorption: at the top of the loop, these ions are moved by what?

active transport

reabsorption: what happens in the distal tubule?

more water and salts are removed, therefore water moves out by osmosis through aquaporins

reabsorption: the concentrated urea and wastes flow into where?

collecting ducts

reabsorption: collecting ducts are..

permeable to water but not to salt ions

reabsorption: in the medulla, the bottom of the collecting duct contains what?

passive urea transporters to move urea transporters to move urea into the interstitial fluid, therefore, increasing the solute concentration in the medulla

secretion: involves the removal of what?

of wastes from the blood and interstitial fluid to be excreted in urine

secretion: wastes secreted from where?

the interstitial fluid into the proximal tubule include H_ ions which are actively secreted

secretion: secretion of H+ ions to balance what?

the acidity of metabolic reactions is coupled w/ HCO3- reabsorption from the filtrate into the plasma in the peritubular capillaries

secretion: small amounts of what are secreted into the tubule?

ammonia

secretion: the concentration of salt causes what?

hormone secretion that caries the amount of K+ / H+ ions secreted into the distal tubule

secretion: active secretion of H+ ions occurs where?

in the collecting ducts, therefore excreting excess H+ that buffer systems cant absorb

why are our kidneys are quite efficient ?

as they reabsorb 178-179L out of the 180L of water filtered per day.

some organisms, like the desert rat are..

even more efficient at reabsorbing water. there is so little water in their urine that it is excreted as a paste