Kidney Flashcards
What are the main functions of the kidneys?
Filtration
Salt and Water Homeostasis
Excretion
Water Reabsorption
Acid/base balance
Renal endocrine functions
Explain the filtration process at the arterial end of the capillaries.
At arterial end of capillary is a high hydrostatic pressure, the osmotic pressure is lower. This means the force pushing things out of the capillary is greater than them being pushed in. This gives a net force for efflux, taking O2 and other required substances into an organ.
Explain the filtration process at the venous end of the capillaries.
At venous end of the capillary there is a lower hydrostatic pressure and a higher osmotic pressure. This means there is a net force for influx, meaning the blood supply can then take away the waste products.
What 3 layers make up the ultrafiltration system of the bowman’s capsule?
Fenestrations of endothelial cells
Basement membrane
Podocytes
Explain the process of ultrafiltration.
Blood arrives at the Glomerulus through the afferent arteriole. The Glomerulus is a capillary bed found within the Bowman’s Capsule of the Nephron. Blood leaves the glomerulus through the efferent arteriole. The afferent arteriole has a wider lumen than the efferent arteriole allowing hydrostatic pressure to build in the glomerulus. This forces water and small molecules (ions, AA, glucose, urea) out through the above barriers, large molecules remain in bloodstream. The fluid is now called filtrate.
Role and processes of the Loop of Henle.
The main function of the Loop of Henle is to produce a low water potential in the medulla of the kidney. It does this by acting as a countercurrent multiplier to produce concentration gradients. The descending limb is permeable to water and so as filtrate flows down this part of the loop its water potential decreases. The filtrate’s water potential is at its lowest at the bottom of the loop. The ascending limb is impermeable to water but allows the movement of Na+ and Cl- out of the filtrate so the water potential of the filtrate rises again. This process allows the kidney to produce urine that is more concentrated than the blood.
Role and processes of the DCT.
Balancing the water needs of the body takes place in the DCT and collecting duct. These are the areas where the permeability of the walls varies with the level of ADH. Cells lining walls have mitochondria so can carry out active transport. If the body lacks salt, sodium ions will be actively pumped out of the DCT with chlorine ions following down the electrochemical gradient. Water can also leave the DCT if the walls are permeable.
Role and processes of the collecting duct.
The collecting duct passes down through the concentrated tissue fluid of the renal medulla. This is the main site where the concentration and volume of the urine produced is determined. Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla. As a result the urine becomes more concentrated. The level of sodium ions in the surrounding fluid increases through the medulla from the cortex to the pelvis. This means water can be removed from the collecting duct all the way along its length, producing very hypertonic urine when the body needs to conserve water.
Why do we need hypertonic urine?
To be able to excrete electrolytes whilst preserving fluid volume
Do effectively dilute the body fluids
