Excretion Flashcards
What is urea and where is it produced?
- Urea is a compound produced by the breakdown of excess amino acids
- It is produced in the liver
What are the two functions of the kidneys?
- Removal of toxic metabolic waste (such as urea)
- Regulation of water levels in the blood (osmoregulation)
What are the ureters?
Tubes that connect each kidney to the bladder which transports urine
What is the bladder?
Organ that stores excess urine
What is the urethra?
Tube that connects the bladder to the exterior (where urine is released)
What are the three regions of the kidneys?
- Cortex - Outermost region of each kidney
- Medulla - Innermost region of each kidney
- Renal Pelvis - Tube linking nephrons to ureter
What is a nephron?
- The functional unit of the kidney (where the kidneys function is actually performed)
- Each kidney contains around a million of them
What are all the parts of the nephron?
(from left to right on a diagram)
- Bowmans capsule - Ring shaped tube around the glomerulus which accepts the filtrate
- Proximal convoluted tubule - Continuation of the bowmans capsule tube where selective reabsorbtion (specifically of glucose and amino acids) happens
- Loop of Henle - Thinner continuation of the PCT where more selective reabsorbtion (specifically of salts and water) happens
- Distal covoluted tubule - Continuation of the loop of henle where more selective reabsorbtion (specifically of more salts and water) happens and the blood pH is regulated
- Collecting duct - Continuation of the DCT where controlled reabsorbtion of water occurs along with the formation of urine occur
What is the process of ultrafiltration?
Important
- Arterioles branching off of the renal artery lead to each nephron where they form a knot of capillaries known as the glomerulus which is surrounded by the bowmans capsule
- The capillaries in the glomerulus get increasingly smaller which increases the pressure (the pressure is already high as the blood is coming from the renal artery)
- This increased pressure forces smaller molecules out of the glomerulus and into the bowmans capsule
- All other molecules stay in the blood
Which molecules get forced into the bowmans capsule through ultrafiltration (which comprise the filtrate)?
- Glucose
- Urea
- Water
- Amino acids (but not big proteins)
- Mineral ions
Glycerol, fatty acids and vitamins also
How and where does the selective reabsorbtion of glucose and amino acids happen?
All selective reabsorbtion happens because the substances are useful (but were small enough to be ultrafiltered)
- It occurs in the promixal convoluted tubule (this is the only place with the necessary gates to facilitate this)
- Capillaries wrapping around the PCT selectively reabsorb the glucose and amino acids through diffusion or active transport (so it requires many mitochondria)
How and where does the selective reabsorbtion of salts occur?
- It occurs in the loop of henle and the distal convoluted tubule
- Capillaries wrapping around the loop of henle and distal convoluted tubule selectively reabsorb the mineral ions (salts) through diffusion
How and where does the selective reabsorbtion of water occur?
- Mostly in the collecting duct, but also in the loop of henle
- Capillaries wrapping around the loop of henle selectively reabsorb water through osmosis and in the collecting duct water osmoses through the collecting duct walls (depending on its permeability)
What happens if there is a decrease in blood water levels with regards to ADH?
- The decrease is detected by the hypothalamus
- More ADH (Anti-direutic-hormone) is released by the pituarity gland
- It travels through the blood and is detected by ADH receptors in the cells in the wall of the collecting duct
- In response, the wall of the collecting duct becomes more permeable by creating aquapores
- As a result, more water is reabsorbed into the blood and the urine is low volume and concentrated
If the water levels get too low, water will osmose out cells and they can become dehydrated and die. Water is also needed for many cellular reactions - therefore this process is essential to conserve water
What happens if there is a increase in blood water levels with regards to ADH?
- The increase is detected by the hypothalamus
- Less ADH (Anti-direutic-hormone) is released by the pituarity gland
- Therefore there is less ADH in the blood and less ADH is detected by the receptors in the wall of the collecting duct
- As a result, the walls of the collecting duct are not permeable
- Therefore, little water is reabsorbed into the blood and the urine is high volume and dilute
If the water levels get too high, water will osmose into cells and they can burst, or swell and put pressure on internal parts of the body. Additionally, the volume of blood becomes too high and this can place stress upon the heart
