The Kidneys Flashcards
Name the functions of the kidneys.
1) They excrete waste products eg urea.
2) They regulate the water potential of the blood.
What is selective reabsorption?
After substances have been filtered out of the blood (when it passes through capillaries in the cortex of the kidneys) and into long tubules that surround the capillaries, the useful substances (eg are then reabsorbed back into the blood.
What is a nephron?
A long tubule joined by a bundle of capillaries which filters the blood.
Describe the process of ultrafiltration.
1) Blood from the renal artery enters smaller arterioles in the cortex of the kidney.
2) Each arteriole splits into a structure called a glomerulus (a bundle of capillaries looped inside a hollow ball called a Bowman’s capsule. (This is where ultrafiltration takes place).
3) The arteriole that takes blood into each glomerulus is called the afferent arteriole and the one that takes filtered blood away from the glomerulus is called the efferent arteriole.
4) The efferent arteriole is smaller in diameter than the afferent so the blood in the glomerulus is under higher pressure.
5) The high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
6) The liquid and small molecules pass through three layers to get into the Bowman’s capsule an enter the nephron tubules (the capillary wall, a membrane and the epithelium of the Bowman’s capsule).
7) Larger molecules eg proteins and blood cells cant pass through so stay in the blood. The substance that enters the Bowman’s capsule is called the glomerular filtrate.
8) The glomerular filtrate passes along the nephron and useful substances are reabsorbed.
Where doe selective reabsorption take place?
As the glomerular filtrate flows along the proximal convoluted tubule the loop of Henle and along the distal convoluted tubule.
How is the proximal convoluted tubule adapted for reabsorption?
The epithelium of the wall of the PCT has microvilli which provide a large surface area for reabsorption.
What modifications do the inner layer of the renal capsule have which allows the filtrate to leave the glomerular capillaries despite resistance?
The inner layer of the renal capsule is made up of podocytes. These cells have spaces between them which allows the filtrate to pass through.
What is osmoregulation?
Osmoregulation is the body’s way of maintaining constant levels of water within the blood and the body.
What happens to the water potential of the blood when it’s too high?
Less water is reabsorbed by osmosis into the blood meaning the urine is more diluted, so more water is lost via excretion.
What happens to the water potential of the blood when it’s too low?
This means that more water is reabsorbed by osmosis into the blood. This means that the urine is more concentrated.
Where is the loop of Henle located?
It is located in the medulla (inner layer) of the kidneys.
Describe the loop of Henle.
It has 2 limbs, the descending limb and the ascending limb.
1) As there’s a lower water potential in the medulla than in the descending limb this means that water moves out of the descending limb into the medulla via osmosis. This makes the filtrate more concentrated (the ions aren’t able to diffuse out of the descending limb).
2) Near the bottom of the ascending limb, Na+ ions diffuse out into the medulla which further lowers the water potential in the medulla. The ascending limb is impermeable to water and so it stays in the tubule.
3) Near the top of the ascending limb sodium ions are moved out via active transport. The ascending limb is impermeable to water and so the water stays inside of the tubule. This creates a low water potential in the medulla as there’s a high concentration of ions.
4) Water moves out of the distal convoluted tubule by osmosis and is reabsorbed into be blood.
How is water potential of the blood monitored?
The water potential of the blood is monitored by cells called
