urine production Flashcards
Define filtration
Filtration means that water and small molecules pass (under high pressure) from the blood into the nephron
What is the first step of filtration?
- Blood entering the nephron in the afferent arteriole contains waste products
What is the 2nd step of filtration?
Small molecules (such as glucose, amino acids, vitamins, some hormones, urea, salts and water) are forced out of the plasma and into the Bowman’s capsule. Here they form a dilute solution called glomerular filtrate.
Where does filtration take place?
Filtration takes place in the glomerulus.
What is the 3rd step of filtration? (how does the structure of the glomerulus help filtration? (3))
- The pressure of the glomerulus is greater than normal blood pressure. filtration in the Bowman’s capsule is called ultra-filtration because of the high pressure.
- The surface area of the capillaries in the glomerulus is large. This increases the area for filtration.
- The walls of the glomerular capillaries are more porous than normal capillaries. The cell wall of the Bowman’s capsule is only one cell thick.
How is the pressure in the glomerulus greater than normal blood pressure?
This is caused by the already high pressure of the afferent arteriole being increased due to to the efferent arteriole being narrower.
What is the 4th step of filtration?
- larger substances do not enter the glomerular filtrate. These include red and white blood cells, platelets, antibodies, clotting proteins and some hormones.
How much of the glomerular filtrate is reabsorbed?
99% is reabsorbed leaving about 1.5 litres of urine to be excreted in a normal day.
- Reabsorption: What happens in the proximal convoluted tubule? (3)
- Most of the water is reabsorbed by osmosis.
- All of the useful molecules (glucose, amino acids, vitamins, etc) are reabsorbed by a combination of diffusion and active transport.
- Most of the salts are reabsorbed by active transport or diffusion.
Define reabsorption
Reabsorption means that molecules pass from the nephron back into the blood
Define active transport
Active transport means that energy (in the form of ATP) is used to move molecules, often against a concentration gradient, i.e. from low to high concentrations.
Define diffusion
Diffusion is the spreading out of molecules from a region of high concentration to a region of low concentration
Do diffusion and osmosis require energy?
No
Does active transport require energy?
yes
What features does the proximal tubule have in order to aid in reabsorption
- It is thin-walled (one cell thick).
- Is long (14mm).
- Has numerous infoldings (called microvilli) in its cells.
- Has a high concentration of mitochondria to provide energy for active transport.
Where is a small amount of water reabsorbed (other than in the proximal convoluted tubule where most is)? What is also reabsorbed with this?
The descending limb of the loop of Henle is permeable to water. In this section of the loop of Henle a small amount of the water is reabsorbed by osmosis. Also, some minerals are reabsorbed.
What happens in the ascending limb of the loop of Henle?
The ascending limb of the loop of Henle is permeable to salts. So, salts move out of the nephron into the fluid of the medulla. Initially, this happens by diffusion, but at the top of the ascending limb sodium is pumped out by active transport.
Where is sodium pumped out by active transport and into the fluid of the medulla?
at the top of the ascending limb of the loop of Henle
The addition of salts (from the ascending limb of the loop of Henle) makes the medulla more concentrated than the fluid in the tubule. what does this cause?
This helps to remove water (by osmosis) from both the descending limb of the loop of Henle and the collecting ducts.
What is the function of the loop of Henle?
to reabsorb water
What is the distal convoluted tubule involved in?
The control of the water, salt and pH values of the blood
What is reabsorbed into the blood in the region of the distal convoluted tubule?
Some water and salts can be reabsorbed from the tubule into the blood in this region.
is the collection duct impermeable to water or permeable?
It is permeable to water
What is reabsorbed from the filtrate in the collecting duct? How does this occur?
a small amount of water is reabsorbed from the filtrate. This occurs by osmosis, due to the high salt concentration in the medulla.
What is the liquid passing from the collecting duct called?
urine
Where does urine flow to from the collecting duct?
It flows into the pelvis of the kidney and on to the bladder through the ureters.
where does secretion take place?
In the distal tube
What is secreted in the distal tube?
potassium ions (K+) and hydrogen ions (H+)
The secretion of potassium ions (K+) and hydrogen ions (H+) in the distal tube help to maintain what?
the pH of blood
Define secretion
Secretion means that some substances pass from the blood into the nephron
How much water is reabsorbed in the proximal convoluted tubule? What else is reabsorbed here and how much?
Most water.
Most salts, glucose, amino acids and vitamins
How much water is reabsorbed in the loop of Henle(descending limb)? What else is reabsorbed here and how much?
A little water.
Some minerals
How much water is reabsorbed in the loop of Henle(ascending limb)? What else is reabsorbed here and how much?
No water, some salts
How much water is reabsorbed in the distal convoluted tubule? What else is reabsorbed here and how much?
Some water.
Some salts
How much water is reabsorbed in thecollecting duct? What else is reabsorbed here and how much?
A little water.
Nothing else
How does glomerular filtrate differ from urine? (2)
- It has more water (i.e. is more dilute) than urine.
- It contains many useful molecules like glucose and amino acids that are not normally found in urine.
