Flashcards in F214:02:05 Formation of urine Deck (40):
Where are afferent and efferent vessels found?
In all organs
What do afferent vessels do?
carry blood into the organ
What do efferent vessels do?
carry blood away from the organ
What is special about the efferent vessel in the glomerulus?
it is a muscular arteriole which can constrict to raise blood pressure in the glomerulus
Define ultrafiltration in terms of its use in the kidneys
The filtration at a molecular level, as in the glomerulus- large molecules and cells are left in the blood and the smaller ones flow out into the Bowman's capsule
What are podocytes?
specialised cells that make up the inner lining of the Bowman's capsule.
Which is wider, the afferent or efferent arteriole in the kidneys?
Why is the afferent arteriole wider than the efferent?
it ensures that the blood in the glomerulus is under a substantial enough amount of pressure in there (more than in the Bowmans capsule) so that fluid tends to flow into there
Describe the barrier between the blood in the capillary and the lumen of the Bowman's capsule
It has 3 layers:
1. the endothelium of the capillary
2. the basement membrane
3. the epithelial cells of the Bowman's capsule
How is the endothelium of the capillaries adapted to allow ultra filtration?
They have narrow gaps between the cells that blood plasma and the substances dissolved in it can pass through
How is the basement membrane adapted to allow ultra filtration?
consists of a fine mesh of collagen fibres and glycoproteins, that act as a filter to prevent the passage of molecules with a relative molecular mass of more than 69000
What is the basement membrane made up of?
strands of glycoproteins and collagen fibres
How small do molecules have to be to be able to pass through the basement membrane?
with a relative molecular mass smaller than 69 000.
What molecules generally cant pass through the basement membrane?
all blood cells
What substances are filtered out of the blood?
inorganic ions (sodium, potassium, chloride- salts)
What is the concentration of water in blood plasma and glomerular filtrate? (in g/dm-3)
What is the concentration of proteins in blood plasma and glomerular filtrate? (in g/dm-3)
What is the concentration of amino acids in blood plasma and glomerular filtrate? (in g/dm-3)
What is the concentration of Glucose in blood plasma and glomerular filtrate? (in g/dm-3)
What is the concentration of Urea in blood plasma and glomerular filtrate? (in g/dm-3)
What is the concentration of inorganic ions in blood plasma and glomerular filtrate? (in g/dm-3)
What remains in the capillaries of the glomerulus after ultra filtration has taken place?
and very small amounts of water, amino acids ,glucose, urea, inorganic ions (sodium, potassium, chloride- salts)
What effect does the presence of proteins in the blood after ultrafiltration has taken place in terms of water potential?
Its very low
Why is it important for there to be a low water potential in the blood after ultra filtration has taken place?
to ensure that water can be reabsorbed at a later date
What is the total volume of fluid filtered out by both kidneys per minute?
What is the total volume of fluid filtered out by both kidneys per day?
What happens in blood pressure is too high in the kidneys?
It can damage the capillaries of the glomerulus and the epithelium of Bowman's capsule
What happens as fluid moves along the nephrons?
some substances are removed from the fluid and reabsorbed into the blood
Where does most of the reabsorption of substances take place in the nephron?
the proximal convoluted tubules
What percentage of reabsorption takes place in the the proximal convoluted tubules?
What is reabsorbed by the blood?
All glucose and amino acids
How are the cells lining the proximal convoluted tubule specialised to achieve reabsorption?
- Cell surface highly folded (microvilli), larger SA
- Membrane contains special co-transporter proteins, to trans proteins or AA in associatiuon with sodium ions (facillitated diffusion)
- opposite membrane is slightly folded + has S/P pumps to lower water potential
- cyt has many mitochondria, indicating active transport is taking place.
microscopic folds of the cell surface membrane to increase the SA of the cell
Define co-transporter proteins
proteins on a cell surface membrane that allows the facillitated diffusion of simple ions to be accompanied by transport of a larger molecules eg glucose
Define facillitated diffusion
diffusion that in enhanced by the action of proteins in the cell membrane
What are sodium-potassium pumps
special proteins in the cell surface membrane that actively transport sodium and potassium against their concentration gradients
How does reabsorption occur?
- S/P pumps reduce concentration of sodium so sodium ions are transported into the cell by fac-diffusion.
- AA and glucose entering cell via fac-diff diffuse out the other side of the cell, sometimes enhanced by active removal
- from tissue fluid substances diffuse into blood
- reabsorption of salts lowers WP, so water enters by osmosis
- Larger molecules absorbed by endocytosis
Suggest what might happen if water is not reabsorbed by the nephron
a large volume of very dilute urine would be produced and dehydration would occur
Explain why the concentrations of glucose and amino acids are the same in the glomerular filtrate as in the blood plasma
Because the AA and proteins have been passed from blood plasma to glomerulus filtrate by ultra filtration in the glomerulus