Kidney Function Flashcards
How is the glomerular filtrate formed during ultrafiltration?
- blood enters through the afferent arteriole, which splits into many small capillaries
- this generates hydrostatic pressure due to the change in width
-this forces out small molecules of water through the gaps in the capillary endothelium - the basements membrane holds back proteins, only allowing the small molecules through
- the podocytes have many feet-like projections to allow the filtrate to pass between them through filtration slits
- this forms the glomerular filtrate
- large proteins and blood cells are too large to fit through the gaps so remain in the blood which leaves via the efferent arteriole
What does the glomerular filtrate contain?
Glucose, amino acids, anything small
What is the purpose of ultrafiltration?
Removes urea from the blood
Where does selective reabsorption take place?
Proximal Convoluted Tubule (PCT)
What gets reabsorbed during selective reabsorption?
- all glucose molecules are reabsorbed by co transport with sodium ions
- 80% of water is reabsorbed by osmosis
What are some adaptations of epithelial cells lining the PCT?
- large surface area due to the presence of microvilli
- many carrier proteins in the cell membrane
- many mitochondria which provide energy for active transport
What are some other features that increase the rate of absorption in the PCT?
- capillaries are close to the PCT so short diffusion pathway
- blood is always moving so the concentration gradient is maintained
How does selective reabsorption of glucose occur?
- Concentration of sodium ions in the PCT cell is decreased as the sodium ions are actively transported out of the PCT into the blood in the capillaries
- Due to the concentration gradient, sodium ions diffuse down the gradient from the lumen of the PCT into the epithelial cells lining the PCT by co-transport, carrying glucose into the cell using a sodium ion/ glucose transport protein
- Glucose can then diffuse out of the PCT epithelial cells lining, down the concentration gradient, into the bloodstream.
What is the function of the loop of Henle?
Maintain a sodium ion gradient
What is the loop of henle made up of?
An ascending limb and a descending limb
How is water reabsorbed into the blood in the loop of henle?
- Mitochondria in the walls of the cells provide energy to actively transport sodium and chloride ions out of the ascending limb, into the surrounding tissue
- The ascending limb is impermeable to water so there is an increased water potential in the filtrate and a decreased water potential in the surrounding tissues
- The descending limb is permeable to water so water diffuses out of the descending limb by osmosis into the tissue fluid where it is reabsorbed by the blood capillaries
How is the sodium ion gradient maintained?
Due to the loss of water by osmosis, there is a very high concentration of sodium and chloride ions in the ascending limb so, diffuse by facilitated diffusion out of the ascending limb and into the tissue fluid.
How is water reabsorbed at the DCT and collecting duct?
- due to all sodium ions being actively transported out of the loop of henle, when the filtrate reaches the DCT it is very dilute
- the filtrate moves into the DCT and the collecting duct and this section of the medulla has a very low water potential
- so even more water diffuses out of the DCT and collecting duct by osmosis into the blood
- what remains is transported to form urine
