15.5 The Functions of the Nephrons Flashcards
What is ultrafiltration?
First stage in removal of nitrogenous waste and osmoregulation of blood
Can you explain the steps involved in blood entering the glomerulus?
- Renal artery supplies blood to glomerulus via wide afferent arteriole
- Blood leaves through narrower efferent arteriole
- Causes pressure in capillaries of glomerulus
- Blood forced out of capillary wall
- Fluid passes through basement membrane
What does ‘afferent’ mean?
Incoming
What does ‘efferent’ mean?
Outward
What is the basement membrane?
Made up of network of collagen fibres and other proteins that make up a second ‘sieve’
What are podocytes?
Special cells in wall of Bowman’s capsule that act as additional filter
What are pedicels?
Extensions of podocytes that wrap around capillaries to form slits
What is the glomerular filtration rate?
Volume of blood that is filtered through kidneys in a given time
What is urea?
Waste product of protein breakdown
What does hypotonic mean?
Less concentrated than
What is the concentration of the ultrafiltrate compared to the blood plasma?
Ultrafiltrate is hypotonic than blood plasma
What is the main function of the nephron after the Bowman’s capsule?
To return most filtered substances back to blood
E.g. water, glucose, salt
What happens in the proximal convoluted tubule?
All glucose, amino acids, vitamins and hormones are moved from filtrate back into blood by active transport
What happens to the ions of the sodium chloride salt?
The sodium ions are moved by active transport
Chloride ions and water follow passively down concentration gradients (passive transport)
What are the adaptions of the cells lining the proximal convoluted tubule?
Covered with microvilli to greatly increase surface area over which substances can be reabsorbed
Many mitochondria to provide ATP needed in active transport systems
What does ‘isotonic’ mean?
At same concentration
What is the loop of Henle?
Section of kidney tubule that allows mammals to produce urine more concentrated than their own blood
What does a countercurrent multiplier do?
Uses energy to produce concentration gradients resulting in the movement of substances from one area to another
E.g. water
What does the loop of Henle act as?
A countercurrent multiplier
Where is the diffusion gradient produced by the loop of Henle acting as a countercurrent multiplier?
Diffusion gradient in medulla
What is the descending limb of the proximal convoluted tubule?
Region where water moves out of filtrate down a concentration gradient
Can you describe the permeability of the descending limb?
Upper part is impermeable to water
Lower part of descending limb is permeable to water and runs down into medulla
Can you describe the change in concentration of the sodium and chloride ions in the tissue fluid of the medulla?
Concentration of sodium and chloride ions increases as you move from cortex to the pyramids
Can you describe the concentration of the blood entering the descending limb of the loop of Henle?
Isotonic with blood
What are the surrounding capillaries of the descending limb called?
Vasa recta
What is the fluid that reaches the hairpin bend like?
Very concentrated and hypertonic to the blood in the capillaries
What passes through the basement membrane and what cannot?
Most plasma contents can pass through
Blood cells and many proteins retained in capillary because of their size
What do pedicels help do?
Ensures any cells, platelets or large plasma proteins that managed to pass epithelial cells AND basement membrane do not get through into the TUBULE
What percentage of water and solutes are removed from the plasma as it passes the glomerulus?
20% of water and solutes
What does ultrafiltration also remove apart from urea?
Water, gluocose, salts and other substances needed in plasma
What percentage of the sodium chloride and water is reabsorbed in the proximal convoluted tubule?
85% of sodium chloride and water
How are sodium and chloride ions and water moved in the proximal convoluted tubule?
Sodium ions moved by active transport
Chloride ions and water follow passively down concentration gradients
What happens to the substances that have been removed from the nephron?
Diffuse down steep concentration gradients into capillary network surrounding tubules
How are the steep concentration gradients of the capillary network surrounding the tubules maintained?
Maintained by constant flow of blood through capillaries
What is the concentration of the filtrate reaching the end of the distal convoluted tubule compared to the tissue fluid surrounding the tubule and the blood?
Filtrate is ISOTONIC with tissue fluid surrounding tubule and ISOTONIC with the blood
Can you describe the movement of the filtrate entering the descending limb?
Filtrate enters descending limb
Water passes out of loop into tissue fluid by osmosis as it travels down limb
Moves down concentration gradient into blood of vasa recta
Is the descending limb permeable to sodium and chloride ions?
No, so no active transport takes place
How permeable is the FIRST section of the ascending limb?
Very permeable to SODIUM and CHLORIDE ions
How do the sodium and chloride ions move out of the first part of the ascending limb?
Diffuse down concentration gradient
What happens in the second section of the ascending limb?
Sodium and chloride ions are actively pumped out AGAINST a concentration gradient into medulla tissue fluid
Can you describe the involvements of water in the SECOND part of the ascending limb?
Ascending limb is IMPERMEABLE to water
So water cannot follow sodium and chloride ions down concentration gradient
Means fluid left in ascending limb becomes increasingly dilute
Tissue fluid gains high concentration of ions that are essential to produce urine MORE concentrated than blood (COUNTERCURRENT MULTIPLIER SYSTEM)
Dilute fluid HYPOTONIC to blood and enters distal convoluted tubule and collecting duct
What part of the loop of Henle is impermeable to water?
Ascending limb
Water cannot follow sodium and chloride ions down concentration gradient
Where does balancing the water needs of the body take place?
Distal convoluted tubule and collecting duct
Where does ADH have an effect?
Collecting duct and distal convoluted tubule
What is an adaptation of the cells in the distal convoluted tubule?
Many mitochondria to carry out active transport
What happens if the body lacks salt?
Sodium ions are actively pumped out of DISTAL convoluted tubule with chloride ions following down an electrochemical gradient
What happens if the body needs water?
ADH
Water LEAVES distal convoluted tubule
Urine becomes more concentrated
What is another role of the distal convoluted tubule apart from water balance?
Balancing blood pH
Where is the collecting duct located?
Passes down concentrated tissue fluid of renal medulla
What is the purpose of the collecting duct?
Area where volume and concentration of urine is determined
How does water move out of the collecting duct?
Diffusion down concentration gradient as it passes through renal medulla
Urine becomes more concentrated
What happens to the sodium ions regarding the collecting duct?
Level of sodium ions in SURROUNDING FLUID increases through medulla, from cortex to pelvis
Means water can be removed ALL ALONG collecting duct’s length
Hypertonic urine produced to save water when needed
