5.1.2 - the kidneys Flashcards
2 major roles of the kidneys
excretion and homeostasis
nephrons
the functional unit of the kidney; responsible for forming urine
sphincter muscle
at the base of the bladder, allowing urine to flow out of the body via the urethra
renal artery
blood entering the kidneys
renal vein
blood leaving the kidneys
‘vasa recta’
blood that enters in the artery branches to beome the capillary network wrapped around the nephron
comparison of the blood in the renal vein (out) to the renal artery (in)
- much reduced urea concentration
- same concentration of glucose and amino acids
- a restored ion balance (back to ideal levels)
why is there slightly less glucose in the blood flowing out the kidney than the blood entered?
kidney cells will remove some of the glucose from theblood for cellular respiration
ultrafiltration
filtering of substances out of the blood at the molecular level
why does ultrafiltration occur?
occurs due to the water potential difference between plasma in glomerular capillaries and filtrate in bowman’s capsule
how does the structure of the arterioles cause ultrafiltration?
afferent arteriole entering the glomerulus has a larger diameter than the efferent arteriole leaving the glomerulus, meaning it enters faster than it leaves, meanung there is a high hydrostatic pressure in capillaries, forcing molecules into the renal capsule
3 layers that the molecules have to pass through in order to be filtrated
- walls of the capillaries (endothelium) - these have pores
- basement membrane of the renal capsule
- special cells called podocytes
what is the basement membrane made up of?
made up of collage and glycoproteins
role of the basement membrane?
acts as a filter as it stops large protein molecules from getting through
podocytes role
additional filter; they have extensions called pedicels that wrap around capillaries, forming slits to ensure any blood cells or large proteins do not enter the filtrate
why do we need selective reabsorption?
as lots of useful molecules left the blood and entered the renal filtrate - we do not want to lose all of these in the urine
when the filtrate is first formed, it is hypotonic to the blood. what does this mean?
it has a higher water potential than the blood plasma (lots of water has left the blood)
where does selective reabsorption take place?
PCT
how are the cells lining the PCT adapted for their role?
- microvilli (increase surface area)
- co-transporter proteins
- lots of mitochondria so lots of ATP for active transport
- tightly packed cells so no fluid can pass between cells
steps of selective reabsorption
- Na- and K+ ion pumps in menrane use ATP to pump Na- out and K+ in
- decreases conc of Na- inside cells so moves back in via cotransporters, with glucose
- conc of glucose then increases inside cells causing glucose to move from cells into tissue fluid and then into capillaries
- this lowers water potential of the blood, causing water to follow my osmosis
what happens to the urea in selective reabsorption?
stays in the filtrate which becomes urine
what substances are reabsorbed?
glucose, amino acids, and some water
what is left in the filtrate after selective reabsorption?
essentially urine, just needs some final water and mineral ion regulation
role of the loop of henle
create a low water potential (high solute concentration) in the the tissue fluid around the nephron, deep in the medulla
what happens in the ascending limb of the loop of henle
na and cl ions are pumped out by active transport
this decreases the water potential of the medulla
however it is impermeable to water, so water cannot leave by osmosis
what happens in the descending limb of the loop of henle
permeable to water, so water moves out by osmosis and is absorbed into the capillaries
increases the conc of urine
what happens in the DCT?
further balancing of the water and salt concentration; if the body lacks salt Na+ ions are actively pumped out of the DCT
adaptations of the DCT
microvilli and lots of mitochondria, and permeable to water
role of the collecting duct
here that the final volume and concentration of urine is determined - water is reabsorbed based on the amount of ADH
why is urine produced hypertonic to the blood?
due to the large volume of water that has been reabsorbed as the filtrate passes along the nephron
what is urine made up of?
water, dissolved salts, urea, and other substances like excess vitamins
why does the length of the loop of Henle vary?
desert animals tend to have lots of nephrons that have very long loops of Henle, so they can have more concentrated urine, so they do not lose as much water
fish have no loop of Henle so cannot produce concentrated urine
osmoregulation
controlling water potentual of blood, plasma and tissue fkuid within very narrow boundaries
why is osmoregulation important?
if water enters our cells by omosis, they may burst
if water leaves our cells by osmosis, they may shrink and die
how is water gained in the body?
respiration in cells, drink and food
how is water lost in the body?
exhaled air, sweat, urine, faeces
where is ADH made
hypothalamus by osmoreceptors
role of the osmoreceptors
monitor the water potential of the blood flowing through the bran, and if this falls, they release more ADH from the posterior pituitary gland
neurosecretory cells
cells that make ADH - different to normal neurones because they make hormones - send nerve impulses
how does ADH work?
- attaches to receptors on cell membranes of collecting duct cells
- triggers formation of cAMP
- vesicles containing aquaporins move and fuse with cell membranes lining collecting ducts
- aquaporin channels are inserted into cell membranes making membrane more permeable to water
- water can move out, making urine more concentrated
the main factors which may cause kidneys to stop functioning normally
kidney infections - damage to parts of kidney
kidney stones - damage kidney tissue
high bp - affect ultrafiltration process
physical injury - rupture a kidney
genetic conditions - e.g. polycycstic kidney disease
main problems of kidney failure
substances that should stay in the blood may end up in urine e.g. glucose
build up of toxic urea in the blood
disrupted electrolyte balance of blood plasma
changes to blood pressure
what is the GMR?
Glomerulus filtration rate - the rate at which substances are filtered out of the blood in the glomerulus
how is the GMR measured?
blood test measuring the amount of creatinine in the blood - filtered out by the kidney - if the conc is higher, it is an indication that the kidneys are not working properly
when estimating GMR, what factors need to be taken into account?
age, gender and fitness levels
what does dialysis mean?
use of a partially permeable membrane to remove urea and excess salts and water from the blood, by the process of simple diffusion
haemodialysis
patient attached to a dialysis machine, for about 8 hours 2-3 times a week
blood leaves an artery in the arm and flows into the machine, where the membranes mimic the basement membrane
why is an anti-coagulant needed in a dialysis machine? and why is it removed before entering the body?
prevent blood clots
needs to be able to clot when it reenters the body
why must people having renal dialysis carefully control their diet?
little protein, to minimise the amount of urea made
regulate salt abd fluid intake - to regulate osmotic and electrolyre balance in blood
reasons for composition of dialysis fluid?
no urea - conc is always higher in blood, so can diffuse into dialysis fluid
normal blood glucose conc - so glucose does not diffuse out of blood (needed for resp)
normal mineral ion conc - any excess mineral ions can leave the blood by diffusion
why do the blood and dialysis fluid flow in opposite directions?
maintain a ‘counter current; - maximusing the rate of diffusuin of urea out of the blood
why might people who receive dialysis feel unwell in between sessions?
urea starts to build up in the blood
may have a salt/mineral ion imabalance - effecr on cells
peritoneal dialysis
occurs inside the body, using a peritoneum membrane, forming the lining of the abdomen
why does the dialysis fluid need replacing after several hours in peritoneal dialysis?
as there is no counter current effect, diffusion will stop when reached equilibrium
what are the side effects of long term dialysis?
sepsis
fatigue
stress/anxiety
low blood pressure
muscle cramps
insomnia
what is the main problem when someone receives a kidney transplant?
risk of rejection, surface antigens on cells of donated kidney may be different to antigens of cells of the recipient
causes an immune response so destruction of the new kidney
how can rejection of a transplant be overcome?
‘matching’ of tissue types
immunosuppresent drugs for rest of their life
pros of a transplant
cheaper than dialysis
more convenient
can lead a normal life without feeling ill all the time
cons of a transplant
major surgery
immunosuppresent drugs
trannsplants do not last forever
presence of glucose in urine
diabetes
monoclonal antibodies
antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body
stages of producing monoclonal antibodies
mouse is injected with hCG so makes appropriate antibody;
the b cells are then removed from the spleen of tge mouse and fused with a myleoma
creates a hybridoma
this reproduced rapidly, resulting in clones of millions of the antibodies
collected, purified abd used
