excretion Flashcards
what is excretion?
the removal of the waste products of metabolism from the body
what is the importance of removing waster products from the body and give 2 examples of metabollic ewaste products
nitrogeneous waste - such as urea from the breakdown of excess amino acids by the liver
carbon dioxide produced as waste product of cellular respiration, excreted from the lungs
need to be removed as they are toxic
describe the blood supply of the liver
the hepatic artery supplies the liver with oxygenated blood
the hepatic portal vein supplies the liver with products of digestion from the intestines.
the hepatic vein returns the deoxygenated blood to the heart
where is the blood from the hepatic artery and hepatic portal vein mixed?
mixed in spaces called sinusoids which is surrounded by hepatocytes, supplying them with enough oxygenated blood
what are kupffer cells?
attached to the walls of the sinusoids and remove bacteria and break down old red blood cells
describe the strucutre of the liver
it is made up of liver lobules (cylindrical structures made of hepatocytes)
each lobule has a central vein in the middle that connects to the hepatic vein. many branches of the hepatic artery, the hepatic portal vein and bile duct are also found in each lobule
hepatic artery and hepatic portal vein are connected to the central vein by capillaries called sinusoids
the bile duct is connected to the central vein by canaliculi
kupffer cells line the walls of the sinusoids to remove bacteria and break down old red blood cells
how does the liver produce bile?
hepatocytes secrete bile from the breakdown of blood into spaces called canaliculi which drain into bile ductiles and then into the gal bladder
describe 3 functions of the liver
storage of glycogen
when blood glucose levels are too high, levels of insulin increase which stimulates hepatocytes to convert glucose to glycogen as storage
detoxification
breakdown of hydrogen peroxide - hepatocytes produce catalse which breaks it down to oxygen and water
breakdown of ethanol - hepatocytes produce alcohol dehydrogenase which breaks down ethanol into ethanal. this is then converted to ethanoate used to make fatty acids or in respiration
formation of urea/deamination
deamination of amino acids takes place as the body cannot store amino acids or proteins. the amine group from the amino acid is removed and converted to ammonia (very toxic) which is converted to urea (less toxic, but needs removing becuase very toxic when in high concentrations)
describe the blood supply of the kidneys
renal artery supplies oxygenated bloods (from aorta) and the renal vein takes away deoxygenated blood (to the inferior vena cava)
what are the 3 sections of the kidney and what do they do?
the cortex
where blood is filtered. has dense capillary network carrying bloods from renal artery to nephron
medulla
contains tubules of nephrons that form pyramids of the kidney and contains collecting ducts
pelvis
central chamber of the kidne where urine collects before passing down the ureter
what is the bowmans capsule?
cup-shaped structure that contains the glomerulus, where ultrafiltration takes place
what is the rpoximal convoluted tubule?
the first coiled region of the tubule after the bowmans capsule found in the cortex of the kidney
this is where many substances are reabsorbed into the blood
what is the loop of henle?
a long loop of tubule that creates a region with very high solute concentration in the tissue fluid deep in the medulla
what is the distal convoluted tubule?
a second twisted tubule where fine tuning of water balance takes place as well as ion blance
its permeability is affected by ADH
what is the collecting duct?
urine passes down the collecting duct through the medulla to the pelvis
fine tuning of water balance takes place and the permeability to water is controlled by ADH
describe ultrafiltration
the glomerulus is supplied by the afferent arteriole and leaves by the efferent arteriole which is much narrower.
this causes a build up of hyrdostatic pressure in the blood
this forces blood out thorugh capillary wall (endothelium) which has gaps to allow passage of substances then through basement membrane which stops the movement of large substances and then podocytes which have finger like projections that ensure gaps to allow passage of substances
this filters out urea along with water and other useful substances that need to be reabsorbed
describe selective reabsorption
in the PCT all the glucose, amino acids, vitamins and hormones are reabsorbed into the blood by active transport. and most water is reabsorbed aswell
once removed from the nephron the substances diffuse into the capillary network surrounding it down steep concentration gradients
in the descending limb water moves out of the filtrate down concentration gradient the upper part is immpermeable and the lower part is permeable to water. the concentration of sodium and chloride ions in the tissue fluid of the medulla gets higher from the cortex to the pelvis so that water diffuses out along full length of descending limb
the descending limb is also not permeable to sodium or chloride ions so no active transport takes place and concentration gradient remains high
the first section of the ascending limb is very permeable to sodium and chloride ions which move out of the concentrated solution by diffusion down concentration gradient. in the second part sodium and chlrodie ions are actively pumped out producing high concentrations in tissue fluid of the medulla
the ascending limb is impermeable to water so water cannot enter.
due to removal of ions, the ascending limb becomes increasingly dilute
the distal convoluted tubule permeability to water is controlled by ADH and can balance the water
the filtrae then enters the collecting duct which permeability is also controlled by ADH which determines the concentration of the urine which passes down the ureter
how does the body control the water potential of the blood?
by a negative feedback mechanisms
osmoreceptors in the hypothalamus detect change in the water potential of the blood and this changes how much ADH is released by the posterior pituitary gland in which ADH is stored (produced by the hypothalamus)
ADH makes the walls of the DCT and collecting ducts more permeable to water
how does ADH work to make a membrane more permeable to water?
ADH binds to the cell surface membrane and triggers the release of cAMP in the cell, this triggers vesicles in the lining of the collecting duct to fuse with the cell surface membrane in contact with the medulla.
the vesicles contain aquaporins which are inserted intp the memebrane which makes it more permeable to water
what are the effects of kidney failure?
loss of electrolyte balance
cannot excrete excess ions causing osmotic imbalance in tissue which can lead to death
build up of toxic urea
high blood pressure
the kidneys maintain water balance, without this too much water in blood gives high blood pressure
can affect glomerula filtrate rate - lower than normal range indicates the kidneys are not working correctly
how is the glomerula filtrate measured?
indirectly, measure the levels of creatine in the blood (from the break down of muscle) if the levels of creatine in the blood increase, it is a sign that the kidneys are not working correctly
what are the two types of renal dialysis?
heamodialysis and peritoneal dialysis
what happens in heamodialysis?
the blood from the artery of a patient flows into the dialysis machine between partially permeable membranes, on the other side is dialysis fluid containing the correct concentrations needed in the blood to prevent loss of useful substances bu contains no urea so that urea in the blood moves out.
the dialysis fluid and blood flow in opposite directions to maximise exchange
what happens in peritoneal dialysis?
dialysis fluid is injected into the abdomen using a catheter, left for several hours for dialysis to take place across the peritoneal membranes
the fluid is then drained off and discarded
what are the issues with kidney transplant?
have to find a good tissue match to prevent rejection
have to use immunosurpressents, leaving the patient more vulnerable to diseases
transplanted organ only lasts 5-10 years
name 2 ways excretroy products can be used in medical diagnosis?
pregnancy testing
testing for anabolic steroid and drugs
how do pregancy tests work?
they detect the hormone hCG that is only found in the urine of pregnant women
a stick is used with an application area that contains monoclonal antibodies of hCG bound to coloured beads
when urine applied to this area, any hCG will bind forming hCG/monoclonal antibody complex
the urine moves up the test strip carrying the beads with it
the test strip has immobilised antibodies to hCG on it
if hCG present, the immobilised antibody binds the the hCG attached to the blue beads and turns the strip blue
how is use of anabolic steroids tested for?
urine is tested by gas chromatograhy and mass spectromemtry which is analysed by computers comparing results to known substnaces to tell what is in the urine sample
Why does the dialysis fluid used in peritoneal dialysis contain dextrose solution rather
than water alone?
idea that (dialysis is replicating function of kidney and)
part of kidney’s function is to remove
(excess) water from blood ;
2 (dextrose / sugar) reduces , water potential /
(of dialysis fluid)
or
(dextrose / sugar , solution)
has a lower , water potential / (than water) ;
3 water moves from blood (into dialysis fluid)
by osmosis
or
prevents water moving into the blood
(from dialysis fluid) by osmosis ;
4 (if it was water alone) cells would , swell / burst ;
Suggest why patients receiving peritoneal dialysis usually need to have the peritoneal
dialysis fluid replaced four times a day, but those receiving haemodialysis only need
treatment three times a week.
1 peritoneal dialysis can remove
less (named) waste
(than haemodialysis) ;
2 idea that
in haemodialysis dialysis fluid is constantly ,
refreshed / changed
(but not in peritoneal dialysis) ;
3
4
haemodialysis uses counter-current flow ;
idea that
haemodialysis maintains concentration gradient
or
in peritoneal dialysis the concentration gradient ,
reduces / is lower ;
5 (in peritoneal dialysis) the fluid reaches equilibrium
with the blood ;
Explain how the longer loop of Henle is able to assist the desert kangaroo rat in preventing
excessive water loss.
1 more (sodium and chloride) ions pumped ,
out of ascending limb / into medulla ;
2 builds up greater water potential gradient ;
3 allows , reabsorption / removal , of more water from ,
collecting duct / M ;
explain the role of the loop of Henle in the production of urine.
role of loop of Henle is to
cause a decrease in water potential in /
establish water potential gradient going down , medulla ;
(as) in ascending limb active transport outwards of ,
solutes / (sodium and chloride) ions ;
(walls of) descending limb permeable to water ;
water removed from descending limb ;
water potential of tissues surrounding collecting duct is
low(er) than fluid inside it ;
water removed from , filtrate / urine (in collecting duct) ;
how can you tell the difference between the hepatic portal vein and the hepatic artery in a diagram of the liver?
the hepatic artery will be much narrower and the hepatic portal vein will be entering through a branched vessel
how is ammonia formed in liver cells
deamination
why does eating salty crisps result in lower urine production?
salted crisps reduce the water potential of the blood due to high salt content
osmoreceptors in the hypothalamus detect the change in water potential in the blood and cause an increase in the release of ADH
ADH causes production of aqua porins in the collecting duct so more water is reabsorbed into the capillaries
so lower volumer of urine is produced
