excretion

Question 1

what is excretion?

Answer 1

the removal of the waste products of metabolism from the body

Question 2

what is the importance of removing waster products from the body and give 2 examples of metabollic ewaste products

Answer 2

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

Question 3

describe the blood supply of the liver

Answer 3

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

Question 4

where is the blood from the hepatic artery and hepatic portal vein mixed?

Answer 4

mixed in spaces called sinusoids which is surrounded by hepatocytes, supplying them with enough oxygenated blood

Question 5

what are kupffer cells?

Answer 5

attached to the walls of the sinusoids and remove bacteria and break down old red blood cells

Question 6

describe the strucutre of the liver

Answer 6

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

Question 7

how does the liver produce bile?

Answer 7

hepatocytes secrete bile from the breakdown of blood into spaces called canaliculi which drain into bile ductiles and then into the gal bladder

Question 8

describe 3 functions of the liver

Answer 8

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)

Question 9

describe the blood supply of the kidneys

Answer 9

renal artery supplies oxygenated bloods (from aorta) and the renal vein takes away deoxygenated blood (to the inferior vena cava)

Question 10

what are the 3 sections of the kidney and what do they do?

Answer 10

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

Question 11

what is the bowmans capsule?

Answer 11

cup-shaped structure that contains the glomerulus, where ultrafiltration takes place

Question 12

what is the rpoximal convoluted tubule?

Answer 12

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

Question 13

what is the loop of henle?

Answer 13

a long loop of tubule that creates a region with very high solute concentration in the tissue fluid deep in the medulla

Question 14

what is the distal convoluted tubule?

Answer 14

a second twisted tubule where fine tuning of water balance takes place as well as ion blance
its permeability is affected by ADH

Question 15

what is the collecting duct?

Answer 15

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

Question 16

describe ultrafiltration

Answer 16

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

Question 17

describe selective reabsorption

Answer 17

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

Question 18

how does the body control the water potential of the blood?

Answer 18

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

Question 19

how does ADH work to make a membrane more permeable to water?

Answer 19

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

Question 20

what are the effects of kidney failure?

Answer 20

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

Question 21

how is the glomerula filtrate measured?

Answer 21

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

Question 22

what are the two types of renal dialysis?

Answer 22

heamodialysis and peritoneal dialysis

Question 23

what happens in heamodialysis?

Answer 23

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

Question 24

what happens in peritoneal dialysis?

Answer 24

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

Question 25

what are the issues with kidney transplant?

Answer 25

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

Question 26

name 2 ways excretroy products can be used in medical diagnosis?

Answer 26

pregnancy testing

testing for anabolic steroid and drugs

Question 27

how do pregancy tests work?

Answer 27

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

Question 28

how is use of anabolic steroids tested for?

Answer 28

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

Question 29

Why does the dialysis fluid used in peritoneal dialysis contain dextrose solution rather
than water alone?

Answer 29

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 ;

Question 30

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.

Answer 30

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 ;

Question 31

Explain how the longer loop of Henle is able to assist the desert kangaroo rat in preventing
excessive water loss.

Answer 31

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 ;

Question 32

explain the role of the loop of Henle in the production of urine.

Answer 32

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) ;

Question 33

how can you tell the difference between the hepatic portal vein and the hepatic artery in a diagram of the liver?

Answer 33

the hepatic artery will be much narrower and the hepatic portal vein will be entering through a branched vessel

Question 34

how is ammonia formed in liver cells

Answer 34

deamination

Question 35

why does eating salty crisps result in lower urine production?

Answer 35

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