5.1.2 - Excretion Flashcards
What is excretion?
the removal of metabolic waste
eg. carbon dioxide, nitrogenous waste
Why is excretion important?
- maintains metabolism and homeostasis
- removes metabolic wastes (eg. carbon dioxide and nitrogenous waste) from the body
What are the functions of the liver?
- to detoxify (toxic products of metabolism + some ingested toxins)
- to produce bile
- to produce and store glycogen
- to deaminate excess amino acids
- to convert one amino acid into another
What is the function of the gall bladder?
store bile
What is the function of the common bile duct?
transport bile from the gall bladder to the intestine
What is the function of the hepatic artery?
deliver oxygenated blood to the liver
What is the function of the hepatic portal vein?
carry products of digestion in deoxygenated blood from the intestines to the liver
What is the liver made up of?
two lobes which are made up of lobules (6 sided structure)
What are Kuffer cells?
specialised macrophages in the liver that destroy bacteria
What are hepatocytes?
specialised liver cells which break down proteins (deamination), produce bile, detoxify, etc
What is a sinusoid?
a channel blood travels along through a liver lobule
What is a bile canaliculus?
a channel bile travels through in a liver lobule
What happens in a liver lobule?
- blood from hepatic artery and portal vein joins together
- blood travels through sinasoids
- hepatocytes produce bile and break down toxic substances into less toxic substances which rejoin the blood
- blood goes into the central vein and then back into the hepatic vein
- bile travels down bile canaliculus to the bile duct
Explain the liver’s function in carbohydrate metabolism
- produces and stores glycogen
- breaks down glycogen back into glucose when more glucose is needed
Explain the liver’s function in transamination
converts one amino acid into a different amino acid
Explain the liver’s function in deamination
-removes amine group from excess amino acids to produce ammonia
(amino acid + oxygen → keto acid + ammonia)
-ammonia is very soluble and very toxic so is converted into urea which is less soluble and less toxic
(ammonia + carbon dioxide → urea + water)
Why does ammonia need to be converted into urea?
- urea is less toxic and less soluble than ammonia
- urea is fine in small amounts in the blood stream
- urea can be transported to the kidneys for excretion
Explain the liver’s function in detoxification
- detoxifies alcohol, antibiotics, steroid hormones, etc
eg. ethanol → ethanal → ethanoate (acetate) which can be used in the Krebs cycle - causes fatty liver, NAD is used to oxidise fatty acids in the liver but when it is used to oxidise alcohols instead, it can’t oxidise fatty acids so they accumulate as fat in the liver
What is the ornithine cycle?
the process in the liver that converts ammonia into urea
What happens in the ornithine cycle?
- ornithine is converted to citruline by the addition of ammonia and CO2 and the removal of water
- this also requires 1 molecule of ATP
- citruline is converted into arginine by the addition of ammonia and removal of water
- arginine is converted back into citruline by the addition of water, producing urea in the process
What is the structure of the kidney?
- three areas: cortex, medulla and pelvis
- ureter leads from kidneys to the bladder
- renal artery carries blood into kidneys
- renal vein carries blood out of kidneys
- made up of hundreds of nephrons
What is the function of the kidney?
-produce urine by filtering out water, urea and ions aka -ultrafiltration -selective reabsorption -water reabsorption -osmoregulation
What are the parts of a nephron?
- Bowman’s capsule
- PCT (proximal convoluted tubule)
- Loop of Henle
- DCT (distal convoluted tubule)
- collecting duct
Where does ultrafiltration occur?
in the Bowman’s capsule
in the nephrons of the liver
What happens in ultrafiltration?
- blood flows to the glomerulus through the afferent arteriole and leaves through the efferent arteriole
- the afferent arteriole is wider than the efferent arteriole
- this builds up a high hydrostatic pressure, meaning the blood in the glomerulus is always under high pressure
- the pressure in the glomerulus is therefore higher than in the Bowman’s capsule
- this forces the fluid to move from the glomerulus into the Bowman’s capsule
In order for the fluid to move from the glomerulus into the Bowman’s capsule (in ultrafiltration), what layers must the fluid pass through?
- endothelium of capillaries
- basement membrane
- epithelial cells of Bowman’s capsule (podocytes)
How is the endothelium of the capillaries adapted for ultrafiltration?
-has fenestrations between cells (allows blood plasma and substances through)
How is the basement membrane adapted for ultrafiltration?
-fine mesh of collagen fibres and glycoproteins (acts as a filter to prevent molecules with a Mr larger than 69000 passing through)
How are podocytes adapted for ultrafiltration?
-specialised shape with major processes (projections which create gaps between cells for fluid to pass through into the lumen of the Bowman’s capsule)
What is filtered out of the blood in ultrafiltration?
anything with a Mr less than 69000
- water
- amino acids
- glucose
- urea
- inorganic ions
What is left in the capillaries after ultrafiltration?
anything with a Mr greater than 69000
- blood cells
- large plasma proteins
Why is it beneficial that large plasma proteins stay in the capillaries after ultrafiltration?
they maintain water potential
What is the glomerulus?
bundle of capillaries under high pressure next to the Bowman’s capsule
What is the Bowman’s capsule?
the start of a nephron where ultrafiltration occurs
Where does selective reabsorption occur?
in the PCT (proximal convoluted tubule)
in the nephrons of the liver
What is reabsorbed in selective reabsorption?
- all of the glucose and amino acids
- some ions and water
What happens in selective reabsorption?
- Na+ are actively transported from cells in the PCT lining into the blood through sodium-potassium ion pumps
- decreases Na+ conc in cells
- Na+ from filtrate (in lumen of nephron) move into the cells in the PCT lining via facilitated diffusion through co-transporter proteins, taking glucose and amino acids with it
- glucose and amino acid concs in the cells increase, causing them to diffuse into the tissue fluid/blood
- Na+ continue being pumped into the blood, decreases its conc in the cells, so that it continues so that more glucose and amino acids can be transported
- water also moves via osmosis to maintain water potential (which changes due to Na+ conc changing)
How are larger molecules reabsorbed?
by endocytosis
-using ATP
Why does some water get reabsorbed in selective reabsorption?
to maintain water potential, which varies because of changing concentrations of sodium ions
Where does water reabsorption occur?
in the loop of Henle
in the nephrons in the medulla of the kidney
Why is water reabsorption necessary?
to increase the conc of salt in the tubule fluid, so that they dissolve into the medulla, giving it a low water potential
What happens in water reabsorption?
- fluid travels down descending limb of loop of Henle (which has a low concentration of Na+/Cl-)
- water leaves tubule via osmosis (descending limb is permeable to water) and Na+ and Cl- diffuse into the tubule from the tissue fluid of the medulla
- fluid travels up ascending limb of loop of Henle
- near bottom of ascending limb, Na+ and Cl- diffuse out of the tubule into the tissue fluid of the medulla
- higher up the ascending limb, Na+ and Cl- are actively transported out of the tubule
- water can not move out (ascending limb is impermeable to water)
- this decreases the water potential of the medulla
Are the walls of the descending limb permeable or impermeable to water?
permeable
Are the walls of the ascending limb permeable or impermeable to water?
impermeable
What happens in the DCT (distal convoluted tubule)?
-active transport to adjust concentrations of ions
What is osmoregulation?
the control of water potential in the body
- done by altering the permeability of the collecting duct
- negative feedback
Where does osmoregulation occur?
in the collecting duct
in the nephrons of the kidney
What is osmoregulation controlled by?
hypothalamus in brain
What is ADH?
hormone involved in osmoregulation (controls how much water is removed from the blood)
- produced in the posterior of the pituitary gland
- acts on the collecting ducts in the kidney
Where is ADH produced?
in the posterior of the pituitary gland
What happens to cause ADH to be produced?
- osmoregulators (in the hypothalamus) monitor water potential of the blood
- when water potential is very low, the osmoregulators shrink (crenate)
- the shrinking of osmoregulators stimulates neurosecretory cells
- neurosecretory cells respond by releasing ADH into blood
- ADH travels in the blood to the collecting ducts in the kidney
What happens (involving ADH) when water levels in the blood are too low?
- ADH binds to receptors on cell surface membranes of collecting duct and triggers cAMP
- cAMP causes vesicles containing aquaporins to fuse to the cell membranes of cells in the collecting duct on the side closest to the tissue fluid
- the insertion of aquaporins makes the collecting duct walls more permeable to water
- more water is reabsorbed by osmosis into the tissue fluid and blood stream
What happens (involving ADH) when water levels in the blood are too high?
- less ADH binds to the receptors on the cell surface membranes of the collecting duct cells so cAMP levels fall
- the cell surface membrane folds inwards to create vesicles, which remove aquaporins from the membrane
- the removal of aquaporins makes the collecting duct walls more permeable to water
- less water is reabsorbed
- more urine with a more negative water potential is produced
What are neurosecretory cells?
specialised nerve cells that secrete ADH
What are aquaporins?
water-permeable channel proteins
What happens when the water potential of the blood is back to normal?
- ADH is no longer needed
- less ADH is released
- ADH is slowly broken down
- collecting duct is no longer stimulated
Why is it important to break ADH down?
- prevents constant stimulation of collecting duct
- prevents too much reabsorption
How should a kidney be disected?
cut in half lengthways
What can be done in a kidney dissection to make the nephrons more visible?
- add hydrogen peroxide
- wipe off effervescence with filter paper
- nephrons should appear white
What can cause kidney failure?
- infections/diseases
- raised blood pressure
- genetic conditions
- diabetes
- obesity
What problems arise from kidney failure?
- waste products (eg. urea) build up (can damage cells)
- fluid accumulates in tissues (excess water can’t be removed by kidneys) so parts of the body swell up
- electrolytes (ions) become unbalanced in cells (blood becomes acidic, bones become brittle, etc)
- anaemia
What is glomerular filtration rate (GFR)?
the rate blood is filtered from the glomerulus
- used as a measure of kidney function as it shows how well the kidneys are filtering
- done by a blood test
What does GFR stand for?
glomerular filtration rate
How can kidney failure be treated?
- kidney transplant
- dialysis (haemodialysis or peritoneal dialysis)
What happens in haemodialysis?
blood is passed through a dialysis machine…
- arterial blood leaves arm through tube and passes through a pump into the dialysis machine
- in the dialysis machine, the blood is separated from the dialysis fluid by a partially permeable membrane
- the dialysis fluid is low in salt and urea so that they move out of the blood into the dialysis fluid
- the dialysis fluid contains normal levels of glucose to ensure there is no net movement of sugars out of the blood
- the blood then passes through a bubble trap to ensure there aren’t any bubbles in the blood, before returning to a vein in the arm
What happens in peritoneal dialysis?
done inside body using peritoneum (natural membranes in abdomen lining)…
- dialysis fluid enters the abdomen using a catheter
- it is left for several hours so that dialysis can occur across membranes
- urea and excess mineral ions pass out of the capillaries, acrodd the peritoneal membranes and into the dialysis fluid
- the dialysis fluid is drained off and discarded
What are the advantages of peritoneal dialysis compared to haemodialysis?
- more flexible
- can be done at home/can carry on with normal life while it’s being done (compared to having to be in hospital for haemodialysis)
- less expensive
What are the advantages of dialysis?
- keeps patient alive until a kidney is available
- less risky than surgery required for a transplant
- readily available
What are the disadvantages of dialysis?
- can’t have a very normal life style (lots of time spent in hospital, etc)
- risk of blood injection (haemodialysis) or abdominal infection (peritoneal dialysis)
What is a kidney transplant?
when a donated kidney is implanted into a patient’s body to replace a damaged kidney
What are the advantages of having a kidney transplant?
- more convenient (no need for frequent appointments needed for dialysis)
- cheaper in the long run
What are the disadvantages of having a kidney transplant?
- body could reject the transplant
- have to take immunosuppressants, which increase risk of infection
- surgery to have transplant is risky
- have to wait for a suitable donor
- new kidney isn’t guaranteed to last a long time
Why are patients who have had a kidney transplant given immunosuppressant drugs?
prevents body rejecting donated kidney
What are monoclonal antibodies?
antibodies from a clone of cells produced to target particular cells or chemicals in the body
-used in pregnancy tests
How are monoclonal antibodies made?
- antigen is injected into mouse
- mouse produced b cells (plasma cells) which make the correct antibody
- the b cells are fused with human tumour cells (myelomas) to produce a hybridoma cell
- the hybridoma cells reproduce rapidly to produce a lot of clones which can produce the antibody
How does a pregnancy test work?
- urine moves along test strip via capillary action
- at the mobile Ab strip, there are monoclonal antibodies (with blue dye beads attached) complementary to hCG, which any hCG present binds to, forming hCG-antibody complex
- at the test strip, there are hCG antibodies, which any hCG-antibody complexes bind to, creating a blue strip
- if no hCG-antibody complexes are present, nothing binds so a blue line is not created
- at the check strip, there are immobile hCG antibodies which any monoclonal antibodies bind to, creating a blue control strip
What substance does a pregnancy test test for?
hCG (hormone produced by developing placenta)
What are anabolic steroids?
drugs which mimic the action of testosterone and stimulate muscle growth
How is urine tested in drug testing?
gas chromatography and mass spectrometry
OR
immunoassay
