5.2 excretion Flashcards
Excretion
The removal of metabolic waste from the body
Metabolic Waste
Substance that’s produced in excess by the metabolic processes in the cells
It may become toxic
What products must be excreted
Carbon dioxide
Nitrogenous compounds
Bile
name and explain the role of the excretory organs
Lungs - carbon dioxide produced by respiration diffuses into the alveoli to be excreted
Liver - converts excess amino acids to urea , substances produced are passed into the bile to be excreted
Kidneys - kidneys remove urea from the blood to be excreted by the urethra
Skin - sweat contains range of substances (urea, uric acid, ammonia)
Importance of excretion
products of metabolism if they are left to build up can become harmful
(CO2 and ammonia are toxic)
Interfere with cell processes by altering the pH - so metabolism is prevented
Other metabolic products - act as inhibitors reduce enzyme activity
Importance of removing CO2
CO2 is transported as hydrogencarbonate ions which dissociates into H+ (and HCO3-)
H+ = affect pH = interferes with bonds in the haemoglobin = changes tertiary structure = reduces affinity for oxygen
H+ can also bind to Hb = haemoglobinic acid
CO2 can bind to Hb = carbaminohaemoglobin acid
both reduces oxygen transport
Importance of removing nitrogenous compounds
Body can’t store excess amino acids
Transported to the liver and the potentially toxic amino acid group is removed (deamination )
Initially forms ammonia and keto acid (toxic)
Converted to less soluble and toxic urea - taken to kidneys to be excreted
Keto acid can be used in respiration or converted to fat/ carbohydrate
name the components of the liver
hepatic artery
hepatic portal vein
hepatic vein
hepatocyte cells
lobules
kupffer cells
sinusoid
bile canaliculas
bile duct
desribe the role of the hepatic artery and the hepatic portal vein
h. artery = oxygenated blood from the heart travels from the aorta via the hepatic artery into the liver - liver cells are very active so lots of oxygen used in respiration
h.p. vein = deoxygenated blood from the digestive system that contains lots of nutrients, may also contain toxic compounds which can be removed by liver
describe the role of the hepatic vein
blood is removed from the liver by the hepatic vein, it rejoins the vena cava and the blood returns the body to bodys normal circulation
describe the role of the bile duct and the bile canaliculus
bile is made in the liver, released into the bile canaliculus, this joins to the bile duct where it transports thebile to the ball bladder
what are liver cells called
hepatocytes
what is the liver made up of/ split into
hepatocytes
liver is spilt into lobes which is further split into hexagonal lobules
what are inter lobular vessels
the hepatic artery and hepatic portal vein splits into smaller vessels - which run between and parallel to the lobules
what is a sinosoid and the role
wide capillary that blood passes through large hepatocyte lined spaces
the blood from the h.a and h.p.v mixes and passes along - as blood passes through the oxygen and nutrients can be removed by the hepatocyte cells
what is a kupffer cell
macrophage that moves about within the sinusoid and breaksdown and recyles rbc
Main functions of the liver
Storage of glycogen
Detoxification
Deamination/ formation of urea
Other functions of the liver
Controls blood glucose levels/ amino acid levels / lipid levels
Synthesis of bile/ plasma proteins/ cholesterol
Synthesis of red blood cells in the foetus
Breakdown of hormones
Destruction of red blood cells
Explain the role of liver in storing glycogen
storage of glycogen makes up about 8% of the weight
Glycogen forms granules in the cytoplasm of the hepatocytes
Can be broken down into blood
Explain what detoxification is and how it works
Detoxification of substances that may cause harm
Toxins broken down by oxidation, reduction, methylation or combination with other molecules
Enzymes
- catalase breaks down hydrogen peroxide
- cytochrome P450 breaks down drugs
Detoxification of alcohol
Broken down in hepatocytes by enzymes
Ethanol - ethanol dehydrogenase -> forms ethanal + H+
NAD takes H away
Ethanol - ethanal dehydrogenase -> ethanoic acid + H+
NAD takes H away
bonds with coenzyme A = acetyl coenzyme A used in respiration
Explain how urea is formed
Excess amino acids need to be converted and excreted
1. Deamination - amine group is removed from the amino acid, produces ammonia (rest of amino acid is a keto group - used in respiration)
2. The ornithine cycle - ammonia broken down to urea
Explain what happens in the orinthine cycle
Ammonia + CO2 = citrulline + H20
Citrulline + ammonia = arginine + H20
Arginine + H20 = urea + ornithine (recycled and used again)
overall word equation of ornithine cycle
ammonia + CO2 -> urea + H20
name the structures of the kidney
capsule
cortex
medulla
pelvis
ureter
renal artery
renal vein
nephrons
what are nephrons
functional unit of the kidney and is tiny tubules
name the features of a nephron (in order)
bowmans capsule
glomerulus
proximal convoluted tubule
loop of henle
-descending limb
-ascending limb
distal convoluted tubule
collecting duct
pelvis
what is the bowmans capsules and glomerulus
surround the glomerulus and fluid is pushed into this by ultrafiltration
a knot of capillaries formed from the renal artery
define ultrafiltration
filtration of the blood under pressure and fluid gets pushed and filtered into the bowmans capsule
name the 3 layers of ultrafiltration
the endothelium of the capillary
the basement membrane
the epithelial cells of the bowmans capsule
desribe the role of the endothelium of the capillary
narrow gaps between cells of the endothelium of the capillary walls
gaps/pores
allow blood plasma and dissolved substances to pass out of the capillary
describe the role of the basement membrane
fine mesh of collagen fibres and glycoproteins
acts as a filter to prevent the passage of molecules with mass greater then 69000 or large molecules
proteins get held in the capillaries
describe the role of the epithelial cells of the bowmans capsule
cells called podocytes that have specialised shape - finger like projections
creates gaps between cells so fluid from the blood in the glomerulus can pass between the cells
what is filtered out of the blood
water
amino acids
glucose
urea
ions
what is left in the capillary during ultrafiltration
blood cells and proteins
define selective reabsorbtion
reabsorbing molecules using active transport and cotransport
function of a nephron
to reabsorb about 85% of fluid in selective reabsorption
leaves product of urine which has low water potential and a high concentration of solutes
what part of the nephron is used for selective reabsorption
proximal convoluted tubule
specialised features of the PCT cells for selective reabsorption
cell surface membrane is highly folded = microvilli = increases surface area for reabsorption
contains cotransporter proteins that transport glucose or amino acids from the tubule into the cell
Na K pumps in membrane
many mitochondria = produce lots of ATP
mechanism of reabsorption
- Na ions are actively pumped out of the cells lining tubule into the blood
- concentration of Na decreases inside
- creates conc. gradient and Na ions diffuse back into cell by a cotransport protein bringing glucose or an amino acid
- causes water to move in by osmosis
- glucose and amino acids diffuse into the blood
role of the loop of henle
reabsorption of water
decreases water potential in the tissue fluid of the medulla (make more salty)
descending limb is permeable to water
ascending limb is not permeable to water and uses active transport to remove ions from filtrate
water potential surrounding collecting duct is lower so water removed from collecting duct
name the components of the loop of henle
proximal convoluted tubule
descending limb
ascending limb
distal convoluted tubule
collecting duct
how are water and ions reabsorbed in the loop of henle
filtrate passes from PCT to the descending limb of loop of henle
water moves out of the d.l by osmosis into the tissue fluid/medulla
at the bottom of the limb = high concentration of urea + ions as water has left
enters ascending limb = impermeable to water left in, permeable to ions
ions move out by facilitated diffusion and active transport as cotransport proteins become saturated/ conc will even out but ions still need to be removed
urea is left in the filtrate
filtrate enters collecting duct
water moves out of collecting duct
urine passes down c.d to the pelvis
what happens to the water potential as you travel down the loop of henle
decreases more as you go deeper (down collecting duct and descending limb)
explain the concentration changes in the tubule fluid
glucose decreases in conc. as its selectively reabsorbed from the PCT
Na+ actively transported out of the ascending limb = conc falls
urea conc increases as water moves out adn urea actively moved in
conc of Na+ increases as water removed in collecting duct
define osmoregulation
the control of water potential in the body and salt levels
when does osmoregulation happen
kidneys alter the volume of urine produced
walls of collectind duct can be made more or less permeable
conserve less water - walls of CD become less permeable = less water is reabsorbed = more urine produced
conserve more water - walls of CD become more permeable = more water is reabsorbed = smaller volume of urine
how does ADH alter the permeabilitly of the collecting duct
ADH level increases in the blood = detected by receptors in DCT and CD = causes aquaporins to be inserted/ water permeable channels = allows more water to be reabsorbed
ADH level decreases in the blood = cell surface membrane folds inwards = creates new vesicles that remove water permeable channels from membrane = more water passes down CD = more urine which is more dilute
ADH
antidiuretic hormone that controls the permeability of the CD
how is the concentration of ADH adjusted in the blood
osmoreceptors in the hypothalamus - detect water potential in the blood
stimulates neurosecretory cells in the hypothalamus - release ADH store it in the postierior pituitary where it then gets secreted into the blood
negative feedback to control water potential
increase in water potential
detected by osmoreceptors in the hypothalamus
less ADH released from posterior pituitary
CD walls less permeable
less water reabsorbed into blood / more urine produced
decrease in water potential
detected by osmoreceptors in the hypothalamus
more ADH released from posterioir pituitary
CD walls are more permeable
more water reabsorbed into blood/ less urine produced
what will kidney failure cause
death as watse products accumlate (urea)
how can kidney failure be assessed
glomerular filtration rate - the rate at which fluid enters the nephron
analysing the urine for substances eg. proteins
causes of kidney failure
diabetes
heart disease
hypertension
infection
name the treatments for kidney failure
dialysis
- haemodialysis
- peritoneal dialysis
transplant
describe how dialysis works
wate products and excess fluids are removed by passing it over a partially permeable membrane
dialysis fluid contains the correct amount of substances
countercurrent flow allows the substances to move down the concentration gradients
describe the difference between haemogdialysis and peritonal dialysis
haemogdialysis - blood from an artery and passed into a machine, contaons dialysis fluid, heparin added to prevent blood clotting, air bubbles removed before returned to the blood, performed 2-3 times a week - has countercurrent flow
peritoneal - dialysis membrane is the bodys abdominal perionel membrane, tube implanted into abdomen, dialysis fluid fills membrane that surrounds the organs, solution drained after several hours - no countercurrent flow
adavnatges of kidney transplant
freedom from time consuming dialysis
feel physically fitter
improved quality of life
improved self image
no longer chronically ill
disadvantages of kidney transplant
need to take immunosuppressants
need for surgery/ general anaesthetic
need for regualr checks for signs of rejection
side effects of immunosuppressants
how does a pregnancy test work
Hormone (HCG) binds to free monoclonal antibodies
complementary shape
forms antigen antibody complex
this attaches to immobilised monoclonal antibody
so coloured pattern form a line
test zone and control zone
testing for anabolic steroids
anabolic steriods increase protein synthesis
gas chromotography can be used
sample vapourised and passed down tube with absorbant lining
substances dissolve differently in the gas and have a different retention time
creates chromatogram
compared to normal chromatograms
