topic 5.1.2: excretion Flashcards
define excretion
removal of toxic waste products of metabolic reactions
what is the overall function of the liver?
-stores glycogen, detoxifies blood and stores urea
give the name, function and structure of the 3 blood vessels into and out of the liver
HEPATIC ARTERY- supplies oxygenated blood (narrow)
HEPATIC PORTAL VEIN- supplies products of digestion (branched)
HEPATIC VEIN- carries blood away
describe and explain the structure of hepatocytes
many mitochondria- more atp to maintain high metabolic rate
large nuclei- active dna transcription
prominent golgi apparatus- high level of protein processing
describe and explain the structure of sinusoids
blood from hepatic artery and portal vein mixes
lined with hepatocytes- thin for short diffusion pathway
increased O content to supply hepatocytes
contain kupfer cells- act as macrophages
describe and explain the structure of canaliculi
spaces where bile is gathered
bile is secreted from hepatocytes from breakdown of RBCs then passes through bile ducts into gallbladder
what are the 3 main functions of the liver?
carb metabolism, deamination and detoxification
describe carbohydrate metabolism in the liver
hepatocytes involved in homeostatic control of glucose
blood glucose rises- insulin stimulates glycogenesis
blood glucose falls- glucagon stimulates glycolysis
describe deamination in the liver
removal of amine group from a molecule
excess diet protein cannot be stored so amine group removed and converted to ammonia
co2 added to ammonia to reduce toxicity to produce urea
what is the ornithine cycle
production of urea from ammonia through a set of enzyme controlled reactions
describe detoxification in the liver
the neutralisation and breakdown of unwanted chemicals such as alcohol
eg hydrogen peroxide is split into O2 and H2O by catalase
ethanol can be broken down by alcohol dehydrogenase into ethanal then ethanoate
what is the main function of the kidney
responsible for excretion of nitrogenous waste and osmoregulation
give the name and function of the 2 main blood vessels in the kidney
renal artery supplies blood
renal vein carries blood away
what are the 3 distinct layers of the kidney
cortex- dark outer layer containing capillary networks carrying blood to nephrons
medulla- contains nephrons
pelvis- where urine collects before leaving for ureter
describe the structure of a nephron
glomerulus- filters small solutes from blood (contained in bowman’s capsule)
proximal convoluted tubule- reabsorption
descending loop of henle- water passes out of filtrate
ascending loop of henle- reabsorption of ions from filtrate
distal convoluted tubule- selectively secretes and absorbs ions
collecting duct- reabsorbs solutes and water from filtrate
where does ultrafiltration take place
glomerulus
how does blood enter the glomerulus
afferent arterioles
what are the 3 sieve membranes involved in ultrafiltration
CAPILLARIES- fenestrations allow filtrate through endothelial cells
BASEMENT MEMBRANE- made of network of collagen fibres, most plasma contents can pass through but RBCs and proteins are retained
PODOCYTES- in walls of bowmans capsule, extensions called pedicels that wrap around capillaries forming slits to filter fluid further
how does blood leave the glomerulus
efferent arteriole (narrower diameter so higher pressure)
what does the filtrate entering the capsule contain
glucose, salt, urea, and other substances in same conc as blood plasma
why does selective reabsorption occur
filtrate is hypotonic to blood plasma so most filtered substances need to return
what happens in the proximal convoluted tubule
all glucose, amino acids, vitamins and hormones actively transported into blood
most NA+ actively transported back, CL- and H2O follows
diffusion into capillary networks
what happens in the descending limb of the loop henle
filtrate is isotonic with blood and tissue fluid
upper part is impermeable to water, lower part is permeable
water moves into tissue fluid in medulla through osmosis down conc gradient, then into blood
not permeable to NA+ and CL-
tissue fluid gains conc which sets up gradient
what happens in the ascending limb of the loop of henle
lower section is permeable to ions and they move out through diffusion down conc gradient
in upper section ions are actively pumped out to set up conc gradient
impermeable to water
filtrate becomes more and more dilute, tissue fluid becomes more and more concentrated
what happens in the distal convoluted tubule
permeability varies with adh levels
if body lacks salt, NA+ actively pumped out with CL- following down electrochemical gradient
water can also leave in presence of adh
what happens in the collecting duct
passes down through medulla
water moves out through osmosis down conc gradient controlled by adh
what is osmoregulation
the process of controlling the amount of water and ions in the blood
what do osmoreceptors do
in hypothalamus
detect changes in water potential. when low, water leaves through osmosis down conc gradient, causing them to shrivel and stimulate posterior pituitary gland to produce more adh
describe the mechanism of adh action
released from p gland, carried in blood to collecting duct
binds to receptors on cell membranes (1st messenger)
triggers formation of cyclic amp (2nd messenger) which relays the signal to molecules inside
vesicles containing aquaporins fuse with membrane which makes it permeable to water
negative feedback loop
what can cause kidney failure
infection, high bp, genetics, physical damage
what can kidney failure cause
large molecules filter out of blood into filtrate, build up of urea in blood
how is kidney failure detected
glomerular filtration rate measured by testing creatine levels (breakdown product of muscles so high levels may indicate kidneys aren’t filtering properly)
how does haemodialysis work
blood enters dialysis machine, dialysis fluid separated by partially permeable membrane. fluid contains no urea and normal plasma levels for glucose and mineral ions
multiple times a week, may require careful diet
how does peritoneal dialysis work
utilises peritoneum in lining of abdomen
dialysis fluid introduced using catheter
fluid left for several hours then drained
what are the drawbacks of a kidney transplant
immunosuppressants required, lack of donors
how are monoclonal antibodies used in pregnancy tests
wick of test submerged in urine, immobilised antibodies in window bind to HCG/antibody complex, more immobilised antibodies bind to mobilised antibodies regardless of whether they are bound to HCG as a control
