excretion Flashcards
define the term of excretion
the process of eliminating waste products of metabolism which would otherwise be toxic e.g urea and co2
explain the importance of removing co2 from bod
co2 from respiration combines reversibly with water to give carbonic acid which in turn dissociates to ives hydrogen ions and hydrocarbonate ions
co2 is excreted via the lungs
the respiratory centre in the medulla oblongata increases the rate of breathing when co2 conc in blood rises. the kidnets remove hydrogen ions to maintain blood PH
explain the importance of removing nitrogenous waste
mammals can’t store proteins of aa, so excess is converted into fats or carbs for storage, or for use in respiration.
the amino group (NH2) of each aa is removed during deamination in the liver, forming a very soluble but very toxic compound ammonia.
this is combined with co2 from r/s in the ornithine cycle in the liver, to give much less toxic but soluble enough, urea (removed from blood by kidneys).
describe structure of liver
made of of several lobes
hepatic artery brings oxygenated blood from the aorta and the hepatic artery brings blood from the gut.
the hepatic vein takes blood to the vena cava.
liver cells, or hepatocytes are arranged in lobules
describe formation of urea in the liver
deamination- excess aa are broken down. the amino group is removed and forms ammonia NH3. the rest of the amino acid forms a Keto acid- which can be respired to release energy or converted to fat to be stored.
ammonia=soluble and v toxic- can’t be allowed to remain in the bod. so combines with co2 to make urea in the liver. urea still toxic but much less soluble and dangerous than ammonia.
the liver releases urea into the blood- dissolves into in the plasma and transported all over bod, removed from blood in kidneys.
how is ammonia converted to urea
in the ornithine cycle. ornithine is an amino acid- but not on that’s used to make proteins. the cycle requires input of energy in the form of ATP
takes in ammonia co2 and ATP to make urea
describe the roles of the liver in detoxification
liver also important in detoxification of alcohol, antibiotics steroid hormones and other unwanted toxic substances. taken up by hepatocytes and then broken down. e.g liver cells absorb ethanol. in their cytoplasm, the enzyme ethanol dehydrogenase catalyses ethanol—-> ethanal–> ethanoate (acetate) ——-> enters krebs cycle
what is the enzyme that catalyses the breakdown of ethanol
ethanol dehydrogenase also known as alcohol dehydrogenase.
describe what happens to ethanol in the liver
ethanol is first converted to ethanal by ethanol dehydrogenase and then to ethanoate by aldehyde dehydrogenase, this can enter the krebs cycle in mitochondria and be metabolised to produce ATP.
what happens if NADH accumulates?
less NAD is available for other reactions. the ethanal is then taken up by the cell’s mitochondria, where it is further oxidized to acetate, which may enter the krebs cycle or be used to synthesis fatty acids
describe structure of the kidneys
each kid made of of a million tubule called nephrons and their associated blood vessels
outerlater = the cortex
inner layer= the medulla
the kidney receives blood from the aorta via the renal artery and returns it to the vena cava via the renal vein
describe structure of the nephron
bowman’s capsule in the cortex and proximal convoluted tubule then the loop of hence which lies in the medulla
the ascending limb leads to another coiled tube in the cortex called the distal convoluted tubule, which leads to a collecting duct
a number of nephrons feed into the same collecting duct which opens into the pelvis of the kidney.
bowmans capsule had an afferent arteriole bringing blood from the renal artery to the glomerulus. the efferent arteriole draining this network is smaller in diameter than the afferent arteriole. the efferent article divides into capillaries that run close to the convoluted tubules and loop of hence before joining as venues to take blood back to the renal vein.
describe and explain the production of urine
the filtration membrane allows all molecules below a certain size to pass through.
what’s the importance of producing urine
to avoid the body being depleted of useful materials, the process of selective reabsorption of the substances the body can’t afford to lose follow ultrafiltration. at the same time most of the water lost from the blood during ultrafiltration is returned to the blood and the hormonally controlled mechanism of osmoregulation takes place
ultrafiltration
the afferent arteriole supplying the capillaries of the glomerulus is wider than the efferent arteriole. this, and the short distance of the kidneys from the aorta provides the necessary hydrostatic filtration pressure.
basement membrane of glycoproteins surrounding the endothelium of the capillaries followed by an inner layer of the bowmans capsule consisting of highly adapted podocytes, which provide support for the membrane with minimum interruption to filtration
water and crystalloid solutes (inc urea) are filtered from the blood into the bowman’s capsule. cells, platelets and colloidal solutes, including the blood proteins with a relative molecular mass greater than 69,000 do not pass through undamaged basement membrane.
