5.1.2 Excretion Flashcards
excretion
removal of metabolic waste products from the body.
important in maintaining metabolism as they may be toxic if they build up and homeostasis as it maintains constant levels of stuff in blood
examples of metabolic waste products
- CO2 (from resp, excreted by lungs)
- bile products (breakdown of Hb, excreted from liver into small intestine)
- nitrogenous waste products (breakdown of excess a.as by liver –> urea/uric acid which are excreted by kidney)
what are the 2 main organs involved in excretion?
kidney and liver
what makes up the portal triads in the liver? (at the edges of hexagonal lobules)
hepatic portal vein (blood loaded w/ products of digestion from intestines)
hepatic artery
bile duct
what is the central vein in the liver?
hepatic vein
sinusoids
blood from hepatic artery and hepatic portal vein mixes, increasing O2 content of blood from portal vein so hepatocytes can be supplied with enough O2 for needs
surrounded by hepatocytes
contain Kupffer cells
canaliculi
bile is secreted into canaliculi and drains into bile ductules, which take it to gall bladder
bile flows in opposite direction to blood
function of Kupffer cells
ingest foreign particles and act as resident macrophages of liver
help protect against disease
function of hepatocytes
secrete bile into bile canaliculi from breakdown of Hb
function of hepatocytes
secrete bile into bile canaliculi from breakdown of Hb
convert a.as to NH3 and then to urea in ornithine cycle
detoxification
functions of the liver (outline)
- carbohydrate metabolism (glycogen storage in granules)
- deamination of excess amino acids
- transamination
- detoxification
carbohydrate metabolism
when blood glucose levels rise, insulin is produced and stimulates hepatocytes to convert glucose into glycogen for storage (glucogenesis)
when blood glucose levels fall, glucagon allows glycogen –> glucose (glycogenolysis)
deamination and ornithine cycle
body can’t store a.a.s so hepatocytes have to remove amine group of excess a.as and convert a.a –> NH3 (deamination)
NH3 is toxic so enters the ornithine cycle where it is converted to urea (less toxic). Urea is excreted in the kidneys and remaining a.as are used in respiration or converted to lipids for storage
detoxification
toxic things detoxified
eg. Alcohol (ethanol)
alcohol dehydrogenase breaks down
ethanol -> ethanal -> ethanoate
eg. Hydrogen peroxide (H2O2)
hepatocytes contain catalase that breaks down H2O2 -> H2O +1/2O2
glycogenolysis
glycogen –> glucose
stimulated by glucagon
stages of the ornithine cycle
Ornithine + NH3 + CO2 –> Citrulline + H20
Citrulline + NH3 –> Arginine + H2O
Arginine + H2O –> Urea + Ornithine
total 2NH3 in 1CO2 in 1H2O in, 2H2O out 1Urea out
transamination
conversion of one a.a to another to correct dietary imbalance
function of the kidney
excretion of urea
osmoregulation
ureter
TWO - one from each kidney. Urine passes down
ureter
TWO - one from each kidney pelvis. Urine passes down into bladder