excretion Flashcards
excretion definition
the process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body
- it is a key part of homeostasis
outline the importance of excretion
metabolic waste products can have serious negative impacts on the body if left to accumulate
mammals are very large + active + endotherms - this means they have high metabolic rates and so produce lots of metabolic waste
give 5 examples of metabolic waste substances
CO2
nitrogenous waste - ammonia, urea, uric acid
bile pigments
how is CO2 produced and why does it need to be excreted
produced during decarboxylation of respiratory substrates
high levels cause cell damage as blood ph falls below normal range - acidosis
how is CO2 excreted
breathed out from lungs
how is ammonia produced and why does it need to be excreted
produced during deamination of excess amino acids
high levels increase the ph of cytoplasm and interferes with metabolic processes e.g. respiration and receptors for neurotransmitters in the brain
how is urea produces and why does it need to be excreted
produced in the orthonine cycle in liver cells
it can readily diffuse into cells, so high levels will decreases cell water potentials causing increased water uptake by osmosis, causing them to eventually burst
how is uric acid produced and why does it need to be excreted
produced in adenine + guanine (purine) break down in liver
high levels can result in uric acid forming crystals in joints causing gout (a form of arthritis)
how are nitrogenous compounds excreted
in urine - after some processing/detoxifying
how are bile pigments produced and why do they need to be excreted
produced during breakdown of haemoglobin - specifically haem groups
high levels accumulate in skin and turn it yellow - jaundice
how are bile pigments excreted
in faeces
another toxic byproduct is H2O2 - how does the body remove this
it is broken down by catalase into H2 and O2
outline 3 functions of the liver
- detoxification + breakdown of toxic substances
- producing excretory waste (urea)
- glycogen storage
outline the blood vessels that run through the liver
hepatic artery - brings liver oxy blood from the heart
hepatic vein - takes deoxy blood form liver back to heart
hepatic portal vein - brings deoxy blood from gut to liver
what is the function of the hepatic portal vein
it allows the liver to metabolise the nutrients absorbed into blood in small intestine
what is good about the many blood vessels that pass through the liver
liver requires a constant blood supply to carry out processes
what is the function of the gall bladder
to store bile salts and bile pigments
what are bile salts
found in gall bladder, these help to digest fat
how are the liver and the gall bladder connected
via the bile duct
bile canaliculi definition
small vessels that drain bile from hepatocyles to bile duct
hepatocyte definition
liver cells specialised to carry out necessary functions
what do hepatocytes do
- synthesise proteins
- transform and store carbs
- synthesise cholesterol and bile salts
- form bile and secrete into bile duct + canaliculi
- absorb substances from blood
- secrete hormones
hepatic lobule definition
small divisions of the liver made of hepatocytes, shaped like irregular polygons, consisting of a portal triad and a central hepatic vein, as well as sinusoid vessels - basic functional units of the liver
these are separated from each other by connective tissue consisting of cells that secretes an extra cellular matrix
sinusoid vessels definition
these are vessels adapted for the exchange of materials between blood and hepatocytes
they have very thin walls made of one layer of thin cells and are wide so have slower blood flow
they also contain kupffer cells - a type of phagocyte
what 3 vessels are in a portal triad
bile duct
hepatic artery
hepatic portal vein
what is orthonine
an amino acid
give the equation for deamination
amino acid + O2»_space;> keto acid + NH3
what is a keto acid
an acid with a carboxylic group and a ketone group
give 2 uses for keto acids
these can be used in the krebs cycle or they can be converted into cholesterol/lipids
outline the orthonine cycle
goes from orthonine»_space;> citrulline»_space;> argenine»_space;> back to orthonine
orthonine + NH3 + CO2 + ATP - H2O = citrulline
citrulline + NH3 + ATP - H2O = argenine
argenine + H2O = urea CO(NH2)2
overall equation:
2NH3 + CO2»_space;> CO(NH2)2 + H2O
what is the point of the orthonine cycle
to remove excess ammonia by converting it into urea
outline the process of alcohol detoxification
ethanol is oxidised by NAD and the enzyme ethanol dehydrogenase - this forms ethanal
ethanal is oxidised by NAD and the enzyme ethanal dehydrogenase - this forms ethanoate/acetate
this is added to coenzyme A - this forms acetyl coA
when NAD is used in oxidation, it gains a H to become reduced - NADH
why can excessive drinking cause fat gain and liver disease
excessive drinking means there is a lot of NAD used up in alcohol detoxification
NAD is also needed for the liver to break down fat, so less NAD = less fat breakdown = more fat being deposited
over time this can lead to liver disease
what happens to acetyl coA after alcohol detoxification
it can be used in respiration
if acetyl coA can be used in respiration why doesn’t drinking alcohol cause an increase in energy
theoretically this would be true, however alcohol is also a depressant, as it blocks nervous receptors
what are 2 important functions of kidneys
osmoregulation - regulation of water content of the blood - this is essential for maintaining healthy blood pressures
excretion - kidneys excrete the toxic waste products of metabolism e.g. urea, as well as substances in excess of requirement e.g. salts