Excretion Flashcards
in excretion?
Excretion is the removal of waste products secreted by cells from the body
some of the substances we remove from the body aren’t?
metabolic waste products - e.g. faeces
Faeces?
- is an e.g. of a substance that is removed from the body, but its removal is not excretion
- bc most of the matter in faeces hasn’t entered cells or taken part in any metabolic reaction, it’ simply been passing thru the digestive system
what is not excretion?
any matter that has not taken part in a metabolic reaction is not metabolic waste so its removal is not excretion
which part of faeces is excretion?
- faeces contains a small amount of bile pigment (produced by the liver, by a metabolic reaction)
why does CO2 need to be removed?
- can lower blood pH when in high conc
- H+ is produced when CO2 +H2O
- the extra H+ can alter the tertiary structure and funtion of proteins
urea journey?
- Made in liver
- travels in blood to kidney where it’s excreted as urine
urea is stored in?
in the bladder (in urine)
2 blood vessels that carry blood to the liver are?
- hepatic artery
- hepatic portal vein
the hepatic artery?
carries oxygenated blood to the liver (for respiration)
the hepatic portal vein?
- carries deox blood that is high in absorbed nutrients
- the vein carries blood straight from the duodenum - a part of the small intestine
the hepatic vein ?
carries deoxygenated blood away from the liver
bile?
produced by hepatocytes, stored in the gall bladder
blood that is travelling in sinusoids?
- is high ox and high in nutrients (blood from HA and HPV mixes in sinusoids)
- ox gets used up by hepatcoytes
bile?
travels in the opposite direction to blood in the sinusoids, bile travels in bile cannaliculi
hepatocytes?
- main cells of the liver
- metabolically active so many mitochondria
Kupffer cells?
- type of macrophage - engulf pathogens
- clean up liver and protect it from disease
why can’t we store excess amino acids?
bc pH would become dangerously high. AAs contain a nitrogen group (amine group) which makes the molecule alkaline
what is the point of deamination?
- if the AAs was simply removed from the body, the energy that they contain would be wasted
- first, ammonia is removed from the AA, the rest of the molecule is called a keto acid which can be used in respiration
why is it called deamination?
bc the amino group has been removed from the AA
what is the point of the ornithine cycle?
the ammonia produced by deamination is toxic, so it needs to be processed further. Ammonia is turned into less toxic urea.
Ornithine cycle overall equation?
CO2 + 2NH3 (+2H2O) -> (NH2)2CO + H2O
Ornithine cycle shorthand?
O ➡C➡A ➡ O…
Stages of the ornithine cycle?
- O➡C: Ammonia and CO2 are added to ornithine and water is removed , this produced citrulline
- C➡A: Ammonia is combined w citrulline and water is removed, this produces aginine
3: A➡O: water is added to arginine and urea is removed, ornithine is REFORMED
What is the benefit of the ornithine cycle?
uses CO2 and urea up, urea is removed to be excreted
intermediates in the ornithine cycle?
Ornithine
Citrulline
Arginine
functions of liver?
- many functions, one of which is storing carbs for regulating blood glucose conc, DETOXIFICATION
what is stored in the liver?
a polysaccharide made of alpha glucose molecules (glycogen) is stored in the liver.
Glycogen takes us less space than glucose and has less of an osmotic effect
Toxins are?
Any molecule that can harm the functioning of cells
Toxins aren’t always ingested,
some are produced during normal functioning of cells (e.g. CO2 in resp)
the liver detoxifies chemicals by?
modifying them. The liver can do this by methylation, oxidation, reduction or combining w other molecules. These processes change the toxin so that it can’t interact with cells in the same way.
catalase?
Enzyme in the liver that deals w the toxin hydrogen peroxide which is produced during normal functioning in cells. Catalase converts the toxic hydrogen peroxide into water + O2
Cytochrome p450?
- family of proteins involved in detox + many other processes
- this involves e- transport in mitochondria, where it transfers e-s to other mols
- bc it’s able to move e-s, it is able to REDUCE molecules, inclu drugs like cocaine and paracetamol
- this modification affects the functioning and break down of medicinal and recreational drugs
something to consider when desigining drugs?
if drugs enter the body and go straight to the liver where they are reduced, they might not have much effect at all
why must alcohol be broken down?
Bc it interferes w nerve cel functioning - slows them down/ kills them
Ethanol -> ethanal -> ethanoic acid
detoxification of alcohol
ethanol is broken down in a 2 step reaction. The reaction results in the production of ethanoic acid and 2 mols of reduced NADH
steps of detox of ethanol?
in each step H atoms are removed to reduce NAD
1) ethanol converted to ethanal, NAD is reduced, this step is catalysed by ethanol dehydrogenase
2) ethanal -> ethanoic acid, catalysed by ethanAL dehydrogenase, reduced NAD is produced
dehydrogenase enzymes?
Take the H away from something, to make something else reduced
Cirrhosis?
- when lots of alcohol is consumed, it needs to be detoxified using up NAD
- NAD is also used to break down fatty acids
- when NAD is being used to break down alcohol, FAs can’t be broken down
- the unmetabolized fatty acids build up in the liver which is known as cirrhosis
Excretion definition and e.g.?
The removal of waste products of metabolism from the organism
removal of urea by kidneys
Secretion definition and e.g.?
The release of a substance from a cell or tissue.
Production of urea by liver cells, and its release into the blood.
Egestion definition and e.g.?
The removal of material that has never left the gut.
Removal of toxic stomach contents by vomiting.
urea is…
- an e.g. of nitrogenous waste
- product of protein metabolism
- excreted by the kidneys into urine
What if CO2 wasn’t excreted?
- CO2 concentration would increase in the blood.
- Normally, CO2 reacts with water in erythrocytes producing carbonic acid, and the H+ ions produced are buffered by haemoglobin, forming haemoglobinic acid - this prevents blood pH from changing.
- Too much CO2, blood pH would drop, causing acidosis ➡ death
What if urea wasn’t excreted?
- Urea would accumulate in the blood.
* At high concentrations urea is toxic.
Liver location?
- found in the abdomen
- below diaphragm
- closely associated with DS - (HPV and bile)
Liver structure?
• 2 lobes
The liver and the digestive system?
- The liver is closely associated with the digestive system, receiving blood from it via the hepatic portal vein, and
- producing bile which is stored in the gall bladder, draining into the small intestine via the bile duct.
overall liver function?
- turning molecules that enter the liver ➡different, more useful, less toxic molecules
- these molecules are either secreted into the blood or stored in hepatocytes
hepatic =?
liver
Liver - how many inputs of blood?
2
HPV, and HA
HPV?
Brings blood into liver from DS. Deox
HA?
oxygenated blood to the liver from the heart
Histology of the liver (lobules)?
- made of units called lobules (1-2mm across)
- Each lobule is hexagonal
- branch of hepatic vein at the centre of the lobule = central vein
- at the corner of lobule, portal triad
Portal triad ?
- formed from 3 vessels
* the vessels are branches of hepatic portal vein, hepatic artery, bile duct
Sinusoids?
• capillaries carrying blood from the HA and HPV to central vein
Bile cannaliculi?
carrying bile from hepatocytes to bile duct
bile and blood moves in?
opposite directions
HPV vs HA
HPV: thin walls, large lumen (shocker)
HA: thick walls, small lumen
walls of bile duct?
• diff structure to blood vessels
Bile duct?
carries bile into gall bladder
hepatocytes are involved in?
molecular processing, producing bile
How to spot HPV and HA on a diagram?
- they converge
* HPV = larger lumen
List of some of the liver’s functions?
- glucose ➡glycogen, and opp.
- glycogen storage
- bile production
- urea formation
- detoxification e.g. alcohol
- hormone breakdown
bile =?
- mixture of substances that neutralise stomach acid
- emulsify fats
• mainly made of water and bile salts
formation of urea {summary}
AA ➡ ammonia ➡ ornithine cycle
ornithine cycle is an _____ req process?
energy
deamination?
removal of amine group from AA, forming ammonia and keto acid
urea formation is a 2 stage process…
- deamination
2. ornithine cycle
after deamination,
amine group ➡ ammonia, which enters ornithine cycle
what happens to the keto-acid?
- it’s basically a carbohydrate
- can be used as a resp substrate
- or converted to lipid for storage
The ornithine cycle inputs?
• ammonia, water, CO2,ATP
The ornithine cycle outputs?
water and urea
OC acronym?
One
Cold
Ant
pathway of urea out of liver?
- secreted from hepatocytes into blood flowing through liver sinusoids
- excreted in urine by kidneys
The detoxification of alcohol
1) ethanol absorbed from DS, enters bloodstream in HPV which leads to liver
2) some ethanol enters hepatocytes
3) Ethanol oxidised to ethanal by ethanol dehydrogenase
4) ethanal oxidised to acetate (ethanoate) by ethanal dehydrogenase
5) NAD is reduced by both reactions
oxidation
Ox Is Loss Red Is Gain of e-s
what do dehydrogenase enzymes do?
remove H atoms. H = H+ + e- so when a substance loses H, it loses e- and becomes oxidised
how does oxNAD become redNAD?
• Picking up H atoms (e-) - RIG
acetate a.k.a.
ethanoic acid and ethanoate
NAD?
- coenzyme (organic cofactor)
* hydrogen carrier
Other reaction of hepatocytes that is disrupted by detox of ethanol?
- beta oxidation of FA
- FA ➡ acetate
- oxNAD needed for this
- if [alcohol] is high, less NAD available for this reaction
- build up of FA in liver
- FA converted to triglycerides
what does the accumulation of FA/ triglycerides lead to?
- fatty acids
* can then lead to cirrhosis which is a build up of scar tissue in the liver, eventually cause liver failure
if liver is damaged then
• many hormones are broken down in the liver so if the liver is damaged, they stay in the blood for longer than they should
