excretion and liver Flashcards
define the term excretion and why its important
-removal from the body of waste products made in cells during metabolism
-many metabolic waste products can be toxic if allowed to build
what are examples of excretory products
- CO2
- Nitrogenous waste (urea in mammals, uric acid in birds and insects or ammonia in fish)
- bile pigments = formed from haemoglobin, leave in faeces
explain the excretory product co2 and its importance
CO2 = waste product in respiration, transported in blood, excreted via lungs
-excess CO2 can cause respiratory acidosis = headaches, drowsiness
and reduce blood pH which is detected by medulla oblongata (respiratory centre) in the brain resulting in increased breathing rate to remove excess co2
explain the excretory product Urea and its importance
-nitrogenous waste product used to eliminate excess nitrogen e.g more protein eaten than body needs
1.protein is broken down into amino acids and absorbed from the ileum (small intestine) into blood = used to build up new protein
2. excess amino acids are delivered to the liver
3. amino group is removed (deamination) forming ammonia which enters the ornithine cycle and combines with CO2 to form urea
4. rest of amino acid molecule is used for respiration or converted to lipids to store (keto acid)
what are the simple word equations for deamination and formation of urea
1)deamination: amino acid + oxygen -> keto acid + ammonia (highly toxic, soluble)
2) formation of urea: ammonia + CO2 -> urea (less toxic and less soluble) + water
2NH3 + CO2 = CO(NH2)2 + H2O
what are the key parts of the ornithine cycle
-hepatocytes convert ammonia to urea via the ornithine cycle
-ammonia reacts with carbon dioxide and water via a series of intermediate molecules (water released and uptaken within reactions)
-urea is less toxic and passes out of hepatocytes into blood stream
-when blood passes through kidneys = excreted as urine
what are the main functions of the liver
-storage of glycogen (key in control of blood glucose concentration)
-detoxification e.g hydrogen peroxide via catalase into h2o and o2, drugs and alcohol,
cytochrome p450 group of enzymes breaking down drugs (these are also important in electron transport chain during respiration= intake of drugs interferes with their ability to complete this role= side effects
-formation of urea and protein metabolism (synthesis of plasma proteins, deamination and transamination-converting between different proteins)
describe the blood vessels of the liver
- Hepatic artery = carries oxygenated blood to the liver from heart
- Hepatic vein carries deoxygenated blood back to the heart
- Hepatic portal vein = carries blood from the intestines and digestive system to liver = blood rich in products of digestion e.g amino acids as well as alcohol
- Bile duct- carries bile from the liver to the gall bladder for storage before addition to small intestine to aid fat digestion
how can you distinguish between the bile duct, hepatic artery and the hepatic portal vein
-hepatic portal vein has a larger lumen than the hepatic artery
-direction of bile flow is away from liver vs towards in the other vessels
what are liver cells called and describe them
hepatocytes
-large number of mitochondria= ATP required for chemical reactions
-form cavities called sinusoids
what is the sinusoid and how its adapted
chamber lined in liver cells where blood from HA and HPV mixes
-close contact between blood in sinusoid and liver cells allows cells to pass molecules from/to the blood
-increased permeability allows larger molecules to enter and leave bloodstream e.g plasma protein
what are kupffer cells
cells attached to walls of sinusoid= specialised phagocytic macrophages
-destroy bacter and foreign particles in blood and destroy old RBCs recycling or removing the breakdown product
-break down haemoglobin from RBCs =eliminated in bile excreted in urin and faeces
