Excretion Bio (Pt1)
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Define the term excretion. (Spec)
The removal of metabolic wastes from the body.
What is metabolic waste?
By-products or unwanted substances, consisting of waste substances that may be toxic or are produced in excess by the reactions inside cells.
How are CO2 and excess amino acids excreted?
- CO2: pss from cells of respiring tissue into bloodstream and transported mostly in form of hydrogencarbonate ions, to lungs, then through alveli and out.
- Amino acid: Urea is produced by breaking down excess amino acids in the liver. This process is called deamination. Urea in blood then transported in kidney in solution (in plasma), then removed fro blood to become part of urine. Urine stored in bladder before being ecreted via the urethra.
Removal of the amine group from an amino acid to produce ammonia.
A high CO2 level has 3 main effects. What are they? List some symptoms for last one.
- Majority of CO2 in blood carried as hydrogencarbonate ions - and forming this also forms hydrogen ions. This occurs inside RBC under influence of carbonic anhydrase. H+ion will compete with oxygen for space on haemoglobin, reducing O2 transport.
- CO2 also combines directly with haemoglobin to form carbaminohaemoglobin. This has lower affinity for O2 than normal haemoglobin.
- Excess CO2 can cause respiratory acidosis - CO2 dissolves in blood, creating carbonic acid, which dissociates to release H+ ions, which make blood more acidic. Small drop can be detected and changed by medulla oblongata, but if pH drops below 7.35 it results in slowed or difficult breathing, headache, drowsiness, restlessness, tremor and confusion. May also be rapid heart rate and change in blood pressure.
What can be the cause of respiratory acidosis?
- High CO2 caused by:
- conditions that affect lungs themselves (eg emphysema)
- blockage of airway due to swelling, vomit or foreign object.
The body cannot ___ proteins or amino acids. Why can't we just simply excrete excess amino acids?
- Because amino acids are very high in energy (almost as much as carbs), so it would be wasteful to simply excrete them whole.
Why must we remove nitrogenous wastes?
Because the amino group is highly toxic
Show the 2 steps involved in the process where an amino acid is broken down and excreted.
- Deamination: amino acid + oxygen -- keto acid (can be used in respiration or converted to carb or fat for storage) + ammonia (highly toxic and very soluble)
- Formation of urea: ammonia + CO2 --- urea + water. (urea is less soluble and less toxic) Ornithine cycle
Liver is supplied with blood from 2 sources. What are they and why?
- Oxygenated blood from heart: Aorta - hepatic artery - liver. Liver cells very active, carrying out many metabolic processes, so need good supply of oxygen for aerobic respiration.
- Deocygenated blood from digestive system: Enters liver via hepatic portal vein. This is rich in products of digestion (from small intestine) - conc of many compounds will need to be adjusted, and may also contain toxic compounds absorbed in ntestine.
What two vessels take blood away from liver?
- Hepatic vein: rejoins the vena cava and blood returns to normal circulation.
- Bile duct: (not a blood vessel). Bile secreted from liver have digestive function and excretory function. Bile duct carries bile from liver to gall bladder where it is stored until recquired to aid digestion of fats in small intestine.
The liver cells, blood vessels and chamebers inside liver arranged to ensure..
the best possible contact between blood and the liver cells.
The inter-lobular vessels are made up of what and what? And they mix to pass along a chamber called what?
- Hepatic artery and hepic portal vein
Blood runs through the ___ and past the ___. These ___ harmful substances, ___ them down, which ____ the blood, to be drained in the branch of the ____ which is a ____ vessel.
- hepatic vein
Where is bile released into in the liver lobule?
- Bile canaliculi
- which connects to branch of bile duct
Describe the liver cell.
- Cuboidal shape
- many microvilli on their surface
- Appears relatively unspecialised, but have many metabolic functions like protein synthesis, detoxification, synthesis of cholesterol and bile salts, transformation and storage of carbs etc and many other processes.
- Therefore, cytoplasm must be very dense and is specialised in the amounts of certain organelles that is contains.
What is a kupffer cell and what is its function?
- Specialised macrophages that move about within sinusoids.
- Involved in breakdown and recycling of RBC and perhaps also remove bacteria.
- One product of haemoglobin breakdown is bilirubin, excreted as part of bile and responsible for brown pigment in faeces.
List some of the functions of the liver. (6)
- Control of: blood glucose levels, amino acid levels, lipid levels
- Synthesis of: bile, plasma proteins, cholesterol, RBC in fetus
- Storage of: vitamins A,D and B12, iron, glycogen
- Detoxification of: alcohol, drugs
- Breakdown of hormones
- Destruction of RBC
Excess amino acids undergo tratment in the liver before the amino component is excreted. List the 2 stages and its important products.
- 1. Deamination: amino acid --- ammonia + keto acid
- 2. Ornithine cycle: ammonia ---- urea
Give the equation for the ornithine cycle.
- 2NH3 + CO2 --- CO(NH2)2 + H20
- ammonia + carbon dioxide --- urea + water
Remember the practice Ornithine cycle drawing.
What is detoxification?
The conversion of toxic molecules to less toxic or non-toxic molecules.
Toxins can be rendered harmless by:
- combination with another molecule
H2O2 (hydrogen peroxide) is toxin produced in body. How is this detoxified in liver?
Liver cells contain enzyme catalase, which converts H2O2 into oxygen and water.
Why must alcohol/ethanol be broken down in the liver? 2 reasons.
- It is a toxic drug that depresses nerve activity (and can damage cells - check!)
- Also contains chemical potential energy, which can be used for respiration.
Describe the steps involved in detoxification of alcohol/ethanol.
- 1. Broken down by enzyme ethanol dehydrogenase to produce ethanal.
- 2. Ethanal dehydrogenated fruther by ethanal dehydrogenase, to pruduce ethanoic acid (or maybe ethanoate - CHECK!)
- 3. Ethanoic acid combines with coenzyme A to form acetyl coenzyme A, which enters process of respiration.
- [ethanol - ethanal - ethanoic acid - acetyl CoA]
The ___ atoms released in this process combines with coenzyme called ___ and form ___ ___.
Why is this a problem? What is the consequence of too much alcohol?
- NAD is also recquired to oxidise and break down fatty acids for use in respiration. If liver has to detoxify too much alcohol, it has insufficient NAD to deal with fatty acids.
- So fatty acids converted back to lipids and are stored in hepatocytes - causing liver to become enlarged.
- Condition known as "fatty liver".
- Can lead to alcohol-related hepatitis or to cirrhosis.
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