5.2.1 - Excretion Flashcards
What is excretion?
The removal of metabolic waste from the body
What is metabolic waste?
A substance that is produced in excess by the metabolic processes in the cells; it may become toxic
What may happen if there is a build up of excess substances from chemical processes? (2 Points)
Inhibit enzyme activity or become toxic altering the pH.
What are the main excretory products? (3 Points)
1) Carbon dioxide from respiration
2) Nitrogen-containing compounds such as urea (i.e nitrogenous waste)
3) Other compounds, such as the bile pigments found in faeces
What are the 3 excretory organs?
1) Lungs
2) Liver
3) Skin
How is the lung an excretory organ?
Carbon dioxide produced from respiration.
It is removed when the carbon dioxide passes from the cells of respiring tissues into the bloodstream, –> where it is transported to the lungs. The Carbon dioxide diffuses into the alveoli to be excreted as you breathe out
How is the liver an excretory organ?
Pigment Bilirubin
Liver has many metabolic roles and some of the substances produced will be passed into the bile for excretion with the faeces.
Liver also involved in converting excess amino acids to urea. Deamination, nitrogen-containing part of the molecule is then combined with carbon dioxide to make urea
How is the skin an excretory organ?
Urea, uric acid and ammonia which may be present in sweat.
How is carbon dioxide transported in the blood?
As hydrogencarbondate ions
How are H+ ions produced from hydrogencarbonate and where does this occur?
CO2+H2O–>H2CO3 (Carbonic Acid)
The Carbonic acid then dissociates to release Hydrogen ions
H2Co3–>H+ HCO3^-
This occurs in the red blood cells and blood plasma, under the influence of the enzyme Anhydrase.
How are the H+ Ions and toxic
1) Affect the pH of the cytoplasm in the redblood cells
2) Hydrogen ions interact with bonds within haemoglobin, changing it’s 3D shape –> Reduces Affinity of haemoglobin for oxygen –> Affecting oxygen transport.
3) H+ Ions can form with haemoglobin to make Haemoglobinic Acid
What happens to the carbon dioxide that is not converted to hydrogencarbonate ions
- Combines directly with haemoglobin, producing carbanimohaemoglobin.
- Carbaminoheamoglobin unable to combine with oxygen as normal –> Reducing oxygen transport further
Excess hydrogen ions can reduce the pH of the blood plasma, why is maintaining the pH of the blood plasma essential?
1) Can alter the structure of the many proteins in the blood that help to transport a wide range of substances around the body. proteins in the blood act as buffers to resist the change in pH
What happens if the change in pH is small in the blood plasma?
Extra hydrogen ions are detected by the respiratory
What is respiratory acidosis?
Rapid heart rate and changes in blood temperature
What can cause respiratory acidosis?
Diseases or conditions that affect the lungs themselves such as asthma or severe penuemonia. Blockage of the airway due to swelling, a foreign object or vomit can also induce acute respiratory acidosis
Why are excess amino acids not excreted?
Amino acids contain almost as much energy as carbohydrates. Instead they are transported to the liver and the potentially toxic amino group is removed via Deamination
What happens to excess amino acids
Amino group converted into something that is slightly less toxic called Urea which is then transported to the kidneys for excretion.
Remaining keto acid can be used directly in respiration to release its energy or it may be converted to a carbohydrate or fat for storage
What is deamination?
Amino acids+ oxygen –> keto acid + ammonia
How is urea formed?
Ammonia+Carbondioxide–> urea + water
2NH3 + Co2 –> (NH2)2CO + H2O
