F214:02:01 Excretion Flashcards Preview

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Flashcards in F214:02:01 Excretion Deck (34):

What is excretion?

the removal of metabolic waste from the body


What does metabolic waste consist of?

waste substance that may be toxic or are produced in excess by the reactions inside cells


Name 2 waste products that are produced in very large amounts

1. CO2 from respiration
2. Nitrogen- containing compounds such as urea


Where is carbon dioxide produced?

in every living cell


Where is urea produced?

In the liver


How is carbon dioxide excreted/

Its passed from respiring cells into the blood stream
Then transported to the lungs


How is urea produced?

By breaking down excess amino acids (known as deamination)


What is deamination?

The removal of an amine group from an amino acid to produce ammonia.


What is Egestion?

the removal of undigested food by the process of defecation


Why cant substances be excreted if they are undigested?

As they havent entered any cells


How is urea removed from the body?

Urea is passed into the blood stream to be transported to the kidneys dissolved in the blood plasma
In the kidneys the urea is removed from the blood to become part of urine
Urine is stored in the bladder and is excreted by the urethra


Why must excess carbon dioxide be removed?

As it can be toxic
(has 3 effects)


What are the 3 main effects of carbon dioxide in the body?

1. Too much Co2 in the blood can reduce the amount of oxygen produced
2. As CO2 directly combines directly with Hb to form carbaminohaemoglobin, which has a lower affinity to O2 than Hb.
3. Leads to respiratory acidosis


How is the majority of CO2 carried in the blood?

as hydrogencarbonate ions


What is the negative side effects of too much hydrogencarbonate being produced?

As when it is formed, hydrogen ions are also formed which then compete with oxygen to join with haemoglobin, so can reduce the amount of oxygen


What do enzyme carbonic anhydrases influence?

The formation of hydrogencarbonate ions in the red blood cells


What is respiratory acidosis

Where carbon dioxide dissolves in blood plasma, and when it has dissolved it can combine with water to produce carbon acid
Carbonic acid then dissociates to release H+ which lowers the bloods pH and makes it more acidic


What is the equation for carbon dioxide forming with water to form carbonic acid?

CO2 + H2O -> H2CO3


What is the equation for carbonic acid dissociating?

H2CO3 -> H+ HCO3


How is a change in pH attempted to be resisted in the blood?

As proteins in the blood act as buffers


What happens if the change of pH is small in the blood?

Then the extra hydrogens are detected by the respiratory centre in the medulla oblongata of the brain
This increases the breathing rate to remove excess CO2


What happens in the blood pH drops below 7.35 pH?

Results in:
slow/difficult breathing
or confusion
May also be rapid heart rate/ changes in blood pressure


What is respitory acidosis caused by?

diseases or conditions that affect the lungs themselves
Also could be caused by blockage of the airway due to swelling, a foreign object or vomit.


Give some examples of conditions that affect the lungs that could cause respitory acidosis

chronic bronchitis
severe pneumonia


Why would it be wasteful to excrete excess amino acids?

As although they cant be stored, they contain almost as much energy as carbohydrates


What happens to excess amino acids?

They are transported to the liver and the potentially toxic amino acid is removed


What happens to amino acids when they have been broken down in the liver?

Amino group forms ammonia, but as this is highly soluble and toxic, it is converted into urea which is transported to the kidneys for excretion
Keto acid can be used directly in resp to release energy or can be converted into fat/carbohydrate for storage


What happens to the keto acid when amino acids are broken down?

used directly in resp to release energy or can be converted into fat/carbohydrate for storage


What is the equation for deamination?

amino acid + oxygen -> keto acid + ammonia


What is the equation for the formation of urea?

ammonia + carbon dioxide -> urea + water


What is the symbolic equation for the formation of urea?

2NH3 + CO2 -> CO(NH2)2 + H2O


Explain the differences between excretion and egestion

Excretion is the removal of metabolic waste from cell processes
Egestion is the removal of undigested food from the digestive system- it has never been in the cells so cannot be classed as excretion.


Explain what causes respiratory excretion

Respiratory acidosis is the result of high CO2 levels in the blood
CO2 dissolves in the watery plasma and reacts to form carbonic acid.
The carbonic acid dissociates, releasing hydrogen and makes the blood more acidic.


Suggest why fish excrete ammonia but mammals must convert it to urea for excretion

As ammonia is highly toxic, fish can use lots of water to dilute it so its not as toxic, and this can be released all the time so it doesnt have to circulate the body.
mammals dont live in water so they must conserve it so they cant release too much as urine, so it must be stored, and in order to transport it safely to the bladder- ammonia must be converted into urea