Excretion

Question 1

What is excretion?

Answer 1

removal of metabolic waste from the body

Question 2

What does metabolic waste consist of?

Answer 2

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

Question 3

Which 2 substances are produced in very large amounts? Where are these produced?

Answer 3

CO2 (from respiration in every living cell in the body)

nitrogen containing compounds like urea (from liver from excess amino acids)

Question 4

What is egestion?

Answer 4

removal of undigested food by the process of defecation (substances have never been in cells so cant be excreted)

Question 5

What is deamination?

Answer 5

removal of amine group from an amino acid to produce ammonia

Question 6

How is urea produced?

Answer 6

deamination then passed into bloodstream and transported to kidneys - dissolved in plasma

Question 7

What happens to urea in the kidneys?

Answer 7

removed form the blood to become part of urine, urine stored in bladder then excreted via urethra

Question 8

How does excess carbon dioxide affect reduce transport?

Answer 8

most CO2 carried in blood as hydrogencarbonate ions, this also forms hydrogen ions in RBCs (enzyme carbonic anhydrase) H ions compete for haemoglobin so oxygen transport reduced if excess CO2

Question 9

What does carbon dioxide do to haemoglobin?

Answer 9

directly combines with haemoglobin = carbaminohaemoglobin, which has lower affinity for O2

Question 10

What happens to carbon dioxide which has dissolved in the blood plasma?

Answer 10

can combine with water = carbonic acid (H2CO3), dissociates to release H ions

Question 11

What do the hydrogen ions from carbonic acid do to the blood?

Answer 11

lower pH so blood more acidic, proteins in blood act as buffers to resist pH change

Question 12

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

Answer 12

Extra H ions detected by respiratory centre in medulla oblongata of brain, increases breathing rate to remove excess CO2

Question 13

What happens is blood pH drops below 7.35?

Answer 13

slowed or difficult breathing, headache, drowsiness, restlessness, tremor and confusion, rapid heart rate and blood pressure change: respiratory acidosis

Question 14

What can respiratory acidosis also be caused by?

Answer 14

emphysema, chronic bronchitis, asthma, sever pneumonia, airway blockage (from swelling, foreign object or vomit)

Question 15

What can the body not store?

Answer 15

proteins or amino acids

Question 16

What happens to amino acids?

Answer 16

Almost as much energy as carbohydrates so transported to liver and deamination occurs, amino group forms ammonia (soluble, highly toxic), converted to urea (less soluble and toxic) then to kidney for excretion

Question 17

What part of the amino acid can be used in the body?

Answer 17

keto acid can be used in respiration or converted to fat or carbohydrate for storing