Excretion PPT.pptx
5.1.2 Excretion as an example of homeostatic control
The kidneys, liver and lungs are all involved in the removal of toxic products of metabolism from the blood and therefore contribute to homeostasis. The kidneys play a major role in the control of the water potential of the blood. The liver also metabolises some toxins that are ingested.
Onderdelen in deze les
5.1.2 Excretion as an example of homeostatic control
The kidneys, liver and lungs are all involved in the removal of toxic products of metabolism from the blood and therefore contribute to homeostasis. The kidneys play a major role in the control of the water potential of the blood. The liver also metabolises some toxins that are ingested.
Learning Objectives:
Define the term excretion.
Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body.
Specification reference: 5.1.2(a)
Excretion
1
Excretion
Excretion is the removal of unwanted products of metabolism.
Main products:
carbon dioxide
urea
bile pigments
This will be discussed in more detail when we look at the liver.
Where does urea come from?
Can you draw the basic structure of an amino acid?
https://www.youtube.com/watch?v=ZxI8LFodJMk
Carbon dioxide
Produced in every living cell during aerobic respiration.
Transported in the blood stream and excreted from the lungs.
Carbon Dioxide Transport
CO2 carried in three ways
5% in solution in plasma as CO2
10% combines with amino groups in Hb molecule (carbaminohaemoglobin)
85% hydrogen carbonate ions
Carbon dioxide transport
Transported in blood as hydrogen carbonate ions
Carbonic anhydrase catalyses the reaction
CO2 + H2O H2CO3
Carbon Dioxide Transport
Carbonic acid dissociates
H2CO3 H+ + HCO3-
H+ ions associate with haemoglobin (buffer) Haemoglobinic acid (HHb)
Chloride Shift
Build up HCO3- causes them to diffuse out of RBC.
Inside membrane positively charged
Cl- diffuse into RBC from plasma to balance the electrical charge
What happens if CO2 is not excreted?
Carbon dioxide is toxic
Hydrogen carbonate ions can reduce the ability to transport oxygen
Forms carbaminohaemoglobin which has a lower affinity for oxygen than normal haemoglobin
Respiratory acidosis
Drop in blood pH
Headache, drowsiness, restlessness, tremor and confusion
Review questions
1. What is meant by the term excretion?
2. Name the two excretory products that are produced in relatively large quantities in the body
3. Explain how respiration can cause a fall in blood pH.
4. Which one of the following statements about excretion is true?
A Ammonia is a safer substance to transport in the blood than urea.
B Deamination is the removal of an amine group from an amino acid.
C Egestion and excretion are the same thing.
D Urea diffuses into the lungs and is breathed out.
Answers to review questions
1. What is meant by the term excretion?
2. Name the two excretory products that are produced in relatively large quantities in the body
3. Explain how respiration can cause a fall in blood pH.
Removal of metabolic waste
Carbon dioxide and urea
Respiration produces carbon dioxide. Carbon dioxide and water react together to produce carbonic acid (catalysed by carbonic anhydrase). Carbonic acid dissociates to release hydrogen ions and hydrogen carbonate ions which can lower the pH.
Answers to review questions
4. Which one of the following statements about excretion is true?
A Ammonia is a safer substance to transport in the blood than urea.
B Deamination is the removal of an amine group from an amino acid.
C Egestion and excretion are the same thing.
D Urea diffuses into the lungs and is breathed out.
B
