1. F214: Communication, Homeostasis and Energy 4.2.1 Excretion
define the term excretion;
explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body;
describe, with the aid of diagrams and photographs, the histology and gross structure of the liver;
describe the formation of urea in the liver, including an outline of the ornithine cycle
describe the roles of the liver in detoxification;

2. Excretion
“The removal of metabolic waste (unwanted substances from cell processes) from the body”
Urea from excess amino acids in the liver
Carbon dioxide from respiration

3. Task
Using textbooks, research the importance of the excretion of both carbon dioxide and nitrogenous compounds
Q. Why must these substances be removed and where/how are these substances excreted?

4. Why Excrete Nitrogenous Compounds?
The body can’t store them
They have almost as much energy as carbohydrates
Transported to liver
Toxic amino acid group removed (deamination)
Amino group forms ammonia
Ammonia converted to urea
Urea transported to kidneys for excretion
Remaining Keto acid used in respiration or stored
Deamination: amino acid + oxygen  keto acid + ammonia
Urea formation: 2NH CO  CO(NH2) H2O
ammonia + carbon dioxide  urea water

5. Why Excrete Carbon Dioxide?
Excess carbon dioxide is toxic
Carbon dioxide is carried in blood as hydrogencarbonate ions producing hydrogen ions that compete with oxygen for haemoglobin
It combines with haemoglobin to form carbinohaemoglobin with a lower affinity for oxygen than normal haemoglobin
Excess carbon dioxide can cause respiratory acidosis- carbon dioxide dissolves in blood plasma producing carbonic acid with dissociates forming hydrogen ions which lower the pH of blood
Carbonic acid production: CO2 + H2O  H2CO3
Dissociation of Carbonic acid: H2CO3  H+ + HCO3-

6. Why Excrete Carbon Dioxide?
Hydrogen ions lower the pH and make the blood more acidic
Proteins in the blood act as buffers to resist the pH change, by adding a hydrogen onto their COO (carboxyl group) to become COOH (They can exist as COO in a neutral solution)
The extra hydrogen ions are detected by the respiratory centre in the medulla oblongata of the brain
The brain causes an increase in breathing rate to remove the excess carbon dioxide
If the pH drops below 7.35, the result is slow, difficult breathing, headache, drowsiness, restlessness, tremor, confusion, rapid heart rate and blood pressure changes
This is called respiratory acidosis
Emphysema, chronic bronchitis, asthma and pneumonia, choking or vomiting can also lead to it

7. Where is the liver located?

8. Where is the liver located?

9. Where is the liver?
The liver lies just beneath the diaphragm towards the right hand side of the body- it is made up of several lobes

10. one of the largest organs in the body
1450cm3 of blood passes through it in one minute
Enormous variety of functions
Uniform structure

13. The Liver 1. Stick in the liver diagram showing the blood vessels
2. Give the function of:
Hepatic artery
Hepatic vein
Hepatic portal vein
Describe the location of the liver in the body

14. The Structure of the Liver
Task: Your task is to describe, with the aid of diagrams and photographs, the histology and gross structure of the liver. You must then present your findings to the rest of the class. You can choose how you would like to do this, and what format you would like to use e.g. PowerPoint, information board, poster etc.

15. Task Guide Decide on the format
Research the liver on the internet using the checklist provided (approx 1-3 hours)
Gather appropriate images (approx 1 hour)
Complete the project including the images and information you have gathered (1-3 hours)
Present your project
You will be assessed by your ability to annotate (label with descriptions) a diagram of the liver

16. Checklist
Blood flow to and from the liver including the hepatic portal vein
Arrangement of cells inside the liver
Structure of liver cells including microvilli
The role of Kupffer cells

20. Blood Supply Blood arrives in two different blood vessels
Hepatic artery leads from the aorta and delivers oxygenated blood to the liver
The hepatic portal vein leads from the small intestine and delivers blood rich in absorbed nutrients (like glucose and amino acids from the intestine) and insulin and glucagon from the pancreas
The hepatic portal vein carries about 3 times more blood per minute than the hepatic artery
Blood from the hepatic portal vein has already travelled through a set of capillaries so is at a much lower pressure than blood in the hepatic artery
The hepatic vein carries blood away from the liver to the vena cava which then transports it back to the heart- it returns glucose to circulation and allows amino acids to enter circulation

21. Histology of the Liver Made up of many lobules
In the centre of each lobule is a branch of the hepatic vein
Between the lobules are branches of the hepatic artery and the hepatic portal vein- blood flows from here, through the lobules and into the branch of the hepatic vein

22. The lobules are made up of many liver cells called hepatocytes arranged in rows that radiate out from the centre like spokes of a wheel
The channels which carry blood between these rows of cells are called sinusoids
Other channels carry bile, which is produced from some of the hepatocytes: these channels are called bile canaliculi

23. Histology of the Liver
The bile flows from the centre of the lobule towards the outside – the opposite direction to the blood flow, where it enters a branch of the bile duct
The rows of hepatocytes are never more than two cells thick, so that each cell is close to the blood in the sinusoids

24. Histology of the Liver
The sinusoids are lined with large, phagocytic macrophages which capture and destroy bacteria entering the liver via the hepatic portal vein from the intestine
These cells are sometimes called kupffer cells.
They are very efficient- if a bacterium comes into contact with the membrane of a kupffer cell, it is taken into the cell by phagocytosis within 0.01 second!!

28. F214: Communication, Homeostasis and Energy 4.2.1 Excretion
define the term excretion;
explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body;
describe, with the aid of diagrams and photographs, the histology and gross structure of the liver;
describe the formation of urea in the liver, including an outline of the ornithine cycle
describe the roles of the liver in detoxification;

29. F214: Communication, Homeostasis and Energy 4.2.1 Excretion
define the term excretion;
explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body;
describe, with the aid of diagrams and photographs, the histology and gross structure of the liver;
describe the formation of urea in the liver, including an outline of the ornithine cycle
describe the roles of the liver in detoxification;

30. F214: Communication, Homeostasis and Energy 4.2.1 Excretion
define the term excretion;
explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body;
describe, with the aid of diagrams and photographs, the histology and gross structure of the liver;
describe the formation of urea in the liver, including an outline of the ornithine cycle
describe the roles of the liver in detoxification;

31. Control of blood glucose, amino acid and lipid levels
Liver Functions
Control of blood glucose, amino acid and lipid levels
Synthesis of Fetal red blood cells, bile, plasma proteins and cholesterol
Storage of vitamins A, D, B12, iron and glycogen
Detoxification of alcohol and drugs
Breakdown of hormones
Destruction of red blood cells

32. Urea Formation
Excess amino acids cannot be stored as the amine groups are toxic
Therefore it goes through two treatments in the liver: Deamination and The Ornithine Cycle

33. + Deamination Ammonia is produced which is soluble and toxic
Keto acid is produced which enters respiration directly to release energy O2
NH2 C H
COOH R + O
NH3
Amino Acid
Keto Acid
Ammonia

34. The Ornithine Cycle (ammonia’s conversion to urea)
Ammonia is combined with carbon dioxide to produce urea
Urea is less soluble and less toxic than ammonia so it can be passed back into the blood to the kidneys
The kidneys filter out the urea from the blood and store it as urine in the bladder
2NH CO  CO(NH2) H2O
Ammonia carbon dioxide  urea water

35. As you can see above, ammonia and carbon dioxide enter the cycle
As you can see above, ammonia and carbon dioxide enter the cycle. ATP is required and Urea is produced. Water is also produced as a by-product.
The body can manufacture ornithine, but it is abundant in meat, fish, dairy and eggs

36. Detoxification Many dangerous substances are broken down by the liver
Some are made harmless, some are excreted into bile
Most of these processes take place in the smooth endoplasmic reticulum in the hepatocytes
Toxins can be made harmless by oxidation, reduction, methylation or combination with another molecule

37. Detoxification Oxidation: loss of electrons
Reduction: gain of electrons
Methylation: the addition of a methyl group
Combination with another molecule
Methylation is the addition of a methyl group

38. Metabolism of Alcohol Alcoholic drinks contain ethanol C2H5OH
Ethanol molecules are small and lipid soluble so diffuse easily across the plasma membranes and enter cells
Ethanol is a toxic substance and can cause damage to liver cells
The liver avoids damage by breaking down ethanol into harmless substances

39. Metabolism of Alcohol
The enzyme alcohol dehydrogenase converts ethanol into ethanal (acetaldehyde)
The enzyme aldehyde dehydrogenase then converts ethanal (acetaldehyde) into ethanoate (acetate)
This can then be combined with coenzyme A to form Acetyl Coenzyme A, which then enters the Kreb’s cycle and be metabolised to produce ATP
Ethanol is therefore a source of energy for cells

40. To Respiration
Ethanol
Ethanal
Ethanoate
Acetyl Coenzyme A
NAD
ReducedNAD
NAD
ReducedNAD
The Hydrogen atoms released are combined with another coenzyme called NAD to form reduced NAD
NAD is also needed to oxidise and break down fatty acids for respiration
If the liver has to detoxify too much alcohol, it does not have enough NAD to deal with the fatty acids, so they are changed back to lipids and are stored in hepatocytes (liver cells), causing the liver to become enlarged- this is called ‘fatty liver’ and can lead to liver cirrhosis.

44. Discuss in pairs... Why must ammonia be converted to urea?
Explain why excess amino acids and alcohol should not be secreted?
Suggest why the liver cells have large numbers of mitochondria and ribosomes?
Write down your responses in pairs and pass it to another pair to look at- do you have the same responses?

45. Discuss in pairs... 1. Why must ammonia be converted to urea?
Ammonia is highly soluble and very toxic- urea is less soluble and less toxic
Explain why excess amino acids and alcohol should not be secreted?
They contain valuable energy that can be used. Amino acids can be converted into others
Suggest why the liver cells have large numbers of mitochondria and ribosomes?
Mitochondria provide ATP for processes e.g. protein synthesis. Ribosomes manufacture the enzymes needed by liver cells

46. F214: Communication, Homeostasis and Energy 4.2.1 Excretion
define the term excretion;
explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body;
describe, with the aid of diagrams and photographs, the histology and gross structure of the liver;
describe the formation of urea in the liver, including an outline of the ornithine cycle
describe the roles of the liver in detoxification;