OCR Biology - Mammalian Physiology and Behaviour; June 2009

The Liver

Hepatic Artery - from aorta to liver, supplies liver with oxygenated blood.

Hepatic Portal Vein - from small intestine to live, supplies liver with nutrient rich blood.

Hepatic vein - takes all blood from liver to vena cava.

Bile Duct - takes bile from liver to gall bladder and duodenum.

Structure:

Liver made of many lobules (100,000 in humans) which are circular with a central vein in the middle. Blood from the two arteries flows from the edge of the lobule to the centre like the spokes of a wheel. This blood passes through channels of liver cells (hepatocytes) called sinosoids. Other channels between these rows of hepatocytes are bile canaliculi, which transport bile made the the hepatocytes to the bile duct, at the edge of the lobule. Large phagocytic macrophages called Kupffer cells line the sinosoids and destroy any bacteria that flows past them. The hepatocytes have microvilli to increase surface area.

Carbohydrate Metabolism:
- glucose in absorbed from blood into hepatocytes.
- if insulin is in blood, it acts on hepatocytes causing them to convert glucose to glycogen (glycogenesis)
- if glucagon (or adrenaline) is in the blood, it acts of hepatocytes causing them to convert glycogen to glucose (glycogenolysis)
- after a long time without food, glucagon and adrenaline cause gluconeogenesis, which is the conversion of substances into glucose.
- eg, amino acids deaminated, turned to pyruvate, condensation reaction to glucose.

Lipid Metabolism:
Lipids are energy dense and are stored in adipose tissue. They can be used as a respiratory substrate by all tissues except for nervous tissue and red blood cells, which must use glucose.

Fat --> Energy:
- Triglycerides hydrolyzed to fatty acids and glycerol by lipase (lipolysis) inside hepatocytes.
- Glycerol can go straight into glycolysis as a substrate.
- Fatty acids broken down to coenzyme A, which is used in the Krebs cycle to make ATP.

Triglycerides are non-polar and so are not water-soluble. They can, however, be transported in blood plasma if they are surrounded by proteins to make a lipoprotein, which can be either 'low density lipoproteins' LDLs or 'high density lipoproteins' HDLs. Cholesterol can be transported as either, but LDL cholesterol can build up plaques leading to atherosclerosis, whereas HDL cholesterol can actually remove plaques from artery walls. So, a high ratio of HDLs to LDLs can reduce the risk of cardiovascular disease.

Cholesterol:
Used for:
- Cell membranes (helping maintain mechanical stability, regulate fluidity, and maintain impermeability to to hydrophilic molecules).
- Making steroid hormones eg, testosterone/oestrogen.
- Waterproofing skin.
- Making vitamin D, when skin is exposed to UV light.
- Making bile salts.

The liver can make it's own cholesterol, but the amount changes depending on how much is in your diet, so it can regulate cholesterol levels a little bit.

Too much bad cholesterol can cause gall stones and cardiovascular disease.

Protein Metabolism:
- Transamination - converting one amino acid to another. (essential amino acids cannot be synthesied in this way)
- Deamination - amino acids can't be stored, so amine group (ammonia) is removed, leaving an organic acid which can enter the Krebs cycle. The ammonia is toxic, so enters the ornithine cycle to make urea, which is less toxic. This urea is released from hepatocytes into the blood, where it enters the urine through the kidneys.

Plasma Protein Synthesis:
Fibrinogen: - blood clotting
- globular, soluble protein.
- in a wound, exposed collagen causes platelets to cause prothrombin into thrombin. Thrombin then catalyses the removal of some amino acids from fibrinogen, which can then polymerise to make fibrin.
- Fibrin is insoluble and forms a mesh around the wound where red blood cells and platelets will get caught.
- This stops blood escaping and stops pathogens entering the wound.

Globulin:
- this is the term for most globular proteins.
- some globulins are made in the immune system eg immunoglobulins (antibodies)
- some globulins made in the liver, which help to transport other molecules in blood plasma such as hormones and lipids.

Albumin:
- Too large to enter tissue fluid through pores in capillaries.
- Albumin lowers the solute potential of the blood plasma.
- At the arterial end of a capillary, the relative hydrostatic pressure is high which forces water out and into the tissue fluid.
- At the venous end, the relative hydrostatic pressure is still trying to force water out, however it is now lower than the solute potential (caused by albumin). This means that the net flow of water is back into the capillary.
- If this didn't occur, then water wouldn't enter back into the capillary, and you would oedema would occur. Kwashiorkor sufferers get oedema because they don't have enough protein in their diet to synthesise enough albumin.

Bile Production:
Bile contains:
- water
- bile salts, made from cholesterol, which emulsifies fats
- cholesterol, makes bile salts water soluble so they are more effective at emulsification. Too much cholesterol migt cause gall stones, which can block the bile duct, and have to be removed with surgery or ultrasound treatment.
- bilirubin, an excretory product.

Erythrocytes (red blood cells) are broken down by the spleen and liver, and the haemoglobin spilts into haem and globin. The globin can be converted to amino acids and used for protein synthesis. The haem group is broken into iron and bilirubin. Iron is stored in the liver, and bilirubin is excreted in bile. Jaundice is a disease where bilirubin isn't excreted efficiently, and a symptom is yellow skin (because bilirubin is yellow and can appear in your skin). Newborn (often premature) babies have jaundice as their liver is not yet fully formed.

Detoxification:
Breaks down drugs and hormones, so they have a time limited effect.

Alcohol Metabolism:
-Ethanol is toxic.
- in hepatocytes, enzyme alcohol dehydrogenase converts ethanol to ethanal.
- Enzyme aldehyde dehydrogenase converts ethanal to ethanoate.
-Ethanoate can enter the Krebs cycle.

This metabolism produced a lot of reduced NAD, which disrupts other metabolic reactions, eg, fatty acid breakdown. This means that fats are stored in hepatocytes, causing 'fatty liver'.

Alcohol also destroys hepatocytes, and the repair often leaves blood supply damaged, with some blood passing straight through the liver without going near any hepatocytes. Hepatocytes may not be replaced properly, and fibrous tissue is laid down in their place. This damage is known as cirrhosis of the liver, and means that liver cells cannot convert ammonia to urea efficiently. This can cause damage to the central nervous system resulting in coma or death.

This is really helpful thanks, am going over digestiona dn the liver tomorrow so shall check this out again tomorrow

No problem! I'm just about to start support and locomotion, so I'll try and figure out the answer to your muscle contraction question

Just got a B in a past paper. Only problem is that i did that paper 3 weeks ago and only just got around to marking it today due to other revision for other exams. So all that information has now gona nad needs to relearned along with more before wednesday

I don't have everyday to do it either as I have an even bigger exam the day ater, which I have also not had time to revise for due to other revision

I'm not very convinced that these notes are very good, so any suggestions or improvements would be brilliant!

Behaviour:

Innate Behaviour - Inherited, no learning needed, instictive and shown my all members of the species, eg dragonfly nymph 'knowing' how to turn into a adult and fly with no apparent practice or learning.

Reflex
- Automatic response to a stimulus not involving the brain (no concious thought).
- Stereotyped response shown by all members of a species.
- Rapid reaction, often with no intermediate neurone.
- instictive, innate behaviour
- eg, loud sound = blink, bright light = pupil gets smaller.
- Reflexes can also be learnt, and these are known as conditioned reflexes.

Some innate behaviour can be influenced by experience to become more effective, eg baby birds learning to turn their heads to get food from their mother quicker.

Habituation - a simple type of learning where an animal learns not to respond to a repeated harmless stimulus.

Pavlov:
Classical Conditioning - where an animal learns to respond to a stimulus that is different to the one that normally elicits response. eg, sound of bell causes salivation.

Pavlov's dogs experiment was where Mr Pavlov measured the volume of saliva produced when meat powder was given to dogs. He then rang a bell before the meat powder was given. Eventually, the dogs learnt that the bell meant food was coming and started to salivate.

Unconditioned stimulus = taste of food.
Unconditioned reflex = taste of food causes salivation.
Conditioned stimulus = sound of bell.
Conditioned reflex = sound of bell causes salivation.

Skinner:
The Skinner box was a box where various animals had to perform a task like push a button to either receive an award or to avoid a punishment.

Associative learning - animal associates task with reward.
Operant learning - animal learns to do something for a reward.

Kohler:
A chimp was given a stick, and a banana was placed outside of its cage, out of reach of the chimps hands. The chimp learned to rake the banana in with the stick. The chimp was then given 2 sticks that could be attached together, and the banana was placed out of reach of just one stick. The chimp tried to reach the banana with one stick and failed and after a while he went a played with the 2 sticks on the other side of the cage. While he was playing, he suddenly realised that one stick could be attached to the other to make a longer stick. Straight away he rushed back to the banana and used the extended stick to rake the banana. This shows 'insight learning' and suggests that the chimp was thinking about the problem. This has been demonstrated with other animals such as pigeons.

Insight learning - animal appears to integrate memories from 2 or more pieces of behaviour to produce a response leading to a reward.

have you got chemistry the day after? cos i do and its really annoying as i dont know which to revise for first.

awesomnia, where are you getting these notes from? not that they're bad notes, in fact theyre very good notes but what i tend to do( due to bad past experiences) is take notes directly from the mark schemes to see exactly what theyre looking for.

They are really good notes, I took notes from nick snowden's sight and my textbook, I think ours are quite similar

awesomnia, where are you getting these notes from? not that they're bad notes, in fact theyre very good notes but what i tend to do( due to bad past experiences) is take notes directly from the mark schemes to see exactly what theyre looking for.

I'm getting my notes from the text book and nick snowden's notes, but also a bit from my notes from school and wikibooks. Once I'm finished I might look through some past papers and add little extra bits in, but if you have any suggestions then I'll be glad to put them it (that means I'm too lazy to sift through past papers myself )

I have chemistry the day after!
So im sticking with biology, then going mental on chemistry as soon as i come back home, maybe pulling an alnighter, hopefully it will pay off

Who's Nick Snowdon, and where can I get these notes?

yeah im thinking of an all nighter too, done a few of them already though.

No idea who he is, I got them off a link from another thread.
Here's a link for them all:
http://www.nicksnowden.net/Other_pages/