The Heart

There are 5 functions of blood:

• Carrying glucose and oxygen to cells.
• Carrying excretory products.
• Carrying hormones.
• Forming part of the immune system.
• Distributing heat. 

• Plasma: contains many dissolved substances to be transported around the body. Also contains fibrinogen, which is a soluble substance vital for the clotting of blood. Its main adaption is that it consists of water. 
• Red blood cell: They contain haemaglobin, which carries oxygen. They are in a biconcave shape with no nucleus to increase surface area. They are flexible to pass through walls. 

• White blood cell: key to immune system in fighting againt infection.  Contain a nucleus and are made in the white bone marrow. They can change shape to squeeze through blood vessels.
• Platelets: are tiny fragments of larger cells. They are involved in blood clotting. 

• Blood clotting prevents too much blood being lost, and prevents pathogens entering the body.
• At the site of the cut, platelets break open and release thromboplastin.
• Thromboplastin catalyses prothrombin -> thrombin.
• Thrombin catalyses fibrinogen -> fibrin.
• Fibrin forms a mesh, trapping blood cells. 
• This is the cascade sequence.
• Platelets also release serotonin, which narrows blood vessels.

• A circulatory system transports oxygen and nutrients around the body, and removes waste from the body.
• Some animals have an open circulatory system, which is blood circulating in large open spaces. 
• This is good for animals with a large surface area:volume ratio, which enables them to rely on simple diffusion.  
• Most large animals have a closed circulatory system, where blood is contained in blood vessels.

• Small, closed circulation animals may have a single circulatory system.
• Deoxygenated blood is pumped from the heart to the lungs. Oxygenated blood is pumped from lungs to body cells. Deoxygenated blood is pumped from body cells back to heart. 

• A double circulatory system conists of systematic circulation and pulminary circulation.
• Pulminary circulation: deoxygenated blood is pumped from the heart to the lungs. Oxygenated blood from lungs to the heart.
• Systematic circulation: oxygenated blood is pumped from heart to body cells. Deoxygenated blood from body cells to heart. 

There are 4 advantages of having a double circulatory system:

• Ensures oxygenated and deoxygenated blood do not mix.
• Maximises oxygen delivery at high pressure.
• Ensures tiny blood vessels do not burst.
• Pumps blood hard to travel around the whole body.

Artery:

• Thick outer walls and thick inner layer to withstand blood at high pressure and thin lumen to maintain it.
• Elastic fibres in inner layer allow artery to stretch and recoil which mainains blood pressure.
• Smooth muscle in inner layer can squeeze blood along.
• Final layer surrounding lumen is the endothelium. 

Vein:

• Thin outer wall and thin inner layer because large lumen gives low blood pressure.
• Large lumen means veins can hold large volumes of blood.
• Veins contain semi-lunar valves, which return low pressure blood to the heart, preventing backflow.
• Inner layer also contains muscles and elastic fibres, for same reasons as arteries.
• Also an inner endothelium layer. 

Capillary:

• Walls are 1 cell thick to allow very easy diffusion in and out of capillaries. 
• Blood travels relatively slowly, giving substances more opportunity to diffuse.
• Endothelium cell wall contains no elastic fibres, smooth muscle or collagen. 

• The heart muscle is myogenic. It can initiate its own contraction without needing an external nervous impulse.
• The heart has intrinsic rythmicity. It can keep beating outside of the body, provided it has the right nutrients and conditions. 

• The sinoatrial node (SAN) is located in the upper right atrium.
• The SAN can spontaneously contract, generating nerve impulses that make atria contract. 
• The atrioventricular node (AVN) is located in the septum between the two atria.
• The AVN sends impulses to the ventricles along the bundle of His. 

• SAN contracts and sends impulse to atria which causes atria to contracts.
• Impulse reached AVN.
• Delay at AVN to ensure ventricles contract after atria.
• Impulse travels to ventricles via bundles of His.
• Ventricles now contract. 

• Atrial systole: atria contract, ventricles relax, atrio-ventricular valves open, semilunar valves closed, blood moving into ventricles.
• Ventricular systole: atria relax, venticles contract, atrio-ventricular valves closed, semilunar valves open, blood moving into arteries.
• Diastole: atria relax, ventricles relax, atrio-ventricular valves open, semilunar valves closed, blood moving into atria and ventricles. 

Atherosclerosis:

• Damage to cells lining artery leads to inflammatory response.
• Build up of white blood cells, cholestrol, calcium salts, fibrous tissue and platelets in damaged area.
• Formation of atheroma (plaque).
• Causes loss of elasticity of artery and narrowing of lumen.
• Causes high blood pressure. 

Aneurysm:

• Lumen of artery is narrowed by plaque (atherosclerosis) and blood builds up behind blockage.
• This causes wall of artery to bulge and become weakened.
• This weakened artery may burst causing internal bleeding.

Angina:

• Plaque builds up in coronary arteries.
• Blood flow to heart muscle reduced.
• Heart muscle needs to respire anaerobically, which builds up lactic acid and oxygen debt.
• This causes pain in chest which can spread to arms and jaw. 

Heart attack:

• Complete blockage in a branch of the coronary artery.
• Part of heart muscle becomes starved of oxygen, preventing aerobic respiration.
• This causes scar tissue, due to death of cells. 

Stroke:

• Caused by an interuption of blood supply to the brain, either by bleeding from damaged blood vessels or from blockage in blood vessels leading to brain.
• Causes dizziness, slurred speach, paralysis of one side of body. 

• The amount of energy stored in food can be measured with a calorimeter.
• It measures the amount of energy released when a known quantity of food is completely burnt in oxygen.
• Energy released is transferred to water and the temperature rise is measured.
• 1 Calourie raises 1g of water by 1 degree. 

• Basal metabolic rate (BMR) is the energy required to keep organs/cells working correctly when you are at rest.
• BMR is calculated by heat loss in humans over a period of time.
• BMR is higher if you have more muscle rather than  fat.

• Whether someone is obese or not can be determined by their body mass index (BMI),                                    = mass/height squared.
• This factors mass against height, so being above a certain value makes you obese.
• Being obese means you are more likely to have high blood pressure, suffer from CVD, have high blood cholestrol, and have type 2 diabetes. 

High density lipoproteins:

• Are made of unsaturated fats, cholestrol and protein. 
• Carry cholestrol from tissues to liver so that it can be broken down.
• So HDLs lower cholestrol level.

Low density lipoproteins:

• Made from saturated fats, cholestrol and protein.
• Carry more cholestrol than HDLs, but carry cholestrol to cell membrane instead of inside liver.
• Too many LDLs can saturate cell membrane, so there are more left in blood.

• Diurretics, Beta blockers, Sypathetic nerve inhibitors and ACE inhibitors all reduce blood pressure.
• However, they may cause blood pressure to drop too low.
• They may also cause coughing, swelling, impotence and fatigue.

• Statins lower cholestrol by blocking the enzyme that makes cholestrol.
• They block LDL synthesis.
• However, they can cause fatal muscle inflammation, or there is a risk the patient may not try to live a healthy lifestyle because drug is so effective.
• Plant stanols and sterols have the same effects as statins. 

• Anticoagulates prevent blood clotting.
• Doses must be carefully monitored otherwise blood will not clot at all.
• May irritate stomach lining.