1.1 how does the circulation work? (2)

In a circulation system a liquid and all particles it contains travel in one direction in a process called mass flow .

In animals the transoprt medium is usually called blood.

The fluid plasma is mainly water, and carries dissolved substances such as food, oxygen and carbon dioxide. proteins, amino acids, salts, enzymes,hormones, aintibodies, urea and the waste products of proteins are just some of the substances transported in plasma.

cells are also carried in the blood; red blood cells, white blood cells and platelets.

blood also helps regualte body temperature and transfering energy around the body.

water is unusual among small molecules, at room temperature most other small molecules such as CO2 are gases, however water remains a liquid.

water is a polar molecule, meaning it has an uneveny distibuted electrical charge.

water is made up of two hydrogen particles and one oxygen.

The hydrogen ends of the molecule are slightly negatively charged and attract towards the slightly positively charged oxygen particles on other water molecules. This bond is called Hydrogen bonding.

Many chemicals dissolve easily in water allowing vital biochemical reaction to occur in the cytoplasm of cells.

free to move around, the chemicals can react.

polar molecules also dessolve easily in water. such polar substances are said to be hydrophilic -'water loving'

non polar substances such as lipids, do not dissolve in water. they are said to be hydrophobic- 'water hating'. In order to be transported by the blood, they combine with proteins to form lipoproteins.

The amount of energy needed to raise the temperature of 1cm2 of water is 1oc, which is very high.

This is because in water a large amount of energy is needed to break the hydrogen bonds.

So a large input of energy causes only a small increase in temperature, so water warms up and cools down very slowly.

This extremely useful for organisms helping then to avoid rapid changes in their internal temperature and allowing them to maintain a stead temperature even when the temperature of their surrounding varies considerably.

Arteries and veins can easily be recognised.

The walls of both vessels contain collagen, a tough fibrous protein which makes them strong and durable. They also contain elastic fibres which allow the to stretch and recoil. smooth muscle allows them to constrict and dilate.

the key differences between arteries and veins are:

arteries:                          veins:

- narrow lumen              - wide lumen                                                                          - thicker walls                - thinner walls                                                                        - more collagen             - less collagen                                                                       - more elastic fibres       - less elastic fibres                                                                - more smooth muscle   - less smooth muscle                                                            - no valves                    - valves       

The capillaries that join the small arties (arterioles) and small veins (veules) are very narrow.

Their walls are only one cell thick allowing substances to easily pass through them.

every time the heart contracts (Systole) blood is forced into arteries and their elastic walls stretch to accommodate the blood.

During Diastole ( relaxation of the heart ) the elasticity of the artery walls cause them  to recoil behind the blood, helping to push the blood foward.

The blood moves along the length of the artery as each section in series stretches and recoils in this way.

By the time the blood reaches smaller arteries and capillaries there is a steady flow of blood.

In the capillaries this allows exchange between blood and the surrounding cells through the one cell thick walls. The network of capillaries that lie close to every cell in the body ensures there is rapid diffusion between the blood and surrounding cells.

The heart has a less direct effect on the flow of blood through the veins.

In the veins blood flow is assisted by the contraction of skeletal muscles during movement of limbs and breathing.

Low pressure develpoed int he thorax (chest cavity) when breathing in also helps draw blood back into the heart from the veins.

Backflow is prevented by the valves wihtin the veins

The steady flow without pulses of blood means the blood is at a low pressure in the veins.

The coronary arteries supply the blood to the heart.

The chambers of the heart alternately contract (systole) and relax (diastole) in a rhythmic cycle.

On complete sequence of  filling and pumping blood is called a cardiac cycle, or heartbeat.

During systole cardiac muscles contract and the heart pumps blood out through the aorta and pulmonary arteries.

During diastole, cardiac muscle relaxes and the heart fills with blood.