Biology Revision Notes

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Circulatory systems
Closed circulatory systems:
• Blood leaves heart under pressure to arteries then arterioles then capillaries. • Capillaries come in large numbers. They exchange substances between the blood and cells. • After passing through capillaries, blood goes back to the heart via veins. • Valves in the veins ensure that blood only flows in one direction. Single circulatory system:

• Heart pumps deoxygenated blood.
• Gaseous exchange (diffusion of CO2 from blood to H2O and diffusion of O2 from H2O into the blood)
• Blood leaves, then goes to rest of body then heart
Double circulatory system:
• Right ventricle pumps deoxygenated blood to the lungs where it receives oxygen. • The oxygenated blood then returns to the heart to be pumped a second time ( by the left ventricle) out to the rest of the body.

In the circulatory system all the particles it contains are transported in one direction in a process known as mass flow. properties of water that make it a good transport medium:
• Water is liquid at room temperature.
• The hydrogen's in the water push away from each other making the molecule V shaped. • Many water molecules can bond together forming hydrogen bonds, as the negatively charged oxygen of one molecule bonds to the positively charged hydrogen of another. • The hydrogen bonding holds them together and results in many of the properties of water. • Many chemicals dissolve easily in water.

• Polar molecules (hydrophilic) dissolve easily in water.
• Non-polar (hydrophobic) substances, e.g. lipids, do not dissolve in water. • Water has a high boiling point because the hydrogen bonds require a lot of energy to break as they are very strong. The heart and blood vessels.

The heart consists of:
• Aorta (to body).
• Pulmonary artery (to lungs).
• Pulmonary veins (from lungs).
• Left and right atrium.
• Left and right ventricle.
• Atrioventricular valves (separates the ventricles and atrium). • Semi-lunar valve (separates the ventricles from the aorta). • Inferior vena cava (from lower body).
• Superior vena cava (from head and arms).

Blood drains into left atrium from along the pulmonary vein. Raising blood pressure in left atrium forces left ventricular valve open. Contraction of left atrial muscle forces more blood through valve. Right side, at the same time, blood enters from body along vena cava. Right atrial muscle contracts and the right AV valve opens due to the pressure difference. Blood enters the right Ventricle – it contracts, then blood leaves semilunar valve along artery to lungs.

Arteries and veins:.
Arteries: narrow lumen, thick walls, more collagen, elastic fibres and smooth muscle, no valves. Veins: wide lumen, less smooth muscle and elastic fibres, thinner walls, has valves. Capillaries: Are only one cell think and join the small arteries and small veins. How does blood move through the vessels?

• Every time the heart contracts (systole) blood is forced into arteries and their walls stretch to accommodate the blood. • During relaxation of the heart (diastole) the elasticity of the walls causes them to recoil behind the blood pushing the blood forward. How the valves in veins work:

How the heart works
The four chambers of the heart.
Phase 1: Atrial systole.
• blood under low pressure flows into the left and right atria from the pulmonary veins and vena cava. • as atria fill pressure against atrioventricular valves pushes them open and blood starts. leaking into the ventricles.

• the atria walls then contract forcing more blood into the ventricles. Phase 2: Ventricular systole.
• Ventricles contract from base upwards increasing the pressure. • this pushes blood up and out through the arteries.
• the pressure of blood against the atrioventricular valves closes them and prevents back-flow into the atria. Phase 3: Diastole.
• Atria and ventricles relax during diastole.
• Elastic recoil lowers pressure in the atria and ventricles. • Blood under higher...
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