Module 1 | Lifestyle, Health and Risk

Question 1

1.1 Understand why many animals have a heart and circulation

Answer 1

To pump blood to supply oxygen and glucose to body cells, and to remove carbon dioxide and wastes from the body by mass transport. This must be done at a high pressure, and high speed. This is necessary to overcome the limitation of diffusion, because many animals have a small surface area to volume ratio and this does not allow diffusion to occur at a sufficient rate to meet their high metabolic demand.

Question 2

1.2 Understand the importance of water as a solvent in transport.

Answer 2

Water has a dipole nature, due to uneven distribution of charge within the molecule - the hydrogen atoms have a partial positive charge and the oxygen atom has a partial negative charge due to the difference in electronegativity, causing one end of the molecule to be more positive than the other. Due to this, water forms hydrogen bonds with other water molecules, and it requires a lot of thermal energy to break these bonds, therefore it has a high latent heat of evaporation.

Question 3

1.3 Understand how the structure of capillaries relates to their functions.

Answer 3

Capillaries have a very narrow lumen, this only allows one blood cell to pass through at once, and therefore slows down the rate of blood flow through the vessel, providing an optimum rate for gas exchange. The capillary itself consists of a very thin endothelium, which is just one cell layer thick - this means that the vessel is very small, and therefore can fit between cells, maintaining the short diffusion distance required for gas exchange.

Question 4

1.3 Explain how the structure of arteries relates to their functions

Answer 4

The artery has a narrow lumen which maintains the high pressure at which blood flows through the vessel. The innermost layer of the artery is the tunica interna, this consists of a smooth inner endothelial lining which reduces friction and resistance to blood flow. The middle layer is the tunica media, this contains smooth muscle which can contract and relax and exert pressure, and control the diameter of the lumen to accommodate for larger blood volumes, as well as elastic fibres - these allow stretching to accommodate higher pressure and recoil to maintain pressure. The outermost layer of the artery is the tunica externa, which contains collagen - this provides structural support, and avoids rupture and damage to the artery as a result of the high blood pressure and high blood volumes that pass through.

Question 5

1.3 Understand how the structure of veins relates to their functions.

Answer 5

Veins have a wide lumen surrounded by a smooth endothelium to minimise the resistance to blood flow, and they contain valves which prevent the backflow of blood. Like arteries, veins have a middle layer consisting of smooth muscle and elastic fibres - however it is much thinner in veins, as there is no need to maintain a high blood pressure. Veins have an outermost layer containing some collagen for structural support, but there is not as much as in arteries, because veins do not generally carry blood at such high pressures that the vessel could rupture or obtain damage.

Question 6

1.4 Know the cardiac cycle.

Answer 6

There are three stages of the cardiac cycle:
Atrial systole - During atrial systole, blood passively flows into the atria under a low pressure generated by atrial elastic recoil. As blood volume increases, the pressure in the atria increases, causing them to contract, forcing the atrioventricular valves open and blood flows into the ventricles.
Ventricular systole - ventricles contract causing an increase in pressure. Ventricular pressure is now greater than atrial pressure and therefore the atrioventricular valves close. Ventricular pressure is greater than arterial pressure and so semi-lunar valves are forced open, and blood flows into the arteries.
Cardiac diastole - The atria and ventricular walls relax by elastic recoil. This decreases the pressure in the ventricles, causing the semi-lunar valves to close. The low pressure in the atria draws blood in from the veins, enabling the cycle to repeat itself.

Question 7

1.4 Relate the structure and operation of the mammalian heart to its functions.

Answer 7

External:
Aorta - ascending - delivers oxygenated blood containing glucose into the systemic circuit.
Pulmonary artery - delivers deoxygenated blood into the pulmonary circuit.
Pulmonary vein - returns oxygenated blood to the heart from the lungs.
Vena cava - returns deoxygenated blood to the heart from the systemic circuit.
Coronary circulation - two arteries - deliver oxygenated blood to the cardiac muscle - two veins - remove carbon dioxide and waste products from the cardiac muscle.

Internal:
Right atrium - Receives deoxygenated blood from the vena cava.
Tricuspid valve - Prevents backflow of blood from the right ventricle to the right atrium.
Semi-lunar valve - Prevents backflow of blood from the main arteries to the ventricles.
Right ventricle - Pumps deoxygenated blood into the pulmonary circuit to be oxygenated via the pulmonary artery.
Left atrium - Receives oxygenated blood from the pulmonary vein.
Bicuspid valve - Prevents backflow of blood from the left ventricle to the left atrium
Left ventricle - thicker muscular wall - pumps oxygenated blood into the aorta at high pressures to enable fast blood flow into the systemic circuit.