6.2 – The Transport System
6.2.1 – Draw and label a diagram of the heart showing the four chambers, associated blood vessels, valves and the route of blood through the heart
6.2.2 – State that the coronary arteries supply the heart muscle with oxygen and nutrients
Coronary arteries are blood vessels that provide oxygen-rich blood and other nutrients to the heart. They attach to and wrap around the heart’s surface. They branch from the aorta to carry blood back to the heart muscle.
The left coronary artery branches off into smaller arteries, including the left anterior descending artery, supplying blood to the front of the heart. The left circumflex artery encircles the heart and supplies blood to the back of the heart. It supplies the left atrium.
The right coronary artery branches to the right marginal branch to supply blood to the lower right side of the heart. This supplies the right atrium.
These vessels carry blood so that the heart muscle cells are supplied with the oxygen and nutrients needed for them to work
6.2.3 – Explain the action of the heart in terms of collecting blood, pumping blood, and the opening and closing of valves
When the heart contracts, the volume of the chambers decreases, increasing the pressure and causing blood to be pushed into a region of lower pressure. The valves in the heart prevent the blood from flowing back again.
The first part to contract is the atria, pushing the blood past the bicuspid valve into the ventricles. The muscles of the atria then relax. The muscles of the ventricles contract, closing the bicuspid valve and forcing blood into the aorta through the semi lunar valves (or pulmonary artery on the right side). Both the atria and ventricle muscles relax, and blood flows into the atria.
Deoxygenated blood enters the right atrium of the heart from the superior and inferior vena cava, whilst oxygenated blood enters the left atrium from the pulmonary veins. As the blood flows into the ventricles, the direction of flow is controlled by the semilunar valves and the atrioventricular valves to prevent any backflow. From the ventricles, the blood is pumped into the arteries.
6.2.4 – Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline)
The heartbeat is described as myogenic in origin because it originates from the heart itself, and does not require nerve impulses to stimulate it. This is why the heartbeat is not voluntary. The pacemaker is a structure in the wall of the right atrium. Impulses are sent to the muscles of the atria through special muscles muscle fibres to trigger contraction of the atria, followed by the ventricles. There is a rest period while the heart refills with blood, where the heart becomes insensitive to stimulation.
This is an involuntary response, controlled in the medulla to speed up or slow down depending on our body’s needs. Two nerves send these messages, and they are described as antagonistic. The heat rate is changed in response to stress, anticipation, emotion, or to low or high blood pressure. This is the result of increased release of adrenaline.
6.2.5 – Explain the relationship between the structure and function of arteries, capillaries and veins
Arteries carry blood away from the heart. They have thick, strong elastic walls due to the presence of collagen fibres and smooth muscle. Blood in the arteries is under high pressure, and travels in pulses, thus they must have strong wall to be able to cope with this. The pressure is increased by the narrow lumen. The middle layer of muscle is very thick to prevent leaks and bulges.
Veins carry blood back to the heart. They also have strong walls, but these are thinner and have fewer elastic fibres. Blood in the veins is under lower pressure and does not travel in pulses. There is little risk of them bursting so they are not as thick as arteries, with only a thin layer of muscle surrounding them. These nearby muscles contract to help push the blood back to the heart. To prevent blood from flowing backwards, veins have valves. They have a wide lumen.
Capillaries branch out from the arteries in veins to bring blood closer to cells. They consist solely of an endothelium, only one cell thick. This allows for more rapid diffusion. They also have pores in their membranes for the secretion of plasma and phagocytes. Capillaries have a narrow lumen, which allows many capillaries to fit in a small space.
𝒂𝒐𝒓𝒕𝒂 → 𝒂𝒓𝒕𝒆𝒓𝒚 → 𝒂𝒓𝒕𝒆𝒓𝒊𝒐𝒍𝒆 → 𝒄𝒂𝒑𝒊𝒍𝒍𝒂𝒓𝒚 → 𝒗𝒆𝒏𝒖𝒍𝒆 → 𝒗𝒆𝒊𝒏 → 𝒗𝒆𝒏𝒂 𝒄𝒂𝒗𝒂
6.2.6 – State that blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes) and platelets
Plasma is the liquid medium of blood in which all the other elements are suspended. Through plasma, substances are exchanged between cells and tissues. It transports nutrients, excretory products like urea, hormones, dissolved proteins, antibodies and heat.
Red blood cells are also called erythrocytes, and they transport the respiratory gases to cells. This includes oxygen and carbon dioxide.
White blood cells are also called leucocytes, and combat infection. Lymphocytes form antibodies as part of the immune system, whilst phagocytes ingest bacteria and cell fragments.
Platelets are important for blood clotting.
6.2.7 – State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat
Blood carries oxygen to all tissues for respiration, and then brings the carbon dioxide which is produced back to the lungs. White blood cells form antibodies, which are also suspended in the plasma.
Nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat are all found in the
plasma, which is the transport medium, taking them to their various destinations in the