A stroke occurs when a small blood clot, often formed in the left atrium, is carried in the blood to the brain, where it blocks a small artery and causes brain damage. Name all of the structures that a blood clot in the left atrium must pass through to reach the blood vessels supplying the brain. The structures must be given in the correct sequence.
Explain why obstruction of a small artery in the brain causes brain damage.
A frequent cause of AF is when a small group of muscle cells in the wall of the left atrium begins to release electrical impulses to the surrounding heart muscle cells. Explain how the control of heartbeat by the sinoatrial node can be disrupted by AF, resulting in rapid and irregular atrial contractions.
Red blood cells take part in transporting oxygen and carbon dioxide in the blood. Fig. 5.1 is a diagram showing the exchange of oxygen and carbon dioxide between a red blood cell in a capillary and a respiring cell. Some of the reactions that happen in the red blood cell are also shown. The diagram is not drawn to scale. Identify enzyme X and molecule Y in Fig. 5.1.
The hydrogencarbonate ions shown in Fig. 5.1 leave the red blood cell and are replaced by chloride ions. State why chloride ions must enter the red blood cell as hydrogencarbonate ions leave.
Identify the aqueous environment, labelled Z in Fig. 5.1, that surrounds the respiring cell.
Oxygen and carbon dioxide are also exchanged between blood capillaries and alveoli in the lungs. Specialised cells in the gas exchange system stop harmful microscopic particles in inhaled air from reaching the alveoli. These particles are linked to many respiratory diseases. Explain how specialised cells in the gas exchange system prevent harmful microscopic particles from reaching the alveoli.