The Circulatory System (Edexcel International A Level (IAL) Biology): Flashcards

Capillaries are microscopic blood vessels that carry blood to the cells and allow for exchange of substances between blood and tissues.

The lumen is the central cavity of a blood vessel through which blood flows.

Arteries have a narrow lumen to help maintain high pressure.

Veins contain valves, which prevent the backflow of blood and help return blood to the heart.

The endothelium is a single layer of cells lining the lumen of all blood vessels, providing a smooth surface to reduce friction.

The elastic tissue in the artery wall helps to maintain blood pressure by stretching and recoiling.

True.

Capillary walls being only one cell thick reduces the diffusion distance for quick exchange of oxygen and carbon dioxide.

Collagen is a strong structural protein in the outer wall of blood vessels that protects them from damage by over-stretching.

Arteries have a thicker layer of smooth muscle and elastic tissue to withstand high pressure and to allow for stretching and recoil as blood is pumped from the heart.

Red blood cells pass through capillaries in single file, which causes blood to travel slowly and provides more time for diffusion.

False.

A pulse is absent in veins because the arteries have stretched and recoiled, so pressure is now low and steady.

A circulatory system is a system that transports fluids containing materials needed by the organism and removes waste materials.

In a closed circulatory system, blood is always contained within blood vessels, whereas in an open circulatory system, blood bathes the organs in the body cavity.

In humans, blood passes through the heart twice in one complete circuit of the body.

The right side of the heart pumps deoxygenated blood to the lungs in the pulmonary circulatory system.

The blood vessel that brings blood from the body to the heart is the vena cava.

The pericardium is a tough, fibrous sac that protects the heart in the chest cavity.

The human heart has four chambers: the two atria (top chambers) and the two ventricles (bottom chambers).

The wall of muscular tissue that separates the left and right sides of the heart is called the septum.

The atrioventricular (AV) valves prevent backflow of blood from the ventricles into the atria when the ventricles contract.

False.

The semilunar valves are closed during diastole to prevent blood from flowing back into the ventricles.

Systole is the contraction of the heart muscle during the cardiac cycle.

When the volume of a heart chamber decreases, the pressure inside it increases.

During ventricular systole, the atrioventricular (AV) valves close and the semilunar (SL) valves open.

During atrial systole, the atria contract, increasing pressure and forcing blood into the ventricles through the open atrioventricular (AV) valves.

Cooperative binding is when the binding of the first oxygen molecule to haemoglobin causes a conformational change that makes it easier for additional oxygen molecules to bind.

Each haemoglobin molecule contains four haem groups, each able to bind one molecule of oxygen.

True.

Haemoglobin can bind to hydrogen ions, forming haemoglobinic acid and preventing the pH of red blood cells from dropping.

A hydrogen carbonate ion (HCO₃^–) is the main form in which carbon dioxide is transported in the blood plasma.

The partial pressure of oxygen is the pressure exerted by oxygen within a mixture of gases, acting as a measure of oxygen concentration.

Haemoglobin is saturated when all of its oxygen binding sites are occupied, meaning it contains four oxygen molecules.

The affinity for oxygen describes the ease with which haemoglobin binds to and dissociates from oxygen. A high affinity means binding easily and dissociating slowly, while a low affinity means binding slowly and dissociating easily.

Cooperative binding is the process by which the binding of one oxygen molecule to haemoglobin changes the shape of the protein, making it easier for additional oxygen molecules to bind.

At low partial pressure of oxygen (pO₂), haemoglobin has a low affinity for oxygen and saturation is low.

True.

The Bohr effect causes haemoglobin’s affinity for oxygen to decrease at high CO₂ levels, so it releases oxygen more readily in respiring tissues.

The Bohr effect is the phenomenon where an increase in carbon dioxide concentration lowers haemoglobin’s affinity for oxygen, causing the oxygen dissociation curve to shift to the right.

Foetal haemoglobin has a higher affinity for oxygen so it can absorb oxygen from the mother’s blood at the placenta. This allows the foetus to obtain enough oxygen for development.

Atherosclerosis is the progressive disease in which fatty plaques (atheroma) build up beneath the endothelium, in the artery wall (tunica intima), narrowing the lumen and reducing blood flow.

Atherosclerosis is also known as hardening of the arteries, and is caused primarily by damage to the endothelium of an artery.

The endothelium is the first blood vessel layer to be damaged in the development of atherosclerosis.

An inflammatory response occurs after damage to the endothelium, attracting white blood cells such as macrophages.

Fatty streaks are formed by the accumulation of lipids, cholesterol, and macrophages under the endothelium.

An atheroma is a plaque formed from the accumulation of cholesterol, lipids, macrophages, and platelets under the endothelium in arteries.

True.

Plaques narrow the lumen of arteries, restricting blood flow and raising blood pressure.

Over time, the atheroma can calcify and harden, reducing elasticity of the artery wall.

Blood clotting is an important process that prevents excess blood loss, stops the entry of pathogens, and provides a barrier for wound healing.

A break in the skin or mucous membranes releases molecules that trigger a chemical cascade resulting in blood clotting.

The process of blood clotting is brought about by a cascade of chemical reactions.

Platelets release thromboplastin, an enzyme that triggers subsequent steps in the blood clotting cascade.

Thromboplastin and calcium ions trigger the conversion of prothrombin to thrombin.

Thrombin catalyses the conversion of soluble fibrinogen to insoluble fibrin, which forms the mesh of a blood clot.

Fibrin fibres mesh and tangle together, trapping platelets and red blood cells.

True.

A blood clot is formed when fibrin fibres mesh together, trapping platelets and red blood cells.

An atheroma is a plaque deposit in an artery that can rupture the endothelium and increase the risk of blood clotting.

A thrombus is a blood clot that forms within a blood vessel and obstructs blood flow.

A blood clot in a vessel can reduce blood flow and restrict the movement of oxygen, reducing the respiration of the surrounding cells.

If a blood clot travels to the brain, it can cause a stroke by blocking blood flow and reducing oxygen delivery to brain cells.

Deep vein thrombosis (DVT) is a condition where a blood clot forms in a deep vein, most commonly in the legs.