OCR (A) Biology A-level: Transport in Animals

Flashcards covering circulatory systems, blood vessel structures, tissue fluid formation, the cardiac cycle, and the properties of haemoglobin.

Open circulatory system

A circulatory system where blood is not confined to blood vessels, for instance in insects.

Closed circulatory system

A circulatory system where blood is confined to blood vessels only, like in fish and mammals.

Single circulatory system

A system consisting of a heart with two chambers where the blood passes through the heart once for every circuit of the body.

Double circulatory system

A system where the heart has four chambers and blood passes through the heart twice for every circuit of the body.

Arteries

Thick-walled vessels adapted to carry blood away from the heart, containing elastic tissue for recoil and smooth muscle to vary blood flow.

Arterioles

Vessels that branch off arteries with thinner and less muscular walls; their role is to feed blood into capillaries.

Capillaries

Smallest blood vessels and the site of metabolic exchange, featuring walls only one cell thick for fast exchange of substances.

Venules

Blood vessels that are larger than capillaries but smaller than veins.

Veins

Thin-walled vessels with a wide lumen that carry blood under low pressure to the heart and contain valves to prevent backflow.

Tissue fluid

A liquid containing dissolved oxygen and nutrients that enables the exchange of substances between blood and cells.

Hydrostatic pressure

Pressure created when blood is pumped along the arteries into arterioles and capillaries, forcing blood fluid out of the capillaries.

Osmotic pressure

Pressure that pushes some tissue fluid back into capillaries caused by the more negative water potential of blood compared to tissue fluid.

Lymphatic system

A system that carries remaining tissue fluid (as lymph fluid) back to the blood and filters out bacteria via lymph nodes and lymphocytes.

Myogenic

The heart’s ability to initiate its own contraction without external nervous stimulation.

Sinoatrial node (SAN)

A region of specialised fibres in the right atrium wall that acts as the pacemaker of the heart by initiating a wave of electrical stimulation.

Atrioventricular node (AVN)

A node located between the two atria that passes electrical excitation to the ventricles via the bundle of His.

Bundle of His

A collection of heart muscle cells specialized for electrical conduction that transmits impulses from the AVN to the apex of the heart.

Purkyne fibres

Branches of the bundle of His that carry the wave of excitation upwards through the ventricle walls, causing them to contract.

Atrial systole

Stage of the cardiac cycle where atria contract, forcing atrio-ventricular valves open and blood into the ventricles.

Ventricular systole

Stage where ventricles contract, closing atrio-ventricular valves and opening semi-lunar valves to pump blood into the aorta and pulmonary artery.

Cardiac diastole

Stage where atria and ventricles relax, lowering pressure inside heart chambers and closing semilunar valves to prevent backflow.

Haemoglobin

A water-soluble globular protein consisting of two alpha and two beta polypeptide chains, each containing a haem ($Fe^{2+}$) group.

Partial pressure

A measure of oxygen concentration; as it increases, the affinity of haemoglobin for oxygen increases.

Dissociation curves

Graphs that illustrate the change in haemoglobin saturation as the partial pressure of oxygen changes.

Fetal haemoglobin

A specific type of haemoglobin with a higher affinity for oxygen compared to adult haemoglobin, allowing oxygen absorption at the placenta.

Bohr effect

The phenomenon where the affinity of haemoglobin for oxygen decreases in the presence of carbon dioxide ($CO_2$).