Animal transport and cardiovascular biology definitions

The heart and cardiac cycle

Mass transport system

A system in which substances are moved in bulk, in a fluid driven by a pump, over distances too great for diffusion to serve.

Surface area to volume ratio

The exchange surface available per unit of volume; it falls as an object gets larger.

Metabolic rate

The rate at which an organism uses energy, and so the rate at which it must be supplied with oxygen and relieved of carbon dioxide.

Atrioventricular valves

The valves between each atrium and its ventricle; tricuspid on the right, bicuspid or mitral on the left.

Semilunar valves

The valves at the base of the aorta and the pulmonary artery, preventing backflow into the ventricles.

Tendinous cords

Inelastic strands running from the atrioventricular valve flaps to papillary muscles projecting from the ventricle wall. The muscles tense as the ventricle contracts, so ventricular pressure cannot turn the flaps inside out; the pressure does the opening and shutting, the cords only stop the flaps going too far.

Coronary arteries

The vessels branching from the base of the aorta that supply the heart muscle itself with oxygenated blood.

Cardiac output

The volume of blood pumped out of one ventricle in one minute: stroke volume multiplied by heart rate.

Stroke volume

The volume of blood pumped out of one ventricle in one beat.

Heart rate

The number of times the heart beats in one minute.

Myogenic

Contracting from within the muscle itself, without needing a nerve impulse to initiate the beat.

Sinoatrial node

The patch of tissue in the right atrium wall that sets the rhythm of the heart.

Atrioventricular node

The only electrical connection between atria and ventricles; it delays the impulse so the atria empty first.

Purkyne fibres

Conducting fibres running from the bundle of His up through the ventricle walls, so contraction begins at the apex.

Electrocardiogram

A recording of the potential difference measured at the skin against time, produced by the wave of depolarisation spreading through the heart muscle.

P wave

The deflection produced by depolarisation of the atria, which atrial contraction follows.

QRS complex

The large deflection produced by depolarisation of the ventricles, large because the ventricle walls hold most of the heart's muscle.

T wave

The deflection produced by repolarisation of the ventricles.

Chemoreceptor

A receptor that detects a chemical change; those controlling heart rate detect the fall in blood pH caused by dissolved carbon dioxide.

Pressure receptor

A receptor in an artery wall that detects a change in blood pressure; also called a baroreceptor.

Medulla oblongata

The region of the brain that receives impulses from the chemoreceptors and pressure receptors and adjusts heart rate through the autonomic nervous system.

Blood vessels, tissue fluid and lymph

Open circulatory system

A circulation in which blood leaves the vessels and bathes the organs directly in a body cavity before draining back to the heart.

Closed circulatory system

A circulation in which blood remains inside vessels at all times and is returned to the heart through them.

Haemocoel

The body cavity of an insect or other arthropod, in which haemolymph collects and washes over the organs.

Haemolymph

The fluid of an open circulatory system, acting as blood and tissue fluid at the same time.

Elastic artery

A large artery near the heart, such as the aorta, whose wall is dominated by elastic laminae and which stretches and recoils to smooth out the pulse.

Muscular artery

An artery further from the heart, such as the femoral or renal artery, whose wall holds more smooth muscle and which distributes blood to organs by vasoconstriction and vasodilation.

Hydrostatic pressure

The physical pressure the blood exerts against the capillary wall, pushing fluid out through the gaps between endothelial cells.

Oncotic pressure

The inward pull created by plasma proteins, which stay in the capillary and lower the water potential of the blood relative to the tissue fluid. Also called colloid osmotic pressure.

Tissue fluid

The fluid surrounding cells, formed by ultrafiltration from capillaries; it is very poor in plasma protein, though not literally protein-free, and has no red blood cells and no platelets.

Lymph

Tissue fluid that has drained into the lymphatic system; similar to tissue fluid but containing lymphocytes and, after a meal, more lipid, carried in chylomicrons.

Lymph node

A swelling in a lymph vessel where lymphocytes collect and pathogens in the lymph are removed.

Haemoglobin and oxygen dissociation curves

Conjugated protein

A protein with a non-protein prosthetic group permanently associated with it.

Prosthetic group

The non-protein component; in haemoglobin, the haem group with its iron(II) ion.

Partial pressure of oxygen

The contribution oxygen makes to the total pressure of a gas mixture, measured in kPa; a measure of how much oxygen is present.

Percentage saturation

The proportion of the oxygen-binding sites on haemoglobin that are actually occupied.

Bohr shift

The rightward shift of the oxygen dissociation curve caused by an increased partial pressure of carbon dioxide and the fall in pH that goes with it, so that oxygen dissociates more readily at any given partial pressure.

Loading

Association of oxygen with haemoglobin, at the gas exchange surface.

Unloading

Dissociation of oxygen from haemoglobin, at respiring tissue.

Carbonic anhydrase

The enzyme in red blood cells catalysing the reversible reaction between carbon dioxide and water to form carbonic acid.

Chloride shift

The movement of chloride ions into a red blood cell as hydrogencarbonate ions move out, maintaining electrical neutrality.

Haemoglobinic acid

Haemoglobin that has taken up hydrogen ions, buffering the contents of the red blood cell.