Transport in Humans – Key Vocabulary

Vocabulary flashcards summarising blood composition, vessel structure, circulation pathways and related disorders in human transport system.

Semi-lunar valves (in veins)

Pocket-shaped valves that prevent back-flow of blood in veins; weakness or damage causes blood to pool and veins to swell (varicose veins).

Skeletal-muscle pump

The squeezing action of contracting skeletal muscles on nearby veins, raising venous pressure and moving blood toward the heart.

Plasma

Straw-coloured liquid (≈55 % of blood) containing water, salts, glucose, amino acids, vitamins, urea, proteins, fats, hormones and dissolved gases; transports nutrients, wastes and signalling molecules.

Red blood cell (erythrocyte)

Biconcave, anucleate cell packed with haemoglobin; carries oxygen from lungs to tissues and helps transport some CO₂.

Haemoglobin

Iron-containing respiratory pigment inside erythrocytes that reversibly binds oxygen to form oxyhaemoglobin.

White blood cell – Lymphocyte

Leucocyte with a large spherical nucleus (≈90 % of cell); produces antibodies for specific immune responses.

White blood cell – Phagocyte

Leucocyte with a lobed nucleus; engulfs and digests pathogens or debris by phagocytosis.

Phagocytosis

Process by which phagocytes surround, engulf and enzymatically digest foreign particles such as bacteria.

Platelet

Membrane-bounded fragment of bone-marrow cells that initiates the clotting cascade when blood is exposed to air or damaged tissue.

Blood clotting

Conversion of liquid blood to a semi-solid clot that seals wounds, limits blood loss and blocks pathogen entry.

Tissue fluid

Plasma lacking plasma proteins; bathes body cells, allowing exchange of nutrients, gases and wastes between blood and tissues.

Capillary exchange

Diffusion of O₂, glucose and amino acids from blood to tissue fluid and CO₂, urea from cells to blood; red cells travel single file, slowing flow for efficient exchange.

Flow of blood pathway

Heart → artery → arteriole → capillary → venule → vein → heart.

Cardiac cycle

Sequence of events in one heartbeat, comprising atrial systole, ventricular systole, atrial diastole and ventricular diastole.

Atrial systole

Contraction of atrial walls forcing blood into relaxed ventricles.

Ventricular systole

Contraction of ventricles; bicuspid & tricuspid valves close, semi-lunar valves open, blood enters aorta and pulmonary artery.

Atrial diastole

Relaxation of atria while ventricles contract, allowing atria to refill from venae cavae and pulmonary veins.

Ventricular diastole

Relaxation of ventricles; semi-lunar valves close, AV valves open, ventricles fill from atria.

Atherosclerosis

Build-up of cholesterol and saturated fat plaques in coronary arteries, narrowing lumen, raising blood pressure and predisposing to thrombosis.

Thrombosis

Formation of a blood clot inside a vessel; in coronary arteries it can block oxygen and glucose supply, causing a heart attack.

Pulmonary circulation

Right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium; carries deoxygenated blood to lungs and returns oxygenated blood.

Systemic circulation

Left ventricle → aorta → body tissues → venae cavae → right atrium; distributes oxygenated blood to organs and returns deoxygenated blood.

Double circulation

Combination of pulmonary and systemic circuits, ensuring blood passes through the heart twice per complete body loop for high pressure delivery.

Artery

Thick muscular, elastic-fiber wall; small lumen; no valves; carries blood away from heart under high pressure (usually oxygenated).

Vein

Thin muscle wall, few elastic fibers; large lumen; contains semi-lunar valves; returns blood to heart under low pressure (usually deoxygenated).

Capillary

Microscopic vessel, wall one cell thick; links arterioles to venules; site of exchange between blood and tissues.

Pulmonary artery

Only artery carrying deoxygenated blood; transports blood from right ventricle to lungs.

Pulmonary vein

Only vein carrying oxygenated blood; returns blood from lungs to left atrium.

Aorta

Largest artery; carries oxygenated blood from left ventricle to systemic circulation.

Vena cava (superior & inferior)

Largest veins; return deoxygenated blood from body to right atrium.

Hepatic artery

Supplies oxygenated blood to the liver.

Hepatic vein

Drains deoxygenated blood from liver into inferior vena cava.

Hepatic portal vein

Carries nutrient-rich blood from intestines to liver for processing.

Renal artery

Delivers oxygenated blood to kidneys for filtration.

Renal vein

Returns filtered, deoxygenated blood from kidneys to vena cava.

Varicose veins

Swollen, twisted veins caused by valve failure, prolonged standing, high venous pressure or inherited weak vein walls.

Factors increasing vein visibility

Low body fat, exercise, heat-induced vasodilation, genetics and ageing can make superficial veins bulge.