Transport in humans flashcards

Topic 11: Transport in humans

Double circulation

Blood passes through the heart twice for each complete circuit of the body.

Pulmonary circuit

Right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium. Low pressure.

Systemic circuit

Left ventricle → aorta → body organs → vena cava → right atrium. High pressure.

Septum

Separates left and right sides, so oxygenated and deoxygenated blood do not mix.

Why is the left ventricle wall thicker than the right?

It pumps blood round the whole body at high pressure; the right ventricle pumps only to the nearby lungs.

Valves during one heartbeat

Ventricles contract: atrioventricular valves close (no backflow to atria) and semilunar valves open. Ventricles relax: semilunar valves close (no backflow to ventricles).

Coronary heart disease: cause and risk factors

A coronary artery is blocked (fatty deposits, clot), so heart muscle is short of oxygen and glucose. Risk factors: diet, sedentary lifestyle, stress, smoking, genetic predisposition, age, gender.

Artery vs vein vs capillary

Artery: high pressure, thick muscular elastic wall, narrow lumen, no valves. Vein: low pressure, thin wall, wide lumen, valves. Capillary: wall one cell thick, short diffusion distance.

Hepatic portal vein vs hepatic vein

Hepatic portal vein: small intestine → liver, rich in absorbed food. Hepatic vein: liver → vena cava.

Functions of the blood components

Red cells: oxygen transport. Lymphocytes: produce antibodies. Phagocytes: engulf pathogens. Platelets: clotting. Plasma: transports cells, ions, glucose, amino acids, hormones, carbon dioxide, urea, vitamins and plasma proteins.

Blood clotting

Soluble fibrinogen is converted to insoluble fibrin threads, forming a clot that stops blood loss and the entry of pathogens.

Tissue fluid

Fluid from plasma that is forced out of capillaries and bathes the cells. Oxygen, glucose and amino acids pass to the cells; carbon dioxide and urea pass back. Much of it returns to the capillaries.