Blood Vessels and the Heart

Blood Vessels• Three Types– Arteries: carry blood away from the heart

• Thick walled, smaller vessels are called arterioles

– Veins: carry blood towards the heart• Thin walled, smaller vessels are called venules• Contains valves

– Capillaries: connect the arteries to the veins• Smallest of the blood vessels• RBC’s travel single file through capillaries• Branch like system to increase surface area for

diffusion• Site of gas exchange

Arterial System

• Transports blood under pressure.• Blood moves in a pulse-like wave.• Contraction & relaxation of arterioles is the major determinant of the overall blood pressure.

Venous System

• Thinner walls, larger diameters & less muscle than arteries.

• Contains 70% of total blood volume.• Most veins work against gravity.– Valves allow one-way flow.– Contraction of skeletal muscles pushes blood toward heart.

Pathways of Blood• Pulmonary Circuit– Right side of heart.– Low-pressure system.– Takes deoxygenated blood to the lungs and back to the heart

• Systemic Circuit– Left side of heart.– High-pressure system.– Takes oxygenated blood to the body and returns

deoxygenated blood back to the heart

Pulmonary Circuit• Right atrium receives oxygen-poor blood from:– Superior vena cava.– Inferior vena cava.

• Blood flows through the tricuspid valve or the right atrioventricular (AV) valve to the right ventricle.

Blood from body

Blood from body

Pulmonary Circuit• Blood flows through the pulmonary semi-lunar valve &

enters the pulmonary trunk, which divides into the left & right pulmonary arteries.– Divides into capillaries where external gas exchange (respiration system) occurs.

• Oxygenated blood enters the left & right pulmonary veins,

returning blood to the left atrium.

Systemic Circuit

• Blood flows through the left AV-valve or bicuspid (mitral) valve to the left ventricle.– Left ventricular walls are two times thicker than in the

right ventricle.

• Blood travels through the aortic semi-lunar valve to the aorta.

Systemic Circuit

• Aorta branches into smaller systemic arteries, which branch into arterioles & then capillaries.– Internal gas exchange occurs.

• Capillaries rejoin as venules & then veins.• Deoxygenated blood returns to the right atrium

via the superior & inferior vena cava.

Coronary Circulation

• Delivers oxygenated blood to the heart muscle.• Consists of the left & right coronary artery.