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.