CARDIOVASCULAR SYSTEM: BLOOD VESSELS (Chapter 15)
1. Blood vessels are tubes that carry blood away from the heart toward the tissues of the body and then
return the blood to the heart.
2. Arteries carry blood away from the heart.
3. Arteries branch extensively and eventually give rise to arterioles.
4. Arterioles branch into capillaries; substances are exchanged between the blood and surrounding tissues
through the walls of capillaries.
5. Capillaries merge to form venules.
6. Venules merge to form veins.
7. Veins merge with each other to form progressively larger veins which carry the blood back to the heart.
8. Vasa vasorum are blood vessels located in the walls of blood vessels to supply oxygen and nutrients to
the tissues that form the blood vessel walls.
1. The walls of arteries consist of three layers:
i. inner tunica internaconsists of endothelium and basement membrane
ii. middle tunica mediaconsists of smooth muscle and elastic fibers
iii. outer tunica externa consists of elastic connective tissue
2. Vasoconstriction occurs when vascular smooth muscle tissue contracts to decrease the diameter of
the lumen (mainly under control by the sympathetic autonomic nervous system). Vasodilation occurs when
vascular smooth muscle tissue relaxes to increase the diameter of the lumen.
3. Two types: large elastic arteries (aorta) and mediumsized muscular arteries that
are important for distribution to target tissues.
1. Small artery that delivers blood to a capillary
2. Play a major role in regulating blood pressure
1. microscopic blood vessel that permit exchanges of gases and nutrients
2. have specializations for transport from the capillaries to surrounding tissue: tight junctions,
intercellular clefts and fenestrations
E. Blood pressure:
1. vital sign, usually 120/80 mmHg, systolic/diastolic
2. blood pressure is influenced by: blood volume, diameter of aterioles, heart rate, constriction or dilation
of venous reservoirs (liver, spleen, skin)
3. central control sensory changes in pressure or CO2 levels and autnomic responses, kidneyrenin
angiotensin system, endocrine response
4. smoking causes vasoconstriction and increases heart rate=hypertensionleads to atherosclerosis
1. small veins that deliver blood from capillaries to veins
1. Veins have relatively thin walls compared to arteries
2. Many veins have valves which:
i. function to prevent backflow of blood and aid in moving blood toward the heart
G. Blood Distribution
1. Systemic veins and venules contain, at rest, about 60% of the blood volume and are therefore called
2. When more blood is needed elsewhere, vasoconstriction reduces the volume of blood in venous
reservoirs in order to provide a greater volume to active tissues (e.g., active skeletal muscles).
3. Vasoconstriction of veins also helps to compensate for blood pressure decrease during he