CIRCULATORY SYSTEM: VESSELS
I. Blood vessels: blood flows from the heart through progressively narrowing vessels; heartàarteryàarterioleàcapillaryàvenulesàveinàheart
A. Structure: arteries and veins have 3 tunics
1. Tunica Externa (adventitia) –
2. Tunica Media ‑ middle, smooth muscle layer, this is the thickest layer in arteries
3. Tunica Intima ‑ innermost
b. Subendothelial layer - c.t.
II. Arteries (carry blood away from heart)
A. Elastic ‑ large amount of elastin in tunica media, largest, expandable
B. Muscular ‑ very little elastin, tunica media is predominantly smooth muscle.
C. Arterioles ‑
III. Capillaries: "Functional units" of circulatory
system, very thin‑walled, allows for exchange of gases, nutrients, &
IV. Venules ‑ usually lack a tunica media. They have the other two tunics
V. Veins: (carry blood to the heart)
- All 3 tunics present
- Most (but not all) veins have valves
- Veins have a very low pressure & large lumens.
Because of the low pressure and large lumens, the blood flow through them is dependent on:
Which of the following allow for exchanges between the blood stream and the tissues?
a. Muscular artery
e. Elastic artery