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

a. Endothelium ‑

b. Subendothelial layer - c.t.

II. Arteries (carry blood away from heart)

A. Elastic ‑ large amount of elastin in tunica media, largest, expandable

Example:

B. Muscular ‑ very little elastin, tunica media is predominantly smooth muscle.

Example:

C. Arterioles ‑

III. Capillaries: "Functional units" of circulatory system, very thin‑walled, allows for exchange of gases, nutrients, & waste products.

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:

A.

B.

Which of the following allow for exchanges between the blood stream and the tissues?

a. Muscular artery

b. Capillary

c. Venule

d. Arteriole

e. Elastic artery