Exercise 21: Anatomy of Blood Vessels

3 Tunics (t. intima, t. media, t. externa)

Figure 11.9b

Very thick tunica media in arteries

Only tunica intima in capillaries

2

1

3

Blood Vessel Tunic DescriptionTunica intima • Most internal tunic;

• Its smooth surface decreases friction

Tunica media Bulky middle tunic contains smooth muscle and elastin;

Tunica externa (adventitia)

Most superficial tunic

Tunic/Vessel

Tunica Intima

Tunica media

Tunica externa*

Artery X X XVein X X XCapillary X

*Also called “Tunica adventia”

Only tunica intima in capillaries

CapillariesWalls of capillaries are only one cell layer

thick to allow for exchanges between blood and tissueOnly capillaries directly serve the needs of the body’s cells. It is through the capillary Walls that exchanges are made between tissue cells and blood.Respiratory gases, nutrients, and wastes move along diffusion gradients.

Artery VeinsVALVE

Blood Vessels: The Vascular System

Figure 11.9a

Elastic recoil of artery propels blood along

They have the greatest amount of elastin, enabling them to expand. When the heart relaxes, the recoil propels blood onward.

Muscular Pumps aids blood flow in VeinsAs skeletal muscles surrounding the veins contract and relax, blood is milked through the veins toward the heart.

Respiratory Pump aids blood flow in veins!

Pressure changes that occur in the thorax during breathing also aid blood return to the heart through the veins.

Arteries are thicker than veins

Because arteries are closer to the pumping action of the heart, they must be able to expand as blood is propelled into them and then recoil passively as the blood flows off into the circulation during diastole. Arterial walls must be strong and resilient to withstand blood pressure fluctuations.