13-1 Arteries, arterioles, capillaries, - PowerPoint Presentation

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13-1 Arteries, arterioles, capillaries, venules, and veins differ in size, structure, and function

Kelsee

, Aimee

How it works

Blood leaves heart through pulmonary trunk and aorta

Vessels branch forming major arteries that carry blood to body organs

More branching within organs forms arterioles

Arterioles provide blood to over 10 billion capillaries

Vital functions of the cardiovascular system occur within the capillaries

Blood flowing out of capillary network enters

venules

(slender vessels that form veins)

Structure of vessel walls

The walls of arteries and veins contain three distinct layers:

Tunica intima-

the innermost layer of a blood vessel, includes the endothelial lining of the

v

essel and an underlying layer of connective tissue dominated by elastic fibers

Tunica media-

the middle layer, contains smooth muscle tissue in the framework of collagen and elastic fibers. When these smooth muscles contract, vessel diameter decreases; when they relax vessel diameter increases

Tunica externa-

outer layer that forms a sheath of connective tissue around the vessel. Its collagen fibers may intertwine with those of adjacent tissues, stabilizing and anchoring the blood vessel.

Arteries

Blood passes through elastic arteries, muscular arteries, and arterioles

Elastic arteries:

large resilient vessels

Ex. Pulmonary trunk and aorta and major arterial branches

Muscular arteries:

medium sized/distribution arteries, distribute blood to skeletal muscles and internal organs

Ex. External carotid arteries of the neck

Arterioles:

much smaller than muscular arteries

Elastic Arteries

Walls are dominated by elastic fibers

Absorb pressure changes that occur during cardiac cycle

During ventricular systole (blood pressure rises quickly) elastic arteries are stretched, diameter increases

During ventricular diastole, (blood pressure declines) the elastic fibers go back to normal

Muscular Arteries and Arterioles

Muscular arteries contain more smooth muscle cells than elastic fibers

Tunica media of an arteriole contains two layers of smooth muscle cells

These muscle layers change the diameter, which alters blood pressure

Capillaries

Single layer of endothelial in basement membrane

No tunica externa or tunica media

Function in a network called capillary bed

The only blood vessels whose walls permit exchange between blood and surrounding interstitial fluid

Walls are thin and diffusion distances are short

Diameter is small, causing the blood flow to be slow which gives adequate time for diffusion

Each capillary is protected by a precapillary sphincter

The process

A single arteriole feeds dozens of capillaries which connect to several

venules

Blood usually flows from arterioles to

venules

at a constant rate however it is variable

Vasomotion

Smooth muscle fibers respond to local changes in interstitial fluid

Autoregulation

The process cont.

Alternate routes for blood flow are formed by anastomosis outlet

The joining of blood vessels

Circumstances can cause blood to completely bypass a capillary bed through an arteriovenous anastomosis

vessel that connects an arteriole to

venule

A single capillary bed can be supplied by an arterial anastomosis

More than one artery fuses and gives rise to arterioles

If one or more artery is blocked the others can

still deliver

blood and tissue will not be damaged

Veins

Collect blood from tissues and organs and deliver it back to heart

Venules

- the smallest

Medium sized veins- similar to size of muscular arteries

Contain valves to prevent backflow of blood

Large veins- include two vena

cavae

and tributaries in abdominopelvic and thoracic cavities

Thin walls due to lower pressure

Pressure is so low it cannot overcome the force of gravity