P. 357-363BLOOD VESSELS

Chapter 13 Cardiovascular System

Blood Vessels

Forms closed circuit that carries blood from the heart to cells and back

Includes: Arteries Arterioles Capillaries Venules Veins

Arteries and Arterioles

Arteries Are strong, elastic vessels adapted to carry blood

away from heart at high pressuresArterioles

Fine branches of arteries

Arterial Wall

3 layers Endothelium (Tunica interna)

Helps prevent blood clotting Helps regulate local blood flow by secreting substances

that dilate or constrict blood vessels Inner layer

Middle Layer (Tunica Media) Makes up bulk of wall Smooth muscle

Outer Layer (Tunica externa) Attaches artery to surrounding tissues

Arterioles Same three layers except much thinner and lead to capillaries

Constriction and Dilation

Vasoconstriction Artery walls reduce diameter by muscle contraction

Vasodilation Relaxing of muscles causes increase in diameter

Atherosclerosis

Nearly half of all deaths in the U.S. are due to this arterial disease

Occurs when soft masses of fatty materials, particularly cholesterol, accumulate on the inner surface of arterial walls Known as plaque

Can cause blood clot formation which leads to a thrombus (blood clot) or embolus (lodging of clot somewhere) or even blood deficiency (ischemia) or tissue death (necrosis)

Atherosclerosis Cont.

Risk factors Fatty diet, elevated blood pressure, smoking, obesity,

and lack of physical exercise Emotional and genetic factors may also increase

susceptibilityThree common treatments

Percutaneous transluminal angioplasty (balloon) Laser angioplasty Bypass graft surgery (triple and quad bypass)

Capillaries

Smallest diameter of vessels that exchange substances between blood and tissues

Slits Openings in walls of capillaries Size depends on type of tissue they are in

Capillary density Depends on tissues rate of metabolism

Tissues with large quantities of oxygen and nutrients are packed with capillaries

Slow metabolic rates lack capillaries (cornea, epidermis)

Exchanges in Capillaries

Pre-capillary sphincters open and close capillaries

Also function to route blood flow When exercising more blood is needed

by skeletal muscles and less in digestive tract or other areas

Gases, nutrients, and metabolic by-products are exchanged between blood in capillaries and tissue fluids

Diffusion, Osmosis and Filtration

Diffusion High concentrations of oxygen and nutrients entering,

substances diffuse through capillary walls to tissues where blood meets CO2 and waste

Filtration Forces molecules through membrane with hydrostatic

pressure. When ventricle walls contract it provides force for filtration.

Osmosis Plasma proteins that remain in capillaries makes

osmotic pressure of blood greater than tissue fluid

D, O, F continued

Blood pressure decreases with distance from heart because friction slows flow

Normally more fluid leaves capillaries than what enters

Unusual events may increase blood flow to capillaries and excess fluid enters spaces between tissue cells.

Veins and Venules

Venules Microscopic vessels that continue from the capillaries to veins

Veins Carry blood back to atria, roughly parallel to arteries Walls are similar to arteries but much weaker Function as blood reservoirs

If hemorrhage cause a drop of blood pressure, veins receive impulse to send more blood to heart to help maintain pressure.

Flapvalves In upper and lower limbs Help prevent blood from backing up by closing Valves are open if blood is flowing toward heart but close if

going in other direction

Table 13.2 summarizes vessels

Important to Remember

Arteries carry oxygenated blood away from heart

Veins carry deoxygenated blood towards heart

Exception Pulmonary artery and pulmonary vein are opposite of

above statement

Review

Describe the wall of an artery.What is the function of smooth muscle in arterial wall?How is the structure of an arteriole different from that of

an artery?Describe the capillary wall.What is the function of a capillary?What structures control blood flow into capillaries?What forces cause the exchange of substances between

blood and tissue fluid?Why is the fluid movement out of a capillary greater at

the capillary’s arteriolar end than at its venule end?How does the structure of a vein differ from that of an

artery?How does venous circulation help to maintain blood

pressure when hemorrhaging cause blood loss?