Chapter 19

Angiogenesis

The growth of new blood vessels

Blood Vessels

Form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body and then return it to the heart

Arteries

carry blood from the heart to the tissues

Arterioles

small arteries that connect and deliver blood to capillaries

capillaries

the site of substance exchange between blood and body tissues

Venules

connect capillaries to larger veins

veins

convey blood from tissues back to the heart

Vaso vasorum

small blood vessels that supply blood to the cells of the walls of the arteries and veins

Three layers of an artery

• tunica interna

• tunica media

• tunica externa

Tunica interna

• simple squamous epithelium known as endothelium

• basement membrane

• internal elastic lamina

Tunica media

circular smooth muscle and elastic fibers

tunica externa

elastic and collagen fibers

Elasticity

allows arteries to accept blood under great pressure from the contraction of ventricles and to send it on through the system

Contractility

allows arteries to increase or decrease lumen size and to limit bleeding from wounds

Sympathetic innervation

• vascular smooth muscle is innervated by sympathetic nervous system

• increase in stimulation causes muscle contraction or vasoconstriction

• decrease in stimulation or presence of certain chemicals (K+, H+, nitric oxide, lactic acid) causes vasodilation

Elastic arteries

• large arteries with more elastic fibers and less smooth muscle

• function as a pressure reservoir

Muscular arteries

• medium sized arteries with more muscle than elastic fibers in tunica media

• capable of greater vasoconstriction and vasodilation to adjust rate of flow

Types of capillaries

• continuous capillaries

• fenestrated capillaries

• sinusoids

Continuous capillaries

• intercellular clefts are gaps between neighboring cells

• skeletal and smooth, connective tissue in lungs

Fenestrated capillaries

• plasma membranes have many holes

• kidneys, small intestine, choroid plexuses, ciliary process and endocrine glands

Sinusoids

• very large fenestrations

• incomplete basement membrane

• liver, bone marrow, spleen, anterior pituitary and parathyroid gland

Varicose veins

• twisted, dilated superficial veins

• caused by leaky venous valves

• allow backflow and pooling of blood

Anastomoses

union of two or more arteries supplying the same body region

Are there more veins or arteries in the body?

Veins

Capillary exchange

movement of materials in and out of a capillary

Bulk flow

• movement of large amounts of dissolves or suspended material in same direction

• important for regulating volumes of blood and interstitial fluid

Edema

• an abnormal increase in interstitial fluid if filtration exceeds reabsorption

• results in excess filtration

• results in inadequate reabsorption

Blood pressure

pressure exerted on the walls of a blood vessel

What factors affect blood pressure?

• cardiac output

• blood volume

• viscosity

• resistance

• elasticity of arteries

Resistance

• opposition of blood flow as a result of friction between blood and the walls of blood vessels

• depends on the diameter of blood vessels, blood viscosity, and total blood vessel length

Systemic vascular resistance

• all of the vascular resistance offered by systemic blood vessels

• most resistance is in arterioles, capillaries, and venules due to their small diameters

Blood flow

the volume that flows through any tissue in a given period of time

Velocity of blood flow

• speed of blood flow in cm/sec is inversely related to cross-sectional area

• blood flow becomes faster when vessels merge to form veins

Venous return

volume of blood flowing back to the heart from the systemic veins

Skeletal muscle pump

contraction of muscles and presence of valves

Respiratory pump

decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium