Vascular Structure and Function

Vascular Structure & Function

Arteries

• Arteries carry blood away from the heart
• Ventricles pump blood into large arteries, which then branch into smaller arteries, then arterioles, and finally into the capillaries
• Arteries branch, diverge, or fork away from the heart
• With the exception of pulmonary arteries, all arteries carry oxygenated blood
• The lumen is the hollow, central, blood-containing space inside arteries
• Arteries consist of three layers

Tunica Intima

• Innermost layer of artery structure, composed of simple squamous epithelium
• Same as the endocardium

Tunica Media

• Middle layer of artery structure, composed of smooth muscle
• Thick layer in arteries that functions to close down arteries and regulate blood distribution
• Vasoconstriction is the squeezing down of the lumen to decrease blood flow
• Vasodilation is the widening of the lumen to increase blood flow

Tunica Adventitia

• Outer layer of artery structure, composed of collagen fibers
• It is very elastic

Artery Functions

• Act as a conduit between the heart and the capillaries
• Act as a reservoir for forcing blood into smaller diameter arterioles
• Dampen oscillations in pressure and flow and produce a more even flow in the capillaries
• Control the distribution of blood in the systemic system via vasoconstriction and vasodilation
• Arteriosclerosis is the hardening of the arteries due to age, stress, smoking, and inactivity
• Hardening increases blood pressure and decreases flow to capillaries

Capillaries

• The smallest blood vessels in the body, where red blood cells travel single file
• Small arterioles carry blood to the capillaries, and small venules pick up blood from the capillaries as it leaves
• Capillaries are composed of simple squamous epithelium
• Functional unit of the circulatory system as they are the sites of nutrient and gas exchange (diffusion)

Veins

• Veins carry blood toward the heart, and are said to merge, join, or converge
• Small venules converge to form small veins, and then large veins
• With the exception of pulmonary veins, all veins carry unoxygenated blood
• 65% of the body's blood supply is found in the veins
• Veins consist of the same three layers as arteries

Vein Structure

• Tunica media is much thinner, thus causing veins to be limp
• Veins have a much wider lumen
• Veins contain valves to prevent the back flow of blood

Blood Movement

• Skeletal muscle contractions squeeze the blood along, acting as a muscular pump
• Breathing acts as a respiratory pump

Varicose Veins

• Enlarged veins distended with blood due to failed valves

Blood Pressure & Pulse

Blood Pressure

• Measured with a sphygmomanometer in mm Hg
• Systolic and diastolic

Systolic Pressure

• Blood pulsing through the arteries due to ventricular contraction
• Normal adult range is 110-140 mm Hg

Diastolic

• Pressure of blood flow during elastic recoil of the arteries
• Normal adult range is 75–80 mm Hg

Pulse

• The difference between systolic and diastolic pressure as blood courses through arteries
• Pulse may be palpated at several different sites on the body, with the radial and carotid pulse being the most easily accessible
• Normal pulse is 60–80 bpm