Ch 11 Vessels Notes

Anatomy & Physiology Circulatory System – Blood Vessels I.

Vascular Structure & Function A. Arteries 1. Arteries carry blood away from the heart. 2. Ventricles pump blood into large arteries, which branch into progressively smaller arteries, then arterioles, and eventually into the capillaries. 3. Since arteries carry blood away from the heart they are said to “branch”, “diverge” or “fork”. 4. All arteries carry oxygenated blood – except for the pulmonary arteries. 5. Lumen – the hollow, central blood containing space. 6. Structure of arteries – three layers a. Tunica intima – innermost layer. Composed of simple squamous epi. Same as the endocardium. b. Tunica media – middle layer composed of smooth muscle. This is a very thick layer in the arteries. It functions to close down the arteries and regulate blood distribution. 1) Vasoconstriction – squeezing down of the lumen to decrease blood flow. 2) Vasodilation – the widening of the lumen to increase blood flow. c. Tunica adventitia – outer layer. Composed of collagen fibers. Very elastic. 7. Functions of the arteries a. Act as a conduit between the heart and the capillaries. b. Act as a pressure reservoir for forcing blood into the smaller diameter arterioles. c. Dampen oscillations in pressure & flow and produce a more even flow in the capillaries. d. Control distribution of blood in systemic system via vasoconstriction and vasodilation. 8. Arteriosclerosis – hardening of the arteries due to age, stress, smoking, and inactivity. Blood pressure increases and flow to capillaries is reduced. B. Capillaries 1. Smallest blood vessels of the body. 2. Red blood cells have to travel single file through them. 3. Small arterioles carry blood to the capillaries and small venules pick up blood as it leaves the capillaries. 4. Capillaries are composed of simple squamous epi. 5. Capillaries are the functional unit of the circulatory system as they are the sites of nutrient and gas exchange (diffusion). C. Veins 1. Veins carry blood toward the heart. 2. Veins are said to “merge”, “join” or “converge”. 3. Small venules merge to form small veins that join to form large veins. 4. All veins carry unoxygenated blood – except for the pulmonary veins. 5. 65% of the body’s blood supply is found in the veins at any one time. 6. Structure of veins – same three layers as arteries a. Tunica media is much thinner thus causing: 1) Veins to be “limp”. 2) Lumen of veins is much wider. b. Veins have valves to prevent the back flow of blood. 7. Blood movement in veins a. Skeletal muscle contractions squeeze the blood along (muscular pump). b. Breathing (respiratory pump). 8. Varicose veins – veins that have become enlarged and distended with blood due to failed valves.

II.

Blood Pressure & Pulse A. Blood pressure 1. Measured with a sphygmomanometer in mm Hg. 2. Systolic / diastolic 3. Systolic = pressure of blood pulsing through the arteries due to ventricular contraction. Normal adults’ systole range from 140 – 110 mm Hg. 4. Diastolic = pressure of the blood flow during elastic recoil of the arteries. Normal adults’ range from 80 –75 mm Hg. B. Pulse 1. The difference between systolic and diastolic pressure as blood courses through arteries. 2. Pulse may be taken (palpated) at several different sites on the body, however the radial pulse and carotid pulse are most easily accessible. 3. Normal pulse is 66 – 80 bpm.