BIO 265 – Human A&P II

1. BIO 265 – Human A&P II Chapter 19 Blood Vessels

2. Blood Vessels • Amazing fact about blood vessels: • 60,000 miles in an adult! • Earth’s circumference is 24,902 miles • What are the different types of blood vessels? • Arteries - elastic, muscular, and arterioles • Capillaries • Veins – venules and veins • Figures 19.1 and 19.2 and Table 19.1

3. Blood Vessels • The inside of a blood vessel is called the lumen • All blood vessels have an internal lining called endothelium (it lines the lumen) • Simple squamous epithelium • This layer is continuous with the endocardium • Capillaries: • Composed of endothelium with a basement membrane • Figure 19.3 and others

4. Structure of Arteries and Veins • Three tunics or layers: • Tunica intima – primarily endothelium • Tunica media – location of circular smooth muscle and elastin • Functions? • Tunica adventitia – layer of connective tissue • Merges with other connective tissue around the vessel • Also contains the vasa vasorum • Figure 19.1 and other figure

5. Structure of Arteries and Veins • Veins have valves that only allow blood to flow toward the heart • The valve structure and function is very similar to the semilunar valves in the heart • Figure 19.1 and other figure

6. Structure of Arteries and Veins • The valves in the veins are critical for returning blood to the heart because there is almost no blood pressure in the veins • Blood is pumped through the veins by respiration (breathing) and by skeletal muscle contractions • Figure 19.6

7. Structure of Arteries and Veins • Varicose veins result from these valves not functioning properly • Pot-bellies, pregnancy, standing, hemorrhoids • Figure 19.6

8. Capillaries • What is the function of capillaries? • Capillary Exchange • gases, nutrients, wastes, etc. • Capillary exchange is driven by 2 things: • Concentration gradients (diffusion) • Most solutes move this way • Fluid movement (primarily moves water to the tissues) • Tissue swelling and the lymphatic system • Figures 19.14, 19.15, 19.2 and others

9. Capillaries • Capillaries are organized into networks called capillary beds • Figure 19.4

10. Capillaries • The structure of the capillary beds allows the regulation of blood flow through the tissues • This involves the precapillary sphincters • Figure 19.4

11. Control of Blood Flow • Blood flow through tissues (tissue perfusion) is tightly controlled • It is related to the metabolic rate and function of the tissue (muscle, liver, kidney, etc.) • O2 (and other nutrients) are the key • They are required for smooth muscle contraction • Figure 19.4

12. Control of Blood Flow • Long-term control involves the number of blood vessels and capillaries • Muscle and heart attack examples • The growth of new blood vessels is called angiogenesis • The density of capillaries primarily depends upon O2 concentration

13. Aging of Arteries • Changes in arteries: • Arteriosclerosis – loss of elasticity in the arteries • What effects does this have? • Atherosclerosis – deposition of material in the arterial walls to form plaques • Effect? • Figure from other text

14. Blood Pressure Regulation • Blood Pressure depends on 3 primary factors: • Cardiac output • Peripheral resistance (this is determined by blood vessel diameter) • Blood volume

15. Blood Pressure Regulation • There are two types of regulation: • Short-term and Long-term • Short-term • Baroreceptors – get with a partner and discuss how this mechanism could affect blood pressure. • They affect the cardiovascular center in the medulla • This can change heart rate and peripheral resistance to raise and lower BP! • Figure 19.8

16. Blood Pressure Regulation • Chemoreceptor Reflexes • When oxygen, pH, or carbon dioxide levels change dramatically, the cardiovascular center can increase blood pressure. • Adrenal Medulla Hormones • What hormones are produced here? • These affect heart rate and peripheral resistance • Increase heart rate • Vasodilation in cardiac vessels • Vasoconstriction in vessels to the skin and viscera

17. Blood Pressure Regulation • Atrial Natriuretic Peptide (ANP) • Released when atria are stretched • Increases Na+ loss in the urine • Also causes vasodilation • Effect? • ADH (vasopressin) – at very high levels causes vasoconstriction • Angiotensin II – vasoconstriction • Inflammatory chemicals (like histamine) cause vasodilation • Alcohol – inhibits ADH and causes vasodilation

18. Blood Pressure Regulation • Long-Term Regulation (these alter blood volume): • Direct renal filtering • High BP causes more fluid to get filtered and lost • Low BP slows filtration and loss down • Atrial Natriuretic Peptide – effect? • Renin-Angiotensin-Aldosterone Mechanism • When BP decreases, the kidneys secrete renin • Renin activates a plasma protein called angiotensin II • Active angiotensin II causes vasoconstriction and the release of aldosterone from the adrenal cortex

19. Blood Pressure Regulation • Aldosterone increases Na+ and Cl- absorption by the kidney which increases water retention • Angiotensin can also stimulate the release of ADH • This mechanism is very important for daily regulation of BP and in countering circulatory shock • ADH – effect?

20. Alterations in Blood Pressure • Hypotension (BP below 100 mm Hg) – usually no problem • Hypertension (BP over 140/90 mm Hg) • Temporary high BP can be normal • Strains the heart • Contributes to atherosclerosis • Can lead to heart failure • Cause is usually unknown

21. Circulatory Shock • Shock is a condition where blood flow is not adequate to meet the body’s needs • (Low blood pressure) • Hypovolemic shock – blood loss, dehydration, extensive burns • Vascular shock – extreme vasodilation • Anaphylactic shock • Septic shock – bacterial toxins