1. Circulatory System: Blood Vessels Exercise 32

2. Structure of Artery and Vein

3. Blood vessels In general a blood vessel has 3 layers: 1. Tunica interna (tunica intima) – Innermost layer, adjacent to lumen/endothelium 2. Tunica media – Middle layer, smooth muscle and elastic fibers 3. Tunica externa – Outermost layer, adjacent to surrounding tissue

4. Arteries & Arterioles

5. Arteries Arteries carry blood away from the heart to the tissues – The walls of the arteries are elastic which allows them to absorb the pressure created by ventricles of the heart as they pump blood into the arteries – Because of the smooth muscle in the tunica media, arteries can regulate their diameter

6. Types of Arteries Elastic arteries (conducting arteries) – Large diameter – More elastic fibers, less smooth muscle – Function as pressure reservoirs Muscular arteries (distributing arteries) – Medium diameter – More smooth muscle, fewer elastic fibers – Distribute blood to various parts of the body

7. Anastomoses An anastomoses is the union of the branches of 2 or more arteries supplying the same region of the body – This provides an alternate route for blood flow – Arteries that do not form an anastomosis are called “end arteries” If an end artery is blocked, blood cannot get to that particular region of the body and necrosis can occur

8. Capillaries Capillaries are microscopic vessels that usually connect arterioles and venules Capillary walls are composed of a single layer of cells and a basement membrane – Because their walls are so thin, capillaries permit the exchange of nutrients and wastes between blood and tissue cells

9. Blood Flow Through Capillaries Capillaries branch to form an extensive capillary network throughout the tissues and are found near almost every cell in the body

10. Types of Capillaries Continuous capillaries

11. Fenestrated capillaries – larger pores, seen in endocrine glands, small intestines and kidney

12. Sinusoids – bone marrow, spleen, liver

13. Veins & Venules

14. Venules Venules are small vessels that are formed by the union of several capillaries Venules drain blood from capillaries into veins

15. Veins Veins are formed from the union of several venules Compared to arteries, veins have a thinner tunica interna and media and a thicker tunica externa – Veins have less elastic tissue and less smooth muscle than arteries Veins contain valves

16. Venous valves

17. Venous Return Venous return, the volume of blood flowing back to the heart through the systemic veins, occurs due to the pressure generated by contractions of the heart’s left ventricle – Venous return is assisted by: Valves Respiratory pump Skeletal muscle pump

18. At rest, the largest portion of the blood is in systemic veins and venules (blood reservoirs)

19. Arteries vs Veins Arteries: thicker tunica media Arteries: elastic layer to expand Veins: valves to prevent backflow Veins: larger lumen to hold more blood – Blood reservoir

20. 2 main circulatory systems 1.Pulmonary system: heart and lungs – Pulmonary arteries carry deoxygenated blood to the lungs – Pulmonary veins carry oxygenated blood back to the heart 2.Systemic circulation: heart and rest of body - Oxygenated blood in systemic arteries is carried away from the heart to the body - De-oxygenated blood via systemic veins is carried from the body to the heart.

23. Hepatic Portal Circulation

24. Fetal circulation Oxygenated blood from placenta goes to right atrium. Most of this blood goes through foramen ovale to left atrium Small amount goes to right ventricle and then on to pulmonary trunk From pulmonary trunk instead of going to nonfunctional lungs passes through ductus arteriosus to aorta

25. Remnants of Fetal circulation Foramen ovale becomes fossa ovalis Ductus arteriosus becomes ligamentum arteriosum