Cardiovascular System

1. Cardiovascular System Vessels and Circulation

2. Vessels and Circulation • Two groups of blood vessels • PULMONARY • SYSTEMIC • Closed system • Begins and ends at the heart • Major types of vessels • ARTERIES • CAPILLARIES • VEINS

3. Size and Direction • Blood moves through arteries that get progressively smaller • Blood moves through veins that get progressively larger • Arteries → Arterioles → Capillaries → Venules → Veins → largest veins superior and inferior vena cava • Arteries carry blood AWAY from the heart • Veins carry blood TOWARD the heart

5. Histology of Blood Vessels • Three layers • 1. Tunica intima – endothelial layer and CT • 2. Tunica media – smooth muscle layer • 3. Tunica externa – CT sheath around the vessel

6. How to tell an artery from a vein • Tunica media is thicker in arteries • In sections arteries will appear round, the veins tend to collapse • Endothelial layer of arteries often has a pleated appearance

8. Types of arteries • ELASTIC ARTERIES • Large vessels • Transport large volumes of blood • Elastic fibers in the tunica media to tolerate blood pressure • Aortic trunk, common carotid, subclavian, common iliac • MUSCULAR ARTERIES • Transport blood to muscles and organs • Fewer elastic fibers, more smooth muscle • External carotids, brachials, femorals, mesenterics • ARTERIOLES • Smaller diameter, little tunica media or tunica externa • Control flow of blood between arteries and capillaries

9. Capillaries • Very small diameter – just larger than the diameter of a red blood cell • Exchange between the blood and surrounding tissues • Capillary density directly related to the metabolic activity of its cells • Tissues with higher metabolic rates have more capillaries per unit area • A capillary is just an endothelial layer of simple squamous cells and CT • Capillary beds form the functional basis of the cardiovascular system • Human body is estimated to have about 50,000 miles of capillaries with a total exchange area of 6300 square meters – two football fields!

10. Capillaries

12. Veins • Veins collect blood from all the tissues and return it to the heart • High volume vessels – hold 60% of the circulating blood • Veins have thinner walls and very little elastic fibers • Venules are small veins that collect blood from the capillaries • Medium size veins • Large veins • Veins have valves to prevent backflow of blood

13. Distribution of blood

15. Pulmonary circuit • Pulmonary arteries carry blood AWAY from the heart to the lungs • This blood is low in oxygen, high in carbon dioxide • Pulmonary veins carry blood BACK to the heart • This blood is high in oxygen and will be sent out to the body tissues through the systemic circuit

17. Arteries

27. Veins

37. Hepatic Portal System • System of TWO capillary beds • Digested material is absorbed from the digestive system by one capillary bed • Goes to the liver for processing in a second capillary bed • Blood returns to venous circulation via the hepatic vein to the inferior vena cava • Hepatic portal vein is formed from the • Superior mesenteric vein • Inferior mesenteric vein • Splenic vein

38. Hepatic portal system

40. Fetal Circulation • Short circuits that bypass fetal lungs • Foramen ovale (fossa ovalis) • Ductus arteriosus (ligamentum arteriosum) • Both of these bypass circuits seal up at birth when the lungs become functional

42. Fetal Heart

43. Cat Vessels