Chapter 11 – Part 3 The Cardiovascular System

1. Chapter 11 – Part 3The Cardiovascular System

2. Blood Vessels: The Vascular System • Blood circulates inside the blood vessels, which form a closed transport circuit. • Takes blood to the tissues and back

3. Blood Vessels: The Vascular System • Like a system of roads, the vascular system has its freeways, secondary roads, and alleys. • Blood leaves the heart via arteries • It then moves into successively smaller and smaller arteries • Blood then moves into arterioles, which feed the capillary beds • Blood enters the capillaries • Capillary beds are drained by venules • Veins empty into great veins, which return the blood to the heart

4. Blood Vessels: The Vascular System

5. Blood Vessels: The Vascular System • Arteries and veins are simply conducting vessels. • Arteries carry blood away from the heart. • Veins carry blood to the heart. • Capillaries serve the needs of the cells. • It is only through their walls that exchanges between the tissue cells and the blood can occur.

6. The Vascular System

7. Three Layers(Tunics) of Blood Vessels • Tunic Intima - Innermost layer • Thin layer of endothelium • Lines the interior of the vessel • Its cells fit closely together and form a slick surface that decreases friction as blood flows through the vessel. • Tunic Media - Bulky middle coat • Mostly smooth muscle and elastic • Controlled by sympathetic nervous system • Responsible for constricting or dilating the vessels • Tunic Externa - Outermost tunic • Mostly fibrous connective tissue • Function is to support and protect the vessels

9. Differences Between Arteries and Veins • The walls of arteries are the thickest; the walls of arteries are thicker than the walls of veins • Arteries are closer to the pumping action of the heart and must be able to expand as blood is forced into them • Artery walls must be strong and stretchy enough to take the continuous changes in pressure • Veins are far from the heart and the pressure in them tends to be low at all times

11. Veins • The blood pressure in veins is usually too low to force the blood back to the heart. • Lumens of veins tend to be much larger than those corresponding arteries • The larger veins have valves that prevent backflow of blood • Skeletal muscle “milks” blood in veins toward the heart

12. Capillaries • Walls of capillaries are only one cell layer thick (just the tunica interna) to allow for exchanges between blood and tissue. • The tiny capillaries tend to form interweaving networks called capillary beds. • The flow of blood from an arteriole to a venule (through a capillary bed) is called microcirculation.

13. Capillary Beds • Capillary beds consist of two types of vessels: • Vascular Shunt – Directly connects an arteriole to a venule • True Capillaries – Exchange vessels • O2 and nutrients cross to cells • CO2 and metabolic waste products cross into blood

14. Capillary Beds • Precapillary Sphincter - surrounds the root of each true capillary and acts as a valve to regulate the blood flow into the capillary. • When the sphincters are open, blood flows through the capillaries and takes part in exchanges with tissue cells. • When the sphincters are closed, blood flows through the shunts and bypasses the tissue cells.

15. Varicose Veins • Common in people who stand for long periods of time (dentists, hairdressers, etc) and in obese individuals. • Common factor is the pooling of blood in the feet and legs and inefficient venous return resulting from inactivity or pressure on the veins. • The overworked valves give way, and the veins become twisted and dilated.