Cardiovascular System: Blood Vessels and Circulation

1. Cardiovascular System: Blood Vessels and Circulation A Presentation

2. Structure and Function • The vital functions of the cardiovascular system occur at the capillary level • Chemical and gaseous exchange between the blood and interstitial fluid occurs across capillary walls. • Tissues relay on capillary diffusion for nutrients and oxygen and to remove metabolic waste.

3. Structure of vessel walls • Three layers • Tunica intima or innermost layer. Includes a lining of endothelium and a connective tissue layer. • Tunica media or middle layer. Contains smooth muscle tissue and collagen and elastic fibers. • Tunica externaforms sheath of connective tissue around the vessel.

4. Arteries • Elastic: large, able to absorb the pressure changes of the cardiac cycle, contain many elastic fibers that stretch and return to original dimension. Examples: aorta, pulmonary trunk • Muscular arteries: medium sized distribute blood to skeletal muscles and internal organs. Not as elastic. Example: external carotid arteries.

5. Arterioles: small (30u), diameter of muscle layer very thin.

6. Capillaries • Only vessels that permit exchange between blood and interstitial fluid. • Walls are thin(no tunica externa or tunica media) • Small diameter slows blood flow • Permits water, small solutes and lipid-soluble materials to pass. • Interconnect to form capillary bed.

8. Veins collect blood and return it to the heart • Venules: smallest • Veins have relatively thin walls. • In medium veins contain valves that prevent the backflow of blood due to low pressure and gravity • Stretching and distortion of these valves cause varicose veins.

10. Pressure and resistance determine blood flow and affect rates of capillary exchange • Highest pressure at the base of the aorta • Resistance opposes movement of blood. • Sources include • Vascular resistance • Viscosity • turbulence

11. Pressures within the systemic circuit • Highest in the aorta and lowest at the vena cava • Arterial pressure rises during ventricular systole and falls during ventricular diastole. • 120/80 reflects the separate systolic and diastolic pressures. • Read the Clinical Note page 435.

12. Forces Acting Across Capillary Walls

13. Venous pressure • Pressure is only 1/10th of the arterial system at the beginning. • When standing two factors help venous return • Muscular compression of skeletal muscles • Respiratory pump: inhalation causes both the vena cava and rt. atria to expand and fill.

14. Cardiovascular Regulation • Involves • Autoregulation • Neural mechanisms • Endocrine mechanisms

16. Pulmonary Circuit • Deoxgenated blood enters the lungs in arteries • Oxygenated blood leaves the lungs in veins.

17. Systemic Circuit • Oxygenated blood from the left ventricle goes to tissues other than the lungs’ exchange surfaces. • Deoxygenated blood returns to the right atrium.

18. Fetal Circulation • Embryonic lungs are collapsed and nonfunctional • All nutritional and respiratory needs are provided by diffusion across the placenta. • Umbilical arteries carry deoxygenated blood from fetus to placenta • Umbilical veins returns oxygenated blood from placenta to fetus.

19. Veins bypass developing liver through ductusvenosus. • Foramen ovalein fetal heart and ductusarteriosus between pulmonary and aortic trunks by pass collasped lungs. • At birth lungs expand and smooth muscles in ductusarteriosus contract closing connection. Increased pressure in L atrium closes foramen ovale.

20. Aging • Decreased hematocrit • Blockage of peripheral veins • Pooling of blood in the veins • Reduction in max. cardiac output • Changes in heart conduction • Reduction in elasticity of cardiac skeleton • Progressive atheroschlerosis • Replacement of damaged heart muscle by scar tissue.

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