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 externa forms 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 ductus venosus.
Foramen ovale in fetal heart and ductus arteriosus between pulmonary and aortic trunks by pass collasped lungs.
At birth lungs expand and smooth muscles in ductus arteriosus 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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