Cardiovascular System Blood Vessels and Circulation A Presentation

Cardiovascular System: Blood Vessels and Circulation A Presentation

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.

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.

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.

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

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 lipidsoluble materials to pass. • Interconnect to form capillary bed.

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.

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

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.

Forces Acting Across Capillary Walls

Venous pressure • Pressure is only 1/10 th 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 fill.

Cardiovascular Regulation • Involves – Autoregulation – Neural mechanisms – Endocrine mechanisms

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

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

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.

• 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 smooth muscles in ductus arteriosus contract closing connection. Increased pressure in L atrium closes foramen ovale.

• • 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.

Template Provided By www. animationfactory. com 500, 000 Downloadable Power. Point Templates, Animated Clip Art, Backgrounds and Videos