The Cardiovascular System Chapter 13

CV System Facts and Function Composed of heart and blood vessels Heart beats over 100,000 times daily Pushes 1000 gallons of blood daily through nearly 60,000 miles of blood vessels Moves blood through the body so that each cell gets oxygen and nutrients and has waste products taken away

The Heart Hollow, muscular pump that propels blood through blood vessels Lies almost in the center of thoracic cavity between the lungs 2/3 of heart lies to the left of mid-line Roughly triangular in shape, apex points down and to the left; top margin is referred to as the base Approx. size of your clenched fist

Heart Coverings Double-layered serous membrane called the pericardium covers the heart and major blood vessels that attach to it Outer layer called parietal pericardium or pericardial sac made of connective tissue Inner layer lies on surface of heart and is called the visceral pericardium or epicardium Potential space between layers is called the pericardial cavity, contains a small amount of fluid that acts as a lubricant; infection within this fluid is called pericarditis

Heart Wall Epicardium often contains fat deposits that help to protect the heart The myocardium makes up the bulk of the heart wall It is composed of cardiac muscle tissue

Do you remember which is cardiac muscle tissue?

Heart Wall cont’d Myocardium contracts to produce movement of blood Cells are arranged in spiral bundles that are supported by interwoven connective tissues (fibrous skeleton) which reinforces the myocardium Lining the interior surface of the heart’s chambers, valves, and blood vessels we find the endocardium or endothelium

Heart Chambers Heart has four internal spaces called chambers The two superior chambers are called atria (atrium is singular) The two inferior chambers are called ventricles

Atria Function as receiving chambers for blood entering the heart Push blood “next door” to ventricles Walls are thin and contain very few muscle fibers Ear-shaped appendages called auricles Fossa ovalis - remains of what was present in fetal heart (blood shunted from right atrium to left atrium, bypassing lungs)

Atria cont’d Right atrium receives blood from vena cava Left atrium receives blood from pulmonary vein

Ventricles Provide force necessary to push blood into the body’s circulatory network Thicker walls than atria (left is thickest) Right ventricle pumps blood into pulmonary artery Left ventricle pumps blood into aorta

Heart Valves Located between chambers of heart and openings into major blood vessels Allow flow of blood in only one direction Remain closed while chamber is filling; open to allow blood to flow when heart muscle contracts

Atrioventricular Valves Located between atrium and ventricle Valve located between right atrium and right ventricle is called the tricuspid valve, because it has three flaps, or cusps Valve located between left atrium and left ventricle is the bicuspid valve, also known as mitral valve

Semi-lunar Valves Resemble half moons Located between ventricles and arteries they empty into Between right ventricle and pulmonary artery is the pulmonary valve Between the left ventricle and aorta is the aortic valve

Cardiac Cycle Made up of events that are required to produce a single heartbeat Include periods of synchronized contraction (systole) and relaxation (diastole) P. 378

Heart Sounds “ Lub – dub” or “Lub – dup” Sound caused from vibrations due to valves slapping shut Lub – closing of AV valves (ventricular systole) Dub – closing of semi-lunar valves (ventricular diastole) Heart Animation

Blood Vessels Form a closed delivery system for blood Consists of arteries, arterioles, capillaries, venules, and veins All but capillaries have a three-layered wall; from superficial to deep: –Tunica adventitia – CT, anchors vessel –Tunica media – smooth muscle and elastic fibers –Tunica intima – CT, rich in elastic fibers

Blood Vessels cont’d The opening in the middle of a blood vessel through which blood flows is called the lumen Blood vessels are all contractile and elastic Contractility helps blood circulate by “squeezing” it along Elasticity is necessary due to changing fluid pressure (can be felt as pulse) Blood vessel comparison

Arteries All arteries carry blood away from the heart Carry oxygenated blood except for pulmonary arteries Thickest walls of any blood vessel; carries blood with the highest fluid pressure Very thick tunica media allows for dramatic vasoconstriction and vasodilation

Typical Artery Cross-section

Arterioles Branch off of arteries Same structure as arteries but smaller diameter Usually unnamed; vary from individual to individual

Capillaries Capillaries are microscopic blood vessels Smallest diameter, single layer of epithelium Wall is thin enough to permit diffusion of gases and nutrients into interstitial fluid Organized into capillary beds which can be opened or closed to regulate flow of blood as needed

Capillary Bed

Capillaries cont’d A central channel called a thoroughfare channel allows blood to pass through when pre- and post-capillary sphincters are closed

Venules and Veins Carry blood toward heart; usually deoxygenated blood Thinner walls than arteries and arterioles; limited contractility and extensibility Carry blood at much lower pressures Lumen contains one-way valves which prevent back-flow of blood Often, surrounding skeletal muscles assist with circulation Distensibility allows for variations in pressure and blood volume; permanent distended state is the cause of varicose veins