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