CARDIOVASCULAR SYSTEM

Introduction

Fully formed by the 4th week of embryonic development

Hollow Muscular Organ That Acts as a Double Pump

Continuous pump - once pulsations begin, heart pumps endlessly until death

Heart Anatomy General

Size: approximately the size of a person’s fist

Coverings: Pericardium

Double layered sac

Contains 10 – 20 cc. Of pericardial fluid to reduce the friction of the beating heart

Heart Wall

Myocardium: heart muscle; thicker on left side of the heart

Endocardium: lining of heart chambers; endothelial tissue continuous with the lining of the blood vessels

Ch

amb

ers

Atria

Ven

tricles

2 upper chambers of heart

Thin walls, smooth inner surface Responsible for receiving blood Right atrium receives deoxygenated (oxygen poor)

blood from the body through the superior and inferior vena cava

Left atrium receives oxygenated (oxygen rich) blood from the lungs through the pulmonary veins

2 lower chambers of the heart Thicker walls, irregular inner surface Responsible for pumping blood away from the heart Right ventricle sends deoxygenated blood to the

lungs via the pulmonary arteries Left ventricle sends oxygenated blood to all parts of

the body via the aorta

Accessory Structures

Septum: muscular wall dividing the heart into right and left halves

Heart valves – prevents the backflow of blood

Papillary muscles

prevent heart valves from turning inside out when ventricles contract

Chordae tendineae

prevent heart valves from turning inside out when ventricles contract

Great Vessels

Superior and inferior vena cava: receive deoxygenated blood from all parts of the body

Pulmonary arteries: carry deoxygenated blood to the lungs from the right ventricle

Pulmonary veins: carry oxygenated blood to the left atrium from the lungs

Aorta: carries oxygenated blood to distribute to all parts of the body

Valves

Tough fibrous tissue between the heart chambers and major blood vessels of the heart

Gate-like structures to keep the blood flowing in one direction and to prevent regurgitation or backflow of blood

Tricuspid valve: between the right atrium and the right ventricle

Bicuspid/mitral valve: between the left atrium and the left ventricle

Pulmonary semilunar valve: between the right ventricle and the pulmonary arteries

Aortic semilunar valve: between the left ventricle and the aortic arch/aorta

Heart Sounds When the AV

(atrioventricular) and semilunar valves close, they make the sound heard as “lub-dub” (auscultated with stethoscope)

d. Abnormal heart sounds = murmur; valve pathology

Pathway of Blood Through the Heart and All Body Tissues Superior and inferior vena

cava Right atrium Tricuspid valve Right ventricle Pulmonary semilunar valve Pulmonary arteries Lungs – (O2 and CO2

exchange - external respiration)

Pulmonary veins Left atrium

Bicuspid/Mitral valve Left ventricle Aortic semilunar valve Aorta - all parts of body via

arteries Arterioles Capillaries of individual

tissues (O2 and CO2 exchange = internal respiration)

Venules Veins Superior and inferior vena

cava

Cardiac Cycle

Right and left sides beat together

Electrical impulses in the heart cause the myocardium to contract in a cyclic manner

Cycle consists of a brief period of rest called diastole followed by a period of ventricular contraction

At the start of a cycle, the atria contract pushing blood into the ventricles

Then the atria relax Blood returning from

the body enters the right atrium

Blood returning from the lungs enters the left atrium

Continued cardiac cycle

While the atria are filling, systole begins and the ventricles contract

Right ventricle pushes blood into the pulmonary artery so it can go to the lungs for oxygen

Left ventricles pushes blood into the aorta so it can be carried to all parts of the body

Last of cardiac cycle

Blood in the right side of the heart is low in oxygen and high in carbon dioxide

When it gets to the lungs, the carbon dioxide is released into the lungs and oxygen is taken into the blood

Oxygenated blood is then carried to the left side of the heart by the pulmonary veins

Now the blood in the left side of the heart is high in oxygen and low in carbon dioxide and ready to be carried to body cells

Conduction pathways

Electrical impulses originating in the heart cause the cyclic contractions of the muscles

Starts at the SA node (sinoatrial), also called the pacemaker of the heart

-a group of nerve cells in the right atria sends electrical impulses that spread over the muscles in both atria

-causes atria to contract

-after the electrical impulse passes through the atria, it reaches the AV node (atrioventricular)

-The AV node picks up the impulse at a group of nerves cells located between the atria and the ventricles

-It sends electrical impulses through nerve fibers into the septum called the bundle of His

More on conduction pathways

Bundle of His

divides into the right and left bundle branch

Right and left bundle branches

-pathways that carry the impulse down through the ventricles

-bundles subdivide into a network of fibers throughout the ventricles called the Purkinje fibers

Purkinje fibers

-spread electrical impulse to all of the muscle tissue in the ventricles

-causes the ventricles to contract

Electrical conduction pattern occurs approximately every 0.8 seconds

Movement of the electrical impulse can be recorded on an (ECG)

Blood Vessels

Arteries› Carries blood away from the heart› Are more muscular and elastic than other blood

vessels› Aorta is the largest artery

Receives blood from the left ventricle Immediately begins branching into smaller arteries

Blood vessels Smallest branches of arteries are arterioles They join the capillaries

Capillaries› Connect arterioles and venuoles, the smallest of

veins› Have thin walls › Allows oxygen and nutrients to pass through to

the cells› At the same time carbon dioxide and metabolic

(waste) products from the cells enter the capillaries

Blood Vessels

Veins are blood vessels that carry blood back to the heart

Veins are thinner than arteries Most contain valves that prevent backwards

flow of blood Venules

› Smallest of veins› Connect to capillaries› Venuoles join together and become larger to form

veins

Blood vessels

Superior and inferior vena cava› Two largest veins› Superior brings blood back from the upper part of

the body› Inferior bring blood back from the lower part of

the body