The Heart OBJECTIVES:

OBJECTIVES Orientation of heart in thorax Explain the circuits of blood flow Gross Anatomy of Heart Blood Flow to the Heart Muscle Histology of Heart Muscle Tissue Electrical Conduction System of Heart Disorders of the Heart

Location and Orientation within the Thorax Heart – typically weighs 250–350 grams (healthy heart) Largest organ of the mediastinum (area between the lungs, thoracic inlet superiorly and diaphragm inferiorly, sternum anteriorly and vertebral column posteriorly) Located between the lungs Apex (pointed part) lies to the left of the midline Base is the broad posterior surface (facing toward left shoulder) The heart is a double pump: one pumps blood to the lung and the other to the body

Location and Orientation within the Thorax The heart is in contact with the diaphragm inferiorly, lungs laterally, sternum anteriorly and the spinal column and great vessels posteriorly. Superiorly, the vessels which enter and exit the heart fill much of the superior mediastinum. Figure 18.2

Four “Corners” of the Heart Superior right At costal cartilage of third rib and sternum Inferior right At costal cartilage of sixth rib lateral to the sternum Superior left At costal cartilage of second rib lateral to the sternum Inferior left Lies in the fifth intercostal space at the midclavicular line

The Pulmonary and Systemic Circuits There are three separate circuits of blood involving the heart: the pulmonary, the systemic and the coronary. The pulmonary circuit goes from the right ventricle to the pulmonary arteries to the lungs and back to the left atrium The sysemic circuit runs from the left ventricle to the aorta and onto the superior and inferior systemic arteries. The coronary circuit involves the arteries and veins which supply the heart muscle itself. It runs from the right and left coronary arteries arising from the aorta. Figure 18.1

Blood Supply to the Heart Functional blood supply Coronary arteries Arise from the aorta Located in the coronary sulcus Main branches Left and right coronary arteries

Coronary Circulation The left coronary artery (LCA) arises from the left side of the aorta, passes posterior to the pulmonary trunk then divides into two branches: the anterior interventricular and the circumflex arteries. The anterior interventricular artery is referred to as the Left Anterior Descending Artery, or LAD and runs inferiorly down thhe interventricular septum and anterior walls of both ventricles. The circumflex artery (Cx), follows the coronary sulcus posteriorly and supplies the left atrium and the posterior part of the left ventricle The Right Coronary Artery (RCA) emerges from the right side of the aorta and descends in the coronary sulcus on the anterior surface of the heart between the right atrium and right ventricle. At the inferior border of the heart, it branches to form the marginal artery. Continuing into the posterior part of the coronary sulcus the right coronary artery gives off a large branch in the posterior interventricular sulcus, the posterior interventricular artery. Clinically this arteries commonly called the posterior descending artery (PDA). The right coronary artery and its branches supply the right atrium and much of the right ventricle Cardiac veins Cardiac veins collect blood from the arteries and returns it to the right atrium. The largest vein is the coronary sinus. It occupies the posterior part of the coronary sulcus and returns almost all the venous blood from the heart to the right atrium. Into the coronary sinus drain three large tributaries: the great cardiac vein the middle cardiac vein in the small cardiac vein

Blood Supply to the Heart Know all of these! Figure 18.16

Structure of the Heart – Coverings Figure 18.3

Structure of the Heart – Coverings Pericardium – two primary layers Fibrous pericardium Strong layer of dense connective tissue Serous pericardium Formed from two layers Parietal pericardium – this is the more superficial layer Visceral pericardium – this layer is in direct contact with the surface of the heart. The function of these layers is to reduce friction while the heart is beating So in total there are three layers of tissue surrounding the heart. The fibers per cardio and is separated from the serous pericardium and protects the heart.

Structure of the Heart – Layers of the Heart Wall This muscle arrangement is very efficient to squeeze out all of the blood Figure 18.4

Structure of Heart Wall Left ventricle – three times thicker than right Exerts more pumping force Flattens right ventricle into a crescent shape Figure 18.7

Heart Chambers Must know all of this! Figure 18.5b

Heart Chambers Must know all of this! Figure 18.5e

Posterior View of the Heart Must know all of this! Figure 18.5d

The Heart A muscular double pump (left and right) Pulmonary circuit (right side) – takes blood to and from the lungs Systemic circuit (left side) – vessels transport blood to and from body tissues Atria – receive blood from the pulmonary and systemic circuits Ventricles – the pumping chambers of the heart

Heart Chambers Right and left atria Right and left ventricles Superior chambers Right and left ventricles Inferior chambers Internal divisions Interventricular septa Interatrial septa External markings Coronary sulcus posterior interventricular sulcus

Right Atrium Forms right border of heart Receives blood from systemic circuit Auricle - the auricle is a separate part of the main atrium known as the atrial appendages Pectinate muscles Ridges inside anterior of right atrium - associated with auricle Fossa ovalis Depression in interatrial septum Remnant of foramen ovale

Right Ventricle Receives blood from right atrium through the tricuspid valve Pumps blood into pulmonary circuit via Pulmonary trunk Internal walls of right ventricle Trabeculae carneae Papillary muscles Chordae tendineae

Left Atrium Makes up heart’s posterior surface Receives oxygen-rich blood from lungs Opens into the left ventricle through Mitral valve (left atrioventricular valve)

Left Ventricle Forms apex of the heart Internal walls of left ventricle Trabeculae carneae Papillary muscles Chordae tendineae Pumps blood through systemic circuit via Aortic semilunar valve (aortic valve)

Blood Flow Through the Heart Figure 18.6

Heartbeat 70 – 80 beats per minute at rest Systole – contraction of a heart chamber Diastole – expansion of a heart chamber Systole and diastole also refer to Stage of heartbeat when ventricles contract and expand

Heart Valves – Valve Structure Each valve composed of Endocardium with connective tissue core Atrioventricular (AV) valves Between atria and ventricles Aortic and pulmonary valves At junction of ventricles and great arteries

Fibrous Skeleton Surrounds all four valves Functions Composed of dense connective tissue Functions Anchors valve cusps Prevents overdilation of valve openings Main point of insertion for cardiac muscle Blocks direct spread of electrical impulses

Heart Valves – Valve Structure Figure 18.8a

Function of the Atrioventricular Valves Figure 18.9a

Function of the Atrioventricular Valves Figure 18.9b

Function of the Semilunar Valves Figure 18.10a, b

Microscopic Anatomy of Cardiac Muscle Figure 18.12a, b

Cardiac Muscle Tissue Figure 18.12c, d

Cardiac Muscle Tissue Not all cardiac cells are innervated Will contract in rhythmic manner without innervation Inherent rhythmicity Is the basis for rhythmic heartbeat

Conducting System Cardiac muscle tissue has intrinsic ability to generate and conduct impulses Conducting system A series of specialized cardiac muscle cells Sinoatrial (SA) node sets the inherent rate of contraction (overrides autorhythmicity)

Conducting System Figure 18.14

Innervation Heart rate is altered by external controls Nerves to the heart include Visceral sensory fibers Parasympathetic branches of the vagus nerve Sympathetic fibers – from cervical and upper thoracic chain ganglia Figure 18.15

Heart Sounds “Lub-dub” – sound of valves closing First sound “lub” The AV valves closing Second sound “dub” The semilunar valves closing

Heart Sounds Each valve sound – best heard near a different heart corner Pulmonary valve – superior left corner Aortic valve – superior right corner Mitral (bicuspid) valve– at the apex Tricuspid valve – inferior right corner

Heart Sounds Figure 18.11

Disorders of the Heart Coronary artery disease – caused by a buildup of fatty plaque called atherosclerosis in the coronary arteries resulting in decreased blood supply to the myocardium of the heart and diminished heart function. The causes of CAD may be lifestyle or genetic. The first step is to make lifestyle changes. If this is insufficient to open the arteries then surgical intervention may be necessary. Atherosclerosis – fatty deposits Angina pectoris – chest pain Myocardial infarction – blocked coronary artery Heart attack Silent ischemia – no pain or warning. Loss of blood supply to a portion of the cardiac muscle.

Disorders of the Heart Heart failure Congestive heart failure (CHF) Progressive weakening of the heart Cannot meet the body’s demands for oxygenated blood Congestive heart failure (CHF) Heart enlarges Pumping efficiency declines Cor pulmonale Enlargement and potential failure of right ventricle