the heart

The Heart

B. Pimentel, M.D.

University of Makati – College of Nursing

Function

1. Generate blood pressure

2. Routing blood

3. Ensuring one way blood flow

4. Regulating blood supply

The Heart

The heart lies obliquely in the mediastinum of the thoracic cavity. Base directed posteriorly and slightly superiorly

Deep to the sternum and extends to the 2nd intercostal space

Apex directed anteriorly and slightly inferiorly 2/3 of the hearts mass lies to the left of midline Approximately 9 cm. to the left of the sternum and is deep to the fifth

intercostal space.

Size - approx. the size of a closed fist

Shape - like a blunt cone, the blunt rounded point of the heart is the apex, and the larger opposite end is the base

ANATOMY OF THE HEARTPericardium


Fibrous pericardium - tough, fibrous connective tissue, outer layer Prevents over distention and anchors the mediastinum Superiorly it is continuous with the connective tissue of

the great vessels, and inferiorly attached to the surface of the diaphragm


Serous pericardium - thin transparent inner layer

Parietal pericardium - part of the serous pericardium that lines the fibrous pericardium

Visceral pericardium (Epicardium) - part of the serous pericardium that covers the heart surface


Pericardial cavity - between the parietal and visceral pericardium

Pericardial fluid - thin layer of serous fluid which reduces friction of the beating heart

ANATOMY OF THE HEART Heart Wall

Epicardium - thin serous membrane of the outer surface of the heart

Myocardium - thick middle layer composed of cardiac muscle

Endocardium - simple squamous epithelium over a layer of connective tissue, continuous with all blood vessels of the body.

ANATOMY OF THE HEART External Anatomy

2 atria and 2 ventricles

Atria - form the superior and posterior portions of the heart Interarterial septum - separates the left and right atria

Ventricles - the anterior and inferior portions and are thick walled

Interventricular septum - separates the right and left ventricles.


Auricoventricular sulcus (Coronary sulcus) - runs obliquely around the heart separating the atria and ventricles

Interventricular sulcus - divides the heart into right and left halves (anterior and posterior)

The major arteries supplying the coronary tissue lie within the coronary and interventricular sulci

ANATOMY OF THE HEART External Anatomy (Blood Vessels)

6 veins

Superior and Inferior vena cava – carry blood to the right atrium

Pulmonary vein (4) – carry blood from the lungs to the left atrium


2 arteries

Pulmonary trunk – from the right ventricle and divides into left and right pulmonary artery

Aorta – from the left ventricle

ANATOMY OF THE HEART External Anatomy (Coronary circulation)

Right and left coronary arteries – from the base of the aorta above the semilunar valves

Left coronary artery is usually dominant over the right Anterior interventricular artery or the left anterior descending artery

supplies blood to most of the anterior wall of the heart and the left ventricle

Left marginal artery supplies the lateral wall of the left ventricle Circumflex artery extends around to the posterior surface and

supplies most of the posterior surface


Right coronary artery Right marginal artery supplies the lateral wall of the right ventricle. Posterior interventricular artery supplies blood to parts of the

inferior and posterior parts of the heart

At rest, coronary arteries provide the heart muscle with 70% of its oxygen vs. 25% in skeletal muscles


Great cardiac vein drains blood from the left side of the heart.

Small cardiac vein drains the right margin of the heart.

Coronary sinus a large venous cavity that the veins converge toward the posterior part of the heart and empties into the right atrium

ANATOMY OF THE HEART Internal Anatomy (Heart Chambers)

Right and left atrium – functions as a reservoir of blood; collects blood from veins before it enters the ventricles

Right atrium – receives blood from the superior and inferior vena cava

Left atrium – receives blood from the pulmonary veins

ANATOMY OF THE HEART Internal Anatomy (Heart Chambers)

Left and right ventricles – eject and force blood to flow through the circulatory system; blood from the atria drains into these chambers

Right ventricle – opens into the pulmonary trunk Left ventricle – opens into the aorta; thicker wall

ANATOMY OF THE HEART Heart Wall

Musculi pectinati - muscular ridges in the interior of auricles and part of right atria.

Crista terminalis - separates the musculi pectinati from the smooth walls of the atria.

Trabecullae carneae - large muscular ridges of the ventricles.

ANATOMY OF THE HEART Heart Wall (left ventricle)

ANATOMY OF THE HEART Heart Wall (right ventricle)

ANATOMY OF THE HEART Internal Anatomy (Heart Valves)

Atrioventricular valves - Between the right atrium and right ventricles and between the left atrium and left ventricle

Tricuspid valve - 3 cusps, between the right atrium and right ventricle Bicuspid valve - two cusps, between the left atrium and left ventricle,

also known as the mitral valve

Contain papillary muscle in each ventricle, cone shaped muscular pillars. Attached to thin strong connective tissue cords called Chordae tendinae. The chordae tendinae attach to the cusps of the valves. When the papillary muscles contract, prevents the valves from opening.


Semilunar valves Aortic valve - between the left ventricle and the aorta. Pulmonary valve - between the right ventricle and the

pulmonary artery.


Does that look like valve to you?....

Where is the pulmonary valve?

BLOOD FLOW

HEART CONTRACTIONAction Potential

HEART CONTRACTIONAction Potential(Cardiac muscle vs. Skeletal muscle)

ELECTRICAL ACTIVITYAction Potential (Cardiac Muscle)


Depolarization phase Na channels open K channels close Ca channels begin to open

Early repolarization phase Na channels close K channels begin to open


Plateau phase Ca channels are open

Final repolarization phase Ca channels close K channels open

ELECTRICAL ACTIVITY Conduction system

Sinoatrial node (SA Node) is medial to the opening of the superior vena cava. Action potentials travel across the wall of the atrium to the atrioventricular node (AV Node) located medial to the right atrioventricular valve.

Action potentials pass through the AV node and along the atrioventricular bundle, which extends from the AV node into the interventricular septum.


The AV bundle divides into right and left bundle branches, the action potential descends to the apex of the heart along the bundle branches.

Action potentials are carried by Purkinje fibers from the bundle branches up along the ventricular walls.

ELECTROCARDIOGRAM (EKG)

A measurement of the action potentials of the myocardium during the cardiac cycle.

A typical EKG consists of a series of three distinguishable waves called deflection waves.

P wave - results from the movement of the depolarization wave from the SA node through the atria, approx. 0.1 sec the atria contract

QRS complex - results from ventricular depolarization and precedes ventricular contraction. Atrial repolarization is obscured by this wave.

T wave - ventricular repolarization

ELECTROCARDIOGRAM (EKG)

CARDIAC CYCLE

The repetitive pumping process that begins with onset of cardiac muscle contraction and ends with the beginning of the next contraction.

Systole – to contract

Diastole – to dilate

CARDIAC CYCLE

1. Systole: Period of Isovolumic Contraction. Ventricular contraction causes the AV valves to close, which is the beginning of ventricular systole. The semilunar valves were closed in the previous diastole and remain closed during this period. The volume of blood in the ventricles does not change.

2. Systole: Period of Ejection. Continued ventricular contraction pushes blood out of the ventricles causing semilunar valves to open.

CARDIAC CYCLE

3. Diastole: Period of Isovolumic Relaxation. Blood flowing back toward relaxed ventricles causes the semilunar valves to close, which is the beginning of diastole. The AV valves are also closed

4. Diastole: Passive Ventricular Filling. The AV valves open and blood flows into the relaxed ventricles, accounting for most of the ventricular filling.

5. Diastole: Active Ventricular Filling. The atria contract and complete ventricular filling.

CARDIAC CYCLE

End diastolic volume – ventricles are filled with 120 to 130 ml of blood during the previous ventricular diastole.

End systolic volume – the volume decreases to 50 to 60 ml at the end of ejection.

Stroke volume – the volume of blood pumped during each heart beat (cardiac cycle), is equal to end diastolic volume minus end systolic volume.

HEART SOUNDS

Heart sounds are produced by valves closing. 1st heart sound

Low pitched sound “lubb” caused by vibration of AV valves and the surrounding fluid as the valves close at the beginning of ventricular systole

2nd heart sound Higher pitched sound “dupp” closure of the aortic and pulmonary

valves, at the beginning of ventricular diastole.

3rd heart sound Occasionally heard, caused by blood flowing in a turbulent fashion

into the ventricles, near the end of the 1st third of diastole.

CARDIAC CYCLE

REGULATION OF THE HEART

Intrinsic – does not depend on either neural or hormonal regulation

Extrinsic – involves neural and hormonal influence

REGULATION OF THE HEART

(Intrinsic)

Venous return – the amount of blood that flows into the right atrium during diastole

Preload – the extent to which the ventricular walls are stretched An increased preload causes an increase in cardiac output Decreased preload, decreased cardiac output. Starling’s Law of the Heart

REGULATION OF THE HEART (Intrinsic)

Afterload – the pressure the ventricles must produce to overcome the pressure of the aorta and move blood into the aorta. Heart is very sensitive to changes in afterload as compared with preload

REGULATION OF THE HEART (Extrinsic)

Parasympathetic Parasympathetic control is via the vagus nerve. Stimulation is inhibitory to heart rate. Can decrease heart

rate by 20 to 30 beats/minute.

Sympathetic Nerve fibers originate in thoracic region. Stimulation increases heart rate and force of contraction

REGULATION OF THE HEART (Extrinsic)

Hormonal Control Adrenal medulla releases norepinephrine and epinephrine. Increases the rate and force of contraction. Occurs in response to increased physical activity, emotional

excitement, or stress. Epinephrine takes a longer time to act on the heart compared

with sympathetic stimulation, but the effect lasts longer.

HEART AND HOMEOSTASIS

1. Barorecptor reflexes – Stretch receptors located in the internal carotid arteries and the aorta.

Detect changes in blood pressure and result in changes in heart rate and in force of contraction.

2. Increased blood pressure decreases sympathetic stimulation and increases parasympathetic stimulation

3. Decreased BP, decreases parasympathetic stimulation and increases sympathetic stimulation

Effect of Extracellular Ion Concentration

Ions that affect cardiac muscle function are the same as those responsible for action potentials in other electrically excitable tissues.

Increased Potassium causes the heart rate and stroke volume to decrease.

Increase in Potassium causes heart block which is loss of the functional conduction action potentials through the conduction system of the heart.

Increase in Calcium increases force of contraction and reduce heart rate.

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the heart

Documents

heart external anatomy

heart internal anatomy

heart heart wall

action potentials

connective tissue

bundle branches

interventricular septum

ventricular walls