The Cardiovascular

System

Ms. Louradel Ulbata-Alfonso,MAN, RN

Heart • A hollow muscular organ• Located in thorax between

2 lungs• 4 chambers• 2 atria (atrium) & 2

ventricles• 4 valves• 2 separate pumps (R & L

sides)• Right side receives blood

from the body and sends it to the lungs (pulmonary)

• Left side receives blood from lungs and sends it to the body (systemic)

• PMI –midclavicular line @ 5th IC space

Position of Heart

3 LAYERS:

1. ENDOCARDIUM2. MYOCARDIUM3. EPICARDIUM

Layers of the HeartLayers of the Heart

Pericardium

Myocardium

Fibrous pericardiumSerous pericardium (parietal layer)

Pericardial spaceSerous pericardium (visceral layer - Epicardium)

Endocardium

• The heart lies between the lungs in a region called the mediastinum. 

• heart is wrapped by some membranes that also hold the heart in its position relative to the diaphragm and lungs.

The PericardiumThe pericardium is the set of membranes

around the heart.  It is actually composed of three layers of membranes.

• visceral pericardium - the innermost• parietal pericardium - the middle, • fibrous pericardium - the outer one is the

extra one, and  is tough. 

•Pericardial Cavity- tiny space between the visceral pericardium and the parietal pericardium  •15-50 ml•Pericardial Effusion VS Cardiac Tamponade

Layers of the HeartLayers of the Heart

Pericardium

Myocardium

Fibrous pericardiumSerous pericardium (parietal layer)

Pericardial spaceSerous pericardium (visceral layer - Epicardium)

Endocardium

CORONARY ARTERIES• L & R coronary arteries –supply arterial

blood to the heart• Originate from the aorta above the aortic

valve leaflets• Perfused during diastole• ↑ HR → ↓ Blood flow → myocardial

ischemia• Heart has high metabolic requirements

(extract 70-80% of the oxygen delivered)

LEFT CORONARY ARTERIES• 3 BRANCHES

• 1. Left main coronary artery• 2. Left anterior descending artery –

anterior wall of the heart• 3. Circumflex artery – circles around to the

lateral left wall of the heart

CORONARY ARTERIES

RIGHT CORONARY ARTERY• Right coronary artery

- inferior wall of the heart

• Posterior descending artery- posterior wall of the heart

- Drains into the coronary sinus

CORONARY ARTERIES

Coronary Arteries

Atherosclerosis is an accumulationof fat on the inner walls of arteries.

When coronary arteries become partially blocked….angina

When coronary arteries becomesignificantly blocked….myocardialinfarction

Chambers of the Heart

Valves of the Heart• 4 valves• One way flow• Leaky valve = heart murmur• 2 atrioventricular valves

– Left AV valve- bicuspid or mitral– Right AV valve- tricuspid

• 2 semilunar valves– Pulmonic semilunar valve– Aortic semilunar valve

Valves of the Heart

Tricuspid Valve

Mitral Valve

Pulmonic Valve

Aortic Valve

Atrioventricular Valves1. Right AV valve• Between right atrium and right ventricle• Also called the tricuspid valve because it has three

cusps.• Cusps close when right ventricle

contracts….preventing blood from going back up into the right atrium

2. Left AV valve• Between the left atrium and the left ventricle• Also called the bicuspid valve because it only has

two cusps• Also called the mitral valve• Cusps close when left ventricle contracts….preventing

blood from back up into the left atrium

Semilunar Valves1. Pulmonary semilunar valve• When right ventricle contracts, blood is forced through

this valve to enter pulmonary trunk2. Aortic semilunar valve• When left ventricle contracts, blood is forced through

this valve to enter the aorta

• Papillary muscles – located on the sides of the ventricular walls and and connected to the valve leaflets by thin fibrous bands called CHORDAE TENDINAE

CHORDAE TENDINAE

2 Pumps

Blood flow in the Heart

CARDIAC ELECTROPHYSIOLOGY

Cardiac Conduction System

The cardiac conduction system generates and transmits impulses that stimulate contraction of the myocardium.

Under normal circumstances, the conduction system first stimulate the contraction of the atria and then the ventricles.

CONDUCTION SYSTEM

SA NODE- main regulator of HR - transmit impulse to the surrounding atrial

muscle.AV NODE- transmit impulses to the

surrounding ventricular muscle.BUNDLE OF HIS- continuation of AV Node

and has a left and right bundles and fuse with purkinje fibers.

PURKINJE FIBERS- terminal branches of the conduction system and are responsible for carrying the wave of depolarization to both ventricular walls.04/28/23

04/28/23

2 TYPES OF SPECIALIZED ELECTRICAL CELLS IN THE HEART• 1. NODAL CELLS• 2. PURKINJE CELLS

• These provide synchronization

ELECTRICAL CELLS

• Nodal Cells – SA and AV nodes• Purkinje Cells – Purkinje Fibers

3 Physiologic Properties of the Electrical Cells

Excitability. The ability of the heart to depolarize in response to a stimulus. Once stimulated, the whole heart muscle contracts. It is influenced by hormones, electrolytes, nutrition, oxygen supply, medications, infection, and nerve characteristics.- “ The ability to RESPOND”

Automaticity/Rhythmicity. The ability of cardiac cells to initiate an impulse spontaneously and repetitively, without external neurohormonal control.

Conductivity. The ability of the heart muscle fibers to propagate/ transmit electrical impulses along and across cell membranes.

CONDUCTION SYSTEM OF THE HEART

• SA NODE (Primary pacemaker)↓

AV NODE ↓

Bundle of his ┴

R bundle L bundle branch branch

┬

PURKINJE FIBERS↓

VENTRICULAR CONTRACTIONS

Conduction System of the Heart

CARDIAC ELECTROPHYSIOLOGY

CARDIAC ELECTROPHYSIOLOGY

CARDIAC ACTION POTENTIAL• IONS1. Sodium2. Potassium3. Calcium

3 PHASES1. Resting membrane state2. Depolarization3. Repolarization

REFRACTORY PERIODS• Myocardial cells must COMPLETELY

repolarize (rest) before they can depolarize/ stimulated again

• 2 PHASES:1. Effective/ Absolute refractory period2. Relative refractory period

ABSOLUTE REFRACTORY• Cell is COMPLETELY UNRESPONSIVE

to any electrical impulse• It is INCAPABLE of initiating early

depolarization

RELATIVE REFRACTORY• If an electrical stimulus is stronger than

normal, the cell may depolarize early or prematurely

• Early depolarization of atrium or ventricle → premature contractions → DYSRHYTHMIAS

CARDIAC HEMODYNAMICS• Principle that fluids flow from a region of

higher pressure to a region of lower pressure

Cardiac Cycle- refers to the events of one complete heart beat. The length of the cardiac cycle is usually about 0.8 sec.

• Systole (contraction of the muscle)- there is ventricular pumping, the chambers of the heart become smaller as the blood is ejected. Occurs secondary to depolarization of cells

• Diastole (relaxation of the muscle)- there

is ventricular filling, the heart chambers fill with blood in preparation for subsequent ejection.

Cardiac Output

• Volume of blood ejected per minute– Each ventricle ejects approximately 70mL of

blood/ beat

• Averages between 4-8L/min• CO = Stroke volume X heart rate =70 ml X 60 beats/min =4,200 ml/min

Changes in SV and HR affects cardiac output

Controls of the heart

1. AUTONOMIC NS- sympathetic and parasym

2. CNS and baroreceptors and chemoreceptors

Baroreceptors- aortic arch and R & L internal carotid arteries- sensitive to changes in BP

Chemoreceptors- sensitive to CO2 level

Subdivisions of ANS

• Parasympathetic – acetylcholine produces inhibitory response

• Sympathetic – catecholamines stimulate– Increase heart rate – Beta 1 receptors– Dilate smooth muscles – Beta 2 receptors– Vasoconstrict vessels – Alpha receptors

Stroke Volume Is Determined By Three Factors

• Preload• Afterload• Contractility

Preload• Degree of stretch of myocardial fibers• Determined by the volume of blood in left

ventricle (LV) at end of diastole• Increased blood volume – increased

preload- increased cardiac output (CO)• Decreased blood volume – decreased

preload – decreased cardiac output (CO)

Frank- Starling Law-the critical factor controlling stroke volume is how much the cardiac muscle cells are stretched just before the contract. The more they are stretched, the stronger the contraction will be. The important factor stretching the heart muscles is the venous return.

Factors Which Increase Preload

• IV fluids• Blood• Vasoconstriction

Factors Which Decrease Preload

• Diuretics• Dehydration• Hemorrhage• Vasodilation

Afterload

• Resistance or pressure the ventricles must overcome to pump blood out

• Left ventricle (LV) affected by systemic vascular resistance (SVR)

• Right ventricle (RV) affected by pulmonary vascular resistance (PVR)

• Related to arterial pressure or diameter of arteries

• As pressure increases, resistance increases, afterload increases

• As pressure decreases, resistance decreases, afterload decreases

Contractility

• Force generated by the myocardium when it contracts – inotropic property

END