THE HEART

Cardiovascular System

The Heart

Size: “fist size” 250 grams in females 350 grams in males

Location: Medial cavity of the thorax 2/3 lies to the left of the sternum

The Heart

Base: widest part posterior Superior surface- 9 cm wide, directed toward the right

shoulder

Apex- directed inferiorly toward left hip Rests on diaphragm

Point of Maximum Intensity: PMI Site where the apex is against the chest wall, between

5th and 6th rib.

Pericardium

Pericardium: double-walled fibersernous sac membrane which:

1. encloses the heart2. anchors the heart

Fibrous PericardiumFibrous Pericardium Serous PericardiumSerous Pericardium

Tough dense connective tissue.

Protects and anchors heart to sternum, diaphragm, and major vessels the enter and exit

Prevents over distension of heart

Thin slippery membrane Parietal layer:

Lines fibrous pericardium

Pericardial Cavity: space filled with pericardial fluid (prevents friction)

Visceral Pericardium- Lines surface of heart,

connective tissue

Pericardium

Wall of Heart

1. Epicardium- composed of serous tissue and mesothelium outer thin layer

2. Myocardium- composed of cardiac muscle tissue-

1. Bulk of heart- layer that contracts (involuntary)2. Cells are tethered together by a layer of fiberous tissue

that crosses

3. Endocardium- a glistening white sheet of endothelium resting on a layer of connective tissue.

1. Lines heart chambers2. Continuous over valves and throughout vascular system.

AtriaAtria VentriclesVentricles

2 Atria (atrium) receive blood from veins– Auricle: an appendage that

increases the atria’s volume capacity.

– Pectinate muscles: muscle bundles that run parallel to one another and allow atrium to expand and contract.

– Interatrial Septum: divides right and left atrium

Foramen ovalis- opening between atria before birth- closes at birth and forms the fossa ovale (a dent)

2 ventricles – pumping organs Right Ventricle: pumps

to the lungs Left Ventricle: pumps to

the systemic circulation

Interventricular Septum:Divides the left and right

ventricles

Heart Chambers

Structure of the Heart

Grooves on the Surface

Atrialventricular groove Coronary Sulcus Encircles juncitino of

atria and ventricles

Anterior Interventricle Sulcus: Marks the anterior

portion of the interventricular septum

Sulci: contains coronary blood vessels and fat

Heart Valves

Atrioventricular Valves (AV) Prevent back flow into

the atria during ventricular contraction

Right Atrioventricular Valve (tricuspid)

Left Atrioventricular Valve (bicuspid, mitrovalve)

Semilunar Valves Prevent back flow into

the ventricles Aortic Semilunar- left

side Pulmonary Semilunar-

right side

Heart Structure

Blood Flow

Path of Nerve Impulse Through Heart

1. Sinoatrial node (SA Node) (Pacemaker)Mass of nerve tissue in right atrial wall near opening of

superior vena cava- connected to medulla oblongata

2. Down the atria3. Atrioventricular node collects4. Passed to bundle of HIS in interventricular

septum5. Down Perkengie Network to Apex6. Up across Ventricle – out of artery

The HeartbeatThe Conducting System of the Heart

Figure 12-9(a)

The Heart: Conduction System

PLAYPLAY

Figure 12-9(b)1 of 6

SA node activity and atrial activation begin.

Stimulus spreads across the atrial surfaces and reaches the AV node.

There is a 100-msec delay at the AV node. Atrial contraction begins.

The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers.

The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins.

Time = 0

SA node

AV node

Elapsed time = 50 msec

Elapsed time = 150 msec

AV bundle

Bundle branches

Elapsed time = 175 msec

Elapsed time = 225 msec Purkinje fibers

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

An Electrocardiogram

Figure 12-10

Nervous Control of Heart Rate

1. Cardiac Acceleratory Center-increased heart rate- connected to S.A. node by cervical sympathetic ganglion

2.Cardiac Inhibitory Center-Vagus Nerve- decreases

3.Bainbridge Reflex-increases HR due to an increased flow of blood back to heart because of exercise

4.Aortic Arch Reflex-decreased HR due to increase of blood pressure in aorta

5.Carotid Sinus-can increase HR when Blood Pressure drops or decrease HR when blood pressure rises

Chemical Controls

Epinephrine: speeds up Noradrenaline: speeds upThoroxyine: speeds upSodium: speeds up, Potassium: slows downCalcium: speeds upNicotine: speeds up initially, then slows

down

Cardiac Cycle

1. 2 atria contract (ventricles relax)2. 2 ventricles contract (atria relax)

Systole- contraction (chamber empties)Diastole- chamber filling (relaxation)Normal 120/80Average cardiac cycle takes .8 seconds

Figure 12-111 of 6

START

(f) Ventricular diastole—late:All chambers are relaxed.Ventricles fill passively.

(e) Ventricular diastole—early:As ventricles relax, pressurein ventricles drops; bloodflows back against cusps ofsemilunar valves and forcesthem closed. Blood flowsinto the relaxed atria.

(a) Atriole systole begins:Atrial contraction forcesa small amount of additionalblood into relaxed ventricles.

(b) Atriole systole endsatrial diastole begins

(c) Ventricular systole—first phase: Ventricularcontraction pushes AVvalves closed but doesnot create enough pressureto open semilunar valves.

(d) Ventricular systole—second phase: As ventricularpressure rises and exceedspressure in the arteries, thesemilunar valves open andblood is ejected.

370msec

100msec

0msec800

msec

Cardiaccycle

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Stroke Volume: Amount of blood ejected from one ventricle in one

contraction (80 ml)

Cardiac Output: Amount of blood leaving heart in one minute

CO = (HR) (SV)