the heart cardiovascular system. the heart size: “fist size” 250 grams in females 350 grams in...
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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)
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