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 5 th and 6 th rib.

Pericardium Pericardium: double-walled fibersernous sac membrane which: 1. encloses the heart 2. anchors the heart

Fibrous Pericardium Serous 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 chambers 2. Continuous over valves and throughout vascular system.

Atria Ventricles 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 atria 3. Atrioventricular node collects 4. Passed to bundle of HIS in interventricular septum 5. Down Perkengie Network to Apex 6. Up across Ventricle – out of artery

The Heartbeat The Conducting System of the Heart Figure 12-9(a) The Heart: Conduction System PLAY

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 up Thoroxyine: speeds up Sodium: speeds up, Potassium: slows down Calcium: speeds up Nicotine: 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 120/80 Average cardiac cycle takes.8 seconds

Figure of 6 START (f) Ventricular diastole—late: All chambers are relaxed. Ventricles fill passively. (e)Ventricular diastole—early: As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria. (a)Atriole systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles. (b)Atriole systole ends atrial diastole begins (c)Ventricular systole— first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. (d)Ventricular systole— second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. 370 msec 100 msec 0 msec 800 msec Cardiac cycle 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)