Cardiovascular System The Heart Chap. 12

The Cardiovascular system is comprised of the heart, blood vessels, & blood The heart acts as a “pump”, creating pressure which causes blood to move through the blood vessels of the body, allowing O 2 & nutrients to be distributed to, & wastes removed from, body tissues

Heart Anatomy Overview Play Heart Anatomy video

Anatomical Features of the Heart The heart lies within the mediastinum of the thoracic cavity Hollow muscular organ with four internal chambers  (2) atria (lt. atrium & rt. atrium)- receive blood from veins  (2) ventricles (lt. ventricle & rt. ventricle)- pump blood into arteries Superior aspect of heart is the “base”, where the blood vessels attach; Inferior is the “apex”, which rests on the relaxed diaphragm

Pericardium The heart lies enclosed within pericardial membranes  Fibrous pericardium (pericardial sac) – outer layer of dense CT that protects & anchors  Serous pericardium – double layered membrane with “pericardial fluid” between Parietal pericardium – lines the pericardial sac Visceral pericardium – covers the heart; also known as the “epicardium” etal cardium

Figure 12.2

Layers of Heart Wall  Epicardium (a.k.a. visceral pericardium)  Myocardium  Endocardium

Figure 12.4 Cardiac Muscle Tissue

Because of the characteristics of cardiac muscle tissue & the arrangement of connective tissue (fibrous skeleton) within the heart, the heart basically has two functional units:  the myocardium of the atria (upper chambers) act as one functional unit  the myocardium of the ventricles (lower chambers) act as the other

This allows the atria to contract simultaneously while the ventricles are relaxed; then the ventricles contract simultaneously while the atria relax

External Features  Auricles  Coronary sulcus – contains the coronary sinus  Anterior interventricular sulcus – contains coronary vessels  Posterior interventricular sulcus – contains coronary vessels

Rt Atrium Lt Atrium Pectinate muscles Interatrial septum SVC IVC Coronary sinus (opening) Deoxygenated blood Pulmonary veins Oxygenated blood Tricuspid valve Bicuspid (mitral) valve Chordae tendineae Papillary muscle Chordae tendineae Papillary muscle

Atrioventricular (AV) valves  Tricuspid  Bicuspid

Rt ventricle Lt ventricle Interventricular septum Trabeculae carneae Aorta Aortic semilunar valve Pulmonary semilunar valve Pulmonary trunk Pulmonary artery Brachiocephalic trunk Lt. common carotid artery Lt. subclavian artery Ligamentum arteriosum

Anatomy

Coronary Circulation  Myocardium receives oxygenated blood from the left & right Coronary arteries – branches off the ascending aorta  Deoxygenated blood is drained through Cardiac veins, which all eventually merge into the coronary sinus Fig. 12.7

Conducting System  Intrinsic regulating system that generates “heartbeat”  comprised of functionally specialized “autorhythmic (conducting) cells” – which can spontaneously generate action potentials Fig. 12.9

 The electrical events that occur in the heart can be detected on the surface of the body  The resulting pattern of activity is known as an ECG (or EKG) - Electrocardiogram

Electrocardiogram (ECG) (atrial depolarization) (ventricular repolarization ) ( ventricular depolarization)

 The activity of the conduction system results in the contraction (systole) & relaxation (diastole) of the heart chambers  The change in volume (size) of the chambers results in changes in pressure within the heart – decreased volume  increased pressure & vice-versa.  Blood will flow through the chambers (and throughout the cardiovascular system) due to the differences in pressure (blood moves from high  low pressure)

Cardiac Cycle  One complete “heartbeat” is referred to as a “Cardiac Cycle”  Average 75 cycles/minute  Each cycle lasts approx. 0.8 seconds  Continuous, repetitive cycle that can be “divided” into 3 phases for ease of understanding:  atrial diastole/ventricular diastole (0.4 sec.)  atrial systole/ventricular diastole (0.1 sec.)  atrial diastole/ventricular systole (0.3 sec.)

Cardiac Cycle atrial diastole/ ventricular diastole atrial systole/ventricular diastole atrial diastole/ventricular systole START “Lub” “dupp”

Cardiac Output  Important physiological measurement of cardiac function  Refers to the amount of blood ejected by the left ventricle each minute  C.O. = stroke volume X heart rate  stroke volume – amount of blood ejected from ventricle each contraction (80 ml average)  heart rate – beats (cardiac cycles) per minute (75 bpm average)  average C.O. = 6000 ml/min (6 L/min)

Cardiac Output Cardiac output is primarily regulated by: 1. Blood volume reflexes – there is a direct relationship between blood entering the heart & amount ejected  increased venous return  atrial reflex (aka Bainbridge reflex)  increased heart rate (through increase in sympathetic activity)  increased venous return  ventricular reflex (aka Frank-Starling principle)  increased stroke volume

Cardiac Output 2. Cardiac center of M.O. – ANS input to SA node to increase/decrease heart rate & stroke volume Cardiac center influenced by:  baroreceptors – detect blood pressure changes  chemoreceptors – detect oxygen/carbon dioxide concentrations  higher brain centers – ie. hypothalamus 3. Hormones – epinephrine/norepinephrine, thyroid hormones, glucagon, etc can increase heart rate & force of contraction