Heart Anatomy and Physiology:ReviewPresentation Transcript
The Cardiovascular System A Review: The Heart
A hollow muscular organ
Located in thorax between 2 lungs
2 atria (atrium) & 2 ventricles
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 )
The heart lies between the lungs in a region called the mediastinum. You can also see that the heart is wrapped by some membranes that also hold the heart in its position relative to the diaphragm and lungs.
Position of Heart
The 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
Layers of the Heart Pericardium Myocardium Fibrous pericardium Serous pericardium (parietal layer) Pericardial space Serous pericardium (visceral layer - Epicardium) Endocardium
Chambers of the Heart
Valves of the Heart
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
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
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
Pulmonary semilunar valve
When right ventricle contracts, blood is forced through this valve to enter pulmonary trunk
Aortic semilunar valve
When left ventricle contracts, blood is forced through this valve to enter the aorta
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.
Electrophysiologic Properties of the Heart
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.
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 electrical impulses along and across cell membranes.
Conduction System of the Heart
Coronary Arteries Atherosclerosis is an accumulation of fat on the inner walls of arteries. When coronary arteries become partially blocked…. angina When coronary arteries become significantly blocked…. myocardial infarction
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.
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
Stroke Volume Is Determined By Three Factors
Degree of stretch of myocardial fibers
Determined by the volume of blood in left ventricle (LV) at end of diastole
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
Factors Which Decrease Preload
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
Force generated by the myocardium when it contracts – inotropic property
Ejection fraction (EF) - percentage of LV end-diastolic volume that is ejected with each contraction
Autonomic Nervous System (ANS) Regulation of Cardiovascular System
Heart rate – chronotropic effect
Contractility – inotropic effect
Conduction velocity at AV node – dromotropic effect
Afterload - vascular resistance – arterial vasoconstriction and dilation