Cardiovascular System Anatomy

Circulatory System Overview

• Key components include the heart, blood, blood vessels, lymphatic system, and the body's immunity

Heart Weight and Location

• Usually weighs between 1/2 and 3/4 lb
• Found in the mediastinum, the space between the lungs
• Positioned just left of the midline, between the 2nd and 7th ribs
• Apical heart beat is located at the 5th rib
• Roughly the size of your fist

Heart Coverings

• Enclosed in a sac called the pericardium
• Parietal pericardium is made of FCT and simple squamous tissue
• Visceral pericardium consists of simple squamous tissue on the heart's surface
• The pericardial sac contains pericardial fluid for lubrication

Heart Wall Layers

• Consists of 3 layers: epicardium, myocardium, and endocardium
• The epicardium is the outer, protective layer made of simple squamous serous epithelium and is the same as the visceral pericardium
• The myocardium is the middle and thickest layer, featuring cardiac muscle
• The endocardium is the inner layer with simple squamous epithelium, continuous with the endothelium of blood vessels

Heart Chambers

• Consists of 4 chambers: two atria (right and left) and two ventricles
• The atria are the two top, smaller chambers, which receive blood from the veins
• Ventricles pump blood out
• The auricle is an ear-like flap on the heart's exterior

Heart's Pumping Action

• Operates as two separate pumps
• The right side pumps deoxygenated blood to the lungs via the pulmonary circuit
• The left side pumps oxygenated blood to the entire body through the systemic circuit
• There is no mixing of oxygenated and deoxygenated blood between the two sides

Blood Flow Through the Heart

• Begins in the right atrium
• Flows through the tricuspid valve
• Then to the right ventricle
• Proceeds through the pulmonary semilunar valve
• Then to the pulmonary artery
• Blood goes to the lungs, pulmonary vein, left atrium
• Then through the mitral valve
• Proceeds to the left ventricle
• Then to the aortic semilunar valve
• Then to the aorta, arteries, arterioles, capillaries, venules, and veins
• Blood returns to the heart via the vena cava and enters the right atrium

Vascular Circuits

• The pulmonary circuit oxygenates blood, pumping deoxygenated blood from the right ventricle to the lungs
• The systemic circuit distributes oxygenated blood, pumping it from the left ventricle to all parts of the body
• The left ventricle is notably larger than the right

Heart Valves

• Atrioventricular valves prevent backflow from the ventricles to the atria
• The right atrioventricular valve is the tricuspid valve, having three flaps
• The left atrioventricular valve is the mitral valve (bicuspid), having two flaps
• Two semilunar valves stop backflow from the arteries into the ventricles
• The pulmonary semilunar valve is between the pulmonary artery and the right ventricle
• The aortic semilunar valve is between the aorta and the left ventricle

Heart Valve Issues

• Leaky or damaged valves result in murmurs
• Stenosis is valve narrowing due to plaque or calcium buildup
• Heart sounds, "LUB-DUB," are the sound of valve cusps slamming shut

Valve Structures

• Atrioventricular valves need supportive chordae tendinae structures to function
• Chordae tendinae connect valve flaps to papillary muscles
• Prevents the backflow of blood through the valve
• Papillary muscles keep tension on chordae tendinae

Blood Supply to the Heart

• 10% of total blood volume is in the myocardium at any time
• Supplied through the coronary arteries
• The left coronary artery provides blood to the myocardium
• Plaque buildup in the coronary arteries restricts blood flow to the heart
• Buildup is due to saturated fats (cholesterol)
• Angina pectoralis is chest pain due to reduced blood flow

Angiogram and Angioplasty Procedures

• Angiogram uses a catheter in the aorta and coronary arteries to inject dye, with X-rays showing blockages
• Angioplasty involves placing a stent in a blocked artery area to allow blood flow

Coronary Artery Bypass Surgery

• Used when a blockage is too severe for angioplasty
• Restores circulation to the myocardium
• Veins harvested from the leg are sewn into the coronary artery to bypass the blocked area

Cardiac Cycle Phases

• Systole: contraction phase
• Diastole: relaxation phase
• Atria fill before contracting, followed by the ventricles
• Atrial diastole lasts 0.7 sec
• Atrial systole lasts 0.1 sec
• Ventricular diastole lasts 0.5 sec
• Ventricular systole lasts 0.3 sec

Cardiac Conduction System

• Specialized cardiac muscle fibers initiate and distribute impulses in the myocardium
• The sinoatrial (SA) node is the primary pacemaker, firing at 70-80 bpm
• The atrioventricular (AV) node is the secondary pacemaker, firing at 40-60 bpm
• The Bundle of His runs down the interventricular septum
• Purkinje fibers are within the walls of the ventricles
• This system coordinates heart contractions for efficient blood flow

Electrocardiogram (EKG)

• EKG measures the electrical activity of the heart
• The P wave represents atrial depolarization
• The QRS complex represents ventricular depolarization
• The T wave represents ventricular repolarization
• Used as a diagnostic tool for heart irregularities

Heart Rate Regulation

• Regulated by the autonomic nervous system
• Both parasympathetic and sympathetic divisions are involved
• The vagus nerve provides a parasympathetic "braking" action on the heart
• Accelerator nerves (sympathetic) increase heart rate
• Heart rate is monitored by the cardiac center

Abnormal Heart Conditions

• Tachycardia: fast heart rate
• Bradycardia: slow heart rate
• Ectopic heart beat: originates outside the SA node
• Arrhythmias: irregular heart rate
• Heart flutter: HR < 350 bpm
• Fibrillation: HR 350-750 bpm