Intro to the Cardiovascular System

Overview of visceral membranes:
- Visceral Pleura: Membrane surrounding the lungs.
- Visceral Peritoneum: Membrane surrounding abdominal and pelvic organs.
- Touching the surface of organs reveals delicate nature of visceral pleura/peritoneum.

Definition: The visceral layer of the pericardium that covers the heart.
Location: On the surface of the heart, containing blood vessels, lymphatic vessels, and nerves.
Clinical Note: Epicardial blood vessels can become clogged, possibly requiring coronary bypass surgery.

Epicardium:
- Synonymous with visceral pericardium.
Myocardium:
- Definition: Thick muscular layer of the heart.
- Function: Responsible for the contraction (the "hard work") of the heart.
- Note: Thickest layer of the heart.
Endocardium:
- Definition: The endothelial lining of the heart chambers and valves.
- Note: Endothelium is a subtype of epithelium that lines internal structures.

Mammalian Heart Structure:
- Four-chambered heart, like birds.
- Chambers divided into two atria (upper chambers) and two ventricles (lower chambers).
Chamber Ratios:
- Atria are larger relative to ventricles, approximately a 1/3 to 2/3 size ratio.
- Ventricles: More muscular and larger than atria.

Muscle Type:
- Cardiac muscle is involuntary (similar to smooth muscle) and striated (similar to skeletal muscle).
- Unique intercalated discs at the junctions of cardiac muscle cells.
Function:
- Contraction phase is termed systole; relaxation phase is termed diastole.
- Sequence: Both atria contract (systole) followed by both ventricles contracting (systole).

Essay Topic: The flow of blood through the heart including all events and structures.
- Important for upcoming exam; should prepare in detail.
Cycle Reference Point:
- Start: Blood returning to the heart from the body via veins.
- Major veins: Superior and Inferior Vena Cavae.
- Superior Vena Cava: Returns blood from the upper body.
- Inferior Vena Cava: Returns blood from the lower body.
- Coronary Sinus: Collects blood returning from the coronary circulation, pooling before the right atrium.

Blood flow from right atrium to right ventricle:
- Passes through the right atrioventricular orifice guarded by the tricuspid valve.
Tricuspid valve:
- Function: Prevents backflow into the right atrium.
- Structure: Comprised of three flaps (cusps).
Chordae tendineae:
- Definition: Cord-like structures tethering the tricuspid valve to papillary muscles in the ventricular wall, ensuring valve closure.
Blood Pressure Dynamics: Gravity assists 70% blood flow from the right atrium to the right ventricle during diastole.
Ventricular Systole:
- Right ventricle contracts, tricuspid closes, pulmonary valve opens, directing blood into the pulmonary trunk.

Blood returns from the lungs via pulmonary veins (oxygenated blood).
- Key Note: Pulmonary veins carry oxygen-rich blood to the heart, contrasting with systemic definitions which typically associate veins with deoxygenated blood.
Left Atrioventricular Orifice:
- Blood flows from the left atrium to left ventricle through this opening, regulated by the bicuspid valve (mitral valve).
Left Ventricle:
- Most muscular part of the heart; pumps oxygenated blood to the entire body through the aorta.
Aortic Valve:
- Opens during left ventricular systole, directing blood into the ascending aorta.

Coronary Arc:
- Blood flow dedicated to supplying the heart muscle itself.
Pulmonary Arc:
- Carries blood to the lungs for gas exchange (oxygenation).
Systemic Arc:
- The typical pathway of blood flow from the heart through arteries to body tissues, unloading oxygen and returning deoxygenated blood via veins.
Vitelline Arc:
- Specific pathway to the placenta in embryonic circulation.

Valves: Total of four heart valves:
- Atrioventricular (AV) Valves: Tricuspid (right) and bicuspid (left).
- Semilunar Valves: Pulmonary and aortic valves.
Valve Functionality:
- Prevention of Backflow: All valves prevent the backflow of blood during systole, ensuring unidirectional flow.

Definition: Network relaying electrical signals through the heart muscle.
Functional Syncytium: Cardiac muscle cells function together as one unit due to gap junctions - allowing for synchronized contractions.
Autorhythmic Cells: Specific cells in the heart capable of initiating action potentials autonomously.
Key Nodes:
- Sinoatrial Node (SA Node): Located in the upper right atrium; sets the pace (70-80 beats per minute).
- Atrioventricular Node (AV Node): Located at the bottom of the right atrium (40-60 beats per minute).
- Bundle of His: Pathway connecting atria and ventricles (20-40 beats per minute).
- Purkinje Fibers: Spread within the ventricle walls, aiding in the contraction.

Initiation of Action Potentials:
- Cardiac cells naturally drift to threshold, resulting in spontaneous depolarization and rhythmical action potentials without external neural input.
Pacemaker Activity: The ability of certain cardiac cells to spontaneously depolarize and create action potentials, leading to heartbeats.
Graphical Representation of Action Potentials:
- Different autorhythmic cells can be mapped with their inherent rates and membrane potential over time. The SA node depolarizes faster than the Purkinje fibers due to differences in cellular properties.

Understanding heart anatomy and its function requires an integrated approach covering structures, flow dynamics, electrical conduction systems, and physiological mechanics. Knowledge of these concepts is essential for navigating cardiac physiology and pathology effectively.