Week 11: The Heart

Describe the anatomy of the heart.
Describe the vascular supply of the heart muscle.
Describe the structure and function of the pericardium.
Compare and contrast the structure and location of the epicardium, myocardium, and endocardium layers of the heart wall.
Trace the flow of blood through the heart, identifying the major blood vessels, chambers, and heart valves.
Describe the conducting system of the heart, identify the location of its components, and trace the pathway of impulse initiation and conduction.

Cardiovascular System Components:
- Heart
- Blood
- Blood vessels
Heart Statistics:
- Beats approximately 100,000 times each day.
- Pumps about 8000 liters of blood per day.

Circuits of Blood Flow:
- Pulmonary Circuit: Carries blood to and from the gas exchange surfaces of the lungs.
- Systemic Circuit: Carries blood to and from the rest of the body.
- Each circuit begins and ends at the heart; blood travels through these circuits in sequence.
Blood Vessel Types:
- Arteries: Carry blood away from the heart.
- Veins: Return blood to the heart.
- Capillaries: Exchange vessels that interconnect the smallest arteries and veins, allowing for exchange of dissolved gases, nutrients, and wastes between blood and surrounding tissues.
Four Chambers of the Heart:
- Right Atrium: Receives blood from the systemic circuit.
- Right Ventricle: Pumps blood into the pulmonary circuit.
- Left Atrium: Receives blood from the pulmonary circuit.
- Left Ventricle: Pumps blood into the systemic circuit.
Heart Structure:
- Orientation: Great vessels connect at the base (superior); pointed tip is apex (inferior).
- Location: Sits between two pleural cavities in the mediastinum.

Function: Surrounds the heart.
Layers of Pericardium:
- Outer Fibrous Pericardium
- Inner Serous Pericardium:
- Outer parietal layer
- Inner visceral layer (epicardium)
Pericardial Cavity:
- Located between the parietal and visceral layers.
- Contains pericardial fluid.
Pericarditis:
- Caused by pathogens in the pericardium.
- Symptoms include inflamed pericardial surfaces rubbing against each other, creating a distinctive scratching sound.
- Can cause cardiac tamponade, which restricts heart movement due to excess fluid in the pericardial cavity.

Chambers: Two thin-walled atria, each with an expandable outer auricle.
Sulci (Grooves): Contain fat and blood vessels, marking boundaries:
- Coronary Sulcus: Marks border between atria and ventricles.
- Interventricular Sulci: Anterior and posterior, marking boundaries between left and right ventricles.
Heart Wall Layers:
- Visceral Layer of Serous Pericardium (Epicardium): Covers the heart's surface.
- Myocardium: Cardiac muscle tissue responsible for contractions.
- Endocardium: Covers the inner surfaces of the heart, consisting of simple squamous epithelium and areolar tissue.

Muscular Partitions (Septae): Separate the heart chambers:
- Interatrial Septum: Separates the atria.
- Interventricular Septum: Thicker, separating the ventricles.
Atrioventricular (AV) Valves:
- Tricuspid Valve: Between right atrium and right ventricle; prevents backflow of blood.
- Mitral Valve: Between left atrium and left ventricle; also prevents backflow.
Semilunar Valves:
- Pulmonary Valve: Prevents backflow into the right ventricle.
- Aortic Valve: Prevents backflow into the left ventricle.

Right Atrium Receives Blood From:
- Superior Vena Cava: Drains blood from the head, neck, upper limbs, and chest.
- Inferior Vena Cava: Drains blood from the trunk, viscera, and lower limbs.
Foramen Ovale (in Fetal Heart):
- Opening through interatrial septum that connects the two atria.
- Closes at birth, forming the fossa ovalis.
Pathway of Blood Flow from Right Atrium to Right Ventricle:
- Blood passes through the tricuspid valve, which has three cusps.
- Free edges of the valve attach to chordae tendineae from papillary muscles, preventing backward opening.
Right Ventricle Anatomy:
- Trabeculae Carneae: Muscular ridges on the internal surface.
- Moderator Band: A muscular ridge that delivers the stimulus for contraction to papillary muscles.
Flow from Right Ventricle to Pulmonary Arteries:
- Through the pulmonary valve to the pulmonary trunk, marking the start of the pulmonary circuit.
Left Atrium Receives Blood From:
- Left and right pulmonary veins.
- Blood passes to left ventricle through the mitral valve.
Left Ventricle Anatomy:
- Similar to right, but without a moderator band.
- Sends blood through aortic valve into the ascending aorta, which turns into the aortic arch then descends.

Compared to the left ventricle, the right ventricle:
- Holds and pumps the same amount of blood.
- Has thinner walls.
- Develops less pressure.
- Is more pouch-shaped than round.

Atrioventricular (AV) Valves:
- Prevent regurgitation during ventricular contractions by closing due to blood pressure.
- Chordae tendineae and papillary muscles contribute to valve stability.
Semilunar Valves:
- Prevent backflow into the ventricles without muscular braces.
- Valvular Heart Disease (VHD): Deterioration of valve function, often due to inflammation.

Function: Supplies blood to the muscle tissue of the heart.
Coronary Arteries: Originate at the aortic sinuses and are maintained by elevated blood pressure and elastic rebound of the aorta.

Supplies the:
- Right atrium
- Portions of both ventricles
- Portions of electrical conducting system of the heart
Gives rise to:
- Marginal arteries
- Posterior interventricular artery

Definition: Areas of partial or complete blockage of coronary circulation.
Importance: Cardiac muscle cells require a constant supply of oxygen and nutrients; reduced blood flow diminishes cardiac performance.
Coronary Ischemia: Reduced circulatory supply due to blockage.

Often a first symptom of CAD.
Temporary ischemia develops with increased cardiac workload; comfortable at rest.
Symptoms: sensations of pressure, chest constriction, and radiating pain from the sternal area.