Describe the location and orientation of the heart and name the coverings and

Question

layers of the heart wall
• Describe the external and internal features of the heart including chambers,
valves, and other key anatomical structures
• Describe the route of blood flow through the heart including how it returns and
exits through the key blood vessels
• Describe the flow of blood through the pulmonary and systemic circuits
• Describe the microscopic features of cardiac muscle cells and the tissue layers of
the blood vessels it supplies

Answer 1

Certainly! Below is a detailed description of the anatomical and physiological features of the heart and the flow of blood through the pulmonary and systemic circuits:

### Location and Orientation of the Heart

**Location and Orientation:**
- **Location:** The heart is located in the mediastinum of the thoracic cavity, which is the central region of the chest. It sits between the lungs, slightly to the left of the midline.
- **Orientation:** The heart has a base and an apex. The base is directed toward the right shoulder, while the apex points downward and to the left, toward the left hip.

### Coverings and Layers of the Heart Wall

**Coverings:**
1. **Pericardium:** This is a double-walled sac that encloses the heart.
- **Fibrous pericardium:** The outermost layer, which is tough and inelastic, providing protection and anchoring the heart.
- **Serous pericardium:** A thin, double-layered membrane divided into:
- **Parietal layer:** Lines the internal surface of the fibrous pericardium.
- **Visceral layer (Epicardium):** Clings directly to the heart muscle (myocardium).

**Layers of the Heart Wall:**
1. **Epicardium:** The outermost layer, also known as the visceral layer of the serous pericardium.
2. **Myocardium:** The middle layer composed primarily of cardiac muscle tissue. This is the thickest layer and is responsible for the contractile function of the heart.
3. **Endocardium:** The innermost layer, a thin layer of endothelial cells lining the interior of the heart chambers and covering the heart valves.

### External and Internal Features of the Heart

**External Features:**
- **Four Chambers:**
- **Atria (singular: atrium):** The upper chambers that receive blood.
- **Right atrium**
- **Left atrium**
- **Ventricles:** The lower chambers that pump blood out.
- **Right ventricle**
- **Left ventricle**

- **Valves:**
- **Atrioventricular (AV) Valves:** Between the atria and ventricles.
- **Tricuspid Valve:** Between the right atrium and right ventricle.
- **Mitral (Bicuspid) Valve:** Between the left atrium and left ventricle.
- **Semilunar Valves:**
- **Pulmonary Valve:** Between the right ventricle and the pulmonary artery.
- **Aortic Valve:** Between the left ventricle and the aorta.

**Internal Features:**
- **Septum:** Divides the heart into left and right sides.
- **Interatrial Septum:** Separates the atria.
- **Interventricular Septum:** Separates the ventricles.
- **Chordae Tendineae:** Tendinous cords that anchor the AV valves to the papillary muscles in the ventricles.
- **Papillary Muscles:** Muscles in the ventricles that anchor the chordae tendineae.
- **Fossa Ovalis:** A remnant of the fetal circulation, located in the interatrial septum.

### Route of Blood Flow Through the Heart

1. **Deoxygenated Blood:**
- Returns to the heart via the superior and inferior vena cava into the right atrium.
- Flows through the tricuspid valve into the right ventricle.
- Pumped through the pulmonary valve into the pulmonary artery to the lungs for oxygenation.

2. **Oxygenated Blood:**
- Returns to the heart from the lungs via the pulmonary veins into the left atrium.
- Flows through the mitral valve into the left ventricle.
- Pumped through the aortic valve into the aorta, and distributed throughout the body.

### Pulmonary and Systemic Circuits

- **Pulmonary Circuit:** Carries deoxygenated blood from the right side of the heart to the lungs and returns oxygenated blood to the left side of the heart.

- **Systemic Circuit:** Distributes oxygenated blood from the left side of the heart to the body and returns deoxygenated blood to the right side of the heart.

### Microscopic Features of Cardiac Muscle Cells and Tissue Layers of Blood Vessels

1. **Cardiac Muscle Cells:**
- **Striated:** Similar to skeletal muscle but with distinct structural and functional characteristics.
- **Intercalated Discs:** Specialized connections that include gap junctions and desmosomes, allowing for synchronized contractions.
- **Single Nucleus:** Each cell typically has a single central nucleus.

2. **Tissue Layers of Blood Vessels:**
- **Tunica Intima:** Innermost layer of blood vessels, composed of endothelial cells.
- **Tunica Media:** Middle layer, primarily smooth muscle. It controls the diameter of the blood vessels.
- **Tunica Externa (Adventitia):** Outermost layer made of connective tissue, providing structural support and elasticity.

Understanding these features helps in comprehending how the heart functions systematically and integratively with the rest of the body to maintain overall health and homeostasis.