5.3: lecture Notes on the Heart and Thoracic Cavity

Thoracic Cavity and Heart Overview

• The heart is located in the thoracic cavity, specifically in the mediastinum.
• It is primarily situated on the left side of the thoracic cavity, pushing the left lung aside and allowing for the anatomical configuration where the left lung has two lobes instead of three.

Heart Positioning

• The heart sits atop the diaphragm and features a base and an apex:
  • Base: The broader top part of the heart.
  • Apex: The pointed tip directed downward and toward the left.
• Functions as a pump in the circulatory system, with two distinct sides:
  • Right Side: Receives deoxygenated blood and pumps it to the lungs (pulmonary circulation).
  • Left Side: Receives oxygenated blood from the lungs and pumps it to the body (systemic circulation).

Anatomy of the Heart

• Surrounding Layers:
  • The heart is encased in a protective membrane called the pericardium:
  • Parietal Pericardium: Outer layer.
  • Visceral Pericardium: Inner layer, touches the heart.
  • Cavity: Contains serous fluid that reduces friction.
  • Additionally, there is a fibrous pericardium that protects the heart from damage.

Major Vessels Associated with the Heart

• The heart is connected to major vessels:
  • Superior Vena Cava: Drains blood from the upper body to the right atrium.
  • Inferior Vena Cava: Drains blood from the lower body to the right atrium.
  • Aorta: Distributes oxygenated blood to the body.
  • Pulmonary Arteries and Veins: Take deoxygenated blood to the lungs and return oxygenated blood to the left atrium, respectively.

Heart Chambers and Valves

• The heart contains four chambers:
  • Right Atrium: Receives blood from the superior and inferior vena cava.
  • Right Ventricle: Pumps blood to the lungs through the pulmonary valve.
  • Left Atrium: Receives blood from the lungs.
  • Left Ventricle: Pumps blood to the body through the aortic valve.
• Valves: Control blood flow between chambers and prevent backflow:
  • Tricuspid Valve: Between the right atrium and right ventricle (three cusps).
  • Bicuspid (Mitral) Valve: Between the left atrium and left ventricle (two cusps).
  • Semilunar Valves: Include the pulmonary valve and aortic valve, preventing backflow into the ventricles after contraction.

Blood Flow Through the Heart

• Blood flow sequence:
  1. Deoxygenated blood enters the right atrium via the vena cavae.
  2. Blood moves to the right ventricle through the tricuspid valve.
  3. Blood is pumped to the lungs via the pulmonary artery through the pulmonary valve.
  4. Oxygenated blood returns to the left atrium from the lungs.
  5. Blood moves to the left ventricle through the bicuspid valve.
  6. Blood is pumped into the aorta to be distributed throughout the body.

Cardiac Muscle and Heart Function

• Myocardium: The muscular layer of the heart, allowing for contraction and blood pumping.
• Pectinate Muscles: Found in the atria; help with contraction.
• Trabeculae Carne: Muscular structures within the ventricles that assist in creating a non-splashing filling effect for blood.

Heart Sounds and Function

• Heart sounds:
  • Lub: First sound from the closing of the AV valves during contraction.
  • Dub: Second sound from the closing of the semilunar valves during relaxation.
• Cardiac Cycle: Consists of systole (contraction) and diastole (relaxation).

Nerve Supply to the Heart

• The heart regulated by two nervous systems:
  • Sympathetic Nervous System: Increases heart rate and function during activity or stress.
  • Parasympathetic Nervous System: Decreases heart rate during rest.
• Normal heart rate is about 70 beats per minute and can fluctuate based on the body's activity.

Blood Supply to the Heart

• The heart has its own coronary arteries that supply blood:
  • Right Coronary Artery: Supplies blood to the right side of the heart.
  • Left Coronary Artery: Supplies blood to the left side of the heart.
• These arteries branch from the aorta shortly after the heart pumps blood out.

Summary

• The heart is a complex, muscular organ vital for circulation, protected by the pericardium and connected to major blood vessels. Understanding its structure and operation is essential for exploring cardiovascular health and disease.