Human Anatomy Week 3 - Thorax, Lungs, Diaphragm, Mediastinum, and the Heart

Thorax Overview

• Protects vital organs and provides structural integrity to thoracic cavity.
• Functions as a cage enabling negative pressure necessary for respiration.
• Serves as attachment points for major joints and muscles.

Thoracic Openings

• Superior Thoracic Aperture (Inlet): Formed by the first ribs and first thoracic vertebrae, entry point to the thoracic cavity.
• Inferior Thoracic Outlet: Defined by the 12th rib, 12th thoracic vertebrae, and subcostal border, marking the lower boundary of the thoracic cavity.

Mediastinum Components

• Central compartment of the thorax containing major blood vessels and connective tissues.
• Divided into superior mediastinum and inferior mediastinum:
  • Superior Mediastinum: Contains the arch of the aorta, returning blood vessels from upper limbs.
  • Inferior Mediastinum: Further split into anterior, middle, and posterior compartments, housing the heart, aorta, esophagus, and thymus gland.

Heart Anatomy

• Heart Chambers:
  • Right atrium: Contains pectinate muscles for blood expansion; interatrial septum separates right and left atria.
  • Fossa ovalis marks the closed foramen ovale of fetal circulation, created at first breath.
• Valves:
  • Atrioventricular Valves: Mitral valve (bicuspid, two leaflets) prevents backflow; mitral valve prolapse reduces cardiac output.
  • Semilunar Valves: Open during ventricular systole, allowing blood flow into pulmonary trunk and aorta.

Cardiac Structure and Function

• Fibrous Skeleton: Dense connective tissue providing support and anchorage for valves.
• Conduction System:
  • Initiated by the sinoatrial (SA) node, controlling heart rhythms and impulses drive contractions from the ventricles.

Heart Layers

• Pericardium:
  • Fibrous layer forms a protective sac; serous layer minimizes friction with two sub-layers: parietal and visceral (epicardium).
• Layers of the Heart:
  • Epicardium (outer), myocardium (muscular layer), and endocardium (inner lining).

Coronary Circulation

• Coronary Arteries: Right and left coronary arteries supply blood to heart tissues; blockage can lead to heart attacks.
• Major Cardiac Veins: Collect venous blood and drain into the right atrium via the cardiac sinus.

Pulmonary System Overview

• Lungs Structure:
  • Right lung has three lobes; left lung has two lobes with a cardiac notch.
  • Surfaces include costal, mediastinal, diaphragmatic, and pleural linings.

Respiratory System Mechanics

• Diaphragm: Primary muscle of respiration; innervated by the phrenic nerve (C3-C5), facilitating inhalation by descending to create negative pressure.
• Additional Respiratory Muscles: Include external intercostals, sternocleidomastoid, and scalenes aiding in rib elevation.

Bronchial Tree

• Trachea: Splits into right and left primary bronchi at T4/T5 level; right bronchus is wider and more vertical.
• Segmental Analysis: Terminal bronchioles lead to alveolar ducts where gas exchange occurs. Lined with cuboidal epithelium and smooth muscle.

Pulmonary Innervation and Lymphatics

• Innervation: Autonomic nervous system regulates bronchoconstriction (vagus nerve) and bronchodilation (sympathetic innervation).
• Lymphatic System: Abundant in the lungs, plays a crucial role in immune defense against inhaled antigens.

Referred Pain Patterns

• Visceral Pain: Involves neurodevelopmental patterns, where pain from the heart or lungs may refer to neck, shoulder, or general thoracic regions, depending on the nerve involved.

Major Blood Vessels

• Major Arteries: Include the coronary arteries, branches of the aorta, and internal thoracic artery, serving thoracic structures.
• Major Veins: Azygos system drains mediastinal blood into the superior vena cava; inferior vena cava collects blood from abdominal viscera.

Surface Anatomy of the Lungs

• Auscultation Points: Notable points for heart sounds include locations along specific intercostal spaces for each valve.
• Pain and Sensory Patterns: Chest pain related to thoracic organs often reflects neuroanatomic connections traced back to spinal levels.