Anatomy: The Thorax

How many lobes are in each lung?

Right lung: 3 lobes (superior, middle, inferior)

Left lung: 2 lobes (superior, inferior)

- Mnemonic: RALS — Right lung Always Larger (3 lobes)

- lobes = secondary bronchi

Where do aspirated foreign bodies most commonly lodge after passing the larynx? Why?

Right main stem bronchus

Why? Wider, Shorter, More vertical

Patient with HR in the 40s and no P waves on EKG—what structure is blocked?

Sinoatrial (SA) node

- Known as the bodies pacemaker can contract 60-100 bpm

term describes the percentage of blood pumped from the ventricles with each contraction (beat) ?

Ejection fraction (EF)

Stroke volume (SV)

volume per beat (mL)

Cardiac output (CO)

volume per minute (L/min)

Heart rate (HR

beats per minute

Which primary lymphoid organ is affected by chemotherapy that causes low blood cell counts?

Bone marrow → site of hematopoiesis

Which part of the mediastinum is bordered posteriorly by the T5-T12 vertebrae?

Posterior mediastinum

- Contents: Esophagus, thoracic aorta, thoracic duct, sympathetic chains

Which thoracic muscle pulls the scapula forward around the thorax?

Serratus anterior

Serratus posterior (superior)

Serratus posterior (inferior)

elevates ribs → assists inspiration

depresses ribs → assists expiration

External intercostal

Internal intercostal

elevates ribs → inspiration

depresses ribs → forced expiration

Muscle attached to the xiphoid process, lower 6 ribs, and lumbar vertebrae. How does it aid in inspiration?

Muscle: Diaphragm

Function: Contracts → pulls central tendon inferiorly → thoracic cavity expands → negative pressure draws air into lungs

Which thoracic muscle inserts on ribs 2-5 and aids in inspiration?

Serratus posterior superior

25-cm tubular structure

Layers: areolar tissue (outer), muscular layer, submucosa with mucous glands, mucosa of stratified epithelium

Esophagus

- Upper 1/3 → striated (voluntary) muscle

Middle 1/3 → mixed striated + smooth

Lower 1/3 → smooth (involuntary) muscle

Superior mediastinum

Above the heart, behind the sternum

Contains: upper esophagus, trachea, great vessels, thymus (in kids)

Anterior mediastinum

In front of the heart

Contains: thymus (mostly kids), fat, lymph nodes

Middle mediastinum

Heart & pericardium

Major vessels coming in/out of heart

Posterior mediastinum

Behind the heart

Contains: lower esophagus, descending aorta, thoracic duct, sympathetic chain

Airway hierarchy

Trachea

Primary (main) bronchi

Secondary (lobar) bronchi

Tertiary (segmental) bronchi

Conducting bronchioles

Terminal bronchioles → end of conducting zone

Respiratory bronchioles → beginning of respiratory zone

Alveolar ducts

Alveolar sacs

- Trunk → branches → twigs → leaves

What are the layers of the pericardium, and which one reflects around the great vessels?

Fibrous pericardium - tough outer layer; anchors the heart; does not reflect around vessels.

Serous pericardium - thin inner layer; does reflect around the great vessels.

Parietal layer - lines the inner surface of the fibrous layer.

Visceral layer (epicardium) - covers the heart surface directly.

Which heart chamber forms the most anterior surface of the heart?

Right ventricle - immediately behind the sternum.

- left atrium is the most posterior chamber.

- left ventricle composes part of the inferior surface.

- right atrium forms the right border.