Anantomy of Bronchopulmonary Segments

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Here is a detailed account of the anatomy of bronchopulmonary segments, drawn from Gray's Anatomy for Students, Fischer's Mastery of Surgery, and the Color Atlas of Human Anatomy.

Anatomy of Bronchopulmonary Segments

Definition

A bronchopulmonary segment is the area of lung supplied by a single segmental (tertiary) bronchus and its accompanying branch of the pulmonary artery. It is the smallest functionally independent region of the lung - the smallest unit that can be surgically isolated and removed without affecting adjacent regions.

Gray's Anatomy for Students, p. 208-210

Structural Features

Each segment has a distinct 3D shape:

Shape: Irregular cone / pyramidal wedge
Apex: Points toward the hilum (origin of the segmental bronchus)
Base: Projected peripherally onto the lung surface

Internal composition (the "bronchoarterial unit"):

Structure	Location within segment
Segmental bronchus	Centrally located (intrasegmental)
Pulmonary artery branch	Central, travels alongside bronchus
Pulmonary vein tributaries	Intersegmental - run along segment margins/boundaries
Bronchial arteries	Follow the bronchial tree

The pulmonary vein tributaries deliberately traveling between segments is what defines segment boundaries and makes surgical isolation possible.

Color Atlas of Human Anatomy Vol 2, p. 214

Bronchial Tree Hierarchy

Bronchial tree with lobar bronchi and segmental bronchi labeled

Fig. 3.48 (A) Bronchial tree. (B) Bronchopulmonary segments - Gray's Anatomy for Students

Hierarchy: Trachea → Main bronchi → Lobar bronchi → Segmental bronchi → Bronchioles → Terminal bronchioles → Respiratory bronchioles → Alveolar ducts → Alveoli

Within each segment, the segmental bronchi subdivide through multiple generations, ultimately reaching bronchioles. Bronchi have cartilaginous wall support; bronchioles do not.

Segments of the Right Lung (10 total)

Bronchopulmonary segments labeled, medial and lateral views of both lungs

Fig. 3.49 Bronchopulmonary segments of right lung (A) and left lung (B) - Gray's Anatomy for Students

Right Superior (Upper) Lobe - 3 segments

#	Segment	Bronchus (endoscopic clock position)
S I	Apical	B1 - orifice at 4 o'clock
S II	Posterior	B2 - orifice at 12 o'clock
S III	Anterior	B3 - orifice at 8 o'clock

Right Middle Lobe - 2 segments

#	Segment	Bronchus
S IV	Lateral	B4 - orifice at 3-6 o'clock
S V	Medial	B5 - orifice at 9-12 o'clock

Right Inferior (Lower) Lobe - 5 segments

#	Segment	Bronchus
S VI	Superior	B6 - at 5 o'clock, just past middle lobe bronchus
S VII	Medial basal	B7 - at 9 o'clock (usually most proximal basal)
S VIII	Anterior basal	B8 - at 1 o'clock
S IX	Lateral basal	B9 - at 3 o'clock
S X	Posterior basal	B10 - at 6 o'clock

Note: In more than half of patients, a subapical (subsuperior) segment is present in the lower lobe, with a posteriorly directed bronchus arising anywhere from the superior segment to the final lobar division.

Fischer's Mastery of Surgery, p. 2058

Segments of the Left Lung (8-10 depending on convention)

The left lung has 8 segments in American/international convention and 10 in British convention. The difference stems from fusion of segments:

Apical (S I) + Posterior (S II) → Apicoposterior segment (S I + II)
Medial basal (S VII) + Anterior basal (S VIII) → Anteromedial basal (S VII + VIII)

Left Superior (Upper) Lobe - 4 segments

Upper division (orifice at 8 o'clock):

#	Segment	Notes
S I+II	Apicoposterior	Fusion of apical + posterior (B1+3 in some systems)
S III	Anterior	B2

Lingular division (orifice at 2 o'clock) - equivalent to the right middle lobe:

#	Segment	Bronchus
S IV	Superior lingular	B4 - orifice at 10 o'clock
S V	Inferior lingular	B5 - orifice at 2 o'clock

Left Inferior (Lower) Lobe - 4 segments

#	Segment	Bronchus
S VI	Superior	B6 - at 6 o'clock, just past origin of lower lobe
S VII+VIII	Anteromedial basal	B8+7 - orifice at 12 o'clock
S IX	Lateral basal	B9 - at 9 o'clock
S X	Posterior basal	B10 - at 5 o'clock

Detailed Segmental Diagram (Anterior & Medial Views)

Color-coded bronchial divisions and bronchopulmonary segments, anterior and medial views of both lungs

Fig. 3.16 Bronchial divisions and bronchopulmonary segments - Color Atlas of Human Anatomy Vol 2, p. 215-216

In this diagram:

Blue = Superior lobe
Green = Middle lobe (right) / Lingula (left)
Red/orange = Inferior lobe
Continuous lines = lobar borders
Dashed lines = segmental borders

Quick Reference Summary Table

Lung	Lobe	Segments
Right	Superior	Apical (I), Posterior (II), Anterior (III)
Right	Middle	Lateral (IV), Medial (V)
Right	Inferior	Superior (VI), Medial basal (VII), Anterior basal (VIII), Lateral basal (IX), Posterior basal (X)
Left	Superior	Apicoposterior (I+II), Anterior (III), Superior lingular (IV), Inferior lingular (V)
Left	Inferior	Superior (VI), Anteromedial basal (VII+VIII), Lateral basal (IX), Posterior basal (X)

Clinical Relevance

Surgery (segmentectomy): Because segments are separated by intersegmental veins with minimal cross-communication, individual segments can be resected (e.g., for small lung cancers or bronchiectasis) - Fischer's Mastery of Surgery, p. 2058
Bronchoscopy: The clock-face positions of bronchial orifices help bronchoscopists navigate to specific segments for biopsy, BAL, or foreign body removal
Postural drainage: Each segment drains best with a specific body position, used in physiotherapy for bronchiectasis and COPD
Aspiration pneumonia: Due to gravity, aspirated material most often settles in the superior segment of the right lower lobe (S VI) and the posterior segment of the right upper lobe (S II) when supine
Radiology: Lobar/segmental collapse patterns on CXR or CT follow these anatomical boundaries

Anatomy of Pleura

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Here is a comprehensive account of pleural anatomy, drawn from Gray's Anatomy for Students, Color Atlas of Human Anatomy, and Fischer's Mastery of Surgery.

Anatomy of the Pleura

Definition and Basic Structure

The pleura is a serous membrane that lines the thoracic cavity and covers the lungs. Each pleural cavity is lined by a single layer of flat cells - mesothelium - and an associated layer of supporting connective tissue; together these form the pleura.

There are two major types:

Type	Location	Characteristics
Parietal pleura	Lines the walls of the pleural cavity	Thicker; somatic innervation; pain-sensitive
Visceral pleura	Covers the lung surface	Thinner; visceral innervation; not directly pain-sensitive

The pleural cavity is the potential space enclosed between the two layers. It normally contains only a thin film of serous fluid (a few mL), which reduces friction and allows the lung surface to glide freely over the thoracic wall during breathing.

Gray's Anatomy for Students, p. 201

Diagram: Pleural Cavities and Parts of Parietal Pleura

Labeled diagram showing parietal and visceral pleura, pleural cavity, mediastinum, and parts of parietal pleura including costal, mediastinal, diaphragmatic, and cervical portions, with suprapleural membrane and pulmonary ligament

Fig. 3.38 & 3.39 - Pleural cavities and parietal pleura. Gray's Anatomy for Students

Parietal Pleura - Parts

The parietal pleura is named according to the wall it covers. There are four named parts:

1. Costal Part

Lines the inner surface of the ribs and intercostal spaces
Separated from the thoracic wall by endothoracic fascia (a layer of connective tissue between the pleura and the internal thoracic wall)
Innervated by intercostal nerves → pain felt in the thoracic wall

2. Diaphragmatic Part

Covers the upper (thoracic) surface of the diaphragm
Innervated by the phrenic nerve (C3, C4, C5) → pain referred to the lateral neck and shoulder (C3-C5 dermatomes)

3. Mediastinal Part

Covers the lateral surface of the mediastinum
Also innervated by the phrenic nerve → same referred pain pattern (neck/shoulder)
In the region of TV-TVII, the mediastinal pleura reflects off as a tubular sleeve around the structures of the root of the lung (bronchi, vessels, nerves, lymphatics)
This sleeve-like covering becomes continuous with the visceral pleura at the hilum

4. Cervical Pleura (Pleural Cupola / Dome of Pleura)

The dome-shaped apex of the pleural cavity projecting into the root of the neck, above the first rib
Filled by the apex of the lung
Covered superiorly by the suprapleural membrane (Sibson's fascia) - a thickened layer of endothoracic fascia attached to the medial margin of rib I and the transverse process of C7
The scalene muscles attach to this membrane and keep it taut
The cervical pleura is at risk during procedures at the root of the neck (e.g., subclavian line, brachial plexus block, first rib resection)
Color Atlas of Human Anatomy Vol 2, p. 214; Gray's Anatomy for Students, p. 201

Visceral Pleura

Covers the lung almost entirely, including the surfaces within the interlobar fissures
Cannot be stripped from the lung surface - it is firmly adherent
Does not cover the hilum or the area between the lung and pulmonary ligament
Continuous with the parietal pleura at the hilum
Innervated by visceral afferent fibers accompanying bronchial vessels - pain is generally not elicited from visceral pleura directly

Pulmonary Ligament

Below the root of the lung, the mediastinal pleura forms a double-layered fold called the pulmonary ligament, which hangs downward from the hilum like a curtain. It anchors the lower lobe of the lung to the mediastinum and allows the lung to expand/move without excess displacement.

Pleural Recesses

The lungs do not completely fill the pleural cavities, so there are potential spaces called pleural recesses where the lung expands during deep inspiration.

1. Costodiaphragmatic Recess (most important clinically)

Diagram showing lung and pleural margins, costodiaphragmatic recess, and costomediastinal recess

Fig. 3.41 - Pleural recesses and lung/pleural margins. Gray's Anatomy for Students

Located between costal pleura and diaphragmatic pleura
Deepest recess; deepest during forced expiration (when lung margins rise up)
The region between the inferior lung margin and inferior pleural margin

2. Costomediastinal Recess

Located anteriorly where costal pleura meets mediastinal pleura
Largest on the left side, overlying the cardiac notch of the left lung
On the right it is narrow

Pleural Reflections - Surface Landmarks

Pleural reflections showing rib VIII at midclavicular line, rib X at midaxillary line, and vertebra TXII posteriorly

Fig. 3.40 - Inferior pleural reflections. Gray's Anatomy for Students

Superior extent

The pleural cavity projects 3-4 cm above the first costal cartilage into the neck
Does not extend above the neck of rib I

Anterior extent

Both pleural cavities approach each other posterior to the upper sternum
On the left, the cavity does not reach the midline as closely as on the right (because the pericardium and heart bulge to the left)

Inferior extent (key landmarks)

Vertical Line	Inferior Lung Margin	Inferior Pleural Margin
Midclavicular line	Rib VI	Rib VIII
Midaxillary line	Rib VIII	Rib X
Vertebral column (posterior)	Vertebra TX	Vertebra TXII

So the inferior pleural boundary runs: Rib VIII → Rib X → T12

The costodiaphragmatic recess lies between the lung margin and the pleural margin in this zone.

Topography: Lung and Pleural Borders in Context

Topography of lungs and mediastinum showing pleural cavity, endothoracic fascia, costodiaphragmatic recess, costomediastinal recess, visceral and parietal pleura

Fig. 84.1D - Pleura topography. Fischer's Mastery of Surgery, p. 2211

Neurovascular Supply and Lymphatics

Parietal Pleura

Region	Arterial Supply	Innervation
Costal part	Posterior intercostal arteries, internal thoracic artery, musculophrenic artery	Intercostal nerves (somatic)
Diaphragmatic part	Musculophrenic and pericardiophrenic arteries	Phrenic nerve (C3-C5)
Mediastinal part	Pericardiophrenic artery	Phrenic nerve (C3-C5)
Cervical (cupola)	Superior intercostal / subclavian branches	Intercostal nerves

Venous drainage: via veins of the thoracic wall

Visceral Pleura

Arterial supply: bronchial arteries (part of the lung's intrinsic supply)
Innervation: visceral afferents - not pain sensitive

Histology

The pleura is composed of:

Mesothelium - a single layer of flat (squamous) cells forming the surface
Connective tissue - providing structural support beneath the mesothelium

The visceral pleura forms an integral part of the lung parenchyma; the parietal pleura is a separate, slidable layer.

Clinical Correlates

Condition	Mechanism	Relevance to Pleural Anatomy
Pleural effusion	Excess fluid in pleural cavity	Accumulates in costodiaphragmatic recess first; aspirated in midaxillary line above rib IX (below rib VIII margin) to avoid neurovascular bundle
Pneumothorax	Air enters pleural cavity	Lung collapses due to tissue elasticity once negative pressure lost
Pleurisy	Inflammation of parietal pleura	Costal pleura involvement = sharp chest wall pain; diaphragmatic/mediastinal = shoulder tip pain (phrenic nerve)
Thoracocentesis	Needle aspiration of pleural fluid	Needle inserted above the upper border of a rib to avoid the intercostal neurovascular bundle
Cervical pleura injury	During neck surgery, subclavian line	Can cause pneumothorax - suprapleural membrane is the protective barrier
Mesothelioma	Malignant tumor of mesothelium	Usually from asbestos exposure; arises from the pleural mesothelium

Gray's Anatomy for Students, p. 202-203; Color Atlas of Human Anatomy Vol 2, p. 224

Anatomy of Blood Supply of Heart

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Anatomy of Blood Supply of the Heart

Overview

The heart has its own dedicated arterial supply through two coronary arteries - the right and left coronary arteries - which arise from the aortic sinuses of the ascending aorta, just above the aortic valve. These are the first branches of the aorta. Venous drainage returns primarily through the coronary sinus to the right atrium.

The coronary arteries lie in the subepicardial fat within the sulci of the heart; their branches often penetrate into the myocardium (myocardial bridges).

Arterial Supply - Overview Diagram

Coronary arteries of the heart - anterior view, showing both right and left coronary arteries, their branches, SA nodal branch, marginal branches, anterior interventricular branch (LAD), circumflex, diagonal, and posterior interventricular branches; also superior view (atria removed) showing coronary sulcus and coronary sinus

Fig. 3.79 Cardiac vasculature - anterior view (A) and superior view showing aortic sinuses and coronary sulcus (B). Gray's Anatomy for Students

Right Coronary Artery (RCA)

Origin: Right aortic sinus of the ascending aorta

Course: Passes anteriorly → descends vertically in the coronary sulcus (between right atrium and right ventricle) → reaches the inferior (acute) margin → turns posteriorly onto the diaphragmatic surface

Branches of the RCA

Branch	Course & Supply
Sinoatrial (SA) nodal branch	Arises early; passes posteriorly around the superior vena cava to supply the SA node (in ~60% of people)
Right marginal branch	Runs along the inferior (acute) margin toward the apex
AV nodal branch	Small branch to the atrioventricular node before giving off the terminal branch
Posterior interventricular branch (= posterior descending artery, PDA)	Terminal branch; runs in the posterior interventricular sulcus

Territory supplied by RCA

Right atrium and right ventricle
SA node and AV node (usually)
Interatrial septum
Posterior portion of left atrium
Posteroinferior 1/3 of the interventricular septum
Posterior part of the left ventricle
Gray's Anatomy for Students, p. 238

Left Coronary Artery (LCA)

Origin: Left aortic sinus of the ascending aorta

Course: The short stem (left main stem) passes between the pulmonary trunk and left auricle → enters the coronary sulcus → emerges from behind the pulmonary trunk → bifurcates into two terminal branches

Two Terminal Branches

1. Anterior Interventricular Branch (= Left Anterior Descending, LAD)

Descends obliquely in the anterior interventricular sulcus toward the apex
Wraps around the apex and usually anastomoses with the posterior interventricular branch of the RCA
May give off 1-2 diagonal branches descending across the anterior left ventricle
Supplies: both ventricles, anterior 2/3 of the interventricular septum, AV bundle and its branches

2. Circumflex Branch

Courses left in the coronary sulcus onto the base/diaphragmatic surface
Usually ends before reaching the posterior interventricular sulcus
Gives off the left marginal artery (following the obtuse margin)
In ~40% of people gives off the SA nodal branch

Territory supplied by LCA

Most of the left atrium and left ventricle
Most of the interventricular septum (anterior 2/3)
AV bundle and its branches

Both Coronary Arteries - Labeled Diagram

Complete anterior view of coronary arteries showing right coronary artery, left coronary artery, SA nodal branch, circumflex branch, left marginal branch, anterior interventricular branch (LAD), diagonal branch, right marginal branch, and posterior interventricular branch; with angiography images of RCA and LCA

Fig. 3.80 - Coronary arteries with angiographic correlation. Gray's Anatomy for Students, p. 240-241

Coronary Dominance

"Dominance" refers to which artery gives rise to the posterior interventricular (descending) branch and therefore supplies the posterior left ventricular wall.

Pattern	Frequency	Description
Right dominant	~70%	PDA from RCA; RCA supplies large portion of posterior LV wall; circumflex is relatively small
Left dominant	~15%	PDA from an enlarged circumflex branch; circumflex supplies most of posterior LV
Co-dominant / Balanced	~15%	Both RCA and circumflex contribute to posterior supply

Left dominant coronary artery pattern showing posterior interventricular branch arising from enlarged circumflex branch of LCA

Fig. 3.81 - Left dominant coronary artery. Gray's Anatomy for Students, p. 241

Color Atlas of Human Anatomy Vol 2, p. 58

Coronary Arteries on Sternocostal and Diaphragmatic Surfaces

Detailed illustration of coronary vessels on sternocostal surface (anterior) and diaphragmatic surface (posterior), with key: 1=RCA, 2=LCA, 3=coronary sulcus, 5=right marginal artery, 6=posterior interventricular sulcus, 7=posterior interventricular artery, 10=anterior interventricular artery, 11=great cardiac vein (anterior interventricular vein), 12=circumflex artery, 15=great cardiac vein, 16=middle cardiac vein, 17=small cardiac vein; also inset C showing origin of coronary arteries from aortic sinuses

Color Atlas of Human Anatomy Vol 2, p. 58-59

Venous Drainage

About 85% of cardiac venous blood drains via the greater coronary venous system (coronary sinus and its tributaries); the remainder drains via small veins directly into cardiac chambers (thebesian veins).

Cardiac Veins - Anterior View

Fig. 273.7A - Cardiac veins, anterior view. Fischer's Mastery of Surgery

Cardiac Veins - Posteroinferior View

Fig. 273.7B - Cardiac veins, posteroinferior view. Fischer's Mastery of Surgery

The Coronary Sinus

A wide venous channel running left to right in the posterior part of the coronary sulcus
Ostium diameter: 5-15 mm
Drains into the right atrium (between the tricuspid valve orifice and the inferior vena cava)
Its transition from the great cardiac vein is marked by the valve of Vieussens (present in 80-90% of hearts) and entrance of the vein/ligament of Marshall (embryonic remnant of left SVC)

Major Tributaries of the Coronary Sinus

Vein	Course	Corresponding Artery
Great cardiac vein	Starts at apex → ascends in anterior interventricular sulcus → turns left in coronary sulcus to coronary sinus	Accompanies LAD (anterior interventricular branch)
Middle cardiac vein	Starts at apex → posterior interventricular sulcus → right end of coronary sinus	Accompanies posterior interventricular artery (PDA)
Small cardiac vein	Begins as marginal vein → right coronary sulcus → right end of coronary sinus	Accompanies right marginal branch
Oblique vein of left atrium	Runs on posterior surface of left atrium	Remnant of embryonic left SVC
Left posterior ventricular vein	Left ventricular posterior surface	Left ventricular branches
Left marginal vein	Along obtuse margin	Left marginal branch

Direct Drainage (Bypassing Coronary Sinus)

Anterior cardiac veins: Drain the anterior right ventricular wall, open directly into the right atrium
Thebesian (smallest cardiac) veins: Tiny vessels that open directly into all four cardiac chambers, especially the right atrium and right ventricle
Fischer's Mastery of Surgery, p. 7365; Fuster and Hurst's The Heart, p. 1070

Lymphatic Drainage

The heart has three overlapping lymphatic networks:

Deep endocardial network
Middle myocardial network
Superficial epicardial network

Larger collecting vessels travel in the epicardium, accompanying the aorta and pulmonary trunk, and drain to the tracheobronchial and anterior mediastinal lymph nodes.

Color Atlas of Human Anatomy Vol 2, p. 59

Clinical Terminology (Cardiology vs. Anatomy)

Anatomical Name	Clinical Name
Short left coronary artery	Left main stem
Anterior interventricular branch	LAD (Left Anterior Descending)
Posterior interventricular branch	PDA (Posterior Descending Artery)
Circumflex branch	LCx

Clinical Correlates

Condition	Vessel involved	Anatomical basis
Anterior STEMI	LAD occlusion	Supplies anterior LV wall and anterior 2/3 of IVS
Inferior STEMI	RCA occlusion (right dominant)	Supplies inferior/posterior LV wall via PDA
Lateral STEMI	Circumflex occlusion	Supplies lateral and posterior LV wall
Complete heart block after inferior MI	RCA - AV nodal branch	RCA usually supplies AV node
Angina	Coronary stenosis	Coronaries are functional end arteries; collaterals insufficient for acute occlusion
Coronary artery bypass graft (CABG)	Bypasses stenosed coronaries	Great saphenous vein, internal thoracic artery, or radial artery used as conduits
Cardiac referred pain	MI visceral afferents	Follow sympathetic fibers entering spinal cord at T1-T4; pain referred to chest wall, left arm, jaw

Gray's Anatomy for Students, p. 242-244; Color Atlas of Human Anatomy Vol 2, p. 58

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