Download Anatomy 21- Lower Airway provide a warm, protected, and of course

Anatomy 21- Lower Airway
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provide a warm, protected, and of course moist environment, as gases must be in aqueous solution in order to
diffuse across the respiratory membrane
Pleurae
Lungs located in pulmonary cavities o either side of the heart
Pleura is in the pulmonary cavities of each lung invested in serous membrane
In the developing embryo, the lungs (like other ventral cavity organs) bud into the coelomic cavity
As the lungs bud into the coelomic cavity they take with them the lining of the cavity-- pleura
The pleura, like other serous membranes of the ventral cavity, consists of two parts
o Parietal pleura: Lines the inner surface of the thoracic wall
o Visceral pleura: Lines the outer surface of the lung
In between the two pleurae is the pleural cavity (clinicians may prefer pleural space)
Lungs are outside the pleural cavity
Parietal Pleura
• The visceral pleura is very tightly adherent to the lungs and is generally not dissectable
• The parietal pleura is thicker, and in both surgeries and dissections may be separated from the thoracic wall
(along a cleavage plane created by the endothoracic fascia)
– It is customary to divide the parietal pleura according to the region in which it lies, or the surface that it
covers
• Costal: Covers internal surfaces of thoracic wall
• Mediastinal : Covers lateral aspects of mediastinum
• Diaphragmatic: Covers diaphragm
• Cervical: Covers apices of the lungs
Lines of Pleural Reflection
• As the parietal pleura passes from one surface to another it abruptly changes directions (reflects)
• Three lines of pleural reflection outline the extent of the pleural cavities
– Sternal, costal, and vertebral
• In pericardiocentesis, as an example, it is important to know the lines of reflection in order to find the
pericardium (and to avoid pneumothorax)
Pleural recesses
• Recesses are gutter-like areas of pleural cavity created by some of the pleural reflections
• These recesses are not entirely occupied by the lungs
– The lungs dip into the recesses during heavy inspiration but do not fill them
• Therefore, in the recesses, parietal pleura is in contact with parietal pleura
• There are two pleural recesses
– Costodiaphragmatic recess: This recess is created where diaphragmatic pleura contacts costal pleura
• This is the deeper recess
– Costomediastinal recess: This recess is created where mediastinal pleura contacts costal pleura
Anatomy 21- Lower Airway
Lung/Pleural Cavity Levels
• Anterior/midclavicular line
– Lungs—rib 6
– Pleural cavity—rib 8
• Lateral/midaxillary line
– Lungs—rib 8
– Pleural cavity—rib 10
• Posterior/vertebral column
– Lungs—T10
– Pleural cavity—T12
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Usually, the posterior-inferior edge of the pleura crosses the 12th rib just lateral to the erector spinae
If the 12th rib is short—i.e., it does not extend beyond the erector spinae—the 11th rib may be mistaken for the
12th
Incision at this level will damage the pleura -- Safer to count ribs from 2nd rib
Pleural Effusion
• Fluid (blood, pus) escaping into the pleural cavity, and accumulating in the pleural recesses (pleural effusion)
may hinder inspiration
– A pressurized pleural cavity pushes against the lungs, making it difficult for them to inflate
• Conversely, the recesses provide an area from which the fluid may be aspired
– Thoracentesis
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Gross Lung
During life, the lungs are soft, spongy, and very elastic
In childhood the lungs are pink, In adulthood they become darker and mottled
The lungs are conical structures made up of various components
– Bronchi and bronchioles
– Alveolar sacs, ducts, and alveoli
– Blood and lymphatic vessels
– Connective tissue
Each lung has an apex, and three surfaces
– The apex projects above the 1st rib into the root of the neck (Even more so in children)
– The base represents the diaphragmatic surface
– In addition there are costal and mediastinal surfaces
Root of the Lungs
• The lungs are attached to the mediastinum by the roots
• A hilum is an area where vessels and nerves enter/exit an organ
– In the lung, the hilum is a wedge-shaped area on the mediastinal surface of each lung
Anatomy 21- Lower Airway
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The root consists of three main structures
– Bronchi
– Pulmonary arteries
– Pulmonary veins
The root also contains lymphatic vessels, nerves, and bronchial blood vessels
If the root is sectioned medially to the branching of the primary bronchus, there is a general arrangement of
root structures
– Arteries are superior (thickwalled)
– Veins are inferior (anterior)
– Bronchi are posterior (very thick—cartilage)
Lung Differences
• Both lungs are very similar in structure, however there are some key differences between them
• Most of these differences are the result of impressions made in the lung by adjacent structures
– Impressions are only observed in the preserved cadaver
Right Lung
• The right lung consists of three lobes
– Inferior, middle, and superior
• The right lung has two fissures
– Oblique and horizontal
• The identification of the completeness of fissures is important prior to lobectomy
– Individuals with incomplete fissures are susceptible to postoperative air leaks
Impressions
• Small cardiac impression
• Groove for esophagus
• Grooves for SVC and IVC
• Groove for arch of azygos vein
• Groove for 1st rib
Anatomy 21- Lower Airway
Left Lung
• The left lung consists of two lobes
– Inferior and superior-- The lung has one less lobe owing to the position of the heart
• The left lobe has one fissure
– Oblique
Impressions
• Large cardiac impression
• Groove for arch of aorta and descending aorta
• Groove for subclavian artery
• Groove for 1st rib
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Oblique fissure parallels the medial border of scapula with hands above head
4th rib: parallels the horizontal fissure on the right side
Tracheobronchial Tree
• Beginning with the trachea, the airway branches in a constant fashion leading to smaller and smaller structures
– Tracheobronchial tree
Trachea
• The trachea is a strong, yet mobile cylindrical tube connecting the larynx to the bronchi
– May alter in length during inspiration
• It begins at the inferior end of the larynx (~C6)
• It ends at the level of the sternal angle (~T4-T5 IV disc)-- bifurcates
Bronchi
• The trachea bifurcates at the level of the sternal angle into the main (primary) bronchi
– Each lung is supplied by a main bronchus which enters the lung at the hilum
• Like the trachea, primary bronchi have C-shaped cartilage rings
• The right main bronchus is ~2.5 cm long (continuation of a trachea)
– It is wider, shorter, and runs more vertically than left main bronchus
• It is a more direct continuation of the trachea and thus represents a more likely destination of
foreign objects
• The left main bronchus is ~5 cm long
Anatomy 21- Lower Airway
Lobar and Segmental Bronchi
• Each main bronchus divides into lobar (secondary) bronchi
– The lobar bronchi serve the lobes of the lung
• There are two lobar bronchi on the left, three on the right
– Each lobar bronchus divides into several segmental (tertiary) bronchi
• 10 in the right lung
• 8-10 in the left lung
– The segmental bronchi serve the bronchopulmonary segments of the lung
• The bronchopulmonary segments are pyramidal-shaped segments of lobe separated by connective tissue
– Apices face the lung root, and bases are at the pleural surface
• The segments are separated by connective tissue septa
– Segments are surgically resectable
Pulmonary Lobules
• ~16 generations of branching of the airways results in microscopic terminal bronchioles
• When the airways lose their cartilage—at ~11th generation and ~1 mm diameter—they become known as
bronchioles
– Terminal bronchioles are the final conducting structures
• The next structures, respiratory bronchioles, contain alveoli
• Bronchus has cartilage, bronchiole does not
• The primary pulmonary lobule is the portion of lung distal to the respiratory bronchiole
• The secondary pulmonary lobule is the smallest subsection of the peripheral lung bounded by connective tissue
septa (fibrous CT)
– It consists of ~six terminal bronchioles
– It is visible on the gross lung, as a slightly pentagonal, or hexagonal shape ~1 cm in diameter
• The secondary pulmonary lobule is a fundamental unit of lung structure as it reproduces the lung in miniature
– Airways, pulmonary vessels, and connective tissue structures are all represented at the level of the
secondary lobule
• Several of these components are normally visible on thin-section computed tomographies
– Recognition of lung abnormalities by examination of the secondary lobule is fundamental to the
interpretation of thin-section CT scans
Vasculature, Innervation, and Lymphatics
Blood Supply
• Blood supply to the lungs is essentially twofold
– Pulmonary arteries and veins
– Bronchial arteries and veins
• Each lung is supplied by a pulmonary artery and drained by two pulmonary veins
– These vessels supply blood to the lungs for gas exchange
• The right and left pulmonary arteries arise from the pulmonary trunk at the level of the sternal angle
• The divisions of the pulmonary arteries basically follow the branching pattern of the bronchial tree
• Each pulmonary artery divides into lobar arteries
– The lobar arteries are paired with the lobar bronchi
• Lobar arteries divide into segmental arteries
– The segmental arteries are paired with the segmental bronchi
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Two pulmonary veins—superior and inferior—on each lung carry oxygen-rich blood to the heart
– The middle lobe vein is a tributary of the right superior pulmonary vein
The pulmonary veins run independently of the arteries and bronchi
– They course in-between bronchopulmonary segments and secondary lobules, along the connective
tissue septa
Anatomy 21- Lower Airway
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The bronchial arteries and veins constitute the “nutritive” vascular system of the lungs
– The “working” tissues of the lungs require highly oxygenated blood, which cannot be provided by the
pulmonary arteries
There are generally two left bronchial arteries—superior and inferior—which arise from the thoracic aorta
directly
There is normally one right bronchial artery, which arises from the aorta indirectly (via 3rd intercostal artery)
The bronchial arteries pass along the posterior aspects of the main bronchi
The most distal branches of the bronchial arteries anastomose with branches of the pulmonary arteries in the
walls of the bronchioles and the visceral pleura
– Parietal pleura is supplied vasculature of the thoracic wall
The bronchial veins only drain part of the blood supplied to the lungs by the bronchial arteries
– Proximal part of the roots of the lungs
The remainder of the blood is drained by the pulmonary veins (most of the venous drainage—which is weird
since they are carrying O2 rich blood
Go to azygous or hemiazygous veins—only drain proximal part of root
Innervation
• The lungs and associated structures are supplied by visceral efferents (sympathetic and parasympathetic) and
visceral afferents
• These fibers are distributed through the anterior and posterior pulmonary plexuses
– The plexuses ultimately originate from the sympathetic trunks and the vagus nerves
• The parasympathetic fibers are bronchoconstrictors, vasodilators, and secretomotor to glands of the bronchial
tree
• The sympathetic fibers are bronchodilators, vasoconstrictors, and inhibitory to type II alveolar cells
• Sensory fibers accompany parasympathetic fibers
– They are involved in reflex activity governing function of the respiratory system
– They relay pain and irritant information
Lymphatics
• The lymphatic vessels draining the lungs originate from superficial subpleural and deep lymphatic plexuses
• All lymph from the lung leaves along the root of the lung and drains to the tracheobronchial lymph nodes
• From there lymph enters paratracheal nodes and ultimately the bronchomediastinal trunks