Respiratory system –Anatomy questions & Answers

SAQ

1. Describe the nasal cavity under the following headings:

(a) Nasal septum
(b) Lateral wall
(c) Blood supply
(d) Nerve supply

(a) Nasal septum

It is a median osseocartilaginous partition between the two halves of the nasal cavity. On
each side, it is covered by mucous membrane and forms the medial wall of both nasal
cavities.

Formation: Bony part is formed by:

1.Perpendicular plate of ethmoid bone-anterior superior part.
2.Vomer - Posterior –inferior part.
Cartilaginous part is formed by-
1. Septal cartilage
2. Septal process of lower nasal cartilage
3. Vomero-nasal cartilage.
(b) Lateral wall
Components of lateral wall:
1.Bony part is formed by- Nasal bone, frontal process of maxilla, lacrimal, labyrinth of
ethmoid with superior and middle conchae,inferior nasal conchae,perpendicular plate
of palatine and medial pterygoid plate.
2.Cartilaginous part is formed by - Superior nasal cartilage,inferior nasal cartilage and 3
or 4 small cartilage of the ala.
3. Cuticular lower part is formed by- fibro fatty tissue covered by skin

Conchae and meatuses:

• The nasal conchae are curved bony projection directed downwards and medially.
1. The inferior concha is an independent bone.
2. The middle concha and superior concha are projection from medial surface of
ethmoidal labyrinth.
• The meatuses of nose are passages beneath the conchae.
1. The inferior meatus lies beneath the inferior concha, is the largest meatus. The naso
nacrimal duct opens into it and the opening is gurded by Hasner’s valve.
2. The middle meatus lies beneath the middle concha. It has a rounded swelling called the
bulla ethmoidalis that is formed by the middle ethmoidal air sinuses, which open on its
upper border. A curved opening, hiatus semilunaris, lies below the bulla. The anterior
end of the hiatus leads into a funnel-shaped channel called the infundibulum into which
frontal sinus opens. The maxillary sinus opens into the middle meatus through the
hiatus semilunaris.
 3. The superior meatus lies below the superior concha. It is small and receives the
openings of posterior ethmoidal air sinuses.

c) Blood supply of the nasal cavity - Arterial supply:

 Sphenopalatine branch of maxillary artery.
 Greater palatine branch of maxillary artery
 Septal branch of facial artery.
 Anterior ethmoidal artery.
Venous drainage:
Venous plexus drains into facial vein,pterygoid plexus and pharyngeal plexus of
veins.

d) Nerve supply of the nasal cavity

Special sensation-smell-Olfactory nerves from the olfactory mucous membrane ascend
through the cribriform plate of the ethmoid bone.

General sensation - Branches of the ophthalmic division of trigeminal nerve-anterior

ethmoidal nerve. Branches of maxillary division of trigeminal nerve-nasal branches.

Nasal cavity-Diagrams
2. Describe the gross anatomy of the following paranasal air sinuses:
(a) Frontal sinus
(b) Maxillary sinus
(c) Ethmoidal sinus
(d) Sphenoidal sinus

Paranasal air sinuses -Introduction

The paranasal sinuses are cavities filled with air, found in the interior of the maxilla, frontal,
sphenoid, and ethmoid bones. They communicate with the nasal cavity through small apertures.
They are lined by pseudostratified ciliated columnar epithelium.

a) Frontal sinus
The two frontal sinuses are present within the frontal bone, posterior to the glabella between the
inner and outer tables of the skull. They are separated from each other by a bony septum.
Frontal sinus is roughly triangular, extending upward above the medial end of the eyebrow and
backward into the medial part of the roof of the orbit. The frontal sinus opens into the infundibulum of
hiatus semilunaris of middle meatus of nose.

Arterial supply - Supra orbital artery.

Venous drainage - Supra orbital vein.
Nerve supply- Supra orbital nerve
Lymphatic drainage- Submandibular nodes.

b) Maxillary sinus
The maxillary sinus is pyramidal in shape and located within the body of the maxilla behind the skin
of the cheek.
The roof is formed by the floor of the orbit and the floor is related to the roots of the premolar and
molar teeth.
The maxillary sinus opens into the middle meatus of the nose through the hiatus semilunaris

Arterial supply – Facial and infraorbital arteries.

Venous drainage - Facial vein and pterygoid plexus of veins.
Nerve supply- Infra orbital and superior alveolar nerves.
Lymphatic drainage- Submandibular nodes.

c) Ethmoidal air sinus

The ethmoidal sinuses are anterior, middle and posterior and they are contained within the ethmoid
bone between the nose and the orbit.They are separated from the latter by a thin plate of bone so that
infection can readily spread from the sinuses into the orbit.
The anterior sinuses (2-8 cells) open into the infundibulum of middle meatus.
The middle sinuses (2-8 cells) open into the middle meatus, on or above the bulla ethmoidalis.
The posterior sinuses (2-6 cells) open into the superior meatus.

Arterial supply – Anterior and posterior ethmoidal arteries.

Venous drainage - Pterygoid plexus of veins.
Nerve supply- Anterior and posterior ethmoidal nerves.
Lymphatic drainage- Submandibular and retropharyngeal nodes.

d) Sphenoidal air sinus

The two sphenoidal sinuses lie within the body of the sphenoid bone.Each sinus opens into the
sphenoethmoidal recess above the superior concha.

Arterial supply – Posterior ethmoidal and internal carotid arteries.

Venous drainage – Cavernous sinus.
Nerve supply- Posterior ethmoidal nerve.
Lymphatic drainage- Retropharyngeal nodes.

Paranasal air sinuses-Diagram

3. Describe the nasopharynx.

Nasopharynx -Introduction
Nasopharynx is situated behind the nose and above the soft palate.It is respiratory in function and
conducts only air. The walls are rigid and non-collapsible to keep air passages patent.

Communication:
Anteriorly it communicates with the nasal cavity through posterior nasal apertures. Inferiorly it
communicates with oropharynx at the pharyngeal isthmus.

Lateral wall of nasopharynx:

The lateral wall presents:
 Pharyngeal opening of the auditory tube at the level of inferior concha.
 Tubal elevation which bounds the tubal opening formed by tubal tonsil.
 Salpingopharyngeal fold, produced by salpingopharyngeus muscle is a vertical fold running
down from the tubal elevation.
 Levator palate muscle raises a fold below the tubal opening.
 Pharngeal recess extends sideways between auditory tube and pre-vertebral muscles.

Roof and posterior wall:

Forms a continuous slope, presents pharyngeal tonsil, collection of lymphoid tissue,well developed in
children, while pathological enlargement is called adenoids.

Blood supply of nasopharynx:

Ascending pharyngeal, tonsillar branches of facial arteries, branches of maxillary and lingual arteries.

Nerve supply of nasopharynx:

Branches of maxillary division of trigeminal nerve.

Lymphatic drainage of nasopharynx:

Directly into the deep cervical lymph nodes or indirectly via the retropharyngeal node.

Nasopharynx -Diagram
4. Describe the larynx under the following headings:
(a) Cartilages
(b) Muscles
(c) Mucosal folds
(d) Blood supply
(e) Nerve supply

a) Cartilages
The framework of the larynx is formed of cartilages that are held together by ligaments and
membranes, moved by muscles, and lined by mucous membrane.
Larynx has nine cartilages, three unpaired and three paired.
-Unpaired cartilages: Epiglottis, thyroid cartilages, cricoid cartilages
-Paired cartilages: Arytenoid cartilages, corniculate cartilages, cuneiform cartilages

 Thyroid cartilage: Largest cartilage consists of two laminae of hyaline cartilage that meet in the
midline in the prominent V angle (the so-called Adam's apple). The posterior border extends
upward into a superior cornu and downward into an inferior cornu. On the outer surface of
each lamina is an oblique line for the attachment of muscles.
 Cricoid cartilage: Formed of hyaline cartilage, having a broad plate behind and a shallow arch
in front.The cricoid cartilage lies below the thyroid cartilage and on each side of the lateral
surface is a facet for articulation with the inferior cornu of the thyroid cartilage. Posteriorly, the
lamina has on its upper border on each side a facet for articulation with the arytenoid cartilage.
All these joints are synovial.
 Arytenoid cartilages: There are two arytenoid cartilages, which are small and pyramid
shaped.They articulate with the upper border of the lamina of the cricoid cartilage. Each
cartilage has an apex above that articulates with the small corniculate cartilage, a base below
that articulates with the lamina of the cricoid cartilage, and a vocal process that projects
forward and gives attachment to the vocal ligament. A muscular process that projects laterally
gives attachment to the posterior and lateral cricoarytenoid muscles.
 Corniculate cartilages: Two small conical-shaped cartilages articulate with the arytenoid
cartilage and give attachment to the aryepiglottic folds.
 Cuneiform cartilages: These two small rod-shaped cartilages are found in the aryepiglottic
folds.
 Epiglottis: This leaf-shaped elastic cartilage lies behind the root of the tongue.It is attached to
the back of the thyroid cartilage. The sides of the epiglottis are attached to the arytenoid
cartilages by the aryepiglottic folds of mucous membrane.

b) Muscles

The muscles of the larynx are divided into two groups: extrinsic and intrinsic.
1. Extrinsic muscles:
These muscles move the larynx up and down during swallowing. These muscles are attached to the
hyoid bone and indirectly to thyroid cartilage. The movements of the hyoid bone are accompanied by
movements of the larynx.
 Elevation of larynx: Produced by digastric, stylohyoid, mylohyoid, geniohyoid,
stylopharyngeus, salpingopharyngeus and palatopharyngeus muscles.
 Depression of larynx: Produced by sternothyroid, sternohyoid and omohyoid muscles.
2. Intrinsic muscles:

Muscle Origin Insertion Nerve supply

Cricothyroid Anterolateral aspect of arch of Inferior horn and inferior margin External
cricoid cartilage. of thyroid cartilage. laryngeal nerve
from vagus.
Posterior From the posterior surface of Posterior surface of the muscular Recurrent
Cricoarytenoid the lamina of thyroid process of arytenoid cartilage laryngeal nerve
cartilage. from vagus.
Lateral Superior surface of the arch of Anterior surface of muscular Recurrent
Cricoarytenoid cricoid cartilage. process of arytenoid cartilage. laryngeal nerve
from vagus.
Transverse Lateral border of posterior Lateral border of posterior Recurrent
arytenoid surface of arytenoid cartilage. surface of opposite arytenoid laryngeal nerve
cartilage. from vagus.
Oblique Posterior surface of muscular Posterior surface of apex of Recurrent
arytenoid process of arytenoid cartilage. adjacent arytenoids cartilage; laryngeal nerve
extends into aryepiglottic fold. from vagus.
Thyroarytenoid Thyroid angle Anterolateral surface of Recurrent
arytenoid cartilage; some fibers laryngeal nerve
continue in aryepiglottic fold. from vagus.
Vocalis Lateral surface of vocal Vocal ligament and thyroid Recurrent
process of arytenoids angle. laryngeal nerve
cartilage. from vagus.

Action of intrinsic muscles:

 Narrowing the inlet: Oblique arytenoid.

 Widening the inlet: Thyroepiglottis.

 Tensing the vocal cords: Cricothyroid.

 Relaxing the vocal cords: Thyroarytenoid (vocalis).
 Adducting the vocal cords: Lateral cricoarytenoid.
 Abducting the vocal cords: Posterior cricoarytenoid .
 Approximates the arytenoid cartilages: transverse arytenoid.

c) Mucosal folds

Two pairs of mucosal folds, the vestibular and vocal folds, which project medially from the lateral
walls of the laryngeal cavity.

1.Vestibular fold:
It is a fixed fold on each side of the larynx,formed by mucous membrane covering the vestibular
ligament and is vascular,pink in color. Lined by respiratory epithelium (pseudostratified ciliated
columnar epithelium). The gap between the vestibular folds is called the rima vestibuli.
2. Vocal fold (vocal cord):
It is a mobile fold on each side of the larynx and is concerned with voice production. It is formed by
mucous membrane covering the vocal ligament and is avascular and white in color. The vocal fold
moves with respiration and its white color is easily seen when viewed with a laryngoscope. Lined by
stratified squamous nonkeratinised epithelium.

The gap between the vocal folds is called the rima glottidis or glottis. The glottis is bounded in front
by the vocal folds and behind by the medial surface of the arytenoid cartilages. The glottis is the
narrowest part of the larynx.

Vocal folds divide the larynx into three regions- vestibule, ventricle and infraglottic cavity.
A. Vestibule - upper chamber between the laryngeal inlet and the vestibular folds.
B. Ventricle - middle part is very thin,lies between the vestibular folds above and the vocal folds
below.
C. Infraglottic cavity - inferior chamber, situated between the vocal folds above and the lower
border of the cricoid cartilage below.

c) Blood supply
Above the vocal fold: Superior laryngeal artery and vein.
Below the vocal fold : Inferior laryngeal artery and vein.
d) Nerve supply
Motor: All the intrinsic muscles are supplied by recurrent laryngeal nerve except
cricothyroid muscle by external branch of superior laryngeal nerve.
Sensory: Above the vocal fold is internal laryngeal nerve.
Below the vocal fold is recurrent laryngeal nerve.

Larynx cartilages-Diagram
Muscles of larynx –Diagram
5. Describe the trachea under the following headings:
(a) Extent,parts
(b) Relations
(c) Blood supply
(d) Nerve supply
(e) Histology with labeled diagram

a) Extent,parts

Extent- It begins as a continuation of the larynx at the lower border of the cricoid cartilage at the
level of the sixth cervical vertebra. It descends in the midline of the neck. In the thorax the trachea
ends by dividing into right and left principal (main) bronchi at the level of the sternal angle (opposite
the disc between the fourth and fifth thoracic vertebrae).

Parts- Cervical part and thoracic part.

b) Relations

1. Cervical part:
Anterior -Isthmus of thyroid, pretracheal fascia, sternohyoid, sternothyroid, investing
layer of deep cervical fascia.
Posterior - Oesophagus, recurrent laryngeal nerve in the tracheo-esophageal groove.
Lateral - Thyroid lobe, common carotid artery.

2. Thoracic part:
Anterior - Manubrium sterni,remains of thymus, left brachiocephalic vein,aortic arch,
and brachiocephalic trunk.
Posterior - Oesophagus, vertebral column.

Right side - Right lung, pleura and vagus.

Left side - Arch of aorta,left common carotid artery, left subclavian artery, left recurrent
laryngeal nerve.
c) Blood supply
Arterial supply-Branches derived from
Inferior thyroid artery, subclavian artery,highest intercostal artery,internal thoracic
Artery and bronchial arteries at the tracheal bifurcation.

Venous drainage -
Small tracheal veins join the laryngeal vein or empty directly into the left inferior
thyroid vein.

d) Nerve supply

Recurrent laryngeal nerve, (which also carries sensory fibers from the mucous membrane).
Sympathetic nerve fibers are derived mainly from the middle cervical ganglion and have connections
with the recurrent laryngeal nerves.

e) Histology

Trachea is made up of 3 layers-mucosa, submucosa and adventitia.

1.Mucosa : Lined by respiratory epithelium consist of ciliated cells, goblet cells, small granule cells,
enteroendocrine cells and short basal cells.Lamina propria is made up of thin layer of connective tissue
with increase in number of elastic fibres.

2. Submucosa : Contains many mucous and serous glands. Submucosa ends with the perichondrium
of the tracheal cartilages.

3. Adventitia: Outer layer which contains C shaped hyaline cartilage. The ends of the cartilage are
bridged by smooth muscle named trachealis.

Trachea-Relations-Diagrams

Trachea-relations –Diagram

Trachea-histology -Diagram

Trachea-Histology -Diagram
6. Describe briefly the pleura under the following headings:
(a) Layers
(b) Recesses
(c) Nerve supply

Pleura - Introduction
It is a serous membrane lined by mesothelium. There are two pleural sacs, one on either side of the
mediastinum. Each pleural sac is invaginated from its medial side by the lungs, forming the outer
layer (parietal layer) and inner layer(visceral or pulmonary pleura).

a) Layers
2 layers: Outer parietal and inner visceral layers.
 Parietal pleura-lines the inner surface of the chest wall, covers the diaphragm, and is
reflected over the structures occupying the middle of the thorax.
 Pulmonary pleura (Visceral layer) – covers the surface of the lung and dips into the
fissures between its lobes.
 The two layers are continuous with one another enclosing the pleural cavity filled by thin
film of pleural fluid.

Parietal pleura: Thicker and subdivided according to their position.

 Costal pleura - lines the inner surfaces of the ribs and intercostal muscles.
 Diaphragmatic pleura- covers the convex surface of the diaphragm.
 Cervical pleura- extends into the neck and covers the apex of the lung.
 Mediastinal pleura- lines the mediastinal surface of the lung.
 Pulmonary ligament (Ligamentum pulmonale)- is a fold of parietal pleura extends between
the lower part of the mediastinal surface of the lung that ends in a free falciform border.

b) Recesses:
There are two recesses (spaces) of parietal pleura,which acts as reserve spaces for the lung to
expand during deep inspiration.
1. Costodiaphramatic recess (phrenicocostal sinus):
 Lies inferiorly between the costal and diaphramatic pleura.
 Extends from the 8th to 10th ribs along the midaxillary line.
 This is the first part of the pleural cavity to be filled up by pleural effusion.

2. Costomediastinal recess :
 Lies anteriorly,behind the sternum and costal cartilages, between the costal and mediastinal
pleurae, particularly in relation to the cardiac notch of left lung.
 This recess is filled up by the anterior margin of the lungs even during quiet breathing.
 It is only obvious in the region of the cardiac notch of the lung.
c) Nerve Supply:
Parietal Pleura- Sensitive to pain, temperature, touch and pressure.
 Costal pleura is segmentally supplied by the intercostal nerves.
 Mediastinal pleura is supplied by the phrenic nerve.
 Diaphragmatic pleura is supplied the phrenic nerve (over the domes) and lower 6
intercostal nerves (around the periphery).

Visceral pleura (Pulmonary pleura) - Sensitive to stretch but insensitive to pain and touch.
 Receives sympathetic nerves from 2nd to 5th spinal segments.
 Parasympathetic nerves from vagus nerve (pulmonary plexus).

Pleura –Layers-Diagram

Pleura –Recesses-Diagram

7. Describe the right lung under the following headings:

(a) Borders & surfaces
 (b) Relations
(c) Bronchopulmonary segments
(d) Blood supply
(e) Histology of lung with labeled diagram
(f) Embryological development

a) Borders & surfaces

3 borders

i)Anterior border- is thin and vertical on the right side.

ii)Posterior border - thick and ill defined.
iii)Inferior border - separates the base from the costal and mediastinal surfaces.

2 Surfaces
i) Costal surface - smooth, convex, in contact with the costal pleura and presents grooves
corresponding with the overlying ribs.
ii) Mediastinal surface- in contact with the mediastinal pleura. It presents a deep
concavity, the cardiac impression, which accommodates the heart; this is larger and deeper
on the left than on the right lung.

b) Relations

Apex - is rounded and extends into the root of the neck, reaching from 2.5 to 4 cm. above the level
of the sternal end of the first rib. Subclavian artery produces a sulcus.

Base - is broad, concave and rests upon the convex surface of the diaphragm, which separates the
right lung from the right lobe of the liver.

Costal surface - is smooth, convex, related to costal pleura with the overlying ribs.

Mediastinal surface - is in contact with the mediastinal pleura. It is related to the following:
 Azygos vein - arched furrow above the hilum.
 Superior vena cava and right brachiocephalic vein - a wide groove below the apex.
 Brachiocephalic artery - a furrow near the apex.
 Esophagus - vertical groove, behind the hilus.
 Inferior vena cava - in front and to the right of the lower part of the esophageal groove.
 Large impression for the right atrium.

Hilum- Structures: Eparterial bronchus, pulmonary artery, hyparterial bronchus, pulmonary

veins,bronchial vessels,nerves and lymphatics.

c) Bronchopulmonary segments:
  The bronchopulmonary segments are the anatomic, functional and surgical units of the lungs.
Each lobar (secondary) bronchus, which passes to a lobe of the lung, gives off branches called
segmental (tertiary) bronchi.
 Each segmental bronchus passes to a structurally and functionally independent unit of a lung
lobe called a bronchopulmonary segment, which is surrounded by connective tissue.
 The segmental bronchus is accompanied by a branch of the pulmonary artery, but the
tributaries of the pulmonary veins run in the connective tissue between adjacent
bronchopulmonary segments. Each segment has its own lymphatic vessels and autonomic
nerve supply.
 Bronchopulmonary segments of right lung:
Superior lobe: Apical, posterior, anterior.
Middle lobe: Lateral, medial.
Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal.

d) Blood supply
Arteries: One bronchial artery arising from posterior intercostal artery.
Veins: 2 bronchial veins drain into azygos vein.

e) Histology

Section of the lung shows the following histological structures:

i) Bronchi: Cartilage rings completely encircle the lumen, but as the bronchial diameter
decreases, replaced with isolated plates of hyaline cartilage. Mucous and serous glands are
present.Lamina propria shows spirally arranged smooth muscle.
ii) Bronchiole:Airways with diameters of 1 mm or less, have neither cartilage nor glands in
their mucosa .In larger bronchioles epithelium is pseudostratified ciliated columnar, but this
decreases in height to become ciliated simple columnar or cuboidal epithelium in the
smaller terminal bronchioles. Goblet cells disappear, but the epithelium of terminal
bronchioles contains the exocrine bronchiolar cells, called Clara cells which secrete
surfactant.The bronchiolar lamina propria is composed largely of smooth muscle and
elastic fibers.

iii) Respiratory bronchiole: Their walls are interrupted by the openings to saclike alveoli
where gas exchange occurs. Portions of the respiratory bronchioles are lined with ciliated
cuboidal epithelial cells and Clara cells.Smooth muscle and elastic connective tissue lie
beneath the epithelium of respiratory bronchioles.

iv) Alveolar Duct:Respiratory bronchioles branch into alveolar ducts that are completely
lined by the openings of alveoli.Both the alveolar ducts and the alveoli are lined with
squamous alveolar cells.Lamina propria shows smooth muscle cells, which disappears at
the distal ends of alveolar ducts.

v) Alveolar ducts open into atria of two or more alveolar sacs. Elastic and reticular fibers
form a network encircling the openings of atria, alveolar sacs and alveoli.

vi) Alveoli : Saclike evaginations (about 200 m in diameter) of the respiratory bronchioles,
alveolar ducts, and alveolar sacs. Alveoli are lined by simple squamous epithelium
 consisting of 2 cell types: Type I and Type II alveolar cells. Alveolar macrophages (dust
cells) are also seen along the internal alveolar surface.

f) Embryological development
The lung develops in 5 stages as follows:

Stage Time Development

Lung buds originate as an outgrowth from the ventral wall of the
Embryonic Week 4 to 5
foregut where lobar division occurs.
Conducting epithelial tubes surrounded by thick mesenchyme are
Pseudoglandular Week 5 to 17
formed, extensive airways branching.
Bronchioles are produced, increasing number of capillaries in
Canalicular Week 16 to 25 close contact with cuboidal epithelium and the beginning of
alveolar epithelium development.
Saccular Week 24 to 40 Alveolar ducts and air sacs are developed
Late fetal to 8 Secondary septation occurs, marked increase of the number and
Alveolar
years size of capillaries and alveoli

Lung-Relations-Diagram
Right lung - Bronchopulmonary segments-Diagram

Lung histology-Diagram
8. Describe the left lung under the following headings:
(a) Borders & surfaces
(b) Relations
(c) Bronchopulmonary segments
(d) Blood supply
(e) Histology of lung with labeled diagram
(f) Embryological development

a)Borders & surfaces

3 borders

i) Anterior border- thin and shows cardiac notch on the left side below 4th costal cartilage.
ii) Posterior border - thick and ill defined.
iii) Inferior border - separates the base from the costal and mediastinal surfaces.

2 Surfaces
i) Costal surface - smooth, convex, in contact with the costal pleura and presents grooves
corresponding with the overlying ribs.
ii) Mediastinal surface- in contact with the mediastinal pleura. It presents a deep
concavity, the cardiac impression, which accommodates the heart; this is larger and deeper
on the left than on the right lung.

b) Relations

Apex - is rounded and extends into the root of the neck, reaching from 2.5 to 4 cm. above the level
of the sternal end of the first rib. Subclavian artery produces a sulcus.

Base - is broad, concave and rests upon the convex surface of the diaphragm, which separates the
left lung from the left lobe of the liver, stomach and spleen.

Costal surface - is smooth, convex, related to costal pleura with the overlying ribs.

Mediastinal surface - is in contact with the mediastinal pleura. It is related to the following:
Aortic arch- furrow above the hilus.
Left subclavian artery- groove in the apex
Left brachiocephalic vein- impression close to the anterior border of the lung
Descending thoracic aorta- vertical furrow behind the hilus and pulmonary ligament
Esophagus- impression near the base of the lung
Large impression for left ventricle
Hilum - Structures: Left principal bronchus, pulmonary artery, pulmonary veins, bronchial
vessels, nerves and lymphatics.

c) Left lung-Bronchopulmonary segments

The bronchopulmonary segments are the anatomic, functional and surgical units of the lungs. Each
lobar (secondary) bronchus, which passes to a lobe of the lung, gives off branches called segmental
(tertiary) bronchi. Each segmental bronchus passes to a structurally and functionally independent unit
of a lung lobe called a bronchopulmonary segment, which is surrounded by connective tissue. The
segmental bronchus is accompanied by a branch of the pulmonary artery, but the tributaries of the
pulmonary veins run in the connective tissue between adjacent bronchopulmonary segments. Each
segment has its own lymphatic vessels and autonomic nerve supply.
Bronchopulmonary segments of Left lung:
Superior lobe: Apicoposterior, anterior.
Lingula: Superior lingular, inferior lingular.
Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal.

d) Blood supply
Arteries: 2 bronchial arteries arising from descending thoracic aorta.

Veins: 2 bronchial veins drain into left superior intercostal vein or hemiazygos vein.

e) Histology

Section of the lung shows the following histological structures:

i) Bronchi: Cartilage rings completely encircle the lumen, but as the bronchial diameter
decreases, replaced with isolated plates of hyaline cartilage. Abundant mucous and serous
glands are also present.Lamina propria shows spirally arranged smooth muscle.
ii) Bronchiole:Airways with diameters of 1 mm or less, have neither cartilage nor glands in
their mucosa .In larger bronchioles epithelium is pseudostratified ciliated columnar, but this
decreases in height to become ciliated simple columnar or cuboidal epithelium in the
smaller terminal bronchioles. Goblet cells disappear, but the epithelium of terminal
bronchioles instead contains other numerous columnar cells: the exocrine bronchiolar cells,
commonly called Clara cells which secrete surfactant.The bronchiolar lamina propria is
composed largely of smooth muscle and elastic fibers.

iii) Respiratory bronchiole: Their walls are interrupted by the openings to saclike alveoli
where gas exchange occurs. Portions of the respiratory bronchioles are lined with ciliated
cuboidal epithelial cells and Clara cells, but at the rim of the alveolar openings the
bronchiolar epithelium becomes continuous with the squamous alveolar lining cells (type I
alveolar cells). Smooth muscle and elastic connective tissue lie beneath the epithelium of
respiratory bronchioles.

iv) Alveolar duct:Respiratory bronchioles branch into alveolar ducts that are completely
lined by the openings of alveoli.Both the alveolar ducts and the alveoli are lined with
squamous alveolar cells.Lamina propria shows smooth muscle cells, which disappears at
the distal ends of alveolar ducts.

v) Alveolar ducts open into atria of two or more alveolar sacs. Elastic and reticular fibers
form a network encircling the openings of atria, alveolar sacs and alveoli.
 vi) Alveoli : Saclike evaginations (about 200 m in diameter) of the respiratory bronchioles,
alveolar ducts, and alveolar sacs. Alveoli are lined by simple squamous epithelium
consisting of 2 cell types: Type I and Type II alveolar cells. Alveolar macrophages (dust
cells) are also seen along the internal alveolar surface.

f) Embryological development
The lung develops in 5 stages as follows:

Stage Time Development

Lung buds originate as an outgrowth from the ventral wall of the
Embryonic Week 4 to 5
foregut where lobar division occurs.
Conducting epithelial tubes surrounded by thick mesenchyme are
Pseudoglandular Week 5 to 17
formed, extensive airways branching.
Bronchioles are produced, increasing number of capillaries in
Canalicular Week 16 to 25 close contact with cuboidal epithelium and the beginning of
alveolar epithelium development.
Saccular Week 24 to 40 Alveolar ducts and air sacs are developed
Late fetal to 8 Secondary septation occurs, marked increase of the number and
Alveolar
years size of capillaries and alveoli

Left lung-Relations-Diagram

Left lung-Bronchopulmonary segments-Diagram

Lung histology-Diagram
 9. Describe the differences between right and left lung.

No RIGHT LUNG LEFT LUNG

1 Relatively larger. Relatively smaller.
2 3 lobes: Superior, middle and inferior lobes. 2 lobes: Superior and inferior lobes.
3 2 fissures : 1 fissure :
i. Oblique fissure: Separates inferior lobe with i. Oblique fissure: Separates superior and inferior lobe.
middle lobe.
ii. Horizontal fissure: Separates superior lobe with
middle lobe.
4 Absence of cardiac notch and lingula. Presence of cardiac notch and lingula.

Mediastinal surface relations: Aortic arch, left subclavian

5 Mediastinal surface relations: Azygos artery,left brachiocephalic vein, descending thoracic
vein,superior vena cava,right brachiocephalic aorta,esophagus and left ventricle.
vein,brachiocephalic artery ,esophagus,inferior
vena cava and right atrium.
6 Hilar structures: Eparterial bronchus, pulmonary Hilar structures: Left principal bronchus, pulmonary
artery, hyparterial bronchus, pulmonary artery, pulmonary veins, bronchial vessels, nerves and
veins,bronchial vessels, nerves and lymphatics. lymphatics.
7 10 bronchopulmonary segments: 9 bronchopulmonary segments:
Superior lobe: Apical, posterior, anterior. Superior lobe: Apicoposterior, anterior.
Middle lobe: Lateral, medial. Lingula: Superior lingular, inferior lingular.
Inferior lobe: Superior (apical), medial basal, Inferior lobe: Superior (apical), medial basal, anterior
anterior basal, lateral basal, posterior basal. basal, lateral basal, posterior basal.

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