2. INTRODUCTION
The lungs are the primary organs of respiration in humans
and many other animals including a few fish and some
snails.
In mammals and most other vertebrates, two lungs are
located near the backbone on either side of the heart.
4. The lungs are located in the chest on either side of the heart in the rib cage. They are
conical in shape with a narrow rounded apex at the top and a broad base that rests on the
diaphragm
The apex of the lung extends into the root of the neck, reaching shortly above the level of
the sternal end of the first rib.
The front and outer sides of the lung face the ribs, which make light indendations on their
surfaces. The bottom of the lungs is smooth and rests on the diaphragm, matching its
concavity.
The medial surface of the lungs faces towards the center of the chest, and lies against the
heart, great vessels, and the carina where the two main bronchi branch off from the base of
Gross anatomy
5. Both lungs have a central recession called the hilum at the root of the lung, where the blood
vessels and airways pass into the lungs. There are also bronchopulmonary lymph nodes on
the hilum.
The lungs are surrounded by the pulmonary pleurae. The pleurae are two serous
membranes; the outer parietal pleura lines the inner wall of the rib cage and the inner
visceral pleura directly lines the surface of the lungs. Between the pleurae is a potential
space called the pleural cavity containing pleural fluid.
Each lung is divided into lobes by the invaginations of the pleura as fissures. The fissures
are double folds of pleura that section the lungs and help in their expansion.
6. The lobes of the lungs are further divided into broncho pulmonary segments based on
the locations of bronchioles.
7.
8. Oblique fissure (Right & Left):
It starts at the 3rd thoracic spine while the arms are elevated, descends downwards,
laterally & anteriorly along the medial border of the scapula touching the inferior
angle of the scapula) cutting the midaxillary line in the 5th rib & ending at the 6th
costal cartilage 3 inches from the midline.
In cadaver it arise at the 2nd thoracic spine.
The transverse fissure (Right):
It arises at the 4th costal cartilage, runs horizontally to meet the oblique fissure in
the midaxillary line in the 5th rib.
LUNG FISSURES:
11. THE BORDERS OF THE PLEURA:
The pleura runs close to the lung except at the lower border which
extends for 3-5 cm below it both anteriorly & posteriorly & 9-10 cm
below in the axilla.
The lower border cuts the 8th rib in MCL, 10th rib in MAL and 12th rib in
Scapular line.
12.
13. Parietal Pleura
Costal pleura:
Lines thoracic wall (ribs, intercostal spaces)
Mediastinal pleura:
Lines corresponding surface of mediastinum; reflected over root of lung & becomes continuous
with visceral pleura around hilum
Cervical pleura:
Extends into neck about 2 inches above 1st costal cartilage & one inch above medial 1/3 clavicle;
covers apex of lung
Diaphragmatic pleura:
Lines superior surface of diaphragm
14. Microanatomy
• The lungs contain the respiratory tract and its lining, which terminate in
alveoli, the tissue in between and veins, arteries, nerves and lymphatic vessels.
• The respiratory tract begins with the trachea and bronchi. These structures are lined
with columnar epithelial cells that possess cilia , small frond-like projections.
• Interspersed with the epithelial cells are goblet cells which produce mucous, and club
cells with actions similar to macrophages. Surrounding these in the trachea and
bronchi are cartilage rings, which help to maintain stability.
15. • The respiratory tract ends in lobules. These consist of a respiratory bronchiole,
which branches into alveolar ducts and alveolar sacs, which in turn divide into
alveoli.
16.
17. Alveoli consist of two types of alveolar cell and an alveolar macrophage. The two types of
cell are known as type I and type II alveolar cells (also known as pneumocytes)
Types I and II make up the walls and septa of the alveoli.
Type I cells provide 95% of the surface area of each alveoli and are flat ("squamous"), and
Type II cells generally cluster in the corners of the alveoli and have a cuboidal shape.
Despite this, cells occur in a roughly equal ratio of 1:1 or 6:4
Type I are squamous epithelial cells that make up the alveolar wall structure. They have
extremely thin walls that enable an easy gas exchange.
18. These type I cells also make up the alveolar septa which separate each alveolus. The septa
consist of an epithelial lining and associated basement membranes. Type I cells are not able
to divide, and consequently rely on differentiation from Type II cells.
Type II are larger and they line the alveoli and produce and secrete ELF and
surfactant. Type II cells are able to divide and differentiate to Type 1 cells.
19.
20. BLOOD SUPPLY
The human lung has a dual blood supply.
The tissue of the lungs receive oxygenated blood via the bronchial circulation, a series
of arteries that leave the aorta and are part of the systemic circulation. There are usually
three arteries, and they branch alongside the bronchi and bronchioles.
The blood volume of the lungs is about 450 millilitres on average, about 9 per cent of the
total blood volume of the entire circulatory system. This quantity can easily fluctuate from
between one-half and twice the normal volume.
21. The lungs also receive deoxygenated blood from the heart and supply it with oxygen,
in a process known as respiration.
In this process, venous blood in the body collects in the right atrium and is pumped
from the right ventricle through the pulmonary trunk and the pulmonary arteries into
the left and right lungs.
Blood passes through small capillaries next to the alveoli in the lung, receives
oxygen, and travels back to the heart. This is called the pulmonary circulation. The
oxygenated blood is then pumped to the rest of the body.
22.
23. NERVE SUPPLY
The lungs are supplied by nerves of the autonomic nervous system. Input from the parasympathetic
nervous system occurs via the vagus nerve.
When stimulated by acetylcholine, this causes constriction of the smooth muscle lining the bronchus and
bronchiole, and increases the secretions from glands.
The lungs also have a sympathetic tone from norepinephrine acting on the beta 2 receptors in the
respiratory tract, which causes bronchodilation.
The action of breathing takes place because of nerve signals sent by the respiratory centres in the
brainstem, along the phrenic nerve to the diaphragm.
26. LUNG VOLUMES
Lung volumes and lung capacities refer to the volume of air associated with different
phases of the respiratory cycle. Lung volumes are directly measured; lung capacities are
inferred from lung volumes.
The average total lung capacity of an adult human male is about 6 litres of air.
Four types
1. Tidal volume
2. Inspiratory reserve volume
3. Expiratory persevere volume
4. Residual volume
29. INSPIRATORY RESERVE VOLUME
Extra volume of air inhaled after tidal volume by max inspiratory effort
3000ml in adult male
(or)
3300 / 1900 = M/F
30. EXPIRATORY RESERVE VOLUME
Extra volume of air that can be exhaled after tidal volume by max
expiratory efforts
1100 in a normal adult male
(or)
1200/700 = M/F
31. RESIDUAL VOLUME
Volume of the air left out in lungs after forceful expiration or
complete expiration
1200/1100 = M/F
32. These are combinations of two or more lung volumes
1. Inspiratory capacity
2. Expiratory capacity
3. Functional residual capacity
4. Vital capacity
5. Total lung capacity
