anatomy and physiology of lung

ANATOMY AND PHYSIOLOGY OFLUNG

JITHA.A.HARI2ND YR MSc NCNK

INTRODUCTIONThe 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.

ANATOMY - LUNG

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 the trachea.

Gross anatomy

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.

The lobes of the lungs are further divided into broncho pulmonary segments based on the locations of bronchioles.

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:

FISSURES & LOBES OF THE RIGHT LUNG

PLEURA

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.

Parietal PleuraCostal 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

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.

• 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.

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.

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.

BLOOD SUPPLYThe 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.

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.

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.

PHYSIOLOGY OF LUNG

LUNG VOLUMESLung 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

TIDAL VOLUME

Normal volume of air inspired or expired during quiet breathing

TV = 500 ml

INSPIRATORY RESERVE VOLUME Extra volume of air inhaled after tidal volume by max inspiratory effort

3000ml in adult male (or) 3300 / 1900 = M/F

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

RESIDUAL VOLUME

Volume of the air left out in lungs after forceful expiration or complete expiration

1200/1100 = M/F

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

INSPIRATORY CAPACITY

Max volume of air that can be inspired after normal tidal expiration

IC = TV+IRV = 500 +3000 = 3500 ml

EXPIRATORY CAPACITY

Max volume of air that can be expired after normal tidal inspiration

EC=TV+ERV (500+1100=1600ml)

FUNCTIONAL RESIDUAL CAPACITY

Volume of air remaining in lungs after normal tidal expiration

FRC= ERV + RV ( 1100 + 1200 = 2300ml)

VITAL CAPACITY

Max Amount of air expelled after deepest possible inspiration

VC = TV+IRV+ERV500+3000+1100= 4600ml

TOTAL LUNG CAPACITY

Volume of air present in lung after max inspiration TLC = VC + RV ( 4600+1200 = 5800ml )