Gross anatomy and development of respiratory system

Gross anatomy and development of respiratory system

Dr Laxman Khanal

Try these……

• The oblique fissure of lung follows…………rib. a. 5th b. 6th c. 7th d. 8th

• Which of the following embryonic germ layer give rise to the inner lining of the respiratory tract??

a. Ectoderm b. mesoderm c. endoderm d. neural crest cells

• Trachea is made up of ….cartilagea. Hyaline b. elastic c. fibro cartilage d. all

• Part of lung aerated by respiratory bronchioles is called as….

a. Pulmonary unit b. broncho pulmonary unit

• Surfactant is produced by which alveolar cells??

a. type1 b. type 2 c. both d. none • Most anterior structure in root of the lung

is..a. Pulmonary vein b. pulmonary arteryc. Bronchus d. bronchial artery

• Consists of respiratory and conducting zones• Respiratory zone– Site of gas exchange – Consists of bronchioles, alveolar ducts, and alveoli

• Conducting zone – Provides rigid conduits for air to reach the sites of

gas exchange– Includes all other respiratory structures (e.g.,

nose, nasal cavity, pharynx, trachea)

Trachea

• Also called as wind-pipe.• Extend from end of larynx(C6) to the point of

bifurcation ( T4).• Its about 15cm in length.• The trachea has 15 to 20 C-shaped bars of

hyaline cartilage that prevent it from collapsing.

• The carina is the upward-directed ridge seen internally at the bifurcation and is a landmark during bronchoscopy.

• The trachea is supplied mainly by the inferior thyroid arteries. Its smooth muscle is supplied by parasympathetic and sympathetic fibers, and pain fibers are carried by the vagi.

Main bronchus

• Trachea divide into two main bronchus- right and left.

• The right main bronchus is shorter, wider, and more vertical than the left.

• Because it is in almost a direct line with the trachea, foreign objects traversing the trachea are more likely to enter the right main bronchus.

Bronchial tree• Main bronchi- lobar bronchi- segmental

bronchi- terminal bronchioles- respiratory bronchioles ( duct- atrium-saccules- alveoli)

• The bronchioles are very narrow and have a diameter of 1mm or less. Respiratory brochioles bronchioles eventually lead into small sac-like structures called the alveoli.

• Pulmonary unitEach respiratory bronchiole aerates a small part of the lung known as a pulmonary unit. The respiratory bronchiole ends in microscopic passages like- alveolar ducts, atria, air saccules and pulmonary alveoli.

• The alveolus is the basic structural unit of gas exchange in the lung.

• New alveoli continue to develop until the age of 8 yrs, by which there are about 300 million alveoli.

Pleura

• The pleura is a thin, glistening, slippery serous membrane, inflammation of which is called pleurisy.

• The pleura lines the thoracic wall and diaphragm, where it is known as the parietal pleura. It is reflected onto the lung, where it is called the visceral pleura.

• Both are derivatives of mesoderm germ layer

• The pleural cavity, which is the potential space between the two layers, contains only a thin film of fluid.

• Air in the pleural cavity (pneumothorax) results in collapse of the lung.

• Irritation of the parietal pleura causes pain referred to the thoraco-abdominal wall to the shoulder (phrenic nerve).

• Visceral pleura is pain insensitive.

• The parietal pleura has costal, mediastinal, diaphragmatic parts and a cupola.

• the cupola of the pleura and the apex of the lung project upward into the neck, hence may be injured in wounds of the neck.

• Their highest point is 2 to 3 cm above the level of the medial third of the clavicle. The sympathetic trunks and first thoracic nerves are found posterior to the cupola.

Lungs

• The lungs are the essential organs of respiration.

• The Latin word pulmo, lung, gives rise to the adjective pulmonary.

• Each lung is attached by its root and pulmonary ligament to the heart and trachea but is otherwise free in the thoracic cavity.

• The main bronchus enters the hilum and subdivides within the substance of the lung to form the "bronchial tree.“

• The right lung, is heavier, shorter (the right dome of the diaphragm being higher) and wider (the heart bulging more to the left) than the left.

Lungs

• Each lung has an apex, three surfaces (costal, medial, and diaphragmatic), and three borders (anterior, inferior, and posterior).

• The right lung is divided into upper, middle, and lower lobes by oblique and horizontal fissures

• The left lung has usually only upper and lower lobes, separated by an oblique fissure.

• The bronchi and pulmonary vessels, which extend from the trachea and heart, respectively, collectively form the root of the lung.

• The part of the medial surface where these structures enter the lung is known as the hilum of lung.

Roots and hila of lungs

• The inferior limit of the lung crosses rib 6 in the midclavicular line and rib 8 in the midaxillary line and then proceeds toward the 10th thoracic vertebra.

• Inferior limit of pleura is rib 8 in MCL, rib 10 in MAL and 12th thoracic vertebra along para-vertebral line.

• The oblique fissure follows approximately the line of rib 6 as far as the inferior border of the lung.

• The horizontal fissure begins at the oblique fissure near the midaxillary line (of the right side), at about the level of rib 6.

• Important for localization of particular lobe during chest injury.

Right lung – related structures

Left lung – related structures

Bronchopulmonary segment

• A bronchopulmonary segment is the area of lung supplied by a segmental bronchus and its accompanying pulmonary artery branch.

• Tributaries of the pulmonary vein tend to pass intersegmentally between and around the margins of segments.

• A bronchopulmonary segment is the smallest, functionally independent region of a lung and the smallest area of lung that can be isolated and removed without affecting adjacent regions.

Clinical importance

• The normal respiratory rate is 12 - 20 breaths per minute. A faster breathing rate is called tachypnoea. Tachypnoea is an important sign of respiratory disease.

• If the breathing rate is increased for a long period of time, dehydration can occur. So it is important to give fluids to patients with respiratory disease or tachypnoea from other causes.

• Types of respirations Abdominal type of respirationThoracic type of respiration • Bronchogenic carcinomaBegins by involving the glands around the

large bronchi.May cause hoarseness in voice.

• Chronic obstructive pulmonary disease (COPD): Damage to the lungs results in difficulty blowing air out, causing shortness of breath. Smoking is by far the most common cause of COPD.

• Pleural effusion: Fluid builds up in the pleural space. If large, pleural effusions can cause problems with breathing.

• Pneumothorax: Air in the pleural space .

Development of respiratory system

Formation of lung bud ( respiratory diverticulum).

• Its an outgrowth from the ventral aspect of foregut ( endodermal tube ).

• This give rise to the larynx, trachea, bronchi and lungs.

• Hence epithelium of the internal lining of the larynx, trachea, and bronchi, as well as that of the lungs, is entirely of endodermal origin.

• cartilaginous, muscular, and connective tissue components of the trachea and lungs are derived from splanchnic mesoderm surrounding the foregut.

• When the diverticulum expands two longitudinal ridges, the tracheoesophageal ridges, separate it from the foregut. when these ridges fuse to form the tracheoesophageal Septum, the foregut is divided into a dorsal portion, the esophagus, and a ventral Portion, the trachea and lung buds.

Abnormalities in partitioning of oesophagus and trachea by tracheoesophageal septum results in esophageal atresia and tracheoesophageal fistula.

• During separation from foregut, lung bud forms trachea and two lateral out pocketing, bronchial buds.

• Each of these buds enlarges to form right and left main bronchi. Later right one divide into 3 and left into 2 secondary bronchi.

• During further development, secondary bronchi divide repeatedly forming tertiary (segmental) bronchi, creating the bronchopulmonary Segments Of The adult lung.

Growth of the lungs after birth is primarily due to an increase in the number of respiratory bronchioles and alveoli and not to an increase in the size of the alveoli. New alveoli are formed during the first 10 years of postnatal life.

• After a pseudoglandular and canalicular phase, cells of the respiratory bronchioles change into thin, flat cells, type I alveolar epithelial cells, intimately associated with capillaries. In the seventh month, gas exchange between the blood and air in the primitive alveoli is possible.

• Before birth, the lungs are filled with fluid with surfactant, which is produced by type II alveolar epithelial cells which forms a phospholipid coat on the alveolar membranes. At the beginning of respiration, the lung fluid is reabsorbed except for the surfactant coat, which prevents the collapse of the alveoli during expiration by reducing the surface tension at the air– blood capillary interface.

Queries ???

Try these……

• The oblique fissure of lung follows…………rib. a. 5th b. 6th c. 7th d. 8th

• Which of the following embryonic germ layer give rise to the inner lining of the respiratory tract??

a. Ectoderm b. mesoderm c. endoderm d. neural crest cells

• Trachea is made up of ….cartilagea. Hyaline b. elastic c. fibro cartilage d. all

• Part of lung aerated by respiratory bronchioles is called as….

a. Pulmonary unit b. broncho pulmonary unit

• Surfactant is produced by which alveolar cells??

a. type1 b. type 2 c. both d. none • Most anterior structure in root of the lung

is..a. Pulmonary vein b. pulmonary arteryc. Bronchus d. bronchial artery

THANK YOU