Bronchus

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Bronchus

A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the respiratory tract

Respiratory tract

In humans the respiratory tract is the part of the anatomy that has to do with the process of Respiration .The respiratory tract is divided into 3 segments:...
that conducts air into the lung

Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s. No gas exchange

Gas exchange

Gas exchange or respiration takes place at a respiratory surface?a boundary between the external environment and the interior of the body....
takes place in this part of the lungs.

trachea

Vertebrate trachea

The traceartes, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16 cm in humans. It commences at the larynx and bifurcates into the primary bronchus in mammals, and from the pharynx to the syrinx in birds, allowing the passage of air to the lungs....
(windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle

Sternal angle

The sternal angle or 'angle of Louis' is the angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint ....
. The right main bronchus

Right main bronchus

The right main bronchus is a bronchus of the respiratory system. It is wider, shorter, and more vertical in direction than the Left main bronchus....
is wider, shorter, and more vertical than the left main bronchus

Left main bronchus

The left main bronchus is smaller in caliber but longer than the Right main bronchus, being nearly 5 cm long. It enters the root of the left lung opposite the sixth thoracic vertebra....
.

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Anatomy

The trachea

Vertebrate trachea

Sternal angle

Right main bronchus

Left main bronchus

The left main bronchus is smaller in caliber but longer than the Right main bronchus, being nearly 5 cm long. It enters the root of the left lung opposite the sixth thoracic vertebra....
. The left main bronchus subdivides into two lobar bronchi while the right main bronchus divides into three. The lobar bronchi divide into tertiary bronchi

Tertiary bronchus

The tertiary bronchi arise from the secondary bronchus. The respiratory epithelium lining their lumen is surrounded by a layer of smooth muscle....
. Each of the segmental bronchi supplies a bronchopulmonary segment

Bronchopulmonary segment

Each of the tertiary bronchi serves a specific bronchopulmonary segment. These segments each have their own artery. Thus, each bronchopulmonary segment is supplied by a bronchus, and an artery....
. A bronchopulmonary segment is a division of a lung that is separated from the rest of the lung by a connective tissue

Connective tissue

Connective tissue is a form of fibrous biological tissue.It is one of the four types of tissue in traditional classifications .Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content....
septum

Septum

A septum is a partition separating two cavities or spaces. Examples include:*Nasal septum: the cartilage wall separating the nostrils of the human nose....
.. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. There are ten segments per lung, but due to anatomic development, several segmental bronchi in the left lung fuse, giving rise to eight. The segmental bronchi divide into many primary bronchiole

Primary bronchiole

The primary bronchioles arise from the tertiary bronchus. They are histologically distinct from the tertiary bronchi in that their walls do not have hyaline cartilage and they have Clara cells in their epithelial lining....
s which divide into terminal bronchiole

Terminal bronchiole

A terminal bronchiole is a bronchiole at the end of the conducting zone. At the transition into the respiratory zone, Pulmonary alveolus become present....
s, each of which then gives rise to several respiratory bronchiole

Respiratory bronchiole

The respiratory bronchioles are the beginning of the respiratory segment of the airway and are just distal to the terminal bronchioles . The epithelium in this segment is simple cuboidal....
s, which go on to divide into 2 to 11 alveolar duct

Alveolar duct

Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end....
s. There are 5 or 6 alveolar sacs associated with each alveolar duct. The alveolus

Pulmonary alveolus

An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood....
is the basic anatomical unit of gas exchange in the lung.

There is hyaline cartilage

Hyaline cartilage

Hyaline cartilage consists of a slimy mass of a firm consistency, but of considerable elasticity and pearly bluish color. It contains no nerves or blood vessels, and its structure is relatively simple....
present in the bronchi, present as irregular rings in the larger bronchi (and not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle

Smooth muscle

Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye....
is present continuously around the bronchi.

In the mediastinum

Mediastinum

The mediastinum is a non-delineated group of structures in the thorax , surrounded by loose connective tissue. It is the central compartment of the thoracic cavity....
, at the level of the fifth thoracic vertebra, the trachea divides into the right and left primary bronchi. The bronchi branch into smaller and smaller passageways until they terminate in tiny air sacs called alveoli.

The cartilage

Cartilage

Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocyte that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers....
and mucous membrane

Mucous membrane

The mucous membranes are linings of mostly germ layer origin, covered in epithelium, which are involved in absorption and secretion. They line various body cavities that are exposed to the external environment and internal organ ....
of the primary bronchi are similar to that in the trachea. As the branching continues through the bronchial tree, the amount of hyaline cartilage

Hyaline cartilage

Hyaline cartilage consists of a slimy mass of a firm consistency, but of considerable elasticity and pearly bluish color. It contains no nerves or blood vessels, and its structure is relatively simple....
in the walls decreases until it is absent in the smallest bronchioles. As the cartilage decreases, the amount of smooth muscle increases. The mucous membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epithelium to simple squamous epithelium

Squamous epithelium

In anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cell called squamous cell....
.

The alveolar ducts and alveoli consist primarily of simple squamous epithelium

Squamous epithelium

In anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cell called squamous cell....
, which permits rapid diffusion of oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
and carbon dioxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli.

Role in disease

Bronchitis

Bronchitis is an inflammation of the large bronchus in the lungs. It can progress to pneumonia. Acute bronchitis is usually caused by viruses or bacteria and may last several days or weeks....
is defined as inflammation of the bronchi. There are two main types: acute and chronic. Acute bronchitis is usually caused by viral or bacterial infections. Chronic bronchitis

Chronic bronchitis

Chronic bronchitis is a chronic inflammation of the bronchus in the lungs. It is generally considered one of the two forms of chronic obstructive pulmonary disease ....
is a form of COPD

COPD

Chronic obstructive pulmonary disease is a group of diseases of the lungs in which the airways become narrowed. This leads to a limitation of the flow of air to and from the lungs causing shortness of breath....
, usually associated with smoking or long-term exposure to irritants. Asthma

Asthma

Asthma is a common chronic obstructive pulmonary disease, in which the Lung constrict, become inflammation, and are lined with excessive amounts of thickened mucus, often in response to one or more triggers....
is hyperreactivity of the bronchi

Bronchial hyperresponsiveness

Bronchial hyperresponsiveness is a state characterised by easily triggered bronchospasm .Bronchial hyperresponsiveness can be assessed with a bronchial challenge test....
with an inflammatory component, often in response to allergen

Allergen

An allergen is a parasite antigen capable of stimulating a type-I hypersensitivity reaction in atopy individuals.Most humans mount significant Immunoglobulin E responses only as a defense against parasitic infections....
s.

While the left mainstem bronchus departs from the trachea at an angle, the right mainstem bronchus is almost a vertical continuation of the trachea. This anatomy predisposes the right lung to several problems:

If food, liquids, or foreign bodies are aspirated, they often will lodge in the right mainstem bronchus. Aspiration pneumonia
Aspiration pneumonia

Aspiration pneumonia is bronchopneumonia that develops due to the entrance of foreign materials that enter the bronchial tree, usually oral or gastric contents ....
may result.
If the endotracheal tube
Endotracheal tube

An endotracheal tube is used in general anaesthesia, intensive care and emergency medicine for airway management and mechanical ventilation. The tube is inserted into a patient's vertebrate trachea in order to ensure that the airway is not closed off and that air is able to reach the lungs....
used for intubation
Intubation

In medicine, intubation refers to the placement of a tube into an external or internal orifice of the body. Although the term can refer to endoscopy procedures, it is most often used to denote tracheal intubation....
is inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
Patients with inadequate cough
Cough

A cough , in medicine, is a sudden and often repetitively occurring defense reflex which helps to clear the large breathing passages from excess secretions, irritants, foreign particles and microbes....
reflexes may develop chronic right middle lobe lung infections such as the Lady Windermere Syndrome
Lady Windermere Syndrome

Lady Windermere syndrome describes infection in the lungs due to Mycobacterium avium complex. It is named after a character in Oscar Wilde's play Lady Windermere's Fan....
.

Bronchus

Anatomy

Role in disease

Additional images