The alveoli are highly elastic, so the alveoli can stretch as they are filled with air during inhalation. They then spring back during exhalation in order to expel the carbon-dioxide-rich air. The alveoli consist of an extremely thin epithelial layer and an extracellular matrix a fluid space made of collagen and elastin that contains no cells ; it is surrounded by many capillaries, the tiniest type of blood vessel.
The fluid extracellular matrix supports the structure of the alveoli and allows gases to dissolve in water, making passive diffusion of those gases with the capillaries possible. In some alveolar walls there are pores between alveoli called the pores of Kohn, that connect alveoli in order to equalize air pressure between the different sacs of an alveolus.
Besides these epithelium cells, there are many macrophages found in the alveoli that provide immune system defense of the alveoli from pathogens and foreign material. The surfactant produced by type II epithelial cells is very important for maintaining the elastic recoil of the lungs. It is a lipoprotein with hydrophilic and hydrophobic ends that reduce the amount of surface tension from water in the lungs. Without surfactant, the surface tension would cause the lungs to collapse during exhalation, making normal breathing impossible.
Surfactant is first produced by human lungs between 24 and 28 weeks in the womb, and many infants born prematurely do not have enough surfactant to breathe on their own after birth. Surfactant replacement therapy is necessary to save the lives of these premature births. The alveoli are the site of alveolar ventilation, and are not normally considered dead space. However, alveoli that are injured and can no longer contribute to gas exchange become alveolar dead space.
This is a common occurrence in people with lung diseases like COPD chronic pulmonary obstructive disorder, i. Physiological dead space is the sum of normal anatomical dead space and alveolar dead space, and can be used to determine the rate of ventilation gas exchange in the lungs.
When any type of dead space increases, the rate of ventilation in the lungs will decrease. Privacy Policy. Skip to main content. Respiratory System. Search for:. Respiratory Zone. Bronchi and Subdivisions A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs and divides into terminal bronchioles. Learning Objectives Illustrate the anatomical structure of the bronchi and their subdivisions. Key Takeaways Key Points The human trachea windpipe divides into two main bronchi also called mainstem bronchi , at the anatomical point known as the carina.
The right main bronchus is wider and shorter than the left main bronchus. The right main bronchus subdivides into three lobar bronchi and the left main bronchus divides into two.
The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment. The segmental bronchi divide into many primary bronchioles that divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into and terminate in tiny air sacs called alveoli.
The mucous membrane of the primary bronchi is initially lined by ciliated pseudostratified columnar epithelium, but eventually the lining transitions to simple cuboidal epithelium, and then to simple squamous epithelium. Learn about its function and anatomy, as well as the conditions that can affect…. The vagus nerve is the longest of the 12 cranial nerves. Here, learn about its anatomy, functions, and the kinds of health problems that can occur.
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The brain is one of your most important organs. The supraspinatus muscle is a rotator cuff muscle located in the shoulder, specifically in the supraspinatus fossa, a concave depression in the rear…. The masseter muscle is a facial muscle that plays a major role in the chewing of solid foods. The muscle is shaped similar to a parallelogram…. Health Conditions Discover Plan Connect.
Like the trachea, the bronchi and bronchioles are part of the conducting zone, so they moisten and warm air and contribute to the volume of anatomical dead space. The bronchi and bronchioles are also part of the mucociliary escalator that removes mucus and pathogens from the lungs.
A unique characteristic of the bronchi and bronchioles is bronchoconstriction , in which the smooth muscle of the bronchi or bronchioles tightens. This leads to coughing, wheezing, and dyspnea shortness of breath. It is caused by activation of the parasympathetic nervous system and release of acetylcholine in the bronchi, as well as by overproduction of mucus or allergic reactions and inflammation.
It is a symptom of diseases such as bronchitis chronic inflammation and mucus production in the bronchi and asthma an acute attack of bronchoconstriction, often allergic. Both cause obstruction of the airways and make it more difficult to breathe. Bronchoconstriction is treated with anti-inflammatory drugs, such as corticosteroids, and prevented by maintaining lung health, such as through avoiding smoking, air pollution, and airborne allergens. The complete respiratory system : This figure details the respiratory system including the bronchi and its many subdivisions.
Anatomy of the Bronchi The human trachea divides into two main bronchi also called mainstem bronchi , that extend laterally but not symmetrically into the left and right lung respectively, at the level of the sternum. Histology The histology of the bronchi are largely similar to that of the trachea. Physiology of the Bronchi Like the trachea, the bronchi and bronchioles are part of the conducting zone, so they moisten and warm air and contribute to the volume of anatomical dead space.
Key Points The human trachea windpipe divides into two main bronchi also called mainstem bronchi , at the anatomical point known as the carina. The right main bronchus is wider and shorter than the left main bronchus.
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