The lungs are key organs in the human body, responsible for bringing oxygen into the body and helping get rid of waste gases with every exhale. Though having both lungs is ideal, it is possible to live and function without one lung. Having one lung will still allow a person to live a relatively normal life.

The alveoli pick up the incoming energy (oxygen) you breathe in and release the outgoing waste product (carbon dioxide) you exhale. As it moves through blood vessels (capillaries) in the alveoli walls, your blood takes the oxygen from the alveoli and gives off carbon dioxide to the alveoli.

The walls of the alveoli share a membrane with the capillaries. That’s how close they are. This lets oxygen and carbon dioxide diffuse, or move freely, between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart.

While in the capillaries, blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from air in the alveoli.

Because we could not survive without the oxygen in the air that we breathe. We could not take in the oxygen if we didn’t have lungs. We also need to breathe out carbon dioxide into the air. Carbon dioxide is made when our bodies use oxygen and other nutrients in our food to give us energy.

Pulmonary surfactant enables to reduce the surface tension so that the alveoli do not collapse during expiration. The capacity of the lungs to stretch is called lung compliance, which plays an important role in gas flow.

Atelectasis (at-uh-LEK-tuh-sis) is a complete or partial collapse of the entire lung or area (lobe) of the lung. It occurs when the tiny air sacs (alveoli) within the lung become deflated or possibly filled with alveolar fluid. Atelectasis is one of the most common breathing (respiratory) complications after surgery.

In emphysema, the inner walls of the lungs’ air sacs (alveoli) are damaged, causing them to eventually rupture. This creates one larger air space instead of many small ones and reduces the surface area available for gas exchange. Emphysema is a lung condition that causes shortness of breath.

Without normal surfactant, the tissue surrounding the air sacs in the lungs (the alveoli) sticks together (because of a force called surface tension) after exhalation, causing the alveoli to collapse.

Alveoli are an important part of the respiratory system whose function it is to exchange oxygen and carbon dioxide molecules to and from the bloodstream. These tiny, balloon-shaped air sacs sit at the very end of the respiratory tree and are arranged in clusters throughout the lungs.

When there is not enough surfactant, the tiny alveoli collapse with each breath. As the alveoli collapse, damaged cells collect in the airways, which makes it even harder to breath. These cells are called hyaline membranes. Your baby works harder and harder at breathing, trying to re-inflate the collapsed airways.

The main functions of surfactant are as follows: (1) lowering surface tension at the air–liquid interface and thus preventing alveolar collapse at end-expiration, (2) interacting with and subsequent killing of pathogens or preventing their dissemination, and (3) modulating immune responses.

Soaps and detergents are made from long molecules that contain a head and tail. These molecules are called surfactants; the diagram below represents a surfactant molecule. The head of the molecule is attracted to water (hydrophilic) and the tail is attracted to grease and dirt (hydrophobic).

Under most conditions, the partial pressure of carbon dioxide (PCO2), or concentration of carbon dioxide, controls the respiratory rate.

Pulmonary surfactant is essential for life as it lines the alveoli to lower surface tension, thereby preventing atelectasis during breathing. Surfactant is enriched with a relatively unique phospholipid, termed dipalmitoylphosphatidylcholine, and four surfactant-associated proteins, SP-A, SP-B, SP-C, and SP-D.

Surfactant is a liquid made by the lungs that keeps the airways (alveoli) open. This liquid makes it possible for babies to breathe in air after delivery. An unborn baby starts to make surfactant at about 26 weeks of pregnancy.

These alveoli are coated with a substance called surfactant, which is made up of certain fats and proteins. By coating the alveoli, surfactant prevents these sacs from sticking together when we breathe out, making breathing easier.

Surfactant is a mixture of fat and proteins made in the lungs. Surfactant coats the alveoli (the air sacs in the lungs where oxygen enters the body). This prevents the alveoli from sticking together when your baby exhales (breathes out).

Type 2 pneumocyte: The cell responsible for the production and secretion of surfactant (the molecule that reduces the surface tension of pulmonary fluids and contributes to the elastic properties of the lungs).

Type I pneumocytes cover 95% of the internal surface of each alveolus. These cells are thin and squamous, ideal for gas exchange. These pneumocytes joined one another and other alveolar cells by tight junctions, forming an impermeable barrier to limit the infiltration of fluid into the alveoli.

Type II epithelial cells are small cuboidal cells which usually reside in the corners of the alveolus, covering roughly 2% of the alveolar surface area. Type II pneumocytes are known to produce surfactant and regenerate alveolar epithelium after injury. In healthy lungs, type I and type II cells exist in a 1:1 ratio.

epithelial cells

At this level, the epithelium consists entirely of non-ciliated bronchiolar or Clara cells. At higher power, one can see an alveolar septum, lined on both surfaces by the cellular extensions of Type I pneumocytes (95% of surface) and occasional Type II pneumocytes or great alveolar cells (about 5% of surface area).

The cilium (from Latin ‘eyelash’; the plural is cilia) is an organelle found on eukaryotic cells in the shape of a slender protuberance that projects from the much larger cell body. There are two types of cilia: motile and non-motile cilia….

These cells were first recognized as a distinct cell type based on morphology and histochemistry in 1881 by Kölliker (1). In 1967, Niden suggested that Clara cells secrete pulmonary surfactant and that the lamellar bodies seen in alveolar type II pneumocytes represented phagocytized surfactant (4).

Ciliated columnar epithelium is composed of simple columnar epithelial cells with cilia on their apical surfaces. These epithelial cells are found in the lining of the fallopian tubes and parts of the respiratory system, where the beating of the cilia helps remove particulate matter.

Ciliated epithelia are found in the airways, the uterus and Fallopian tubes, the efferent ducts of the testes, and the ventricular system of the brain.

Epithelial tissues are widespread throughout the body. They form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands.

Ciliated cells are located on the epithelium terminal bronchioles to the larynx and their function is to move rhythmically.