Gas Exchange - Session 2

We have studied that the cartilage rings are found in particular parts of the respiratory system. What is the function of these cartilage rings? The cartilage rings are made of hyaline cartilage. Hyalin cartilage is a type of cartilage that is tough and somewhat flexible. Cartilage rings are shaped like the letter-C when viewed in cross section. This shape allows for structural support while also accommodating the movement of surrounding structures.

Cartilage rings are found in the trachea and the bronchi. The cartilage rings are incomplete posteriorly, meaning that the ends of the C shape do not meet at the backside of the airway. Instead, they are connected by a band of smooth muscle called the trachealis muscle. This arrangement allows for flexibility and expansion of the airway during breathing and swallowing.

The primary function of the cartilage rings is to maintain the openness of the airways. The rings prevent collapse of the trachea and the bronchi. They ensure that these air passages remain open for the passage of air to and from the lungs. While the cartilage rings provide stability and support to the airway, their incomplete design allows for some amount of flexibility and movement. This flexibility is important for actions such as swallowing. During swallowing, the trachea and the bronchi might need to adjust their position slightly to accommodate the passage of food through the esophagus.

Smooth muscles are found throughout the respiratory system. They are abundant in the walls of bronchi and bronchioles. When the smooth muscles in the walls of the bronchi and bronchioles contract, they cause the airway diameter to decrease. This narrowing of the airways is known as the bronchoconstriction.

The bronchoconstriction reduces the diameter of the airways, leading to increased resistance to airflow. As a result, less air can pass through the narrowed airways, resulting in decreased airflow to and from the lungs. Substances released during allergic reactions or respiratory infections can trigger the bronchoconstriction. Exposure to allergens, pollutants, smoke, or other irritants can also induce bronchoconstriction as a protective response.

The bronchodilation occurs when the smooth muscles in the airways relax. The bronchodilation leads to a widening of the airways, reducing resistance to airflow. This allows for increased airflow into and out-of the lungs, facilitating ventilation. Anti-inflammatory medications such as corticosteroids can also help relax smooth muscles and dilate the airways by reducing inflammation.

Elastic fibers are found in the connective tissues of the respiratory system, including the walls of the trachea, bronchi, bronchioles and alveoli. Elastic fibers are composed primarily of the elastin protein, which gives them elasticity and resilience. These fibers are arranged in a network that allows them to stretch and recoil, providing structural support to the respiratory system. Elastic fibers help maintain the openness of the airways by providing structural support. They prevent collapse of the airways during exhalation by recoiling after stretching during inhalation.

Elastic fibers in the alveolar walls contribute to lung recoil. Lung recoil is essential for the passive expiration of air from the lungs. During inhalation, the expansion of the lungs stretches the elastic fibers, storing potential energy. During exhalation, these fibers recoil, helping to push air out of the lungs.

Ciliated epithelium consists of columnar or pseudostratified columnar epithelial cells. These cells are tall and closely packed. They form a continuous layer that lines the surface of the respiratory tract. Ciliated epithelium is found in nasal cavity, trachea, bronchi and larger bronchioles.

The defining feature of ciliated epithelium is the presence of numerous microscopic hair like structures called cilia. Cilia are found on the apical surface of the epithelial cells. Each cilium is a slender, motile extension of the cell membrane. It is composed of microtubules arranged in a nine plus two pattern. This arrangement refers to nine pairs of microtubules surrounding a central pair. This provides structural support and allows for coordinated movement.

The primary function of the ciliated epithelium is to facilitate the movement of mucus and trapped particles out of the airways. The ciliated epithelium plays a crucial role in protecting the respiratory tract from harmful substances, such as bacteria, viruses, and inhaled debris. The continuous movement of the cilia helps to sweep these particles out of the airways. The ciliated epithelium contributes to the humidification and filtration of inhaled air. As air passes over the moist surface of the respiratory epithelium, it picks up moisture and is filtered of particulate matter. This provides humidified and cleaner air to the lungs.

Goblet cells are typically flask shaped or columnar in structure. Goblet cells are mainly found in the epithelium lining the nasal cavity, trachea, bronchi and larger bronchioles. The primary function of the goblet cells in the respiratory system is to produce and secrete mucus. Mucus is a sticky, gel like substance composed of water, ions, proteins and mucins. Mucins are the glycoproteins produced by the goblet cells.

Mucus serves several important roles, including trapping and removing inhaled particles, such as dust, pollen and pathogens from the airways. It also helps to humidify and moisturize the air. This protects the delicate epithelial cells lining the respiratory tract from drying out. Mucus produced by goblet cells, along with the cilia of adjacent ciliated epithelial cells, forms the mucociliary escalator. This mechanism facilitates the movement of mucus and trapped particles out of the airways. The coordinated beating of cilia propels the mucus layer upwards towards the throat, where it can be swallowed or expectorated.

Squamous epithelial cells are thin and flattened. They resemble irregularly shaped tiles or scales. These cells are closely packed and have minimal intercellular material between them. Squamous epithelial cells have a centrally located nucleus, which might appear flattened due to the cell's thinness. Squamous epithelium is found specifically in the alveoli of the lungs. The main function of the squamous epithelium in the alveoli is to facilitate gas exchange between the lungs and the bloodstream.

Pulmonary capillaries surround the alveoli. In the alveoli, oxygen molecules from inhaled air dissolve into the thin layer of moisture that lines the alveolar walls. This creates a high concentration of oxygen in the alveoli. Deoxygenated blood from the pulmonary arteries is pumped into the pulmonary capillaries surrounding the alveoli. The blood flows through these capillaries in near proximity to the alveolar walls.

Due to the concentration gradient, oxygen molecules diffuse from the alveoli across the alveolar membrane and into the bloodstream. The oxygen molecules move from an area of high concentration to an area of low concentration facilitated by simple diffusion.Once in the bloodstream, oxygen molecules bind to hemoglobin molecules in red blood cells, forming oxyhemoglobin. This oxygenated blood is then carried away from the lungs by the pulmonary veins and distributed to the body's tissues.

Deoxygenated blood returning from the body's tissues contains high levels of carbon dioxide as a waste product of cellular metabolism. This blood is pumped into the pulmonary capillaries surrounding the alveoli. Carbon dioxide diffuses from the bloodstream across the alveolar membrane and into the alveoli. Once in the alveoli, carbon dioxide is exhaled from the lungs during expiration, along with the rest of the air in the alveoli.