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Anatomy of Respiratory System with Special Reference to Anatomy of Lungs

Air passes through the body's airways through the nose and nasal cavity, which are the main external entrances to the respiratory system.

Anatomy of the respiratory system


Nasal cavity and nose

Air passes through the body's airways through the nose and nasal cavity, which are the main external entrances to the respiratory system. There is an anatomical structure on the face that includes cartilage, bone, muscle, and skin that provides support and protection to the nasal cavity. It is lined with hairs and mucus membrane and consists of a hollow space inside the nose and skull. Before reaching the lungs, air enters the nasal cavity where it is heated, moistened, and filtered. The mucus and hair lining the nasal cavity keep dust, mold, pollen, and other pollutants from reaching the body's internal organs. The moistened air that is exhaled into the environment returns to the nasal cavity as a result of exhalation through the nose.

Mouth

Oral cavity is a second external entrance for the respiratory tract, which is located in the mouth. The nasal cavity performs most of the functions of breathing in normal life, but the oral cavity can supplement or even replace them when needed. As a result of the shorter pathway for air entering the body from the mouth, air entering the lungs from the mouth cannot be heated or moisturized as well as air entering the body through the nose. In addition, there are no hairs or sticky mucus in the mouth to filter the air moving through the nasal cavity. By breathing through the mouth, you can get more air into your body more quickly due to its shorter distance and larger diameter.

Pharynx

In addition to being a muscular funnel, the pharynx also includes the esophagus and larynx, which are located at the superior ends of the esophagus and larynx. Each of the three parts of the pharynx is separated by a membrane: the nasal cavity, the oropharynx, and the laryngopharynx. Located behind the nasal cavity, the nasal cavity is known as the nasal cavity. The nasal cavity produces air that is inhaled through the nasopharynx, which descends through the oropharynx, which lies posterior to the oral cavity. Oropharynx is the entry point for air that enters the pharynx from the oral cavity. The air is then diverted to the laryngopharynx by the epiglottis, where it enters the larynx. Located between trachea and esophagus, epigallottis is a flap of elastic cartilage. The epiglottis covers the opening of the esophagus to ensure that air passes into the trachea when swallowing. It is during swallowing that the epiglottis covers the trachea, providing food with oxygen and preventing choking.

Larynx

In addition to connecting the laryngopharynx and the trachea, the larynx is also known as the voice box. The larynxes are located just anterior to the hyoid bone and superior to the trachea on the anterior region of the neck. There are several cartilage structures that make up the larynx. During swallowing, the epiglottis serves as a cover for the larynx, one of the laryngeal cartilage pieces. Located just below the epiglottis is a thyroid cartilage, known as the Adam's apple due to its common appearance in males. Thyroid hormone is responsible for maintaining the opening of the larynx and protecting the vocal folds. Cricoid cartilage is located beneath the thyroid cartilage, supporting the larynx posteriorly and holding it open. Vocal folds are special structures present in the larynx, as well as cartilage, that allow the body to produce the sounds associated with speech and singing. Voices are made by vibrating mucous membranes in the vocal folds. Vocal folds vibrate at varying speeds and tensions depending on the pitch.

Trachea

There are five rings of hyaline cartilage in the trachea, or windpipe. Its inner surface is made up of pseudostratified ciliated columnar epithelium. The larynx and bronchi are connected by the trachea, which allows air to flow from the neck into the thorax. Tracheal cartilage rings leave the airways always open because the trachea consists of cartilage rings. To accommodate the massive amounts of food that enter the esophagus, the open end of the cartilage rings faces posteriorly. In short, the trachea is responsible for providing airways for entering and exiting the lungs. The tracheal epithelium also produces mucus to prevent dust and other contaminants from entering the lungs. Mucus is transported from the pharynx to the gastrointestinal tract by cilia attached to the surface of the epithelial cells.

Bronchi and bronchioles

A bronchial divide occurs at the inferior end of the trachea, where there are left and right bronchi, respectively. Right and left bronchi split into smaller secondary bronchi prior to entering the lungs. These bronchi are the pathways through which air enters the lungs. Right and left lobes of the lung are supplied with air by secondary bronchi. Within each lobe, tertiary bronchi are divided back into numerous smaller branches. Several smaller bronchioles branch out from the tertiary bronchi that extend throughout the lungs. There are also smaller branches of bronchioles called terminal bronchioles that extend from the main bronchiole. The lung's alveoli are supplied with air by the millions of terminal bronchioles. In the process of splitting the bronchi and bronchioles into tree-like branches, the airway's walls begin to change structure. Its cross-section resembles a flattened circle or letter D due to its many C-shaped cartilage rings that keep the airway open. Further branching of the bronchi causes the cartilage to become widely separated and more smooth muscle and elastin protein to accumulate in their walls. A major difference between bronchioles and bronchi is that bronchioles never contain cartilage at all. A smooth muscle and elastin scaffold supports the bronchi and bronchioles that are smaller and more flexible. In the process of splitting the bronchi and bronchioles into tree-like branches, the airway's walls begin to change structure. During development, the primary bronchi include many C-shaped cartilage rings that hold the airway open while giving it a circular cross-section. Further branching of the bronchi causes the cartilage to become widely separated and more smooth muscle and elastin protein to accumulate in their walls. A major difference between bronchioles and bronchi is that bronchioles never contain cartilage at all. Because the smaller bronchi and bronchioles are covered with smooth muscles and elastin, they are much more flexible and contractile.

Anatomy of Lungs

The lungs, which are large, spongy organs located directly above the diaphragm in the thorax, are located either side of the heart. Pleural membranes surround every lung, which provide space for expansion and negative pressure in comparison to the outside of the body. Negative pressure facilitates passive air filling as the lungs relax. The left lung is slightly smaller and its shape differs from the right due to the heart pointing left. Due to these differences, the left lung is a bit smaller than the right lung, with just two lobes instead of three on the right lung. A lung's interior is composed of more than 30 million tiny sacs, an alveolus, and a vast network of capillaries. Located at the terminals of the bronchioles, the alveoli are cup-shaped structures encircled by capillaries. A thin squamous epithelium lines the alveoli, which enables the air entering the alveoli to exchange gases with blood flowing through the capillaries.

Muscle respiration

The muscles that surround the lungs are responsible for causing air to be exhaled or inhaled. Humans breathe through their diaphragms, thin sheets of skeletal muscle that make up the floor of the thorax. Diaphragm contraction expands the thoracic cavity and increases lung capacity by moving the diaphragm inferiorly into the abdominal cavity. Diaphragm relaxation during exhalation allows lungs to empty. Several intercostal muscles help expand and compress the lungs when the diaphragm contract or expands. In the inner and outer intercostal spaces, there are two separate muscle groups. The deeper set of intercostal muscles centers in the middle of the ribs, compressing the thoracic cavity to force the lungs to expel air from them. Intercostals are located superficially on the ribs and act to elevate the ribs, allowing more air to enter the thoracic cavity and the lungs.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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