Pharynx

The respiratory system is divided into the upper and lower respiratory systems. The upper respiratory system includes the structures above the larynx, while the lower respiratory system includes the structures below the larynx.

The upper respiratory system includes the paranasal sinuses, nasal conchae, nose, nasal cavity, posterior nasal apertures, nasopharynx, tongue, and hyoid bone.

The lower respiratory system includes the larynx, esophagus, trachea, bronchi, lungs, clavicle, bronchioles, right lung, ribs, left lung, and diaphragm.

The pharynx is a passageway that connects the nose, mouth, and throat. It starts at the base of the skull and extends to the inferior border of the cricoid cartilage (C6), where it connects to the esophagus.

The pharynx is composed of skeletal muscle and mucous membranes and is divided into three parts: the nasopharynx, oropharynx, and laryngopharynx.

The nasopharynx is the uppermost section of the pharynx and lies posterior to the nasal cavity, extending to the soft palate. It contains the pharyngeal opening of the auditory (Eustachian) tube, the pharyngeal tonsil (adenoids when enlarged), and lymphoid tissue in the roof and posterior nasopharynx.

The oropharynx is the middle section of the pharynx and extends from the soft palate to the superior border of the epiglottis. It consists of the pharyngeal arch and uvula and contains the salpingopharyngeal fold, which covers the salpingopharyngeus muscle. The soft palate forms the posterior portion of the roof of the mouth.

The laryngopharynx is the lowest section of the pharynx and extends from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it is continuous with the esophagus. It lies posterior to the larynx and marks the entrance to the trachea and esophagus.

The pharyngeal muscles are divided into two layers: the external circular layer and the internal longitudinal layer. These muscles help elevate the larynx and pharynx during swallowing and are innervated by the vagus nerve (CN X) and glossopharyngeal nerve (CN IX).

The pharynx receives blood supply from the ascending pharyngeal, superior thyroid, ascending and descending palatine arteries, and pharyngeal branches of the maxillary artery. It is drained by the pharyngeal venous plexus, which flows into the internal jugular vein.

The pharyngeal plexus is formed by the glossopharyngeal nerve (CN IX), vagus nerve (CN X), and postganglionic sympathetic fibers from the superior cervical ganglion. This plexus innervates the pharyngeal constrictors and soft palate.

The palatine tonsil, one of the tonsils in the pharynx, is innervated by the glossopharyngeal nerve (CN IX). It receives blood supply from the tonsillar branch of the facial, ascending palatine, and dorsal lingual arteries.

Lymphoid tissue is found in the tonsils, pharyngeal, and posterior nasal walls and is part of Waldeyer's tonsillar ring, which includes the lingual tonsils, tubal tonsils, and pharyngeal tonsil.

The respiratory system is responsible for gas exchange, which is the process of taking in oxygen and releasing carbon dioxide.

The upper respiratory system filters, warms, and humidifies air before it reaches the lungs.

The lower respiratory system is where gas exchange takes place in the tiny air sacs called alveoli.

The larynx is a cartilaginous box that connects the pharynx to the trachea. It contains vocal cords, which vibrate to produce sound during speaking.

The trachea is a tube that carries air from the larynx to the bronchi. It is made of cartilage rings that keep it open.

The bronchi are two branches of the trachea that lead to the lungs. They further divide into smaller and smaller tubes called bronchioles.

The lungs are two spongy organs that are responsible for gas exchange. They are located in the chest cavity and are protected by the rib cage.

The diaphragm is a muscular sheet that separates the chest cavity from the abdominal cavity. It plays a key role in breathing by contracting and relaxing to change the volume of the chest cavity.

The alveoli are tiny air sacs in the lungs where gas exchange takes place. Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.

Breathing is the process of inhaling and exhaling air. Inhalation brings oxygen into the lungs, while exhalation removes carbon dioxide from the lungs.