My Respiratory Anatomy Paper

I know you will be just thrilled to read my descriptions of the respiratory anatomy!

1. Pharynx

a. Nasopharynx

The external nares, or nostrils, lead to the nasopharynx. The nasopharynx lies between the internal nares, or choanae, and the soft palate. On the lateral walls of the nasopharynx are the triangular pharyngeal ostia of the auditory tubes. These are bounded behind by the torus or cushion, a firm prominence formed by the medial end of the cartilage of the tube which elevates the mucous membrane. A vertical fold of mucous membrane, the salpingopharyngeal fold, stretches from the lower part of the torus; it contains the Salpingopharyngeus muscle. A second and smaller fold, the salpingopalatine fold, stretches from the upper part of the torus to the palate. Behind the ostium of the auditory tube is the pharyngeal recess, or fossa of Rosenmüller. The pharyngeal tonsils, or adenoids, are found on the posterior wall. Above the pharyngeal tonsil, the pharyngeal bursa forms an irregular flask-shaped depression which sometimes extends up as far as the basilar process of the occipital bone. The surface of the nasopharynx is covered by pseudostratified columnar epithelium. Goblet cells secrete mucus, which cleans, warms and moistens incoming air before it moved deeper into the respiratory tract. Blood vessels are seen at the base of the epithelium.

b. Oropharynx

The Oropharynx reaches from the soft palate to the epiglottis and hyoid bone. It opens anteriorly, through the isthmus faucium, into the mouth. In its lateral wall, between the two palatine arches, is the palatine tonsil.

c. Laryngopharynx
The Laryngopharynx, or hypopharynx, is the bottom part of the pharynx. It extends from the epiglottis to the cricoid cartilage of the larynx.
Along the oropharynx and the laryngopharynx, the epithelium changes to nonkeritinizing stratified squamous epithelium. The basement membrane varies in thickness and contains blood vessels as well.

2. Larynx
The larynx is a 1.5 inch long tube that is located in the throat below the base of the hyoid bone and tongue and anterior to the esophagus. Its walls are made up of nine rings of supportive cartilages supported by interconnecting ligaments, intrinsic and extrinsic muscles, and lined with mucosa. At the front is the thyroid cartilage, which creates the Adam's apple. The inferior horns of the thyroid cartilage rest on the ring-shaped cricoid cartilage which connects the larynx to the trachea. The cricoid cartilage is narrow in front and broader in back. The arytenoid cartilages are pyramid shaped. They sit on top of the back plate of the cricoid cartilage. At the superior tip of each arytenoid cartilage is a corniculate cartilage. They are shaped like small triangles. The cuneiform cartilages support the soft tissues of the aryepiglottic folds, which connect the arytenoid cartilages to the epiglottis. During swallowing, the cartilages close the entrance to the larynx so food and liquids cannot enter. The larynx also houses the vocal folds and ligaments. The vocal folds consist of connective tissues, muscles, and the vocal ligament which vibrates to produce the vocal sounds. The surfaces of the vocal folds are covered by stratified squamous epithelium. Directly above the vocal folds are the vestibular, or false folds. They are formed by a thick layer of respiratory mucosa and a vestibular ligament. The vestibular folds lubricate and protect the vocal folds. The glottis forms the entryway to the vocal folds. It opens to allow for sounds.

3. Trachea
The trachea is 4 to 5 inches long. It runs through the lower neck and chest. It lies just anterior to the esophagus. It conducts air between the larynx and the primary bronchi. It is composed of 16-20 hyaline cartilage rings.
The tracheal wall is composed of four layers of tissue. The luminal surface is lined by respiratory mucosa. Its epithelium contains goblet cells to produce mucus which warms, moistens and removes foreign particles from air flowing to the trachea.
The submucosa consists mostly of loose connective tissue. It contains seromucous glands, which secrete water and mucus to the luminal surface of the trachea through narrow ducts.
The cartilage rings compose the next layer of the trachea. The outermost layer is the adventitia. It is a band of loose connective tissue which holds the trachea in place in the chest cavity.

4. Bronchi
The primary bronchi split off from the trachea and one enters each lung. The secondary bronchi, also known as lobular bronchi, each enter one lobe of the lungs. The tertiary bronchi branch off from the secondary bronchi. They conduct air to and from the ten bronchopulmonary segments in the right lung and eight in the left lung. The bronchi also have a layer of respiratory mucosa on their luminal surface with mucus-secreting goblet cells. The next layer is a broken ring of smooth muscle fibers which contract during exhalation and relax during inhalation. There are plates of hyaline cartilage which supports the tissue. In the micrograph of the bronchus wall, the alveoli can be seen. The mucosa of the bronchus wall is stained deep pink. The cartilage plates are light blue.

5. Lungs
The lungs are relatively cone-shaped sacs. They lie behind the rib cage. The lungs of mammals have a spongy texture and are honeycombed with epithelium having a much larger surface area in total than the outer surface area of the lung itself. A healthy lung is pink. The base of the lungs rests on the diaphragm muscle. The right lung is slightly larger and has three lobes while the left has only two. The lungs contain the bronchi and alveoli. The lungs are enveloped by plurae. The visceral pleura adheres to the outer surface of the lung. The parietal pleura is an extension of the visceral pleura. The pleurae are serous membranes. They secrete a thin layer of pleural fluid into the cavity that separates them.

6. Bronchial Tree
The bronchial tree is composed of the branches from the main bronchi that penetrate the lungs to deliver air to the alveoli. It is called the bronchial tree because it has the appearance of an inverted tree with the trachea as the trunk, branching into the primary bronchi, which then branch into the secondary bronchi, which branch into the tertiary bronchi, which terminate in the alveoli. The alveoli are the “leaves” of the tree.

7. Alveoli
The alveoli are the spherical outcroppings of the respiratory bronchioles. They resemble clusters of grapes in their appearance. They have radii of about 0.1 mm and wall thicknesses of about 0.2 µm. They are the primary sites of gas exchange in the lungs. Alveoli have an epithelial layer and an extracellular matrix surrounded by capillaries. In some alveolar walls, there are pores between alveoli. There are two major pneumocytes in the alveolar wall: Type I cells that form the structure of an alveolar wall and type II cells that secrete surfactant to lower the surface tension of water The alveoli have an innate tendency to collapse because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids and pores help to equalize pressures and prevent collapse.
Bordering the lumen of the alveoli are wandering cells called alveolar phagocytes, or macrophages. These cells engulf dust, bacteria and other inhaled particles that are trapped in the pulmonary surfactant. After they become filled with debris, the macrophages migrate to the bronchioles, where they then get carried by ciliary action to the pharynx where they get swallowed. Alternatively, they may also migrate into the interstitium where they are then removed via the lymphatic vessels.
Information gathered from http://en.wikipedia.org/wiki/Alveoli and http://www.bioeng.auckland.ac.nz/physiome/ontologies/respiratory/cells.php

8. Type I and II alveolar cells
Type I alveolar cells cover about 95% of the alveolar surface. Type I alveolar cells are extremely thin. They occupy most of the alveolar surface area. Their external surfaces are covered with capillaries. Both their thinness and the capillaries surrounding them make these ideal cells for the diffusion of gases. They form a thin barrier through which gas exchange occurs. The basement membranes of the alveolar I cells and the capillary endothelium are actually fused together. Thus the exchange surface consists of the alveolar I cell membrane, the endothelial cell membrane, and the fused basement membranes. Type I alveolar cells do not divide.
Type II alveolar cells are cuboidal in shape with short microvilli along their apical surface. Their primary function is the secretion of surfactant.
Information primarily found at http://www.mededsys.com/courses_online/302/index.html