respiratory system

Respiratory system:

External respiration refers to the gas exchange between the lungs and blood. Internal respiration is between the cells and the circulatory system

The underside of the external nose contains two external nares, or nostrils. The root of the nose is the superior attachment, between the eyes. The inside of the internal and external nose make up the nasal cavity, divided into halves by the nasal septum. The anterior portion is the vestibule, surrounded by cartilage. The posterior, or upper nasal cavity is surrounded by bone. The vestibule is lined with coarse hair that strains large particles from the air. The conchae of the skull divide the upper nasal cavity into superior, medial, and inferior meatuses. These are lines with a sticky mucus (not to mention the nerve endings for our sense of smell) traps dust particles and the numerous capillaries. The surface cells also are covered in cilia, which moved the trapped particles in the mucus to the throat

The uppermost section of the pharynx, or throat, is the nasopharynx, which is located posterior to the soft palate. In it's walls are four openings: two internal nares and two opening of the eustachian tubes. THe posterior wall also contains the pharyngeal tonsils, or the adenoids. The nasopharynx is lined with pseudostratified ciliated epithelium

The middle portion of the pharynx is known as the oropharynx. It has only one opening, the fauces, the opening from the mouth

The laryngopharynx, the inferior throat, extends from the hyoid down to the split of the pharynx into the esophagus and trachea. It is lined with stratified squamous epithelium

The larynx, or voice box, is a small passage which connects the pharynx and the trachea, located between the fourth and sixth cervical vertebrae. On either side of the vocal cards are fleshy folds of tissue called the ventricular folds, or false vocal cords

The thyroid cartilage, or Adam's apple, is two plated of cartilage fused together in a triangular shape to protect the top of the trachea on the anterior aspect

Rings of cartilage keep the trachea open at all times. The most superior and thickest of these rings is the cricoid cartilage. On the superior border of the cricoid cartilage are small, pyramidal outcroppings: the arytenoid cartilages. Their actions move the vocal cords

The trachea terminates in the chest, dividing into the left and right primary bronchi. These, in turn become the secondary (lobar) bronchi, then the tertiary (segmental) bronchi, dividing into the bronchioles. The bronchioles divide into terminal bronchioles, the overall branching effect referred to as the bronchial tree

Each main segment (lobe) of the lungs is then divided into smaller parts called lobules. Lobules each contain a lymphatic vessel, an arteriole, a venule, and a branch from one of the terminal bronchiole. The terminal bronchiole then breaks up into microscopic branches by the name of respiratory bronchioles. The simple epithelium goes from cuboidal to squamous, and then divide into two to eleven alveolar ducts

About each alveolar duct the alveoli. The alveoli are cup-shaped pouches lined with simple squamous epithelium (two types of cells: squamous pulmonary epithelial cells and septal cells. The first are larger and make up the main bulk of the walls. The septals secrete a phospholipid called surfactant to lower surface tension in the alveoli), interspersed with free alveolar macrophages, commonly called dust cells. Over the alveoli, the venules and arterioles become a delicate network of capillaries to gather up the needed oxygen

Breathing in, or inspiration, is done by pulling the diaphragm down and expanding the ribs, thus decreasing the total air pressure in the lungs and drawing in outside air. The diaphragm and muscles drawing the rib cage relax, and the pressure increases, forcing the air out (expiration). The main muscle used in this process are the various abdominis muscles, diaphragm, internal and external intercostals, and a little bit of help from the scalenus and sternocleidomastoid