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Bronchi and Bronchioles



At the inferior end of the trachea, the airway splits into left and right branches known as the primary bronchi. The left and right bronchi run into each lung before branching off into smaller secondary bronchi. The secondary bronchi carry air into the lobes of the lungs—2 in the left lung and 3 in the right lung. The secondary bronchi in turn split into many smaller tertiary bronchi within each lobe. The tertiary bronchi split into many smaller bronchioles that spread throughout the lungs. Each bronchiole further splits into many smaller branches less than a millimeter in diameter called terminal bronchioles. Finally, the millions of tiny terminal bronchioles conduct air to the alveoli of the lungs.

The trachea

The trachea


The trachea (or windpipe) is a wide, hollow tube that connects the larynx (or voice box) to the bronchi of the lungs. It is an integral part of the body’s airway and has the vital function of providing air flow to and from the lungs for respiration.

The trachea begins at the inferior end of the larynx in the base of the neck. It is located along the body’s midline, anterior to the esophagus and just deep to the skin, so that it is possible to feel the larynx through the skin of the neck. From its origin at the larynx, the trachea extends inferiorly into the thorax posterior to the sternum. In the thorax, the trachea ends where it splits into the left and right bronchi, which continue onward toward the lungs.

The larynx

The larynx


The larynx is a tough, flexible segment of the respiratory tract connecting the pharynx to the trachea in the neck. It plays a vital role in the respiratory tract by allowing air to pass through it while keeping food and drink from blocking the airway. The larynx is also the body’s “voice box” as it contains the vocal folds that produce the sounds of speech and singing.

The pharynx

The pharynx


The pharynx is cone-shaped passageway leading from the oral and nasal cavities in the head to the esophagus and larynx. The pharynx chamber serves both respiratory and digestive functions. Thick fibres of muscle and connective tissue attach the pharynx to the base of the skull and surrounding structures. Both circular and longitudinal muscles occur in the walls of the pharynx; the circular muscles form constrictions that help push food to the esophagus and prevent air from being swallowed, while the longitudinal fibres lift the walls of the pharynx during swallowing.

The nasopharynx

The nasopharynx


The nasopharynx is, by definition, the upper part of the throat behind the nose. It is a part of the pharynx, which comprises three separate segments: the nasopharynx, oropharynx, and the hypopharynx.

The nasopharynx is 2 to 3 cm wide and 3 to 4 cm long and situated behind the nasal fossa inside the occipital bone. The nasopharynx is the space above the soft palate at the back of the nose and connects the nose to the mouth, which allows a person to breathe through the nose. The soft palate separates the nasopharynx from the oropharynx, which sits just below the soft palate.

Nose, Sinuses and Smell

Nose, Sinuses and Smell


Smell is often considered the least important of all the senses, but it may be one of the oldest, and probably acts on the subconscious more than the other senses.

Most of the nose is concerned with filtering and providing a passage for air on its way to the lungs. The walls of the nasal cavity enable both these functions. In particular, the nasal conchae are filled with mucosal respiratory membranes coated in cilia-tiny hair-like cells that act to move waves of mucus toward the throat. These protections trap inhaled bacteria, dirt, viruses, and chemical particles in the mucus. The cilia and swallowing action then serve to sweep the allergens and infectious agents into the back of and down the throat for destruction (digestion) in the stomach.

The mouth

The mouth


Also known as the oral cavity, the mouth is the hollow cavity that allows food and air to enter the body. The mouth contains many other organs - such as the teeth, tongue, and the ducts of the salivary glands - that work together to aid in the ingestion and digestion of food. The mouth also plays a major role in the production of speech through the movements of the tongue, lips and cheeks.

The mouth is a hollow cavity formed by the space between the lips, cheeks, tongue, hard and soft palates and the throat. Its external opening is located along the body’s midline inferior to the nose and superior to the chin. The external opening of the mouth is usually much longer in the horizontal plane, but may be extended through the movement of the jaw to become nearly as wide in the vertical plane as well.

Lungs and Respiratory System of the Chest



The respiratory system of the upper abdomen and chest includes the structures involved in the vital delivery of atmospheric air and the exchange of gases between the body and atmospheric air. The human body requires a constant supply of oxygen from the atmosphere for the cellular growth and metabolism that keep the body alive. At the same time, carbon dioxide that forms as a waste product of cellular metabolism must be eliminated from the body and released into the atmosphere before reaching toxic levels.

Atmospheric air enters the body through the mouth and nose and arrives in the chest through the trachea, or windpipe. The trachea is a large open tube lined with rings of cartilage. The cartilage of the trachea provides a flexible rigidity that maintains an open airway to and from the lungs at all times. At its inferior end the trachea branches into two bronchi that each enter one of the lungs. Inside the lung each bronchi further branches into several smaller secondary bronchi, which in turn further branch into many smaller tertiary bronchi and finally branch into many tiny, flexible bronchioles. These air passages are collectively known as the bronchial tree and serve to deliver air to the millions of tiny cup-like alveoli found throughout each lung.

The anus

The anus


The anus, or anal canal, is the final segment of the gastrointestinal tract. It acts as the orifice that feces pass through during defecation.

Anatomy of the anus

The anus is a short tube at the end of the rectum that ends at the body’s exterior. It is around 1 inch (2-3 cm) long and varies widely in its diameter depending on how distended it is. The superior end of the anus is continuous with the tissue of the rectum and is lined with simple columnar epithelial tissue. This tissue forms folds known as anal columns, with valleys known as anal valves between the folds.

The rectum



The rectum is the final segment of the large intestine that connects the colon to the anus. It stores fecal matter produced in the colon until the body is ready to eliminate the waste through the process of defecation.

Anatomy of the rectum

The rectum is a hollow muscular tube about 8 inches (20 cm) in length and 2½ inches in diameter at its widest point. It extends from the inferior end of the sigmoid colon along the anterior surface of the sacrum and coccyx in the posterior of the pelvic cavity. At its inferior end, the rectum tapers slightly before ending at the anus.