Respiratory system

The cells of the human body require a constant stream of oxygen to stay alive. The respiratory system provides oxygen to the body’s cells while removing carbon dioxide, a waste product that can be lethal if allowed to accumulate. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration. The airway, which includes the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles, carries air between the lungs and the body’s exterior. The lungs act as the functional units of the respiratory system by passing oxygen into the body and carbon dioxide out of the body. Finally, the muscles of respiration, including the diaphragm and intercostal muscles, work together to act as a pump, pushing air into and out of the lungs during breathing.

Pulmonary Ventilation
Pulmonary ventilation is the process of moving air into and out of the lungs to facilitate gas exchange. The respiratory system uses both a negative pressure system and the contraction of muscles to achieve pulmonary ventilation. The negative pressure system of the respiratory system involves the establishment of a negative pressure gradient between the alveoli and the external atmosphere. The pleural membrane seals the lungs and maintains the lungs at a pressure slightly below that of the atmosphere when the lungs are at rest. This results in air following the pressure gradient and passively filling the lungs at rest. As the lungs fill with air, the pressure within the lungs rises until it matches the atmospheric pressure. At this point, more air can be inhaled by the contraction of the diaphragm and the external intercostal muscles, increasing the volume of the thorax and reducing the pressure of the lungs below that of the atmosphere again.

To exhale air, the diaphragm and external intercostal muscles relax while the internal intercostal muscles contract to reduce the volume of the thorax and increase the pressure within the thoracic cavity. The pressure gradient is now reversed, resulting in the exhalation of air until the pressures inside the lungs and outside of the body are equal. At this point, the elastic nature of the lungs causes them to recoil back to their resting volume, restoring the negative pressure gradient present during inhalation.

The respiratory system of the head and neck marks the starting point for where oxygen enters the body. The system begins at the nose and mouth where oxygen is inhaled. The areas of the respiratory in the head and neck allow air to flow in and out of the lungs.

The important parts of the respiratory system in the head and neck include the nasal cavity, which processes the airflow on its way through to the lungs. Connected to the nasal cavity is the pharynx that is actually a part of the respiratory and digestive systems. It allows for the passage of both food and air. It lies behind and to the sides of the larynx, or voice box, which forms part of a tube in the throat that carries air to and from the lungs and houses the epiglottis. At rest, the epiglottis is upright and allows air to pass through the larynx and into the rest of the respiratory system. During swallowing, it folds back to cover the entrance to the larynx, preventing food and drink from entering the windpipe. The trachea, or windpipe, allows the head and neck to twist and bend during the process of breathing.

All of these parts in the head and neck play a significant role in directing oxygen to the lungs so that the body can breathe in oxygen.

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.

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.

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 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.

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 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 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.