Respiratory System - High School Biology

The respiratory system is responsible for the exchange of oxygen and carbon dioxide gases between the body and its external environment. The respiratory organs—the lungs—contain alveoli, where gas exchange occurs in concordance with expiration and inspiration, or breathing.

The other choices refer to other organ systems—namely the circulatory, immune, and excretory systems—which should not be confused with the respiratory system.

The respitory system transports oxygen to the blood, removes CO2 from the blood, regulates blood acidity, and helps to regulate body temperature. It is the endocrine system that secretes hormones into the blood.

The alveoli are small vessels which increase the surface area available for gas exchange into and out of blood. Oxygen diffuses into the blood while carbon dioxide diffuses out of the blood. These vessels have no control over how much blood is present in the lungs. Also, while these vessels do keep certain things out of the bloodstream, their purpose is not to filter particles. The main filter for our lungs is the mucus coating over the tissues and in our mouth and nose.

The larynx, or voice box, contains the vocal cords, which are the source of sound production. The pharynx, or throat, has a dual role in respiration and digestion. The pharynx receives air from the nasal cavity and food and drink from the oral cavity. The trachea, or windpipe, is a rigid tube that transports air from the larynx to the bronchi. The bronchi in turn transport air into the lungs. The alveoli are thin-walled sacs where the exchange of gasses between the lungs and the blood occurs.

The diaphragm separates the thoracic cavity from the abdominal cavity. When it contracts, it flattens downward and permits the lungs to expand, promoting inhalation. When it relaxes, it rises and compresses the lungs, promoting exhalation. The internal oblique muscle fibers are directed upward from the iliac crest (hip bone) to the lower ribs. The masseter muscle is involved in chewing. The deltoid is a large triangular muscle that covers the shoulder joint. The vastus lateralis extends the leg and is located in the anterior thigh.

Hiccups are reflex spasms of the diaphragm, causing an involuntary inhalation followed by a sudden closure of the glottis that produces an audible sound, the "hic." Snoring is the sound produced while breathing through the mouth during sleep. Sneezing is caused by irritants in the nasal cavity. The glottis stays open while the tongue and soft palate block the flow of air from getting out. Then they suddenly release to let air burst through the nose. Coughing is triggered by irritants in the respiratory tract. High pressure forms in the lower respiratory tract when the glottis closes and muscles contract. The glottis then suddenly opens to release an explosive blast of air. Anxiety may trigger an increase in respiration, hyperventilation, which results in lowered carbon dioxide levels.

The respiratory system is responsible for moving air into and out of the lungs, where gas exchange occurs between the alveoli and the pulmonary capillaries. The lungs exchange oxygen and carbon dioxide via alveoli and networks of small blood vessels known as capillaries. Production of gametes is a function of the reproductive system. Movement of blood and nutrients throughout the body is the primary function of the circulatory system. Movement and coordination is controlled by the nervous system and requires the structures of the muscular and skeletal systems.

Tidal volume is nominally and conceptually similar to an ocean tide. Under calm conditions, a tide is not particularly extreme at either its low or high points. During normal, relaxed respiration, an animal breathes in and out moderate volumes of air, creating its tidal volume.

As the air enters the human body when it is inhaled, it passes through the mouth (or nose) and is warmed. It then passes through the pharynx and into the cartilage-ringed trachea. From the trachea, the air can pass into either the right or left bronchi, which brings air to the right or left lung, respectively. The bronchi branch into many bronchioles and eventually into alveoli, where gas exchange occurs.

The esophagus is part of the digestive system, and transports food from the mouth to the stomach.

The mouth and pharynx are the first two structures air travels through during inspiration, or inhalation, in the respiratory system. The pharynx is located at the back of the mouth, and is the upper region of the throat that connects the nose and mouth.
Although there is a tendency to confuse the trachea and the esophagus, students should understand the fundamental difference. The trachea is a respiratory structure, which transports air and gases between the external atmosphere and the internal environment of the lungs. The esophagus is a digestive system structure, which, through the muscular contractions of peristalsis, carries ingested food down to the stomach. Thus, esophagus is the correct answer.

The larynx contains the vocal cords and conducts air from the pharynx to the trachea.

The pharynx is the region of the back of the mouth/nose and upper throat. The trachea conducts air between the larynx and the bronchi. The bronchi conduct air from the trachea to the lungs. The epiglottis is a flap of cartilage in the pharynx that covers the opening to the larynx during swallowing and directs food and liquids down the esophagus.

The organs of the respiratory system are organized into the upper respiratory tract and the lower respiratory tract. The upper respiratory tract includes the nasal mucosa, the trachea, the bronchi, and the larynx. The lower respiratory tract consists of the bronchioles and alveoli.

Pre-alveolar and post-alveolar refer to the transfer of oxygen and carbon dioxide between air and blood. Exocrine and endocrine refer to organs needed in the creation and release of hormones and secretions.

The pharynx, larynx, trachea, and bronchi are all part of the respiratory tract.

The esophagus is part of the digestive tract, while the thyroid gland is part of the endocrine system.

The respiratory system is primarily used to transport air, while the digestive system is used to transport fluids (such as water) and solids (such as food particulates). The respiratory and the digestive systems share the region of the mouth and upper throat, where air, fluids, and solids can be mixed. This region is known as the pharynx, and is the correct answer.

The larynx is a region located below the pharynx and is the area in which the tract divides into the respiratory tract and digestive tract. Solids and liquids are transported through the esophagus and into the stomach, while air enters the trachea to be transported to the lungs via the bronchi. The epiglottis is a cartilage flap that prevents solids and liquids from entering the trachea. The vocal cords are located in the respiratory tract only.

The larynx is considered to be the "voice box" and contains the vocal cords. Speech is created by vibrations in the flaps that make up the vocal cords.

Other parts of the respiratory system include the trachea and bronchus, which both help to transport air to the lungs. The epiglottis is a flap attached to the entrance of the larynx in order to prevent foreign objects, such as food or water, from entering. The uvula hangs from the posterior edge of the middle of the soft palate.

The trachea divides into two when it enters the lungs, a process known as bifurcation. The result is the two pathways known as the prinary bronchi. The bronchi continue to branch into more and more bronchioles throughout the lungs.

The nasal mucosa helps warm incoming air. The trachea becomes thinner when it enters the lungs, as opposed to wider and thicker. Alveoli are responsible for absorbing oxygen; oxygen cannot be absorbed by neighboring capillaries in the trachea or bronchi.

The trachea bifurcates (splits in two) to create the left and right bronchi upon entering the lungs.

Bronchioles arise from the subsequent branching of the bronchi, and eventually send oxygenated air to the alveoli for gas exchange with deoxygenated blood via adjacent capillary beds. The esophagus is used to transport food and liquids from the mouth to the stomach, and is not involved in the respiratory system or lungs.

The process of air moving into and out of the lungs is called pulmonary ventilation. Cellular respiration refers to the process by which fuel molecules are converted into energy molecules such as ATP (think back to glycolysis, Krebs cycle, and electron transport). Pulmonary respiration refers to the specific process of gas exchange between the body (capillaries) and the environment (air inside the alveoli).

Aleveoli are small sacs in the lungs which help with the exchange of carbon dioxide and oxygen from the bloodstream to the lungs. The trachea and bronchi are surrounded by thick connective tissue (cartilage) and thus, their walls are much too thick to allow gas exchange, thus they function to transport air to and from the alveoli. The pleura are the membranes surrounding the lungs and lining the thoracic wall, and thus never come into direct contact with air. The thorax is not a part of the lungs, rather, it is the anatomical region we commonly refer to as the chest.