The Respiratory System

The Respiratory System Chapter 21

Introduction • The trillions of cells making up the body require a continuous supply of oxygen to carry out vita functions • We can survive only a few minutes without oxygen • As cells use oxygen, they give off carbon dioxide a waste product of cellular respiration which the body must eliminate

Introduction • The major function of the respiratory system is to supply the body with oxygen and dispose of carbon dioxide • To achieve this function four distinct processes, collectively called respiration occur • Pulmonary ventilation • External respiration • Transport of respiratory gases • Internal respiration (cellular respiration)

Introduction • Pulmonary ventilation • Air must be moved in and out of the lungs so that the gases in the air sacs (alveoli) of the lungs are continually changed and refreshed • This air movement is commonly called ventilation or breathing

Introduction • External respiration • Gas exchange (oxygen loading and carbon dioxide unloading) must occur between the blood and the air-filled alveoli of the lungs

Introduction • Transport of respiratory gases • Oxygen and carbon dioxide must be transported between the lungs and tissue cells of the body • This is accomplished by the cardiovascular system, which uses blood as the transporting fluid

Introduction • Internal respiration • At the systemic capillaries, gas exchanges (oxygen unloading and carbon dioxide loading) must be made between the blood and tissue cells

Respiratory System • The organs of the respiratory system include the nose, nasal cavity, paranasal sinuses pharynx, larynx, trachea, bronchi, and the lungs which contain the terminal air sacs or alveoli

Respiratory System • Functionally, the respiratory structures are divided into respiratory and conducting zones • Visible structures represent the conducting zone • Respiratory zone structures are small and lie deep within the lungs

Respiratory System • Functionally, the respiratory system consists of the respiratory and the conducting zones • The respiratory zone, the actual site of gas exchange, is composed of the respiratory bronchioles, alveolar ducts, and alveoli • The conducting zone includes all other respiratory passageways, which provide fairly rigid conduits for air to reach the sites of gas exchange

Respiratory System • Organs of the conducting zone clean, warm and humidify the incoming air • Thus, the air reaching the lungs contain must less dust than what entered the nose and is warm and damp

The Nose • The nose is the only externally visible part of the respiratory system • The external framework of the nose

The functions of the nose include Providing an airway for respiration Moistening and warming entering air Filtering inspired air and cleansing it of foreign matter Serving as a resonating chamber for speech Housing the olfactory (smell) receptors The Nose

The Nose • The structures of the nose are divided into the • External nose • Nasal cavity • Surface features • Root (between eyes) • Bridge • Dorsum nasi • Apex • Philtrum • External nares • Alae

The Nose - Nasal Cavity • The nasal cavity lies in and posterior to the external nose • During breathing air enters the external cavity by passing through the external nares or nostrils • The nasal cavity is divided by a midline nasal septum • The nasal cavity is continuous posteriorly with the nasal portion of the pharynx through the internal nares

The Nose - Nasal Cavity • The roof of the nasal cavity is formed by the ethmoid and sphenoid bones of the skull • The floor is formed by the palate which separates it from the oral cavity below • Anteriorly, where the palate is supported by the maxillary processes and the palatine bones is considered the hard palate • The unsupported posterior portion is the muscular soft palate

The Nose - Nasal Cavity • The vestibule is lined with skin containing sebaceous and sweat glands and numerous hair follicles • The hair, or vibrissae, filter coarse particles from inspired air

The Nose - Nasal Cavity • The nasal cavity is lined with two types of mucous membrane • The olfactory mucosa, lining the slitlike superior region of the nasal cavity, contain the receptors for the sense of smell • The balance of the nasal cavity is lined with respiratory mucosa

The Nose - Respiratory Mucosa • The respiratory mucosa is made up of pseudostratified columnar epithelium, containing scattered goblet cells, that rests on a lamina propria • This lamina propria is richly supplied with compound tubuloalveolar glands that contain mucous and serous cells • Mucous cells secrete mucus, whereas serous cells in glands secrete a watery fluid containing digestive enzymes

The Nose - Respiratory Mucosa • Each day the mucous glands secrete about a quart of sticky mucous containing lysozyme, an antibacterial enzyme • The mucous traps inspired dust, bacteria and other debris, while lysozyme attacks and destroys bacteria chemically • The epithelial cells of the respiratory mucosa also secrete defensins, natural antibotics that help to get rid of invading microbes

The Nose - Respiratory Mucosa • The ciliated cells of the respiratory mucosa create a gentle current that moves the sheet of contaminated mucus posteriorly toward the throat where it is swallowed and digested by stomach juices • These ciliated cells become sluggish in cold weather allowing mucus to accumulate in the nasal cavity where it “runs” on a cold day when you come inside

The Nose - Respiratory Mucosa • The nasal mucosa is richly supplied with sensory nerve endings • A sneeze reflex is stimulated when irritating particles (dust, pollen) contact this sensitive mucosa • The sneezing propels air outward in a violent burst, expelling the irritant from the nose

The Nose - Respiratory Mucosa • A rich plexus of thin walled capillaries underlies the lamina propria of the nasal mucosa and warms the incoming air as it flows across the mucosal surface • Blood flow increases when the temperature decreases • Because of its superficial location and the extent of vessels, nosebleeds are common and often profuse

The Nose - Nasal Conchae • Protruding medially from each lateral wall of the nasal cavity are three mucosa-covered projections, the superior, middle of the ethmoid bone and inferior conchae which is a separate bone

The Nose - Nasal Conchae • The groove inferior to each concha is a meatus • As inhaled air moves over the concha the turbulance created increases the amount of contact between the nasal mucosa and this inspired air • This acts to trap particulates in mucus

The Nose - Nasal Conchae • The conchae and nasal mucosa not only function during inhalation to filter, heat, and moisten air, but also act during exhalation to reclaim this heat and moisture • This reclamation mechanism minimizes the amount of moisture and heat lost from the body through breathing, helping us to survive in dry and cold climates

The Nose - Paranasal Sinuses • The nasal cavity is surround by sinuses located in the frontal, sphenoid, ethmoid and maxillary bones • They function to • Produce mucus • Lighten the skull • Warm the air • Voice resonance

The Pharynx • The pharynx is the funnel shaped passage way than connects the nasal cavity and mouth superiorly to the larynx and the esophagus inferiorly • Nasopharynx, oropharynx, laryngopharynx

The Pharynx • The pharynx serves as a common pathway for food and air • The pharynx extends for about 5 inches from the base of the skull to the level of the sixth cervical vertebrae • In the context of the digestive tract, the pharynx is commonly called the throat

The Pharynx • On the basis of location and function, the pharynx is divided into nasopharynx, oropharynx, laryngopharynx • The muscular wall of the pharynx consists of skeletal muscle throughout its length, but the nature of the mucosal lining varies among the three pharyngeal regions

The Nasopharynx • The nasopharynx lies above the point of food entry, it serves only as an air passageway • During swallowing the uvula reflects posteriorly to close off the nasopharynx and prevent food from entering the nasal cavity

The Nasopharynx • The nasopharynx is continuous with the nasal cavity through the internal nares • It ciliated pseudostratified epithelium produces mucus • Mucosa high on the posterior wall contains masses of lymphatic tissue, the pharyngeal tonsils or adenoids

The Oropharynx • The oropharynx lies posterior to the oral cavity and is continuous with it through an archway called the fauces • Both swallowed food and air pass through • Lined with stratified squamous epithelium for protection from food abrasion and chemical trauma

The Oropharynx • Two tonsils lie embedded in the oropharyngeal mucosa • Paired palatine tonsils • Lingual tonsil (posterior surface of the tongue)

The Laryngopharynx • The laryngopharynx serves as a common pathway for food and air and is lined with stratified squamous epithelium • It lies directly posterior to the upright epiglottis and extends to the larynx where the digestive and respiratory pathways diverge

The Laryngopharynx • The esophagus conducts food to the stomach while air enters the larynx anteriorly • During swallowing food has the “right of way” and air passage temporarily stops

The Larynx • The larynx attaches to the hyoid bone superiorly and opens into the laryngopharynx • Inferiorly is is continuous with the trachea

The Larynx • The larynx has three important functions • It provides an airway for respiration • Act as a switching mechanism to route air and food into the proper channels • Vocal cords housed in larynx are used in voice production

The Larynx • The framework of the larynx is an arrangement of nine cartilages connected by membranes and ligaments • Except for the epiglottis, all laryngeal cartilages are made of hyaline

The Larynx • The large, shield shaped thyroid cartilage is formed by the fusion of two cartilage plates • The laryngeal prominence marks the midline fusion point • The cricoid cartilage is anchored to the trachea inferiorly

The Larynx • Three pairs of small cartilages, the arytenoid, cuneiform and corniculate form part of the lateral and posterior walls of the larynx • The arytenoid anchors the vocal cords

The Larynx • The ninth cartilage the flexible, spoon shaped epiglottis is composed of elastic cartilage • It is almost entirely covered by mucosa • The epiglottis extends from the posterior aspect of the tongue to its anchoring point on the thyroid cartilage

The Larynx • When only air is flowing into the larynx, the inlet to the larynx is open wide and the free edge of the epiglottis projects upward • During swallowing the larynx is pulled superiorly and the epiglottis tips to cover the laryngeal inlet

The Vocal Folds • The vocal ligaments attach the arytenoid and thyroid cartilages • These ligaments are composed of elastic fibers • The vocal cords vibrate, producing sound as air rushes up from lungs

The Vocal Folds • The opening through which air passes is the glottis • Superior to the vocal cords are the vestibular cords which play no part in voice production

Vocal Folds • Stratified squamous epithelium lines the superior portion of the larynx, an area subject to food contact • Below the vocal folds the epithelium is pseudostratified ciliated columnar epithelium • Cilia move the mucus away from our lungs

Voice Production • Speech involves the intermittent release of expired air and opening and closing of the glottis • The length of the true vocal cords and the size of the glottis are altered by the action of the intrinsic laryngeal muscles most of which move the arytenoid cartilages • As the length and tension of the vocal folds change, the pitch of the sound is altered

Voice Production • The glottis is wide when we produce deep tones and narrows to a slit for high pitched sounds • Length and thickness of the vocal folds changes for males during puberty • Loudness of the voice depends on the force with which the airstream rushes across the vocal cords • The greater the force, the stronger the vibration and the louder the sound

Sphincter Functions of Larynx • The vestibular folds can perform a sphincter function under certain conditions • In abdominal straining associated with defecation and urination, inhaled air is held temporarily in the lower respiratory tract by closing the epiglottis • The abdominal muscle then contract and the interabdominal pressure rises • The action know as the Valsalva manuever can also stabilize the trunk when one lifts a heavy load

Innervation of the Larynx • The larynx receives its sensory and motor innervation through the superior laryngeal branch of each vagus nerve and from the recurrent laryngeal nerves, which branch off the vagus in the superior thorax and loop superiorly to ascend through the neck • The backtracking course these nerves is unusual

The Respiratory System