10. The Respratory System

Learning Objectives Differentiate between internal and external respiration. List the secondary functions of the respiratory system. List the components of the upper respiratory tract and describe their structure and functions. List the components of the lower respiratory tract and describe their structure and functions. Describe the events that occur during inspiration and expiration. List the muscles involved in inspiration and expiration. Define the terms tidal volume, minute volume, and residual volume. Describe the processes of oxygen and carbon dioxide exchange between the alveoli and the blood. Describe the mechanical and chemical respiratory control systems.

Respiratory System Primary Function: bring O 2 into the body and CO 2 out of it Respiratory system works together with the cardiovascular system Secondary functions Phonation (voice production) Regulation of body temperature Regulation of acid-base balance Sense of smell

Respiration External respiration - exchange of O 2 and CO 2 between the inhaled air and the blood flowing through the pulmonary capillaries Internal respiration - exchange of O 2 and CO 2 between the blood in the systemic capillaries and all the cells and tissues of the body

Structures of Respiratory System Upper Respiratory Tract (outside the lungs) Nostrils Nasal passages Pharynx Larynx Trachea

Nose and Nasal Passages Nares (nostrils): external openings of the respiratory tube Lead into the nasal passages Nasal Passages: between the nostrils and the pharynx

Nose and Nasal Passages Nasal septum: separates the left and right nasal passage Hard and soft palates: separate the nasal passages from the mouth.

Nose and Nasal Passages Turbinates (nasal conchae): Divide each nasal passage into 3 main passageways Thin, scroll-like bones covered with nasal epithelium Dorsal and ventral

Nose and Nasal Passages Nasal passages lined with pseudostratified columnar epithelium Cilia project from the cell surfaces up into a layer of mucus Mucus is secreted by mucous glands and goblet cells

Nasal Passages Functions Warm, humidify, and filter inhaled air Air is warmed by blood flowing through blood vessels just beneath the nasal epithelium. Air is humidified by mucus and other fluids on the epithelial surface. Air is filtered as it passes through the winding passages produced by the turbinates. Particles do not readily pass through but become trapped in the mucous layer; cilia move mucus and trapped foreign material upward to the pharynx, mouth

Paranasal Sinuses Paranasal Sinuses: ciliated outpouchings of the nasal passages contained within spaces in certain skull bones Most animals have two frontal sinuses and two maxillary sinuses within the frontal and maxillary bones

Pharynx Common passageway for respiratory and digestive systems Soft palate divides pharynx into the dorsal nasopharynx (respiratory passageway) and the ventral oropharynx (digestive passageway) Caudal end of pharynx opens dorsally into the esophagus and ventrally into the larynx

Pharynx Reflexes control actions of the muscles around the pharynx. Larynx and pharynx work together to prevent swallowing from interfering with breathing, and vice versa. Swallowing - breathing stops, opening into larynx is covered, material to be swallowed moves to rear of pharynx, esophagus opens After swallowing, larynx is reopened and breathing resumes

Larynx Short, irregular tube connecting pharynx with the trachea Composed of segments of cartilage that are connected to each other and the surrounding tissues by muscles Supported in place by the hyoid bone Cartilage components - epiglottis, arytenoid cartilages, thyroid cartilage, cricoid cartilage

Larynx Cartilages Epiglottis - single, leaf-shaped; projects forward from the ventral portion of the larynx During swallowing, the epiglottis is pulled back to cover the opening of the larynx Arytenoid cartilages - paired; attachment is the site of the vocal cords Muscles adjust the tension of the vocal cords by moving the cartilages. Arytenoid cartilages and the vocal cords form the boundaries of the glottis.

Larynx Functions Voice Production Vocal cords - two connective tissue bands attached to the arytenoid cartilages Stretched across lumen of larynx parallel to each other Vocal cords vibrate as air passes over them. Muscles attached to the arytenoid cartilages control the tension of the vocal cords. Complete relaxation opens the glottis wide; no sound Lessening the tension produces lower-pitched sounds Tightening the tension produces higher-pitched sounds

Larynx Function Prevention of foreign material being inhaled During swallowing, muscle contractions pull the larynx forward and fold the epiglottis back over its opening. Control airflow to and from the lungs Small adjustments in the size of the glottis aid movement of air.

Trachea Short, wide tube Extends from the larynx into the thorax Divides into the two main bronchi that enter the lungs Bifurcation of the trachea Composed of fibrous tissue and smooth muscle held open by hyaline cartilage rings Lined with ciliated epithelium

Trachea C-shaped rings of hyaline cartilage Open part of tracheal rings face dorsally Gap between the ends of each ring bridged by smooth muscle

Structures of Respiratory System Lower Respiratory Tract Bronchi Bronchioles Alveolar ducts Alveoli

Bronchial Tree Each bronchus divides into smaller bronchi, which divide into even smaller bronchi, and then tiny bronchioles Bronchioles subdivide into alveolar ducts

Bronchial Tree Alveolar ducts end in groups of alveoli Arranged like bunches of grapes Alveolar sacs: groups of alveoli

Bronchial Tree Autonomic nervous system controls smooth muscle fibers in wall of bronchial tree Bronchodilation - bronchial smooth muscle relaxes Aids respiratory effort during intense physical activity Bronchoconstriction - bronchial smooth muscle partially contracts Reduces size of the air passage Irritants in inhaled air can cause bronchoconstriction

Alveoli Site of external respiration Tiny, thin-walled sacs of simple squamous epithelium Surrounded by networks of capillaries Lined with fluid that contains surfactant

Lungs Each lung has a base, an apex, and a convex lateral surface. Base is in caudal part of thoracic cavity Lies directly on cranial surface of diaphragm Apex lies in cranial portion of thoracic cavity

Lungs Convex lateral surface lies against inner surface of the thoracic wall Mediastinum - area between the lungs

Lungs Lungs are divided into lobes (in most species) Pattern varies with species Lobes are distinguished by the major branches of the bronchi Hilus - small, well-defined area on medial side of lung Site where air, blood, lymph, and nerves enter and leave the lung

Pulmonary Circulation Deoxygenated blood enters the lungs from right ventricle of heart through the pulmonary artery Pulmonary artery splits into left and right pulmonary arteries that enter the two lungs Pulmonary arterioles enter capillary networks around the alveoli Oxygenated blood returns to the left side of heart in the pulmonary veins.

Thoracic Cavity Bound by thoracic vertebrae dorsally, ribs & intercostal muscles laterally, the sternum ventrally Mediastinum – area between lungs Contains heart, trachea, esophagus, blood vessels, nerves, lymphatic structures

Pleura Thin membrane that lines thoracic cavity and covers organs and structures in the thorax Visceral layer covers thoracic organs and structures Parietal layer lines the cavity Space between the two pleural layers is filled with a small amount of pleural fluid Helps ensure that surfaces of organs slide smoothly along the lining of the thorax during breathing

Diaphragm Thin, dome-shaped skeletal muscle sheet Forms caudal boundary of thorax Important respiratory muscle Flattens when it contracts Enlarges volume of the thorax and aids inspiration

Process of Respiration Pressure within the thorax is negative with respect to atmospheric pressure. Pulls lungs tight out against the thoracic wall Lungs follow passively as movements of the thoracic wall and diaphragm alternately enlarge and reduce the volume of the thorax. Negative intrathoracic pressure helps draw blood through veins and into the atria

Inspiration Process of drawing air into lungs (inhalation) Results from enlargement of the volume of the thoracic cavity by the inspiratory muscles Main inspiratory muscles: diaphragm and external intercostal muscles External intercostal muscles located in the external portion of the intercostal spaces (between ribs)

Expiration Process of pushing air out of lungs (exhalation) Results from decrease in size of thoracic cavity Main expiratory muscles: internal intercostal muscles and abdominal muscles Internal intercostal muscles located between the ribs, deep to the external intercostal muscles Contraction of abdominal muscles pushes abdominal organs against the diaphragm and pushes diaphragm back into its full dome shape.

Respiratory Volumes Tidal volume - volume of air inspired and expired during one breath Varies according to the body's needs Minute volume - volume of air inspired and expired during 1 minute of breathing Residual volume - volume of air remaining in the lungs after maximum expiration

Alveolar Gas Exchange Simple diffusion of gas molecules according to concentration gradient O 2 diffuses from the alveolar air into the blood of the alveolar capillary CO 2 diffuses from the blood into the alveolus

Partial Pressure of Gases Pressure of each individual gas in a mixture of gases Example: Atmospheric air ~ 21% O 2 Total atmospheric pressure ~ 760 mm of mercury (Hg) Partial pressure of oxygen (PO 2 ) in atmosphere: 21% × 760 mm Hg = 159.6 mm Hg Partial pressures of O 2 and CO 2 in the blood of alveolar capillaries is determined by the partial pressures of O 2 and CO 2 in alveolar air

Respiratory Center Area in the medulla oblongata of the brain stem Controls respiratory muscle contractions Directs timing and strength of contraction Individual control centers - inspiration, expiration, breath holding Can be consciously controlled for brief periods

Mechanical Control System Stretch receptors in the lungs set limits on routine resting inspiration and expiration. Respiratory center sends out nerve impulses when lungs inflate to a certain point Stops muscle contractions that produce inspiration and starts contractions to produce expiration Another set of nerve impulses sent when lungs deflate sufficiently Stops expiration and starts the process of inspiration again

Chemical Control System Adjusts the normal rhythmic breathing pattern produced by the mechanical control system Chemical receptors in carotid artery and aorta monitor blood CO 2 , pH, and O 2

Chemical Control System Blood level of CO 2 and blood pH are usually linked Increased CO 2 in blood and decreased blood pH triggers respiratory center to increase rate and depth of respiration Decreased CO 2 in blood increases blood pH; increased blood pH level triggers respiratory center to decrease rate and depth of respiration

Chemical Control System Hypoxia - decrease in blood O 2 level Slight hypoxia triggers respiratory center to increase the rate and depth of breathing Severe hypoxia - neurons of the respiratory center can become so depressed that adequate nerve impulses cannot be sent to the respiratory muscles Can cause breathing to decrease or stop completely

10. The Respratory System

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10. The Respratory System

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