Respiratory SystemA (1).pptx

Respiratory System Respiratory System • Consists of the respiratory and conducting zones • Respiratory zone – Site of gas exchange – Consists of bronchioles, alveolar ducts, and alveoli Respiratory System • Conducting zone – Provides rigid conduits for air to reach the sites of gas exchange – In...

Respiratory System Respiratory System • Consists of the respiratory and conducting zones • Respiratory zone – Site of gas exchange – Consists of bronchioles, alveolar ducts, and alveoli Respiratory System • Conducting zone – Provides rigid conduits for air to reach the sites of gas exchange – Includes all other respiratory structures (e.g., nose, nasal cavity, pharynx, trachea) • Respiratory muscles – diaphragm and other muscles that promote ventilation Activity • Arrange list in correct sequence form first to last in pathway of inspiration: A. alveolar ducts and alveoli B. bronchi and bronchiloes C. larynx D. Mouth and nose E. pharynx F. trachea (Place a check mark next to the structures forming upper respiratory system.) Respiratory System Figure 22.1 Major Functions of the Respiratory System • To supply the body with oxygen and dispose of carbon dioxide • Respiration – four distinct processes must happen – Pulmonary ventilation – moving air into and out of the lungs – External respiration – gas exchange between the lungs and the blood Major Functions of the Respiratory System – Transport – transport of oxygen and carbon dioxide between the lungs and tissues – Internal respiration – gas exchange between systemic blood vessels and tissues Function of the Nose • The only externally visible part of the respiratory system that functions by: – Providing an airway for respiration – Moistening and warming the entering air – Filtering inspired air and cleaning it of foreign matter – Serving as a resonating chamber for speech – Housing the olfactory receptors Structure of the Nose Figure 22.2b Nasal Cavity Figure 22.3b Nasal Cavity • Inspired air is: – Humidified by the high water content in the nasal cavity – Warmed by rich plexuses of capillaries • Ciliated mucosal cells remove contaminated mucus Pharynx • Funnel-shaped tube of skeletal muscle that connects to the: – Nasal cavity and mouth superiorly – Larynx and esophagus inferiorly • Extends from the base of the skull to the level of the sixth cervical vertebra Pharynx • It is divided into three regions – Nasopharynx – Oropharynx – Laryngopharynx Larynx (Voice Box) • Attaches to the hyoid bone and opens into the laryngopharynx superiorly • Continuous with the trachea posteriorly • The three functions of the larynx are: – To provide a patent airway – To act as a switching mechanism to route air and food into the proper channels – To function in voice production Framework of the Larynx Figure 22.4a, b Trachea • Flexible and mobile tube extending from the larynx into the mediastinum • Composed of three layers – Mucosa – made up of goblet cells and ciliated epithelium – Submucosa – connective tissue deep to the mucosa – Adventitia – outermost layer made of Cshaped rings of hyaline cartilage Trachea Figure 22.6a Conducting Zone: Bronchi • The carina of the last tracheal cartilage marks the end of the trachea and the beginning of the right and left bronchi • Air reaching the bronchi is: – Warm and cleansed of impurities – Saturated with water vapor • Bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs • Air passages undergo 23 orders of branching in the lungs Conducting Zone: Bronchial Tree • Tissue walls of bronchi mimic that of the trachea • As conducting tubes become smaller, structural changes occur – Cartilage support structures change – Epithelium types change – Amount of smooth muscle increases Conducting Zone: Bronchial Tree • Bronchioles – Consist of cuboidal epithelium – Have a complete layer of circular smooth muscle – Lack cartilage support and mucusproducing cells Respiratory Zone • Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles • Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli • Approximately 300 million alveoli: – Account for most of the lungs’ volume – Provide tremendous surface area for gas exchange Respiratory Zone Figure 22.8a Respiratory Zone Figure 22.8b Respiratory Membrane • This air-blood barrier is composed of: – Alveolar and capillary walls – Their fused basal laminas • Alveolar walls: – Are a single layer of type I epithelial cells – Permit gas exchange by simple diffusion – Secrete angiotensin converting enzyme (ACE) • Type II cells secrete surfactant Alveoli • Surrounded by fine elastic fibers • Contain open pores that: – Connect adjacent alveoli – Allow air pressure throughout the lung to be equalized • House macrophages that keep alveolar surfaces sterile Respiratory Membrane Figure 22.9b Respiratory Membrane Figure 22.9.c, d Pulmonary ventilation • Respiratory cycle-one complete breath; includes inspiration and expiration • Quiet respiration—relaxed, unconscious, automatic breathing • Forced respiration—deep or rapid breathing (eg. Exercising, singing, blowing balloon) Inspiration • The diaphragm and external intercostal muscles (inspiratory muscles) contract and the rib cage rises • The lungs are stretched and intrapulmonary volume increases • Intrapulmonary pressure drops below atmospheric pressure (−1 mm Hg) • Air flows into the lungs, down its pressure gradient, until intrapleural pressure = atmospheric pressure Inspiration Figure 22.13.1 Expiration • Inspiratory muscles relax and the rib cage descends due to gravity • Thoracic cavity volume decreases • Elastic lungs recoil passively and intrapulmonary volume decreases • Intrapulmonary pressure rises above atmospheric pressure (+1 mm Hg) • Gases flow out of the lungs down the pressure gradient until intrapulmonary pressure is 0 Expiration Figure The Respiratory muscles Respiratory muscles Principal muscles • Diaphragm (prime mover) • Intercostal (external and internal) Accessory muscles • Sternocleidomastoids • Scalene • Pectoralis • Serratus anterior of chest Brainstem respiratory centers • Automatic, unconscious breathing controlled by 3 pairs of respiratory centers in medulla oblongata and pons • VRG—ventral respiratory group • DRG—dorsal respiratory group • Pontine respiratory group VRG • Primary generator of respiratory rhythm • Nucleus in the medulla with 2 groups of neurons: In quiet breathing: • a. inspiratory neurons (I)—fires about 2 seconds at a time b. expiratory neurons (E) –relaxed expirations lasts about 3 seconds DRG • Integrating center that receives input from several sources • Influenced by: a. pontine respiratory group b. central chemoreceptors of the medulla c. chemoreceptors in major arteries Pontine respiratory group • Found on each side of the pons • Modifies the rhythm of the VRG • Receives input from higher brain centers including hypothalamus, limbic system, cortex • Issues output to both VRG and DRG which will influence breathing—(shorter and shallower; longer and deeper) Central and Peripheral Input Central receptors Peripheral receptors • Central chemoreceptors— brainstem neurons responding to changes is pH of CSF. • pH of CSF reflects CO2 level in blood • Regulating respiration helps maintain pH • Located in carotid (via glossopharyngeal nerve) and aortic bodies (via vagus nerve)of large arteries • They respond to O2 and CO 2 content of the blood and mostly to pH • Stretch receptors found in smooth muscle of bronchi and bronchioles (via vagus nerve) • Irritant receptors—nerve endings of epithelial cells or airway (via vagus)—respond to smoke, dust, pollen (Note: pH lower than 7.35— acidosis pH higher than 7.45—alkalosis) Carotid and Aortic bodies Voluntary control of breathing • Important eg. Singing, speaking, breath-holding • Originates in motor cortex • Neurons send impulses to integrating centers in spinal cord Bronchodilation • Increase of diameter of bronchus or bronchioles • Epinephrine and sympathetic nerves (norepinephrine) stimulate bronchodilation • This increases airflow Bronchoconstriction • Reduction of diameter of bronchus and bronchiole • Histamine, parasympathetic nerves (acetylcholine), cold air and chemical irritants stimulate bronchoconstriction • Note: deep breathing spreads pulmonary surfactant throughout small airways. Other respiratory terms • Anatomical dead space—air that fills conducting pathway that will not exchange gases with blood (about 150mL—1mL per pound of body weight) • Tidal volume—amount of air inhaled and exhaled per cycle (500mL in quiet breathing) • Residual volume—amount of air remaining after maximum expiration Homeostatic imbalances Chronic obstructive pulmonary diseases • Chronic bronchitis • Emphysema Asthma Tuberculosis Lung cancer