Respiratory System PDF

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...

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 C-shaped 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 mucus-producing 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 22.13.2 The Respiratory muscles  Respiratory muscles Principal muscles Accessory muscles Diaphragm (prime mover) Sternocleidomastoids Intercostal (external and Scalene internal) Pectoralis Serratus anterior of chest  Brainstem respiratory centers Automatic, unconscious VRG—ventral breathing controlled by respiratory group 3 pairs of respiratory DRG—dorsal respiratory centers in medulla group oblongata and pons 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 Located in carotid (via chemoreceptors—brainstem glossopharyngeal nerve) and aortic bodies (via vagus nerve)of neurons responding to large arteries changes is pH of CSF. They respond to O2 and CO 2 pH of CSF reflects CO2 level in content of the blood and blood mostly to pH Regulating respiration helps Stretch receptors found in smooth muscle of bronchi and maintain pH bronchioles (via vagus nerve) Irritant receptors—nerve endings (Note: pH lower than of epithelial cells or airway (via 7.35—acidosis vagus)—respond to smoke, dust, pollen 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