Chapter 6 - Respiratory System PDF

ANSCI 3300 (Anatomy and Physiology of Domestic Animals) Prepared by: ALONA T. BADUA E-mail Address: [email protected] Central Luzon State University Science City of Muñoz 3120 Nueva Ecija, Philippines...

ANSCI 3300 (Anatomy and Physiology of Domestic Animals) Prepared by: ALONA T. BADUA E-mail Address: [email protected] Central Luzon State University Science City of Muñoz 3120 Nueva Ecija, Philippines Instructional Material for the Course ANSCI 3300 ANATOMY AND PHYSIOLOGY OF DOMESTIC ANIMALS Chapter 6 The Respiratory System Overview This chapter covers topic on the gross structures of the respiratory system. The phases of respiration, regulation of respiration lung volumes and capacities are important in understanding the functions of the lungs. A better perspective of the respiratory system will be discussed especially its function maintaining homeostasis in the body. I. Objectives Upon successful completion of this chapter, the student will be able to: 1. Identify the gross respiratory structures and their functions 2. Describe the phases and regulation of respiration 3. Distinguish the different lung volumes and capacities 4. Describe the types of breathing/respiration II. Learning Activities A. Anatomy of the Respiratory System Respiration is most simply defined as the process by which gas exchange between a living cell and its environment is affected. Respiration involves more than the act of breathing. The circulatory system could not carry oxygen and 1  ANSCI 3300 (Anatomy and Physiology of Domestic Animals) carbon dioxide to and from the cells unless the respiratory system performed its function of making oxygen available to the blood relieving it of carbon dioxide. Two steps are needed for respiration to take place in an animal’s body— external respiration and internal respiration. External respiration occurs in the lungs. It is the exchange of oxygen and carbon dioxide between the air inhaled into the lungs and the blood flowing through the pulmonary (lung) capillaries. Internal respiration, on the other hand, occurs all over the body. It is the exchange of oxygen and carbon dioxide between the blood in the capillaries all over the body (the systemic capillaries), and all of the cells and tissues of the body (Colville & Bassert,2016). 1. Functions of the respiratory system Supplies oxygen to the blood and removes carbon dioxide from the blood Gas exchange between blood and cells at the level of the tissues Assist in the regulation of the acidity of the extracellular fluid of the body Assist in temperature regulation Elimination of water Phonation (voice production) 2. Structures of the respiratory system: The external respiratory system is essentially a series of passages and tubes that commence at the exterior of the animal and end blindly in a multitude of tiny, thin-walled, closed sacs or alveoli. The structures involved in the system are: the nasal cavity, pharynx, larynx, trachea, bronchi, lungs, pleurae and thoracic cavity (Fails & Magee,2018) (Figure 1). a. nostrils (external nares) are the external openings of the respiratory tract b. nasal cavity The nasal cavity is separated from the mouth by the hard and soft palates and separated into two isolated halves by a median nasal septum. It is lined with mucous membrane. The sinuses are outpouchings of the nasal passages that are contained within spaces in certain skull bones. c. pharynx - is a funnel-shaped musculomembranous organ which is a common passageway for food and air. d. larynx - connects the pharynx and the trachea. It supports the epiglottis, which regulates the passage of air and prevents the aspiration of food or other foreign bodies. It also serves as the voice box. e. trachea - is a non-collapsible tube formed by a series of adjacent cartilage rings. It is a passageway to the duct system of the lungs. f. lungs - are two elastic membranous sacs whose interior is in free communication with the outside air via a system of passages. The general scheme of the duct system of the lungs is as follows (Figure 2): 2  ANSCI 3300 (Anatomy and Physiology of Domestic Animals) 1) trachea 2) primary or stem bronchi 3) secondary bronchi 4) bronchioles 5) alveolar sacs 6) alveolar ducts 7) alveoli – smallest subdivision of the air passages and the true respiratory structures where the exchange of gases between the bloodstream and the inspired air takes place https://www.vetmed.wsu.edu/outreach/Pet-Health https://en.wikipedia.org/wiki/Bronchiole#/media/File:Illu_bronchi_ Topics/categories/cat-and-dog-anatomy/respiratory-system- lungs.jpg of-the-dog Figure 2. The air passages of the lungs Figure 1. The nasal passages and trachea g. pleurae - are serous membrane, which covers the inner wall of the thorax and the thoracic structures. h. diaphragm - is a musculomembranous partition that completely separates the thoracic from the abdominal cavity. It is a muscle for respiration. i. thoracic cavity – surrounds the heart and its structures, lungs and part of the trachea and esophagus, mediastinal structures and the great vessels entering and leaving the heart. It is bounded by: thoracic inlet – anterior diaphragm – posterior thoracic vertebrae and muscles – dorsal ribs, costal cartilage and costal muscles – lateral sternum, sternal muscles and transverse thoracic muscle – ventral 3  ANSCI 3300 (Anatomy and Physiology of Domestic Animals) 3. Physiology of respiration The lungs are suspended within the thoracic cavity, which is divided into the right and left pleural cavities by the pleural membranes. The pleural cavities contain a vacuum and, as they are totally enclosed, any increase in their volume will result in negative pressure and air will be sucked into the lung tissue. Conversely, if the volume of the pleural cavity decreases, the increase in pressure will push air out. This is the principle behind inspiration and expiration or pulmonary ventilation (Aspinall & Cappello,2015). Alveolar ventilation is a more specific term that refers to the movement of air into and out of alveoli. Panting is a mechanism to dissipate heat. Panting is characterized by an increased ventilatory rate but with a reduced tidal volume. Alveolar ventilation increases minimally in panting animals, because the increase in air movement is primarily in the upper airways that are not sites of gas exchange. These airways are considered to be anatomic dead space (Fails & Magee,2018). Pulmonary ventilation is dependent on three types of pressure: atmospheric, intra-alveolar, and interpleural. Atmospheric pressure is the amount of force that is exerted by gases in the air surrounding any given surface, such as the body. Atmospheric pressure can be expressed in terms of the unit atmosphere (atm), or in millimeters of mercury (mm Hg). One atm is equal to 760 mm Hg, which is the atmospheric pressure at sea level. Intra- alveolar pressure is the pressure of the air within the alveoli, which changes during the different phases of breathing. Because the alveoli are connected to the atmosphere via the tubing of the airways, the interpulmonary pressure of the alveoli always equalizes with the atmospheric pressure. Intrapleural pressure is the pressure of the air within the pleural cavity, between the visceral and parietal pleurae. Similar to intra-alveolar pressure, intrapleural pressure also changes during the different phases of breathing. However, due to certain characteristics of the lungs, the intrapleural pressure is always lower than, or negative to, the intra-alveolar pressure (and therefore also to atmospheric pressure) (Fails & Magee,2018). A respiratory cycle is one sequence of inspiration and expiration. In general, two muscle groups are used during normal inspiration: the diaphragm and the external intercostal muscles. So when the diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs. Contraction of the external intercostal muscles moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity. Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs. The process of normal expiration is passive, meaning that energy is not required to push air out of the lungs. Instead, the elasticity of the lung tissue causes the lung to recoil, as the diaphragm and intercostal muscles relax following inspiration. In turn, the 4  ANSCI 3300 (Anatomy and Physiology of Domestic Animals) thoracic cavity and lungs decrease in volume, causing an increase in interpulmonary pressure. The interpulmonary pressure rises above atmospheric pressure, creating a pressure gradient that causes air to leave the lungs (OpenStax College,2017). 4. Regulation of respiration a. respiration is regulated by the complex action of the various muscles of respiration Three sets of muscles are responsible for respiration (Aspinall & Cappello,2015): (1) Diaphragm is a dome-shaped muscular structure that forms the boundary between the thoracic and abdominal cavities.When the diaphragm contracts, it flattens and increases the volume of the thoracic cavity. (2) External intercostal muscles contract and lift the ribs upwards and outwards, thus increasing the volume of the thoracic cavity. (3) Internal intercostal muscles fill the intercostal spaces and lie deep to the external intercostal muscles. During forced expiration they contract in conjunction with the abdominal muscles to force air out of the lungs. b. respiratory center (medulla oblongata and pons) which is influenced by both sensory nerves and chemical changes in the blood and controls the rate and depth of breathing 5. Lung volumes and capacities Figure 3 shows the different lung volumes and capacities. a. Tidal Volume (TV) – the amount of air that moves into the lungs with each inspiration or the amount that moves out with each expiration b. Inspiratory Reserve Volume (IRV) – the volume inspired after passive inspiration c. Expiratory Reserve Volume (ERV) – the volume expelled by an active expiratory effort after passive expiration d. Residual Volume (RV) – the volume of air left in the lungs after maximal expiratory effort e. Total Lung Capacity (TLC) – sum of all of the lung volumes (TV, ERV, IRV and RV) f. Vital Capacity (VC)– amount of air that can move into or out of the lungs and is the sum of the volumes except RV g. Inspiratory Capacity (IC) – is the maximum amount of air that can be inhaled past a normal tidal expiration and it is the sum of the TV and IRV h. Functional Residual Capacity (FRC) – amount of air that remains in the lung after a normal tidal expiration and it is the sum of the ERV and RV 5  ANSCI 3300 (Anatomy and Physiology of Domestic Animals) https://commons.wikimedia.org/wiki/File:Lung_capacity_measures.png Figure 3. Lung volumes and capacities 6. Types of breathing/respiration a. costal (thoracic) – involves considerable movement of the ribs b. abdominal (diaphragmatic) – diaphragm contraction produces visible movement of the abdomen c. eupnea – normal quiet respiration; the diaphragm and external intercostal muscle must contract d. dyspnea – difficult breathing e. apnea – absence or cessation of respiration f. hyperpnea – increase in depth or rate of breathing or both g. polypnea – rapid shallow breathing III. References Aspinall, V. & Cappello, M.(2015). Introduction to Veterinary Anatomy and Physiology Textbook. (3rd ed.). Elsevier. Colville ,T. & Bassert, J.M. (2016). Clinical Anatomy and Physiology for Veterinary Technicians. (3rd ed.). St. Louis, MO: Elsevier. Fails, A. D. & Magee, C. (2018). Anatomy and Physiology of Farm Animals. (8th ed.). Hoboken, NJ: Wiley-Blackwell. OpenStax College. (2017). Anatomy and Physiology. OpenStax. https://openstax.org/details/books/anatomy-and-physiology. https://www.vetmed.wsu.edu/outreach/Pet-Health-Topics/categories/cat-and- dog-anatomy/respiratory-system-of-the-dog https://en.wikipedia.org/wiki/Bronchiole#/media/File:Illu_bronchi_lungs.jpg https://commons.wikimedia.org/wiki/File:Lung_capacity_measures.png 6