Chapter 10 - Respiratory System PDF

Why do we need a Respiratory System? For respiratory functions: Provides an extensive area for gas exchange between air and circulating blood Moves air to and from the exchange surfaces of the lung Protects respiratory surfaces from dehydration, temperature changes or other environmental varia...

Why do we need a Respiratory System? For respiratory functions: Provides an extensive area for gas exchange between air and circulating blood Moves air to and from the exchange surfaces of the lung Protects respiratory surfaces from dehydration, temperature changes or other environmental variations and defends the respiratory system (and other tissues) from invasion by pathogens Why do we need a Respiratory System? Also, for non-respiratory functions! Regulates blood pH- by changing levels of carbon dioxide in the blood Produces sounds involved in speaking, singing and non-verbal communication Provides olfactory sensations to the CNS from the olfactory epithelium in the superior portion of the nasal cavity Produces chemical mediators- HSC 113 Renin- Angiotensin- Aldosterone System- Regulates Blood pressure and Fluid Balance When blood volume or sodium levels in the body are low, or blood potassium is high, cells in the kidney release the enzyme, renin. Renin converts angiotensinogen, which is produced in the liver, to the hormone angiotensin I (Ang I). An enzyme known as ACE or angiotensin- converting enzyme found in the lungs metabolizes Ang I into Ang II. Ang II causes blood vessels to constrict and blood pressure to increase. Angiotensin II stimulates the release of the hormone aldosterone in the adrenal glands, which causes the renal tubules to retain sodium and water and excrete potassium. If the renin-angiotensin system becomes overactive, consistently high blood pressure results. Chapter 7- Endocrine System Anatomy of the Respiratory System Structurally: Upper Respiratory Tract Lower Respiratory Tract Functionally: Conducting zone- carries gases Respiratory zone- exchange of gases Organs: Nose Pharynx Larynx Trachea Two bronchi Bronchioles Two lungs Muscles- Intercostal muscles, diaphragm Various versions of the Egyptian hieroglyph depicting the Respiratory System Examination of ancient Egyptians’ depictions of the respiratory tract, dating back to the 30th century BC, reveals their awareness of the pulmonary anatomy: reinforced with cartilaginous rings, the trachea is split into two main bronchi, which then enter the lungs (lungs being divided into pulmonary lobes). A Conventional depiction (from the Rosette- Mury© hieroglyphic font ); B Depiction on a broken first dynasty vessel, surrounded by two other glyphs; C Depiction on a sixth dynasty vessel D Depiction from an 18th dynasty tomb (photography courtesy of Vincent Euverte) Reference Kwiecinski, Jakub. “First images of respiratory system in ancient Egypt: Trachea, bronchi and pulmonary lobes.” Canadian respiratory journal vol. 19,5 (2012): e33-5. doi:10.1155/2012/640292 The Upper Respiratory Tract Nose and nasal cavity Primary passage for air entering respiratory tract Air enters the vestibule – flexible tissues of nose Epithelium of vestibule contains course hairs - large airborne particles get trapped and are prevented from entering the nasal cavity. The nasal septum divides into right and left portions. The superior portion is the olfactory region. Conchae: increase the surface area, contain blood vessels which deliver heat and moisture and secrete fluid which helps keep the nasal cavity clean and moist. The Upper Respiratory Tract Pharynx Hollow muscular structure lined with epithelial tissues, begins behind the nasal cavities and divided into 3 parts: Nasopharynx – air breathed in through here, contains lymphatic tissue (adenoid, pharyngeal tonsils) and eustachian tubes. Oropharynx – air next moves in here, anything that is swallowed goes through here also, contains tonsils. During swallowing the uvula and soft palate move posteriorly to protect nasopharynx and nasal cavity. Laryngopharynx – part of both the respiratory and digestive system, lined with non-keratinized stratified squamous epithelium, extends from the epiglottis to the esophagus carrying food and fluid to the stomach; anteriorly it conducts air to the larynx. Nasopharynx → Oropharynx → Laryngopharynx The Upper Respiratory Tract Larynx (Voice Box) Semi-rigid structure Composed of several types of cartilage Connected by muscle and ligaments that provide movement of the vocal cords to control speech.  Thyroid and cricoid cartilage- provide structural support to airways to prevent them from collapsing and blocking airflow in and out of the lungs. Glottis – opening that leads into the larynx and eventually the lungs. Epiglottis – leaf shaped fibrocartilage flap-like structure located above the opening, has selective closure- glottic/sphincter mechanism closes over the larynx when you swallow and opens when you breathe. Vocal cords – area of division between upper and lower airways. Lower airway starts below the vocal cords. What is Adam’s Apple? Notch at the top of the thyroid cartilage Men and women both have Adam’s apples. Larger and more visible in men because their thyroid cartilage grows more during puberty, enlarging the larynx and deepening the voice. The Lower Respiratory Tract Trachea Begins under larynx and runs down behind sternum. Next divides into two smaller tubes called primary bronchi, one for each lung, and then further into secondary and tertiary bronchi and bronchioles. Composed of about 20 rings of tough cartilage. Structure Function Fibrous, elastic outer layer Ensures the tube has no kinks, folds, obstructions as head and neck moves. Cartilages and smooth muscle Allows trachea to change shape bands (trachealis muscle)- middle and accommodate food bolus in layer esophagus. Ciliated epithelium with mucus Mucus traps inhaled debris or secreting goblet cells (inner lining) foreign particles, Cilia propels mucus towards pharynx where it is swallowed. Nerve endings Sensitive to irritation, leading to cough reflex. The Lower Respiratory Tract Bronchial Tree (Trachea and structures of Bronchi) Bronchi are airways leading from trachea into lungs, and then branch off into progressively smaller structures until they reach the alveoli: - 1 right and 1 left primary bronchus - 3 right and 2 left secondary bronchi - 10 right and 8 left tertiary (segmental) bronchi Made of cartilage, smooth muscle, and mucous membranes. Cartilage keeps bronchi from collapsing during breathing. Trachea and upper bronchi contain C-shaped cartilage, the smaller bronchi have "plates" of cartilage. As the bronchi subdivide into smaller (subsegmental) bronchi, cartilage decreases and smooth muscle increases in amount, till no cartilage in bronchioles and alveoli. Receives blood from bronchial artery and branches of pulmonary artery. The Lower Respiratory Tract Lungs Left smaller than right to accommodate heart, has indentation called cardiac impression. Hilum- slit through which bronchus, blood and lymphatic vessels, nerves enter Right lung- 3 lobes- superior, middle, inferior, Left lung- 2 lobes- superior, inferior Right lung- oblique fissure separates middle and inferior lobe, horizontal (transverse) fissure separates superior and middle lobe, Left lung- oblique fissure separates superior and inferior lobe Each lung has a double layered pleural membrane: (i) parietal pleura attached to inside of thoracic cavity and (ii) visceral pleura attached to surface of the lung Pleural cavity filled with pleural fluid which reduces friction, and allows free movement during breathing The Lower Respiratory Tract Alveoli About 150 million in adults, 70m2 surface area for gas exchange Lined with simple squamous epithelium- why? Two cell types: Type I- simple squamous cell, gas exchange Type II- cuboidal cells, secretes alveolar fluid (i) to keep surface between air and cells moist, (ii) includes surfactant (made up of phospholipids and lipoproteins)- lowers surface tension Larger particles trapped by nasal hairs and in mucus of bronchi Smaller particles (< 2µm) phagocytosed by macrophages (dust cells) in alveoli Alveoli surrounded by numerous capillaries- alveolar + capillary walls = respiratory membrane, allows gas exchange between air and blood. How are alveoli adapted to ensure gas exchange? 500 million alveoli, each 200-300 µm dia. Alveolar walls have a single layer of simple squamous epithelial cells. The gases easily cross the ultra thin (< 2 µm) (alveolar + capillary membranes). The respiratory bronchioles and alveoli are surrounded by a network of capillaries – seat of gas exchange. Type II cells are cuboidal (instead of squamous) cells- produce lipid-based surfactant. Surfactant prevents alveoli from collapsing during expiration- alveoli remain inflated to enable gaseous exchange. Alveolar macrophages (dust cells)- remove bacteria, carbon particles, and other debris. Accessory muscles of Respiration Physiology of the Respiratory System Respiration = process by which O2 and CO2 are exchanged between the atmosphere and body cells Consists of three distinct phases: Pulmonary ventilation (breathing) – inhalation (inspiration) and exhalation (expiration) of air → exchange of air between atmosphere and alveoli. External respiration – diffusion of gases between alveoli and pulmonary capillaries across the respiratory membrane. O2 diffuses from the alveoli to the pulmonary capillaries, whereas CO2 moves from the pulmonary capillaries to the alveoli. Internal respiration – diffusion of gases between blood in the systemic capillaries and the tissues. O2 diffuses from the systemic capillaries to the tissues and CO2 moves from the tissues to the systemic capillaries. Respiratory mechanics Pressures important during inspiration and expiration Mechanism of breathing Lung Volumes and Lung Capacities Control of Respiration- Nervous and Chemical Depth and rate of ventilation are controlled through negative feedback to regulate homeostasis. The respiratory system has two main functions: (i) maintaining PO2 at normal levels so that it supplies adequate O2 to the cells; (ii) by removing CO2 from the body, it maintains CO2, and thus pH, within normal limits. A. Nervous control Centers in the CNS control main respiratory pattern. Located partly in the medulla and partly in the pons. Motor fibers extend into the spinal cord through the cervical region to the phrenic nerve to the diaphragm. Located in the pons are: (a) Pneumotaxic center- inhibits the inspiratory center, limits contraction of the inspiratory muscles, and prevents the lungs from overinflating. (b) Apneustic center- stimulates the inspiratory center, prolongs contraction of inspiratory muscles. Located in the medulla is: (c) Medullary inspiratory center- generates impulses that stimulate contraction of the inspiratory muscles (diaphragm and external intercostal muscles). Normally, expiration occurs when these muscles relax. Rapid breathing- inspiratory center facilitates expiration by stimulating the expiratory muscles (internal intercostal muscles and abdominal muscles). Control of Respiration- A. Nervous and B. Chemical B. Chemical control The respiratory centers are influenced by stimuli received from the following groups of sensory neurons: 1. Central Chemoreceptors (CNS nerves)– located in medulla, sensitive to chemicals dissolved in CSF, pH changes stimulate central chemoreceptors. In response to the decrease in pH, the central chemoreceptors stimulate the respiratory center to increase the inspiratory rate. 2. Peripheral chemoreceptors (PNS nerves)- located in aortic bodies in the wall of the aortic arch and in carotid bodies in the walls of the carotid arteries, monitor the chemistry of the blood. An increase in pH or pCO2, or a decrease in pO2, causes these receptors to stimulate the respiratory center. 3. Stretch receptors/ Mechanoreceptors – located in the walls of bronchi and bronchioles, activated when the lungs expand to their physical limit, signal the respiratory center to discontinue stimulation of the inspiratory muscles, allowing expiration to begin. This response is called the inflation (Hering‐Breur) reflex. Vestibule of nose= nostrils, flexible tissues of nose Vestibule of ear= part of the inner ear that helps the body maintain its postural equilibrium. Vestibule → a chamber or channel opening into another. Ex. vulva vestibule contains the opening to the urethra and the vaginal opening. Atmospheric pressure and Partial pressure Atmospheric pressure (760 mmHg) = sum of all gases in the air, that is, nitrogen (N2) (78%), oxygen (O2) (21%), argon (Ar) (0.93), carbon dioxide (CO2) (0.04%), variable amounts of water (H2O) (0- 4% depending on where you are), and other gases (0.06%). Partial pressure = proportion of total air pressure exerted by the particular gas, i.e. the amount of any particular gas in solution is in direct proportion to the partial pressure exerted by the gas in the air surrounding it. ✓ Ex. at sea level, the atmospheric pressure of the air = 760 mm Hg ✓ O2 is 21% of air, therefore the partial pressure of O2 (PO2) is 21% of 760 = 21/100 × 760 = 160 mm Hg. External Respiration Exchange between alveoli and pulmonary circulation Blood in pulmonary artery collected from systemic circulation is low in O2 and high in CO2. PO2 higher in alveoli so O2 moves out of alveoli into circulation and to left side of heart. PCO2 lower in alveoli than in pulmonary circulation, CO2 diffuses into alveoli finally to be exhaled. Internal Respiration Exchange between systemic circulation and tissues/ cells Blood in systemic capillary is high in O2 and low in CO2. PO2 higher in alveoli compared to tissues so O2 moves into tissues. PCO2 higher in tissues than in blood, so CO2 diffuses out from the tissues into blood to be carried through pulmonary circulation. Internal Respiration External Respiration Exchange between systemic circulation and Exchange between alveoli and pulmonary circulation tissues/ cells O2-depleted blood, transported from metabolizing tissues, Metabolizing cells have a high demand for O2 flows through the pulmonary capillaries where O2 diffuses while CO2 is to be removed from the cells. from the alveolar air into the blood. CO2 diffuses out of the blood into the alveolar air. So, pO2 is low (40 mmHg) and pCO2 is high in the tissue. pCO2 in the blood is 45 mmHg while that of the alveolar air is 40 mmHg. Therefore, the exchange of carbon In the blood, pO2 is high (100 mmHg) and dioxide occurs from the blood into the alveolar air. pCO2 is low. So, O2 diffuses out of the blood into the tissue while CO2 diffuses out from the The final pO2 is 100 mmHg and PCO2 is 40 mmHg in the tissue into the blood. blood which leaves the lungs. Thus, the blood which leaves the lungs is called oxygen-rich blood. O2 and CO2 exchange across pulmonary and systemic capillaries caused by partial pressure gradients External Respiration Exchange between alveoli and pulmonary circulation Internal Respiration Exchange between systemic circulation and tissues/ cells Transport of Gases Oxygen is transported in two forms: Small amount transported in plasma (1.5%). Almost all binds with hemoglobin in RBCs (98.5%). A hemoglobin molecule has four iron-containing heme regions. Each binds with one molecule of O2. To enter cells O2 must separate from hemoglobin. O2 is released into areas where O2 concentration is low. Carbon dioxide is transported in three forms: 7% dissolved in plasma. 23% combines with hemoglobin and plasma proteins to form carbaminohemoglobin. 70% transported as bicarbonate ions. As the CO2 diffuses into the systemic capillaries it reacts with water, in the presence of carbonic anhydrase (CA) it forms carbonic acid (H2CO3) which easily dissociates into hydrogen (H+) and bicarbonate (HCO3–) ions: CA  Oxygen- Hemoglobin (O2- Hb) Dissociation Curve Relationship between O2 levels and Hb saturation. At high pO2 (> ~ 40 mm Hg), Hb saturation remains rather high (~75 - 80%): flat part called 'plateau.’ 40 mm Hg = pO2 in cells At rest, only ~20 - 25% of Hb molecules give up O2 in the systemic capillaries → there is a substantial O2 reserve → if you become more active and cells need more O2, blood (Hb) has lots of O2 to provide. When active, pO2 in (active) cells may drop → as oxygen levels decline, hemoglobin saturation also declines steeply → blood (Hb) 'unloads' lots of oxygen to active cells (which need more O2). Factors affecting Oxygen- Hemoglobin (O2- Hb) Dissociation Curve pO2 – higher the partial pressure of O2, meaning more availability of O2 → % saturation will be more. pCO2 – higher the partial pressure of CO2, meaning less availability of O2 → % saturation will be less → Hb releases more O2. Acidity/ low pH – affinity of Hb for O2 decreases → % saturation will be low → shift to right → O2 unloading more. Temperature – at higher values affinity of Hb for O2 decreases → % saturation will be low → shift to right (heat by-product of metabolism- active vs. non-active cells) 2,3- BPG – formed when RBCs catabolize glucose to ATP → lowers affinity of Hb for O2 → increased O2 unloading