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Lec.7 Human Respiratory System The respiratory system is a biological system that is responsible for gas exchange. It involves an interconnected group of organs and tissues that help you breathe. The main parts of this system are the airways, the lungs and linked blood vessels, and the muscles that enable breathing Airways The primary job of the human respiratory system is gas exchange - to bring in fresh oxygen and expel carbon dioxide. The airways are pipes that carry oxygenrich air to your lungs and carbon dioxide (a waste gas), out of your lungs. The airways include your: Nose and linked air passages called nasal cavities Mouth Larynx or voice box Trachea or windpipe Tubes called bronchial tubes or bronchi, and their branches Air initially enters the respiratory system through the nasal and oral cavities. Both of these passageways meet at the same place- the pharynx. The pharynx then leads to the larynx, and down to the trachea. The trachea then branches in two different paths, known as the left and right primary bronchi. These small tubes carry the fresh oxygen deep into the lungs. 1 Mr. Ali H . Alhamdany Msc . physiology The respiratory tract It is divided into two sections: Upper Respiratory Tract and the Lower Respiratory Tract. Included in the upper respiratory tract are the Nostrils, Nasal Cavities, Pharynx, Epiglottis, and the Larynx. The lower respiratory tract consists of the Trachea, Bronchi, Bronchioles, and the Lungs. Functions Function of the respiratory system – supplies the body with oxygen and disposes of carbon dioxide Respiration – a collective term for the following processes: o o o o Pulmonary ventilation Movement of air into the lungs (inspiration) Movement of air out of the lungs (expiration) External respiration Movement of oxygen from the lungs to the blood Movement of carbon dioxide from the blood to the lungs Transport of respiratory gases Transport of oxygen from the lungs to the tissues Transport of carbon dioxide from the tissues to the lungs Internal respiration Movement of oxygen from blood to the tissue cells Movement of carbon dioxide from tissue cells to blood In addition to these main processes, the respiratory system serves for: Regulation of Blood pH, which occurs in coordination with the kidneys, and as a 'DEFENSE AGAINST MICROBES Control of body temperature due to loss of evaporate during expiration 2 Mr. Ali H . Alhamdany Msc . physiology Upper Respiratory Tract Nose Functions Provides and airway for respiration Moistens and warms entering air Filters and cleans inspired air Resonating chamber for speech Detects odors in the airstream Pharynx Three regions of the pharynx Nasopharynx – air passage (pseudostratified columnar epithelium) Oropharynx – passageway for air, food, and drink (stratified squamous epithelium) Laryngopharynx – passageway for air, food, and drink (stratified squamous epithelium) Air enters through the nostrils of the nose and is partially filtered by the nose hairs, then flows into the nasal cavity. The nasal cavity is lined with epithelial tissue, containing blood vessels, which help warm the air; and secrete mucous, which further filters the air. The endothelial lining of the nasal cavity also contains tiny hair like projections, called cilia. The cilia serve to transport dust and other foreign particles, trapped in mucous, to the back of the nasal cavity and to the pharynx. There the mucus is either coughed out, or swallowed and digested by powerful stomach acids. After passing through the nasal cavity, the air flows down the pharynx to the larynx. Larynx (voice box) The larynx ,colloquially known as the voice box, is an organ in our neck involved in protection of the trachea and sound production , The larynx contains two important structures: the epiglottis and the vocal cords. 3 Mr. Ali H . Alhamdany Msc . physiology Functions Keeps food and drink out of the airway Sound production Acts as a sphincter during abdominal straining (ex. During defecation and heavy lifting) Selected anatomical features Nine c-rings of hyaline cartilage form the framework of the larynx Muscular walls aid in voice production and the swallowing reflex Glottis – the superior opening of the larynx Epiglottis – prevents food and drink from entering airway when swallowing False vocal cords – aid in closing the glottis when swallowing True vocal cords – produce sound when air passes between them The shorter and thinner these membranes are, the faster air moves over them – produces high pitched sounds The longer and thicker these membranes are, the slower air moves over them – produces low pitched sounds Lower Respiratory Tract Lower Respiratory Tract consists of the trachea, bronchioles and lungs (including alveoli) Trachea which is also known as the windpipe. The trachea divides into two main bronchi, and one bronchi each enters one of the pair of lungs Functions Air passageway Cleans, warms, and moistens incoming air Selected anatomical features Rings of hyaline cartilage – reinforce the trachea and keep it from collapsing when you inhale 4 Mr. Ali H . Alhamdany Msc . physiology The Passage Way From the Trachea to the Bronchioles : There is a point at the inferior portion of the trachea where it branches into two directions that form the right and left primary bronchus. This point is called the Carina which is the keel-like cartilage plate at the division point. We are now at the Bronchial Tree. It is named so because it has a series of respiratory tubes that branch off into smaller and smaller tubes as they run throughout the lungs. Bronchi Function Solely an air passageway Selected anatomical features Left and right primary bronchi branch off from trachea Once the left and right primary bronchi enter the lungs they are subdivided into smaller tubes: Alveolar sacs are clusters of alveoli Diagram of the lungs Alveoli are the site of gas exchange Lungs Right and left lung Left Divided into 2 lobes Smaller than the right lung Cardiac notch accommodates the heart Right Divided into 3 lobes Each lobe is separated by connective tissue and has its own arteries and veins Allows for compartmentalization, esp. when portions of the lungs are diseased. Serous membranes cover the entire surface of the lungs and produce pleural fluid Pleural fluid enables the lungs to expand and contract with minimal friction 5 Mr. Ali H . Alhamdany Msc . physiology Gas exchange Homeostasis is maintained by the respiratory system in two ways: gas exchange and regulation of blood pH. Gas exchange is performed by the lungs by eliminating carbon dioxide, a waste product given off by cellular respiration. As carbon dioxide exits the body, oxygen needed for cellular respiration enters the body through the lungs. ATP, produced by cellular respiration, provides the energy for the body to perform many functions, including nerve conduction and muscle contraction. Lack of oxygen affects brain function, sense of judgment, and a host of other problems. Peripheral control and Gas Transport Oxygen – most bound to hemoglobin of red blood cells; small amount dissolved in blood plasma CO2 is converted to HCO3; most CO2 produced at the tissue cells is carried to lungs in the form of HCO3 Homeostasis and Gas Exchange Carbon dioxide Transported in three forms o Carbonic acid – 90% of carbon dioxide reacts with water to form carbonic acid CO2 & H2O form carbonic acid (H2CO3) changes to H CO3 & H+ ions result is H+ ions are buffered by plasma proteins o Carboamino compounds – 5% binds to plasma proteins and hemoglobin o Dissolved gas – 5% carried in the blood as dissolved gas Breathing and Lung Mechanics Two phases of pulmonary ventilation Inspiration, or inhalation a very active process that requires input of energy , Air flows into the lungs when the thoracic pressure falls below atmospheric pressure. 6 Mr. Ali H . Alhamdany Msc . physiology The diaphragm moves downward and flattens, when stimulated by phrenic nerves. External (inspiratory) intercostals muscles and thoracic muscles can be stimulated to contract and expand the thoracic cavity Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 Upon inhalation, alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres). These walls are composed of a single layer of epithelial cells (type I and type II epithelial cells) close to the pulmonary capillaries which are composed of a single layer of endothelial cells. The close proximity of these two cell types allows permeability to gases and, hence Expiration, or exhalation a passive process that takes advantage of the recoil properties of elastic fibers Air is forced out of the lungs when the thoracic pressure rises above atmospheric pressure. The diaphragm muscles relax. The elasticity of the lungs and the thoracic cage allows them to return to their normal size and shape. To exhale more than usual, internal (expiratory) intercostals muscles and other muscles can be stimulated. and expiratory External Respiration External respiration is the exchange of gas between the air in the alveoli and the blood within the pulmonary capillaries. A normal rate of respiration is 12-25 breaths per minute. In external respiration, gases diffuse in either direction across the walls of the alveoli. Oxygen diffuses from the air into the blood and carbon dioxide diffuses out of the blood into the air. 7 Mr. Ali H . Alhamdany Msc . physiology Most of the carbon dioxide is carried to the lungs in plasma as bicarbonate ions (HCO3-). When blood enters the pulmonary capillaries, the bicarbonate ions and hydrogen ions are converted to carbonic acid (H2CO3) and then back into carbon dioxide (CO2) and water. This chemical reaction also uses up hydrogen ions. The removal of these ions gives the blood a more neutral pH, allowing hemoglobin to bind up more oxygen. De-oxygenated blood "blue blood" coming from the pulmonary arteries, generally has an oxygen partial pressure (pp) of 40 mmHg and CO2 pp of 45 mmHg. Oxygenated blood leaving the lungs via the pulmonary veins has a O2 pp of 100 mmHg and CO2 pp of 40 mmHg. It should be noted that alveolar O2 pp is 105 mmHg, and not 100 mmHg. The reason why pulmonary venous return blood has a lower than expected O2 pp can be explained by "Ventilation Perfusion Mismatch". Internal Respiration Internal respiration is the exchanging of gases at the cellular level. Cellular Respiration First the oxygen must diffuse from the alveolus into the capillaries. It is able to do this because the capillaries are permeable to oxygen. After it is in the capillary, about 5% will be dissolved in the blood plasma. The other oxygen will bind to red blood cells. The red blood cells contain hemoglobin that carries oxygen. Blood with hemoglobin is able to transport 26 times more oxygen than plasma without hemoglobin. Our bodies would have to work much harder pumping more blood to supply our cells with oxygen without the help of hemoglobin. Once it diffuses by osmosis it combines with the hemoglobin to form oxyhemoglobin. Now the blood carrying oxygen is pumped through the heart to the rest of the body. Oxygen will travel in the blood into arteries, arterioles, and eventually capillaries where it will be very close to body cells. Now with different conditions in temperature and pH (warmer and more acidic than in the lungs), and with pressure being exerted on the cells, the hemoglobin will give up the oxygen where it will diffuse to the cells to be used for cellular respiration, also called aerobic respiration. Cellular respiration is the process of moving energy from one chemical form (glucose) into another (ATP), since all cells use ATP for all metabolic reactions. 8 Mr. Ali H . Alhamdany Msc . physiology