Respiratory System PDF

Topic 9 Respiratory System The respiratory system consists of organs that exchange gases between the atmosphere and blood. Nose Pharynx (throat) Larynx (voice box) Trachea (windpipe) Bronchi Lungs This is divided into 2: → The upper respiratory...

Topic 9 Respiratory System The respiratory system consists of organs that exchange gases between the atmosphere and blood. Nose Pharynx (throat) Larynx (voice box) Trachea (windpipe) Bronchi Lungs This is divided into 2: → The upper respiratory system: Nose Throat Associated structures → The lower respiratory system: The remainder of the system Conducting portion: This consists of a series of interconnecting cavities and tubes both outside and within the lungs that filter, warm and moisten the air and conduct it in the lungs. - Nose - Pharynx - Larynx - Trachea - Bronchi - Bronchioles - Terminal bronchioles Respiratory portion: This consists of tissues within the lungs where gas exchange occurs. - Respiratory bronchioles - Alveolar ducts - Alveolar sacs - Alveoli The bony framework is made up of: - The frontal bone - The nasal bones - Maxillae The cartilaginous framework is made up of: Septal cartilage - The anterior portion of the nasal septum Lateral nasal cartilage: - Inferior to the nasal bones Alar cartilages: - Form a portion of the walls of the nostrils The nose: - An external portion (made up of 2 nasal bones) - An internal portion (inside the skull) – made up of cartilages A large cavity in the skull that lies o Inferior to the cranium o Superior to the mouth o Anteriorly, the internal nose merges with the external nose. o Posteriorly, it communicated with the pharynx through two openings called the internal nares (choanae). o Four paranasal sinuses (frontal, sphenoidal, maxillary, and ethmoidal) and the nasolacrimal ducts also open into the internal nose. Paired laryngeal cartilages – posterior view of the larynx: Arytenoid cartilages: - Pyramidal in shape - Located at the superior border of the cricoid cartilage. - They attach to the vocal cords and pharyngeal muscles, and their action can move the vocal cords. Corniculate cartilages: - Cone-shaped - One is located at the apex of each arytenoid cartilage. Cuneiform cartilages: - Rod-shaped cartilages - Connect the epiglottis to the arytenoid cartilages. The Pleura: The pleural membrane encloses and protects each lung. - The outer layer is attached to the wall of the thoracic cavity and is called the parietal pleura. - The inner layer, the visceral pleura, covers the lungs themselves. Between the visceral and parietal pleura is a small potential space, the pleural cavity.  - This contains a lubricating fluid secreted by the membranes that prevents friction between them. The lungs: o Paired, cone-shaped organs. o Separated from each other by the heart and other structures in the mediastinum. o The lungs extend from the diaphragm to a point about 1.5 to 2.5 cm superior to the clavicles and lie against the ribs anteriorly and posteriorly. o The broad, inferior portion of the lung, the base, is concave and fits over the convex are of the diaphragm. o The narrow superior portion of the lung is termed the apex. o The mediastinal surface of the lung contains a vertical slit, the hilus, through which bronchi, pulmonary vessels, lymphatics, and nerves enter and exit. The trachea: o A tubular passageway o 12 cm in length and 2.5 in diameter o Located anterior to the oesophagus and extends from the larynx to the 5th thoracic vertebra, where it divides into the right and left primary bronchi. → Tracheal Epithelium: - It is of the mucosa, and it is pseudostratified. - It consists of: o Ciliated columnar cells that reach the luminal surface o Goblet cells o Basal cells that do not reach the luminal surface. - Seromucous glands and their ducts are present in the submucosa. The bronchi: At the sternal angle, at the level of the 5th thoracic vertebra. The trachea bifurcated into: - A right primary bronchus to the right lung – more vertical, shorter, and wider than the left. Foreign objects in the air passageways are more likely to enter it than the left and frequently lodge in it. - A left primary bronchus to the left lung. The primary bronchi contain incomplete ringed of cartilage and are lined by pseudostratified ciliated epithelium. Lobes and Fissures of the Lungs: Each lung is divided into lobes by one or more fissures. Both lungs have an oblique fissure, which extends downward and forward. The right lung also has a horizontal fissure. Each lobe receives its own secondary (lobar) bronchus. The right primary bronchus gives rise to three secondary (lobar) bronchi called the superior, middle, and inferior Secondary (lobar) bronchi. The left primary bronchus gives rise to a superior and an inferior secondary (lobar) bronchus. Within the substance of the lung, the secondary bronchi give rise to the tertiary (segmental) bronchi. The segment of lung tissue that each supply is called a bronchopulmonary segment. The Exchange Site – Alveolar-Capillary Membrane: The exchange of respiratory gases between lungs and blood takes place by diffusion across the alveolar and capillary walls. The alveolar-capillary membrane is about 0.5 um in thickness and consists of: - A layer of squamous pulmonary epithelial cells with septal cells and free alveolar macrophages that make up the alveolar (epithelial) wall. - An epithelial basement membrane underneath the alveolar wall. - A capillary basement membrane that is often fused to the epithelial basement membrane. - The endothelial cells of the capillary. Pulmonary Ventilation: Pulmonary Ventilation (breathing) is the process by which gases are exchanged between the atmosphere and lung alveoli. Air flows between the atmosphere and the lungs because a pressure gradient exists. We breathe in (inspiration) when the pressure inside the lungs is less than the air pressure in the atmosphere. Diaphragm and external intercostal muscles contract. Thoracic cavity increases in size and the lungs expand. Intrapulmonic pressure decreases INSPIRATION We breathe out (expiration) when the pressure in the lungs is greater than the pressure in the atmosphere. Summary of gas exchange in the body: → Pulmonary Ventilation: - This is breathing. - It is the mechanical flow of air into and out of the lungs. - It is constituted by inhalation and exhalation. → External Respiration: - The exchange of gases between the air spaces of the lungs and the blood in the pulmonary capillaries. - Exchange of gases takes place in this process. → Internal Respiration:  - The exchange of gases between blood and in systemic capillaries and tissue cells - Cellular respiration occurs when oxygen is used up and carbon dioxide is given off in metabolic reactions in the cell. Lung Compliance: Compliance is the ease with which the lungs and the thoracic wall can be expanded. High compliance means that the lungs and the thoracic wall expand easily. Compliance is related to 2 principal factors: 1. Elasticity 2. Surface tension Lung tissue is rendered elastic by the presence of elastic fibres resulting in high compliance. If the surface tension within the lung tissue were high, the tissues would resist expansion. However, surfactant lowers the surface tension and therefore, increase compliance. Any disease of the lung that destroys lung tissue or causes a decrease in lung surfactant decrease lung compliance. Pulmonary Surfactant: The inner surface of each alveolus is covered with a thin layer of fluid called alveolar fluid. The surface tension of alveolar fluid together with elastic tissue in the lungs is the cause of the tendency of the lung to recoil. Therefore, the surface tension of alveolar fluid is reduced by surfactant. This is a phospholipid that is produced by cells in the alveolar epithelium. Surfactant coats the water molecules in alveolar fluid with a layer of chemical groups, which have a lower attractive force between them. In this way, the surface tension of alveolar fluids is reduced. If the surfactant were not present, the surface tension of alveolar fluid would be much higher and therefore the lung would have a higher tendency to collapse and would be less complaint. Surfactant is important: - To decrease the muscular effort required for inspiration. - To prevent collapse of the alveoli. Airway Resistance: Flow of air through the airways depend upon: The resistance offered by the walls of the airways and the pressure gradient. The volume of airflow is directly proportional to the pressure gradient between atmosphere and the alveoli. The volume of airflow is indirectly proportional to the resistance. The resistance itself depends on the diameter of the airways. The larger the diameter, the lower the resistance and vice-versa. The airways diameters usually offer little total resistance to airflow. However, in certain diseases, the diameters of the airways may be decreased by contraction of bronchiolar smooth muscle or by plugs of mucus. Lung Volumes and Lung Capacities: One Respiration = One Inspiration + One Expiration During each respiration, the lungs exchange various amounts of air with the atmosphere. The apparatus used to measure these amounts, and the rate of ventilation is a spirometer. There are 4 important lung volumes: 1. Inspiratory reserve volume (IRV) 2. Tidal volume (TV) 3. Expiratory reserve volume (ERV) 4. Residual volume (RV) There are 4 important lung capacities: 1. Vital capacity 2. Total lung capacity 3. Inspiratory capacity 4. Functional residual capacity IRV – excess inhaled air Toal inhalatory capacity = IRV + TV ERV – excess exhaled air RV – remaining air after maximal exhalation Anatomical Adaptations Helping External Respiration: The total thickness of the alveolar-capillary membrane is only 0.5 um thick to improve diffusion. The surface area of the alveoli over which takes place is large 70m2. Lying over the alveoli are countless capillaries so that 900ml of blood can participate in gas exchange at any time. The capillaries are so narrow that the red blood cells must flow through them in single file. This gives each red blood cell maximum exposure to the available oxygen. Regulation of Respiration: Spontaneous respiration is produced by the rhythmic discharge of motor neurones that innervate the respiratory muscles. This discharge is dependent on nerve impulses from the brain. This is in turn regulated in arterial PO2, PCO2 and H+ concertation. This chemical control of breathing is supplemented by a few nonchemical influences. The Respiratory Centre:  A group of nerve cells found in the brain. It is divided into 3 major areas and another area: 1. The inspiratory area: o This plays a significant role in the control of respiration. o It can generate its own action potentials in a rhythmic manner. o It is active during inspiration for about 2 seconds. It is dormant during expiration for about 3 seconds. o Its activity causes the diaphragm and intercostal muscles to contract. 2. The expiratory area: o This remains dormant during quiet respiration. o It only becomes active when the inspiratory area is more active than normal. o This increased activity stimulates the expiratory area, which causes the expiratory muscles to contract. 3. The pneumotaxic area: o Its function is primarily to limit inspiration. o It is continually transmitting impulses to the inspiratory area so that the lungs never become too full of air. o Since it limits inspiration, it will determine the rate of breathing. o A strong pneumotaxic signal can increase the rate of breathing up to about 30 breaths per minute while a weak signal may decrease the rate to inly a few breaths per minute. 4. The apneustic area: o This transmits signals to the inspiratory area preventing its turn-off that is keeping it active. o However, the activity of the pneumotaxic are normally overrides the activity of the apneustic area. The Chemo sensitive Area: This is situated within the respiratory centre. It is sensitive to changes in CO2 and H+ concentrations. Increased concentrations to these substances stimulate the chemosensitivity area. The chemo sensitive area stimulates the inspiratory area. The rate and depth of respiration increases. Hyperventilation occurs. This will remove the extra CO2 until the CO2 level returns to normal. The Peripheral Chemoreceptors: These are situated outside the nervous system. They are found in the carotid and aortic bodies. There are 2 carotid bodies located near the bifurcation of the carotid artery on each side. There are 2 or more aortic bodies near the arch of the aorta.  FATE OF OXYGEN IN THE BLOOD Oxygen delivery to a particular tissue depends on: - The amount of O2 entering the lungs. - The adequacy of pulmonary gas exchange. - The blood flow to the tissue. - The capacity of the blood to carry 02. The blood flow depends on: - The degree of constriction of the vascular bed in the tissue. - The cardiac output. The amount of O2 in the blood is determined by: - The amount of O2 dissolved. - The amount of haemoglobin in the blood. - The affinity of haemoglobin for O2. FATE OF CARBON DIOXIDE IN THE BLOOD In plasma 1. Dissolved. 2. Formation of carbamino compounds with plasma protein. 3. Hydration, H+ buffered, HCO3- in plasma. In red blood cells 1. Dissolved. 2. Formation of carbamino-Hb. 3. Hydration, H+ buffered, 70% of HCO3 enters the plasma. 4. Cl shifts into cells.