Lecture 1 Physiology of Respiratory System PDF

The Respiratory System PSOL 213 2024-2025 The process of respiration is divided into: External Respiration: Includes four processes involved in exchange of O2 and CO2 between body and external e...

The Respiratory System PSOL 213 2024-2025 The process of respiration is divided into: External Respiration: Includes four processes involved in exchange of O2 and CO2 between body and external environment. 1. Pulmonary ventilation: means the exchange of air between the lungs and atmosphere. 2. Exchange of gases between alveoli and capillaries by simple diffusion. 3. Transport of O2 and CO2 in blood 4. Exchange of gases between blood and body tissues Internal Respiration: The utilization of O2 and production of CO2 by the cells (Cellular respiration).  Functions of respiratory system 1) Respiratory function: The main function is to provide O2 to the tissues and remove CO2 through gas exchange. 2) Non respiratory function: Acid –Base balance: Regulation of the pH of the blood by washing out extra carbon dioxide. Phonation: Is the production of sounds by the movement of air through the vocal cords. Site for olfactory sensation: Sense of smell by the receptors in roof of nose Pulmonary defense: The respiratory mucus membrane has mucocilliary barrier filter, and it secretes: Immunoglobulin A (Ig A) The pulmonary macrophages in the alveoli: engulf smaller foreign particles which pass through the mucocilliary barrier filter. Cough reflex: initiated by slight foreign bodies irritation of bronchi and trachea. Sneezing reflex: like the cough reflex, it applies to the nasal passageways instead of the lower respiratory passages. 5) Regulation of body temperature and water balance. 6) Activation of Angiotensin I to angiotensin II with the help of angiotensin converting enzyme (ACE) formed by the lungs. 7) Secretion of important substances like surfactant.  Functions: 1. Respiratory function: The main function is to provide O2 to the tissues and remove CO2 through gas exchange. Exchange of gasses takes place within the alveoli. STEPS 1. Pulmonary Ventilation 2. Diffusion of O2 & CO2 3. Transport of gases 4. Exchange of gases between blood, body tissues and cells. Functions: 2. Non respiratory function: 1. Acid –Base balance 2. Phonation 3. Immune function 4. Filtration function 5. Metabolic function Acid –Base balance (regulation of blood pH): One mechanism the body uses to control blood pH, involves the release of carbon dioxide from the lungs. Carbon dioxide, which is mildly acidic, is a waste product of metabolism, and is constantly produced by cells. It then passes from the cells into the blood. The blood carries carbon dioxide to the lungs, where it is exhaled. As carbon dioxide accumulates in the blood, the pH of the blood decreases (acidity increases). The brain regulates the amount of carbon dioxide that is exhaled by controlling the speed and depth of breathing (ventilation). The amount of carbon dioxide exhaled, and consequently the pH of the blood, increases as breathing becomes faster and deeper. By adjusting the speed and depth of breathing, the brain and lungs are able to regulate the blood pH minute by minute. Respiratory mechanism of pH control The second line of defense against acid-base disturbances is control of extracellular fluid CO2 concentration by the lungs under control of the nervous system. An increase in ventilation eliminates CO2 from extracellular fluid, which, reduces the H+ concentration. Conversely, decreased ventilation increases CO2, thus also increasing H+ concentration in the extracellular fluid. Chemoreceptors These are receptors that respond to changes in the partial pressures of oxygen and carbon dioxide in the blood and cerebrospinal fluid. They are located centrally and peripherally. Central chemoreceptors These are located on the surface of the medulla oblongata and are bathed in cerebrospinal fluid. ↑ arterial PCO2 (hypercapnia), even slightly→ the central chemoreceptors respond by stimulating the respiratory center→↑ ventilation of the lungs and reducing arterial PCO2. Peripheral chemoreceptors. These are situated in the arch of the aorta and in the carotid bodies. They respond to changes in blood CO2 and O2 levels, but are much more sensitive to carbon dioxide than oxygen. Even a slight rise in CO2 levels activates these receptors, triggering nerve impulses to the respiratory center via the glossopharyngeal and vagus nerves →↑ the rate and depth of respiration. An increase in blood acidity (decreased pH or raised [H+]) → stimulates the peripheral chemoreceptors→→↑ ventilation, increased CO2 excretion and increased blood pH. Phonation Produces sounds, allowing for speech and other forms of communication. Air flows through the voice box and mouth→ Vibration of air over vocal cords produces sound waves. Immune Function Phagocytosis: Tissue macrophages in alveolar wall. Respiratory organs act as defense against pathogens also, entrap foreign particles from incoming air. Purify, warm, cool and humidify the incoming air. Filtration Function Filter incoming air and transport air in and out of lungs. Nostrils: removal of particles > 6 micrometer diameter Smaller bronchioles: 1-5 micrometer Alveoli : < 1 micrometer adhere to alveolar fluid < 0.5 micrometer in alveolar air (in Expiration goes out) Metabolic Function Endothelial cells of pulmonary capillaries secrete angiotensin-converting enzyme (ACE), part of the homeostatic mechanism for maintaining BP. Synthesis & secretion of cytokines, prostaglandins, nitric oxide, histamine, heparin.  Structures of the Respiratory Tract Respiratory tract – passageways that carry air to and from the exchange surfaces of the lungs. Nose Pharynx Larynx Trachea Bronchi Bronchioles Lung- Alveoli The Components of the Respiratory System. Frontal sinus Nasal cavity Sphenoidal sinus Nasal conchae Nose Internal nares Pharynx Tongue Hyoid bone Larynx Esophagus Trachea Bronchus Bronchioles Vein Artery RIGHT LEFT LUNG LUNG Diaphragm Capillary network Alveolus  Respiratory Passages Upper Respiratory Tract: Nostrils: external openings Nasal Cavity: connected to mouth by a hard and soft palate. Pharynx: common passageway for food and air, but not at the same time. Epiglottis: a valve-like structure that shuts when swallowing food. Components of the Upper Respiratory Tract Larynx: maintains an open airway, assists in sound production. Lower Respiratory Tract: Trachea: transports air to and from lungs Bronchi: branch into lungs Bronchioles: small tubes from the bronchi Lungs: transport air to alveoli for gas exchange Components of the Lower Respiratory Tract Functional Zones of the Respiratory Tract A) Conductive portion: From nasal cavity to the end of terminal bronchioles. Include: nose, nasal cavity, pharynx, larynx, trachea, bronchi, and terminal bronchioles. Conduct, and distribute air to respiratory surfaces, also filters, warms, cool, and humidifies air – protects alveoli from pathogens and environmental extremes. B) Respiratory portion Include: respiratory bronchioles, alveolar duct, alveoli and lungs. Function in gas exchange: Gas exchange takes place within the alveoli in the respiratory membrane (between air and blood).  Nose The only externally visible part of the respiratory system. Air enters the nose through the external nares (nostrils). The interior of the nose consists of a nasal cavity divided by a nasal septum. Nasal Cavity Olfactory receptors are located in the mucosa on the superior surface→ participate in the sense of smell. The rest of the cavity is lined with respiratory mucosa. Traps incoming foreign particles. Cold air warmed to body temperature and moistened. Dry air →→ inhibits activity of the cilia of the respiratory airway. Lateral walls have projections called conchae which increases surface area. Increases air turbulence within the nasal cavity. The nasal cavity is separated from the oral cavity by the palate. Anterior hard palate (bone). Posterior soft palate (muscle). The Pharynx Pharynx—shared by respiratory and digestive systems. Muscular passage from nasal cavity to larynx. Three regions of the pharynx: 1. Nasopharynx – superior region behind nasal cavity 2. Oropharynx – middle region behind mouth 3. Laryngopharynx – inferior region attached to larynx The oropharynx and laryngopharynx are common passageways for air and food. Figure: The Nose, Nasal Cavity, and Pharynx. Larynx (Voice Box) Routes air and food into proper channels.. Plays a role in speech. Vocal cords - vibrate with expelled air to create sound (speech). Made of eight rigid hyaline cartilages and a spoon-shaped flap of elastic cartilage (epiglottis). Structures of the Larynx Thyroid cartilage: Largest hyaline cartilage, protrudes anteriorly (Adam’s apple). Cricoid cartilage: A ring of cartilage just inferior to thyroid cartilage. Epiglottis: Superior opening of the larynx, prevents entry of liquids and food into respiratory tract. Glottis: Opening between vocal cords. Epiglottis Hyoid bone Extrinsic (thyrohyoid) Corniculate cartilage ligament Cuneiform cartilage Larynx Thyroid False vocal cords Vocal cords cartilag e Ligament Arytenoid cartilages Cricoid cartilage Ligament Tracheal cartilages Trachea Anterior view. Posterior view. Figure: The Anatomy of the Larynx and Vocal Cords.  Trachea (Windpipe) Connects larynx with bronchi. Runs from cricoid cartilage (bottom of larynx) to branches of primary bronchi. Walls supported by C-shaped tracheal cartilages. Lined with ciliated mucosa. – Expel mucus loaded with dust and other debris away from lungs. Open part of cartilages: Face posteriorly Are connected by smooth muscle, the trachealis muscle. Under ANS control, sympathetic stimulation dilates trachea. Figure: The Anatomy of the Trachea. Bronchi and bronchioles Trachea branches into: Right primary bronchus: supplies right lung. This is wider, shorter and more vertical than the left bronchus and is therefore more likely to become obstructed by an inhaled foreign body. It is about 2.5 cm long, after entering the right lung at the hilum it divides into three branches, one to each lobe. Each branch then subdivides into numerous smaller branches. Left primary bronchus: supplies left lung. It is about 5 cm long and is narrower than the right. After entering the lung at the hilum it divides into two branches, one to each lobe. Each branch then subdivides into numerous smaller branches. Bronchioles Entire bronchial tree branches about 23 times. Each branch is smaller in diameter, loses cartilage and gains smooth muscle. The initial bronchioles are about 1 mm in diameter with no cartilage. They continue to branch to terminal bronchioles. Terminal bronchioles are 0.3–0.5 mm in diameter. Branch into respiratory bronchioles. May have some gas exchange ability. Lead into alveolar ducts. Sympathetic nervous system causes bronchodilation—increases airflow. Parasympathetic nervous system causes bronchoconstriction—decreases airflow.  Alveolar Ducts and Alveoli Connect the respiratory bronchioles to the alveolar sacs. Ducts end at alveolar sacs. Each lung contains about 150 million alveoli. Give lung spongy, airy appearance. Greatly increase surface area to about 140 m2 Allows for extensive, rapid gas diffusion to meet metabolic needs. Structure of Alveoli Alveolar epithelium has major cell types 1- Type I alveolar epithelial cells (type I pneumocytes): thin, delicate, sites of gas exchange. 2- Type II alveolar epithelial cells (type II pneumocytes): (10% of the surface area of alveoli). Secrete surfactant, reduces surface tension of water in alveoli to prevent collapse. 3- Alveolar macrophages Engulf the foreign bodies that reach the alveoli.  Lungs Occupy most of the thoracic cavity Each lung is cone shaped and divided into lobes by deep fissures. Left lung has two lobes: superior and inferior. Right lung has three: superior, middle, and inferior. Apex extends to superior border of first rib. Concave base of lung rests on diaphragm. Mediastinal surface of left lung has cardiac notch. Coverings of the Lungs: Visceral pleura covers outer surface of lungs. Parietal pleura lines inside of chest wall. Pleural layers secrete serous fluid, reducing friction.  Figure: The Gross Anatomy of the Lungs. Pleura and pleural cavity The pleura consists of a closed sac of serous membrane surrounding the lungs which contains a small amount of serous fluid. It forms two layers: one adheres to the lung called visceral pleura and the other covers inner surface of chest or thoracic cavity called parietal pleura. The pleural cavity This is only a potential space between visceral and parietal layers of pleural sac and contains no air, so the pressure within is negative relative to atmospheric pressure. The two layers of pleura are separated by a thin film of serous fluid (pleural fluid), which allows them to glide over each other, preventing friction between them during breathing.  The Respiratory Membrane (Air-Blood Barrier) Where diffusion of gases takes place. Can be very thin as 0.1–0.5 µm. Diffusion of gases is very rapid Both oxygen and carbon dioxide are lipid soluble so they move easily from alveoli to bloodstream and vice versa. Gas Exchange Between the Blood and Alveoli Pulmonary blood supply: The pulmonary trunk divides into the right and left pulmonary arteries, carrying deoxygenated blood to each lung. Within the lungs each pulmonary artery divides into many branches, which eventually end in a dense capillary network around the alveoli. The walls of the alveoli and the capillaries each consist of only one layer of flattened epithelial cells. The exchange of gases between air in the alveoli and blood in the capillaries takes place across these two very fine membranes together called the (respiratory membrane). The pulmonary capillaries merge into a network of pulmonary venules, which in turn form two pulmonary veins carrying oxygenated blood from each lung back to the left atrium of the heart.  The flow of blood between heart and lungs Innervations of lungs and bronchi Innervated by autonomic nervous system. Sympathetic stimulation releases epinephrine (adrenaline) causes dilatation of the bronchi. Parasympathetic stimulation releases acetyl choline causes constriction of the bronchi. Parasympathetic nerves are also activated by irritation of the epithelial membrane of the respiratory passageways by noxious gases, dust, cigarette smoke, or bronchial infection. Local Secretory Factors e.g. histamine secreted by the mast cells due to allergy (as in patients with asthma) often cause bronchial constriction and increased airway resistance leading to forced breathing.