Respiratory Physiology and Pathophysiology PDF

# Physiology and Pathophysiology of Respiratory System ## **By** **Dr. Noha Fawzy** Lecturer of Pharmacology and Toxicology Faculty of Pharmacy MTI University ## The Respiratory System - **Upper Airways:** - Nasal Cavity - Nasopharynx - Oral Cavity - Oropharynx - Laryngoph...

# Physiology and Pathophysiology of Respiratory System ## **By** **Dr. Noha Fawzy** Lecturer of Pharmacology and Toxicology Faculty of Pharmacy MTI University ## The Respiratory System - **Upper Airways:** - Nasal Cavity - Nasopharynx - Oral Cavity - Oropharynx - Laryngopharynx - Larynx - Trachea - Apex of lung - **Lower Airways:** - Carina - Right Superior Lobar Bronchus - Left Main Bronchus - Right Main Bronchus ## Function of Respiratory System - The major function of the respiratory system is **breathing (ventilation)**. - During ventilation, air is taken into the body on inhalation (inspiration) and travels through respiratory passages to the lungs. - Oxygen (O2) in the lungs replaces carbon dioxide (CO2) in the blood (at the alveoli) during perfusion, and then CO2 is expelled from the body on exhalation (expiration). - The lungs contain about 300 million pulmonary alveoli, which are grapelike clusters of air-filled sacs at the ends of the respiratory passages. - Here, gas exchange takes place by diffusion (the passage of gas molecules through respiratory membranes). ## Gas Exchange Between Alveoli and Capillaries - A diagram displays the movement of oxygen from the alveoli to the red blood cells and carbon dioxide from the red blood cells to the alveoli. ## Structure of Alveoli - An image illustrates the structure of the alveoli, including: - Smooth muscle - Respiratory bronchiole - Terminal bronchiole - Pulmonary vein - Pulmonary artery - Capillary bed - Alveoli - Alveolar duct - Alveolar sac - Alveolar pore ## Mechanism of Breathing - **Ventilation cycle:** One inspiration and expiration - **Ventilation Rate (f):** - In the range of 12-20 breaths per minute. - The normal respiration rate for an adult at rest is 12 to 20 breaths per minute. - A respiration rate under 12 or over 25 breaths per minute while resting is considered abnormal. - For an infant, a normal rate is up to 44 breaths per minute. - **Depth of Ventilation**: - Refers to the amount of air that is inhaled and exhaled. - This amount of air that reaches the lungs carrying O2 and then departs carrying CO2 depends on three factors: 1. **Lung volume and Capacity:** The amount of air that's moved in and out of the lungs. Conditions such as tuberculosis create lung changes that reduce the lungs' capacity for air. 2. **Compliance (The lungs' ability to expand)**: Deacreased by destruction of the lung's elastic fibers. The lungs become stiff, making breathing difficult. The alveoli capillary membrane may also be affected, causing hypoxia. 3. **Resistance to Airflow:** Airway resistance accounts for about 80% of all respiratory system resistance. It's increased in such obstructive diseases as asthma, chronic bronchitis, and emphysema. - With increased resistance, a person has to work harder to breathe, especially during expiration, to compensate for narrowed airways and diminished gas exchange. ## Regulation of Respiration - **Respiratory Center:** Located in the medulla oblongata of the brain stem. - Sends impulses which control the rate and depth of respiration. - **Respiratory Chemoreceptors:** A sensory receptor that transduces a chemical signal into an action potential. ## Central Chemoreceptors - A diagram illustrates how the central chemoreceptors in the medulla oblongata are stimulated by an increase in carbon dioxide levels in the cerebrospinal fluid. - This stimulates the respiratory centers to increase the rate and depth of ventilation. - **KEY:** - Stimulus - Receptor - Afferent pathway - Integrating Center - Systemic Response ## Causes of Stimulation of Respiratory Chemoreceptors - Three cases lead to stimulation of respiratory chemoreceptor and change rate of respiration: 1. **Increase in Carbon Dioxide:** Concentration due to exercise or stress leads to a decrease in the pH of blood due to the production of H+ ions from carbonic acid. - The carbon dioxide crosses the blood-brain barrier easily and acidifies (lowers the pH of) the cerebrospinal fluid (CBF). - The respiratory center (in the medulla ) sends nervous impulses to increase rate and depth of respiration to remove excess Co2 and neutralize PH. 2. **Low Amount of CO2:** Due to hyperventilation as in anxiety attack, less carbonic acid in blood, so the concentration of hydrogen ions decreases and the pH of the blood rises, making blood alkaline. - The chemoreceptors detect this change, and send a signal to the medulla, which signals the respiratory muscles to decrease the ventilation rate so carbon dioxide levels and pH can return to normal levels. - This process is called **Respiratory Buffer System**. 3. **Low Oxygen Suppy (Hypoxia):** Reduction in the supply of oxygen to the tissues causes hypoxia. - Chemoreceptors initiate impulses to the respiratory center increased rate of respiration. ## Special Case: Central Chemoreceptors - Central chemoreceptors are desensitized against hypoxia (oxygen deficiency) and increased carbon dioxide. - This is due to respiratory depression by **opiates**, which inhibits the buffering systems and causes a drop in pH. - **Therefore, the kidneys have to excrete more hydrogen ions in addition to an increase in bicarbonate reabsorption.** ## Chemoreceptor Reflex - A diagram illustrating the location of carotid and aortic bodies. - Both contain chemoreceptor cells that respond when blood flow decreases. ## Main Chemoreceptors Involved in Respiration 1. **Central Chemoreceptors:** - These are located on the medulla oblongata and detect changes in the pH of cerebrospinal fluid. 2. **Peripheral Chemoreceptors:** - Include: - **Theortic body**: Detects changes in blood oxygen and carbon dioxide, but not pH. - **Carotid body:** Detects all three as they detect arterial **acidosis** (resulting from the increase of CO2 in the blood) and are most sensitive to the oxygen content of the blood. - **Hypoxia (low oxygen) and hypercapnia (high carbon dioxide) are detected by the peripheral chemoreceptors. Signals carried back from the carotid and aortic bodies to the brainstem, which response accordingly by increasing ventilation**. ## The Defense Mechanisms of the Respiratory System - **Defense mechanisms, including:** - **Irritant reflex:** Is triggered when inhaled particles, cold air, or toxins stimulate irritant receptors. Reflex bronchospasm then occurs to limit the exposure, followed by **coughing**, which expels the irritant. - **Mucociliary system:** Produces mucus, which traps foreign particles. Foreign matter is then swept to the upper airway for expectoration. - **A breakdown in the epithelium of the mucociliary system can cause the defense mechanisms to malfunction. This allows atmospheric pollutants and irritants to enter and cause inflammation to occur in the lungs.** - **Secretory immunity:** Protects the lungs by releasing an antibody in the respiratory mucosal secretions that initiates an immune response against antigens. ## Respiratory Disorders 1. **Bronchial Asthma** - Asthma is a chronic reactive airway disorder that can present as an acute attack. - Causes airway obstruction resulting from bronchospasms, increased mucus secretion. - The three most common signs and symptoms: cough, dyspnea, wheezing, and chest tightness 2. **Emphysema** - A form of COPD, accompanied by destruction of the elastic fibers in alveolar membranes which causes airflow limitation. - **Pathogenesis:** - Emphysema may be caused by a deficiency of Alpha-1 antitrypsin which inhibit the inactivation elastase enzyme which degrade elastin so, alveoli lost its elasticity by **cigarette smoking.** - Emphysema is a lung condition that causes **shortness of breath**, the inner walls of the air sacs weaken and rupture - creating larger air spaces instead of many small ones. This reduces the surface area of the lungs and, in turn, the amount of oxygen that reaches bloodstream. - During exhalation, the damaged alveoli don't work properly and old air becomes trapped, leaving no space for fresh, oxygen-rich air to enter - **Signs and symptoms of emphysema include:** - **Dyspnea (initial symptom)** - **Barrel-shaped chest.** - **Prolonged expiration** - A Diagram illustrates a person with barrel-shaped chest.