Structure and Functions of the Respiratory System PDF

STRUCTURE AND FUNCTIONS OF RESPIRATORY SYSTEM DR ASHFAQ BUKHARI ASSISTANT PROFESSOR- PHYSIOLOGY  LEARNING OBJECTIVES At the end of the lecture, students will be able to: 1. Explain the functional anatomy of the respiratory system, including the structure of the airways, lungs,...

STRUCTURE AND FUNCTIONS OF RESPIRATORY SYSTEM DR ASHFAQ BUKHARI ASSISTANT PROFESSOR- PHYSIOLOGY  LEARNING OBJECTIVES At the end of the lecture, students will be able to: 1. Explain the functional anatomy of the respiratory system, including the structure of the airways, lungs, and thoracic cavity. 2. Describe the mechanisms involved in inspiration and expiration, including the roles of respiratory muscles and the relationship between pressure changes and airflow.  INTRODUCTION ❖Body’s cell continually use oxygen (O2) for the metabolic reactions that release energy from nutrient molecules and produce ATP, at the same time, these reactions release carbon dioxide (CO2). ❖This system also participates in regulating blood pH ❖This system helps to contributes to homeostasis by providing for the exchange of gases oxygen & carbon dioxide between air, blood and tissue cells.  STRUCTURE ❖Respiratory system parts can be classified according to either structure or function. ❖Structurally the respiratory system consist of two parts: 1) Upper respiratory system( Nose, Nasal cavity, Pharynx and associated structure) 2) Lower respiratory system (Larynx, Trachea, Bronchi and Lungs)  STRUCTURE ❖Functionally the respiratory system consist of two parts: 1) Conducting zone: (Nose, Nasal cavity, Pharynx, Larynx, Trachea, Bronchi, Bronchioles and terminal Bronchioles). 1) Respiratory zone: (Respiratory bronchioles, Alveolar ducts, Alveolar sacs, Alveoli). Structure's of the Respiratory System  BREATHING Breathing (pulmonary ventilation). consists of two cyclic phases: Inhalation, also called inspiration - draws gases into the lungs. Exhalation, also called expiration - forces gases out of the lungs. RESPIRATORY EVENTS Pulmonary ventilation = exchange of gases between lungs and atmosphere External respiration = exchange of gases between alveoli and pulmonary capillaries Internal respiration = exchange of gases between systemic capillaries and tissue cells  PHASES OF PULMONARY VENTILATION Inspiration, or inhalation - A very active process that requires input of energy. The diaphragm contracts, moving downward and flattening. Expiration, or exhalation - A passive process that takes advantage of the recoil properties of elastic fiber. The diaphragm relaxes. The elasticity of the lungs and the thoracic cage allows them to return to their normal size and shape.  PHYSIOLOGY OF RESPIRATION The process of gas exchange in the body, called respiration, it has three basic steps: 1. External Pulmonary ventilation: Involves the exchange of air between the atmosphere and the alveoli of the lungs. 2. Internal (pulmonary) ventilation: It is the exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries across the respiratory membrane. In this process, pulmonary capillary blood gains O2 and loses CO2.  CONT. 3. Internal (tissue) respiration It is the exchange of gases between blood in systemic capillaries and tissue cells. In this step the blood loses O2 and gains CO2. Within cells, the metabolic reactions that consume O2 and give off CO2 during the production of ATP are termed cellular respiration  INHALATION Breathing IN is called inhalation (inspiration) Each inhalation, the air pressure inside the lungs is equal to the air pressure of the atmosphere, which is about 760 mmHg. Air to flow into the lungs, the pressure inside the alveoli must become lower than the atmospheric pressure. This condition is achieved by increasing the size of the lungs. EVENTS OF INSPIRATION  EXHALATION Breathing out or exhalation starts when the inspiratory muscles relax. As the diaphragm relaxes, its dome moves superiorly owing to its elasticity. As the external intercostals relax, the ribs are depressed. The pressure in the lungs is greater than the pressure of the atmosphere. Normal exhalation during quiet breathing  CONT. It is a passive process because no muscular contractions are involved. Instead, exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched. Two inwardly directed forces contribute to elastic recoil: a. The recoil of elastic fibers that were stretched during inhalation b. The inward pull of surface tension due to alveolar fluid. STEPS OF EXPIRATION  MINUTE RESPIRATORY VOLUME This is the total amount of new air moved into the respiratory passages each minute. Normally, this is ~ 500 ml x 12 breaths/min = 6L/min.  ALVEOLAR VENTILATION The key area to bring new air in is to the alveoli, where gas exchange occurs with the pulmonary blood. Air that does not reach the gas exchange areas is called “dead space air”. The normal amount of dead space air in a young adult male ~ 150 ml.  EXTERNAL RESPIRATION OR PULMONARY GAS EXCHANGE External respiration in the lungs converts deoxygenated blood (depleted of some O2) coming from the right side of the heart into oxygenated blood (saturated with O2) that returns to the left side of the heart. As blood flows through the pulmonary capillaries, it picks up O2 from alveolar air and unloads CO2 into alveolar air, this process is called an “exchange” of gases, this process is carried by diffusion.  INTERNAL RESPIRATION The left ventricle pumps oxygenated blood into the aorta and through the systemic arteries to systemic capillaries. The exchange of O2 and CO2 between systemic capillaries and tissue cells is called internal respiration or systemic gas exchange  SURFACE TENSION Surface tension is the force that arises due to the attraction between water molecules at the air-liquid interface within the alveoli. In the lungs, the alveoli are lined with a thin layer of fluid, and the water molecules in this fluid have a tendency to stick together, creating tension that would naturally lead to alveolar collapse.  SURFACTANT Surfactant is a lipoprotein substance secreted by Insert fig. 16.12 specialized alveolar cells (type II pneumocytes) in the lungs. Its primary function is to reduce surface tension within the alveoli, which are the tiny air sacs where gas exchange occurs.  EFFECTS OF SURFACE TENSION WITHOUT SURFACTANT Tendency for Alveolar Collapse: Smaller alveoli experience greater surface tension, which increases the pressure inside them This makes smaller alveoli more prone to collapse and leads to instability in the lung.  CONT. Increased Work of Breathing: If unopposed, surface tension would make it much harder for the lungs to expand during inhalation, requiring excessive effort to breathe. Unequal Alveolar Inflation: Without a mechanism to counteract surface tension, smaller alveoli would collapse into larger ones, leading to uneven gas exchange and impaired oxygenation.  FUNCTIONS OF SURFACTANT 1.Reduction of Surface Tension: 1. Surfactant decreases the cohesive forces between water molecules on the alveolar surface. 2. This prevents alveoli from collapsing during exhalation and ensures they remain open for efficient gas exchange. 2.Improved Lung Compliance: 1. By reducing surface tension, surfactant increases the lungs ability to expand and contract, making breathing easier. 3. Prevention of Alveolar Collapse (Atelectasis): 1. During exhalation, the alveoli naturally tend to shrink due to surface tension. Surfactant helps maintain their stability, ensuring they do not completely collapse. 4. Facilitation of Uniform Alveolar Expansion: 1. Surfactant ensures that smaller alveoli do not collapse into larger ones due to differences in pressure, promoting uniform expansion of alveoli. 5. Role in Host Defense: 1. Surfactant contains proteins that contribute to immune defense by facilitating the clearance of pathogens and debris from the alveoli.  BOYLE’S LAW Changes in intrapulmonary pressure occur as a result of changes in lung volume. – Pressure of gas is inversely proportional to its volume. Increase in lung volume decreases intrapulmonary pressure. – Air goes in. Decrease in lung volume, raises intrapulmonary pressure above atmosphere. – Air goes out.  QUIET INSPIRATION Active process: – Contraction of diaphragm, increases thoracic volume vertically. – Contraction of parasternal and internal intercostals, increases thoracic volume laterally. – Increase in lung volume decreases pressure in alveoli, and air rushes in. Pressure changes: – Alveolar changes from 0 to –3 mm Hg. – Intrapleural changes from –4 to –6 mm Hg. – Transpulmonary pressure = +3 mm Hg. (Is the difference between the alveolar pressure and the intrapleural pressure )  EXPIRATION Quiet expiration is a passive process. – After being stretched, lungs recoil. – Decrease in lung volume raises the pressure within alveoli above atmosphere, and pushes air out. Pressure changes: – Intrapulmonary pressure changes from –3 to +3 mm Hg. – Intrapleural pressure changes from –6 to –3 mm Hg. – Transpulmonary pressure = +6 mm Hg. https://www.youtube.com/watch?v=ldSov_z6sJA