Respiratory System PDF

Respiratory system Dr. Sally mohamed Lecturer Of Physiology FOM-SCU  Objectives: Organization of the respiratory system Type of respiration Mechanism of breathing Transport of blood gasses. Control of breathing  Organization of the Respiratory System...

Respiratory system Dr. Sally mohamed Lecturer Of Physiology FOM-SCU  Objectives: Organization of the respiratory system Type of respiration Mechanism of breathing Transport of blood gasses. Control of breathing  Organization of the Respiratory System The Airways Upper Lower Airways Airways Trachea Nose Bronchial Pharynx tree larynx Alveoli  Organization of the Respiratory System The upper respiratory tract: 1- The nose: warming and humidification of the inspired air, and filtration and cleaning. 2- The pharynx: “throat”. (pharynx is a passage common to both air and food). 3- The larynx: The pharynx branches into two tubes, the esophagus through which food passes to the stomach, and the larynx, which is part of the airways. - The larynx houses the vocal cords. The flow of air past the vocal cords causes them to vibrate, producing sounds.  Organization of the Respiratory System The lower respiratory tract: 1. The trachea: the larynx opens into a long tube called the trachea. 2-The bronchi: Trachea branches into two bronchi, each one enters a lung. - The walls of the trachea and bronchi contain cartilage, which gives them their cylindrical shape and supports them. 3- The bronchioles: the first airway branches that no longer contain cartilage  Organization of the Respiratory System The lungs consist mainly of tiny air-containing sacs called alveoli which number approximately 300 million in an adult. The alveoli are the sites of gas exchange with the blood. Steps of respiration  Phases Of Respiration Respiration occurs in two phases: 1. Inspiration during which air enters the lungs from atmosphere 2. Expiration during which air leaves the lungs. During normal quiet breathing, inspiration is an active process and expiration is a passive process.  Expiration is active during…….. During exercise or voluntary hyperventilation, expiration becomes an active process. Under these conditions, a larger volume of air must be exhaled more rapidly The most important muscles of expiration are the muscles of the abdominal wall. Contraction of these muscles pushes inward on the abdominal contents and increases abdominal pressure. As a result, the diaphragm is pushed upward more rapidly and more forcefully toward its preinspiration position.  Mechanics of Respiration Air moves by bulk flow from a region of high pressure to one of low pressure The movement of air into and out of the lungs occurs as a result of pressure differences induced by changes in lung volumes.  Pressures affecting respiration All pressures in the respiratory system, are given relative to atmospheric pressure, which is 760 mmHg at sea level For example, the alveolar pressure between breaths is said to be 0 mmHg, which means that it is the same as atmospheric pressure. Intrapleural pressure is the pressure existing in pleural cavity. It is always negative caused by elastic recoil of both lungs and chest wall (As the lungs tend to collapse and the thoracic wall tends to expand, they move ever so slightly away from each other creating this pressure)  Stretchability of the lung (compliance) Refers to the ease with which the lungs can expand under pressure. Two major determinates of lung compliance: 1.Stretchability of the lung tissues, particularly their elastic connective tissues. Therefore, a thickening of the lung tissues decreases lung compliance 2.Surface tension at the air–water interfaces within the alveoli.  Surface Tension The inner surface of the alveolar cells is moist, so the alveoli can be pictured as air-filled sacs lined with a layer of liquid. At an air–water interface, the attractive forces between the water molecules, known as surface tension, make the water lining like a stretched balloon that constantly tends to shrink and resists further stretching. Therefore, expansion of the lung requires energy not only to stretch the connective tissue of the lung but also to overcome the surface tension of the water layer lining the alveoli.  Surfactant markedly reduces the cohesive forces between water molecules on the alveolar surface. The net result is that surfactant lowers the surface tension, which increases lung compliance and makes it easier to expand the lungs. Secreted by the type II alveolar cells. Surfactant becomes interspersed between water molecules at the water– air interface; this reduces the hydrogen bonds between water molecules  Transport of blood gases TRANSPORT OF OXYGEN: Transport of Carbon dioxide: 1. As dissolved form (7%) 1. As dissolved form (3%) 2. As bicarbonate (63%) 2. In combination with haemoglobin (97%) 3. As carbamino compounds (30%).  Control of Respiration Control of respiration is achieved by two mechanisms: 1- neural control 2- chemical regulation  1- Neural Generation of Rhythmical Breathing Inspiration is initiated by a burst of action potentials in the nerves to the inspiratory muscles. Then the action potentials stop, the inspiratory muscles relax, and expiration occurs as the elastic lungs recoil.  1- Neural Control of Breathing Medullary inspiratory neurons: located in the medulla, discharge in synchrony with inspiration and stop discharging during expiration. They provide the rhythmic input to the motor neurons innervating the inspiratory muscles.  Medullary respiratory centers Inspiratory center Expiratory center (dorsal (ventral respiratory group) respiratory group) Active only during forced breathing Always active (exercise)  2- Chemical Regulation of Respiration Control of Ventilation by PO2, PCO2, and H Concentration: 1. Peripheral chemoreceptor 2. Central chemoreceptor  2- Chemical Regulation of Respiration The peripheral chemoreceptors are stimulated mainly by a decrease in the arterial PO2 and an increase in the arterial H and CO2 concentration. They send signals to the brainstem. There they provide excitatory synaptic input to the medullary inspiratory neurons.  2- Chemical Regulation of Respiration The central chemoreceptors are located in the medulla and they provide excitatory synaptic input to the medullary inspiratory neurons.  The central chemoreceptors They are stimulated by an increase in the H concentration of the brain’s extracellular fluid. such changes result mainly from changes in blood PCO2. 2- Chemical Regulation of Respiration