Respiratory System

Non-respiratory functions of the system: 1-water loss and heat elimination, also keeps alveoli wet 2-inhances venous return 3-acid-base balance 4-enables speech 5-defends against foreign inhaled matters. 6-removes, modifies, & activate or inactivate materials “prostglandins” 7-smelling 8-shape of the chest 9-protects heart & vessels 10-aireate the blood between respiratory phases

Respiratory Physiology Structure : Air conducting channels Respiratory spaces  lungs float in the thoracic cavity + pleura

Respiratory passages comprises two portions A- Conducting part 1- Nose and mouth 2- Nasal cavity 3- Pharynx 4- Larynx 5- Trachea 6- Bronchi and Bronchioles Inside lungs B- Respiratory part 1- Alveolar ducts, Alveolar Sacs and alveoli inside lungs Larynx

Respiratory Physiology Steps: 1- pulmonary ventilation: air flow between the atmosphere and the lungs. 2- diffusion of gasses between the alveoli and the blood. 3- transport. 4- regulation.

Steps of external respiration Atmosphere Steps of external respiration 1 Ventilation or gas exchange between the atmosphere and air sacs (alveoli) in the lungs O2 CO2 Alveoli of lungs 2 Exchange of O2 and CO2 between air in the alveoli and the blood CO2 O2 Pulmonary circulation 3 Transport of O2 and CO2 between the lungs and the tissues FIGURE 12-1: External and internal respiration. External respiration encompasses the steps involved in the exchange of O2 and CO2 between the external environment and tissue cells (steps 1 through 4). Internal respiration encompasses the intracellular metabolic reactions involving the use of O2 to derive energy (ATP) from food, producing CO2 as a by-product. Systemic circulation CO2 O2 4 Exchange of O2 and CO2 between the blood and the tissues Food + O2 CO2 + HO2 + HTP Internal respiration Tissue cell Fig. 12-1, p. 366

Mechanics of ventilation 1.By down word and upward movement of the diaphragm  lengthen or shorten(Normal) 2.By elevation and depression of the ribs (anteropost ) ribs and sternum moves away from the spine (20% more)

Mechanics of ventilation Muscles : 1- Inspiratory : - Diaphragm External intercostals Sternocloidomastoid Sternum - Scalini (2 ribs) Anterior serrati

Mechanics of ventilation 2- Expiratory muscles : - internal intercostals Abdominal recti

Accessory muscles of inspiration Internal intercostal muscles Sternocleidomastoid Scalenus Muscles of active expiration Sternum Ribs External intercostal muscles FIGURE 12-10: Anatomy of the respiratory muscles. Diaphragm Abdominal muscles Major muscles of inspiration Fig. 12-10, p. 373

Respiratory muscles

Airway resistance.. Due to friction when air moves through airways. Medium-sized bronchi contribute most of the resistance. Small airways contribute 20 %.

Factors responsible for elastic recoil of lungs Elastic fibers in the lungs & chest wall. The surface tension in the fluid lining the alveoli.

Cont… At end of quit exp-5 cm H2o. At end of quit insp -8 cm H2o. More (-) during maximal inspiration. Becomes (+) during maximal expiration.

Lollipop “Lung” “Pleural sac” Water-filled balloon “Pleural sac” Right pleural sac Left pleural sac FIGURE 12-4: Pleural sac. (a) Pushing a lollipop into a water-filled balloon produces a relationship analogous to that between each double-walled, closed pleural sac and the lung that it surrounds and separates from the thoracic wall. (b) Schematic representation of the relationship of the pleural sac to the lungs and thorax. One layer of the pleural sac closely adheres to the surface of the lung, then reflects back on itself to form another layer, which lines the interior surface of the thoracic wall. The relative size of the pleural cavity between these two layers is grossly exaggerated for the purpose of visualization. Parietal pleura Right lung Left lung Thoracic wall Visceral pleura Pleural cavity filled with intrapleural fluid Diaphragm Pleural cavity filled with intrapleural fluid Fig. 12-4, p. 369

Respiratory pressure 1- Pleural pressure: fluid pressure slight suction that helps the lungs to open at rest . (-5 to -7.5)cm H2O, during normal inspiration.

Cont… At end of quit exp-5 cm H2o. At end of quit insp -8 cm H2o. More (-) during maximal inspiration. Becomes (+) during maximal expiration.

Respiratory pressure A- Glottis open, no air flow 0 cm H2O 2- Alveolar pressure : the pressure Inside the Alveoli: A- Glottis open, no air flow 0 cm H2O B- Inward flow sub atmospheric (-1 cm H2O) within 2s C- Outward flow positive (1 cm H2O) within 2-3s.

Atmospheric pressure (the pressure exerted by the weight of the gas in the atmosphere on objects on the Earth’s surface—760 mm Hg at sea level) Atmosphere 760 mm Hg Airways Thoracic wall Intra-alveolar pressure (the pressure within the alveoli—760 mm Hg when equilibrated with atmospheric pressure) Plural wall FIGURE 12-5: Pressures important in ventilation. Lungs Intrapleural pressure (the pressure within the pleural sac—the pressure exerted outside the lungs within the thoracic cavity, usually less than atmospheric pressure at 756 mm Hg) 756 mm Hg Fig. 12-5, p. 370

Respiratory pressure 3- Transpulmonary pressure : Pressure difference between the alveolar pr. and pleural pr. [pr.differ. b/w alveoli and outer surfaces of the lungs] it measures elastic forces that tend to collapse the lungs each point of expansion [recoil pressure] .

Numbers are mm Hg pressure. Airways Pleural cavity (greatly exaggerated) Lung wall Lungs (alveoli) Thoracic wall FIGURE 12-7: Transmural pressure gradient. Across the lung wall, the intra-alveolar pressure of 760 mm Hg pushes outward, while the intrapleural pressure of 756 mm Hg pushes inward. This 4-mm Hg difference in pressure constitutes a transmural pressure gradient that pushes out on the lungs, stretching them to fill the larger thoracic cavity. Transmural pressure gradient across lung wall = intra-alveolar pressure minus intrapleural pressure Transmural pressure gradient across thoracic wall = atmospheric pressure minus intrapleural pressure Numbers are mm Hg pressure. Fig. 12-7, p. 371

Inspiration Expiration Intra-alveolar pressure Atmospheric pressure Transmural pressure gradient across the lung wall Intraplural pressure FIGURE 12-13: Intra-alveolar and intrapleural pressure changes throughout the respiratory cycle. Fig. 12-13, p. 375

760 760 760 760 760 756 756 Traumatic pneumothorax Puncture wound in chest wall 760 760 760 760 756 756 FIGURE 12-8: Pneumothorax. (a) Traumatic pneumothorax. A puncture in the chest wall permits air from the atmosphere to flow down its pressure gradient and enter the pleural cavity, abolishing the transmural pressure gradient. Traumatic pneumothorax (Continue to the next slide) Numbers are mm Hg pressure. Fig. 12-8a, p. 371

Spontaneous pneumothorax Numbers are mm Hg pressure. 760 Hole in lung 760 760 760 760 756 756 FIGURE 12-8: Pneumothorax. (c) Spontaneous pneumothorax. A hole in the lung wall permits air to move down its pressure gradient and enter the pleural cavity from the lungs, abolishing the transmural pressure gradient. As with traumatic pneumothorax, the lung collapses to its unstretched size. Spontaneous pneumothorax Numbers are mm Hg pressure. Fig. 12-8c, p. 371

(Continue to the next slide) Numbers are mm Hg pressure. 760 760 760 760 760 760 756 FIGURE 12-8: Pneumothorax. (b) When the transmural pressure gradient is abolished, the lung collapses to its unstretched size. Collapsed lung (Continue to the next slide) Numbers are mm Hg pressure. Fig. 12-8b, p. 371

Compliance of the lungs Expandability of the lungs  stretch ability of the lungs. The extent to which the lungs will expand for each unit increase in transpulmonary pr. total compliance of both lungs is around 200 ml/cm H2O transpulmonary pressure .

Compliance of the lungs The extent to which the lungs expand for each unit increase in transpulmonary pressure. Compliance= Normal value= 200 ml/cm H2O V P

Chest wall compliance Chest wall is an elastic structure. Compliance of the respiratory sys is a combination of both, lung & chest wall compliance.

Compliance of the lungs A. the curves in the figure above depend on the elastic forces of the lungs : 1) elastic forces of the lung tissue (elastin and collagen fibres) (1/3 of the total force) 2) Surface tension of the fluid (2/3 of the total force) Surface tension is huge when surfactant is absent : H2O molecules on the surface of the water have an extra strong attraction for one another attempting to contract and collapse the alveoli.

Compliance of the lungs B. Surfactant : surface-active agent in water secreted by type II alveolar epithelial cells (10% of surface area of alveoli). Phospholipids, dipalmitoylphosphotidylcholine (DPPC) proteins (apoprotein), and ions (calcium) that help in spreading phospholipids

Compliance of the lungs Without surfactant With surfactant Surface tension 50 dynes/cm 5-30 dynes/cm Collapsing pressure In one alveoli 18 cm H2O 4 cm H2O

Compliance of the lungs Pressure generated by S.T = 2x S.T. Radius Effect of size of the alveoli on collapsing pr.: The Radius is inversely proportional to coll. pr. So smaller alveoli have greater pr. than the larger ones. premature babies have small alveolar radius and less surfactant  tendency for lung collapse is 6-8 times greater than in adults  Respiratory distress syndrome of the newborn

The Relationship Between Pressure & Surface Tension in Alveolus Laplace’s law

Rule of surfactant… The tension is decreased with decrement of radius therefore the pressure kept constant. Causes surface tension to vary with surface area of the alveolus.

Physiological advantage of surfactant Increase lung compliance. Prevents collapsing tendency of the alveoli. Decrease surface tension.

Compliance of the lungs -Compliance of thorax and lungs : 110 ml/cm H2O pr. - At high volume or compressed to low volumes, the compliance can be as little as one-fifth that of lungs alone .

Work of breathing -Work of breathing: 1.work required to expand the lungs against the lung and chest elastic forces (compliance work) 2.work required to overcome the viscosity of the lung and chest wall (tissue resistance work) 3. work required to overcome airway resistance (airway resistance work)

Energy required for respiration: 3-5% of total body energy and can increase to 50 fold during heavy exercise and some obstructive diseases.