Respiratory System

1. Respiratory System Ch. 16 Section 3-6

2. 16.3 Breathing Mechanism • Breathing, ventilation • Movement of air from outside the body into and out of the bronchial tree and alveoli. • Inspiration – inhalation • Expiration - exhalation

3. Inspiration Atmospheric pressure: force that moves air into the lungs. If pressure inside the lungs and alveoli decreases, atmospheric pressure will push outside air into the airways. The diaphragm contract, moves downward, thoracic cavity enlarges, the pressure decreases within the alveoli. Air is pushed into lungs. While diaphragm moves downward, external intercostal muscles contract, raising ribs and elevates the sternum, enlarging the thoracic cavity even more.

4. Pleural Membranes Any separation of the pleural membranes decreases pressure in the intrapleural space, holding these membranes together. Thin film of serous fluid separates the parietal pleura on the inner wall of the thoracic cavity from the visceral pleura. Pleura expands when the lungs expand. Moist inner surface of alveoli: attraction of water molecules creates a force called surface tension; makes it difficult to inflate the alveoli and may actually cause them to collapse. Alveolar cells, create a mixture of lioproteins called surfactant: secreted into alveolar air spaces, reduces the alveoli’s tendency to collapse, especially when lung volumes are low.

6. Newborns Surfactant is very important in the minutes after birth. Premature infants often suffer respiratory distress syndrome because they do not produce sufficient surfactant. Physicians drip synthetic surfactant into the tiny lungs through an endotracheal tube. Ventilator machine assists breathing.

7. Newborn It takes twenty times the energy to take the first breath as for subsequent breaths. This is because each of the millions of alveoli start out only partially inflated.

8. Expiration Forces for expiration come from the elastic recoil of tissues and from surface tension. Lungs and thoracic have a lot of elastic tissue, lung expansion during inspiration stretches this tissue. The elastic tissues causes the lungs and thoracic cage to recoil and return to their original shapes as the diaphragm and external intercostal muscles relax. The surface tension that develops between the moist surfaces of the alveolar linings decreases the diameters of the alveoli. This increases alveolar pressure above atmospheric pressure so that the air inside the lungs is forced out through respiratory passages. (expiration is a passive process)

9. hiccup Spasmodic contraction of the diaphragm while the glottis closed. Air striking the vocal folds causes the sound of the hiccup.

10. Respiratory Air Volumes and Capacities • Spirometry: measures air volumes in lungs. • Respiratory volumes: 4 • Tidalvolume: volume of air that enter during a single respiratory cycle. (Normal 500mL of air) • Resting tidal volume: normal, resting. • Inspiratoryreservevolume: forced inspiration, air in addition to the resting tidal volume. (max 3,000mL) • Expiratoryreservevolume: forced expiration, the lungs can expel up to about 1,100 mL of air beyond the resting tidal volume. • Residualvolume: air that remains in the lungs, 1,200mL

11. Cont… Respiratory cycle – inspiration plus the following expiration Combining two or more of the respiratory volumes –respiratory capacities. Inspiratory reserve volume (3,000mL) + tidal volume (500mL) + expiratory reserve volume (1,100mL) = vitalcapacity (4,600mL) which is the maximum volume of air a person can inhale following a resting expiration.

12. Cont… Expiratory reserve volume (1,100mL) + residual volume (1,200mL) = functionalresidualcapacity (2,300mL) which is the volume of air that remains in the lungs following a resting expiration. Vital capacity + residual volume = totallungcapacity (about 5,800mL) Varies with age, sex, and body size. Some air does not reach the alveoli (150mL) remains in the passageways of the trachea, bronchi and bronchioles. This air is said to occupy anatomicdeadspace.