Chapter 22 Respiratory System Lecture 8 Part 1: Gases and Ventilation

1. Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 22 Respiratory System Lecture 8 Part 1: Gases and Ventilation

2. Gases and Pressure • Our atmosphere is composed of several gases and exerts pressure • 78% N2, 21% O2, 0.4% H2O, 0.04% CO2 • 760 mm Hg, 1 ATM, 29.92” Hg, 15 lbs/in2,1034 cm H2O • Each gas within the atmosphere exerts a pressure of its own (partial) pressure, according to its concentration in the mixture (Dalton’s Law) • Example: Atmosphere is 21% O2, so O2 exerts a partial pressure of 760 mm Hg. x .21 = 160 mm Hg. • Partial pressure of O2 is designated as PO2

3. Air Movements If volume (of container) increases, pressure decreases and vice versa Stated mathematically: P  1/V (Boyle’s Law) • Moving the plunger of a syringe causes air to move in or out • Air movements in and out of the lungs occur in much the same way Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

4. Lungs at Rest When lungs are at rest, the pressure on the inside of the lungs is equal to the pressure on the outside of the thorax Figure from: Hole’s Human A&P, 12th edition, 2010 Think of pressure differences as difference in the “concentration” of gas molecules and use the rules of diffusion. Higher pressure means higher concentration (ignoring temperature difference)

5. Normal Inspiration An active process • Intra-alveolar (intrapulmonary) pressure decreases to about 758 mm Hg as the thoracic cavity enlarges • Atmospheric pressure (now higher than that in lungs) forces air into the airways • Compliance – ease with which lungs can expand Figure from: Hole’s Human A&P, 12th edition, 2010 Phrenic nerves of the cervical plexus stimulatediphragm to contract and move downward and external (inspiratory) intercostal muscles contract, expanding the thoracic cavity and reducing intrapulmonary pressure. Attachment of parietal pleura to thoracic wall (negative pressure) pulls visceral pleura, and lungs follow.

6. Maximal (Forced) Inspiration Thorax during normal inspiration • Thorax during maximal inspiration • aided bycontraction ofsternocleidomastoid and pectoralis minor muscles Compliance decreases as lung volume increases Costal (shallow) breathing vs. diaphragmatic (deep) breathing Figure from: Hole’s Human A&P, 12th edition, 2010

7. Normal Expiration • due to elastic recoil of the lung tissues and abdominal organs • a PASSIVE process (no muscle contractions involved) Normal expiration is caused by - elastic recoil of the lungs (elastic rebound) and abdominal organs - surface tension between walls of alveoli (what keeps them from collapsing completely?) Figure from: Hole’s Human A&P, 12th edition, 2010

8. Maximal (Forced) Expiration Figure from: Hole’s Human A&P, 12th edition, 2010 • contraction of abdominal wall muscles • contraction of posterior (expiratory) internal intercostal muscles • An active, NOT passive, process

9. Terms Describing Respiratory Rate • Eupnea – quiet (resting) breathing • Apnea – suspension of breathing • Hyperpnea – forced/deep breathing • Dyspnea – difficult/labored breathing • Tachypnea – rapid breathing • Bradypnea – slow breathing Know these

10. Nonrespiratory Air Movements • coughing – sends blast of air through glottis and clears upper respiratory tract • sneezing – forcefully expels air through the nose and mouth • laughing – deep breath released in a series of short convulsive expirations • crying – physiologically same as laughing • hiccupping – spasmodic contraction of diaphragm against closed glottis • yawning – deep inspiration through open mouth • valsalva maneuver – expiration against a closed glottis

11. Alveoli and Respiratory Membrane • consists of the walls of the alveolus and the capillary, and the basement membrane between them Figure from: Hole’s Human A&P, 12th edition, 2010 Surfactant resists the tendency of alveoli to collapse on themselves.

12. Blood Flow Through Alveoli Mechanisms that prevent alveoli from filling with fluid: • cells of alveolar wall are tightly joined together • the relatively high osmotic pressure of the interstitial fluid draws water out of them • there is low (hydrostatic) pressure in the pulmonary circuit Low pressure circuit Figure from: Hole’s Human A&P, 12th edition, 2010

13. Review • The atmosphere is composed of a mixture of gases • Each gas exerts a partial pressure (Pg) • Sum of all partial pressures = atmospheric pressure (14.7 lbs/in2,760 mm Hg., …) • Gases move from a higher concentration (pressure) to a lower concentration (pressure) • Function of the diaphragm is to create a lower intrpulmonary pressure so that atmospheric gases flow into the lungs

14. Review • Normal inspiration • An active process • Phrenic nerve and diaphragm • External (inspiratory) intercostal muscles • Role of the lung pleura • Normal expiration • A PASSIVE process • Due to elasticity of lung/abdominal organs and alveolar surface tension • Forced inspiration • Forced expiration

15. Review • The respiratory membrane • Simple squamous epithelium of the alveoli and capillaries • Basement membrane between them • Terms used to describe breathing (know these)