1. Physiology of the Respiratory System

2. Pulmonary Ventilation
Breathing, 2 phases
Inspiration: air moves into the lungs
Expiration: air moves out of the lungs
Gas moves down a pressure gradient
Air in the atmosphere exerts pressure of 760 mm Hg

4. Inspiration
Diaphragm contracts, it flattens, which makes thoracic cavity longer
Intercostals muscles contract, elevated sternum & ribs, which enlarges thoracic cavity
Lungs pulled out because of cohesion of the pleura
Air pressure in alveoli & tubes decrease & air moves into lungs

5. Elastic recoil
Tendency of the thorax & lungs to return to their preinspiration volume

6. Expiration Inspiratory muscles relax, decreasing size of thorax
Alveolar pressure increases thus positive pressure gradient from alveoli to atmosphere & expiration occurs

7. Pulmonary Volumes
Tidal volume= volume of air exhaled after a typical inspiration; normal TV=500 ml
Expiratory reserve volume= largest additional volume that can be forcibly expired after expiring tidal air; normal ERV= ml
Inspiratory reserve volume= amount of air that can be forcibly inspired over and above normal inspiration; normal IRV=3300 ml
Residual volume= air that can not be forcibly expired but is trapped in alveoli, RV=1200 ml

8. Vital capacity
Largest volume of air that an individual can move in and out of the lungs
VC=IRV=TV=ERV

9. Alveolar Ventilation
Volume of inspired air that actually reaches the alveoli
Part of air inspired fills our air passageways, this is the anatomical dead space
Anatomical dead space is approximately 30% of TV, thus alveolar ventilation is 70 % of TV

10. Pulmonary Gas Exchange
A gas diffuse “down” its pressure gradient
Concentration of O2 in air is about 21% thus the partial pressure of O2 is about 160 mmHg
21% x 760 mm Hg = 160 mm Hg

12. Amount of Oxygen that diffuses into blood depends on:
Oxygen pressure gradient
Total functional surface area of alveolus
Respiratory minute volume
Alveolar ventilation

13. Hemoglobin
4 polypeptide chains (2 alpha & 2 beta) each with an iron containing heme molecule
Oxygen can bind to iron in heme group
CO2 can bind to amino acids in chain

14. Transport of Oxygen Oxygen travels in two forms in blood:
Dissolved in plasma
Associated with hemoglobin as oxyhemoglobin (most)
Increasing PO2 in blood accelerates hemoglobin association with O2

15. Transport of Carbon Dioxide
Dissolved carbon dioxide (10%)
Bound to amine (NH2) groups of amino acids to form carbaminohemoglobin (20%)
In the form of bicarbonate ions (more than 2/3)
CO2 + H20 H2CO3  H + HCO3
Catalyzed by carbonic anhydrase

16. Carbon Dioxide and pH
Increasing carbon dioxide content of blood increases H ion concentration thus increases the acidity and decrease the pH

18. Respiratory Control Centers
Main integrators that control nerves that affect inspiratory & expiratory muscles are located in brainstem
Medullary rhythmicity center generates basic rhythm of respiratory cycle
Can be altered by input inputs from:
Apneustic center in pons stimulates to increase length and depth of respiration
Pneumotaxic center in pons inhibits apneustic center to prevent overinflation of the lungs

19. Factors that influence breathing
PCO2 acts on chemoreceptors in medulla:
Increasing PCO2 increases RR
Decreasing PCO2 decreases RR
Decrease in blood pH stimulates chemoreceptors in carotid & aortic bodies
Arterial blood PO2 has little influence if it stays above a certain level
Decrease in PO2 below 70 mmHg increases RR

20. Arterial blood pressure & breathing
Sudden rise in blood pressure results in reflex slowing of respirations

21. Hering-Breuer reflexes
Help control respiratory depth & volume of tidal air

22. Miscellaneous factors
Sudden painful stimulations produces reflex apnea (no respirations) but continued painful stimulus cause faster & deeper respirations
Sudden cold stimuli on skin causes reflex apnea
Stimulation of pharynx or larynx by irritating chemicals or touch causes temporary apnea-choking reflex