Outline-3, BIO 2320, Respiratory Physiology

C. Respiration

1. Overall function

Movement of gases, gas exchange, transport of gas (oxygen and carbon dioxide)

2. Pulmonary Ventilation

a. Boyle’s Law

Gas pressure in closed container is inversely proportional to volume of container

b. Pressure differences and air flow

Air flows from area of higher pressure to lower pressure

c. Atmospheric pressure

760 mm Hg at sea level

d. Intrapleural pressure (756mmHg)

Pressure between pleural layers, helps to keep lungs expanded

e. Intrapulmonary pressure

Pressure inside lungs, changes with size of lungs & Boyle’s law

3. Inspiration/Inhalation

a. Diaphragm & Intercostal muscles

Contract and lowers diaphragm, elevates ribs

b. Volume thoracic cavity


c. Volume of lungs


d. Intrapulmonary pressure (758mmHg)

As volume (container) increases, pressure drops (Boyle’s law), now air moves from atmospheric pressure (760 mm Hg) into lungs (758 mm Hg)

4. Expiration/Exhalation

a. Volume thoracic cavity


b. Volume of lungs


c. Intrapulmonary pressure (763mmHg)

As volume decreases, pressure increases, now air moves from lungs (763 mm Hg) out to atmosphere (760 mm Hg)

d. Relaxed muscles

Diaphragm returns to dome shape and ribs lower

e. Forced expiration

Abdominal muscles and intercostal muscles can contract and further decrease size of thoracic cavity

5. Factors that influence pulmonary air flow

a. F=P/R

b. Diameter of airways; esp. bronchioles

c. Parasympathetic & Sympathetic Stimulation

6. Surface tension

a. Lung collapse

Surface tension tends to oppose alveoli expansion

b. Pulmonary surfactant

Phospholipid/protein made by alveolar cells that greatly reduce surface tension

7. Lung volumes & capacities

a. Tidal volume

Volume of air in or out of lungs at rest, 500 mls

1. Respiratory rate

12 breaths/minute at rest

2. Minute respiratory volume[6000ml/min] 12 x 500

b. Inspiratory reserve volume[3000,2100 mls]

Air that can be inspired in addition to quiet tidal volume

– Inspiratory capacity [TV + IRV]

c. Expiratory reserve volume[1200,800 mls]

Air that can be forced out after quiet tidal volume

1. Residual volume[1200 ml]

Air that cannot be expired no matter how hard you try

2. Functional residual capacity[ERV + RV] air left in lungs after exhaling quiet tidal volume

d. Vital capacity[IRV + TV + ERV; 4700, 3400 mls] Maximum amount of air that can be moved in and out of lungs

e. Total lung capacity

f. Dead air volume

Air not in alveoli

8. Alveolar ventilation efficiency

a. R.R. x (Tid. Vol. – Dead Air Vol) = A.V. (4200)

b. Double R.R. (A.V. = 8400 ml/min)

c. Double T.V. (A.V. = 10,200 ml/min)

9. Matching alveolar airflow with blood flo

a. Pulmonary vessels

Vessels can constrict in areas where oxygen is low

b. Respiratory passageways

Airways can dilate where carbon dioxide levels are high

D. Gas exchange

1. Partial pressure

Each gas in atmosphere contributes to entire atmospheric pressure, denoted as P

2. Gases in liquid

Gas enters liquid and dissolves in proportion to its partial pressure

3. O2 & CO2 exchange

Inhaled air mixes with old air in lungs, PO2 is 105 mmHg in alveoli and PO2 is 40 in alveolar capillaries, thus net diffusion of oxygen into blood. PCO2 is 45 in alveolar capillaries and 40 in alveoli, so carbon dioxide diffuses into alveoli.

E. Gas transport

1. O2 transport in blood

a. Hemoglobin

Oxygen binds to heme group on hemoglobin, 4 oxygen/hemoglobin

b. PO2

PO2 is the most important factor determining whether oxygen and hemoglobin combine or dissociate.

c. O2-Hb dissociation curve

If PO2 is low, hemoglobin binds less oxygen, if PO2 is high, hemoglobin binds more oxygen

d. pH & CO2

Acidic pH, high carbon dioxide levels shift the curve to the right

e. Temperature

Increased temperature shifts the curve to the right


Increased levels of metabolic byproducts shifts the curve to the right

2. CO2 transport in blood

a. 7% plasma

b. 23% carbamino compounds (globin of Hemoglobin)

c. 70% bicarbonate

1. Carbonic anhydrase-enzyme

CO2 + H2 O<–> H2CO3 <–> H+ + HCO3

2. Chloride shift

As bicarbonate moves out of RBC, chloride must move in etc…

F. Control of respiration (ventilation)

1. Medullary Rhythmicity area

a. Medullary inspiratory neurons

Main control of breathing

1. Pons neurons

a. Pneumotaxic area (limits period of inspiration)

b. Apneustic area (prolongs inspiration)

2. Lung stretch receptors=Mechanoreceptors (inhibits inspiration)

b. Medullary expiratory neurons

Only active with exercise/forced expiration

2. Control of rate & depth of respiration

a. Arterial PO2

When PO2 is VERY low, alveolar ventilation is stimulated

b. Arterial PCO2 [5 mmHg increase, increases ventilation by 100%]

The major regulator of alveolar ventilation is PCO2.

c. Arterial pH

As hydrogen ions increase, alveolar ventilation increases, but hydrogen ions can’t diffuse into CSF as well as CO2

G. Effects of exercise

1. Neural signals [rate & depth increase]

2. PCO2 (PO2& pH)

3. Cardiac output

4. Maximal hemoglobin saturation

5. Dilate airways

Respiratory Airflow Video

Lung Volumes Video

Partial Pressure Video

Gas Exchange Video

Carbon Dioxide Transport Video