RESPIRATORY SYSTEM

RESPIRATORY SYSTEM

We will begin with

CHAPTER 17

Pages 43 through 53

In the CB

Respiratory Structures:

Be certain to view Figures 17.2, 3, & 4

Look at these!

LUNG STRUCTURES

Conducting zone
Trachea
Bronchi
Bronchioles
Terminal bronchioles
Respiratory structures
Respiratory bronchioles
Alveolar ducts
Alveoli

RESPIRATORY STRUCTURES

Diaphragm
Thorasic cage
Ribs (12 pairs)
Sternum
Intercostal muscles:

External and internal

ALVEOLI

Surrounded by capillaries
300 - 500 million
75 m² total surface area
Very short diffusion distance

To illustrate, try breathing through a garden hose

DEAD SPACE

You must subtract the volume of each breath that does not reach the alveoli to get the alveolar ventilation rate

TIDAL VOLUME vs. ALVEOLAR VENTILATION

500 ml / breath x 12 breaths / min
150 ml / breath x 40 breaths / min
1000 ml /breath x 6 breaths / min

IN EACH CASE TIDAL VOLUME = 6 L / min

SO, WHICH ONE IS BEST?

(500 - 150 ml) / breath x 12 breaths / min

= 4200 ml / min

(150 - 150 ml) / breath x 40 breaths / min

= 0 ml / min

(1000 - 150 ml) /breath x 6 breaths / min

5100 ml / min

LaPlace’s Law as applied to alveoli:

P = 2T / r

P = 2T/r

P = Transpulmonary pressure
Pressure keeping the lung and alveoli inflated
Greater P inside lung (atmospheric air at 760 mm Hg) than in pleural space (757 mm Hg)
R = radius of an alveolus
T = Tension in wall of alveolus
Passive elastic tension plus the surface tension

SURFACE TENSION:

Due to its polar nature, water molecules adhere together, giving rise to surface tension at air - water interfaces

Surface Tension

Wall tension of an Alveolus:

FROM INHALATION TO EXHALATION:

P = 2 X 50 dynes/cm P = 2 X 50 dynes/cm

0.05 cm 0.025 cm

P = 2000 dynes/cm² P = 4000 dynes/cm²

Therefore, surface tension must decrease as alveolar radius decreases!

Thus, as alveolar radii decrease, the (2T / r) or alveolar wall tension gets larger than the pressure and alveoli would collapse.

How do alveoli adjust to prevent this?

TO DECREASE SURFACE TENSION, ADD DETERGENT! (also called SURFACE ACTIVE AGENT
or SURFACTANT)

Secreted by Alveolar

Type II Pneumocytes

THUS Surface Tension is proportional to 1/ [DPL] at the surface of the water layer in the alveoli and it changes as alveoli change radii during respiration

As alveolar r decreases during exhalation, LaPlace’s Law

P = 2T/r

is satisfied and the alveoli do not collapse.

Hyaline membrane disease:

An insufficiency of DPL secretion by a new born

Pulmonary Circulation (vs. Systemic)

Low Arterial Pressure
15 vs. 93 mm Hg
Low Right Ventricle -- Left Atrium Pressure Difference (~ 10 mm Hg)
Low Resistance
Very compliant pulmonary vessels
Dilated pre-capillary sphincters
Capillary recruitment
Capillary distention

Capillaries in the Lung:

Pulmonary
Systemic

Fluid Movement in Lungs

Water leaves systemic capillaries
Although BP is low, surface tension offsets this and favors movement out of capillaries into lung interstial fluid
Lung lymphatic system drains interstitial space

Venous Admixture

Mixing oygenated with unoxygenated blood
Yeilds a low VA/ Q ratio
Alveolar ventillation rate/ pulmonary blood flow = 0.8 normally (4 L/min / 5 L/min)
Two causes
Anatomical R - L shunt
Alveolar shunt