Outline-4, BIO 3360, Respiration II – Gas Transfer

I.  Gas Transport in Air Breathing Animals

A. Oxygen and Carbon Dioxide move from high to low pressure

B. Lung ventilation (breathing) (convection)

C. Lung diffusion

D. Blood circulation(convection)

E. Tissue diffusion

F. Mammalian Lung

1. Gas exchange occurs between the blind-ended alveoli and respiratory capillaries

2. Surface area is enormous and wall of alveoli and blood capillaries is thin

II. InspirationInhalation – breathing in – per Boyle’s law as the closed container increases in size and volume, the intrapulmonary pressure decreases to below atmospheric pressure, therefore air flows in.  As one inhales, the chest cavity increases in size, and since the lungs are elastic, they also increase in size.  This increase in size, decreases the intrapulmonary (inside lungs) pressure to lower than atmospheric pressure.  Air naturally moves from higher pressure to lower pressure and into the lungs.

III. Expiration Exhalation – breathing out – per Boyle’s law, as the closed container decreases in size and volume, the intrapulmonary pressure increases to above atmospheric pressure, therefore air flows out. Quiet expiration is passive – which means no muscles have to actively contract, they just relax.

Video of ventilation in humans

IV. Lung Distensibility or Compliance-how easy it is to stretch a structure due to elastic fibers in the lungs, elastic recoil is opposite of distensibility in how readily structure returns to resting shape.  To illustrate distensibility, emphysema is a disease in which case the lungs become very compliant and are easy to inflate.  However, due to elastic fiber breakdown, they do not deflate and spring back very well.

V. Surface Tension– resists lung inflation and reduces lung compliance

A. Thin layer of fluid lining alveoli resulting from hydrogen bonding between water molecules leading to two wet surfaces wanting to stick together

B. Surfactant is a lipoprotein made by lung cells that reduces surface tension.  It is made by the fetus very late in gestation, and therefore a premature baby who does not have surfactant, has difficulty breathing.

C. Surfactant increases lung compliance

IV. Dead Space

A. Tidal volume is amount of air moving in or out of lung with each breath

B. Dead air volume is that volume not in the alveoli and therefore not useful for gas exchange

C. Volume of air in alveoli = Tidal Volume – Dead Air volume

D. Alveolar Ventilation rate is related to breaths per minute;

(V A )f =(V T – V D ) f

(VA) stands for alveolar ventilation

f stands for frequency or breaths per minute

VT stands for Tidal Volume

VD stands for Dead Air Volume

Which is more efficient at increasing alveolar ventilation, doubling tidal volume or doubling breaths/minute?  The equation shows the answer is doubling tidal volume or breathing deeper.

VII. Alveolar Blood Gas Exchange

A. Oxygen and Carbon Dioxide will diffuse according to their pressure gradients

B. Hemoglobin inside RBCs (RBC= Red blood cell)carries oxygen. Hb (Hb is hemoglobin) presence allows diffusion of more oxygen into the blood.  Be amazed that one human RBC has 250 million hemoglobins which can each carry 4 oxygen molecules; therefore one RBC can carry a billion oxygen molecules.

VIII. Tissue Blood Gas Exchange – follows the same principles

Video of gas exchange in humans

Video of understanding partial pressures