Exam 4 (#24) - External respiration, gas transport, internal respiration

What is ventilation - perfusion coupling?

Obtaining optimal gas exchange

• Ventilation
  - how much gas (air) goes into alveoli

• Perfusion
  - the rate of blood flow in alveoli

How is ventilation able to happen?

Measuring P(CO2) in the smooth muscle of the upper bronchi helps decide whether to constrict or dilate

In the lower bronchi, smooth muscles in capillaries - P(O2) constrict or dilate via capillary sphincters

Explain dilation of bronchioles:

When PCO2 is high:

• ^ air flow in/out of respiratory zone

• → lead to ^ up external respiration

Explain dilation of pre-capillary sphincters:

When PO2 is increased:

• ^ blood flow to the respiratory membrane

• → lead to ^ up external respiration

What is gas transport?

The movement of respiratory gases (mainly O2 and CO2) between the lungs and the body tissues

How is oxygen transported throughout the body?

1.5% - dissolved (in plasma)

98.5% - attached to hemoglobin (in RBC)

Explain hemoglobin:

Oxyhemoglobin:
- Heme bound to oxygen (R or “relaxed)

Deoxyhemoglobin:
- Heme with no oxygen (T or “taut”)

CO2 can bind to globin

Explain O2 affinity (relation to hemoglobin):

Up to four O2 can bind to hemoglobin - each O2 can bind to 1 heme (4 hemes in hemoglobin)

• Low affinity to deoxyhemoglobin
  - higher as more binds

• CO2 affinity is opposite
  - less as more O2 binds

What is the path of O2 in the lungs/body in relation to hemoglobin?

• Leave the lungs
  - hemoglobin is bound to four O2

• In the tissues
  - some O2 leave hemoglobin - but a very low percent

• Back to the lungs
  - O2 picked up at respiratory membrane

Explain oxygen loading and unloading:

• O2 binds easily in lung

• O2 dissociates easily in tissue

Where does hemoglobin shed O2?

At the tissues

What is internal respiration?

Movement of gases in and out of blood - tissue

How is carbon dioxide transported throughout the body?

10% - dissolved in plasma

20% - bound on globin

70% - found as bicarbonate ions

Explain H+ Ions:

• Cause the Bohr effect:
  - decreases O2 affinity for Heme

• Does not influence pH much - due to the bicarbonate (base)
  - only slight shifts in pH when lots of CO2 produced

Why does a pH shift matter?

Active cells → CO2 produced → slight decrease in pH of blood at that tissue…

Decreased pH → O2 has lower affinity for hemoglobin… CO2 has higher