Pulmonary Ventilation
respiratory gases between atmosphere and alveoli of the lungs
- Net movement of oxygen from atmosphere to alveoli during inspiration
- net movement of carbon dioxide from alveoli to atmosphere during expiration
Alveolar Gas Exchange
exchange of respiratory gases between alveoli and blood in the pulmonary capillaries
- oxygen diffused from alveoli into blood
- carbon dioxide from blood into alveoli
Gas Transport
transport of respiratory gases in blood between lungs and systemic cells of the body
- oxygen is transported from lungs to systemic cells
- Carbon dioxide is transported from system cells to lungs
Systemic Gas Exchange
exchange of respiratory gases between the blood and the systemic capillaries and systemic cells of the body
- Oxygen diffuses from blood into systemic cells
- Carbon Dioxide diffuses from systemic cells into blood
Intrapleural pressure vs intrapulmonary pressure?
intrapleural pressure:
- pressure in pleural cavity
- fluctuates with breathing
intrapulmonary pressure
- pressure in alveoli of the lungs
- fluctuates with breathing
How do lungs remain inflated?
- intrapulmonary pressure is greater than intracellular pressure
- the pressure insides greater than the pressure outside
- about 4mm Hg lower than intrapulmonary pressure between breaths
- Difference in pressure keeps the lungs inflated due to output pull of chest and inward pull of lungs with consequent “suction”
How do the pressure gradient between the atmosphere and lungs drive inspiration and expiration?
- air moves from area of high pressure to area of low pressure when pressure gradients are established by changes in volume.
What are the muscles involved in quiet breathing?
increase the dimensions of the thoracic cavity
- Diaphragm and external intercostals
- involved in normal rhymic breathing at rest
- alternatively contract and relax, resulting into movement of air into and out of the lungs
what is the relationship between volume and pressure?
Boyle’s law- volume and pressure are inversely related
How does the relationship between volume and pressure exhibited in inspiration?
In inspiration, the diaphragm contracts, which increases the volume of the lungs. Therefore, the intrapulmonary pressure becomes less than atmospheric pressure and air flows in.
How does the relationship between volume and pressure exhibited in exspiration?
In expiration, the diaphragm relaxes, which decreases the volume of the lungs. Therefore, the intrapulmonary pressure becomes greater than atmospheric pressure and air flows out.
What are the structures of the respiratory zone? and describe
composed of respiratory bronchioles, alveolar ducts, and alveoli
-Respiratory bronchioles subdivide to alveolar ducts that lead to alveolar sacs (clusters of alveoli)
Alveoli
saccular outpocketings
-each lung contains 300 to 400 million alveoli
Alveolar pores
openings providing collateral ventilation (inflate at once)
-surrounds by pulmonary capillaries
What are the two cells that form the alveolar cell wall
Type I
Type II
Type I cells
- simple squamous alveolar cells
- 85% of alveolar surface area
- part of thin barrier separating air from blood
Type II cells
- septal cells
- secrete oily pulmonary surfactant which coats the inside of the alveolus and opposes collapse during expiration
Describe the structure of the respiratory membrane
-consist of alveolar type I cells, an endothelial cell of a capillary, and their fused basement membranes
What is the function of the respiratory membrane
this is where oxygen and carbon dioxide diffuse across during gas exchange because the alveoli and the blood in the pulmonary capillaries
Describe the process that happens at the respiratory membrane
1) oxygen diffuses from the alveolus across the respiratory membrane into the pulmonary capillary-allowing erythrocytes in the blood to become oxygenated
2) oxygen is then transported by the blood to systemic cells
3) Carbon dioxide diffuses from the blood within the pulmonary capillary through the respiratory membrane to enter each alveolus-once in the alveoli, carbon dioxide is expired from the respiratory system into the external enviroment
What are three ways in which carbon dioxide can be transported in the blood?
- CO2 dissolved in plasma
- CO2 attached to the globin portion of hemoglobin
- Bicarbonate (HCO3-) dissolved in plasma
Carbon Dioxide loading?
occurs as blood moves through systemic capillaries and carbon dioxide moves into the blood plasma
o CO2 diffuses into an erythrocyte
o CO2 is joined to H2O to form H2CO3 (carbonic acid) by carbonic anhydrase
o Carbonic acid splits into bicarbonate (HCO3-) and hydrogen ion (H+)
o HCO3- moves out as Cl- moves in (chloride shift)—————->HCO3- is transported in plasma
o H+ attaches (and is buffered) by hemoglobin
• Formula
• CO2 -> CO2 + H2O -> H2CO3 by carbonic anhydrase
o HCO3- -> leaves and Cl- moves in
o H+ binds to Hb
Carbon Dioxide unloading
process is reversed as blood moves through pulmonary capillaries
- HCO3- moves in while Cl- moves out of the erythrocyte
- HCO3- recombines with H+ to form H2CO3
- H2CO3 dissociates into CO2 and H20
- CO2 diffuses out and into an alveolus
Describe the oxygen-hemoglobin curve
the amount of oxygen bound to a hemoglobin is expressed as the percent oxygen saturation of hemoglobin
-Determined by several variables – PO2 being the most important. As PO2 increases, hemoglobin saturation increases. The binding of each O2 molecules causes of conformational change in hemoglobin that makes it progressively easier for each additional O2 molecule to bind to an available ion – cooperative binding effect.
- The plotted points produce a sigmoidal curve.
