Nasal cavities have several folds, or shelves, called nasal conchae, which expose a large area of nasal membrane to the air
Sinuses produce nitric oxide (NO) – helps with uptake of O2
Cells of the nasal epithelium contain cilia, which act like a brush to catch dust particles, pathogens, and irritants
Goblet cells produce mucus, trapping dust, smoke, bacteria, etc.
Inhaled air takes up moisture from the mucus, and heat from underlying bloodvessels, becoming almost completely saturated with water vapor and almost at body temperature by the larynx
On exhalation, the mucus in the cool and dry nose re-captures some of the warmth and moisture from that exhaled air by condensation
Goblet cells secrete mucus and form a mucus sheet, which is continually transported away from the lungs (towards the mouth) by the coordinated movement of the cilia, serving as a dust-trap
Has a VERY important film of water on the inner surface that allows gas exchange to take place
Surface tension can cause the alveoli to collapse
Alveolar cells produce surfactant, which forms a layer around the inside of the alveoli, creating a barrier between the air and water, decreasing the surfacetension
Premature babies (born before 28 weeks) have less surfactant, more surface tension and are more at risk of lungcollapse, called infant respiratory distress syndrome (RDS)
O2 is loaded into the blood stream and CO2 is unloaded from the bloodstream by diffusion due to partial pressure gradients (differences in partial pressure or concentration)
O2 has a partial pressure gradient of ~60 mmHg (100 mmHg in alveolar air and 40 mmHg in deoxygenated blood)
CO2 has a partial pressure gradient of only 6 mmHg (46 mmHg in deoxygenated blood and 40 mmHg in alveolar air), but has higher solubility in blood
So-called deoxygenated blood isn't completely lacking in O2, it has a partial pressure of 40 mmHg, and not all CO2 is removed from the blood as oxygenated blood still contains 40 mmHg
V and Q must be balanced to maintain efficient gas exchange in the alveoli
If V is slowed due to a blockage in the airways, CO2 levels in the alveoli increase but O2 levels decrease, causing the alveolar capillaries to constrict to reduce blood flow (Q)
If Q decreases due to a bloodcapillaryblockage, the low level of CO2 stimulates the bronchioles to constrict, leading to a drop in ventilation (V)
External Respiration: Exchange of gases between the lungs and blood
1. The bloodstream delivers O2 to the cells and removes waste CO2 from the cells
2. When oxygenated blood reaches the narrow capillaries that surround the tissues, the red blood cells release the O2 and it diffuses through the capillary walls into body tissues
3. At the same time, CO2 diffuses from the tissues into the red blood cells and plasma
4. The deoxygenated blood carries the CO2 back to the lungs for release by exhalation