what is the pathway of airflow
(upper respiratory system) nasal cavity -> pharynx -> larynx -> (lower respiratory system) trachea -> primary bronchi (right/left) -> many smaller bronchi -> 20-22 bronchioles -> alveoli
main functions of the respiratory system
- gas exchange (O2 uptake, CO2 release)
- homeostatic regulation of body pH
- conditioning inspired air
- protection (filtering and clearing foreign particles)
- vocalization
what is external respiration
- the movement of gases between the internal environment of the body and the external environment (atmosphere)
what are the steps of external respiration
- exchange l -> The exchange of air between the atmosphere and the lungs (ventilation)
- exchange ll -> the exchange of O2 and CO2 between the lungs and the blood.
- transport of gases in the blood (the transport of O2 and CO2 by the blood)
- the exchange of gases between blood and the cells
where are the lungs located
- in the thoracic cavity
which muscles are used for quiet breathing
- external intercostals and diaphragm
- these muscles contract and the lungs expand -> air flows in
which muscles are used for forceful breathing
forceful inspiration
- sternocleidomastoids
- scalenes
- external intercostals
- diaphragm
forceful expiration
- internal intercostals
- abdominal muscles
what are the 2 types of pleural membranes and explain
- fluid filled balloon that wraps around the lungs
- visceral pleural membrane = on the inside
- parietal pleural membrane = sticks to thoracic cavity
- each pleural membrane is composed of a thin layer of secretory epithelial cells (produce fluid) and a thin layer of connective tissue (hold everything together)
what is the function of the fluid filled pleural sac
- protects the lungs
- pleural fluid lubricates membranes and allows them to slide against each other as lungs move with breathing
- sticks the lungs tightly to the thoracic wall (fluid creates suction) -> important for keeping the lungs inflated
what is the main role of the airways
- filter out foreign substances (ciliated epithelium lining the trachea and bronchi sweeps mucus up to the mouth)
- warm air to body temp
- add water vapor so that the moist exchange epithelium doesn’t dry out (evaporates from mucosal lining)
explain the ciliated epithelium of the respiratory tract
- epithelial cells lining the airways and submucosal glands secrete saline and mucus
- submucosal gland produces much more mucus than goblet cells
- cilia move the mucus layer toward the pharynx, removing the trapped pathogens and particulate matter
- made of ciliated columnar cells
explain the cross sectional area of the bronchioles and the velocity of air
- the total cross-sectional area increases with each division of the airways.
- Total cross-sectional area is lowest in the upper respiratory tract and greatest in the bronchioles, analogous to the increase in cross-sectional area that occurs from the aorta to the capillaries in the circulatory system
- velocity of air flow is greatest in the upper airways and slowest in the terminal bronchioles
how do the airways create resistance to air flow
flow = change in pressure / resistance
resistance = Ln/r^4
- since the total length of the airways (L) and the viscosity of air (n) are constant, resistance is changed by control of radius
- radius of trachea and bronchi cannot be changed because of cartilage in their walls but mucus build up here is a common cause of increased airway resistance
- bronchioles are collapsible (no cartilage) so their radius can be changed by neural, hormonal, and paracrine effects on smooth muscle
obstructive lung diseases _____ airway resistance
increase
explain how velocity depends on total cross sectional area and parallel pathways reduce resistance
- most of the resistance to flow is in the trachea and bronchi (small total cross sectional area)
- cross sectional area of bronchioles is large so resistance is normally very low
- but bronchoconstriction can significantly increase resistance at this level to reduce the flow of air to/from the alveoli
- cross sectional area in trachea = 2.5 cm2
- cross sectional area in bronchioles = 5x10^3 cm2
what is bronchodilation
- decreased resistance to air flow
- paracrine response to increases CO2 (want to bring in more O2)
- SNS response -> NE/E bind to b2 adrenergic receptors = relaxation of bronchiole smooth muscle
- Gs -> AC -> cAMP -> PKA -> inhibits MLCK = relaxation
what is bronchoconstriction
- increased resistance to air flow
- paracrine response to histamine released by local mast cells in an immune response
- PNS response -> ACh binds to muscarinic receptors (M3) -> constriction of bronchiole smooth muscle
-Gq -> PLC -> IP3 -> IP3R -> Ca2+ = bronchocontriction
how many alveoli
- 300 million alveoli
- 600 ft2 of surface area
explain alveoli and its components
- make up bulk of the lung tissue
- each alveolus is made up of one layer of epithelial cells
- type 1 alveolar cells
- type 2 alveolar cells
explain type 1 and type 2 alveolar cells
- type 1 = gas exchange
-> make up 95% of alveolar surface area - type 2 = make and secrete surfactant
what is surfactant
- fluid that lines all the alveoli making them easier to expand and preventing them from collapsing
- reduces surface tension
explain alveolar exchange surface
- optimized for diffusion
-> very thin
-> very little interstitial fluid
-> alveolus and capillary held close together bu fused basement membrane
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