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Respiratory System Class Notes Clear, concise notes for the respiratory system.

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York University
Kinesiology & Health Science
KINE 3012
Tara Haas

Respiratory System Lung Structure  The conducting zone determines air flow o Trachea, bronchi, bronchioles o Cartilaginous rings in the larger airways (trachea, bronchi, bronchioles) prevent collapse o Low resistance pathway that warms, humidifies, and filters air  The respiratory zone enables gas exchange o Respiratory bronchioles, alveolar ducts, alveolar sacs o There is an incredibly large surface area Cellular Composition of Lungs  All airways are lined with cuboidal epithelial cells o Ciliated in the conducting zone: traps foreign particles and sweeps them up; also have mucus-secreting epithelial cells  Bronchioles are wrapped with smooth muscle cells o Responsible for dilation and constriction (when you have asthma/allergic reaction it is likely a malfunction in these)  Macrophages in the airways and alveoli remove airborne particles and bacteria  Type I Alveolar cells are flat epithelial cells and compose most of the alveolar wall  Type II Alveolar cells are rounded epithelial cells (non-continuous line), found intermittently and secrete surfactant (important in inflating alveoli)  Thin epithelial cells lining the alveoli and capillaries allow for easy gas exchange because it is so thin Lung pressure  Lungs are partially expanded between breaths o It requires a lot of energy to inflate your lungs from a completely deflated state (think about blowing up a balloon) o This is because intrapleural pressure is lower than atmospheric/alveolar  Caused by the pull from the ribs and the elastic contracting of the lungs’ walls (opposing outward and inward forces)  Ie there is positive transpleural pressualv(ip-P ) under normal conditions (negative would indicate collapse) Pneumothorax  If there is a hole between the pleura then the negative intrapleural pressure will disappear and the lung will collapse Mechanism of Breathing  Inspiration occurs because lung (alveolar) pressure < atmospheric pressure o Expiration is the opposite  By expanding the thoracic cavity (increase in volume), you decrease the pressure (and vice versa) o Controlled by the diaphragm and intercostal muscles of the ribs  Transpulmonary pressure (P = tp-P alveiprmines lung volume o Increases and decreases in magnitude—never negative (unless lung collapses) Other Ways to Inflate Lungs  Raising P atm(lower altitudes, respirators)  Change P bipchanging chest pressure (Iron lung) which expands your thorax through a vacuum Compliance vs. Elasticity  Compliance refers to how easily the lungs stretch/inflate o Usually related to restrictive disorders  Pulmonary fibrosis (scarring of lung tissue—unable to inflate as easily)  Elasticity refers to how easily the lungs recoil/deflate o Related to some obstructive diseases (need to force air out)  Emphysema (decrease in elastic recoil) and other Chronic Obstructive Pulmonary Diseases (COPD)—increases airway resistance Determinants of Compliance Structural Composition of Lung  The amount and type of connective tissue in lungs o Stiff type 1 collagen (most abundant—but you do not want a lot in your lungs) and compliant elastin Surface Tension  Alveoli have a water lining which tries to collapse the air sacs (hydrogen bonding exerts inward force)  Law of Laplace states that pressure inside a sphere (alveoli) varies directly with surface tension and inversely with radius o Ie the higher the surface tension, a greater pressure difference is required to expand the alveoli o A larger alveolus (radius) requires less work to inflate a lung  Air in a smaller alveolus will flow to a larger alveolus (balloon demonstration)  Surfactant is produced by type II alveolar cells and reduces alveoli surface tension by disrupting hydrogen bonding between water molecules o Surface tension decreases most in the smallest alveoli (makes sense—smaller alveoli = smaller surface area) Alveolar Interdependence  Refers to how the walls of an alveolus is shared with surrounding alveoli o Prevents collapse because they are basically playing tug of war with surrounding alveoli Breathing Mechanics  Flow = difference in pressure/resistance  Resistance is primarily determined by the radius o Normally resistance is not considered because it is very small in healthy individuals  Resistance is increased by: o Acute airway constriction refers to something that occurs shortly (allergies, etc.) o Chronic narrowing of airways (mucous, inflammation, etc.) Bronchiole structure  Mast cells are located along the outside of the bronchioles  Smooth muscle can contract for very long periods of time o Normally do nothing; activation of these mast cells are responsible for allergic reactions o Activated by different allergens (varies with the individual) o Filled with granules that are released through vesicles upon stimulation (degranulation) o Release histamine and leukotriene that affect the smooth muscle surrounding the bronchioles (cause contraction), reducing bronchiole diameter  Binds to the H1 receptor which causes constriction  To prevent mast cell Activation: Epinephrine binds to the mast cell’s beta2 adrenergic receptor increasing cyclic AMP (cAMP) which reduces the secretion of histamine (although the cell is still activated) and also binds to the smooth muscle cells’ same beta2 adrenergic receptors to cause dilation o Anti-histamines and CO ca2 also relax the smooth muscle cells Asthma  Intermittent smooth muscle contraction from mast cell stimulation (see above)  Chronic inflammation leads to hyper responsive smooth muscle and swelling of the airway Partial Pressure  Partial pressure is dependent on temperature and concentration  Alveolar air is higher temperature and higher humidity than inspired air o As a result, the partial pressures of the individual gases (CO2, O2, and N2) differ from the two samples o There is a substantially higher pressure of CO 2nd less O , 2nd a slight change in N2in the alveoli compared with inspired air  Alveoli are the sites for gas exchange Gas Exchange  Occurs by diffusion (between gas and liquid phases) o So that the partial PRESSURE of O in 2he air is equal to the partial PRESSURE of O in t2e liquid  There is a rapid equilibration of oxygen in a normal lung; a diseased lung takes longer (and may not even reach equilibrium)  Affected by pressure gradient o You can increase the amount of oxygen in the inspired air to increase the amount of oxygen in alveolar air, thus enhancing the rate of oxygen diffusion  Higher altitudes have lower pressure—harder to breathe  Hyper/hypoventilation will increase/decrease the rate of oxygen diffusion Ventilation-Perfusion Matching  Alveoli want good ventilation and capillaries want good perfusion o Amount of ventilation and perfusion differ throughout the lung  98% of blood goes through alveoli with good ventilation and O p2rtial pressures are equilibrated (100 mmHg)  CO 2nfluences changes in bronchiolar smooth muscle and O influ2nces arterial smooth muscle o Influences ventilation and perfusion, respectively  When ventilation is higher than perfusion, there is greater O2and less CO ,2bringing about arterial smooth muscle dilation and bronchiole smooth muscle constric
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