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Mechanics • The branches of the bronchial tree filter incoming air and distribute to alveoli in all parts of the lung • Cilia & mucous amounts decrease the further in you go • Though they have no cilia or mucous, the inner surface of alveoli are still moist
Mechanics • Water molecules tend to stick together • Creating surface tension • Attraction between the molecules would cause the alveoli to collapse with lung expansion • Cells secrete surfactant which disrupts surface tension • Prevent alveoli collapse during inspiration
Alveoli • The alveoli are thin-walled air sacs • Large surface area • House macrophages to clean • Ease of gas exchange with surrounding capillaries …more on gas exchange later
Mechanics • Air moves into the lungs by the force of atmospheric pressure • This pressure is exerted on all things that contain the air so the inner surfaces of the lungs are receiving roughly the same amount of pressure as the thoracic wall
Control • The Respiratory Center is spread throughout the medulla and pons • Ventral group (medulla): basic rhythm • Dorsal group (medulla): increase respiratory movement; more forceful inspiration • Pneumotaxic area (pons): regulate stimulation of dorsal group
Mechanics • To initiate inspiration an impulse is sent down the phrenic nerve to trigger the diaphragm to contract • This expands the volume of the lungs which decreases the pressure – allowing air to rush in • 758 vs. 760
Mechanics • Expiration is passive • Force comes from recoil of tissues with lots of elastin • Lung • Abdominal • Push diaphragm back up • Decrease volume increase pressure • Air forced out until pressure balanced
Control • Several factors can affect rate and depth of breathing • PO2 • Minor role in regulation • PCO2 • Too much lowers blood pH • Chemoreceptors signal need for increased rate • Stretch in lung tissue • Emotional state
Control • Parasympathetic stimulation constriction of airways • Histamine does this too • Sympathetic stimulation dilation of airways • epinephrine
Gas Exchange • Since there are only two cells layers separating the air sac from the blood, gases can diffuse to areas of lower concentration easily • Discussed in terms of respiration as differences in partial pressure • Also why breath order can be diagnostic • Blood alcohol level • Acetone smell of diabetics
Gas Exchange • As gases enter the blood, they either dissolve in the plasma or combine with other molecules • 98% of O2 in blood is attached to hemoglobin
Gas Exchange • The PO2 determines the amount of oxygen that combines with hemoglobin • It is normally completely saturated (4 oxygens) • But the bonds are unstable • In tissues the PO2 decreases so hemoglobin releases the oxygen • Also triggering release of oxygen: • Increase PCO2 • Decrease in pH • Increase in temperature
Gas Exchange • The CO2 diffuses into the blood and is carried to the lungs in three forms: • Dissolved in plasma (7%) • Bound to hemoglobin (20%) • Bicarbonate • Result of reactions triggered by CO2 reacting with water.