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Biological Sciences
Peter A.Bowler

11/16/12 Respiratory system Respiration: gas exchange between the atmosphere and cells has several steps 1. Oxygen comes into the alveoli of the lungs from the outside. 2. The blood picks up the oxygen, the oxygen circulates through the lungs. 3. The oxygen is transported to the cells and is transported at the capillary beds. 4. Carbon dioxide is released from the cells and whisked out of the lungs, back into the atmosphere Anatomy of the respiratory system—upper and lower Fig17-2 -Two possible ways to breathe in: through your nose or through your mouth +these two possible air passage ways connect at the pharynx -Upper respiratory system: includes the nasal cavity, tongue, larynx, esophagus, vocal chords, and pharynx i.e. runny nose is an upper respiratory problem -Lower respiratory system: neck down—includes trachea, right lung, left lung, right bronchus, diaphragm, left bronchus 1. Mouth or nose  pharynx esophagusstomach OR Mouth or nose pharynxlarynxtrachealungs -The left lung (has 2 lobes) and is smaller because the heart is slightly displaced to the left Skeletal muscles not completely under conscious (voluntary) control [only need to know diaphragm] -there’s both intrinsic and a level of conscious control -during quiet breathing, only the diaphragm is contracting -we have muscles of inspiration for breathing in and muscles of expiration for breathing out Anatomy of the respiratory system air goes through larynxtracheathen the primary bronchus divides/branches 22 more times, terminating in a cluster of alveoli Branching of the airways Fig 17-4:: same tubes but opposite direction (in/out) Trachea (just one) Bronchi (single: bronchus) are semi-rigid tubes; cartilage reinforcement so that they don’t squish flat too easily -Bronchioles are collapsible and their walls have smooth muscle (can become skinnier or larger) -Alveoli (3-6 million) :: the speed of air flow is smaller because it has the greatest cross-sectional area (cm ) Flow rate = volume/time or Q= vA Capillary beds surround alveoli -Each cluster of alveoli is surrounded by elastic fibers and a network of capillaries -pulmonary capillaries are in very close association with the alveoli -capillaries lie on top of the alveoli (they do not pierce the alveoli) -Most alveoli: Type 1 alveolar cells for gas exchange of oxygen and carbon dioxide across the cells -capillaries are by the red blood cells -Type II alveolar cell (surfactant cell) synthesizes surfactant—helps the alveoli to stay open and makes it harder for them to close or stay closed -Alveolar macrophage ingests foreign material; white blood cells help to protect you against infections; filters out the bad stuff when you breathe in Exchange surface of alveoli Fig 17-2h) purple = alveolar cell red = wall of the capillary (epithelial cell that makes the capillary wall) -oxygen has to make its way from the alveolar air space to the red blood cell, crossing the alveolar cell, and capillary wall to reach the red blood cell (5 membranes total) -carbon dioxide has to make its way from the plasma to the alveolar air space to be exhaled Gas laws Fig 17-6 Partial pressure of a gas = P atm(% of gas in atmosphere) Find the partial pressure of oxygen in dry air:: = P /total(% of gas in atmosphere) = atm =760mmHg x 0.21=160mmHg -Dry air is about 21% oxygen and nitrogen is the most abundant gas (an inert gas) -Each gas in a mixture exerts a partial pressure (add them all to get total pressure of gas) 760 mm Hg = 1 atm Partial pressure of a gas in humid air = (P atm– PH20 x (% of gas) = (760-24) x 21=155 mmHg -The partial pressure of a gas is lower in humid air Using gas laws to help us understand how lungs fill with air Fig 17-6 ideal gas law: PV = nRT -Boyle’s Law: P V1= 1 V d2sc2ibes the inverse relationship of pressure and volume (keep nRT constant) +Decreasing volume increases collisions and increases pressure Fig 17-8 Diaphragm At rest, the diaphragm is relaxed. Diaphragm contracts (flattens out), and the thoracic volume increases, so the pressure drops. As the diaphragm relaxes, the thoracic volume decreases Example of a syringe and a bicycle pump: uses an increase in volume to pull air in when partial vacuum (lower pressure) is generated [air moves from areas of higher pressure outside to area of lower pressure inside the syringe!] -Inspiration of air is pulled in by the lower pressure (caused primarily by diaphragm contraction) Diaphragm relaxes for exhaling and contracts for inhaling (bringing air in) How much air moves in and out of lungs (ventilation)? similar to Fig 17.7 1. First, breathe out as much as you can. Not zero! The bronchi and bronchioles didn’t flatten—there’s still some stale air in there. This remaining volume or the volume of air in the respiratory system after maximal exhalation is the Residual volume.
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