RESPIRATORY SYSTEM
Review anatomy
Lung Capacity F 16
Total lung capacity - sums of defined volumes
Inspiratory capacity
Resting tidal volume - normal vol in and out, are = ; at rest about 500ml
Inspiratory reserve vol - deepest inspiration
Functional residual capacity - at resting position, vol remaining in
lungs, 2500ml
Expiratory reserve vol - max contraction expels 1500ml
Residual vol - 1000ml still left
Vital capacity - RTV + IRV + ERV
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Alveolar ventilation - vol of fresh air entering alveoli/min F 17, T 4
Alv. vent. (ml/min) =
Tidal vol (ml/breath) - Dead space (ml/breath) X resp. rate (br/min)
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Exchange of gases F 18, 19
Assuming normal metabolism: 250ml/min
O2 consumption and 200ml/min CO2 prod.
Air entering alveoli - 21% of 4000ml = 840ml/min
O2 - 250ml crosses alveoli and enters capillaries
O2 transported to tissues - 250ml/min leaves blood into interstitial
fluid and cells
Reverse for CO2
What drives this? Fig 19
Net diffusion down pressure gradient [Partial pressure of O2 and CO2]
Atmospheric gas pressures: O2 160 mmHg; CO2 0.03 mmHg
Normal alveolar gas pressures: PO2 = 105 mm Hg; PCO2 = 40 mmHg
Interst. fl/cell gas pressures: O2 < 40 mmHg; CO2 > 46 mmHg
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How are gases transported?
Oxygen
1 L arterial blood contains: 3 ml dissolved O2 (1.5%)
197 ml bound to Hb (98.5%)
Total 200 ml O2
Cardiac output 5L/min
O2 carried to tissues/min = 5 ml/min X 200ml O2/L = 1000 ml O2/min
Erythrocytes contain the oxygen binding protein - hemoglobin (280
million molecules per cell)
Deoxyhhemoglobin: no O2 bound
Oxyhemoglobin: 4 Heme groups - contain Fe++ each iron binds a
mol of O2
Carboxyhemoglobin: iron may also bind CO
Oxygen-hemoglobin dissociation curve F23
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Factors affecting oxygen transport: [increase in variable shifts dissoc.
curve to rt]
pH 7.4 - normal affinity
7.6 - increased affinity
7.2 - decreased affinity
temp 37 C - normal affin
lower - incr. affin
higher - decr. affin
DPG - a byproduct of glycolytic pathway made by erythrocytes
lower conc. - incr affin
higher conc - decr affin
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Carbon dioxide
10% dissolved in H2O of plasma and erythrocyte
30% carbamino Hb
60% production of bicarbonate:
carbonic anhydrase in erythrocyte
reacts with H2O to form H2CO3 (carbonic acid),
dissociates onto HCO 3 - and H+
chloride shift - antitransport moves HCO3 out of cell
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Regulation of the Resp System
Ventilation
Skel. muscles involved require stimulation by somatic motor neurons
Network of neurons in medulla oblongata [brain stem] communicate with
motor
neurons to diaphragm and intercostals [sk muscles]
Two sets of neurons in medulla:
dorsal resp group - normal inspiration - I neurons
ventral resp group - active expiration - E neurons
deep inhalation (exercise)
- I+ neurons
Protective reflexes
Irritant receptors trigger brain
Stim bronchiolar smooth muscles via parasympathetic neurons -
Response bronchoconstriction, coughing
Stim by limbic system during emotional or autonomic activities
Some conscious control
Responsive to changes in Pco2 and Po2, pH
How are blood parameters sensed? What is response?
Chemoreceptors
Peripheral: carotid and aortic bodies [remember these sites also
contain
baroreceptors]
Receptor cells gather sensory info on Po2 and pH,
Stim by decrease in Po2 (high alt or disease) or rise in pH
Send info to medulla via afferent pathways
Excite inspiratory neurons
Efferent pathway - to muscles, increase ventilation
Central: located in medulla ob.
Sensitive to increase in H+ from CO2 in cerebrospinal fluid
[not metabolic H+]
Excite inspiratory neurons - incr ventilation
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Acidosis and alkalosis
Ventilation pH Pco2 Condition
Normal 7.35 - 7.45 39 - 41 mmHg
Hypoventilation low high Resp. acidosis
Compensatory low low Metabolic acidosis
hypervent.
Hyperventilation high low Resp. alkalosis
Compensatory high high Metabolic alkalosis
hypovent.