BMS Exam 2: Respiratory System & Acid-Base

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BMS Exam 2

visceral pleura

covers outer surface of lungs; no sensory nerves

parietal pleura

lines inner surface of chest & diaphragm
innervation - intercostal nerves

pleural space

potential space w/ little fluid (~15mL in adults)

intrapleural pressure is subatmospheric


violation of pleural space, collapsed lung


normally an active process

muscles involved:
- diaphragm (major muscle), innervated by phrenic nerve, spinal roots C3,4 & 5
- external intercostals - ↑ intrathoracic volume
-accessory muscles (seen in Dz): sternocleidomastoid & scalenes


usually a passive process

muscles involved (note: only in forced expiration)
- rectus abdominus
- internal intercostals

↑ compliance (stretchability) causes?

lung Dz's that cause obstruction

ex: emphysema

↓ complaince (stretchability) causes?

lung Dz's that cause scarring & fibrosis

ex: Pulmonary fibrosis

obstructive lung Dz

↑ compliance lung Dz - ex: emphysema

- tissue loss (↓ recoil forces) causes easily compressed airways
- produces ↓ air flow rates & ↑ airway resistance
- pts work hard to overcome airway resistance on expiration

restrictive lung Dz

↓ compliance lung dz - ex: pulmonary fibrosis

- fibrosis causes ↑ elastic recoil
- ↑ radial traction→ airway dilation
- produces → ↑ air flow rates & ↓ airway resistance
- pts work hard to overcome ↑ elastic recoil during inspiration

what is the cause if a pt has to work hard to overcome airway resistance on expiration?

obstructive lung Dz

what is the cause if a pt has to work hard to overcome increase elastic recoil during inspiration?

restrictive lung Dz


ability to retract or recoil from tissue & surface tension forces

tissue forces

generated by molecules of elastin & collagen

surface tension forces

generated primarily by water
reduced by surfactant

pulmonary surfactant

- synthesized by type II alveolar cells & coats lining of alveolous
- ↓ intermolecular forces between water molecules
- usually present by 35 weeks gestation

airway resistance

any impediment to flow of air throughout respiratory tree

what is airway resistance determined by?

- Major factor: airway diameter
-- note: if radius ↓ then resistance to airflow ↑

- rate of gas flow

major site of airway resistance = medium sized bronchi

Adrenergic stimulation causes what in airways?

name 2 β2-selective adrenergic agents

- bronchodilation
- β2-receptor stumlation = smooth muscle relaxation

β2-selective adrenergic agents:
- albuterol (short acting)
- salmetrol (long acting)

beta blockers causes what in airways? who is this bad for?

bronchial constriction

bad for asthmatics, people w/ obstructive Dz

cholinergic stimulation in airways causes? what agent would you administer?

bronchoconstriction & ↑ mucus production

administer anticholinergic agents for bronchodilation
ex: ipratropium

nonadrenergic, noncholinergic activity for control of airway resistance

neuropeptides that contol airway smooth muscle
eg. vasoactive intestinal peptide (VIP), nitric oxide (NO)
note: no clinically available therapeutic agents for these substances yet

what inflammatory mediator controls airway resistance & what are its effects? what agent would you administer?

Leukotrienes (LT) - potent bronchoconstrictor

LT inhibitors (modifiers) for bronchodilation
LT inhibitors - Zafirlukast, Montelukast

tidal volume

air inspired or expired w/ each breath ~ 500mL (adult)

inspiratory reserve volume

additional air inspired above tidal volume (3L)

expiratory reserve volume

air that is forcefully expired after normal expiration (1.3L)

residual volume

gas that remains in lungs after a maximal expieration (1.2L)

total lung capacity

volume in lungs after maximal inspiration (6L)

vital capacity

volume that can be expired after maximal inspiration

inspiratory capacity

maximal volume that can be inspired after normal expiration

functional residual capacity

air that remains in lungs after normal expiration

dead space

volume of conducting airways ~ 150mL

forced vital capacity (FVC)

evaluated resistance properties of airways

forced expiratory volume in 1 sec (FEV1)

screening test for airway Dz
indicated volume of FVC expired in 1st second - shows flow resistance properties of airways


% of VC expired in 1 second (FEV1/FVC)
normally FEV1% > 75-80% FVC

peak flow meter

measures peak expiratory flow rate (PEFR) ~ FEV1
normally ~ 500 L/min

Barometric pressure of air

760mmHg & air is 21% of O2

Partial pressure of O2 (PO2) in air


what does pulse oximetry (pulse-ox) measure? what is is dependent on?

- using a red light emitting diode, pulse-ox indirectly measures O2 saturation (SaO2)
- measurement dependent upon adequate tissue perfusion

what does arterial blood gas (ABG) measure?

directly measures O2 & other parameters

what is the normal value for PO2 (or PaO2)?


what is the normal value for PCO2 (or PaCO2)?

~ 35-45 mmHg

what is the normal value for pH?


what is the pH range compatible with life?


what is the normal value for SaO2?


what is the normal value for [HCO3-]


explain oxygen transport in the lungs

- O2 diffuses across alveolus
- dissolves in plasma of pulmmonary capillaries
- diffuses into RBC & binds w/ Fe w/in Hb molecule
- deoxyhemoglobin → oxyhemoglobin (normal Hb=12-15 g/dL blood)

explain oxygen transport in the tissues

- PO2 is low secondary to metabolism
- O2 dissociates from Hb
- moves across RBC membrane
- dissolves in plasma
- diffuses across capillary wall
- finally enters interstitial tissue

An arterial O2 tension of ~ 85-100mmHg results in Hb saturation of?



- Hb + carbon monoxide (CO)
- gives skin a cherry color
- binding affinity of CO: 200x > O2


Fe+2 → Fe+3 state → unable to bind O2

- gives skin "bluish" cyanotic color
- caused by drugs/foods (nitrates, fava beans) esp in pts w/ G6PD deficiency

explain carbon dioxide transport w/in the RBC

- 90% of CO2 enters RBC & is returned to lungs
w/in RBC
- CO2 + H2O + carbonic anhydrase → H2CO3 → HCO3- + H+
- HCO3 - then diffuses out of RBC into plasma

how is most of CO2 carried in blood?

carried in blood as HCO3-

explain carbon dioxide transport in the lungs

HCO3- in blood enters RBC + H+ → H2CO3 → H2O + CO2

CO2 exists cell into alveolous

ventilation (V)

alveolar ventilation

perfusion (Q)

pulmonary blood flow

what is the normal V/Q ratio


list factors that affect V&Q?

- gravity
- alveolar hypoxia, hypercapnia (↑ [CO2]) & acidosis → pulmonary vasoconstriction
- generalized alveolar hypoxia → ↑ total pulmonary vascular resistance

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