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85 Cards in this Set

  • Front
  • Back
respiratory system primary function is:
to obtain Oxygen for use by cells and eliminate carbon dioxide produced by cells
Respirtation is two separate processes:
Internal and External respiration
Internal (cellular) respiration:
mitochondria metabolize foodstuffs; usually involves use of oxygen;results in production of carbon dioxide and water
External respiration:
exchange of gases between environment and cells
Steps of external respiration: (4)
1. ventilation or gas exchange between atmosphere and air sacs (alveoli) in lungs
2. exchange of oxygen and carbon dioxide between air in alveoli and blood
3. transport of oxygen and carbon dioxide between lungs and tissue ( in circulatory systemnot respiratory system)
4. exchange of oxygen and carbon dioxide between blood and tissues ( internal respiration)
Nonrespiratory functions:
route for water loss and heat elimination;enhances venous return (respiratory pump);contributes to maintenance of normal acid-base balance;enables vocalizations;defends against inhaled foreign matter (cilia, mucus);modifies, activates, and inactivates materials passing thru circulatory system;nose = organ for smell
respiratory system components:
lungs (2) left and right, each with several lobes; nasal passage/ oral cavity (1), pharynx, larynx, trachea, bronchi (2), bronchioles (32), terminal bronchioles (60,000), respiratory bronchioles (500,000), alveolar ducts (500,000), alveolar sacs (8 million), alveoli (~300 million) , and associated muscles for movement
alveoli =
sites of gas exchange
alveolar sacs surrounded by pulmonary capilaries =
very important for gas exchange. proximity ro capillaries and tremendous surface area = great rte of exchange by diffusion
smooth muscle around bronchioles - autonomic nervous system stimulation of smooth muscle
alveoli - thin walled, inlatable sacs
fick's law of passive diffusion
thickness, surface area, molecular weight, concentration gradient, permeability
alveoli walls :
single layer of flattened Type I alveolar cells. alveolar epithelium also contains type II alveolar cells which secrete pulmonary surfactant (facilitates lung expansion). alveolar macrophages also present (immune defense)
lung tissue: series of highly branched airways, alveoli, pulmonary blood vessels, amd lots of elastic connective tissue
occupies most of the volume of the thoracic cavity
outer chest wall: 12 pairs of curved ribs , which join sternum and thoracic vertebrae (protection)
diaphram: skelaetal muscle for breathing. it separates the thoracic cavity from the abdominal cavity
pleural sac: separates each lung from the thoracic wall (chest wall) prevents pain from friction from breathing
pleural cavity: the inside of the pleural sac

pleural surfaces secrete fluid into this cavity
atmospheric pressure:
pressure produced by weight of the air on objects on surface of earth. it is 760 mmHG at sea level. it decreases with increasing altitude above sea level
intra-alveolar pressure (intrapulmonary pressure):
pressure in alveoli
intrapleural (intrathoracic pressure):
pressure in pleural sac. it averages 756 mmHG at rest. it is also written as -4 ( 4 units below 760 mmHG atmospheric pressure). it is lost during pneumothorax (air in pleural cavity)
transmural pressure: the lungs are normally stretched filling the thorax
this is due in part to intrapleural fluid's cohesiveness (sticking to itself). this stickiness pulls the lungs outward.
transmural pressure gradient across lung wall:
net outward pressure differential between intra-alveolar pressure and intrapleural pressure
the transmural pressure gradient pushes lungs outward when intra-alveolar pressure is greater than pressure outside alveoli
(that is, the intrapleural pressure - this helps keep the lungs open)
transmural pressure gradient across thoracic wall:
net inward pressure differential between atmospheric pressure and intrapleural pressure
transmural pressure gradient across lung wall=
intraalveolar pressure - intrapleural pressure
transmural pressure gradient across thoracic wall =
atmospheric pressure minus intraplerual pressure
changes in intra-alveolar pressure produce air flow in and out of lungs
when intra-alveolar pressure < atmospheric pressure, air enters lungs.
when intra-alveolar pressure > atmospheric pressure, air exits lungs
intra-alveolar pressure changed according to
boyle's law (P1V1 = P2V2)

there is an inverse relationship between the pressure exerted by a puantity of gas and its volume. (increased gas volume, decreased gas pressure)

changes in volumes are accomplished by muscles
contraction of inspiratory muscles and expansion of thoracic cavity decreases intrapleural pressure (754 mmHG)
contraction of inspiratory muscles:
diaphram: innervated by phrenic nerve.
external intercostal muscles: innervated by intercostal nerves.
75% enlargement of thoracic cavity during quiet respiration due to contraction and flattening of diaphragm
expansion of thoracic cavity decreases intrapleural pressure (754 mmHG):
lung drawn into area of lower pressure; they expand.
increase in lung volume lowers intra-alveolar pressure below atmospheric pressure.
pressure gradient : air enters lungs
relaxation of inspiratory muscles ( diaphragm and muscles of chest wall, plus elastic recoil of the alveoli: decrease size of chest cavity)
Expiration cont: intrapleural pressure increases: lungs compressed.
there is decreased lung volume and an increased intra-alveolar pressure ( increased to level above atmospheric pressure, air is forced out = expiration)
forced expiration:
contraction of expiratory muscles further increases pressure gradient between alveoli and atmosphere
airway resistance influences rate of airflow
F = chnage in Pressure gradient / resistance
increased difference between atmospheric and intra-alveolar pressures:
increased air flow ( F and P are directly proportional)
increased resistance decreases airflow
F and R are inversely proportional
major determinant of resistance:
radius of conducting airways
autonomic nervous system controls contraction of smooth muscle in walls of bronchioles
ANS can change conducting airway radii. sympathetic stimulation and epinephrine: bronchodilation. parasympathetic stimulation (at rest): bronchoconstriction (demand for airflow is low)
increased airway resistance with chronic obstructive pulmonary disease COPD:
group of 3 chronic diseases: chronic bronhitis, ashtma, and emphysema
two properties allow lungs to behave as balloons, stretchng and recioling:
elastic recoil and compliance
elastic recoil- how readily lungs rebound if stretched:
allows lungs to return to preinspiratory volume when inspiratory muscles relax at end of inspiration
compliance- effort required to stretch (distend) lungs:
analogous to effort required to blow up a balloon. thin balloon more compliant than a thick balloon. a highly compliant lung stretched farther for a given increase in pressure than a less compliant lung. decreased lung compliance in fibrotic lungs.
pulmonary elasticity depends on:
1. pulmonary elastic connective tissue ( lots of elastin fibers arranged to ehnance elasticity)
2. alveolar surface tension (tension determined by thin liquid film lining each alveolus. this film allows alveolus to resist expansion. this film also squeezes alveolus, producing recoil. the coating of the pulmonary surfactant prevents alveolus from collapsing from this surface tension.)
pulmonary surfactant:
mixture of proteins and lipids secreted by type II alveolar cells. it is found between water molecules in fluid lining alveolus.
pulmonary surfactant:
by reducing alveolar surface tension, it increases pulmonary compliance, reducing work required to inflate lung. it also reduces lungs tendency to recoil, so they do not readily collapse.
the work of breathing normally requires 3% of total energy expenditure
4 situations increase amount of work necessary:
decreased pulmonary compliance, increased airway resistance, decreased elastic recoil, and need for increased ventillation :exercise
~500 ml of air is inspired and expired during each quiet breathing cycle
the lungs do not completely empty after each expiration
lung volume and capacities are measured using a spirometer
tidal volume (TV): air entering or leaving lungs in a single breath. it equals the difference between end-expiratory and end-inspiratory volume
pulmonary ventilation ( or minute ventilation):
volume of air breathed in in an out in 1 minute
respirtory rate:
number of breaths/minute
pulmonary ventilation =
tidal volume ( ml/breath)X respiratory rate (breaths/min)
average pulmonary ventilation =
500ml/breath X 12 breaths/min = 600 ml or 6L
anatomic dead space:
not all inspired air reaches alveoli, where gas exchange can occur, some in conducting airways. alveolar ventilation less than pulmoary ventilation because of anatomic dead space
alveolar ventilation =
(tidal volume - dead space) / breath


respiratory rate
average alveolar ventilation=
(500ml - 150ml)/breath X 12 breaths per minute = 4200ml/min
breathing patterns (deep or slow) can affect alveolar ventilation
rest, quiet: alveolar ventilation = 4200ml/min

deep, slow breaths (increased TV, decreased rate): 5250ml/min
alveolar dead space also exists but:
it is usually small
resistance of individual alveoli can be adjusted independently by local controls which act on
smooth muscle of the airways
accumulation of carbon dioxide in the alveoli:
decreases airway resistance by causing airway supplying alveoli to relax
decreased carbon dioxide has opposite effects:
increased contraction of airways supplying alveoli, reduced airflow
ventilation and perfusion should:
diffusion of oxygen and carbon dioxide across respiratory epithelium:
transport of gases:
breathing movements:
supply air to respiratory surface
key to gas eschange:
partial pressures
oxygen and carbon dioxide exchange at pulmonary and tissue capillaries via:
simple exchange
mixture of gases
partial pressure of each gas depends onits percentage in total atmospheric pressure (760 mmHG)
EX) oxygen is 21% of air

0.21 X 760 = 160 mmHG
79% nitrogen in air
partial pressure = 0.79 X 760 mm HG = 600.4 mmHG
partial pressure gradient:
two partial pressures for a gas in different regions of the body
the parital pressure of oxygen:
is greater in alveoli (100mmHG) vs. in blood of pulmonary capillaries (40mmHG)
oxygen diffuses from alveoli into:
partial pressure of carbon dioxde:
is greater in the blood of pulmonary capillaries (46 mmHG) vs. alveoli (40mmHG)
carbon dioxide diffuses into alveoli from:
parital pressure of oxygen
is greater in the blood (100mmHG) vs. in tissue cells (40 mmHG)
oxygen diffuses from blood into :
tissue cells
partial pressure of carbon dioxide:
is greater in tissue cells (46 mmHG) vs. in blood (40 mmHG)
carbon dioxide diffuses into blood from:
tissues cells
oxygen partial pressure gradient from alveoli to blood =
100-40= 60mmHG
carbon dioxide partial pressure gradient from blood to alveoli =
46-40 = 6 mmHG
oxygen partial pressure gradient from blood to tissue cells=
100-40 = 60 mmHG
carbon dioxide partial pressure gradient from tissue cells to blood =
46-40= 6 mmHG
other factors that affect rate of gas transfer:
srface area, distance, gas diffusion coefficient
surface area:
increase SA, increased reate of exhcange.
alveoli collectively: tremendous surface area
increased pulmonary blood pressure from an increased cardiac output increases surface area.
thin walls = rapid gas exchange

alveolar and capillary walls = thin
pulmonary edema, pulmonary fibrosis, pneumoni thicken areas for gas exchange
gas diffusion coefficient:
exchange directly proportional to diffusion coefficient for a gas. the coefficient for carbon dioxide is 20 times that of oxygen (CO2 is more soluble)
98.5% of oxygen is bound to hemoglobin

1.5% is physically dissolved
10% of CO2 is physically bound
30% of CO2 is bound to hemoglobin
60% of CO2 as bicarbonate (HCO3)