Lecture 24 Respiratory 1 Flashcards by Sarah underwood

Primary functions of respiratory system

supply O2 and eliminate CO2
maintain acid-base balance via regulation of CO2 in blood
ventilation and gas exchange

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4 integrated processes

Ventilation
gas exchange
transport of O2 and CO2 in the blood
exchange of O2 and CO2 between blood and cells

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Conducting zone

nasal cavity 
pharynx 
larynx 
trachea
primary bronchi 
bulk flow region, no gas exchange = anatomic "dead space"

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Upper respiratory

nasal cavity

pharynx

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Lungs

secondary, tertiary, and smaller bronchi
bronchioles
terminal bronchioles

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respiratory zone

respiratory bronchioles 
alveolar ducts 
alveolar sacs
alveoli 
gas exchange region

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Alveoli

primary sites of gas exchange
huge surface area 
type 1 cells - simple squamous 
type 2 cells - surfactant cells 
alveolar macrophages ("dust cells")

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Pulmonary Capillaries

surround alveoli, exchange O2 and CO2 with air in the alveoli

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Thoracic Cavity

chest wall, diaphragm, pleurae, intrapleural space, respiratory muscles

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Chest wall

surrounds thoracic cavity (ribs, intercostal muscle, etc.)

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Diaphragm

separates thoracic and abdominal cavities

primary muscle of inspiration

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Pleurae

serous membranes surround each lung, form fluid-filled pleural sacs
parietal pleura lines chest wall and diaphragm
visceral pleura covers the lungs

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Intrapleural space

thin, fluid filled space between parietal and visceral pleurae
fluid in the intrapleural space connects lungs to chest wall and diaphragm

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Inspiration

muscles

primary: diaphragm
secondary: external intercostals, neck muscles

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Expiration

muscles

passive: elastic recoil of lungs
active: internal intercostals, abdominal muscles

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Mechanics of air breathing

Pressure
Air flow
Forces

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Pressure

P of gas is inversely related to volume (V)
Boyle’s law P1V1=P2V2 (closed system)
during inspiration, resp. muscles contract -> lungs expand -> V increases -> P decreases

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Air Flows

in and out of lungs because of pressure differences between lungs and atmosphere
air flows from higher pressure to lower pressure
during inspiration, P decreases -> air flows in
during expiration, P increases -> air flows out

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Forces

are transmitted between chest wall and lungs through fluid in the intrapleural space
opposing recoil forces of the lungs (inward) and chest wall (outward) create a negative pressure in the intrapleural space

Pressures involved in breathing

atmospheric
alveolar
intrapleural space

atmospheric

(Patm) = 760 mm Hg at sea level (= “0 mm Hg” used as reference)

alveolar

intrapulmonary Palv - air pressure in the alveoli
P alv= P atm (=0) at end of expiration
Palv < Patm during inspiration, Palv>Patm during expiration

intrapleural

Pip

pressure inside the intrapleural space = -4 mm Hg (0 lung coppalses (atelectasis)

Inspiration pressure changes during breathing

resp. muscles contract -> Pip decreases (< -4 mm Hg) -> V increase -> Palv decreases -> air flows in

Expiration changes during breathing

resp. muscles relax -> Pip increases )back to -4 mmHg) -> V decreases -> Palv increases -> air flows out

Physical Properties of lungs

compliance elasticity airway resistance

compliance

ease of expansion | increase compliance -> easier to expand lungs -> decrease work of breathing

elasticity

stretching force; ability to return to normal length or volume inward recoil force of lungs is due to elastic tissue and surface tension of fluid lining alveoli

airway resistance

mostly depends on diameter of small airways | smooth muscle of bronchioles -> bronchoconstriction/dilation

Surface tension

results from forces between water molecules at air-water interface contributes to inward recoil force in lungs, tends to collapse alveoli inward greater effect on small alveoli than large alveoli (Law of LaPlace: P=2T/r)

Pulmonary Surfactant

secreted by type II alveolar cells -> reduces surface tension increase compliance, decreases work of breathing stabilizes alveoli by reducing surface tension more in small alveoli

Respiratory distress syndrome (RDS)

in premature infants is due to insufficient surfactant

Lung Volumes

are non overlapping volumes that add up to total lung capacity

Lung capacities

are combinations of two or more lung volumes

Residual Volume

minimum lung volume = 1200 mL

Functional residual capacity (FRC)

volume in lungs at end of relaxed expiration = 2500 mL

Tidal volume

Vt volume inspired and expired in each breath = 500 mL (quiet breathing) a portion of tidal volume remains in anatomic dead space (DSV=150mL)

Vital Capacity

VC | maximum breathing volume =4000-5000 mL

total pulmonary ventilation

minute volume Ve = ventilation rate (RR) x tidal volume resting: VE = (12breaths/min) X (500mL/breath) = 6000 mL/min

how does minute volume increase

increases in proportion to gas exchange requirements (a to metabolic rate)

Alveolar ventilation

"effective" ventilation of fresh air to gas exchange surfaces Va =RR X (Vt-DSV) 12 breaths/min X (500 - 150 mL/breath) = 4200 mL/min

Restrictive disorders

e.g. pulmonary fibrosis | reduced lung compliance -> difficult inspiration, reduced vital capacity

Obstructive disorders

e.g. asthma | increased airway resistance -> difficult expiration, lower rate of expiration

Obstructive Pulmonary disease

COPD | emphysema, asthma, chronic bronchitis

Emphysema

involves destruction of alveolar tissue fewer, larger alveoli -> decreased surface area for gas exchange reduced elastic recoil of lungs -> difficult expiration, small airways collapse -> air trapping

force expiratory volume (FEV) test

normal FEV1 = 80% | FEV1 < 70% indicated OPD