Chapter 17 mechanics of breathing

general functions of the respiratory system

• exchange of gases

• regulation of pH by altering CO2 levels

• protection of inhaled pathogens and irritants

• vocalization

challenges of the respiratory system

heat and water loss

movement of materials in cardiovascular

transports substances throughout the body through the heart pumping blood

movement of material in respiratory

facilitates gas exchange through movement of thoracic cavity of air

both cardiovascular and respiratory system use 

convection and diffusion 

pressure gradient

drive flow of air into and out of the lungs

resistance

determined by diameter of airways

external respiration 

exchange of gases between atmosphere and blood 

ventilation

exchange between atmosphere and lungs

inspiration

air in

expiration

air out

air conducting systems 

upper respiratory tract, lower respiratory tract, alveoli, and musculoskeletal pump

upper respiratory tract

mouth → nasal cavity → pharynx → larynx

lower respiratory tract

trachea → primary bronchi → bronchial tree

alveoli

functional units for gas exchange

musculoskeletal pump 

bones, and muscles of the thoracic cavity 

muscles move bones and alter

thoracic volume

diaphragm

forms floor, dome shaped muscles in relaxes state

intercostal muscles

between rib

internal intercostal muscles 

expiration, close to sternum, ribcage smaller 

external intercostal muscles

inspiration, lateral, lifting of ribcage

scalenes

move 1st rib

parts of movement of thoracic cavity

diaphragm, intercostal muscles, and scalene

pleural membrane 

double membrane that surrounds the lungs 

types of pleural membranes

parietal, visceral, and pleural space

parietal pleura

adherent to thoracic wall

visceral pleura

adherent to lung

pleural space 

filled with small amount of pleural fluid 

the airways function to

conduct, warm, humidify, and filter air into lungs

pharynx

common passage for food, air, and liquids

larynx

vocal cords

trachea 

flexible tube, held open by cartilage rings and branches in bronchi 

bronchial tree

primary bronchi to each lung

bronchial tree branches into

conducting bronchi and bronchioles

conducting bronchi

terminal bronchioles (2-11) conducting system

bronchioles 

(12-23) respiratory bronchioles for exchange system

mucociliary escalator

ciliated epithelium of trachea and bronchi covered in saline and mucus 

structure of alveoli that promotes gas exchange

connective tissue that generates elastic recoil

Type I pneumocytes

thin epithelial cell lining most of surface that forms a minimal barrier

Type II pneumocytes

smaller surface area, secrete surfactant, move fluid out of air space, and replace damaged type I cells

pulmonary circulation 

high volume and low pressure system 

parts of pulmonary circulation

flow rate and low pressure fl

flow rate

higher than systemic and receive entire cardiac output volume

resistance is low in pulmonary vessels due to

large cross-sectional are and more distensible

boyles law 

pressure volume relationship

P1V1 =

P2V2

boyles law respiratory system

thoracic volume generates pressure gradients that drive air flow

boyles law inspiration

pressure decreases and volume increases

boyles law expiration 

pressure increases and volume decreases 

daltons law

total pressure exerted by a mixture of gases is sum of pressures exerted by individual gases

partial pressure

pressure of a single gas in a mixture

how daltons law applies to gas diffusion

establishes that it is driven by differences in partial pressures

role of intrapleural pressure 

allow for lungs to move as thoracic cage moves 

negative intrapleural pressure

forces acting on the two membranes pull in opposite directions generating subatmospheric pressure

pneumothorax

penetrating injury to the rib cage

pneumothorax injury causes

breaking of fluid bond and lungs to collapse due to elastic recoil of lung

contributors to lung stretchability 

compliance and elastance 

inhalation cyclic pattern

air flows into lungs as atmospheric pressure is greater than alveolar pressure

brain controls activation of

inspiratory muscles

increased alveolar volume =

decreased alveolar pressure

contraction of diaphragm = 

increase in thoracic cavity and increase in alveolar volume

exhalation cyclic pattern

air flows out of lungs because atmospheric pressure is less than alveolar pressure

relaxation of muscles =

decrease in thoracic volume and decrease in alveolar volume

decreased alveolar volume =

increased alveolar pressure

quiet expiration 

passive 

active expiration

additional actions of abdominal and internal intercostal muscles

compliance

measurement of forces needed to stretch long and force generated by thoracic cavity movement

high compliance =

easy to stretch

fibrosis compliance 

stiff and require higher pressure to expand 

emphysema compliance

alveolar walls lost, loose, floopy, and high compliance

elastance

result of elastic properties of connective tissue

high elastance =

returns to shape easily

fibrosis elastance 

stiff, greater force to return to resting volume, and high elastance

emphysema elastance

recoil force reduced and low elastance

surfactant

reduces cohesive forces between water molecules that reduce surface tension s

surfactant is secreted by

type II cells

alveolar importance of surfactant 

• prevents collapse

• maintains lung compliance

• efficient gas exchange

• protection

elastance and compliance are

inversely related

airway resistance factors

• length of system (constant)

• viscosity of fluid (constant)

• radium of the system

trachea and bronchi resistance 

most resistance as cartilaginous support keeps open

bronchioles resistance

constriction of bronchiolar smooth muscle increases resistance

histamine resistance

bronchoconstriction

CO2 levels and epinephrine

bronchodilation

total pulmonary ventilation

volume of air moved by lungs per unit of time

tidal volume 

volume of air in or out per breath 

anatomical dead space

air stuck in conducting pathway not available for gas exchange

alveolar ventilation

volume of air available for gas exchange

alveolar ventilation formula

tidal volume - anatomical dead space

ventilation perfusion matching 

airflow matching blow flow to ensure adequate oxygenation of blood 

decreased tissue around underventilated alveoli

constrict arterioles diverting blood to better ventilated alveoli

asthma

bronchiole smooth muscle spasticity and mucus plug

treat met for asthma

brochiole dilators

types of bronchiole dilators 

beta2-agonists, anti-cholinergic, and anti-inflammatory steroids