Respiratory System Notes
I.
Overview
a. Mechanical means by which we obtain O2 for metabolism
i. Get rid of CO2
ii. Regulation of pH in blood
b. Respiration
i. Cellular respiration: a series of metabolic reactions
1. not part of the respiratory system
2. respiration provides O2
ii. Internal respiration: exchange of gasses between blood and tissues
1. associated with the cardiovascular system
iii. External respiration: exchange of gasses between lungs and blood
c. Ventilation
i. Chief mechanical function of lungs
ii. Inspiration – air moves into the lungs
iii. Expiration – air moves out of the lungs
iv. End result – gas exchange
v. Secondary function
1. vocalization
2. increase venous return
3. compression to abdominal cavity in defecation, urination, childbirth
d. Gross anatomy
i. Nose
1. only externally visible part of the respiratory system
2. external nares – nostrils
3. nasal cavity – divided by nasal septum
4. conchae – projections/lobes in the sides of the nasal cavity
5. palates – hard (anterior), soft (posterior) separate the oral cavity from the
nasal cavity
6. paranasal sinuses – frontal, sphenoid, ethmoid, maxillary
ii. Pharynx – common conduit for food and air - throat
1. nasopharynx – above soft palate & posterior to internal nares
2. oropharynx – from soft palate to epiglottis
a. Palatine tonsils & lingual tonsils
3. laryngopharynx – hyoid bone to larynx
iii. Larynx – voice box
1. located inferior to the pharynx
2. Vocal cords
3. Nine rings of cartilage
4. thyroid cartilage – largest of the cartilage disks
5. epiglottis – protects the opening of the larynx, prevents food from entering
the lungs
iv. Trachea – trunk of the tree
1. series of cartilaginous rings that help keep it open
2. rings are incomplete posterior to allow expansion during swallowing
3. pseudostratified ciliated columnar epithelium – mucociliary escalator
v. Lungs – paired
II.
1. mediastinum – central area that houses the heart, blood vessels, bronchi,
esophagus
2. apex – inferior to clavicle
3. base – superior to the diaphragm
4. visceral and parietal pleura
5. left lung has two lobes
6. right lung has three lobes
vi. Respiratory tree
1. trachea forms trunks
2. primary bronchi go to R & L lungs
3. secondary bronchi go to lobes of lungs
4. tertiary bronchi – bronchiole pulmonary segments
5. tertiary bronchi branch into smaller and smaller bronchioles and
eventually terminal bronchioles
6. respiratory bronchioles are functional bronchioles – gas exchange
a. branches off terminal bronchioles
7. respiratory bronchioles branch into alveolar ducts and terminate in
alveolar sacs
8. alveolar sacs are clusters of alveoli
9. alveoli – small air sacs - like bunches of grapes
a. where capillaries complete gas exchange
b. some located on respiratory ducts
vii. Gas exchange
1. gas exchange occurs in individual alveoli
2. need a respiratory membrane contusive to diffusion
3. two types of cells found in alveoli
a. type I – simple squamous epithelium
b. type II – septal cells
i. secrete material to keep walls from sticking – surfactant
ii. decrease surface tension in inner walls
iii. phospholipids
4. macrophages found in alveoli
5. respiratory membrane – where gas exchange occurs
a. epithelial cells of alveoli (type I & II)
b. basement membrane of alveoli
c. basement membrane of capillary
viii. Pleura – serous sacs surrounding lungs
1. visceral inside layer
2. parietal outside layer
3. space – pleural cavity – between layers
a. serous fluid in cavity that creates surface tension to hold lungs in
place – to walls of thorax
b. pneumothorax – separation of visceral and parietal pleura – lets air
in the space
Respiratory Physiology
a. Movement of gasses
i. Boyles Law – volume of gas is inversely related to pressure
1. need to change volume in our lungs to move air in and out
2. Inhalation – increase thoracic volume
3. Exhalation - decrease thoracic volume
b.
c.
d.
e.
f.
ii. pressures involved in breathing
1. atmospheric pressure
2. intra-aveolar pressure (in lungs)
3. intra-pleural pressure (in space)
4. intra-aveolar pressure is always equal to atmospheric pressure at end of
inspiration and at end of expiration
Inspiration – increase volume of thorax
i. External intercostals and diaphragm contract
ii. Abdominal muscles relax, diaphragm pushes viscera downward and outward
iii. Diaphragm expands cranial-caudal dimension of the thorax
iv. External intercostals muscles lift ribs
1. lower ribs expand thorax in side to side dimension
2. upper ribs expand in anterior-posterior dimension
v. deep inspiration
1. scalenes, pec major & minor, serratus anterior, sternocleidomastoid
quiet expiration
i. passive
ii. relax muscles
iii. lungs expel air through elastic recoil
forced expiration
i. requires muscular effort
ii. internal intercostals muscles depress ribcage
iii. abdominal muscles contract and force diaphragm upward
iv. latissimus dorsi and quadratus lumberum depress the rib cage
compliance
i. change in lung volume per unit change in intraaveolar pressure
ii. how easily lungs expand and recoil
iii. low compliance – stiff lungs that are difficult to expand
factors affecting gas movement and solutality
i. Dalton’s law – each gas in a mixture exerts a pressure that is proportional to its
concentration in the mixture
1. each gas will diffuse down its won pressure gradient
2. partial pressure – the proportional pressure of each gas in a mixture
3. atmospheric pressure – sum of all partial pressures
ii. Henry’s law – solubility of gases – each gas in a mixture will dissolve to extend
of its own partial pressure
1. Increase partial pressure, increase solubility
2. each gas will dissolve in proportion to its solubility coefficient
a. CO2 has high solubility, O2 has low solubility
3. can have an affect under physiologically stressful conditions
a. high altitude, deep sea diving
iii. Ficks law – diffusion across a membrane – diffusion is faster with small
molecules across a thin membrane then vice versa
1. highly soluble molecules at increase partial pressure will diffuse fastest
2. greater surface area of membrane, the greater the diffusion rate
iv. Factors involved in gas exchange
1. partial pressures
2. total surface area
3. thickness of membrane
4. solubility and size of particles
III.
IV.
g. gas transport
i. external perspiration – oxygenating the deoxygenated blood
1. inc. P O2 in alveoli and dec. P O2 in capillaries
2. dec. P CO2 in alveoli and inc. P CO2 in capillary
ii. Internal respiration – oxygen out of capillaries and into tissues, CO2 out of tissues
and into capillaries
iii. O2 is carried by hemoglobin in RBC’s
1. Inc. P O2 = O2 and Hb will bind readily
2. dec. P O2 = Hb will release O2
3. Bonr Effect
a. Inc. P CO2 = Hb releases O2
b. Dec. P CO2 = Hb holds O2
Respiratory Volumes & Capacities
a. Tidal volume (TV)
i. Normal quiet breathing
ii. The amount of air that flows in and out of the lungs with each breath
b. Inspiratory reserve volume (IRV)
i. The amount of air that can be inspired forcibly beyond the tidal volume
c. Expiratory reserve volume (ERV)
i. The amount of air that can be evacuated from the lungs after a tidal volume
d. Residual volume (RV)
i. The air that remains in the lungs after the most strenuous expiration
ii. Helps keep the alveoli inflated and prevents the lungs from collapsing
e. Inspiratory capacity (IC)
i. The total amount to f air that can be inspired after a tidal expiration
ii. The sum of the TV & IRV
f. Functional residual capacity (FRC)
i. The combined residual and expiratory reserve volumes
ii. Represents the amount of air remaining in the lungs after tidal expiration
g. Vital Capacity (VC)
i. The total amount of exchangeable air
ii. The sum of the TV, IRV, ERV
h. Total lung capacity (TLC)
i. The sum of all lung volumes
ii. Tend to be larger in males due to size
i.Dead space
i. The volume of air that fills the conducting passageways and never contributes to
gas exchange
Neurochemical control of breathing
a. Respiratory centers
i. Medullary rhythmicity center
1. primary respiratory control
2. located in medulla oblongata
3. quiet respiration – inspiration uses dorsal respiratory group
a. impulses travel from DRG down the phrenic nerve and intercostals
nerve which cause expansion of thoracic cavity
b. passive expiration
c. series of intermittent impulses
4. forced inspiration and expiration uses ventral respiratory group
a. synchronous impulses to muscles of inspiration and expiration
b. impulses to diaphragm, external intercostals, pectorals, scalenes
c. impulses to internal intercostals, abdominals, quadratus laborum,
latissimus dorsi
ii. Apreustic and pneumotoxic center
1. adjusts rate of respiration
2. located in pons
3. pneumotoxic – speeds rate of DRG
4. apneustic – slows rate of DRG
iii. inputs into medullary respiratory center
1. cerebral cortex and hypothalamus
2. irritant reflex in bronchioles
3. inflation reflex from pulmonary stretch receptors
4. chemical reflexes
a. dec. P O2 – inc. ventilation
b. Inc. P CO2 – inc. ventilation
c. Peripheral chemoreceptors – carotid bodies and aortic arch
d. Dec. pH in blood triggers chemorecptors
i. Medullary respiratory center triggered
ii. Inc. ventilation