The Respiratory System
• Cells continually use O2
& release CO2
• Respiratory system
designed for gas
exchange
• Cardiovascular system
transports gases in blood
• Failure of either system
– rapid cell death from O2
starvation
Nose -- Internal Structures
Pseudostratified ciliated columnar with goblet cells
lines nasal cavity
-warms air due to high vascularity
-mucous moistens air & traps dust
-cilia move mucous towards pharynx
•entrance – external nares
• two nasal cavities with bony outgrowths =
nasal conchae (superior, middle, inferior)
• nasal cavities separated by nasal septum
and nasal bone
•superior most region of the cavity – site for
olfactory epithelium - olfactory receptors
for odors (smell)
• lacrimal glands drain into nasal cavities
• nasal cavities communicate with cranial
sinuses (air-filled chambers within the skull)
• nasal cavities empty into the nasopharynx upper portion of the pharynx
•connection between nasal cavity and
nasopharnyx – internal nares
•functions: warm, moisten, and
filter incoming air
Eustacian tube
With tubal tonsil
The Pharynx
Nasopharynx
•
From internal nares to soft
palate
– Anatomical Landmark:
openings of auditory
(Eustachian) tubes from
middle ear cavity
– adenoids or pharyngeal
tonsil in roof
•
Oropharynx
Laryngopharynx
•
•
•
Extends from epiglottis to cricoid
cartilage
Anatomical Landmark: the
epiglottis
Common passageway for food & air
& ends as esophagus inferiorly
Passageway for air only
•
From soft palate to epiglottis
– Anatomical Landmark: behind the
uvula
– palatine tonsils found in side walls,
lingual tonsil in tongue
•
Common passageway for food & air
Tortora & Grabowski 9/e 2000 JWS
23-5
The Larynx
• triangular box = “voicebox”
• top of the larynx is a hole = glottis
• covered with the epiglottis
• contains the vocal cords - mucosal folds
supported by elastic ligaments
•Epiglottis---leaf-shaped piece of elastic
cartilage
• filters, moistens, vocal
production
–during swallowing, larynx moves
upward bringing the glottis up to the
epiglottis
–epiglottis bends slightly to cover glottis
• Laryngeal cartilages:
• 1. thyroid cartilage (Adam’s apple)
• 2. cricoid cartilage
• 3. arytenoid cartilage – for the attachment of
true vocal cords and arytenoideus muscles
Tortora & Grabowski 9/e 2000 JWS
23-6
Vocal Cords
• False vocal cords (ventricular
folds) found above the true
vocal cords
• True vocal cords attach to
arytenoid cartilages
• True vocal cord contains both
skeletal muscle and an elastic
ligament (vocal ligament)
• When intrinsic muscles of the
larynx contract they move the
artytenoid cartilages & stretch
the true vocal cords tighter
• When air is pushed past the
tightened vocal ligament,
sound is produced
Larnyx and Vocal Cords
•
true vocal cords vibrate upon passage of air > speech
• thickness determines frequency of vibration
and timber of sound
 thicker the cords – slower they vibrate – lower
the pitch
 thinner the cords – faster they vibrate – higher
the pitch
• thickness also controlled by testosterone
•
pitch can also be controlled by tightening the
vocal cords voluntarily
-arytenoideus muscle and the intrinsic muscles
of the true vocal cords can alter the “tightness”
of the cords
 tighter the cords – faster they will vibrate
23-8
Tortora & Grabowski 9/e 2000 JWS
23-9
Trachea
•
•
•
•
flexible cylindrical tube - Size is 5 in long & 1 in diameter
sits anterior (in front of) the esophagus
splits into right and left primary bronchi – enter the lungs
held open by “C” rings of hyaline cartilage = tracheal cartilage
–16 to 20 incomplete rings
•open side facing esophagus contains smooth muscle = tracheal ligament
• layers:
– innermost layer (mucosa) = pseudostratified columnar with cilia & goblet cells
–outer layer (submucosa) = loose connective tissue & mucous glands
•functions: conducts air into the lungs, filtration,
moistens
mucosa
submucosa
Trachea and Bronchial Tree
•
•
•
•
•
Primary bronchi supply each lung
Secondary bronchi supply each lobe of the lungs (3 right + 2 left)
Tertiary bronchi splits into successive sets of Intralobular bronchioles that supply each
bronchopulmonary segment ( right = 10, left = 8)
IL bronchioles split into Terminal bronchioles -> these split into Respiratory Bronchioles
each RB splits into multiple Alveolar ducts which end in an Alveolar sac
Gross Anatomy of Lungs
• Base, apex (cupula), costal
surface, cardiac notch
• Oblique & horizontal
fissure in right lung results
in 3 lobes
• Oblique fissure only in left
lung produces 2 lobes
• Blood vessels & airways
enter lungs at hilus
• Forms root of lungs
• Covered with pleura
(parietal becomes visceral)
Alveoli
• Respiratory bronchioles branch into multiple Alveolar ducts
• Alveolar ducts end in a grape-like cluster = alveolar sac or lobule
-each grape = alveolus
Respiratory membrane
= 1/2 micron thick
Alveoli
• site of gas exchange by
simple diffusion
• from heart (right ventricle)->
Pulmonary artery  multiple
branches ending as the
Pulmonary arteriole 
Capillary bed over Alveolus
 Pulmonary venule 
multiple veins  Pulmonary
vein  heart (left atrium)
• deoxygenated blood flows
over the alveolus & picks up
O2 via diffusion because the
alveolar wall is very thin
Cells Types of the
Alveoli
• Type I alveolar cells
– simple squamous cells where gas
exchange occurs
• Type II alveolar cells (septal
cells)
– free surface has microvilli
– secrete alveolar fluid containing
surfactant
O2
CO2
• Alveolar dust cells
– wandering macrophages remove
debris
• Respiratory membrane = 1/2 micron thick
Bronchioles
• surrounded by “ring” of bronchiolar smooth
muscle that can control the diameter of the
bronchiole
smooth muscle
23-16
Pleural Membranes & Pleural Cavity
• Visceral pleura covers lungs
• Parietal pleura lines ribcage & covers upper surface
of diaphragm
• Pleural cavity is space between the two pleura
– contains a small amount of fluid
Mechanism of Breathing: Boyle’s Law
• As the size of closed container decreases, pressure
inside is increased
• As the size of a closed container increases, pressure
decreases
Mechanism of Breathing
Inspiration:
-at rest: pressure inside lung = pressure outside lungs (atmospheric pressure)
-inhale - diaphragm contracts and drops, external intercostal muscles swing the ribcage up and
out
-increase in thoracic cavity volume results
-due to the cohesiveness of intrapleural fluid – lung volume increases also
-pressure inside the lung drops = Boyle’s Law
-air rushes in to equalize
-SO: muscles of inspiration do not act directly on the lungs but act to change the volume of the
thoracic and pleural cavities
Mechanism of Breathing
Expiration: occurs because of the elasticity of the lungs - PASSIVE
-in addition: relaxation of diaphragm and intercostal muscles returns
thoracic and pleural cavity volume to normal
-pressure of air in the lungs increases over atmospheric pressure
-air leaves lungs to equalize
23-20
Summary of Breathing
• Alveolar pressure decreases & air rushes in
• Alveolar pressure increases & air rushes out
Labored Breathing
• Forced expiration
– abdominal mm force
diaphragm up
– internal intercostals
depress ribs
• Forced inspiration
– sternocleidomastoid,
scalenes & pectoralis
minor lift chest
upwards as you gasp
for air
Respiratory Volumes and Capacities
• tidal volume (TV) = amnt of air that enters or exits the lungs
500 ml per inhalation
• inspiratory reserve volume (IRV) = max. amnt of air taken in after
a normal inhalation, 3000 ml
• expiratory reserve volume
(ERV) = amnt of air forcefully
exhaled, 1100 ml
•residual volume (RV) = amnt of air
left in lungs after forced expiration
1200 ml
23-23
Body tissue
O2 and CO2 transport
• most O2 is carried in the blood bound to hemoglobin of
the RBC
•
some is dissolved in blood plasma ( O2 not very soluble in water)
• CO2 is carried by the blood in 3 ways:
1. 90% of the CO2 enters the RBC - combines with water
of the cytosol to form carbonic acid
•
•
immediately dissociates into bicarbonate and H+ ions (binds to Hb)
catalyzed by the RBC enzyme called carbonic anhydrase
2. some CO2 dissolves in the water of the plasma as carbonic
acid  H+ and bicarbonate
3. CO2 can combine directly with hemoglobin to form
carbaminohemoglobin
• in the lungs – Hb releases its H+ ion – it combines with
the HCO3- to reform carbonic acid
• carbonic acid breaks up into H2O and CO2
• CO2 is also released by Hb
• CO2 diffuses into the alveolar air and is breathed out
CO2 produced
CO2 transport
from tissues
Interstitial
CO2
fluid
Plasma
within capillary CO2
H2O
Red
blood
cell
Capillary
wall
CO2
H2CO3
Hb
Carbonic
acid
HCO3 
Bicarbonate
HCO3
H+
To lungs
CO2 transport
to lungs
HCO3
HCO3 
H2CO3
Hemoglobin (Hb)
picks up
CO2 and H+.
H+
Hb
Hemoglobin
releases
CO2 and H+.
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung
Respiration Rate: controlled by a respiratory center made up of a
Medullary rhythmicity area in the medulla and two nuclei in the
pons
-MRA -group of neurons with an automatic, rhythmic discharge
-groups are called the dorsal and ventral respiratory groups
-controls rate and depth of breathing
-dorsal group is called the inspiratory center which send signals via
the motor neurons of the phrenic nerve and intercostal nerves that supply
the inspiratory muscles (diaphragm and external intercostals)
-ventral group contains expiratory neurons – inactive during normal
quiet breathing but called into play with active breathing
Respiratory
Center
• Respiration also controlled by
neurons in pons
• Pneumotaxic Area
– constant inhibitory impulses to
inspiratory area
• inhibits inspiration before lungs
become too expanded
• Apneustic Area
– stimulatory signals to inspiratory
area to prolong inspiration
Respiratory
Center
• Chemical regulation
• Central chemoreceptors in medulla
– respond to changes in H+ or pCO2
• Peripheral chemoreceptors
– respond to changes in H+ , pO2 or pCO2
– aortic body---in wall of aorta
• nerves join vagus
– carotid bodies--in walls of common
carotid arteries
• nerves join glossopharyngeal nerve
• Cortical Influences
Tortora & Grabowski 9/e 2000 JWS
– voluntarily alter breathing
patterns
– limitations are buildup of CO2 &
H+ in blood
– inspiratory center is stimulated by
23-27
increase in either
Negative Feedback Regulation of Breathing
• Negative feedback control
of breathing
• Increase in arterial pCO2
• Stimulates receptors
• Inspiratory center
• Muscles of respiration
contract more frequently &
forcefully
• pCO2 Decreases