RESPIRATORY SYSTEM
•Vertebrate respiratory organs
•Human (mammalian) respiratory process
Catalin Bogdan
bcatal@uic.edu
Wednesday, Friday 8am-12pm
http://www2.uic.edu/~bcatal1
What is respiration ?
• Chemical and physical processes by which
animals and plants obtain oxygen and use it
to release energy from food molecules
• Essential to life
Phases of respiration
• EXTERNAL
• Delivery of Oxygen to
each cell of body
• Removal of Carbon
Dioxide (gaseous byproduct)
• In animals with lungs,
breathing represents
external respiration
• INTERNAL
• Occurs in every cell of
body
• Involves chemical
reactions that liberate
energy from food
• Food molecules are
usually combined w/
Oxygen and Carbon
Dioxide is released
External Respiration
• In lower animals external respiration is
simply an exchange of O2 and CO2 across
cell membranes along concentration
gradients
• Inside the body the concetration of O2 is
lower than that of surrounding water/air
while the concentration of CO2 is greater
• Oxygen difuses into the organism while
Carbon dioxide difuses out
• Examples: sponges
• Complex animals require more oxygen than
it can be obtained via diffusion thru body
surfaces
• Specialized gas exchange structures
evolved:
• GILLS – aquatic
• LUNGS – terrestrial
Fish
• Aquatic animals have
gills
• Gills consist of several
gill arches on each
side
• Each gill arch has 2
rows of gill filaments
further subdivided into
lamelllae (thin)
• Area of gills is
proportional to how
active the fish is
• Fish gills exhibit an important
characteristic: countercurrent flow
• Efficiency is increased as blood flows in
opposite direction to that of water over the
gills
• Water movement over gills is accomplished
via a dual pumping system
• Pressure Pump – fish opens & closes mouth
• Suction Pump – opening & closing
“beating” of opercular flaps
• When swimming at high enough speeds (> 0.5
m/s) some fish change to RAM Ventilation
• Keep mouth open, water flows in thru the mouth
and out between the gills
• All other kinds of respiration stop
• More energy efficient due to overall lower
Oxygen consumption
Air Respiration - LUNGS
• Most terrestrial animals have them
• Are located inside the body
• Have no direct contact with air – so they can stay
moist
• There is however need for an elaborate
circulatory system to transport oxygen in the
body
• Why are gills NOT suited for air respiration ?
Why are gills NOT suited for air respiration ?
• Gills are poorly suited to air respiration
because they cannot keep moisture
• They collapse and stick together
• Some fish can breathe thru gills if air is cool
and moist though (lung fish)
• So then what are the advantages of using
lungs for respiration ?
So then what are the advantages of using
lungs for respiration ?
• Oxygen concentration in air is several
orders of magnitude higher than in water
• Oxygen diffuses much more readily in
water than in air
• Less energy is expended by respiratory
process because air is much easier to move
than water
Amphibians
• Lungs are thin walled,
connected to mouth via
glottis.
• Lung surface is increased
by inner partitions richly
innervated by blood
vessels
• Amphibians ventilate
their lungs via a
mechanism called
pressure pump
• Frog inflates its lungs by fillings its mouth with
air, then closing the mouth, opening the glottis
and pushing the air into the lungs by raising the
floor of its mouth  pressure pump
• Lungs are however too small to sustain high
levels of activity
• Frog’s skin serves as supplementary organ of gas
exchange. It is well vascularized but must
remain moist
• Summer, Hot, High Metabolism (high O2
consumption)  Lungs and skin
• Winter, Cold, Low Metabolism (low O2
consumption)  Skin mainly
Reptiles
• Skin of reptiles is dry and scaly so it cannot
be used for gas exchange
• Lungs are more efficient, higher surface
area, better vascularization
• Lung ventilation is dependant on a new
mechanism called suction pump
Lung Ventilation by Suction Pump
• Lungs are inflated and deflated by repeated
expansion and contraction of the thoracic
cavity
• Reptiles, Birds, Mammals
• Pressure difference – in the closed thoracic
cavity during inhalation the air pressure is
lower than outside
• Ventilation (Inhalation / Exhalation) is
usually aided by the muscles of the thoracic
cavity, rib cage (intercostals) muscles, and
diaphragm muscle
Mammalian Respiratory System
• Air is drawn thru nose or mouth into the pharynx (throat)
• Pharynx opens to both esophagus (to stomach) and trachea
(to lungs)
• Position of epiglottis – a tissue flap above the larynx – will
determine which passage is open
• Usually one does not breathe while one is swallowing food
or he’d choke.
• When you inhale, air moves into trachea
• Trachea branches into two bronchi, each leading to a
lung
• Each lung is surrounded by a pleural membranes and
protected by the rib cage
• Visceral Pleura covers the lung while the Parietal Pleura
lines the thoracic cavity walls
• Inside each lung, air moves into finer and finer
branching called bronchioles
• A bronchiole terminates in a grape-like cluster of sacs
called alveoli
• Alveoli are very thin and are surrounded by capillaries
equally thin
• Thus gases diffuse rapidly in both directions
• Ventilation of lungs consists of two stages
inhalation and exhalation
• Ventilation of lungs is NOT constant nor is it
unidirectional it is tidal (in & out)
• Tidal breathing limits the concentration difference
that drives oxygen diffusion in blood
• Fresh air is not moving into the lungs during half
the respiration cycle
Facts and Numbers
• Lung Volume ~ 5% of total body volume,
regardless of body size
• Mammalian lung surface area ~ 120 m square
• Alveolar and capillary walls have a combined
thickness of just ~ 0.5micrometres
• Cost of breathing
• @ rest ~1.2% of total oxygen consumption
• @ heavy exercise ~ 3%
• Trachea and bronchi and
larger bronchioles have
incomplete cartilage rings
that prevent collapse
• Terminal Bronchioles and
alveolar ducts and alveoli
do NOT have such
cartilage rings
• These terminal airways
collapse during
exhalation
Lung capacities
Tidal Volume
~ 500
mL
Amount of air inhaled/exhaled
at rest
Vital Capacity ~4.5 L Maximum volume in/exhaled
during forced breathing
Male
Vital Capacity ~3.4 L Maximum volume in/exhaled
during forced breathing
Female
Residual
Volume
~1.2 L Always present; this air cannot
be forcefully exhaled; reduces
Oxygen partial pressure in lungs
In regards to epithelial lining of major airways…
• Cilia (always beating upwards towards the
pharynx)
• Mucus for trapping dust, pollen. Mucus is
pushed upwards towards pharynx thru beating of
cilia then passed into esophagus [mucociliary
escalator]
• Particles may also be phagocytized by
macrophages and removed via lymphatic system
(alveoli do not have cilia)
•Material such as inhaled toxic substances and small
particles will enter bloodstream
The only way to truly remove particles (smoke, dust,
fumes) are sneezing (nasal) & coughing (lungs)
ex. Emphysema (smoking) lungs become stretched and
inelastic
Ventilation of Lungs
Review ?
• Lungs are located in thoracic cavity
• Lungs are covered by visceral pleura
• An intrapleural space exists between lungs and
the the parietal pleura which covers the thoracic
wall
• Volume of thoracic cavity is determined by the
contractions of the diaphragm muscle and of the
intercostals muscles
Inhalation
• Rib cage volume increases
thru outward & upward
expansion (intercostals)
and downward expansion
(diaphragm)
• Lung volume increases
• Air pressure inside the
lung is less than pressure
outside
• Air flows from HI  LO
pressures
• Inhalation is an active
process
Exhalation
• Rib cage volume decreases
thru inward & downward
movement of ribs and
upward movement of
diaphragm
• Lung volume decreases
• Air pressure inside the lung
is higher than pressure
outside
• Air flows from HI  LO
pressures
• Exhalation is usually a
passive process
• Exhalation @ rest is a passive process and occurs
thru the relaxation of the muscles of inhalation
(external intercostals, diaphragm)
• Forced inhalation & exhalation require more
muscles
• Forced Inahalation  scalenus &
sternocleidomastoid
• Forced Exhalation (active)  external oblique,
rectus et transversus abdominis
Airflow thru airways… ?
• Amount of air entering the lungs is also
dependent on airway resistance & lung elasticity
• Airway resistance  resistance to the passage
and flow of air thru a “pipe”
• High diametre  Low resistance
• Histamine (allergic rxns) constrict airways
• Asthma
• Epinephrine expands airway diametre
• Lung Elasticity  ease with which lungs
expand
• Dependant on elastin fibers (elastic…duh
connective tissue)
• Fibrosis (caused by asbestos) increases amount
of inelastic fibers
• Surfactant  substance in alveoli which
reduces the surface tension that opposes the
expansion of lungs. Without it, alveoli would
simply collapse.
• Lack of surfactant: Respiratory Distress
Syndrome , often in newborns
…He annoyed us so far yet he
forgot to talk about BIRDS…
Don’t they breathe too ?
Yeah they breathe…so what ?
Birds
• Birds are endothermic animals (warm blooded)
with body temperature ~40-41 degrees
• Most birds are very active (flying)
•  Need of lungs with high gas exchange
efficiency
• Bird lung ventilation is similar to mammalian
ventilation with one exception: the presence of
air sacs
Air sacs
No gas exchange
Reduce bird density
Avian Respiratory System
• Small lungs + 9 air sacs
• Air sacs permit unidirectional flow of air thru the
lungs
• Air sacs not directly involved in gas exchange
• Unidirectional flow means that air moving thru
bird is always fresh and with higher partial
pressure of oxygen
• What other class of vertebrates had another
unique feature for respiration? … You guessed it
right… FISH (countercurrent flow)
Blood flow in bird lung is actually crosscurrent NOT
Countercurrent (as in fish) as drawn here. Still, there is
an improved gas exchange compared to mammals.
Air flow thru avian lungs and air sacs
• 1 - On first inhalation, air flows through the
trachea & bronchi & primarily into the posterior
(rear) air sacs
• 2 - On exhalation, air moves from the posterior
air sacs & into the lungs
• 3 - With the second inhalation, air moves from
the lungs & into the anterior (front) air sacs
• 4 - With the second exhalation, air moves from
the anterior air sacs back into the trachea & out