Biology – Premed Windsor University
School of Medicine
Gaseous Exchange
Pre Med – Biology ChapterGaseous Exchange
There is more to lectures than the power point
slides!
Engage your mind
2008-2009gills
alveoli
elephantseals
Gas ExchangeRespiratory Systems
Why do we need a respiratory system?
O2
food
ATP
CO2
respiration forrespiration
Gas exchange• O2 & CO2 exchange between
environment & cells
• Atmospheric Gases:• Oxygen -- 21%• Nitrogen -- 78%• CO2 -- 0.04%
• Diffusion from area of [High partial pressure] to [Low partial pressure]
Optimizing gas exchange• Why high surface area?
– maximizing rate of gas exchange– CO2 & O2 move across cell membrane by diffusion
[High concentration] to [Low concentration]• rate of diffusion proportional to surface area
• Why moist membranes? – moisture maintains cell membrane structure– gases diffuse only dissolved in water
High surface area?High surface area!Where have we heard that before?
Gas exchange in many forms…one-celled amphibians echinoderms
insects fish mammals
endotherm vs. ectothermsize
cilia
water vs. land ••
Large & Thin Surface Area
• Respiratory Surfaces:
• Lung alveoli in mammals• Gill lamellae in fish• Leaf in Plants• Cell membrane in Protozoa• Skin in Amphibians
Evolution of gas exchange structuresexternal systems with lots of surface area exposed to aquatic environment
Aquatic organisms
moist internal respiratory tissues with lots of surface area
Terrestrial
Gas Exchange in Water: Gills
Counter current exchange system• Water carrying gas flows in one direction,
blood flows in opposite direction
just keepswimming….
Why does it workcounter current?Adaptation!
• Blood & water flow in opposite directions– maintains diffusion gradient over whole length of gill
capillary
– maximizing O2 transfer from water to blood
water
blood
How counter current exchange worksfront back
blood
100%15%
70% 40%
watercounter-current
concurrent
Gas Exchange on Land
• Advantages of terrestrial life – air has many advantages over water
• higher concentration of O2
• O2 & CO2 diffuse much faster through air – respiratory surfaces exposed to air do not have to be
ventilated as thoroughly as gills• air is much lighter than water & therefore much
easier to pump– expend less energy moving air in & out
• Disadvantages– keeping large respiratory surface moist
causes high water loss• reduce water loss by keeping lungs internal
Why don’t land animalsuse gills?
Terrestrial adaptations
• air tubes branching throughout body• gas exchanged by diffusion across
moist cells lining terminal ends, not through open circulatory system
Tracheae
Lungs Exchange tissue:spongy texture, honeycombed with moist epithelium
Why is this exchangewith the environmentRISKY?
The lungs
• organs that allow gas exchange
• oxygen in / CO2 out
trachea- has rings of cartilagebronchi (bronchus)bronchiolesalveoli (alveolus)
computer animation
Alveoli (air sacs)
• provide large surface area for gas exchange
• one lung equivalent to a tennis court of surface area using alveoli
footprints alveoli
air sac in lungs deoxygenated blood
oxygenated blood
body cells
air in
air out
Features of Alveoli for efficient Features of Alveoli for efficient gas exchangegas exchange
• large surface area to absorb oxygen.• moist surface to allow oxygen to
dissolve.• thin lining to allow easy diffusion of
gases.• dense network of blood capillaries for
easy gas exchange.
Features of capillaries for Features of capillaries for efficient gas exchangeefficient gas exchange
• dense network to carry CO2 and O2
• Large surface area to transport gases
• Lining is one cell thick so gases can pass through quickly and easily.
Alveoli• Gas exchange across thin epithelium of
millions of _________________– total surface area in humans ~100 m2
Negative pressure breathing• Breathing due to changing pressures in lungs
– air flows from higher pressure to lower pressure– pulling air instead of pushing it
Mechanics of breathing • Air enters nostrils
– filtered by hairs, warmed & humidified– sampled for odors
• Pharynx glottis larynx (vocal cords) trachea (windpipe) bronchi bronchioles air sacs (alveoli)
• Epithelial lining covered by cilia & thin film of mucus– mucus traps dust, pollen,
particulates– beating cilia move mucus upward
to pharynx, where it is swallowed
don’t wantto have to thinkto breathe!
Autonomic breathing control• Medulla sets rhythm & pons moderates it
– coordinate respiratory, cardiovascular systems & metabolic demands
• Nerve sensors in walls of aorta & carotid arteries in neck detect O2 & CO2 in blood
Medulla monitors blood• Monitors CO2 level of blood & cerebrospinal
fluid bathing the brain• CO2 + H2O H2CO3 (carbonic acid)• if pH decreases then
increase depth & rate of breathing & excess CO2 is eliminated in exhaled air
Breathing and Homeostasis• Homeostasis
– keeping the internal environment of the body balanced
• Exercise• need more ATP• bring in more O2 & remove more CO2
• Disease• need to work harder to bring in O2 & remove CO2
O2
ATP
CO2
Diffusion of gases• Concentration gradient & pressure drives
movement of gases into & out of blood at both lungs & body tissue
blood lungs
CO2
O2
CO2
O2
blood body
CO2
O2
CO2
O2
capillaries in lungs capillaries in muscle
Hemoglobin• Why use a carrier molecule?
– O2 not soluble enough in H2O for animal needs• blood alone could not provide enough O2 to animal cells • hemocyanin in insects = copper (bluish/greenish)• hemoglobin in vertebrates = iron (reddish)
• Reversibly binds O2
– loading O2 at lungs or gills & unloading at cells
cooperativity
heme group
Heme Group of Hemoglobin
Cooperativity in Hemoglobin • Binding O2
– binding of O2 to 1st subunit causes shape change to other subunits
• conformational change
– increasing attraction to O2
• Releasing O2
– when 1st subunit releases O2, causes shape change to other subunits
• conformational change
– lowers attraction to O2
O2 dissociation curve for hemoglobin
Bohr Shift drop in pH
lowers affinity of Hb for O2
active tissue (producing CO2) lowers blood pH& induces Hb to release more O2
PO2 (mm Hg)
0102030405060708090
100
0 20 40 60 80 100 120 140
More O2 delivered to tissues
pH 7.60
pH 7.20pH 7.40
% o
xyhe
mog
lobi
n sa
tura
tion
Effect of pH (CO2 concentration)
O2 dissociation curve for hemoglobin
Bohr Shift increase in
temperature lowers affinity of Hb for O2
active muscle produces heat
PO2 (mm Hg)
01020304050
6070
8090
100
0 20 40 60 80 100 120 140
More O2 delivered to tissues
20°C
43°C37°C
% o
xyhe
mog
lobi
n sa
tura
tion
Effect of Temperature
Transporting CO2 in blood
Tissue cells
Plasma
CO2 dissolvesin plasma
CO2 combineswith Hb
CO2 + H2O H2CO3
H+ + HCO3–
HCO3–
H2CO3
CO2
Carbonicanhydrase
Cl–
• Dissolved in blood plasma as “bicarbonate ion”
carbonic acidCO2 + H2O H2CO3
bicarbonateH2CO3 H+
+ HCO3–
carbonic anhydrase
Releasing CO2 from blood at lungs• Lower CO2 pressure
at lungs allows CO2 to diffuse out of blood into lungs
Plasma
Lungs: Alveoli
CO2 dissolvedin plasma
HCO3–Cl–
CO2
H2CO3
H2CO3Hemoglobin + CO2
CO2 + H2O
HCO3 – + H+
Adaptations for pregnancy• Mother & fetus exchange O2
& CO2 across placental tissueWhy wouldmother’s Hb give up its O2 to baby’s Hb?
Fetal hemoglobin (HbF)
What is the adaptive advantage?
2 alpha & 2 gamma units
• HbF has greater attraction to O2 than HbA– low % O2 by time blood reaches placenta– fetal Hb must be able to bind O2 with greater attraction
than maternal Hb
LungsLungs
Can you?• Label the internal structures of the lungs• State the features of the alveoli which
allow efficient gas exchange• Explain the role of diffusion in gas
exchange• State the features of the capillary network
that allow efficient gas exchange
Smoking Cilia: Hair-like extensions lining the trachea
Traps dust and particles Traps microorganisms Mucus secretion
Cigarette smoking prevents cilia from beating in wave-like pattern, moving the microorganisms upward
Effects ---- Bronchitis, Emphysema
Bronchitis
• Inflammation of the lung airways• Mucus accumulation
Emphysema
• Damage to alveoli in lungs, lose elasticity• Reduced surface area for gas exchange
