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Chapter 22 Organismal Respiration – The
Exchange of Gases
1) Intro
a) gas exchange or respiration
i)
interchange of O2 and the waste product CO2
between an animal and its environmen
2) Overview: Gas exchange involves breathing, the transport of
gases, and the servicing of tissue
a) organismal respiration makes it possible for animals to put
the food molecules of digestion to work
b) Figure 22.1
i)
breathing
(1) respiratory surface – thin, moist
(2) diffusion of O2 across cells into blood
(3) diffusion of CO2 across cell into lungs
ii) transport of gases by circulatory system
(1) O2 binds to hemoglobin within RBCs
(2) carries O2 to body tissues
(3) CO2 carried in blood from body tissues to lungs
iii) tissue cells take up O2 from blood and release CO2
(1) O2 is final electron acceptor in ETC
(2) CO2 is breakdown product of oxidized food molecules
3) Respiratory Surface
a) site where O2 diffuses in and CO2 out of animal
b) living cells, usually single layer (simple epithelium)
c) wet (moist) plasma membranes
i)
O2 must dissolve in water before diffusing into cell
d) large surface area to interact with a lot of O2 and get rid of a
lot of CO2
e) Figure 22.2 – four types of respiratory surfaces
i)
yellow is resp. surface
ii) green area has nothing do to with respiration
iii) Earthworm resp. surface
(a)entire outer skin (“skin-breathers”)
(b) skin-breathers must live in damp places or water
(c)most skin-breathers are small and long/flat – why?
(d) most animals don’t have enough skin surface or
surface is covered in dead cells like humans or some
other impermeable material.
iv) aquatic animals – gills
(1) extensions of body surface that interact with water
v)
terrestrial animals
(1) respiratory surfaces folded into body
(2) Insects
(a)tracheae (plural) – extensive branching networks
(3) vertebrates
(a)lungs – extensive branching with many internal sacs
for gas exchange
4) Gills are adapted for gas exchange in aquatic environments
a) gill surface greater than whole body surface
b) tiny blood vessels covered with one or a few layers of cells
i)
blood cells must travel single file through vessels
c) Advantage: always wet (they live in water)
d) Problem: not as much O2 in water as in air (3-5% that of air)
i)
warmer and saltier, the less O2
ii) bottom line: gills must be efficient
e) Figure 22.3
i)
4 gill arches on each side of body
ii) 2 rows of gill filaments from each arch
iii) each filament has platelike structures called lamellae
iv) lamellae are the respiratory surfaces
v)
blue arrows represent flow of water
vi) ventilation – mechanism by which water or air with
O2 are brought to respiratory surface
(1) fish inhales and gill covers (opercula) close
(2) exhales by closing mouth, pumping water over gills,
and opening opercula to let water escape
(3) a lot of energy is spent ventilating gills (dense water,
low O2 content)
vii) countercurrent flow - water flow is opposite blood
flow (22.4)
(1) enhances O2 transfer
(2) countercurrent exchange – transfer of something in
fluid moving in opposite directions
(3) opposite flows maintain a diffusion gradient
(4) allows fish to remove >80% of dissolved O2 in water
5) Tracheal system of insects provides direct exchange between
the air and body cells
a) advantages to breathing air
i)
air has higher O2 content than water
ii) air is lighter and easier to move than water
(1) costs less energy to ventilate lungs than aquatic
b) Main problem
i)
loss of water to the air by evaporation
c) tracheal system of insects (Figure 22.5B)
i)
air tubes that branch throughout body
ii) tracheae – largest tubes
(1) open to outside and reinforced by chitin
iii) tracheoles – narrowest tubes
(1) extend to nearly every cell in body
(2) tips contain fluid
(3) gases dissolve in fluid and diffuse across tips
(4) RESULT: circulatory system NOT involved
iv)
air sacs
(1) enlargements near large organs that require a large O2
supply
(2) muscles contract around air sacs and air is pumped into
and out of body
6) Terrestrial vertebrates have lungs
a) Reptiles, birds, mammals and many amphibians
b) restricted to one part of body
i)
circulatory system must be used to transport gases
c) amphibians
i)
small lungs
ii) some lack altogether
iii) rely on diffuse across body surfaces
(1) supplements gas exchange in lungs
d) most reptiles, birds, mammals rely on lungs
e) turtles are acception
(1) shells prevent breathing movements
(2) gas exchange occurs in mouth and anus
f) size and complexity correlated with metabolic rate
i)
endotherms (warm-blooded) have greater surface
areas than ectotherms (cold-blooded)
g) humans (Figure 22.6A)
i)
surface area = 100m2 (racquet ball court)
ii) lungs in chest cavity
iii) diaphragm – sheet of muscle at bottom of cavity
iv) Respiratory Path
(1) Air enter nostrils
(2) Nasal Cavity
(a)filtered by hairs
(b) warmed
(c)humidified
(d) sampled for odors
(3) Mouth breathing skips nasal processing
(4) pharynx
(5) larynx – voice box
cords – voluntary tense muscles and stretch
cords to make them vibrate = sound
(i) high pitch – high tension
(ii) low pitch – low tension
(6) trachea (windpipe)
(a) shape maintained by rings of cartilage (keeps from
collapsing)
(i) like vacuum cleaner hose rings
(b) goblet cells – secrete mucous
(c)ciliated columnar cells – cilia push mucous up into
pharynx to be swallowed
(i) mucous traps fine particles/ dirt/ mircoorganisms
in air
(7) forks into bronchi (plural)
(8) bronchus branches and branches to bronchioles (fine
tubes)
(a)upside down tree
(9) bronchioles dead end in alveoli (plural) – grapes on tree
(a)each lung contain millions
(b) each alveolus lined by simple cuboidal epithelium =
respiratory surface
(c)O2 dissolves in film of moisture and then diffuses
across epithelium and into capillary. CO2 goes
opposite way. (Fig. 22.6C)
(a)vocal
7) Smoking is one of the deadliest assaults on our respiratory
system
a) Tobacco smoke
i)
4,000 chemicals in a single drag
ii) 43 known carcinogens
iii) smoke destroys cilia and macrophages that fight
microorganisms
(1) more toxins now reach alveoli
(2) coughing then becomes the systems method of
cleansing itself
iv) 430,000 people a year die from smoking
(1) lung cancer (Figure 22.7AB)
v)
increased risk of other cancers
vi) emphysema – alveoli become brittle and many rupture
(1) lungs can’t exchange gas as well
(2) RESULT: breathless and consistent fatigue
(3) more energy diverted for breathing
(4) heart has to work harder to pump more blood
(a)leads to heart disease
vii) every cigarette estimated at 5 minutes of life lost
viii) second hand smokers also at risk
8) Breathing ventilates lungs
a) breathing – alteration of inhaling and exhaling (Fig. 22.8A)
i)
diaphragm contracts, moving down
ii) muscles b/w ribs contract expanding rib cage
iii) negative pressure breathing
(1) increasing volume of chest cavity lowers air pressure in
lungs below atmospheric pressure
(2) higher pressure air rushes in
iv) exhale is opposite of inhale (Fig. 22.8A)
v)
typical breathe is 500ml of air
vi) 4 million to 10 million breathes/year
b) vital capacity – max volume of air one can inhale
i)
3400ml females (college age)
ii) 4800ml males (college age)
c) residual volume
i)
you can’t have zero air in your lungs
ii) air left over after exhaling as much as possible
d) Total air volume = vital + residual volume
e) Birds (Fig. 22.8B)
i)
one-way flow of air
ii) several air sacs in addition to lungs
iii) air sacs don’t do gas exchange
(1) both air sacs fill during inhalation
(2) posterior sac gets fresh air
(3) anterior sac gets air from lungs
(4) during exhale both sacs deflate
(a)posterior sac enters lungs
(b) anterior sac leaves mouth
(5) no alveoli in lungs, but parallel tubes (.5mm across)
(a)blood flow in opposite direction (countercurrent)
(6) one way means no residual volume
(7) birds get 5% more air than humans
9) Breathing is automatically controlled
a) some conscious control
b) involuntary most of the time
i)
automatic control centers in brain
(1) ensures coordination b/w resp and circ. system and
body metabolic needs
(2) breathing control centers
(a)found in pons and medulla oblongata (medulla)
(i) nerves from here trigger contraction of respiratory
muscles
(ii) 10-14 inhalations per minute
(iii)pons smoothes out signal from medulla
(iv) medulla
1. monitors CO2 levels in blood by watching
blood pH
a. CO2 + H20  H2CO3 (carbonic acid)
b. CO2 is high then there is more H2CO3 and
pH goes down
c. medulla speeds up breathing
ii) hyperventilating
(1) excessively taking rapid, deep breathes
(2) hard on your body
(3) purges blood of CO2, pH rises, control center stops
sending signals to breathe – breathing stops until more
CO2 produced and pH decreases
c) O2 used when CO2 is formed (cellular resp)
i)
indirectly measure O2 when you measure CO2
ii) Some large arteries have O2 sensors that signal
medulla
d) Breathing centers are only effective if coordinated with
circulatory system
i)
breathing faster will not get O2 to your cells faster
10)
Blood transports the respiratory gases, with
hemoglobin carrying the oxygen
a) need to understand circulatory system (Fig. 22.10A)
i)
heart
(1) right side handles oxygen poor blood from body and
sends to lungs
(2) left side handles oxygen rich blood from lungs and
sends to body
ii) gases diffuse along pressure gradients
(1) pressure of a gas increases with
(a)more molecules per unit volume
(b) higher temperature
(2) total pressure of a gas equals the sum of the pressure of
each gas in the mixture
(3) gases diffuse down their partial pressure gradients
iii) oxygen is transported bound to hemoglobin in RBCs
(1) very little dissolves directly in blood
(2) 4 hemes, each with an iron that binds one oxygen (total
of 4 per hemoglobin)
(3) carries O2 from alveoli to tissue
iv) hemoglobin also helps (Fig. 22.11AB)
(1) transport CO2
(a)CO2
diffuses out of tissue, into blood plasma and into
RBC
(b) Some binds to hemoglobin
(c)rest forms H2CO3 with the help of enzyme carbonic
anhydrase
(d) very small amount dissolves in blood plasma
(2) buffer blood (prevent drastic pH changes)
(a)picks up H+ when H2CO3 is formed
(b) H2CO3 becomes HCO3- (bicarbonate), which
diffuses out of RBC into blood
(i) HCO3- buffers the blood
(c)At alveoli, HCO3- turns back to CO2 and is removed
The human fetus exchanges gases with the mother’s
bloodstream
a) amniotic fluid – fluid surrounding fetus
b) lungs full of amniotic fluid – not functioning
c) placenta
i)
composite organ – made of tissues from both fetus and
mother
(1) fetal blood vessels from umbilical cords interact with
maternal blood vessels
(2) fetal hemoglobin
(a)special hemoglobin with higher O2 affinity than adult
hemoglobin
d) When baby is born
i)
CO2 stops diffusing into placenta
ii) CO2 levels rise and pH drops in fetal blood
iii) stimulates control center in brain
iv) signals sent to diaphragm and rib cage muscles to start
breathing
11)