Transcript Chapter 42 pulmonary only 2008

Chapter 42
Circulation and Gas Exchange
Material Exchange
The exchange of materials from inside
to outside is an important function for
organisms.
 It’s easy for unicellular organisms.
 It becomes more difficult for
multicellular organisms.
 Complex organ systems have evolved to
move materials throughout an
organism.

GAS Exchange in Animals

RESPIRATORY SYSTEM
– OXYGEN IS NEEDED FOR AEROBIC
RESPIRATION
– GAS EXCHANGE: UPTAKE OF O2 &
DISCHARGE OF CO2
– RESPIRATORY MEDIUM: SOURCE OF
OXYGEN
 AMOUNT OF DISSOLVED O2 IN WATER LESS
THAN IN THE AIR
RESPIRATORY SURFACE
PART OF ANIMAL WHERE GAS EXCHANGE
OCCURS
 DIFFUSION
 THIN AND LARGE MAXIMIZE DIFFUSION
 CELLS MUST BE BATHED IN WATER TO
MAINTAIN PLASMA MEMBRANE

– SURFACES THUS ARE MOIST
– SIZE INFLUENCED BY SIZE OF ANIMAL
– ENDOTHERM HAS LARGER R.S. THAN ECTOTHERM
OF SAME SIZE
Respiratory System

EXTENSIVE FOLDING OR BRANCHING
– ENLARGENS SURFACE AREA FOR GAS EXCHANGE
In animals that don’t respire through their
skin, there are three common respiratory
surfaces:
 1. Gills
 2. Trachea
 3. Lungs

1. Gills
Are out-foldings of the body
surface suspended in water.
 Creates a large surface area
 They are loaded with
capillaries.

Animals with gills ventilate
them which moves water
with a high concentration of
O2 over them.
 This ventilation consumes a
lot of energy!!

1. Countercurrent Exchange Gills
Blood moves in an opposite direction to the
movement of water past the gills.
 The O2 transfer is highly efficient.
 This is called counter-current exchange, and loads
the blood with O2.
 It keeps a diffusion gradient over the entire length
of the capillary.

PROBLEMS ASSOCIATED WITH
WATER AS A RESPIRATORY MEDIUM

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
O2 CONCENTRATIONS ARE LOW
THE WARMER, THE LES DISSOLVED OXYGEN IT CAN
HOLD
THE SALTIER, THE LES DISSOLVED OXYGEN IT CAN
HOLD
OVERCOME BY VENTILATION
FISH OPENS WATER, WATER PASSES THROUGH
PHARYNX & OVER GILLS
(FISH EXPEND A LOT OF ENERGY VENTILATING
GILLS!!)
Terrestrial breathing: Air has
advantages over water as a
respiratory medium
Higher O2 conc
 Gas exchange faster through air
 Less ventilation of Resp. Surfaces required

AND DISADVANTAGES:
 Resp surfaces continuously desiccate ( dry out)
 Evolution overcomes this problem: surfaces
within animal)

2. Tracheal System


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
Found in insects.
Tubes that branch through the body
Delivers air to all body cells
Air enters tracheae through pores (spiracles) at the
surface, passes through smaller tracheoles; end at
cellular membranes.
Air sacks
3. Lungs

Restricted to one location in body.

Circulatory system connects respiratory
surface with all body cells.

They have a dense net of capillaries
immediately below the epithelium on
the respiratory surface.
Air Pathway

Nares, pharynx, larynx, trachea, bronchi,
bronchioles, alveoli

It is like a tree tipped upside down.

The epithelial lining of the three major
branches of the respiratory system are
covered by cilia and a thin film of mucus.
Air Pathway
The mucus traps particulate matter and
the cilia sweeps it out.
 O2 dissolves in the moist film covering
the epithelium and quickly diffuses into
the web of capillaries surrounding the
alveolus.
 CO2 diffuses in the opposite direction.

Alveoli
Tips of smallest bronchioles
Clusters of dead-ended air sacs
Site of gas exchange
Surrounded by web of capillaries
Diffusion by differences in partial
pressures (air is only part oxygen/CO2)
 High to low

Oxygen Transport


By respiratory pigments in the blood
Hemoglobin –most vertebrates
– Reversible binding
– Iron

Cooperative unloading
– Unloading of O2 from one heme group stimulates
unloading from the other three in a hemoglobin
molecule

Bohr shift is the lowering of hemoglobin’s
affinity for oxygen upon a drop in pH.
– This occurs in active tissues due to the entrance of
Heme
group
CO2
into
Ironthe
atom blood
O2 loaded
in lungs
O2 unloaded
O2
Oxygen Transport

Cooperative unloading
– Unloading of O2 from one heme group
stimulates unloading from the other three in a
hemoglobin molecule

Bohr shift is the lowering of hemoglobin’s
affinity for oxygen upon a drop in pH.
– This occurs in active tissues due to the
entrance of CO2 into the blood
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
O2
O2
Carbon Dioxide Transport

Most transported in the plasma as
bicarbonate ions: HCO3-
CO2 enters RBC’s
 In RBC’s, CO2 converted into bicarbonate.


Then diffuses out of RBC’s into the plasma
1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
Some CO2 is picked up and
transported by hemoglobin.
1
Blood plasma CO
2
within capillary
Capillary
wall
2
CO2
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
HCO3–
7
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
To lungs
CO2 transport
to lungs
HCO3–
8
H2CO3
Hb
9
11 CO2
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
6
HCO3– + H+
5
8
Red
Hemoglobin
H2CO3
blood Carbonic acid Hb
picks up
cell
CO2 and H+
5
+ H+
Bicarbonate
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
3
4
HCO3–
4
7
Interstitial CO
2
fluid
H2O
3
CO2 transport
from tissues
CO2 produced
CO2
CO2 10
CO2 11
Alveolar space in lung
diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).
Elite Animal Athletes

Migratory and diving mammals
– Have evolutionary adaptations that allow
them to perform extraordinary feats
Diving Mammals-seals, dolphins,
whales Google
– Stockpile O2
 Higher myoglobin concentration in their
muscles
 Large spleen-store blood
– and deplete it slowly
 Blood diverted FROM muscles
 Pulse slows upon diving
Diving Mammals-seals, dolphins,
whalesGoogle Image Result for http-bp3_blogger_com-_5v0u3ocGyrYRyLZteHqzUI-AAAAAAAAAxMgkbrVHneoMk-s400Cachalot_jpg.mht
Breathing
The diffusion of a gas depends on
partial pressures.
 When water is exposed to air, the
amount of gas dissolved in the water is
proportional to the partial pressure in
the air, and its solubility in water.
 Gases always diffuse from regions of
high partial pressure to regions of low
partial pressure.

How an Amphibian Breathes

An amphibian such as a frog
– Ventilates its lungs by positive pressure
breathing, which forces air down the trachea
How a Mammal Breathes

Mammals ventilate their lungs
– By negative pressure breathing, which pulls
air into the lungs
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
EXHALATION
Diaphragm relaxes
(moves up)

Lung volume increases
– As the rib muscles and diaphragm contract
Breathing & Amount of air
inhaled
Tidal volume is the volume of air inhaled &
exhaled with each breath.(.5 l)
– Vital capacity: The MAXIMUM -- during
forced breathing is 3-4.8L
 Residual volume is the amount remaining in
the lungs after a forced exhale.

Breathing
Human breathing is mostly under
autonomic control.
 2 regions of the brain control this:

– The pons and the medulla.

The pons controls the medulla which
sets a basic breathing rhythm.
Breathing
Sensors in the aorta and carotid arteries
exert secondary control over breathing.
 These sensors monitor O2, CO2 and blood
pH.
 The pH is largely controlled by CO2 levels.

Breathing
When CO2 levels increase, carbonic acid
levels increase lowering the blood pH.
 When pH drops, the depth and rate of
breathing increases helping to remove
excess CO2.
 O2 levels only have an effect on
breathing rate at high altitudes.

Breathing
In addition to transporting O2,
hemoglobin helps transport CO2 and
assists in buffering.
 Respiring cells produce CO2. Carbonic
anhydrase catalyzes the reaction of CO2
with H2O to form H2CO3.
 H2CO3 dissociates into H+ + HCO3 Most of the H+ attaches to hemoglobin
and other proteins minimizing the
change in blood pH.

Breathing
HCO3- diffuses into the plasma.
 As blood flows through the lungs, the
process is reversed.
 Diffusion of CO2 out of the blood shifts the
chemical equilibrium in favor of the
conversion of HCO3- to CO2.
