Download BIOL212respCircNotes10MAY2012

BIOL212 – Notes on Respiration and Circulation
(in place of lecture 10 May 2012)
While we have been looking at the digestive, circulatory and respiratory systems “separately” and
still have immune and reproductive systems to add to the story, these systems all work in coordination,
along with all the other organ systems that make up the body of an organism. Not that all the other
systems do not, think of that “shot of adrenaline” (epinephrine) example, but the circulatory and respiratory
systems are very integrated at many points.
Gas – as you have seen, all aerobic organisms require oxygen, which they obtain from the air or
water around them. Air is made up of mostly nitrogen (~78%). Other gases in unpolluted air include:
· 21% oxygen
· 1% other gases:
Carbon dioxide ~ 0.03%
· Argon (0.9%)
· Neon (less than 0.01%)
· Helium (less than 0.01%)
· Krypton (less than 0.01%)
· Xenon (less than 0.01%)
· Radon (less than 0.01%)
A column of air (or water) exerts pressure (due to its weight) on whatever lies below it. So total air
pressure at sea level is higher (the air column is longer, so heavier) than the air pressure at the top of
Mount Rainier (the air column is shorter, so lighter). Each of the gases in the list above contributes to the
total pressure. The proportion each contributes is referred to as its partial pressure. In other words,
partial pressure is the pressure exerted by a particular gas in a mixture of gases.
Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in
partial pressure.
Notice, that gases and fluids behave similarly in these respects:
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•
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Animals can use air or water as a source of O2, or respiratory medium
In a given volume, there is less O2 available in water than in air
Obtaining O2 from water requires greater efficiency than air breathing
INTERCONNECTEDNESS
REDUCE – REUSE – RECYCLE
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BIOL212 – Notes on Respiration and Circulation
(in place of lecture 10 May 2012)
Respiratory surfaces:
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•
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Animals require large (surface area), moist respiratory surfaces for exchange of gases between
their cells and the respiratory medium, either air or water
Gas exchange across respiratory surfaces takes place by diffusion
Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and
lungs
There are four breathing/respiration strategies:
Gills –
Gills are out-foldings of the body that create a large surface area for gas exchange and associated
with aquatic animals, such as sea stars, crayfish, juvenile and some adult amphibians, besides fish.
The source of oxygen, water in this case, must move across the surface where diffusion takes
place. The animal moves through the water or moves the water over the surfaces, gills, and is called
ventilation.
Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to
water passing over the gills; hence the blood is always less saturated with O2 than the water it meets.
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(Look at diagram in text, fig. 42.23, p. 917 [9 Ed.])
Tracheae –
Tracheal systems are found in insects; hence they are the most common method of terrestrial
animal respiration, even if lungs, since they are what we use, are more familiar and consist of tiny
branching tubes that penetrate the body, delivering O2 directly to the body’s cells.
The system consists of tracheae, open to the outside, then to tracheoles with moist epithelium
lining the tips next to the cells where the gas exchange occurs. Because of this close association, this is a
case where the circulatory system is not involved. (E.g. test question: in which animal class is the
circulatory system not usually associated with the respiratory system? Describe and name this respiratory
system.)
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See figure 42.24, p. 918 in text (9 Ed.)
Lungs –
Lungs are found in adult amphibians, reptiles, birds and mammals, in a number of varieties. Most
are extensively divided to provide a large surface area for gas exchange.
Amphibians also exchange gases across their moist skin and other body surfaces, in addition to in
the lungs, so amphibian lungs tend to be small and even missing in some species.
Structures of the mammalian respiratory system:
(Nose & Mouth)
Nasal cavity
Pharynx
Larynx
Trachea
Lungs, right & left
Bronchi (s. bronchus)
Bronchioles
Alveoli (s. alveolus)
pulmonary arteries
pulmonary veins
capillaries
diaphragm
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Figs. 42.25, p. 919, 42.28, p. 921 (9 ed. of text)
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BIOL212 – Notes on Respiration and Circulation
(in place of lecture 10 May 2012)
Cartilage (often in rings) keeps many of these tubes open.
Epithelium lines all these inner surfaces (mucous membranes).
The epithelium is covered by cilia and the mucus produced by the mucous membranes.
Particulate matter (e.g. dust and pollen) gets trapped in the mucus.
The cilia then moves the mucus with the trapped contaminants up the “mucus escalator” to the pharynx
where is swallow or “coughed up & spit out” cleansing the respiratory system.
Muscles also help operate breathing, in particular the diaphragm, expanding & contracting the lungs.
The circulatory system is intimately entwined in the respiratory system via the capillaries that surround the
alveoli. It is here the bulk of gases are exchanged: O2 taken in, CO2 expelled.
Surface tension of liquids tends to cause them to “ball up” minimizing surface area. This would happen in
the alveoli, except for the presence of a surfactant, which reduces surface tension. It is not
present in fetuses until about 32 weeks of gestation. Preterm infants born six weeks or more early
are given artificial surfactants to prevent respiratory distress syndrome. (pg. 919 – 920)
Positive pressure breathing:
Amphibians inflate their lungs with forced airflow by muscular lowering of the oral cavity, closing
the mouth and nostrils and raising the floor of the oral cavity forcing air into the lungs.
Negative pressure breathing:
This is how we breathe: the diaphragm contracts, pulling down the lungs and drawing in air into
the lungs. (Inhalation) Relaxing the diaphragm pushes the lungs up, compressing them and
causing exhalation.
Avian respiration –
Birds have a system of air sacs, in addition to lungs and inhalation and exhalation moves the air
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through their system in a continuous flow. (Fig. 42.27, p. 921, 9 Ed.):
1.) On first inhalation, air moves all the way to the posterior air sacs.
2.) On first exhalation, the air in the posterior air sacs moves forward (anterior) into the lungs.
3.) On second inhalation, the air passes through the lungs into the anterior air sacs.
4.) On second exhalation, the anterior air sacs contract and the air is forced out of the body.
This increases efficiency since, incoming oxygenated air never mixes with deoxygenated air being
expelled and the air passes over the gas exchange surfaces in only one direction. There are no alveoli.
Instead, birds have parabronchi, which are tiny channels (unlike the “dead-end” alveoli.) Note that two
cycles of inhalation and exhalation are required to move air all the way through the system and complete
one cycle.
(Also, most birds have two larynxes; so can make two different notes at the same time, allowing more
complex calls and songs than other animals. And the volume of the respiratory system is relatively large
due to the 8 – 9 air sacs that also act like bellows.)
Tidal volume
Vital capacity
Residual volume
Control of breathing (humans)
- pH is indicator of CO2 conc. in blood (via cerebrospinal fluid)
- Medulla oblongata uses the cerebrospinal fluid pH & nerve signals from muscles around lungs to
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control breathing via neurons in its breathing control center (Fig. 42.29, p. 922, 9 Ed.)
- Note that the circulatory system is intimately involved here!
INTERCONNECTEDNESS
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BIOL212 – Notes on Respiration and Circulation
(in place of lecture 10 May 2012)
Respiratory pigments
(They get the name pigments from their color.)
Respiratory pigments are complexes of proteins associated with metals that circulate in the
hemolymph or blood transporting O2 usually contained in specialized cells.
Hemocyanin –
A blue pigment that has copper as it’s oxygen-binding component and is found in arthropods and
many molluscs.
Hemoglobin –
The red pigment with iron as it’s oxygen-binding component in a cofactor called heme and is
found in all vertebrates and many invertebrates. pH changes the shape of the hemoglobin molecule,
which allows the release of one O2 molecule. (see Bohr shift) This release further changes the molecule’s
shape and makes it easier to release the other 3 O2 molecules it carries.
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In vertebrates, hemoglobin is carried in the erythrocytes (“RBC’s”). See fig. 42.32, p. 925 (9 Ed.)
CO2 decreases pH. Too much and the pH would become dangerously low. Hemoglobin helps
transport CO2 and preventing the blood pH dropping to low.
Myoglobin –
A highly efficient O2-storing protein found in muscles of deep (long) diving mammals. This and
many other adaptations allow whales, Weddell seals, Elephant seals (and other deep & long divers) to
stay underwater between breaths for more than 2 hours and reach depths of 1,500m (almost a mile deep)!
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These are great examples of both natural selection and physiological adjustments. (9 Ed. pg. 925 – 926)
INTERCONNECTEDNESS
REDUCE – REUSE – RECYCLE
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