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Gas Exchange or Respiration (Chapter 10)
gas exchange - physical methods organisms have for obtaining O2 from
their environment and removing excess CO2
We often use the term respiration to refer to this, but do not
confuse it with cellular respiration which is a series of complex series
of chemical reactions taking place mainly in mitochondria of organisms
to release energy.
Some terminology:
Breathing- physical act of taking air into lungs (inhalation) and
breathing out (exhalation). Not all organisms breathe!
External respiration- exchange of O2 and CO2 between air & blood
Internal respiration- exchange of O2 and CO2 between blood and
surrounding cells
respiratory surface- surface through which gas exchange occurs
These surfaces must have the following characteristics:
•
thin-walled for rapid diffusion into and out of cell
•
moist because O2 and CO2 pass into cells dissolved in a liquid (a
solution) via diffusion
•
in contact with a source of O2 in the environment
•
large enough surface area to aid in efficiency (i.e. size of human
lung)
In protists and small animals like hydra, gas exchange takes place
directly between cell and environment (via cell membrane usually).
•
multicellular organisms, must be in contact with a transport system
that carries dissolved materials to and from cells. Gas exchange
areas in these multi-layered organisms are moist and have a big
surface area for more gas exchange in a given time period(human
lungs or fish gills).
Gas Exchange in Animals
Complex animals require a complex transport system to exchange
gases during cellular respiration. The work of the respiratory system is
called respiration. Blood is fluid that carries O2 for most animals. Red
blood cells have hemoglobin which carries O2 into the cells and CO2 out.
Respiration in Humans
Multicellular animals live on dry land and need a respiratory
system to carry O2 to inner tissues. This is aerobic respiration because
it needs oxygen. The function of the respiratory system is rather simple
in concept: to bring in O2 from the atmosphere and remove CO2 from the
blood.
The trachea leads to the lungs which are the gas exchange organs.
All mammals, birds, reptiles and adult amphibians have lungs.
When you inhale:
- air enters the nasal passages (where it is filtered, warmed and
moistened) and the mouth
- passes into the pharynx or throat; then into the larynx or voice box and
downward into the trachea or windpipe
There is a flap over trachea called epiglottis and it closes over
during swallowing to prevent food from going into your windpipe;
epiglottis is open during breathing.
- air travels through trachea and into two branched tubes called the
bronchi
- bronchi branch into smaller branches in the lungs called bronchioles
- at the end of the bronchioles in the lungs are fine, moist, blood-rich air
sacs called alveoli which increase the surface area for gas exchange with
surrounding capillaries.
O2 is passed to the hemoglobin and CO2 passes out of the
capillaries during exhalation.
Control of Breathing
When you inhale, air is drawn into the lungs. When you exhale,
air is pushed out of your lungs. This is breathing.
During inhalation, the rib cage muscles (intercostals) move up and
out and the muscular diaphragm contracts pulling down on the lungs
and increasing lung capacity. This creates less air pressure inside the
lung than outside the lung; as a result, air comes into the lungs to
balance out the pressure.
During exhalation, the rib cage muscles move down and in and the
diaphragm relaxes (up) while abdominal muscles contract. This
decreases the lung capacity which increases the pressure inside the lungs
to be greater than outside so air rushes out to create an equilibrium.
Nerve impulses at the base of the brain on the medulla oblongata
at the back of the skull control the breathing mechanism. This is called
the breathing control center or the respiratory center. Nerve endings
from the carotid arteries tell the medulla oblongata when breathing
should take place. This is based on the amount of CO2 in the blood.
When inhalation is needed, because there is too much CO2 in the bloodnerve impulses from the medulla are sent to the intercostal muscles and
diaphragm telling them to contract. The more exercise, the more CO2
there is in the blood, so the more the breathing mechanism operates.
Normal breathing rates are 12-25 times/minute.
Cough- body’s method of clearing inner (lower) airways
Sneeze- caused by irritation; body’s method of clearing upper airways
Hiccup- repetitive contraction (spasm) of diaphragm
More on gas exchange:
The concentration of O2 in inhaled air is greater than concentration
of O2 in blood of capillaries surrounding alveoli so O2 will diffuse across
capillary walls into bloodstream. The opposite is the case for CO2.
The air we breathe in contains more O2 than the air we breathe out
because all of our cells use O2 for cellular respiration to get energy!
The air we breathe in contains less CO2 than the air we breathe out
because our cells produce CO2 during cellular respiration!
Lung Capacity
A device called a spirometer is used to measure different volumes
of air inhaled or exhaled from lungs. The results can help to diagnose
respiratory disorders or diseases.
Different volumes measured include:
Tidal volume (TV)- The volume of air inhaled and exhaled in normal
(quiet) breathing movement (about 0.5 L).
Inspiratory reserve volume (IRV)- The additional volume of air that
can be forcefully inhaled following a normal quiet inhalation. (about
2.5 - 3.5 L).
Expiratory reserve volume (ERV)- The additional volume of air that
can be forcefully exhaled after a normal or resting exhalation (about 1.0
L).
Vital capacity (VC)- The total volume of gas that can be moved in or
out of lungs. (about 4.5 L).
VC = TV + IRV + ERV
Residual volume (RV)- The volume of air remaining in the lungs and
respiratory passageways after a full, forceful exhalation (about 1.0 L).
This volume never leaves the respiratory system; if it did, the lungs and
passageways would collapse. The RV is not exchanged with outside air
so it has little value for gas exchange!
Inspiratory capacity (IC)- The amount of air that the lungs will hold
after a normal exhalation (i.e. IRV + TV).
Functional residual capacity (FRC)- The amount of air remaining in
the lungs after a normal quiet exhalation (i.e. ERV + RV).
See Fig. 10.11 on p. 341 and read over lab on p. 340-341.
Diseases of Respiratory System
Lung health is impacted by quality of our external environment and
personal lifestyle choices!
Disorders of respiratory system significantly impair ability to
breathe and exchange O2 for CO2.
Lung cancer- condition in which tumours or masses of tissue form in
the lungs as a result of irregular or uncontrolled cell growth.
Carcinoma- malignant tumour
Death not usually because of difficulty breathing, but b/c cancer
moves or metastasizes to other body parts like the brain.
Carcinogens- cancer causing agents. Smoking has been directly
linked with lung cancer. Also second hand smoke & radon exposure
(cracks in foundation).
CT scan & medical history to diagnose; symptoms may be
immediate or take years to appear. Surgery (maybe), radiation,&/or
chemotherapy are treatments. Radiation & chemo destroy cancerous &
healthy cells.
Pneumonia- condition in which the alveoli inflame & become filled
with fluid which prevents the exchange of gases in the lungs. Cells
starved of O2. Can result in death, especially elderly. Either lobar (a
lobe) or bronchial (patches) pneumonia; caused by bacteria (most
serious), virus, mycoplasma, fungus, or some chemicals.
Asthma- severe allergic reaction which causes wheezing, coughing and
breathing difficulties. During an asthma attack, bronchioles go into
spasms and squeeze the passages. Mild to severe effects. Asthma
attacks but underlying inflammation causing airways to narrow is
constant.
3 changes in lungs during asthma attack:
- airway swells
- bronchial muscles tighten
- increased mucous secreted into airway
Triggers need to be avoided:
colds; chest infections; cold air; exercise/sports; exposure to pollen,
plants, trees, grass, cigarette smoke, dust, pet dander, mould/mildew;
outdoor air pollution (i.e. vehicle emissions); certain foods;
odours/fumes
Medications include anti-inflammatories & bronchodilators (prevent
obstruction)
Bronchitis- condition in which linings of bronchial tubes become
irritated and swollen. Passageways to alveoli may swell and clog with
mucus which often causes severe coughing and makes it hard to breathe.
This condition is more common in smokers than non-smokers.
Emphysema- condition in which lungs lose elasticity and the walls of
the alveoli become damaged which makes the respiratory surface
smaller. This condition causes shortness of breath and smoking greatly
increases your chance of getting emphysema.
Environmental concerns re: respiratory difficulties & clean air:
 scent-free policies for perfumes, deodorants, etc.
 mould
 air quality indicators
Over the counter drugs and their effect on respiratory system:
Nicotine- irritation, inflammation, constriction of blood vessels
Codeine- depresses (slows) respiratory system
Prescription meds- depress (slow) respiratory system
Smoking
Should smoking areas be provided at high schools?
Provincial policies/laws re: smoking restrictions & second hand smoke
(children in car)…what do you think?