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Resp/Circ

The Respiratory SystemCOMPOSITION OF AIR• All oxygen in the air is a result of photosynthesis.

o Dry air = 78.09% N2 + 20.95% O2 + 0.93% (inert gases) + 0.03 CO2

• The purpose of gas exchange is to obtain oxygen and get rid of carbon dioxide.o Heterotrophs obtain energy from carbon compounds in a process called

cellular respiration, a process which requires oxygen and produces carbon dioxide.

• Gases diffuse across cell membranes and this requires the exchange surface to be moist.o Diffusion is driven by the difference in oxygen concentration between

the interior of the organism and the external environment.• Gases are distributed in the body by the circulatory system.

Evol. of Resp. Systems

EVOLUTION OF COMPLEX RESPIRATORY SYSTEMS• Oxygen diffuses too slowly to be efficient over more than 0.5 mm, which

limits the size of organisms. Protists are small enough to utilize simple diffusion but as size increases, surface area to volume ratio decreases. For organisms to be larger, a better method of getting oxygen is necessary.

• Most primitive phyla do not possess special respiratory organs but get oxygen by creating a water current to constantly replace water over the diffusion surface.

• More advanced invertebrates and vertebrates possess respiratory organs with an increased surface area over which diffusion occurs. This system provides contact between the external environment and internal circulating fluids (like blood). A larger surface area enables organisms to get more oxygen from the environment.o Gills

§ Disadvantage of external gills− Difficult to constantly circulate water past the diffusion

surface because the highly branched gills resist water movement.

§ Internal gills− Water passes through the mouth into two cavities.− Water then passes out of body after passing over the gills

and through the cavity. This is a one way flow of water over the gills.

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Gills

Lungs

o Lungs§ Gills are not useful for terrestrial animals because they must be kept

wet at all times and the fine filaments of gills would clump together if not surrounded by water.

§ Terrestrial organisms constantly lose water to the atmosphere and gills would be a huge surface area for water loss.− Amphibians

o The low efficiency of the simple lungs is offset by the high concentration of oxygen in the air.

o A large amount of oxygen is obtained by diffusion through the skin.

o Being inactive and ectotherms decreases the O2 demand.− Reptiles

o More active so have a greater need for oxygen.o Cannot obtain oxygen through watertight skin.o Lungs are more developed to provide a larger surface area.

− Mammalso The high activity level and warm body temperature of

mammals require a large amount of oxygen.

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Human lungs

HUMAN LUNGS• Air normally enters through the nostrils. The nostrils are lined with hairs that

filter out dust.• Air enters the trachea, which branches into two bronchi - one for each lung.• Bronchi further branch into smaller and smaller tubes. The narrowest ones

are called bronchioles.• The bronchioles end in clusters of tiny air sacs called alveoli.

o All gas exchange occurs across the walls of alveoli.o Branching and alveoli provide a huge total surface area. In humans, this

is about 60-80 m2.

Gas Exchange

Carbon dioxide

OxygenOxygen

Carbon dioxide

Oxygen

Carbon dioxide

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Breathing

• Air flow in the lung:

§ The diaphragm and intercostal muscles relax.

§ The volume of the thoracic cavity and lungs decreases, increasing the pressure.

§ The increase in pressure forces air out.

§ Rib intercostal muscles contract, expanding ribcage.

§ The diaphragm contracts and lowers increasing the volume of the chest (thoracic) cavity.

§ The increased volume causes a decrease in pressure in the lungs so that air flows in.

Total Lung Capacity

• Air volumes of human lungs:o Tidal volume (TV) - the volume of air inhaled and exhaled in a single

breath.§ About 500 ml of air but can be increased to 3000 ml during

exercise.o During normal breathing, the total lung capacity is not used.

§ Inspiratory reserve volume (IRV) - additional air available breathing in maximally.

§ Expiratory reserve volume (ERV) - additional air expelled by breathing out maximally.

§ Vital capacity (VC) - total useable lung capacity achieved by forceful, maximum inhalation and exhalation.

§ VC = IRV + TV + ERVo Maximum expiration does not remove all air from the lungs; air left in

lungs is the residual volume (RV).o Total lung capacity = VC + RV

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Respiratory Rate

o Respiratory rate - number of breaths per unit time.o Respiratory rate and tidal volume determine the lung ventilation.

§ The total amount of air moved in and out of the lungs each minute depends upon two factors:− The size of each breath (tidal volume).− The number of breaths/minute (respiratory rate).

§ Lung ventilation = tidal volume x respiratory rate§ It is a measure of air entering and leaving the lungs per minute.§ Normally, it is 5 L/min, but it can be as high as 130 L/min.

Control of breathing

CONTROL OF BREATHING• Breathing is an automatic process controlled by a part of the brain called

the breathing control center.o Nerve signals are sent to the diaphragm and intercostal muscles,

triggering inhalation.o When the signals stop, exhalation begins.

• The automatic control can be voluntarily overridden.• When breathing stops, [CO2] increases and is detected by the special cells

in the aorta and carotid artery.o They send impulses to the breathing control center to start

breathing.• In hyperventilation, so much CO2 is removed from the blood that the

breathing control center sends a stop breathing message.

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Breathing Disorders

BREATHING DISORDERS• Allergens trigger the release of histamine which constricts muscles to

narrow the diameter of the bronchioles. This results in lower air flow.• Bronchitis is an inflammation of the airways that causes mucous to

accumulate. The normal cleansing activity of cilia is reduced and not sufficient to remove the mucous. Coughing attempts to clear the mucous. Smoking and other irritants increase mucus secretion and diminish cilia function.

Emphysema

• Emphysema occurs when the alveolar walls become less flexible. Damage to the walls also reduces the amount of surface area available for gas exchange.o Emphysema is associated with environmental conditions, diet, infections,

and genetics. It can result from chronic bronchitis when the airways become clogged with mucous and air becomes trapped within the alveoli.

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Effects of Smoking

Yellow smoking stain in lung

• Effects of cigarette smoke:o Cigarette smoke prevents the cilia from beating and stimulates mucous

secretion.o Coughing expels excess mucous but contributes to bronchitis and

emphysema.o Cigarette smoke contains compounds that are modified in the body to

form carcinogens. Smoking causes 80% of lung cancer deaths.

Healthy human lung Emphysema

Smoker's lung

Cancerous Lung