respiratory system vol 1

8/8/2019 Respiratory System Vol 1

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Vol. 1


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` Therespiratory system's function is to allow gas

exchange through all parts of the body. Thespace

between the alveoli and the capillaries, the

anatomy orstructure of theexchangesystem, andthe precise physiological uses of theexchanged

gases vary depending on organism. In humans

and othermammals, forexample, the anatomical

features of therespiratory system includeairways, lungs, and therespiratory muscles.


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` Molecules of oxygen and carbon dioxide are

passively exchanged, by diffusion, between the

gaseousexternal environment and the blood. This

exchange process occurs in the alveolarregion ofthe lungs.


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` Ventilation

Ventilation of the lungs is carried out by the muscles ofrespiration.

` Control

Ventilation occurs under the control of the autonomicnervoussystem from parts of the brain stem, themedulla oblongata and the pons. This area of the

brain forms therespiration regulatory center, a seriesof interconnected brain cells within the lowerandmiddle brain stem which coordinaterespiratorymovements.


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` Thesections are the pneumotaxic center, the

apneustic center, and the dorsal and ventral

respiratory groups. Thissection isespecially

sensitive during infancy, and the neurons can bedestroyed if the infant is dropped and/orshaken

violently. Theresult can be death due to "shaken

baby syndrome.


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` Inhalation

` Inhalation is initiated by the diaphragm and supported

by theexternal intercostal muscles. Normal resting

respirations are 10 to 18 breaths perminute, with a

time period of 2 seconds. During vigorous inhalation

(at ratesexceeding 35 breaths perminute), or in

approaching respiratory failure, accessory muscles of

respiration arerecruited forsupport. These consist of

sternocleidomastoid, platysma, and thescalenemuscles of the neck.


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` Undernormal conditions, the diaphragm is the primarydriverof inhalation. When the diaphragm contracts, theribcageexpands and the contents of the abdomen aremoved downward. Thisresults in a largerthoracic volumeand negative (suction) pressure (withrespect to

atmospheric pressure) inside the thorax. As the pressure inthe chest falls, airmoves into the conducting zone. Here,the air is filtered, warmed, and humidified as it flows to thelungs.

` During forced inhalation, as when taking a deep breath, theexternal intercostal muscles and accessory muscles aid in

furtherexpanding the thoracic cavity.


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` Exhalation` Exhalation is generally a passive process;however, active

orforcedexhalation is achieved by the abdominal and theinternal intercostal muscles. During this process air isforced orexhaledout.

` The lungshave a natural elasticity: as they recoil from thestretch of inhalation, air flows back out until the pressuresin the chest and the atmospherereachequilibrium.

` During forced exhalation, as when blowing out a candle,expiratory muscles including the abdominal muscles andinternal intercostal muscles, generate abdominal andthoracic pressure, which forces airout of the lungs.


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` Gas exchange` The majorfunction of therespiratory system is gasexchange between theexternal environment and anorganism's circulatory system. In humans andmammals, thisexchange facilitates oxygenation of theblood with a concomitant removal of carbon dioxideand othergaseous metabolic wastes from thecirculation. As gasexchange occurs, the acid-basebalance of the body is maintained as part ofhomeostasis. If properventilation is not maintained,

two opposing conditions could occur: respiratoryacidosis, a life threatening condition, and respiratoryalkalosis.


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` Upon inhalation, gasexchange occurs at the alveoli, thetiny sacs which are the basic functional component of thelungs. The alveolarwalls areextremely thin (approx. 0.2micrometres). These walls are composed of a single layerofepithelial cells (type I and type II epithelial cells) in close

proximity to the pulmonary capillaries which are composedof a single layerofendothelial cells. The close proximity ofthese two cell types allows permeability to gases and,hence, gasexchange. This whole mechanism of gasexchange is carried by thesimple phenomenon of pressuredifference. When the atmospheric pressure is low outside

the air from lungs flow out. When the airpressure is lowinside, then the vice versa.


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` Vocalization

` The movement of gas through the larynx, pharynx

and mouth allowshumans to speak, orphonate.

Vocalization, orsinging, in birds occurs via thesyrinx, an organ located at the base of the

trachea. The vibration of air flowing across the

larynx (vocal chords), in humans, and thesyrinx,

in birds,results in sound. Because of this, gasmovement isextremely vital forcommunication

purposes.


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` Temperature control

` Panting in dogs and some otheranimals provides

a means of controlling body temperature. This

physiological response is used as a coolingmechanism.


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` Coughing and sneezing

` Irritation of nerves within the nasal passages or

airways, can induce coughing and sneezing.

Theseresponses cause air to beexpelledforcefully from the trachea ornose,respectively. In

this manner, irritants caught in the mucus which

lines therespiratory tract areexpelled ormoved to

the mouth where they can beswallowed.


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` Explain in yourown words the process of

respiration.

` Turn yourpapers in.


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` See you tomorrow!

respiratory system vol 1

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