1. The main job of the respiratory system is to get oxygen into the body and waste gases out of the body. It is the function of the
respiratorysystem to transport gases to and from the circulatorysystem.
2. Respiration is a vital function of all living organisms.
3. Respiration occurs at two different levels:
a. The level of the cell. In the mitochondria of eukaryotic cells, aerobic respiration requires oxygen to break down glucose,
releases carbon dioxide, and produces large amounts of atp. This level of respiration is called internal respiration or cellular
b. Thelevelof the organism. An organism mustgetoxygen into its cellsandcarbondioxideback out. This level of respiration is
called external respiration because the exchange of gases takes place with the external environment. The exchange of gases,
oxygen (O2) and carbon dioxide (CO2) between air and blood.
4. External respiration involves the respiratorysystem.
5. A respiratory system is a group of organs working together to bring about the exchange of oxygen and carbon dioxide with the
6. A single-celled organism living in water (diffusion) gets its oxygen directlyfrom its surroundings (the water). The oxygen easily
diffuses across the cell membrane. Carbon dioxide also diffuses across the cell membrane; thus single-celled organisms do not
need a respiratorysystem.
7. In multicellularorganisms,eachcell consumesoxygenandproducescarbondioxide. Large multicellular organism must have a
respiratorysystem to ensure the effective exchange of gasses with the atmosphere quicklyand efficientlyto survive.
8. This occurs everytime an organism takes a breath.
9. The atmosphere of planet earth is approximately 78% nitrogen and 21% oxygen. The remaining 1% is made up of carbon
dioxide, water vapor, and other trace gases.
10. Humans are air breathers; our respiratory system has adapted to these concentrations of gases in the atmosphere. If the
amount of oxygen falls much below 15 %, our respiratory system will be unable to provide enough oxygen to support cellular
The passage of air and the respiratorystructures
1. The human respiratory system consist of the nose, nasal cavity, pharynx, larynx, trachea, smaller conducting passageways
(bronchi and bronchioles), and lungs.
2. The respiratorysystem maybe divided into the upper respiratorytract and the lower respiratorytract.
3. The upper respiratory tract consists of the parts outside the thoracic (chest) cavity: the air passages of the nose, nasal cavities,
pharynx (windpipe), larynx (voice box), and upper trachea.
4. Thelower respiratorytract consists of the parts found in the thoracic (chest) cavity: the lower trachea and the lungs themselves.
5. Air enters the respiratorysystem through the mouth or nose.
6. Air entering the nose passes into the nasal cavity. The nasal cavityis richlysupplied with arteries, veins, and capillaries, which
bring nutrients and water to its cells.
7. As airpushes backfrom the nasal cavity, it enters the pharynx. Thepharynx is located in the back of the mouth and serves as a
passageway for both air and food. When food is swallowed, a flap of cartilage, called the epiglottis, presses down and covers the
opening to the air passage (ever have food go "down the wrong way"?).
8. From the pharynx, the air moves through the larynx, the upper end of the trachea, and into the trachea (windpipe), which leads
directlyto the lungs.
9. These passageways provide a direct connection between the outside air and some of the most delicate tissue in the body.
10. These passageways must filter out dust, dirt, smoke, bacteria, and a varietyof other contaminants found in air.
11. The first filtering is done in the nose. The nose will do three things to the air we breathe in:
a. Filterthe air
b. Warm the air
c. Provide moisture(watervapor or humidity)to the air.
12. As air passes through the nasal cavities it is warmed and humidified, so that air that reaches the lungs is warmed and moist.
13. Thenasalairwaysare linedwith ciliaandkeptmoistby mucoussecretions.Thecombination of cilia and mucous helps to filter
out solidparticlesfrom the air anwarm andmoistenthe air, whichprevents damage to the delicate tissues that form the respiratory
14. The moisture in the nose helps to heat and humidify the air, increasing the amount of water vapor the air entering the lungs
15. This helps to keep the air entering the nose from drying out the lungs and other parts of our respiratorysystem.
16. When air entersthe respiratory system throughthe mouth,muchlessfilteringis done. It is generallybetter to take in airthrough
17. At the top of the tracheais the larynx (voice box or adam'sapple). Inside, andstretchedacross the larynx are two highlyelastic
folds of tissue (ligaments) called the vocal cords. Air rushing through the voice box causes the vocal cords to vibrate producing
18. From the larynx, the warmed, filtered, and moistened air passes downward into the thoracic cavitythrough the trachea.
19. Thewallsof the tracheaaremadeupof c-shapedringsof tough flexiblecartilage. These rings of cartilage protect the trachea,
make it flexible, and keep it from collapsing or over expanding.
20. Thecellsthatlinethe tracheaproducemucus;themucushelpstocapture things still in the air (dust and microorganism s), and
is swept out of the air passagewaybytiny cilia into the digestion system.
21. Within the thoracic cavity, the tracheadividesinto two branches,the right and left bronchi. Eachbronchusentersthelung on its
respectiveside. Thelungsarethe site of gas exchangebetweentheatmosphereandtheblood. The right lung has three divisions
or lobes, and is slightly larger than the two lobed left lung. The lungs are inside the thoracic cavity, bounded bythe rib c age and
diaphragm. Lining the entire cavity and encasing the lungs are pleura membranes that secrete a mucus that decreases friction
from the movement of the lungs during breathing.
22. The further branching of the bronchial tubes is often called the bronchial tree.
23. Imagine the trachea as the trunk of an upside down tree with extensive branches that become smaller and smaller; these
smaller branches are the bronchioles.
24. Both bronchi and bronchioles contain smooth muscle tissue in their walls. This muscle tissue controls the size of the air
25. The bronchioles continue to subdivide until they finallyend in clusters of tinyhallow air sacs called alveoli. Groups of alveoli
look like bunches of grapes. All exchange of gases in the lungs occurs in the alveoli.
26. Thealveoliconsistof thin, flexiblemembranesthatcontainanextensive network of capillaries. Themembranes separate a gas
from liquid. The gas is the air we take in through our respiratorysystem, and the liquid is blood.
27. The functional unit of the lungs is the alveoli; it is here that the circulatory and respiratory systems come together, for the
purpose of gas exchange. All exchange of gases in the lungs occurs in the alveoli. Each lung contains nearly300 million alveoli
and has a total surface area about 40 times the surface area of your skin.
Mechanism of breathing
1. Breathing is the entrance and exit of air into and from the lungs.
2. Ventilation is the term for the movement of air to and from the alveoli.
3. Every single time you take a breath, or move air in and out of your lungs, two major actions take place.
a. Inhalation - also called inspiration, air is pulled into the lungs.
b. Exhalation - also called expiration, air is pushed out of the lungs.
4. These two actions deliver oxygen to the alveoli, and remove carbon dioxide.
5. The continuous cycles of inhalation and exhalation are known as breathing. Most of us breathe 10 to 15 times per minute.
6. The lungs are not directlyattached to anymuscle, so theycannot be expanded or contracted.
7. Inhalationandexhalationareactuallyproduced bymovements of the large flat muscle called the diaphragm and the intercostal
(between the ribs) muscles.
8. The diaphragm is located along the bottom of the rib cage and separates the thoracic cavityfrom the abdominal cavity.
9. Before inhalationthediaphragm is curved upward into the chest. During inhalation, the diaphragm contracts and moves down,
causing the volume of the thoracic cavityto increase.
10. When the diaphragm moves down, the volume of the thoracic cavityincreases and the air pressure inside it decreases.
11. The air outside is still at atmospheric pressure, to equalize the pressure inside and out, the air rushes through the trachea into
the lungs - inhaled.
12. When the diaphragm relaxes, it returns to its curved position. This action causes the volume of air in the thoracic cavity to
13. As the volume decreases, the pressure in the thoracic cavityoutside the lungs increases. This increase the air pressure and
causes the lungs to decrease in size.
14. The air inside the lungs is pushed out or exhaled.
15. We generallybreathewith the diaphragm andintercostalmuscles(rest),underextremeconditionswecanuseother muscles in
our thoracic cavityto breathe (activity).
16. Since our breathing is based on atmospheric pressure, the lungs can onlywork properlyif the space around them is sealed.
17. When the diaphragm contracts,theexpandedvolume in the thoracic cavityquicklyfills as air rushes into the lungs. If there is a
small hole in the thoracic cavity, the respiratorysystem will not work.
18. Air will rush into the cavitythrough the hole, upset the pressure relationship, and possiblycause the collapse of a lung.
Gas exchange and transport (figure 46-17)
1. Chemical analysis of the gases that are inhaled and exhaled:
gas inhaled -vs- exhaled
o2 20.71% 14.6%
co2 0.04% 4.0%
h2o 1.25% 5.9%
2. Three important things happen to the air we inhale:
a. Oxygen is removed
b. Carbon dioxide is added
c. Water vapor is added.
3. Thisoccursinthealveoli inthe lungs; ourlungs consistof nearly300millionalveoliwheregasexchangeoccurs(theexchangeof
carbon dioxide and oxygen).
4. Blood flowingfrom the heart enterscapillariessurroundingeachalveolusand spreads around the alveolus. This blood contains
a large amount of co2 and verylittle o2.
5. Theconcentrationofthe gasesin the bloodandthe alveolus arenot equal(concentrationgradient). This causes the diffusion of
co2 from the blood to the alveolus and the diffusion of o2 from the alveolus into the blood. (figure 46-17)
6. The blood leaving the alveolus has nearlytripled the total amount of oxygen it originallycarried.
7. Two special molecules help this process of gas exchange work effectively:
a. Macromolecules - soaplike, consisting of phospholipid and protein, theycoat the inner surface of the alveolus.
b. Hemoglobin - an oxygen carrying molecule that is a component of blood. Hemoglobin is a red colored protein found in red
bloodcells. Eachhemoglobinmoleculehas foursites to whicho2atomscanbind.Thus,onehemoglobinmolecule can carryup to
four molecules of oxygen. Most of the oxygen - 97 percent - moves into the red blood cells, where it combines with hemoglobin.
Regulation of breathing
1. Breathing is such an important function that your nervous system will not let you have complete control of it.
2. Breathing is an involuntaryaction under control of the medulla oblongata in the lower part of the brain. Sensoryneurons in this
region control motor neurons in the spinal cord.
3. Although you can consciously controlled breathing to a limited extent-such as holding your breath-it cannot be consciously
suppressed. The need to supplyoxygen to our cells and remove carbon dioxide is a powerful one.
4. You can onlyhold your breath until you lose consciousness - then the brain takes control and normal breathing resumes.
5. Carbon dioxide and hydrogen ions (blood acidity) are the primarystimuli that causes us to breathe.
6. The nervous system must have a wayto determine whether enough o2 is getting into the blood.
7. Two special sets of sensory neurons constantly check the levels of gases in the blood. These special sensoryreceptors are
sensitive to the levels of gases in the blood, especiallythe level of carbon dioxide.
8. One set is located in the carotid arteries in the neck, which carryblood to the brain.
9. The other set is located near the aorta, the large arterythat carries blood from the heart to the rest of the body.
10. When carbon dioxide dissolves in the blood, it forms an acid known as carbonic acid. Carbonic acid is so unstable that it
immediatelybreaks down into hydrogen ion (h+) and a bicarbonate ions (hco3-).
co2 + h20 h2co3 h2co3 h+ + hco3-
12. Most carbon dioxide travels in the blood as bicarbonate ions. When the blood reaches the lungs, the series of reactions is
reversed. Thebicarbonateions combine with a proton to form carbonic acid, which in turn forms carbon dioxide and water. The
carbon dioxide diffuses out of the capillaries into the alveoli and is exhaled into the atmosphere.
13. The hydrogen ions change the acidity(ph) of the blood, and it is this change in aciditythe special sensorycells respond to.
14. The lungs of an average person have a total air capacity of about 6.0 liters. Only about 0.6 liter is exchange during normal
breathing. This is all the air we need at rest.
15. Duringexercise,deepbreathingforcesout much more of the total lung capacity. As much as 4.5 liters of air can be inhaled or
exhaled with effort.
16. Themaximum amountof airthat canbemoved intoand out of the respiratorysystem is knownas the vital capacityof the lungs.
17. The vital capacityis always 1 to 1.5 liters less than the total capacitybecause the lungs cannot be completelydeflated without
18. Theextracapacityallows us to exercise for long periods of time. Rather than breathing 12 times a minute, as most of us do at
rest, a runner maybreath as often as 50 times a minute.
19. For rapid and deep breathing during vigorous exercise you use the muscles of the rib cage.
The entire process of respiration includes ventilation, external respiration, transport of gases,
internal respiration, and cellular respiration.
The three pressures responsible for pulmonary ventilation are atmospheric pressure,
intraalveolar pressure, and intrapleural pressure.
A spirometer is used to measure respiratory volumes and capacities. These measurement s
provide useful information about the condition of the lungs.
The frontal, maxillary, ethmoidal, and sphenoidal sinuses are air filled cavities that open into the
The pharynx, commonly called the throat, is a passageway that extends from t he base of the
skull to the level of the sixth cervical vertebra.
The larynx, commonly called the voice box, is the passageway for air between the pharynx
above and the trachea below.
The trachea, commonly called the windpipe, is the main airway to the lungs.
The trachea divides into the right and left primary bronchi, which branch into smaller and
smaller passageways until they terminate in tiny air sacs called alveoli.
The two lungs contain all the components of the bronchial tree beyond the primary bronchi.
The right lung is shorter, broader, and it is divided into three lobes.
The left lung is longer, narrower, and it is divided into two lobes.