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The respiratory system is a series of organs responsible for
delivering oxygen to the body and expelling carbon dioxide. Red blood cells
transport air inhaled air from the lungs to the rest of the body, as well as
carry carbon dioxide from the body, back to the lungs.  Inhalation and
exhalation are the processes of breathing (Zimmermann, 2016).  The respiratory is comprised of a upper and
lower tract. The organs in the upper tract include the nose, the pharynx, and
the larynx; which are located outside the chest cavity. The lower tract,
located in the chest cavity, contains the trachea, the lungs, and all segments
of the bronchial tree. Cellular respiration is the process in which molecules
are broken down by cells and used for their energy. Oxygen is used to fuel
these reactions, while carbon dioxide is a waste product generated from the
work. Oxygen breathed in and glucose from food is turned into carbon dioxide,
water and sweat, as well as energy in the form of ATP (‘What Is the Chemical
Equation for Cellular Respiration?’ n.d.). Cellular respiration is a crucial
part to life as without it cells would not have the energy required to sustain
and perform necessary functions.

The nasal cavity conditions air to be received by the
respiratory system. Passing air is warmed or cooled to 1 degree within body
temperature, as well as humidified. A sticky mucous membrane lining the nasal
cavity traps any debris and dust particles. Short thick hairs called vibrissae
aid in the filtration of air in conjunction with microscopic cilia (“Nasal
cavity,” n.d.). Commonly referred to as the throat, the pharynx connects the
nasal and oral cavities to the larynx and esophagus. It allows for the movement
of air from the nose and mouth to the larynx as part of the respiratory journey
(“Pharynx,” n.d.). The epiglottis keeps the passage to the windpipe covered
when swallowing, to prevent food from entering the larynx and trachea. The
larynx connects the pharynx to the trachea in the neck. It is more commonly
known as the voice box as it has the folds necessary for the production of
sound. In the larynx sound is created as air moves through the vocal cords, a
pair of movable folds in the mucous membrane (“Larynx Anatomy and Physiology,”
n.d.).  The trachea is a hollow tube that
connects the larynx (voice box) to the bronchi of the lungs. It is 2.6cm in
diameter and has a thin, membranous wall with C-shaped rings of cartilage
embedded into it (“Trachea Windpipe,” n.d.).

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There are four layers of tissue that make up the trachea;
the mucosa (innermost layer), submucosa, hyaline cartilage and adventitia
(outermost layer). Muscles in the wall of the trachea allow for it to expand or
contract depending on what action is being performed (coughing, breathing,
swallowing). The lungs are one of the biggest and most important organs in the
body. The right and left lungs are not the same size and width, with the right
lung divided into 3 lobes versus 2 on the left lung. These lobes are made of
sponge-like tissue which is enveloped by a membrane called pleura; it separates
the lungs from the chest wall. Half of each lung has its own pleura sack. When
they expand lungs pull air and oxygen into the body.  When they compress, carbon dioxide is
expelled. The diaphragm and rib cage pump the lungs to allow for expansion and
compression (Bradford, 2015). The bronchi are the main passageway into the
lungs.  Air travels from the trachea into
the bronchi (first part of branching system) and then into smaller and smaller
branches. A bronchus (there are 2) is a sub division of the windpipe that
enters the lungs (“Bronchi Function, Parts and Location – A part of Lungs,”
n.d.). The mucous lining of the lumen inside a bronchus protects the lungs
against dust, germs and dirt particles. The bronchioles branch out from the two
bronchi to disperse air throughout the lungs. 
At the very end of each bronchiole is the alveolus sac; where the
transfer of carbon dioxide and oxygen to the blood takes place. The bronchioles
are divides into three sections that progressively gets smaller: Lobular
bronchioles, Terminal bronchioles and Respiratory bronchioles (Eldridge, n.d.).
The bronchioles are lined with smooth muscle tissue that allows for contraction
and dilation to control the flow of air.  There are hundreds of millions of microscopic
alveoli at the end of the respiratory tree. The interactions between the walls
of the alveoli is when the respiratory system comes into direct contact with
the circulatory system to exchange gases (“What Are the Functions of Alveoli in
the Lungs?” n.d.). Blood vessels around the alveolus sac quickly absorb air and
carry it through the blood stream. Oxygen and other gases such as carbon
dioxide are separated in the blood. Each alveolus sac is surrounded by a thin
layer of fluid that allows air to pass through to cells (McDougal, n.d.).

The alveoli physically expand when deep breaths are taken,
and relax when we exhale. Through diffusion, gas exchange occurs at the site of
the alveoli. The alveoli wall is lined with epithelial cells, an extracellular
matrix and small blood vessels known as capillaries. Blood arriving at the
alveoli deposit the waste product of cellular respiration (CO2) and pick up O2
to carry throughout the body.  The
concentration gradient between the alveoli air and the blood in the
capillaries, allows carbon dioxide to diffuse out of the blood while oxygen
diffuses into the blood (“GCSE Bitesize Science – Gaseous exchange in the
lungs,” n.d.). Oxygen makes up 20.95% of the atmosphere that we breathe, with
the other 78.09% being nitrogen gas (“Atmosphere of the Earth,” n.d.). It is
essential for cellular respiration. Oxygen is a covalent, non-polar molecule. O2
only has London dispersion forces as it is not a polar molecule (cannot have
London dispersion forces) and it does not have hydrogen bonding. CO2 only
accounts for 0.04% of Earths atmospheric gases. Carbon dioxide has is a
nonpolar, covalent molecule, therefore the only intermolecular force it has is
London dispersion forces. It is a waste product that is manufactured in the
body and expelled through the process of breathing. The primary muscle used to
pump the lungs for inhalation or exhalation. It is a dome shaped sheet that is
located behind the lower ribs. It is a thin skeletal muscle that contracts
voluntarily. During inhalation, the muscles in the diaphragm contract, and pull
the central tendon inferiorly into the abdominal cavity. This action enlarges
the thorax and allows air to fill the lungs (“Diaphragm Function, Definition
& Definition | Body Maps,” 2015). During exhalation, the diaphragm relaxes
and elevates to a dome-shaped position in the thorax while the rib cage drops
to resting position. Air in the lungs is forced out as the thoracic cavity
decreases in size. Kinetic Molecular Theory (KMT) – The idea that all
substances are composed of entities that are in constant, random motion. There
are five parts to the KMT of gases: 1) Gas particles are in constant random
motion. They have translational, vibrational and rotational kinetic energy. 2)
Gas particles are considered point masses. They have no volume. 3) Gas
particles do no exert attractive or repulsive forces on each other. 4)
Collisions of gas particles with themselves or the container walls are elastic 5)
The average kinetic energy of gap particles is directly related to temperature.
Kinetic molecular theory describes the behavior of ideal gases – a hypothetical
gas made of particles that have mass, but no volume and no attractive forces
between them. These properties are true for all gases as long as they are at
normal temperatures: all gases behave the same, gases are compressible, they
expand as temperature increases so long as pressure is constant, gases have low
viscosity, less dense than solids or liquids, all gases are miscible. The
properties that all gases display is crucial to how we breathe and take in
oxygen. With low density and viscosity, gases are easy to inhale and as a
result our respiratory systems have evolved to adapt to such properties. Since
there is so much space between gas particles they can be easily
compressed.  This is beneficial when
oxygen needs to be compressed and stored in a tank for usage later on. Pressure
– the force that is exerted on an object per unit of surface area. It is
directly related to the force applied and inversely related to area. Pressure
inside close containers is due to the frequency of gas molecule collisions with
the walls. Factors like volume and temperature affect pressure.  During diaphragm contraction, the chest cavity
expands to hold larger volumes of air. This expansion results in a lower
concentration of gas molecules as the volume increases but the number of
molecules remains the same. The pressure during inhalation is also lower since
there are fewer molecular collisions (gas particles colliding with the walls).
The pressure outside of the lungs (external pressure) is constant, meaning that
it is now at a higher pressure than the air within the lungs. Since gas moves
from higher areas of pressure to lower areas of pressure, gaseous molecules rush
into the lungs to equalize the pressure. Kinetic molecular theory is applicable
to all gases including oxygen. It describes the behavior of such gas when
pressure increases or decreases (collisions with same particles or container
walls), they are in constant random motion and display no attractive or
repulsive forces on itself. Boyles law describes the relationship between
inhalation; expansion of thoracic cavity to lower pressure and increase volume,
with the following equation, where P is pressure and V is volume. The process
of exhalation is the opposite of inhalation. 
As the muscles in the diaphragm relax, lung volume decreases and
therefore increases pressure within the lungs (less volume with same quantity
of gas molecules = more collisions with the wall = higher pressure). Since the
external pressure is lower than the pressure in the lungs, air is pulled out of
the lungs in order to travel from high to low pressure. Again, Boyles law is in
effect during the process of exhalation, in which volume decreases causing
pressure to increase as long as temperature remains constant. Respiration is
the cyclic process of creating pressure differences to pull air into or out of
the lungs. Atmospheric pressure (air pressure): the force exerted on a surface
by the air above it a gravity pulls it towards Earth. It decreases as altitude
increases since there are less entities that make up air.  Atmospheric pressure increases when altitude
decreases as it there are more layers of atmospheric to exert a force on it. Air
particles are also more densely packed closer to the Earth. The summit of Mount
Everest is 8850m (29,000 feet) above sea with about 33% of the oxygen content
found at sea level. With about 2/3 less oxygen than what we’re used to, the
body has to breathe more to get the same amount of oxygen into the bloodstream
(“Valerio Massimo Everest Expedition 2009,” n.d.). At high altitudes, the
external air pressure is lower than it is inside the lungs, making air want to
leave the lungs rather than flow into it (air travels from high to low
pressure). The body needs to work harder to pull in thinner air and plump blood
throughout the body. This overworking can lead to high blood pressure, heart
rate, dizziness and altitude sickness. Decompression Sickness (DCS) is caused
by the formation of bubbles of gas (mainly nitrogen) in the blood when the body
undergoes changes in pressure during scuba diving. While diving, body tissues
absorb nitrogen from breathing gas in proportion to the surrounding pressure.
Nitrogen gas in the body is not used by the body and builds up in tissues
overtime. As long as a diver remains at the same pressure, there is no risk of
injury (“The Bends: Symptoms, Treatment & Prevention,” n.d.). However, if a
diver surfaces too fast, excess nitrogen comes out rapidly as gas bubbles in
the blood stream. DCS can occur in mild cases yet it can also cause severe
complications if not treated properly. When high levels of bubbles occur
reactions might take place in the spinal cord or brain. Numbness, paralysis
and disorders of higher cerebral function may result.

Signs of DCS include: blotchy rash paralysis, muscle
weakness, confusion, amnesia, staggering, coughing up bloody, frothy sputum,
collapse or unconsciousness and more (“Decompression Illness: What Is It and What
Is The Treatment?” n.d.). The only treatment for decompression sickness is
recompression; isolation in a compression chamber in which pressure is slowly
brought back to surface level. A few gas laws include Boyles law (P1V1 = P2V2),
Charles law (V1/T1 = V2/T2) and Gay Lussac’s Law (P1/T1 = P2/T2). The combined
gas law, as its name suggests, combines these three gas laws into one equation:
P1V1/T1 = P2V2/T2. When performing calculations to solve for pressure, volume
or temperature it is crucial to take into account proper units. Pressure is
often expressed in KPa (kilo-pascals) while temperature must be expressed in
Kelvin. SATP (Standard ambient temperature and pressure) – a condition in which
pressure is at 101.325KPa and temperature is 298K STP (standard temperature and
pressure) – a condition in which pressure is at 101.325KPa with temperature
being 273.15K. Pulmonologist – someone who specializes in diagnosing and
treating patients with lung problems. This includes conditions such as asthma,
lung cancer, tuberculosis, COPD, sleep disorder, pulmonary vascular disease and
many others. These specialists may work in surgery, medical clinics and
emergency rooms (“Medical professions,” n.d.). 
Respiratory Therapist – These people diagnose breathing problems and
suggest treatments to patients. Respiratory therapists usually work intensive
care units, general hospitals or rehabilitation centers. They perform chest
exams, talk with patients and analyze tissue. They also manage any breathing
devices that the patient might use such as ventilators, in order to ensure that
the equipment it working properly and that the patient is safe (“Medical
professions,” n.d.). 












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