Download Respiratory System

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The primary function of respiratory system is gas exchange. This the exchange of
oxygen and carbon dioxide between our body and outside air.
But like any other system in the body, it has many collateral functions.
The nose plays a role in speech production and other audible sounds like laughing
and crying.
Smell is another function of the respiratory system. We have specialized cells in our
nose that detect odors.
One function that you might not consider right away is pH regulation. When carbon
dioxide reacts with water in the blood plasma, as we’ll discuss shortly, an acid is
created. If we do not exhale carbon dioxide, this acid would build up in our blood
making it acidic rather than neutral.
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The respiratory system has multiple organs, we will begin with the nose and nasal
cavity.
The nose functions to warm, cleanse, and humidify the air. It also detects odors and
amplifies the voice. Within the nose we can find a number of structures.
1. The nostrils, also nares, are the openings into the nose.
2. Inside the nostrils, the flared area is called vestibule. Within the vestibule is the
vibrissae. They are guard hairs that trap particles and debris. They are called
vibrissae, because they vibrate or move.
3. The internal chamber of the nose is the nasal cavity.
4. The cavity is divided into R&L by the nasal septum. The cavity is formed by the
vomer and ethmoid bones.
5. Also within the nasal cavity is the nasal conchae. The conchae are tissue folds that
provide more surface area for the tissues to contact the air. This allows mucous to
moisten and clean the air. Also, there are a lot of blood vessels in the tissues of the
conchae which warms incoming air. There are three different folds: superior, middle,
and inferior.
6. Each nasal conchae is separated by a nasal meatus. They form a passage way for
air. There are three meastuses: superior, middle, and inferior. They increase the
surface area inside the nose, so the air stays in the longer to humidify and warm
up if necessary.
7. The end of the nasal cavity is referred to as the posterior nasal aperture.
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At the back of the septum and conchae is a small patch of specialized ciliated
pseudostratified columnar epithelium called Olfactory mucosa. It is used for sensory
and detects smell. The cilia here are not mobile, but function to trap odor particles.
The respiratory mucosa covers rest of the cavity and into lungs. It is non-sensory and
made of pseudostratified columnar epithelium and has goblet cells and cilia. It also
cleans the air.
The visible portion of the nosed is formed by the nasal bones and cartilage.
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The pharynx is a muscular funnel shaped structure that cleans air and is a passage
way for both air and sometime food, leading from the nasal and oral cavity. It extends
from the posterior nasal aperture to the larynx and forms the superior portion of the
throat. There are 3 regions: nasopharynx, oropharynx, and laryngopharynx.
The Nasopharynx is in the posterior of the nasal cavity and makes a 90 degree turn
downwards which helps trap particles. This portion of the larynx only passes air. It
also contains the Pharyngeal Tonsil. Tonsils are lymphatic tissue and usually have
antimicrobial function.
The Oropharynx is the next segment. It is inferior to the nasopharynx and connects
to the posterior portion of the oral cavity. Both food and air pass through the
oropharynx. It also contains the palatine and lingual tonsil.
The Layrngopharynx is next and superior to the larynx and esophagus. The
laryngopharynx passes food and air.
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The larynx is also part of the throat and found in the superior portion of the neck. It
is made up of cartilages that functions to keep food out of the trachea and also
produce sound. The larynx is made up of 9 cartilages. The predominant one is called
the thyroid cartilage and is shaped like a shield. What we refer to as the “Adam’s
Apple” is the peak or ridge shape on the anterior surface. Males usually have a large
“Adam’s Apple” than females and this is due to testosterone. The levels of
testosterone in males stimulate the peak of the thyroid cartilage to grow and become
more prominent. The thyroid cartilage forms a ring with the cricoid cartilage below it.
It is commonly referred to as our voice box.
There are few other structures within the larynx.
The glottis is the opening and has vocal chords.
The epiglottis is at the superior opening to larynx. It is a cartilage that closes over the
glottis so that food does not get into trachea when swallowing, but adults can
swallow fine without it. And sometime food does go into the top part of trachea and
then we cough vigorously to get it out. In infants, the larynx and epiglottis are higher
in the throat. The epiglottis helps to direct milk down the esophagus so that they can
nurse and breath at the same time.
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The vocal chords are inferior folds of the wall of the larynx. They produce sound
when air flows over them. The chords contain vocal ligaments and are covered with
stratified squamous epithelium.
Sound production is when the vocal ligaments vibrate from air passing over them.
Muscles control the vocal chords by pulling on the cartilages. Depending on their
direction of rotation, varying frequencies are produced. In males, cords are longer
and thicker so they vibrate more slowly than females, therefore producing lower
frequencies. Loudness is caused by force of air. Speech is formed by the shape of the
oral cavity and placement of the lips and tongue.
Also, associated with the vocal cords are the vestibular folds. The vestibular folds do
not actually contribute to the production of speech, but close off the larynx when we
are swallowing.
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The trachea is a rigid tube supported by C-shaped rings of hyaline cartilage and
commonly referred to as your “wind pipe”. The c-shaped cartilage rings help provide
support to the trachea as an passageway for air to the lungs. The ring shape also
allows for the trachea to be flexible as food passes along the esophagus which runs
posteriorly, or behind, the trachea. The trachea is lined with pseudostratified
columnar epithelium. Recall from the lecture on tissue that pseudostratified
columnar epithelium is associated with cilia to sweep things/particles along and
goblet cells that produce mucous. The mucous traps air particles to further clean the
air. The trachea is a physical connection between the larynx and bronchial tree.
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The next set of structures is referred to as the bronchial tree. It is a network of highly
branched air tubes that starts when the trachea splits into right and left Main
Bronchi. The Main Bronchi go to each lung. Once in the lung, the tube splits again so
that each lung lobe receives an air tube. This branch is referred to as the Lobar
Bronchi. The right lung has three lobar bronchi, one each for the superior, middle,
and inferior lobes. The left lung has two lobar bronchi, one to the superior and one to
the inferior lobe. Once in the lobe, the tube will branch a number of times. These
branches off of the lobar bronchi are called the Segmental Bronchi.
The Main Bronchi continue the C-shaped rings but the Lobar and Segmental Bronchi
transition to cartilage plates that overlap one another.
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Bronchioles are continuations of the airway, but they loose the supportive cartilage.
The bronchioles also transition from skeletal muscle to smooth and pseudostratified
epithelium to ciliated cuboidal. The terminal bronchioles are the last branch of the
air ducts that act solely as an air passageway. They do not have goblet cells, but still
retain the cilia. Each terminal bronchiole branches into two respiratory bronchioles.
This branch is considered the beginning of the respiratory division because the
corresponding alveoli are the site of respiration. In the respiratory bronchi, we start
to loose the smooth muscle and cilia and the cells start to become smaller. The next
structure to follow the respiratory bronchioles lead to the alveolar ducts. The alveolar
ducts are thin walled passages. They are not ciliated and become simple squamous
epithelium and end at the alveolar sacs.
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Our bronchial tree, the c-shaped cartilage rings, and the mucous escalator.
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The lungs are divided into various lobes. The right lung has 3 lobes: the superior,
middle, and inferior lobes. And the left lung has 2 lobes: the superior and inferior
lobes. Since the heart lies towards the left side of the thoracic cavity, the left side has
less space and therefore fewer lobes.
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In this diagram we can see airway as it starts at the larynx, continues down the
trachea and splits into right and left main bronchi. We can also see the different
lobes of each lung and on the right, we can see the lobar bronchi that deliver air into
each individual lobe. Once in the lobe, the airway will then branch into the
segmental bronchi (not labeled above).
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The alveoli is where gas exchange will occur within the lungs. A group of alveoli is
referred to as the alveolar sacs. The alveoli consist of the following cell types.
Type I cells are simple squamous cells, and make up 95% of surface area. They are
needed for rapid gas exchange.
Type II cells are cuboidal cells, account for 5% of the surface area, but are actually
more numerous. Their job is to repair alveolar epithelium when Type I cells are
damaged. They also secrete pulmonary surfactant (lipids and proteins that coat
alveoli). Surfactant prevents the walls of the alveoli from sticking together, so
inflating them the next time will be easier.
In the picture above, you can see the alveoli and alveolar sacs and the capillaries that
surround them. Also notice the bronchiole, terminal bronchiole, and respiratory
bronchiole mentioned in previous slides.
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The lungs also have a protective covering. They have a visceral and parietal pleura,
which should sound somewhat familiar after our heart discussion.
The visceral pleura is a serous membrane that covers the surface of the lung. The
parietal pleura is formed by the visceral pleura folding back onto itself (opposite of
the pericardium) and covers the inner surface of the rib cage and the superior portion
of diaphragm and adheres to the mediastinum (concave portion of lungs). The
Pleural Cavity is the space between the pleurae. It also contains a pleural fluid that
functions to reduce friction, creation of a pressure gradient, and compartmentalizes
the thoracic cavity (this is to prevent infection from spreading from one organ to
another). While the term cavity implies this massive space, it is actually very
minimal.
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The respiratory membrane is the structural barrier between air and blood. It consists
of the alveolar wall, endothelium of the capillary wall, and a SHARED basement
membrane. As previously mentioned, the alveolar wall has two types of cells, Type I
and Type II cells. We can also find Macrophages (also known as dust cells). These are
the most numerous cells in lungs, they wander the internal space of alveoli and
connective tissues, and keeps the alveoli clear and phagocitizes particles like dust and
bacteria. They also help if there is bleeding in the lungs (they phagocitize bacteria
and blood cells). These cells are then pushed up the trachea by the mucous escalator
and swallowed by the esophagus
The second part of the respiratory membrane is the capillary wall. The capillary wall
is made of squamous epithelium. The entire alveoli is surrounded by a network of
capillaries.
The respiratory membrane is where gas exchange in the lungs occurs.
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Respiration refers to three different processes that occur.
First, it is the exchange of gasses that occurs between the atmosphere and alveoli.
This is called Pulmonary ventilation.
Secondly, it is the exchange of gases between the alveoli and blood.
And lastly the gas transport, ie how gasses are transported in blood. it is the exchange
of gases between the blood and the body cells.
Finally, the use of oxygen in cellular metabolism, as in the production of ATP, can also
be referred to as respiration. We are going to focus on the first two types in our
discussion of respiration.
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Pulmonary ventilation is one complete cycle of inhalation and exhalation
Inspiration/inhalation is an active process, meaning muscles are contracting. 2 major
muscle groups are used, the external intercostals to elevate the ribs to open space
and the diaphragm which pulls down to further create space. The basic principle is
that if you increase space you decrease pressure. This is referred to as Boyle’s Law.
Decreased pressure allows for diffusion and flow of gasses down their pressure
gradient (pressure gradients are the same concept as concentration gradients but
based on the amount of pressure a gas is exerting not necessarily how much is there).
Also, as the temperature increases the volume of air will increase (known as Charles
Law). Think of a hot air balloon. In order for the balloon to rise and float, the air is
warmed and expands within the balloon. As for respiration, the warmer the air, the
more it expands and fills up the lungs, this is why we have nose.
Expiration, in contrast, is a passive process, muscles are returning to their original
position. With the decrease in space there is an increase pressure. The air flows
along the pressure gradient and out of the body. The decreasing size of the thoracic
cavity also physically pushes the air out, like when you push on a bag.
There is a difference between quiet and forced respiration. Quiet is when a person is
at rest and forced is a deeper, more rapid breathing from exercise, like from singing,
playing instruments, etc.
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Expiration, in contrast, is a passive process, muscles are returning to their original
position. With the decrease in space there is an increase pressure. The air flows
along the pressure gradient and out of the body. The decreasing size of the thoracic
cavity also physically pushes the air out, like when you push on a bag.
There is a difference between quiet and forced respiration. Quiet is when a person is
at rest and forced is a deeper, more rapid breathing from exercise, like from singing,
playing instruments, etc.
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Respiration is based on the movement of gases down their pressure gradients. Gases
always flows from higher pressure to lower pressure. There are two types of pressure
found in the lungs.
Alveolar (intrapulmonary) Pressure is pressure within alveoli. As space in the cavity
increases, the pressure here drops.
Negative pressure in comparison to atmospheric pressure, or there is less pressure
here than the outside of the body. When we when start our respiration cycle by
expanding the thoracic cavity, the amount of pressure drops about 3 mmHg.
Intrapleural Pressure is the pressure between the two pleurae layers. Pressure drops
during inspiration as the parietal pleura is pulled away and creates space. This is a
negative drop in pressure again. It drops from 4-6 mmHg.
This all leads to the EXCHANGE OF AIR.
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Air is composed of:
78.6% nitrogen
20.9% oxygen
0.04 % carbon dioxide
Few other gases make up a TINY %
The atmospheric pressure, is the total pressure of all the gasses combined. According
to Dalton’s law each gas in a mixture of gases exerts its own pressure as if no other
gases were present
Partial Pressure is the amount of pressure exerted by each individual gas. Partial
pressure in particular is what drives exchange. As I mentioned, it works like a
concentration gradients. Gasses will flow from high pressure to low pressure.
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Let us review the respiratory cycle. First, during inspiration, the thoracic cavity is
expanded by the elevation of the ribs and the flattening of the diaphragm. This
decreases the air pressure inside the lungs, also known as intrapulmonary or alveolar
pressure, in comparison to the air pressure outside of the body. The pressure within
the pleura cavity also decreases, contributing the overall effect. The decrease in
pressure allows air to flow into the lungs. During expiration, the diaphragm rises and
the rib cage settles back into its position. This physically forces the air out, but it also
decreases the space within the thoracic cavity. The decrease in space increases the
pressure causing the air to flow out.
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Recall the respiratory membrane mentioned a few slides back. The alveoli and the
endothelium are both made of simple squamous epithelium which allows for the
oxygen and carbon dioxide to easily travel across the membrane.
The partial pressures of oxygen and carbon dioxide facilitate exchange. Instead of a
concentration gradient, we have a pressure gradient. The gases move from high to
low pressure just as ions diffuse from high to low concentrations. This occurs both in
the lungs and out in the body.
Once we breath in, oxygen has a higher pressure in the alveoli than in the capillaries.
Therefore, it travels out of the lungs and into the blood. The reverse is true of carbon
dioxide. The blood is returning from the body where carbon dioxide was a by product
of metabolism. The blood has a higher level of carbon dioxide than the lungs so the
carbon dioxide travels out of the blood down its pressure gradient to the lung. We
now have oxygen rich blood with low levels of carbon dioxide. This blood then travels
out to the rest of the body were the oxygen will travel out of the blood and into the
tissues where it is needed. It does this through diffusion down the pressure gradients
in the tissues. Carbon dioxide will leave the tissues via diffusion. We know have
oxygen poor blood with high levels of carbon dioxide. The blood returns the heart
and lungs and repeats gas exchange in the lungs.
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Let us return to the diagram of the alveoli. In the alveoli of the lungs the pressure of
oxygen is high, but the capillaries have a low oxygen pressure. Therefor oxygen will
flow from the lungs to the capillaries. It is the reverse for carbon dioxide. The partial
pressure of carbon dioxide is low in the lungs, but high in the capillaries, so it travels
from high to low along its pressure gradient.
As the blood leaves the lungs, it is backed full of fresh oxygen. It then travels to the
rest of body. The cells of the body are low on oxygen, so again, it flows from the high
pressure levels in the blood to the low pressure levels within the cell. Carbon dioxide
will do the opposite. Cells produce great abundance of carbon dioxide as a waste
product. The cell disposes of it by having it diffuse into the blood where there are
low pressure levels of carbon dioxide.
The blood then returns to the heart and lungs and the process starts all over again.
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The video linked in slide demonstrates gas exchange via pressure gradients.
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As was mentioned in our blood unit, Oxygen is primarily transported via hemoglobin,
about 98.5% of it. Recall that oxygen travels in molecule form, O2, and hemoglobin
can carry for 4 molecules, or a total of 8 oxygen atoms. Hemoglobin is called
Oxyhemoglobin is when there is 1 or more O2 molecules bonded to hemoglobin. The
remainder 1.5% of oxygen is transported as a dissolved gas in the blood plasma.
Carbon Dioxide can actually be transported in 3 forms. About 90% of carbon dioxide
travels through blood in the form of bicarbonate and hydrogen ions. When CO2
enters the blood, it reacts with H2O to form carbonic acid which then dissociates
(breaks apart) into bicarbonate and hydrogen ions. This reaction reverses at the
lungs. CO2 is then free to diffuse out of the blood and into the alveoli. 5% of CO2
binds to the amino groups of the plasma proteins and hemoglobin. CO2 doesn’t
compete with O2 for a spot on the hemoglobin. Remember, CO2 binds to the globin
chains. Although CO2 doesn’t compete, carbon monoxide does. Carbon monoxide
binds to the heme group and doesn’t let go. As a person is exposed to more and
more carbon monoxide, their heme groups are taken and oxygen cannot be
transported in the blood and the individual slowly suffocates.
5% of Carbon Dioxide also dissolves into blood as a gas, like it does in soda pop which
gives it the bubbles.
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A few points about how our breathing is controlled. The exact mechanism for setting
the rhythm of respiration remains unknown. Breathing depends on repetitive stimuli
of skeletal muscles from brain. Neurons in the medulla oblongata and pons control
the unconscious breathing. While voluntary control is provided by the motor cortex.
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The automatic, unconscious cycle of breathing is controlled by three pairs of
respiratory centers in the reticular formation of the medulla oblongata and the pons.
The medullary rhythmicity center is found in the medulla oblongata and has two
groups. The ventral respiratory group (VRG) sets the rhythm of breathing, how often
you are inhaling. The dorsal respiratory group (DRG) also works on inhalation, in that
it modifies the rate to adapt to varying conditions.
The pneumotaxic center is found in the pons. It regulates the shift from inspiration to
expiration in quiet breathing.
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