Transport and Respiration in Biology

This document provides a comprehensive overview of the transport and respiration processes in biology. It covers the structures of the heart, including the chambers, valves, and blood vessels. It explains the different types of circulation and the consequences of blockage in the circulatory system. The document also discusses the cardiac cycle, the role of the pacemaker, and the differences between cardiac output and blood pressure. It is a valuable resource for biology students.

0
Biology
Biology
Transport and Respiration
MAY 28, 2019
Student Details:

1
Biology
Contents
Introduction......................................................................................................................................2
Transport and Respiration................................................................................................................3
Structures of the heart with their function...................................................................................3
Difference between the coronary, pulmonary and systematic circulation...................................4
Comparison of consequences of blockage in the circulatory system..........................................5
Cardiac cycle with electrical stimulation.....................................................................................6
Role of pacemaker.....................................................................................................................10
Difference between cardiac output and blood pressure.............................................................10
Similarities and differences in cardiac output and blood pressure at rest and exercise.............11
Components of Respiratory System..........................................................................................12
Explanation of the structure and function of the components of the respiratory system..........14
Mechanism of breathing............................................................................................................20
Pressure changes in the thorax during breathing at a higher place............................................21
Conclusion.....................................................................................................................................23
References.....................................................................................................................................24

2
Biology
Introduction
The heart is a muscular organ of the body. It consists of muscle fibers, blood vessels named
arteries, veins, and blood capillaries. It works by the help of electric signals generated by sino-
atrial node (SA), atrioventricular node (AV) and Purkinje fibers. It functions for the circulation
of oxygenated blood throughout the parts of the body and deoxygenated blood from the different
parts of the body to the lungs. It is located behind the sternum in the chest above the diaphragm.
The size of the normal heart is equal to fist size and it is of 298 grams or 10.5 ounces in weight.
It has double circulation named pulmonary circulation and systematic circulation. Besides this
one more circulation named coronary circulation is also situated in the heart. Blockage in these
circulatory systems may lead to consequences like heart failure, stroke, arrhythmia, dyspnea,
chest pain and many more diseases (Junior, 2019).
The respiratory system includes many organs of the body like the nasal cavity, larynx, pharynx,
trachea, lungs, and diaphragm. By the help of these organs, inhalation and exhalation process of
breathing takes place (Zimmermann, 2018).

3
Biology
Transport and Respiration
Structures of the heart with their function
The heart is the part of the body made up of muscles, 4 chambers, wall, valves, blood vessels,
two electric signal generating nodes and fibers. Four chambers of heart named as left atrium
(LA) carry oxygenated blood from the lungs, “left ventricle (LV)” carry “oxygenated blood from
LA”, right atria take away “deoxygenated blood” from the body parts and right ventricle (RV)
carry deoxygenated blood from right atria (RA) . The heart has four valves. One is “mitral valve
(bicuspid valve)” which is situated in between LA and LV through which oxygenated blood from
left atria to ventricle get passed. Second is “aortic valve” situated in between “left ventricle and
the aorta” by which “oxygenated blood” gets passed to different parts of the body. The third is
“tricuspid valve” stated in between “right atrium and right ventricle” and pass “deoxygenated
blood” from right atria to the right ventricle. The last one is “pulmonary valve” situated in
between pulmonary artery and right ventricle and pass “deoxygenated blood” to lungs to get
“oxygenated” (Newman & Sullivan, 2018). Heart consists of three kinds of blood vessels which
are named to be “arteries which carry out oxygenated blood except for pulmonary artery”, veins
named superior and inferior vena cava which carry out the deoxygenated blood except for
pulmonary vein, and capillaries helps in exchange of compounds like nutrients, water, waste and
oxygen from near about tissues (Lewis & Writer, 2016).
A wall of muscles named septum isolates LA and LV from RA and RV. Three layers of the
tissue named “epicardium, myocardium, and endocardium” combinedly form the wall of the
heart and covered by pericardium tissue layer. Sino-atrial (SA) lies in the top of RA and known
to be a pacemaker. It generates an electric signal for the contraction of atria and passes down of

4
Biology
blood into the ventricles. AV node situated in the bottom of right atrium passed electric signals
to make the gap in the contraction of atria and ventricles. Then Purkinje fibers in the ventricle
walls and generate signal to heart muscle to produce contraction in the ventricles and causes
“diastole (relaxation of atria)”and ventricles filled with blood and “systole (contraction of atria)”,
ventricles get filled by the blood, contraction of ventricles and pumping of blood outside the
heart) to the heart (Beckerman, 2019).
Difference between the coronary, pulmonary and systematic circulation
Coronary Circulation Pulmonary Circulation Systematic Circulation
“Coronary circulation”
provide blood supply to the
right atrium, right
ventricle, SA node, AV node
and to the selected part of
LA of the heart, blood
supply provided by right
coronary artery (RCA). To
the LA and LV, the blood
supply is provided by left
circumflex artery (LCX)
and left anterior descending
artery (LAD) which are the
parts of left coronary artery
(LCA) (Rehman &
“Pulmonary circulation”
function for the circulation of
deoxygenated blood from the
RA to RV through the
tricuspid valve. Then from
here, deoxygenated blood
pumped into the pulmonary
artery that carries
deoxygenated blood into the
lungs (Boyette & Burns,
2019).
“Systematic circulation”
work to circulate oxygenated
blood from LA of the heart
passed into the left ventricle
through the bicuspid valve.
Then from here, blood
pumped into the aorta to
supply oxygenated blood
throughout the different body
parts (Lakna, 2017).

5
Biology
Rehman, 2019).
It helps in coronary
vasodilation.
Inside the lungs
deoxygenated blood gets
oxygenated by releasing
carbon dioxide in the
pulmonary vesicles and by
addition of oxygen into the
bloodstream. Then this
oxygenated blood carried out
to the LA chamber of the
heart from the lungs by
pulmonary veins.
Deoxygenated blood carried
out from the different body
parts to the right atrium
chamber of the heart through
superior vena cava and
inferior vena cava.
It is composed of RCA and
LCA (Rehman & Rehman,
2019).
This circulatory system
consists of the pulmonary
artery and pulmonary vein
(Boyette & Burns, 2019).
In this circulatory system,
superior and inferior vena
cava, aorta takes place
(Lakna, 2017).
Comparison of consequences of blockage in the circulatory system
Coronary Circulation Pulmonary Circulation Systematic Circulation
Due to the occurrence of
blockage in the coronary
artery, narrowing and
Due to blockage in the
pulmonary artery and vein,
pulmonary hypertension takes
Due to blockage in the aorta,
superior and inferior vena
cava, it causes arrhythmia,

6
Biology
stiffness would occur to the
artery, blood flow would get
reduced. Due to this,
diseases like acute coronary
syndrome, heart attack,
heart failure, dyspnea, and
arrhythmia may take place
(Staff, 2018).
place. This affects the lungs
and right side of the heart.
Due to which narrowing of
artery and vein, chest pain,
heart failure, arrhythmia,
dyspnea, pulmonary emboli
takes place (Staff, 2017).
heart failure, stroke (Staff,
2018) and dyspnea, swelling
in the body (Fletcher &
Sullivan, 2017).
Cardiac cycle with electrical stimulation
The cardiac cycle is a collective process of mechanical and electrical events occurring in
between initiation of one heartbeat to the next heartbeat by the help of ions like calcium and
potassium ions. On cardiac cycle would be completed in 0.8 seconds. The cardiac cycle begins
with the electric potential generation of sinoatrial node to AV node to Purkinje fiber. “Cardiac
cycle” comprises two phases named “diastole and systole”. “Period of relaxation” would be
called “diastole” and “period of contraction” would be stated as “systole”. It consists of six
phases named “atrial systole, isovolumetric contraction, rapid ventricular ejection, isovolumetric
relaxation, and ventricular filling”. On ECG, P wave generated due to atrial systole, the complex
of QRS is represented due to isovolumetric ventricular contraction and T wave represented on
ECG due to rapid ventricular ejection (Ahmad, 2018).

7
Biology
Time duration to complete cardiac cycle
Phases of the Cardiac Cycle

8
Biology
After the contraction of ventricles, isovolumetric relaxation takes place with closed aortic valve
and mitral valve and low blood pressure. In this, diastole gets initiated. Low blood pressure
generates a potential gradient for the opening of the mitral valve and initiates ventricular filling
and high blood pressure generated into ventricles. High blood pressure initiate closing of the
mitral valve with systole and causes heart sound. Firstly atrial systole takes place with electrical
pulse generation by atria. Then ventricular systole takes place with isovolumetric contraction
with increment in ventricles pressure than to atrial pressure. It leads to the closing of AV valves.
It is the time period between “closing of the mitral valve and opening of the aortic valve”. Due to
pressure increment in ventricles leads to ventricle ejection with the opening of the aortic valve.
During aortic valve closing and relaxation period initiation, second heart sound generates
(Pollock & Makaryus, 2019).

9
Biology

10
Biology
Components introducing ECG waveforms, Source: (Rawshani, 2017).
Role of pacemaker
Pacemaker cells collectively form the sinus node or pacemaker who generate an electric impulse.
These electric impulses conveyed to the right atrium by perinodal cells or transitional cells to the
AV node and then passed to another electrical conduction system of the heart (Mulpuru, et al.,
2017). Pacemaker generates an electric impulse to introduce myocardial contraction and help in
blood distribution in the different body parts. Regular electrical impulses generation would be
helpful in the introduction of normal rate and rhythm in the healthy heart (Basit, et al., 2019).
Difference between cardiac output and blood pressure
Cardiac output Blood Pressure
“Cardiac output” is “the amount of blood”
pumped by the heart in one minute for
“completing need for oxygen and nutrients”
Blood pressure is the “measurement of force
or pressure on the blood vessels” during the
pumping of blood out of the heart for the

11
Biology
in the parts of the body. It is calculated by
multiplying heart rate and stroke volume. The
measurement unit of cardiac output is litre per
minute (L/min).
body parts. The upper limit of blood pressure
is known to be systolic blood pressure and the
lower limit is known as diastolic blood
pressure. Measuring unit of blood pressure is
millimeters of mercury (mmHg).
During rest, the cardiac output would be 3-4
L/min.
During rest, blood pressure would be 120/80
mmHg.
During exercise, the cardiac output would
be 35L/min (King & Lowery, 2019).
During exercise, systolic blood pressure can
be increased at the range of 160-200mmHg
(Miller, 2018).
Similarities and differences in cardiac output and blood pressure at rest and exercise
Similarities from the graph would be evaluated that cardiac output and right atrial pressure are
directly proportional to each other. It means that when cardiac pressure gets increased then atrial
pressure would also be increased. At the rest cardiac output and pressure of RA remains normal
and increased at a normal rate. It indicates the “normal cardiac output curve” having a resting
cardiac output of 5 L/min at a right atrial pressure of 10 mmHg. During the exercise, the heart is
not pumping normally and cardiac output and blood pressure would get increased as sudden.
Because during the exercise, energy demand would be increased in the body, due to this cardiac
output would be increased and atrial pressure would be increased to “fulfill oxygen and
nutrients” demand inside the body. The uppermost curve shows the cardiac output in hearts that
are pumping well than normal to fulfill body needs. Stationary phase in both rest and exercise
came on the same right atrial pressure at 11 mmHg (Calvert & Lefer, 2012).

12
Biology
Differences from the graph would evaluate that exponential phase of rest grows slowly while
during exercise, the exponential phase increase rapidly. During rest, the exponential phase of
cardiac output is 5 L/min at right atrial pressure of 10 mmHg. While during exercise, the
exponential phase gets elevation shown at cardiac output 4L/min at right atrial pressure of 3
mmHg (Calvert & Lefer, 2012).
Components of Respiratory System
Organs of the Respiratory System (Kahathuduwa, 2017).
The respiratory system is divided into two part named as upper respiratory tract and lower
respiratory tract (Ball & Padalia, 2019).

13
Biology
The Upper Respiratory Tract (Kahathuduwa, 2017).

14
Biology
Lower Respiratory Tract (System, 2019).
Explanation of the structure and function of the components of the respiratory system
Components Structure Function
Nasal Cavity It is the hollow structure on
the face inside the nose and
skull. It is made up of bone,
cartilage, skin, and muscles.
Hair and mucus lining are
present inside the nasal
It provides moisture, warm
and filtration of air before
entering inside the body. By
the help of hairs and mucus
lining, entry of dust particles,
pollen and other

15
Biology
cavity. contaminants of air would be
prevented.
Pharynx It is a muscular funnel and
initiated from the “exterior
end of the nasal cavity” and
situated up to “superior end
of esophagus and larynx”. It
is also known to be throat. It
is further divided into three
types named as
“nasopharynx, oropharynx,
and laryngopharynx”
It helps in the intake of food,
air, and liquid.
Larynx It is located at the “interior
portion of the neck”, which is
at “inferior of the hyoid bone
and superior from the
trachea”. It is made up of
cartilage structures. It is also
called a voice box.
It produces vocal sound.
Trachea It is also known to be
windpipe. It is a 5-inch long
tube. It is made up of C-
shaped hyaline rings and
It helps to provide an air
pathway through which air
enters inside the body. The
mucus is produced by the

16
Biology
lined by pseudostratified
ciliated columnar epithelium.
The cartilage rings work in
collaboration with trachea
and continue to open all time.
The open end of cartilage
rings situated posteriorly
towards the esophagus.
epithelium lining present
inside the trachea. By the
help of the mucus, dust
particles and other
contaminants get trapped into
the trachea (Barclay &
Curreli, 2018).
Pleural membranes and
pleural cavity
Pleural membranes are made
up of serous membrane and it
has two-layered membrane
structure. The outer layer is
known to be a parietal pleural
membrane which is attached
with the chest wall. The inner
layer is known to be a
visceral pleural membrane
which help is the covering of
lungs by the help of bronchi,
blood vessels, and nerves.
“Pleural cavity” is “the space
between the parietal pleural
membrane and visceral
It helps in the functioning of
the lungs without getting
damage due to bones and
surface gliding in between the
chest walls and the lungs. It
helps in the movements of
chest walls during the
breathing process of the lungs
(Charalampidis, et al., 2015).

17
Biology
pleural membrane” of the
lungs. It contains a small
amount of pleural fluid.
Lungs
“Lungs” are “the pair of
spongy and large organs”. It
is located at the thorax lateral
side from the heart and the
superior of the diaphragm. By
the help of the pleural
membrane, both lungs are
covered. The left lung is
smaller in size from the right
lung. Therefore “left lung” is
made up of “two lobes” and
“right lung” is made up of
“three lobes”.
The pleural membrane helps
in the expanding of the lung
by providing space and also
help in providing negative
pressure inside the lung as a
comparison of exterior
pressure of the body. Due to
negative pressure, the air gets
filled passively inside the
lungs during relaxation of the
lungs.
Bronchi Trachea gets splits into left
and right branches at the
inferior end of trachea and
known to be bronchi. These
bronchi get to enter into the
lungs and further split into
the smaller secondary bronchi
It carries out air from the
trachea to the lungs. Smooth
muscles help in the dilation
of the walls during the
exercise period for the
regulation of more amount of
air inside and outside of the

18
Biology
in the lungs with two in the
left lung and three in the right
lung. These secondary
bronchi split into tertiary
bronchi inside each lobe of
the lungs. “Primary bronchi”
made up of “C-shaped
cartilage rings” and provide
cross-sectional shape to the
bronchi. Then “secondary and
tertiary bronchi” made up of
“smooth muscles, and elastin
protein in the walls”.
lungs. During rets, smooth
muscles fibers get contracted
to prevent hyperventilation.
Mucus and cilia would be
used inside the bronchi to
trap dust and contaminants
and keep away these dust and
contaminants from the lungs.
Bronchioles
“Tertiary bronchi” get splits
further into many
bronchioles. These
bronchioles spread into the
entire lungs and further gets
split into smaller size
branches of diameter less
than a millimeter. It is made
up of smooth muscles and
elastin protein.
It helps in the “conduction of
air to the alveoli of the
lungs”. It helps in passing
more air inside and outside
the lungs during the exercise.
It helps in the trapping of dust
and other contaminants and
keeps away from the lungs by
the help of mucus and
bronchioles.

19
Biology
Alveoli Lungs contain many cup-
shaped structures covered by
capillaries. These structures
are known to be alveoli.
These alveoli are “present at
the end of the terminal
bronchioles”. These are
covered by “thin simple
squamous epithelium”.
It helps in the exchange of
gases with the blood present
inside the capillaries over
alveoli.
Intercostal muscles These muscles present in
between ribs. These are
divided into two types. One is
internal intercostal muscles
and the other one is external
intercostal muscles. It works
in the assistance of
diaphragm.
Internal intercostal muscles
provide depression on the ribs
due to which the thoracic
cavity gets compressed. This
compression of the thoracic
cavity helps in the exhalation
of air from the lungs. The
“external intercostal muscles”
provide elevation to the
thoracic cavity and helps in
the “expanding the volume of
the thoracic cavity”. This
expanding helps in the
inhalation of the air to the

20
Biology
lungs.
Diaphragm In the human body, the
diaphragm is the principal
muscle of the respiration. It is
made up of a thin sheet of
skeletal muscle. It is present
on the floor of the thorax.
It helps in the inhalation and
exhalation of the air inside
and outside the lungs. During
the contraction of the
diaphragm, it gets moves
some of the inches inferiorly
inside the abdominal cavity
and provide space inside the
thoracic cavity and helps in
the inhalation of air inside the
lungs. During the relaxation
of the diaphragm, it moves
outside the abdominal cavity
and allows air to get out of
the lungs during the
exhalation (Barclay &
Curreli, 2018).
Mechanism of breathing
Air gets inhaled by “the nose and mouth” of Erica. Then the air goes down through the throat of
Erica to “the trachea” and passed into “the bronchial tubes” to bronchioles and then to “alveoli”.
From the alveoli, “oxygen from the inhaled air” gets enter to the alveoli walls and then enter into

21
Biology
“the blood capillaries” around “the alveoli”. After absorption of oxygen, blood passes out “to the
lungs and send to the heart” of Erica. Then the blood “pumps” out of the heart and then
“oxygenated blood” provided to “the cells, tissues, and organs of the body” of Erica. Then
“oxygen” get used by the cells and “carbon dioxide” would be “released by the cells” and
“absorbed into the blood” of Erica. Then “carbon dioxide” send back to the lungs of Erica
through the blood and then carbon dioxide gets exhaled outside the body (Blahd, 2017). During
the ventilation process during the normal process, “negative pressure” would be “generated
inside the lungs”. In the pleural cavity “negative pressure” gets established. Due to this, negative
pressure gets generated into the trachea and the air gets inhaled inside the lungs. During the
normal condition pressure inside the body of Erica would be 100ml/cmH2O (Carpio & Mora,
2019). This breathing mechanism follows the Law of Boyle where pressure and volume have an
inverse relationship. Due to this, during the inhalation of oxygen volume of lungs gets increased
and pressure gets decreased in the lungs as comparison of outside. Because of this air gets
inhaled inside the trachea. During exhalation, the volume of lungs gets decreased due to elastic
recoiling and air get exhaled due to pressure increment as a comparison of the outside
atmosphere (Hallett & Ashurst, 2019).
Pressure changes in the thorax during breathing at a higher place
At the high place amount of oxygen get decreased and pressure would be increased at a higher
place. When Erica goes to the higher place then she needs to work harder for climbing. Due to
this, energy intake would be increased in the body. Then cardiac output and atrial pressure would
be increased to provide a “sufficient amount of oxygen and nutrients to the cells” of the Erica.
Due to a decrement in partial oxygen pressure, sympathetic activation gets occurred in the body
by the “stimulation of peripheral chemoreceptors in the carotid bodies”. Due to this activation

22
Biology
ventilation process gets increased. This process takes place to recover the amount of oxygen by
recovering partial oxygen pressure in the hemoglobin. Vasoconstriction would be placed by
sympathetic activation in the pulmonary circulation. Due to vasoconstriction, pulmonary artery
pressure would be increased. Due to these process inside the body, Erica finds difficulty in
breathing (Parati, et al., 2018).

23
Biology
Conclusion
Heart and lung are a very important part of the body. They help with transport and respiration.
They help in blood regulation and breathing which is very helpful for the lives. They would help
in the regulation of oxygenated blood to the different body parts and deoxygenated blood from
the different body parts to the lungs by the help of heart. Lungs would also take part in the
breathing process. Cardiac output and blood pressure play a major role in the functioning of the
parts of the body. If any disorder like acute coronary syndrome, cardiac failure caused in heart
and lung cancer caused in the lung and their parts, can cause improper functioning in the body.
Sometimes, this improper functioning in the body may lead to the death of a person. Cardiac
output and blood pressure get elevated during any changes such as the menstrual cycle,
pregnancy in the body of a person. During these changes, cardiac output and blood pressure
would get fluctuated.

24
Biology
References
Ahmad, M., 2018. Cardiac Cycle, Phases Of Cardiac Cycle, Cardiac Cycle & ECG. [Online]
Available at: https://www.medicosite.com/cardiac-cycle/
Ball, M. & Padalia, D., 2019. Anatomy, Airway. s.l.: StatPearls Publishing LLC.
Barclay, T. & Curreli, S., 2018. Respiratory System. [Online]
Available at: https://www.innerbody.com/anatomy/respiratory
Basit, H., Kashou, A. H., Kashou, H. E. & Chhabra, L., 2019. Physiology, Sinoatrial Node (SA
Node). s.l.: StatPearls Publishing LLC.
Beckerman, J., 2019. Anatomy and Circulation of the Heart. [Online]
Available at: https://www.webmd.com/heart-disease/high-cholesterol-healthy-heart#1
Blahd, W., 2017. How the Lungs and Respiratory System Work. [Online]
Available at: https://www.webmd.com/lung/how-we-breathe
Boyette, L. C. & Burns, B., 2019. Physiology, Pulmonary Circulation. s.l.:StatPearls.
Calvert, J. W. & Lefer, D. J., 2012. Overview of Cardiac Muscle Physiology. Muscle, Volume 1,
pp. 57-66.
Carpio, A. M. L. & Mora, J. I., 2019. Ventilator Management. s.l.: StatPearls Publishing LLC.
Charalampidis, C. et al., 2015. Pleura space anatomy. PMC, February, 7(1), pp. S27-S32.
Fletcher, J. & Sullivan, D., 2017. What's to know about superior vena cava syndrome?. [Online]
Available at: https://www.medicalnewstoday.com/articles/318668.php
Hallett, S. & Ashurst, J. V., 2019. Physiology, Tidal Volume. s.l. StatPearls Publishing LLC...

25
Biology
Junior, W. S. C., 2019. Medical Definition of Heart. [Online]
Available at: https://www.medicinenet.com/heart_health_pictures_slideshow/article.htm
Kahathuduwa, C., 2017. Respiratory Physiology - Introduction. [Online]
Available at: https://owlcation.com/stem/Respiratory-Physiology
King, J. & Lowery, D. R., 2019. Physiology, Cardiac Output. s.l.: StatPearls Publishing LLC.
Lakna, 2017. Difference Between Pulmonary and Systemic Circulation. [Online]
Available at: https://pediaa.com/difference-between-pulmonary-and-systemic-circulation/
Lewis, T. & Writer, S., 2016. Human Heart: Anatomy, Function & Facts. [Online]
Available at: https://www.livescience.com/34655-human-heart.html
Miller, J., 2018. About Systolic & Diastolic Blood Pressure During Exercise. [Online]
Available at: https://www.livestrong.com/article/183287-about-systolic-diastolic-blood-pressure-
during-exercise/
Mulpuru, S. K. et al., 2017. Cardiac Pacemakers: Function, Troubleshooting, and Management:
Part 1 of a 2-Part Series. Journal of the American College of Cardiology, 17 January, 69(2), pp.
189-210.
Newman, T. & Sullivan, D., 2018. The heart: All you need to know. [Online]
Available at: https://www.medicalnewstoday.com/articles/320565.php
Parati, G. et al., 2018. Clinical recommendations for high altitude exposure of individuals with
pre-existing cardiovascular conditions: A joint statement by the European Society of Cardiology,
the Council on Hypertension of the European Society of Cardiology, the European Societ.
European Heart Journal, 01 May, 39(17), pp. 1546-1554.

26
Biology
Pollock, J. D. & Makaryus, A. N., 2019. Physiology, Cardiac Cycle. s.l.:StatPerals.
Rawshani, A., 2017. Principles of cardiac electrophysiology and ECG interpretation. [Online]
Available at: https://ecgwaves.com/introduction-electrocardiography-ecg-book/
Rehman, S. & Rehman, A., 2019. Physiology, Coronary Circulation. s.l.:StatPearls.
Staff, M. C., 2017. Pulmonary hypertension. [Online]
Available at: https://www.mayoclinic.org/diseases-conditions/pulmonary-hypertension/
symptoms-causes/syc-20350697
Staff, M. C., 2018. Aortic valve stenosis. [Online]
Available at: https://www.mayoclinic.org/diseases-conditions/aortic-stenosis/symptoms-causes/
syc-20353139
Staff, M. C., 2018. Coronary artery disease. [Online]
Available at: https://www.mayoclinic.org/diseases-conditions/coronary-artery-disease/
symptoms-causes/syc-20350613
System, T. R., 2019. Lower Respiratory Tract. [Online]
Available at: https://www.therespiratorysystem.com/category/lower-respiratory-tract/
Zimmermann, K. A., 2018. Respiratory System: Facts, Function, and Diseases. [Online]
Available at: https://www.livescience.com/22616-respiratory-system.html