Lower Respiratory System & Gaseous Exchange

This assignment delves into the intricacies of the lower respiratory system, highlighting its structural components like trachea, bronchi, and alveoli. It explains how these structures facilitate efficient gaseous exchange through diffusion, driven by concentration gradients. The discussion emphasizes the role of physical principles in this process, illustrating how oxygen moves from alveoli to the bloodstream while carbon dioxide travels in the opposite direction. The assignment concludes by summarizing the lower respiratory system's vital role in ensuring proper gas exchange for survival.

Running head: HUMAN ANATOMY AND PHYSIOLOGY
Human anatomy and physiology
Name of the Student
Name of the University
Author note

1HUMAN ANATOMY AND PHYSIOLOGY
The lower respiratory system or tract comprises of trachea, bronchus and bronchioles,
alveoli that comprises of lungs. This system pulls the air from the upper respiratory system in
absorbing oxygen and releasing the carbon dioxide outside the body in exchange. There are other
supplementary structures like rib or thoracic cage, diaphragm provides support and protect the
above mentioned structures. The upper respiratory tract has the function to take in the air and
pass it to lower respiratory tract towards trachea or wind pipe. There are alveolar and bronchial
structures and the anatomy is such that there is drawing in of air and its processing by the
structures of lower respiratory tract that facilitate gas exchange. Therefore, the following essay
involves the discussion of structure and function of lower respiratory system facilitating gaseous
exchange in reference to physical principles that regulate this process of gas exchange.
Physical principles of gaseous exchange involve diffusion of oxygen and carbon dioxide
through the respiratory membrane, ventilation, pulmonary perfusion and exchange of gases. The
lower respiratory tract facilitates gaseous exchange working in reference to the above physical
principles of gas exchange. Firstly, the trachea covered by cartilaginous rings is an inch in
diameter and tubeless. It extends from bottom of larynx below and behind the sternum where it
starts branching into smaller tubes called bronchi. At the time of inhalation, air is warm and
filtered by upper respiratory tract passing from pharynx to larynx into trachea going down to
bronchi and lungs (Cunningham et al. 2014). The cartilaginous rings around the trachea tube
support it and help to prevent it from over-expansion or collapse when air is sucked too hard.
These rings are C-shaped with gap on posterior side that aid trachea in bending when oesophagus
presses hard against swallowed food. The deoxygenated air from lungs passes back up to trachea
during the process of exhalation.

2HUMAN ANATOMY AND PHYSIOLOGY
The next structure is bronchi being the passageways that bring air inside and out of
lungs. The tubes of the primary bronchus branch off from bottom of trachea subdividing into
further secondary and tertiary bronchi finally into bronchioles. These small airways serve the
purpose of delivering oxygen-rich air to the lungs from trachea. During the process of exhalation,
deoxygenated blood having rich carbon dioxide leaves the lungs through reverse route (Ionescu
2013). Another mechanism takes place in bronchioles where smooth muscle relaxation of
bronchioles causes dilation allowing greater ventilation and bronchoconstriction that causes the
opposite effect in bronchioles.
Figure 1: Trachea (Cunningham et al. 2014)

3HUMAN ANATOMY AND PHYSIOLOGY
Lungs are the main and essential organs for the gaseous exchange in the respiratory
system. The main gaseous exchange takes place in this organ and responsible for the exchange
between oxygen and carbon dioxide. The organ is protected inside the thoracic cage divided into
left and right lung. The left lung comprises of two lobes and has slight small volume as
compared to right lung. There is a curve at the cardiac notch accommodating heart. Right lung
comprises of three lobes being slightly shorter as the diaphragm muscle sits higher below where
the liver is accommodated. Oxygen taken from the air is absorbed into the bloodstream that
passes through the microscopic sacs called alveoli into surrounding capillaries (Albertine 2016).
The deoxygenated air or carbon dioxide waste diffuses the opposite way from capillaries to
alveoli. After this, lungs expel the deoxygenated air during the exhalation process. In this organ,
Figure 2: Bronchus (Ionescu 2013)

4HUMAN ANATOMY AND PHYSIOLOGY
physical principle of gaseous exchange takes place called diffusion. Blood present in the
pulmonary capillaries takes oxygen and takes out carbon dioxide through the process of
diffusion. In this, the exchange of carbon dioxide and oxygen takes place between alveoli in
lungs and blood (Protti et al. 2015). From alveoli oxygen diffuses into the bloodstream and
oxygen from blood enters the alveoli. This is carried out through diffusion requiring a
concentration gradient where partial pressure or concentration of oxygen in alveoli is kept at a
high level or gradient than blood and similarly, partial pressure or concentration of carbon
dioxide in alveoli should be less as compared to in blood. This would facilitate gaseous exchange
through diffusion in alveoli in lungs and bloodstream (Mercer and Crapo 2015).
Figure 3: Lungs (Albertine 2016)

5HUMAN ANATOMY AND PHYSIOLOGY
External respiration also takes place in alveoli, as these microscopic air sacs served by
bronchioles exist inside lungs facilitates gaseous exchange. The terminal ends of respiratory tract
where external respiration takes place called alveoli are filled with air during inhalation from the
bronchioles. The oxygen diffuses through the pulmonary networks in alveoli surrounding it and
pumped into bloodstream. From the deoxygenated blood, carbon dioxide diffuses into alveoli
from capillaries expelled through exhalation (Leong and Leong 2016).
Figure 4: alveolar gaseous exchange (Weibel 2015)

6HUMAN ANATOMY AND PHYSIOLOGY
Diaphragm is the organ that provides muscle for breathing forming the floor for thoracic
cavity. This organ provides the physical process of breathing during inhalation and exhalation.
During the process of inhalation, contraction of diaphragm takes place and movement takes
inferiorly towards abdominal cavity. This mechanism allows thoracic cavity and lungs’ volume
to increase a it takes place during a deep breath (Weibel 2015). During the process of normal
exhalation, relaxation of diaphragm takes place along with external intercostals muscles and
lungs and thoracic cavity decrease takes place as air is expelled.
In all the above organ’s structure and functions, physical properties of gaseous exchange
are involved. The primary function of respiratory system in humans is the exchange of gases;
carbon dioxide and oxygen. Three main principles or processes are involved in the exchange of
gases (oxygen and carbon dioxide) from the external environment to the lungs flowing in the
bloodstream, ventilation, perfusion and diffusion. Ventilation mechanism takes place in which
Figure 5: gaseous exchange in alveoli (Mercer and Crapo 2015)

7HUMAN ANATOMY AND PHYSIOLOGY
the air moves inside and outside of the lungs. Another mechanism, diffusion is the process in
which there is spontaneous movement of gases without any effort or energy between the blood in
capillaries of lungs and gas in alveoli (Morrell 2015). Perfusion is also involved in the gaseous
exchange process where the heart pumps oxygenated blood throughout the lungs.
The partial pressure is important for the exchange of carbon dioxide and oxygen in
external respiration between external environment and cells. There are efficient thin walls in
alveoli and capillaries that are abundant providing total surface area of 75 square metres.
Similarly, in internal respiration, there is intracellular oxygen sue for producing ATP and by the
process of simple diffusion along the partial pressure gradients. Pulmonary perfusion is the
process where actual blood flow takes place through pulmonary circulation. The exchange of
Figure 6: Diffusion (Morrell 2015)

8HUMAN ANATOMY AND PHYSIOLOGY
gases takes place at the air-blood interface facilitated by alveolar-capillary membrane due to
large surface area and thinness. The blood pumped into lungs by right ventricle via pulmonary
artery. This artery is divided into right and left branches supplying blood to both lungs. These
divided parts branch out and supply to each lung with 2% blood pumped by right ventricle that
does not perfuse into the alveolar capillaries. This blood is called shunted blood draining into left
side heart without the participation of alveolar gaseous exchange (Gilbert-Barness, Spicer and
Steffensen 2014).
From the above discussion, it can be concluded that lower respiratory system structure is
made in such a way where it facilitates efficient exchange of gases; carbon dioxide and oxygen.
The gaseous exchange that takes place in lower respiratory tract involves the physical principles
Figure 7: ventilation and perfusion (Gilbert-Barness, Spicer and Steffensen 2014)

9HUMAN ANATOMY AND PHYSIOLOGY
of this regular mechanism. Diffusion takes place in alveoli of lungs due to diffusion towards the
concentration gradient. Trachea warms the air and filters it down from pharynx to larynx into
trachea finally to lungs. Bronchi act as passageways bringing oxygen rich air from trachea to
lungs. Lungs being the essential organs comprises of alveoli are important for the gaseous
exchange where oxygen diffuses into alveoli and surrounding pulmonary capillaries to the
bloodstream. Similarly, carbon dioxide from deoxygenated blood diffuses into alveoli from
capillaries via diffusion and is expelled through exhalation. This is the way lower respiratory
tract facilitates gaseous exchange efficiently aligning with the physical principles of gaseous
exchange.

10HUMAN ANATOMY AND PHYSIOLOGY
References
Albertine, K.H., 2016. Anatomy of the lungs. In Murray and Nadel's Textbook of Respiratory
Medicine (Sixth Edition) (pp. 3-21).
Cunningham, F., Leveno, K., Bloom, S., Spong, C.Y. and Dashe, J., 2014. Williams Obstetrics,
24e. Mcgraw-hill.
Gilbert-Barness, E., Spicer, D.E. and Steffensen, T.S., 2014. Respiratory system. In Handbook of
Pediatric Autopsy Pathology (pp. 329-354). Springer, New York, NY.
Ionescu, C.M., 2013. The human respiratory system. In The Human Respiratory System (pp. 13-
22). Springer London.
Leong, F.J.W.M. and Leong, A.S.Y., 2016. Anatomy and Histology of the Human Lung. A Color
Atlas of Comparative Pathology of Pulmonary Tuberculosis, p.31.
Mercer, R.R. and Crapo, J.D., 2015. Architecture of the gas exchange region of the lungs.
In Comparative Biology of the Normal Lung (Second Edition) (pp. 93-104).
Morrell, M.J., 2015. One hundred years of pulmonary function testing: a perspective on ‘The
diffusion of gases through the lungs of man’by Marie Krogh. The Journal of physiology, 593(2),
pp.351-352.
Protti, A., Andreis, D.T., Milesi, M., Iapichino, G.E., Monti, M., Comini, B., Pugni, P., Melis,
V., Santini, A., Dondossola, D. and Gatti, S., 2015. Lung anatomy, energy load, and ventilator-
induced lung injury. Intensive care medicine experimental, 3(1), p.34.