Evolution and Mechanism of Pulmonary Respiration in Humans

The assignment provides a comprehensive study on pulmonary respiration and cellular metabolism in humans, focusing on how oxygen is transported from the lungs to tissues and utilized for energy production. It covers the mechanisms of aerobic and anaerobic respiration, detailing glycolysis, oxidative decarboxylation, and the Krebs cycle. The role of enzymes like carbonic anhydrase in CO2 transport is highlighted, alongside the physiological adaptations that support efficient gas exchange and metabolic processes. Through a review of existing literature, including Ivanov (2012) on pulmonary respiration evolution, the paper aims to elucidate the integrated nature of respiratory and cellular functions essential for maintaining human life.

Running head: BIOLOGY
Biology
Name of the Student
Name of the University
Author Note

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Table of Contents
Task 3.........................................................................................................................................2
M2..........................................................................................................................................2
Answer a.............................................................................................................................2
Answer b............................................................................................................................2
Task 4.........................................................................................................................................7
M3..........................................................................................................................................7
Answer a.............................................................................................................................7
Answer b............................................................................................................................7
References................................................................................................................................12

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Task 3
M2
Answer a
The main transport system in multi-cellular organisms is circulatory system. It helps
in the transport of the nutrients to the body tissues. Circulatory system also transports waste
products to the cells to the excretory system and aids in the conduction of hormones from one
part of the body to another. The unicellular organism has single cell as opposed to multi-
cellular organism and thus they do not need a complex circulatory system as their circulation
occurs via diffusion (Noordergraaf 2012).
Answer b
Transport of Blood
The circulation of the blood inside the body is maintained by systemic circulation and
pulmonary circulation. Pulmonary circulation supplies blood the lungs and systemic
circulation supplies blood rest of the body other than the pair of lungs. Systemic circulation is
also termed as peripheral circulation or greater circulation. The transport of the blood
towards the lungs for the process of purification is known as pulmonary circulation.
The arteries transport blood under high pressure. The transportation occurs towards
the tissues and thus arteries have strong vascular walls. In the arterial system, the arterioles
are the terminating smaller branchces. They control special conduits via which the blood
transported and released into the capillaries. Capillaries help in the exchange of fluid,
electrolytes, nutrients, hormones and other substances. This exchange occurs between
circulating blood and interstitial fluid. Thus, the walls of capillaries are thin. Veins act as
conduits that assist in transportation of blood from the venules towards the heart. They also

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act as the major reservoir of extra blood. Since the blood pressures inside the veins are low,
the venous walls are thin (Stanfield 2012).
Figure: Distribution and Circulation of Blood in different parts of the respiratory
system
(Source: Hall 2015)
Transport of Lymph
The flow of the lymph takes place via the lymphatic system. It is the exchange of
fluid that occurs between the interstitial space and blood. Thus lymphatic system is also
represented as an accessory route. One of the main function of the lymphatic system is it
carries large particulate matter and proteins away from the tissue spaces. The importance here
lies in the fact that neither of these can be removed via absorption from the capillaries. All the
tissues that are present inside the body have lymph channels. Lymph channels directly drain
out excess fluid into the interstitial spaces. However, there are exceptions like superficial

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portions of the skin, central nervous system, bones and the endomysium of muscles. Special
lymph vessels that originate from the posterior portion of the body drain into thoracic duct.
Thoracic duct in turn empties into the blood venous system. This synopsis occurs at the
junction of the left subclavain vein and left internal jugular vein (van der Putte 2012).
Figure: Lymphatic System
(Source: Hall 2015)
Transport of oxygen and nutrients
Oxygen is diffused from the alveoli and then gets dissolved inside the pulmonary
blood. The O2 dissolved pulmonary body transports oxygen to all parts of body including
peripheral tissues via the help of pulmonary capillaries. The transport of the blood takes place
in combination of haemoglobin. The presence of haemoglobin in the red blood cells (RBC)
accelerates the rate of transport of blood. While the oxygenated blood reaches the tissue, the
oxygen reacts with foodstuffs to release energy and in turn gets converted to carbon dioxide.
The carbon dioxide in turn enters inside the tissue capillaries. It is then transported back to
the lungs where the exchange of carbon dioxide with oxygen takes place (Derby 2012).

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The absorption of the nutrients from the gastrointestinal tract occurs via the intestine.
Absorption of nutrients inside the body fluid does not take place via the stomach because it is
devoid of villus, a type of special absorptive membrane and also has tight junction.
Absorption occurring via small intestine is mostly facilitated by carbohydrate (Derby 2012).
Transport of CO2
When oxygen is utilised by the cells in order to release energy, it is converted into
carbon dioxide. This leads to the increase in the intracellular concentration of PCO2. Due to
the high tissue cell PCO2, CO2 diffuses from the cell and goes inside the tissue capillaries.
From the capillaries, CO2 is transported by the blood towards the lungs. While inside the
lungs, it diffuses through the pulmonary capillaries and enters alveoli. Finally CO2 is expired
into the external atmosphere. The transport of CO2 is exactly opposite to that of oxygen (Hall
2015).
Transport of Nitrogenous Waste

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Figure: The fate of Amino Acid Breakdown and formation of Urea
(Source: Nelson and Cox 2013)
The amino nitrogen that is produced because of the breakdown of amino acid is
excreted in the form of urea (ureotelic organism). Ammonia thus produced as the byproduct
of the amino acid catabolism is deposited into the mitochondria of liver cells and is converted
into urea via the process of urea cycle. The urea thus produced is excreted out through urine.
The basic difference between urea and uric acid is, degradation of purine produces uric acid
and degradation of pyrimidine produces urea (Nelson and Cox 2013).
Transport of Hormone
Water-soluble hormones like catecholamine and peptides are transported from their
site of synthesis to the site of the target tissues via getting dissolved into the plasma. While
reaching their target site, the water soluble hormones diffuse out of the capillaries. This water
soluble hormone then into the interstitial fluid and then finally manages to enter into the

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target cell. The steroid and thyroid hormones circulate in the blood via remaining bonded
with the plasma protein. However, each hormone has its own characteristics that it defined by
its onset, duration of action (Hall 2015).
Evidence
Ford, E.S., Greenlund, K.J. and Hong, Y., 2012. Ideal cardiovascular health and
mortality from all causes and diseases of the circulatory system among adults in the
United States. Circulation, pp.111. DOI: 10.1161/CIRCULATIONAHA.111.049122
This report provides a detailed overview about the importance of proper functioning
of the cardiovascular system and how any kind of malfunctions that is affecting the
equilibrium of the system harms the health of the human being.
Task 4
M3
Answer a
Need of ventilation in humans
Every microorganism has the mechanism to draw oxygen rich air in to their body
from the surroundings and removing carbon dioxide from the body. The main goal of gaseous
exchange is thus the production of energy and the removal of carbon dioxide from the body.
In order to achieve the goals of respiration the respiration is divided in to four important
functions (Lalley 2013).
1. Pulmonary ventilation- refers to the inflow and the outflow of air from the alveoli of the
lungs to the surrounding.

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2. Transport of gases like oxygen and carbon dioxide through the blood and the body fluids
such as lymph.
3. Diffusion of oxygen and carbon dioxide between the lung alveoli and the blood
4. Regulation of the ventilation
Answer b
Mechanism of breathing
The mechanism of breathing occurs due the changes in the pressure within the thorax
and the surrounding. The process of breathing is brought about by the contraction and the
relaxation of the diaphragm and the intercostal muscles (Lalley 2013). During inspiration, the
diaphragm muscles contract and the lower surface of the lungs is pulled downward. At the
time of expiration, as the diaphragm relaxes, the chest wall compresses the lungs and expels
the air outside. At the time of heavy breathing the elastic forces of the lungs alone cannot
force the rapid expulsion of the air, in such cases the accessory muscles pushes the diaphragm
squeezing the lungs and expelling the air. The normal breathing is also brought about by the
changes in the pleural pressure, alveolar pressure and the transpulmonary pressure.
Usually the air is breathed in and out by the nose. The inhaled air moves through the
nasal cavity from where it reaches the larynx. The inhaled air reaches the lower airways
consisting of the trachea and bronchi. The bronchi branches in to bronchioles, finally giving
rise to alveoli.
Gaseous exchange at the alveolar surface
Blood is the fluid connective tissue that is responsible for transporting the oxygen to
the lungs. The deoxygenated blood is brought to the lungs by the help of the pulmonary
artery, which divides into capillaries around the alveoli. The alveolar walls and the walls of

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the capillaries are made up of epithelial cells that facilitate the exchange of gases. Normally
there is more oxygen in the alveolar air compared to that of the capillaries. The pressure
difference between the oxygen and the carbon dioxide in the alveoli and the blood capillaries
facilitates the diffusion of oxygen rich alveolar air in the blood capillaries. The carbon
dioxide rich capillary air is transported to the alveoli. The oxygenated blood is then taken to
the heart from the lungs by the pulmonary vein.
(Source: Hall 2015)
Transport of oxygen to the tissues
The blood protein called the haemoglobin brings about transport of oxygen. This
protein is rich in iron, which is responsible for the red color of the blood. 97% of the oxygen

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is transported to the tissue by the haemoglobin whereas the plasma of the blood transports
only 2%. Oxyhaemoglobin molecule is formed by the combination of haemoglobin with four
oxygen molecules by the formation of a reversible bond with the haemoglobin (West 2012).
At the time when the oxygen rich blood reaches, the tissue surface there is a high
concentration of CO2 in the tissue as most of the oxygen has been used up. Due to this, the
bond between the oxygen molecules and the haemoglobin becomes unstable, the oxygen is
released, and the blood takes up the CO2.
(Source: West 2012)
Transport of carbon dioxide to lungs from tissues
The blood transports the carbon-dioxide, owing to its high solubility. The CO2
produced by the active tissues is transported to the lungs in 3 ways - CO2 is transported
directly by the plasma, or CO2 directly gets combined with the haemoglobin molecules
forming carbamino-haemoglobin (Gilbert-Barness et al.2014). CO2 can remain dissolved in
the blood plasma as the bicarbonate with the help of carbonic anhydrase enzyme.
Cellular respiration
In cellular respiration, all the living organisms take up the oxygen of the blood. This
oxygen molecule is used to oxidize the glucose molecules to produce ATP (Adenosine
Triphospahte). Respiration can be classified as aerobic respiration (takes place in the
presence of oxygen), anaerobic respiration (absence of oxygen). 38 molecules of ATP are
generated by the oxidation of 1 molecule of glucose in aerobic respiration (Gilbert-Barness et

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al.2014). Only two molecules of glucose are produced as the product of anaerobic respiration.
Glycolysis helps to break one molecule of glucose into 2 molecules of pyruvate. Oxidative
decarboxylation of pyruvate generates Acetyl CoA with one molecule of NADH. Finally, the
kreb's cycle and the oxidative phosphorylation occurring in the mitochondria produce 36
molecules of ATP (Wikstrom et al.2015).
Flowchart of cellular respiration
(Source: Hall 2015)
Evidence:
Ivanov, K.P., 2012. Evolution of pulmonary respiration in the higher mammals. Journal
of Evolutionary Biochemistry and Physiology, 48(2), pp.214-218. DOI:
10.1134/S0022093012020119

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This paper describes how pulmonary respiration has evolved in higher multicellular
organisms from unicellular organisms. It describes the rationale why the pulmonary
respiratory process has evolved as per the needs of ventilation among the humans. The paper
provides a detailed mechanism of how pulmonary respiration takes place, its importance and
finally the fate of cellular respiration. Hence, this paper is suitable for my research.

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References
Contributors, W., 2012. Human Physiology. Blacksleet River.
Derby, B., 2012. Printing and prototyping of tissues and scaffolds. Science, 338(6109),
pp.921-926.
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.
Hall, J.E., 2015. Guyton and Hall Textbook of Medical Physiology E-Book. Elsevier Health
Sciences.
Lalley, P.M., 2013. The aging respiratory system—pulmonary structure, function and neural
control. Respiratory physiology & neurobiology, 187(3), pp.199-210.
Nelson, D.L., Coz, M.M., 2013. Lehninger Principles of Biochemistry (Vol. 4). . WH
Freeman & Co
Noordergraaf, A., 2012. Circulatory system dynamics (Vol. 1). Elsevier.
Stanfield, C.L., 2012. Principles of human physiology. Pearson Higher Ed.
van der Putte, S.C., 2012. The development of the lymphatic system in man (Vol. 51).
Springer Science & Business Media.
West, J.B., 2012. Respiratory physiology: the essentials. Lippincott Williams & Wilkins.
Wikström, M., Sharma, V., Kaila, V.R., Hosler, J.P. and Hummer, G., 2015. New
perspectives on proton pumping in cellular respiration. Chem. Rev, 115(5), pp.2196-2221.