The Mechanism of Gaseous Exchange in the Alveoli

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The human respiratory system refers to a series of organs that are responsible for oxygen intake and carbon dioxide expelling. The respiratory system is particularly adaptive to its function of facilitating gaseous exchange. This system is responsible for all body functions because of the one element, ‘oxygen,’ whose deficiency can cause a complete dysfunction of all body organs and tissues. The gases that bear different utility in the body are exchanged across a semi-permeable membrane. Carbon dioxide is expelled as a byproduct of substrates that are broken down to release energy, and even though it may not be invaluable for humans, it is the basis for plant life.

The anatomy of the respiratory system is not as convoluted as when compared with other body systems like the nervous system.  The system is made of three major parts; the airway, the lungs, and the respiration muscles (Marieb, and Hoehn, 2007). The air is carried to and from lungs and the body exterior of the body through the airway which is made up of the bronchioles, the bronchi, trachea, larynx, pharynx, mouth, and nose (Netter, 2017). The oxygen is passed into the body and carbon dioxide out of the body through the lungs; in this regard, the lungs act as the functional units of the respiratory system (Netter, 2017). Finally, the pumping as well as pushing of air into and out of the lungs during the process of breathing is facilitated by the respiration muscles; they include the intercostal and the diaphragm muscles (Netter, 2017). All these subparts and respiratory muscles work in unison to ensure the completion of the breathing process. The work of the trachea/ the windpipe is to allow passage of air that is obtained by the nose from the external environment (Netter, 2017). The bronchi, in the singular bronchus, are passages of air that branch directly from the trachea, leading to finer tubes called the bronchioles (Netter, 2017). The alveoli or air sacs permit the diffusion of gases across a semi-permeable membrane in and out of the bloodstream.

3.1 The Process of Ventilation and The Tissues Involved

Inspiration process. Inhalation begins from the nasal cavity. Once clean air is breathed in through the nose, it is conditioned to fit further transmission. The tiny hair present inside the nose trap any dust and also warm the air inhaled (Kleinstreuer, 2010). With the help of a concentration gradient that exists between the atmosphere and the lungs, air is further pushed down the trachea. Inspiration requires a drop of pressure inside the lungs to prompt the atmospheric pressure, which is higher, to flow inside. The three types of pressures involved in the ventilation process are the atmospheric, intra-pleural and the intra-alveolar (Marieb, and Hoehn, 2007). The diaphragm which is located just above the abdomen contracts while volume in the thoracic cavity or the chest increases (Marieb, and Hoehn, 2007).

Exhalation process. The pressure gradient is created from the relaxation of the diaphragm and decrease in volume of the chest cavity. High pressure is generated against the atmospheric pressure which causes an imbalance that expels air from the lungs consequently deflating them (Kleinstreuer, 2010).

3.2 The mechanism of gaseous exchange in the alveoli

The alveoli are structurally modified to perform their task of facilitating the exchange of gases. They have adaptive features that ease the flow of gases in and out of the bloodstream. There are approximately a million air sacs in each lung. Air coming from the bronchioles enters the alveoli, which are in close proximity to blood capillaries, directly. During inhalation oxygen from the outside environment is dissolved by a moisture layer on the surface of the alveoli and diffuses across the blood vessels (pulmonary vein) into the red blood cells (Kleinstreuer, 2010). This blood is renamed oxygenated blood and is transported to the heart so that it can be supplied to other organs. During exhalation, carbon(iv) oxide from the blood is dissolved in the moist film of the alveoli and diffused into the air sacs which expel it out (Kleinstreuer, 2010).

3.3 How the structure of the alveoli relates to its function.

The alveoli are surrounded by a layer of moisture which hastens the absorption of gasses to and from the blood vessels. Gasses dissolve easily and faster in water (Kleinstreuer, 2010). Alveoli also have a large number of air sacs; their main purpose is to create a large surface area for the passage of gasses; the larger the surface area, the faster the diffusion of gasses (Kleinstreuer, 2010). The wide network of blood vessels that surround the alveoli reduce the distance of exchange hence quick absorption. The thin semipermeable membrane of the alveoli makes it possible for gases to be exchanged easily. Alveoli have a small size that also increases surface area to volume ratio for maximum gaseous exchange (Kleinstreuer, 2010). The fast movement across membranes facilitates the development of a steep concentration gradient that allows for the continuous flow of material.

LO4.Demonstrate an understanding of the effects of smoking on the human body

Cigarettes contain three main components alongside other carcinogenic elements; these are tar, nicotine and carbon monoxide (Onor et al., 2017). Each of these components plays a role in the impairment of the body's functions. According to Saha (2007), these ingredients can increase cholesterol concentrations, oxidative stress and dysfunction of the endothelial. Respiratory tract disorders arise from the inhalation of chemical substances that harmful; tobacco is one of these substances. On the other hand, nicotine is responsible for the addictiveness of tobacco although it is not carcinogenic.

Smoking does not only affect the addicts but also those close to them. For instance, it can result in premature ageing whereby the skin loses its lustre and becomes pale (Onor et al., 2017). Because the main passages of smoke are located in the respiratory system, sensitivity to smell and taste can be reduced or lost altogether (Saha, 2007). Ulceration on the lining of the stomach can occur as a result of the corroding effect of smoke in addition to vision impairment and bleeding of the gums (Onor et al., 2017). The risk of developing throat and food pipe cancer heightens for smokers more than nonsmokers because of cancer causing elements such as benzo(a)pyrene (Onor et al., 2017).

Mothers who smoke during maternal period subject the unborn babies to adverse effects. Second-hand smoke can also harm the fetus (Barnoya & Glantz, 2005). Mothers who are hooked on tobacco are likely to give birth to children with physical deformities because of nicotine’s effect; it hampers proper growth (Schane, Ling & Glantz, 2010). Physical deformities such as cleft palate and cleft lip are likely to form on a child exposed to tobacco smoke (Schane, Ling & Glantz, 2010). Chances of involuntary termination of the fetus and premature births are high for smoking expectant mothers (Schane, Ling & Glantz, 2010). Other diseases caused by maternal smoking may manifest later in the adult life of the baby; these include diabetes, obesity, high blood pressure and stroke (Schane, Ling & Glantz, 2010). Smoking generally attenuates the body's defence mechanisms, making it susceptible to all manner of infections such as influenza. Increased illness lifespan and a decrease in protective properties render the body indefensible. Additionally, smoking affects the sexual functions of men; for instance, it can lead to low sperm count and deformation which consequently causes infertility (Sharma et al., 2016). Reduced blood flow to tissues subsequently affects the normal flow of blood in the penis.

4.1 Analyze the effects of smoking on the cardiovascular and respiratory systems

Tar affects the lungs by occupying its spaces beside being highly carcinogenic. Generally, smoke clogs the lungs with poisonous substances such as tar which weaken and irritate it. Chain smokers have frequent episodes of coughing due to the vulnerability of the lungs to infections. Smoke also impairs the voice box and can lead to loss of vocal sound (Mattes, 2014). The passageway of air like the trachea suffers from irritation that is outwardly shown by the constant clearing of the throat.

The respiratory and cardiovascular systems are interconnected through blood vessels that act as intermediaries between the lungs and the heart. Impairment of some parts of the breathing system will certainly affect how the blood vessels function. Smoking causes heart attacks by eroding the lining of blood vessels such as the artery which encourage the formation of layers that lead to constriction hence increased blood pressure (Schane, Ling & Glantz, 2010). Tobacco smoke causes stickler blood that is more prone to clotting hence can cause sudden death (Onor et al., 2017). The risk of suffering from a stroke are higher because smoke decreases the blood flow to the brain (Schane, Ling & Glantz, 2010). More so, adrenaline produced by nicotine excites and overworks the heart (Mattes, 2014).


Barnoya, J., & Glantz, S. A. (2005). Cardiovascular effects of secondhand smoke: nearly as large as smoking. Circulation, 111(20), 2684-2698.

Kleinstreuer, C. and Zhang, Z., 2010. Airflow and particle transport in the human respiratory system. Annual review of fluid mechanics, 42, pp.301-334.

Marieb, E.N. and Hoehn, K., 2007. Human anatomy & physiology. Pearson Education.

Mattes, W., Yang, X., Orr, M. S., Richter, P., & Mendrick, D. L. (2014). Biomarkers of tobacco smoke exposure. In Advances in clinical chemistry (Vol. 67, pp. 1-45). Elsevier.

Netter, F.H., 2017. Atlas of Human Anatomy E-Book. Elsevier Health Sciences.

Onor, I. O., Stirling, D. L., Williams, S. R., Bediako, D., Borghol, A., Harris, M. B., ... & Sarpong, D. F. (2017). Clinical effects of cigarette smoking: epidemiologic impact and review of pharmacotherapy options. International journal of environmental research and public health, 14(10), 1147.

Saha, S. P., Bhalla, D. K., Whayne, T. F., & Gairola, C. G. (2007). Cigarette smoke and adverse health effects: An overview of research trends and future needs. International Journal of Angiology, 16(03), 77-83.

Schane, R. E., Ling, P. M., & Glantz, S. A. (2010). Health effects of light and intermittent smoking: a review. Circulation, 121(13), 1518-1522.

Sharma, R., Harlev, A., Agarwal, A., & Esteves, S. C. (2016). Cigarette smoking and semen quality: a new meta-analysis examining the effect of the 2010 World Health Organization laboratory methods for the examination of human semen. European Urology, 70(4), 635-645.

August 04, 2023


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