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The chest is a cavity in the upper region of the body located between the neck and the waist or the abdomen. In human beings, it is commonly known as the thoraxic cavity. The chest’s major function is to protect the major organs in the body found in the thorax. The heart and lungs are the major organs protected by the chest (Wijkstrom-Frei, El-Chemaly, & Ali-Rachedi 2003).
However, there are many other organs in the region, including the major and minor pectoral muscles, trapezius muscles, the neck muscles and part of the spine. The chest itself is supported and protected by various muscles covering the ribcage, the spine, and shoulders. All these organs and muscles function together to ensure proper body function.
To understand the structure and importance of the chest, a study of the various organs found in the chest paramount. For the purpose of this study, emphasis will be given to the heart as the ‘engine’ of blood circulation and the organs of the respiratory system such as the lungs, the trachea and diaphragm (Frank, Netter & Carlos 2007).
The Heart Structure and Function
The heart is located in the middle of the thorax (mediastinum) between the lungs and is more inclined to the left below the sternum. This is because the left half is bigger because it is responsible for pumping blood to the whole body. Because of this reason, the left lung is smaller than the right one (Romer, Parsons & Thomas 1997).
The Heart cells (called cardiomyocytes) develop into muscle fibers that aid in the conduction of electrical impulses. The first and prime organ in the chest is the heart. It is about the size of a clenched fist and is located between the lungs in a camber that is well protected by the rib cage. It is made of a special muscle called the cardiac muscle and is the only organ that has that kind of muscle (Jardins 2012).
The heart slows or speeds in response to automatic signals from the brain, in line to the needs of the body. It has the sole work of ensuring that every cell in the body gets the necessary nutrients and oxygen needed for sustenance. It does this by pumping oxygenated blood from the lungs and nutrients from the alimentary canal to the cells.
Once the waste products and the carbon dioxide are released, the heart then helps to pump this blood back to the lungs and kidneys where carbon dioxide and urea are emitted respectively. Analogically, the heart is the organ that sustains life (Jardins 2011). The heart works automatically throughout the human life. The heart is made up of three muscles or layers.
The function of the outer part of the heart (the pericardium) is to keep the heart in its right position. The pericardium has two functional and structural layers. The first layer is a fibrous pericardium made up of great vessels and a posterior surface of the sternum and majorly supports the heart in its position. The inner layer of the pericardium is also made up of two layers (Guyton & Hall 2006).
The outer layer is called the parietal layer. I functions by providing coverage to the outer fibrous sac and the inner or visceral layer. In turn, the visceral layer covers the heart muscle. When the heart beats, the serous membrane produces serous fluid in the space between the visceral and parietal layers. This fluid is functionally important because it minimizes the friction between the membranes (Travis, Conway & Zabner 1999).
The middle layer of the heart is called the myocardium and it is made of a specialized muscle called the cardiac muscle. In addition, it is worth noting that this is the position in which blood circulation takes place. It is thickest in the left ventricle, thinner towards the right ventricle and thinnest in the artrium.
The endocardium is the innermost lining of the heart, which is much thinner and smoother. This phenomenon is results from the nature of the flattened epithelial cells that cover the entire region, including the valves and line of the blood vessels (Jardins 2008).
The Structure of the Heart
The heart is partitioned into two regions- the left and the right side. A major muscle called the septum is the chief anatomical feature that provides this partitioning. Each of the two partitions is then divided an upper and lower chamber. The upper chambers are the auricles or atriums while the lower chambers are the ventricles. The auricles receive blood from the veins, while the ventricles expel it to the arteries (Campbell 2005).
The artrio-ventricular valve separates the ventricles and artriums. These valves ensure the blood flow is in one direction from the auricles to the ventricles.
The right valve is called the tricuspid and it has three flaps. The valve on the left is known as the mitral valve and has two flaps. The valves open with the blood pressure. However, they are prevented from opening the opposite way by the Chordate tendineae or cords found on the walls of the ventricles (Hicks 2000).
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Figure 1: Anatomy of the human heart (Jardins 2007)
The Circulation of the blood
The flow of the blood happens in three phases the first phase is called the pulmonary circulation. It is responsible for movement of deoxygenated blood from the right ventricle via the pulmonary artery to the lungs and then the oxygenated blood is taken from the lungs to the left auricle of the heart via the pulmonary veins (Maton, Jean, Charles, McLaughlin, et al 1993).
The pulmonary veins then take the blood to the left artrium. The second phase of blood circulation is known as the systemic circulation, which is responsible for supplying nutrients and oxygen to the body and then taking the deoxygenated blood back to the heart. It happens from the left ventricle then to the main artery or the aorta that then transports the blood to the rest of the body.
It is then brought back to the right auricle via the superior and inferior venacava (Maton, et al 1993). The final phase of circulation is known as the portal circulation and which takes place in the digestive system from the spleen, pancreas and the gall bladder whose veins join to form the portal vein that then takes the blood to the liver and leaves via large hepatic veins that join the inferior Vena Cava to the heart (Marieb 2003).
The structure of the Lungs
In nature, the two human lungs are located on the chest region, each on one side of the heart. Although they are similar, the right lung has three lobes while the left one has two (Richardson, Randall & Speck 2005). The lobes are divided into partitions, which are further subdivided to lobules. Each of the lung lobes is surrounded by the pleural cavity, which is made up of two pleurae.
They are the parietal pleura that lie on the rib cage, and the visceral pleura that lie on the surface of the lungs (Frank, Netter & Carlos 2007). The trachea branches to the two main bronchi in the left and the right lungs respectively (Cecie, Christine & Lisa 2009). They then progressively divide to smaller of bronchi and bronchioles until subsequently the alveoli are reached.
Gaseous exchange happens in the alveoli. The central nervous system, the diaphragm and chest wall muscle, and the circulatory system (Jardins 2007) coordinate the whole process. The muscular diaphragm controls breathing. This diaphragm is located at the bottom of the thorax.
The diaphragm functions by contracting and relaxing, which increases the lungs ability to breathe in and out. The opposite happens when air is exhaled out through the nose (Macdonald 2009). The oxygen-rich blood returns to the heart via the pulmonary veins to be pumped back into systemic circulation (Crigg & Johansen 1987).
Figure 2: Anatomy of the Human lungs (Jardins 2012)
Although a mention of the pleura has already been made, it is necessary to look at the anatomical aspect of them in a deeper manner. Anatomically, the pleura are serous membranes surrounding each of the two lungs. They are found in doubled-layers in nature and provide mechanical protection to the lungs.
Noteworthy, the lungs are an important organ that provides a concise and maintained source of oxygen, an important gas required for various biochemical and physiological functions. In fact, living things can barely survive without oxygen. The connection between the lungs and the source of oxygen (the air) is a vital anatomical aspect worth discussion.
The lungs must have a system and method of protecting themselves from irritants and other dangerous objects inhaled along with air. Therefore, it is worth looking at the upper respiratory region as a functional part of the chest anatomy. First, the inner linings of breathing tubes (bronchus and bronchioles) are covered with a layer of mucus-producing cells. Such cells produce a thin layer of mucus in form of phlegm.
The phlegm is involved in trapping irritants inhaled along with the air before they reach the lungs. The phlegm, together with its contents, is then swept up the upper respiratory system towards the mouth. Noteworthy, the inner lining of the upper respiratory tract, including the nose, have a large covering of cilia. The cilia, normally appearing as small hairs, aid in the exit of the mucus and its contents from the tubes to the mouth.
The epiglottis is yet another important anatomical region worth discussion. It functions as a “gate” through which inhaled air passes on its way to the lungs. The epiglottis is highly innervated because it responds to the presence of irritants in the system.
It is connected to the parasympathetic system for the function of ‘fight-or-flight’ mechanism. It must open up to allow an upwards sweep of undesired contents in the inhaled air. This is not a voluntary mechanism, which means that innervations are necessary.
The bronchioles are major anatomical features in the chest region. Anatomically, they are small tubes that branch from the tertiary bronchi. It is worth noting that the difference between the two is based on their sizes. While the bronchioles are smaller, the bronchi are relatively larger (Cecie, Christine & Lisa 2009). In addition, the composition of their walls forms another source of anatomical difference.
For instance, bronchioles have a dense composition of elastic fibers as well as smooth muscles. On the other hand, the bronchi have hyaline cartilaginous rings that make up the largest part of their walls. For the purpose of their functionality, the bronchioles have a potential to increase and decrease their diameter.
When large volumes of oxygen are in demand within the body, the bronchioles must expand and increase their diameter, which allows an increase in the volume of air entering the lungs. In addition, the bronchioles can constrict in response to pollutants entering the system, which protects the lungs from infection and mechanical damage caused by irritants.
These are the chief anatomical parts of the lungs involved in the entry of air in and out of the lungs (Campbell 2005). They are found in alveolar sacs, some small clusters at the end of the bronchiole. They are hollow in nature, with a cup-like cavity surrounded by a large number of blood capillaries.
The study of the anatomy of the chest is very important because the importance of the heart and lungs is seen. These organs are most important in sustaining life. We are also able to know the structure of the chest and its other organs.
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