Respiration plays an important role in humans and animals. It is a process where they obtain energy by breathing or taking in oxygen. The principle of oxidation reaction drives respiration by using oxygen to oxidize the carbon-containing compounds in the body into carbon dioxide and water. During this oxidation reaction energy in the form of Adenosine triphosphate (ATP) is released (Bettelheim, et al. 2007). The process of respiration is a complex process and involves a number of systems in order to deliver oxygen, which is needed in the organism’s cell, and releases carbon dioxide, a waste product from the cell.
The respiratory system is the one responsible for taking in oxygen and releasing carbon dioxide out of the body, and serves as the passage way for the two. The air we breathe enters the nasal passages, where the dust particles are filtered by the cilia. The air is also warmed and moistened in the nasal passages before it enters the windpipe called trachea, and then passes through the bronchus. Each bronchus leads to a lung. On each bronchus there are bronchioles which appear as tiny branches of the bronchus and at the end of each bronchiole are millions of little air sacs called alveoli (The Respiratory System 2009).
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Alveolus is where an exchange of gas takes place. The alveoli take oxygen from the air that enters into the lungs. The oxygen that the alveoli have taken passes the oxygen to the blood cells. Before the alveoli have passed the oxygen to the blood cells, these blood cells were carrying carbon dioxide which is then passed to the alveoli. And this gas exchange occurs simultaneously. This exchange of gas occurring in the alveoli is based on the principle of diffusion.
Diffusion is a natural phenomenon that occurs in our body. This transport does not require a bulk motion of particles. This results from the difference in molecule concentration between two regions of space. As a result of the difference in concentration, molecules from higher concentration region move to the lower concentration region of space. And this movement is what drives the movement of oxygen from blood cells to the tissues and cells which lack or need oxygen. This type of diffusion is what is called the simple diffusion. However, if molecules move using channels embedded in a membrane, it is termed as a facilitated diffusion.
The rate at which oxygen diffuses into the cells that require it is described by Fick’s Law. Fick’s Law is dependent on the thickness of the membrane through which the molecule crosses the surface area for the gas exchange, and the mass and solubility of the molecule (Blood and Diffusion n.d.).
The circulatory system serves to take oxygen from the lungs and pass it to the tissues. It is also responsible for taking the waste products of the cell in order for them to be eliminated out of the body. This circulation is made possible by blood cells which carry oxygen, and these blood cells are carried by capillaries to arteries and veins. Capillaries are the smallest blood vessels in the body. The molecule which serves to carry oxygen is called Hemoglobin. The Hemoglobin molecule which contains Fe2+ ion and because of it the oxygenated blood is red (Bailey, R 2006).
The oxygen-containing blood cells are circulated to the tissues by the circulatory system. The circulation of the blood throughout the body is achieved through the process of mass transfer. In the circulation of blood the heart serves as a pump. Blood flows or circulates in the body due to the pressure produced by pumping of the heart, which pushes blood to circulate. This mass transfer where an external force is used to drive such a transfer to happen is called forced convection (Young et al. 2004).
How the blood cells pass oxygen to the tissues is based on the principle of diffusion. The tissue cells have low oxygen concentration while blood cells have high oxygen concentration. This difference in oxygen concentration creates a concentration gradient between the tissue cells and blood cells. And as a result, oxygen diffuses to the cells with low oxygen concentration.
All the processes occurring in the body, including diffusion, need energy. We obtain energy from the food we eat. The conversion of food to energy is made possible by the digestive system.
The food is first chewed in the mouth. The starch in the food we eat is hydrolyzed by the enzyme salivary amylase to convert it to maltose. Starch is polymer of sugar, which means that it is rich in carbohydrate. Thus, it is a major source of energy. The alkaline environment in the mouth breaks the glycosidic bonds in the starch. After breaking of large molecules, food goes to the esophagus and then to the stomach. In the stomach food is stored for further digestion. Pepsinogen secreted from the gastric gland reacts with the hydrochloric acid present in the stomach to produce an enzyme called pepsin, which breaks protein molecules to peptides.
Food after being completely broken down then goes to the small intestine. In the small intestine there are enzymes which act to digest the nutrients into smaller molecules in order for them to be absorbed by the body. These enzymes include maltase which acts on maltose, protease on protein, lipase on fats, etc. The nutrients which are the product of the actions of these enzymes go to the villi cells present in the small intestine. And in these villi are embedded microvilli. The microvilli are responsible for absorption of the nutrients produced in digestive system. Then the nutrients pass through the blood vessels called capillaries. These capillaries are placed close to all cells present in the body; that is why distribution of nutrients is always possible.
However, the materials which remain undigested after digestion and which the body cannot use go to the large intestine or what is commonly known as the colon. The function of the large intestine is to absorb water and store and process the non-digested foods. The residues that remain after removal of water are stored in the rectum. These intestinal matters are called feces. Feces are then passed through the anus to complete the digestion process by eliminating it out of the body (Basic Functional Anatomy 2012).
Diffusion accounts for distribution of the nutrients in the body. The most important product of digestion which is converted into energy is the blood sugar glucose. After absorption of glucose by the blood cells, blood cells have high glucose concentration. Glucose present in the bloodstream diffuses to the cells with low glucose concentration due to the concentration gradient. The type of transport occurring between two cell membranes is passive diffusion. This type of diffusion depends only on the permeability of the membrane and does not require energy to do this transport (Blood and Diffusion n.d.).
When glucose molecules enter the cell, it will react with the oxygen present in the cell to produce carbon dioxide and energy in the form of ATP (Bettelheim et al. 2007).
C6H12O2 (glucose) + O2 → CO2 + H2O + ATP
The ATP produced during cell respiration is used by the cell in the processes occurring inside of it. The water produced can be used as an electron acceptor in some processes inside the cell. The carbon dioxide which is a waste product from the cell is then transported to the lungs by the circulatory system. The gas exchange will then take place between the blood cell that carries carbon dioxide and the alveoli of the lungs. Then carbon dioxide will pass through the trachea and, finally, out of the body through every single exhale made by the organism (The Respiratory System 2009).
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