- Jason Carr
Homeostasis is a basic biological order in which opposing forces within the body has to have a constant condition of balance in order for the body to be maintained. The state of the internal environment needs to remain constant as possible within certain ranges and is done so by being rigidly controlled by the body. The process at which homeostasis happens is controlled by sophisticated mechanisms, that responds accordingly as sensitive changes happens and this then is what affects the body’s internal environment. These include positive feedback mechanisms and negative feedback mechanisms as well as other components that regulate homeostasis which are the detectors, control centre and effectors.
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Components that regulate homeostasis are known as the detectors, control centre and the effectors. Detectors receive messages about any changes that happen in the internal/external environment. An example of a detector are located within blood vessels, they receive information that the blood pressure has risen out its normal range. This detector then determines what is happening and sends these messages to the control centre, which is located in the brain. The control centre receives information that blood pressure has risen and decides what range that the blood pressure should be within. The control centre decides what particular value anything should be within the body and the action this then takes is what achieves the maintenance of homeostasis. The effectors are what make these changes happen after the control centre has decided what the set value should be and these are located in the muscles or organs. In this example, the effectors will receive the correct set point for the blood pressure and will then correct it by lowering it.
Positive feedback mechanisms are designed to push levels out of normal ranges and do not help keep the body at a homeostatic condition. Although this process can be beneficial it rarely occurs within the body as it pushes the variable even further away from homeostasis. One example that occurs within the body is blood platelet accumulation, the process of blood clotting (Fig1. Gamelas S, 2010). When someone suffers from a cut, blood platelets form and continue to form until the bleeding is halted. The reason this example is a positive feedback mechanism is because the process keeps increasing further and further away from the normal set point rather than returning to its original set point. Negative feedback mechanisms consist of reducing the output of any organ or system to return the level back to its normal level of functioning which then enables the process of homeostasis to continue. An example of a negative feedback mechanism is temperature control. The hypothalamus that monitors the body temperature is capable of detecting even the slightest change of the normal body temperature. The response to overheating is the stimulation of glands producing sweat to reduce temperature, or in the response to the cold various muscles could be signalled to shiver to increase body temperature. Both are equally as important for the body to function correctly and if damaged or altered complications may arise.
Blood is responsible for the transportation of many substances throughout the body such as nutrients, wastes, and gases and this is what helps to maintain homeostasis. Blood is made up from red blood cells, white blood cells, platelets and plasma. Red blood cells, or referred to as erythrocytes are the most common of all blood cells. Common features of these are that they have no nucleus, they are produced in red bone marrow and the shapes that these cells come in are biconcave-disks. The reason for this unique shape is it allows them to have a high surface area to volume ratio which allows them to fold to fit into thin capillaries. Erythrocytes job is to transport oxygen through the red pigment (haemoglobin). The haemoglobin is rich in iron and proteins which increase the oxygen carrying capabilities and also is responsible for gas transportation. White blood cells or leucocytes only make up a very small amount of total number of cells in the bloodstream. These cells play an important part within the immune system as they are concerned with the defence against microbes and invading foreign material. Unlike the red blood cells these contain a nucleus and are much larger. There are two major classes of these cells, granulocytes which contain granules within the nucleus, capable of digesting bacteria and foreign materials. Agranulocytes which do not have granules within the nucleus are responsible for the production of antibodies and destruction of molecules. Platelets or thrombocytes are small cell fragments that are involved in the clotting process. They’re produced in the red bone marrow and similar to red blood cells contain no nucleus. Platelets only survive in the body for approximately a week before they are then digested by the macrophages. Plasma is the liquid portion of the blood and is around 90% water. Glucose, oxygen, carbon dioxide, electrolytes, nutrients and cellular waste products are all dissolved within the plasma which then has the ability to transport these substances.
The cardiovascular system consists of the heart, blood vessels, and the approximately 5 litres of blood. The cardiovascular system is responsible for the transportation of oxygen, nutrients, hormones, and cellular waste products throughout the body. All of this is supported by the heart, the muscular pumping organ. Another function of the cardiovascular system is protection via the white blood cells. These fight pathogens that have entered the body and platelets also help this process by creating scabs over wounds preventing any pathogens entering. The cardiovascular system also helps regulation within the body and keeping homeostatic control. Blood vessels help the maintenance of body temperature by either opening if temperature rises or constrict only allowing the flow to vital organs. Also, because of the albumins present in plasma this helps to balance the osmotic concentration of the body cells. (Taylor, T)
The respiratory system consists of the nose and naval cavity, pharynx, larynx, trachea, bronchi, bronchioles, the lungs, pleura, intercostal muscles and the diaphragm. It is utilized when oxygen and carbon dioxide needs to be exchanged between the blood and lungs, essential for the cellular metabolic function. The exchange of gasses process is inspiration, which brings in the oxygen and expiration, the excretion of carbon dioxide. As inspiration takes place and the oxygen begins its journey to the lungs the air is either cooled or warmed to optimum body temperature. Water vapour then begins to moisten along with being cleaned of dust and other particles which adheres to the membrane lining of the tract being coated with the mucus. The way the respiratory system maintains homeostasis is by the exchange of gasses, breathing in the oxygen and excreting the carbon dioxide.
The central nervous system is an important component for the maintenance of homeostasis. It consists of neurons, the brain and the spinal cord. The brain is the control centre of the body and consists of three main components: the forebrain, the brainstem and the hindbrain. The forebrain is used for a wide aspect of functions including receiving and processing sensory information, some of the structures contained within the forebrain also help to relay sensory information and controlling autonomic functions. The midbrains involvement within the brain is that it connects the hindbrain and forebrain. As well as being involved in the motor function it also helps in the auditory and visual responses. The hindbrain is an extension from the spinal cord and connects to the midbrain. This component assists in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. Structures also assist in helping autonomic functions such as breathing, heart rate and digestion.
The spinal cord is a bundle of nerve fibres that runs down the spinal column extending from the neck to lower back. It functions like a two way process, the ascending nerve tracts send information from body organs and the external stimuli to the brain and the descending nerve tract sends information from the brain to the rest of the body.
Neurons are located within the cells of the nervous system and each one contains nerve processes. These nerve processes are able to conduct and transmit signals that branch out to various areas of the body. There are three different types of neurons and these are motor, sensory or interneurons and although they all have similar functions each relays different information to the various places in the body. The motor neurons relay information from the central nervous system to organs, glands and muscles whereas the sensory neurons are the complete opposite. These neurons send information to the central nervous system from the internal organs or external stimuli. Interneurons responsibility is then to relay these signals between the motor and sensory neurons (Bailey, R).
These three components that make up the central nervous system are vital for the maintenance of homeostasis and help the positive and negative feedback mechanisms function. As described above the brain receives the sensory information and helps to relay any changes that occur in the body. The neurons are what relay these messages received via the feedback mechanisms and either relays to the central nervous system or relays information from it and the spinal cord runs down from the neck to lower back and this also assists in transporting the messages received from the feedback mechanisms.
The exchange of gases takes place in the alveoli, a large sac like structure located at the end of the bronchioles. Pulmonary capillaries surround the alveoli and are able to facilitate rapid diffusion as they are one cell in thickness and as well as having these capillaries the alveoli wall produces a surfactant, a detergent type of liquid that prevents the alveoli from collapsing. As the oxygen is inhaled from the atmosphere it diffuses and travels through into the red blood cell that is then transported by the blood to the various different body tissues. The carbon dioxide that is first produced by the body’s metabolism is returned to the lungs via the blood that diffuses across the capillaries and alveolus is then removed from the body by the process of expiration.
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Before the transportation of oxygen can happen within the body it must first pass through a number of different passages including the mouth, larynx, trachea and the lungs. Once in the lungs it has to pass through a series of bronchial tubes until it finally reaches the alveoli where there, as explained above, then diffuses into the blood. Once the oxygen has reached the blood it then combines with the haemoglobin located within the red blood cells, for the red blood cells to then travel around the body it then gets pumped by the heart. The haemoglobin is a large protein and these contain a globular protein called globin and also a pigmented iron complex called haem. As haemoglobin molecule contains four globin chains, four haem units that has an iron atom attached to each one that attaches to oxygen it then has the ability to carry 4 oxygen molecules per haemoglobin molecule thus making it the most efficient way for oxygen to get around the body. As the iron atoms within the haemoglobin become full the molecule becomes saturated, that is then referred to as oxyhaemoglobin. For our body to function correctly we must ensure it has a constant flow of oxygen as this is what we use to function all of cells and organisms. Oxygen assists with the body movement, growth, repair and the defence against bacteria as well as oxidising the nutrients we digest to also turn that into energy.
As well as blood transporting oxygen around the body, it also helps with the transportation of nutrients where it is needed. Although very similar to oxygen diffusion, instead of dissolving in the blood cells the nutrients dissolve in the plasma. Once the nutrients are absorbed by the walls of the small intestines it travels down to where it is either absorbed by the blood or continues to the large intestine for the remaining water to be absorbed from the indigestible food and transmits the waste products from the body. During the digestion phase the nutrients contained within the food are formed into more suitable forms for it to be able to be effective in the body and many chemical reactions break the food down into molecules. Just before entering the blood cells for transportation the molecules first converge with the oxygen, creating stored energy. The body’s metabolism can then change these molecules into heat energy. Once the nutrient molecules has converged with the oxygen molecules it can then be transported around the body where needed by the red blood cells. The different nutrients we digest assist the oxygen with providing energy for the body and helping the immune system by defending our body against bacteria. The different food types we digest also have slightly different roles to one another. Carbohydrates provide fuel for the body, protein help to rebuild and repair tissue and fats are stored as energy until our body has utilized all of the available carbohydrates.
The skeletal system has a number of functions and assists in the body’s growth and development. The skeleton forms the framework for the body, the structure and keeps the natural shape of our body. It provides the point of attachment for most skeletal muscles and as these are attached together, assists in the movement as the muscles contract. As the body’s internal organs are also at risk from damage or injury the skeleton provides a natural protection barrier. An example being the rib cage, this protects the heart and lungs from damage, vital organs that assist in the function of the human body. The bone tissue has the ability to store minerals and chemical energy that when required, is released when there is an imbalance within the body. Our bones grow from the extremities, the ends, and usually continue to develop up until our early twenties. Bone marrow that is the cavity inside the bone also assists in the development as this produces stem cells such as red and white blood cells.
There are three different blood vessels that consist in the body and these are arteries, veins and capillaries. Arteries carry blood away from the heart. These are thick, elasticated and muscular allowing them to withstand the high pressure they are put under and are situated deeply within tissues. As they become further away from the heart they branch out and become smaller, becoming arterioles. Veins are responsible for carrying blood to the heart and contain a one way valve to prevent any backflow from happening. As the flow of pressure isn’t as high the walls are much thinner and less elastic, and the means of travel is a wave like motion rather than being a forcing motion that is apparent in the arteries. Capillaries are the smallest of the vessels and are connected to arterioles and venules. The function of capillaries is that they transport oxygen, nutrients and various other substances to various cells and tissues enabling development and the body to function properly. Through capillary exchange waste products and carbon dioxide is also removed from the body.
There are various challenges that homeostasis has to has to address and rebalance. Diseases are a primary source to homeostatic failure, creating an imbalance in the internal environment in the body. Due to the process involved this can cause the altering of tissues and organs causing severe adjustments specifically in the immune system and renal. The mechanisms specific to fighting the invading pathogens can then mistakenly fight itself. Examples such as Alzheimer’s disease and heart arrhythmia show this as homeostatic functioning are disrupted as the capabilities of organs dwindle. Another example could be the control of blood sugar. The amount of glucose must be maintained within certain ranges, as we eat a sugary food the pancreas is able to recognise this and insulin is immediately released to try and remove this excess sugar. The pancreas then receives information from the negative feedback mechanism that blood sugar has dropped, thus glucagon is then released to raise blood sugar. Underlying medical conditions though can cause problems with this process. Insulin may not be released efficiently that then cause an imbalance in blood sugar levels, this condition is also known as diabetes. We are able to fight this by injecting our body with insulin that can then convert these certain food types into energy for our body to regulate properly. Another example that also demonstrates how homeostasis demonstrates strategies to redress any changes is body temperature and the variable that can affect this is dehydration. Dehydration can prevent homeostasis from occurring as our body temperature rises and cannot be cooled due to the lack of water in the body. The way our body prevents the loss of water as we sweat is because of the two layers that make up our skin. One of the layers is much thicker and known as the dermis. There dermis is responsible for retaining moisture and regulating water, this gets utilized as our body temperature increases that then reduces our temperature and sweating, helping us to retain our water internally.
Homeostasis helps our body to develop and for growth to take place. By constantly fighting of pathogens and by the production of platelets, this prevents any foreign material or bacteria entering our body so we are able to keep healthy and fight of any illnesses. Bone homeostasis also allows for calcium to be released preventing our bones for weakening and as we grow, also strengthening them. As homeostasis assists in transporting nutrients, oxygen, and excreting waste products it also enable our bodies to keep healthy and strong, with the nutrients providing energy and oxygen keeping our body regulating efficiently.
Bailey, R. ().Central Nervous System. Available: http://biology.about.com/od/organsystems/ss/cent-ral-nervous-system.htm. Last accessed 17th Jan 2014.
Fig.1. Gamelas, S (2010) Homeostasis. [Image] Available: http://www.studyblue.com/notes/note/n/ homeostasis/deck/7890237. Last accessed 13th Jan 2014.
Taylor, T. ().Cardiovascular system.Available: http://www.innerbody.com/anatomy/cardiovascular-male. Last accessed 15th Jan 2014.
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