With Reference to Specific Examples and Mechanisms Assess the Significance of Homeostasis to the Human Body.
With Reference to Specific Examples and Mechanisms Assess the Significance of Homeostasis to the Human Body
Homeostasis derives from the Greek word homeo meaning same and stasis meaning staying, therefore homeostasis refers to the maintenance of the stability of the internal environment within a body, giving an organism a level of internal independence from the external environment (1).
The actual environment of the cells of the body is the interstitial component of the Extra-Cellular Fluid (ECF), this fluid has to be kept constant from the changing external environment or necrosis occurs. Since normal cell function depend upon the constancy of this fluid, it is not surprising that in multicellular animals, an immense number of regulator mechanisms have evolved to maintain it. W.B cannon used the term homeostasis to describe the various physiological arrangements which serve to restore the normal state once it has been disturbed (2).
Homeostatic mechanisms involves the interactions of many organs and systems in providing the optimum conditions for the cells, which results in optimum environment for the enzymes to work in thus keeping the cell alive. The mammalian kidney is central to homeostasis, being involved in the regulation of water and salt balance, pH and metabolites levels. The liver is centrally concerned in the regulations of the metabolite levels and thermogenesis. The hypothalamus monitors pH, osmotic pressure and temperature and it brings about the regulation either by direct affect on the nervous system or via the hormones from the pituitary gland. (1)
The buffering properties of the body fluids and the renal respiratory adjustments to the presences of excess acid and fluid are more examples of homeostatic mechanisms. The other factors in the internal environment which must be maintained within narrow limit include temperature, glucose levels, O2 and CO2 levels. (3)
The homeostatic processes which intend to maintain a possible alternating feature within narrow limits all use a mechanism known as negative feedback. In these mechanic systems there are three basic elements; detector/receptor which send information to the control centre/integrator. This control centre determines the limits within which the changeable feature is kept. This receives information from one or more receptors and sends out signals appropriate to this information to the effector (4). The effector responds to the incoming signals sent by the control centre and affirms that modifications are needed.
There are generally two ways the body can respond to a change. In the negative feedback mechanism the effector response negates the effect of the original stimulus thus restoring homeostasis. This level is called the 'norm' because it is which the body finds most suitable. There is also the possibility of positive feedback mechanism. In these mechanisms, the result or response enhances the original stimulus so that the activity (output) is accelerated. This feedback mechanism is "positive" because the change that occurs proceeds in the same direction as the initial disturbance, causing the variable to deviate further and further from the original value or range (5). This does not return to the norm and has a destabilising effect and therefore not result in homeostasis. There are two behavioural mechanisms that are involved in homeostasis; they are intrinsic and extrinsic regulation.
Intrinsic involves internal motivation which benefit the body such as organs and muscles contraction and extrinsic is stimulated by external conditions which benefit the person such as putting on a jacket.
Homeostasis is so important that most diseases is regarded as a results of its disturbance, a condition called homeostatic imbalance (6). Homeostatic imbalance is therefore the disruption of homeostatic mechanism where there is little change in homeostatic mechanisms in young and old during rest but it has been demonstrated that the rate of readjustment to normal equilibrium after stress is slower in old compared to ...
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Intrinsic involves internal motivation which benefit the body such as organs and muscles contraction and extrinsic is stimulated by external conditions which benefit the person such as putting on a jacket.
Homeostasis is so important that most diseases is regarded as a results of its disturbance, a condition called homeostatic imbalance (6). Homeostatic imbalance is therefore the disruption of homeostatic mechanism where there is little change in homeostatic mechanisms in young and old during rest but it has been demonstrated that the rate of readjustment to normal equilibrium after stress is slower in old compared to young. This prolonged duration of stress-response profoundly increases
risk of dying (7).
Aging makes us more vulnerable to disease due to changes in structure and function therefore shows a decline in restoring homeostasis (8).
Negative Feedback Mechanisms and Imbalances
If the body's temperature was allowed to rise out of control, protein and therefore enzyme structure would be affected, perhaps with disastrous results (9). In order for the enzymes to work at their optimum, temperature control needs to be monitored carefully so that they are kept within narrow ranges. These are important due to the fact the body needs to maintain the core temperature so that processes occurring internally are not affected.
The skin or integument has a very large surface and accounts for about 7 % of total body weight in the average adult (10). It protects us from bacteria as well as water and heat loss. The two distinct levels are dermis and epidermis. The epidermis is composed of epithelial tissue and provides biggest form of protection, fibrous connective tissue makes up the dermis which is most of the skin. The dermis has a network of vessels flowing providing its nutrients, the epidermis layer receives its nutrients via diffusion through the tissue fluids as it is not vascularised. There is a layer of dead cells which protects the epidermal layer, these are called keratinocytes. And they produce keratin which gives waterproof and protective properties. There are also melanocytes cells producing the pigment melanin which is responsible for the colouring of the skin.
Metabolic activities results in heat production and during vigorous exercise active organs produce excess heat (11) which needs removing from the body to prevent a harmful rise in body temperature and the potential development of heat stroke (12). If there is a change in the temperature then the loss of heat through the skin is specifically maintained by neurones controlling the extent of dilation of the arterioles. When the temperature of the body is increased by 0.25 to 0.5 C the sweat glands are stimulated to secrete sweat, which is conveyed to the surface of the body by ducts (13). The capillary beds are filled with blood due to the dilation of arterioles and thus releases the excess heat as sweat through the sudoriferous (sweat glands) and out of the pores. The sweat is then converted into water vapour and evaporates from the skin thus cooling the body down.
The temperature-regulating centre in the hypothalamus regulates skin blood flow by autonomic nerve stimulation of the sweat glands. The vasomotor centre in the medulla oblongata consists of the vasoconstrictor centre which decreases blood vessel diameter (increasing blood pressure), and the vasoconstrictor centre which increases blood vessel diameter (decreasing blood pressure).
If there is a decrease in temperature then the constriction of arterioles occur and there are also hairs on the skin which help to attract warm air if preservation of heat is needed.
Skin cancer is a disorder of the skin. There are three types, Basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma (MM). BCC accounts for 78 % of all skin cancers. The tumours arise from cells in the stratum basale of the epidermis and metastasise around the body of not treated early. SCC arise from squamous cells in the epidermis and makes up 20%. Melanoma is where malignant cells are found in melanocytes and accounts for about 2 % (14).It has to be treated early or it metastasises to the brain and other parts and reduces chance of recovery (15).
Cellular respiration yields energy and requires glucose therefore maintenance of blood glucose levels is important. If the level rises too much the normal behaviour of cells is affected and serious problems can arise. The ideal level of blood glucose is about 1mg/cm3 (16).
The pancreas detects the level of glucose and the hormone released is dependant on the level of glucose. The ? cells of the pancreas produce glucagon, and ? cells produce insulin. They work antagonistically thus minimising variation in glucose levels. Eating will increase the blood glucose level and exercise will decrease it. Insulin and Glucagon reduces and increases the level of glucose by:
Insulin
Glucagon
Using excess glucose by more cell respiration.
Slowing the use of glucose via respiration
Increases amount of glucose absorbed into the body cells (particularly the liver).
Increases amount of glucose absorbed into the body cells (particularly the liver).
Turning the glucose into glycogen (Glycogenisis)
Turning the glucose into glycogen (Glycogenisis)
Glucagon promotes Gluconeogenisis, the conversion of fatty acids into glucose.
Table Source: http://www.s-cool.co.uk/topic_quicklearn.asp?subject_id=3&Topic_ID=9&Quicklearn_ID=4&loc=ql
http://www.s-cool.co.uk/topic_quicklearn.asp?subject_id=3&Topic_ID=9&Quicklearn_ID=4&loc=ql
In Diabetes mellitus Type 1 the pancreas cannot produce insulin They use up all the glucose in their blood and then go into a coma and insulin is injected if blood glucose level is too high and if its too low they have to eat.. The urine also becomes more concentrated with glucose (glucosuria). In Type 2 pancreas still produces insulin, just not enough to meet the body's needs therefore a diabetic cannot store glucose as glycogen.
Source : http://www.life-with-diabetes.com/html/types-of-diabetes.php3
Positive Feedback Mechanism and Imbalance
Clotting is a haemostatic process (stopping bleeding). This turns liquid blood a gel called a clot. It consists of protein fibres called fibrin in which traps the formed elements of blood (17). The gel forms a cap over a wound.
Clotting factors are substances involved in clotting and they create a cascade of interactions that results in clot formation.
The clotting process is a positive feedback mechanism: once a clot is formed it continues to expand and external factors are required to hold it in check.
Clotting occurs in three stages. The first stage can occur via two distinct pathways, intrinsic or extrinsic, and results in the formation of the enzyme prothrombinase. This phase can be described as a cascade of interactions between clotting factors (18).
Source: Marieb EN, 2004, Human Anatomy & Physiology, Sixth Edition, San Fransisco, Pearson Benjamin Cummings; Page 663
Source: http://www.the-scientist.com/images/yr2002/sep16/figure.gif
Haemophilia is a disorder of the blood clotting system. There are different types of haemophilia and it depends on the deficiency of the blood clotting factors. The person suffering from haemophilia will not stop bleeding. Treatment involves transfusions of fresh plasma or concentrates of the deficient clotting factor to relieve fro tendency to bleed (19). Other examples of positive feedback mechanisms are lactation and labour contractions.
To summarise the significance of homeostasis, the homeostatic system of the body is which organs work together to maintain its structure and functions through assortment of dynamic equilibriums carefully controlled by interdependent regulation mechanisms. The system reacts to every change in the environment, or to every random disturbance, through a series of modifications of equal size and opposite direction to those that created the disturbance (20). The aim of these adjustments is to maintain the internal balances.
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0) Marieb EN, 2004, Human Anatomy & Physiology, Sixth Edition, San Francisco, Pearson Benjamin Cummings; Page 152
1) Marieb EN, 2004, Human Anatomy & Physiology, Sixth Edition, San Francisco, Pearson Benjamin Cummings; Page 155
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