Factors Affecting The Function Of The Liver Biology Essay

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Describe the causes and effects of alcohol toxicity on the structure and function of the Liver. To effectively describe the causes and effects of alcohol toxicity on the structure and functions of the liver, an understanding of the liver and some of its functions should be necessary to provide a better understanding to reasons why the liver is affected or more likely to be affected by alcohol toxicity.

The liver, which is the largest gland in the body, is a reddish-brown organ, weighing approximately 1.4kg in adults and made up of about 70% liver cells known as hepatocytes. It is located within the upper right abdominal cavity, just below the diaphragm. It is connected to three blood vessels, the hepatic artery supplying it with oxygenated blood, the hepatic vein removing deoxygenated blood, then the hepatic portal vein supplying it with blood containing nutrients and substances requiring metabolism from the gastrointestinal tract (Marieb and Hoehn 2007).

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The liver has so many functions which makes it one of the important organs in the body. Some of its functions include: The assimilation and storage of fat-soluble vitamins (A, D, E and K), the creation of bile, the purification and clearing of waste products, the storage of important nutrients such as glycogen, vitamins, minerals and synthesizing of blood proteins to name a few. However, one out of its various functions makes it susceptible to alcohol toxicity. Its function of purification and clearing of waste products and toxins from the blood means that it has to clear alcohol whenever it is present in the body.

Alcohol can not be stored in the body, as a result, it has to be eliminated, about 90% of alcohol consumed is oxidised by the liver. The liver metabolises alcohol by oxidising it to acetaldehyde, which is further oxidised to acetic acid and finally to carbon dioxide, before its elimination. The excessive intake of alcohol is likely to lead to the accumulation of acetaldehyde in the liver, which is a harmful substance that has the ability to impair the mitochondrial function of the liver cells, responsible for energy generation. Acetaldehyde is also known to promote collagen synthesis and fibrogenesis and as a result, could seriously damage the liver when present in high concentration. It is also believed that the high concentration of acetaldehyde in some liver lobules, giving rise to a low concentration of oxygen may be a contributory factor to liver damage (Porth and Matfin 2009).

Excessive alcohol consumption therefore, is harmful to the liver and could end up compromising other vital functions it performs. Some of the effects on the liver's functions as a result of alcohol toxicity include:

A possibly increase in lactate production, leading to a reduced renal ability to excrete uric acid. There is a risk of hypoglycaemia due to impaired carbohydrate metabolism by the liver. The liver could also have impaired lipid metabolism and there is also the risk of an alteration of steroid metabolism, leading sometimes to hormonal disturbances in chronic alcoholism.

The structure of a diseased liver as a result of alcohol toxicity is usually characterised by three stages namely: fatty change, which is the accumulation of fat in the hepatocytes, it then leads alcohol hepatitis, which is the intermediate stage between fatty change and cirrhosis, then finally cirrhosis, which is usually the end stage of a chronic liver disease; Cirrhosis is a progressive disease which is characterised by the replacement of healthy functional tissues by fibrous tissues (MacSween et al 1987).

Section B

Jaundice and Pruritus are two symptoms associated with liver disease. Describe these two symptoms and explain the physiological changes that cause them.

Jaundice:

Jaundice, which is one of the signs associated with liver disease, is the yellowish discolouration of the skin and deep tissues of the body. It is more likely to be noticed in the eye when the white conjunctiva becomes yellow. The yellowing occurs as a result of the high level of a substance known as bilirubin, in the blood (Porth and Matfin 2009).

Bilirubin is the substance that gives the bile its colour, it is formed when the red blood cells are broken down, producing bilverdin (a dark-green bile pigment), which is then quickly converted to bilirubin. Bilirubin is of two kinds, the free and the conjugated. The free bilirubin which is insoluble in blood plasma is attached to plasma albumin and transported by the blood to the liver, where it is released from the albumin and conjugated by glucuronic acid. The conjugated bilirubin which is now soluble is then secreted as one of the bile's constituents into the small intestine and excreted in faeces.

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The inability of the liver to conjugate the free bilirubin with glucuronic acid, which a person suffering from liver disease is usually faced with, will mean that the free form of bilirubin which is still insoluble will build up in the blood and discolour the skin and other tissues of the body, leading to jaundice.

Pruritus:

Pruritus, which is one of the symptoms associated with liver disease, is the medical name for itching. Itching is an irritation of the skin that creates the craving to scratch the affected area (NHS Choices 2009). It would be important to note that although pruritus is one of the possible symptoms of liver disease, there are other health problems that can lead to pruritus.

The connection between pruritus and liver disease is cholestasis. Pruritus is actually a symptom of cholestasis, while cholestasis is one of the conditions of liver disease. It would then be essential to firstly, understand cholestasis and the physiological changes which leads to it, to successfully link pruritus as a symptom of liver disease.

Cholestasis is a condition whereby; there is either a partial or a complete blockage of the bile duct due to liver disease, resulting to a reduced or no flow of bile into the duodenum (Porth and Matfin 2009). The Bile is made up of water, bile salts, bilirubin, cholesterol and some by-products of metabolism. The set-in of cholestasis will mean that there will be less or no secretion of the bile and its constituents into the duodenum for excretion, which will result to its accumulation in the blood. The high level of accumulated bile salts in the blood is what leads to the irritation and itching of the skin, medically known as pruritus. Therefore, a person with liver disease who eventually develops cholestsasis, should exhibit the symptoms of pruritus due to the high level of bile salts which irritates the skin.

Endocrine System

Section A

Describe the physiological changes that occur to the structure and functions of the body in Type 1 Diabetes Mellitus.

To effectively describe the physiological changes that occur to the body's function and structure in type 1 diabetes mellitus, an understanding of the expected functional range of the body with regards to glucose level and how the endocrine system works to bring about the equilibrium which the body requires, will be necessary to realize the physiological changes that takes place in the body as a result of type 1 diabetes mellitus.

The endocrine system is a system of ductless glands, each of which secretes a type of chemical known as hormones into the bloodstream to regulate the body's system. These regulatory functions of hormones are required in metabolism, homeostasis and reproduction. The endocrine system mostly functions on the concept of negative feedback mechanism, although a few times it could be positive (Hinson et al 2007).

There are hormones that are released by the endocrine system that act to either increase the concentration of circulating glucose in the body, or to reduce its concentration. Glucose which is the by-product of carbohydrate found in the food we eat is the primary source of energy required by the body for its day to day activities; however, glucose is expected to be within a certain range to be regarded as being normal. The body should under normal circumstances, be able to maintain a glucose level range of between 4 to 7mmols per litre of blood (WHO 2009). This suggests that any constant glucose level above or below this range signifies the presence of a health illness whereby, the body is unable to regulate itself.

The complex method, by which the blood's glucose level is regulated, falls on an endocrine gland known as the pancreas. The beta cells (β-cells) found in the pancreas, are responsible for the creation and secretion of a hormone known as insulin, which is responsible for the reduction of the blood's glucose level. This it does by oxidising glucose to produce energy and also converting glucose into glycogen and storing it in the liver and muscles. If the level is still high, it then has to reduce it by converting it into fat and storing it in the adipose tissues of the body. A shortage of insulin production or its ineffectiveness, leads to an elevated level of glucose in the blood resulting to a condition known as diabetes mellitus.

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The type 1 diabetes mellitus is caused as a result of insufficient or no creation of insulin by the beta cells found in the pancreas. This type of diabetes actually originates from an autoimmune disease whereby, the immune system wrongly targets and destroys the beta cells, which are responsible for the production of insulin. This then leads to insulin deficiency and an elevated glucose level in the blood (DeFronzo et al 2004).

The type 1 diabetes mellitus was previously referred to as juvenile diabetes and insulin-dependent diabetes mellitus (IDDM) because it more often affects young people and also it requires insulin intake for its management. People with this condition are usually thin due to ketoacidosis, urinate frequently due to osmotic diuresis and also experience increased thirst due to dehydration. However, it will also be important to note that there may be the destruction of the beta cells with no evidence of autoimmunity, which sub-divides the type 1 diabetes mellitus into two categories namely, the Type 1A diabetes mellitus (which comes from autoimmune disease) and Type 1B diabetes mellitus (which comes with no evidence of autoimmune disease).

Section B

Polyuria and Lethargy are two symptoms associated with Type 1 Diabetes Mellitus. Describe these two signs/symptoms and explain the physiological changes that occur with each one.

Polyuria:

Polyuria which is one of the symptoms of type 1 diabetes mellitus is a condition whereby, there is an excessive formation of urine leading to its frequent passage (Porth and Matfin 2009). The formation of urine is the function of the kidney; this condition however, did not originate form the kidney, it will then be necessary to have a bit of knowledge regarding the expected functioning of the kidney, to understand the physiological changes in type 1 diabetes mellitus that leads to the kidney's excessive formation of urine.

The kidney, which has the function of urine formation leading to its excretion, has an estimated volume of urine which should be produced. This then brings the question: what could be regarded as an excessive urine formation and what leads to it? About 180 litres of blood-derived fluid is processed daily by the kidney and out of this amount, only about 1.5 to 2 litres of urine is formed, the rest returns to the body (Marieb and Hoehn 2007). This then suggests that the passage of urine of perhaps about 3 litres and above in a day, could be regarded as an excessive urination.

Polyuria occurs as a result of the elevated level of glucose in the blood, which increases the glucose level of the glomerular filtrate, leading to osmotic diuresis. This occurrence then hinders the re-absorption of water from the kidney tubules, leading to its retention and an enormous urine output. Type 1 diabetes mellitus therefore, should lead to polyuria because the elevated glucose level in the blood will lead to osmotic diuresis in the kidney and consequently, increase urine formation and excretion.

Lethargy:

Lethargy is also one of the symptoms which could be associated with type 1 diabetes mellitus. Lethargy is a state of drowsiness, which is usually as a result of mental or physical fatigue (Marieb and Hoehn 2007). An individual affected with this condition, is unlikely to function to the level of his/her normal ability. It will then be necessary to understand how type 1 diabetes mellitus brings about the physiological changes in the body, which exhibit this symptom.

Going back to the description on polyuria, bearing in mind the fact that type1 diabetes mellitus leads to excessive urination, this will subsequently lead to a reduction in blood volume due to the loss of water. The blood volume reduction will result to a reduced circulation of oxygen and glucose to the brain, organs and body muscles. The reduction of oxygen and glucose in circulation will then, reduce the body's metabolic activities and subsequently, lead to a low energy output. This low energy output is responsible for the low level of mental and physical performance, known as lethargy.