What is homeostasis? (96 words)
Homeostasis is the process of maintaining internal equilibrium, regardless of external influences. Every internal process has a desirable environment, known as the norm, at which operations are carried out most effectively e.g. maintaining a temperature a constant core body temperature. Any deviation from the norm will be automatically corrected, this process is known as negative feedback e.g. a rise in blood pressure leads to a slow in heart rate. Each major organ within the body, plays a part in maintaining homeostasis e.g. the endocrine system excretes hormones rate regulate the level of glucose in the blood. (Biologyonline 2009)
Part 1- How is body temperature maintained including why this is necessary for the organism? (301 words)
When proteins are too far away from their optimum temperature they cease function. To combat this homeostasis uses a number of different functions to regulate temperature. Heat is sensed by thermo-regulators within the skin and the hypothalamus. Messages received from external thermo-regulators are sent to the cerebellum and then on to the hypothalamus. The role of the cerebellum is to activate voluntary behavioural responses, so that we make adaptations to change our body temperature e.g. taking off a layer of clothing if we are too hot or putting on a coat if we are too cold. However, this may not be enough for the body to become the right temperature, so internal steps must be used to compliment this process.
If the temperature gets to low we can develop hypothermia and eventually cells will freeze. To combat this vasoconstriction occurs at the skins capillaries, reducing the flow of cool blood back from the skin. This can be combined with shivering, as it forces the muscles to generate heat; heat is involuntarily produced as a waste product. The skins’ hairs becoming erect, which traps air between the hairs, this is done by the contraction of erector pili. As well as an increase in the metabolic rate of the body.
If the body gets too hot, vasodilation occurs at the capillaries near the skin; this increases the flow of warm blood to allow the outside temperature to cool it down, so that it is cooler when it heads back to the core. Alongside this, to cool the body down, sweating can also occur. The evaporation process draws heat away from the body via the skin. Erector pili relax, allowing heat out of the body more easily and the bodies’ metabolic rate reduces. If we remain too warm, the body will start to dehydrate. (Biologyonline 2009)
Part 2- Water is important for homeostasis, how are water levels maintained within the body and why is it important to do so? (298 words)
Water necessary in the distribution of nutrients and oxygen around the body, it also carries away waste products. Water primarily enters the body through ingested liquids, however, some is through food sources and some is from metabolic processes. The output of water should be the same as the input, when we require water, the brain sends a message to the thirst reflex, which stimulates us to voluntarily drink. This reflex is stimulated in a number of ways; the level of saliva drops, there is an increase in the osmotic pressure which leads to stimulation of the hypothalamus via osmoreceptors and blood volume drops which also stimulates the hypothalamus. Water is stored in the body in two ways; intracellular fluid is the liquid found within a cell and extracellular fluid, which relates to the fluid found outside of the cell. Through the process of osmoregulation, water can pass through the semi-permeable cell membrane, to the area of highest concentration. The body also uses Active transport, to allow the liver to keep hold of important substances, such as glucose and ions.
If the solution outside of the cell becomes hypertonic, water will leave the cell. In the case of red blood cells, this can cause the cell to shrink and lose its hope, rendering it no longer able to carry oxygen around the body.
The kidneys are involved in removing waste products from the body and keeping the water and ion concentration within the blood. Water regulation is controlled by an Anti-Diuretic Hormone (ADH). Through a process of negative feedback, the body controls how much ADH is in the blood, this hormone encourages the reuptake of water within the blood, until levels are balanced. If the kidneys stop working, waste products within the body can build up and eventually kill a person. (Biologyonline 2009)
Part 3- Insulin and Glucagon are homeostatic hormones, how is this the case and why are they necessary? (400 words)
Blood glucose levels are vital to the effective functioning of a cell and is a source of immediate energy. It enters the body through external functions and is then regulated by internal ones. Through a negative feedback system, Insulin and Glucagon are released in to the blood according to the levels of glucose.
The endocrine system, helps to control and coordinate bodily functions, by using hormones, in an attempt to maintain homeostasis. It is made up of 9 major glands spread throughout the body. Insulin and glucagon are secreted by the endocrine pancreas, they are essential components in regulating blood glucose levels within a set range.
Whilst a low level of insulin is always secreted, after food sources are ingested, the levels of insulin within the blood increase, to combat the rise in blood sugar. In response to these increased levels of insulin; cells take the glucose from the blood, cells are more effective in using glucose as an energy source, it speeds up the formation of glycogen and it stimulates fat synthesis. All of these actions help to bring glucose levels back down to the desired levels.
Glucagon is secreted only in to the blood stream when blood glucose levels are low, this normally occurs between meals and during exercise. It essentially causes; the liver to release its stored glucose in to the blood, an increase in the breakdown of fats to fatty acids for use as energy and it stimulates glucose synthesis in the liver. All of these actions help to bring glucose levels back up to the desired levels.
If the systems fail to regulate themselves, the body can develop one of two types of Diabetes. Type 1 is a disease where the immune system attacks and destroys the pancreatic cells that produce insulin. Without insulin, glucose levels will remain dangerously high; this glucose will be lost in urine, as well as a high amount of water, which will eventually lead to dehydration, over long periods of time damage may be caused to; nerves, body tissue, kidneys and the cardiovascular system. People with Type 2 Diabetes have persistent hyperglycaemia, this is due to cells being insulin resistant. This reduced sensitivity stops the body from realising that it doesn’t need any more glucose. (Biology Reference 2001)
Part 2- For each of the subdivisions you have labelled above, explain their functions within the nervous system and in the case of certain answers their relationship to each other. (193 words)
The brain is made up by a number of important areas. Each of these areas control different systems within the body e.g. the visual cortex deal with vision and the cerebellum control voluntary movement. The main route for the brain to send messages to the peripheral nervous system is through the spinal cord. The peripheral nervous system is made of up two main systems; the Somatic system and the autonomic system.
The somatic system is involved in voluntary actions, such as lifting things up. Impulses are sent to whichever muscle and set of nerves is required for the chosen movement. It is controlled by the cerebellum.
This Autonomic System mainly deals with control systems. It is a self-regulating system that brings around change through neural stimulation or by releasing hormones from the endocrine glands. This is controlled in the brain by the Hypothalamus. The ANS is made up of two systems; the sympathetic system which is involved in the involuntary adjustments the body has to make in reaction to danger or its need for an increase in energy and the parasympathetic system is involved in building up the bodies’ resources for dangerous times. (Biology Guide n.d.)
Both play a big role in homeostasis
Both use chemical messengers to transmit messages; some chemicals affect both systems e.g. dopamine
The systems help to regulate one another
Both use negative feedback systems
Regulation for both system occurs due to the hypothalamus and pituitary gland
They both effect body functions; the nervous system causes us to breathe and the endocrine system helps us to metabolise the oxygen
The Hypothalamus controls some of the chemicals both systems require
Reactions can take anything from minutes to weeks to occur
Reactions to stimuli occur immediately
Reactions tend to be long lasting
Reactions tend to be short term
Any cell within the body can be targeted, potentially causing widespread effects
Specific areas are targeted, creating specific and local effects
Responses occur involuntarily within the body
Responses are external- motor control
The hormones gain response by first being created, they then travel though the blood until they reach their target cell where they enter or signal the cell
Neurons carry neurotransmitters to the stimuli, where response occurs rapidly
Glands, from different locations around the body secrete the hormones
Messages are sent from the central nervous system
Discuss the similarities between the endocrine system and the nervous system as well as the differences. (191 words)
Explain the relationship between structure and function of the excretory system and what structures do they have to carry out this role, use annotated diagrams as part of your answer. (305 words)
The function of the excretory system is to remove waste from the body. There are a number of specialised organs that assist this process with the help of connecting networks.
The liver essentially breaks gown toxic chemicals and poisons that enter the body. When protein is metabolised to produce ATP, it produces a by-product called ammonia, which is toxic to the body. To combat this, the liver turns ammonia in to urea, which is a less toxic chemical. Urea is then transported via the bloodstream to the kidneys where it can be expelled. When we eat, the liver releases bile in to the intestines, to break down the food products in to unusable waste and fat. The intestines absorb these by-products in to the blood stream and what is transported back in to the liver. The liver then removes these waste products and passes them on to the kidneys.
Blood enters the kidneys through the renal arteries, to be filtered by nephrons. The structure is broken up in to; the Bowman’s capsule, the proximal tubule, the loop of Henle, the distal tubule and the collecting duct.
Blood passes through the glomerulus within the Bowman’s capsule. Plasma then moves into the proximal tubule, where useable materials are retrieved and sent back in to the bloody via active transport. The blood then moves in to the distal tubule, where more useable materials are retrieved and sent back in to the blood stream. The fluid that is left is moved in to the collecting duct and this is known as urine, it is made up of; water, salts, organic compounds, uric acid and urea. Urine is then, carried by ureters and expelled from the body via the bladder. The bladder stores urine until it is full, then a message is sent from the brain telling us to urinate. (Cliffs Notes n.d.)
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Anon. (n.d.). The Important Role of Insulin and Glucagon in Maintaining Homeostasis. Available: http://biomed.brown.edu/Courses/BI108/BI108_2002_Groups/pancstems/stemcell/insulin_glucagon.htm. Last accessed 14th April 2015.
Anon. (n.d.). Homeostasis of Glucose Levels: Hormonal Control and Diabetes. Available: http://study.com/academy/lesson/homeostasis-glucose-levels-and-osmolarity-hormonal-control.html. Last accessed 14th April 2015.
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Aspirin: Mechanisms of Action, Absorption and Elimination
Today, there are many medicines used to treat human diseases and one of the medicines is called Bayer aspirin. Aspirin (acetylsalicylic acid) is a white or colourless crystalline powder. Anthony (2002). It is used to treat mainly minor pains, but has their benefits like lowering fever, inflammation, and reduces blood from clotting. The trade name of aspirin is Bayer and the chemical name is acetylsalicylic acid. The manufacture name is time cap laboratories Inc that produces aspirin. Bayer aspirin contains both active and inactive ingredients. In each tablet the active ingredient is acetylsalicylic acid. Other than the active ingredients other components are the inactive ingredient. Now I will be mentioning the absorption, mode of administration, mechanism of action and the elimination of aspirin.
Both carboxylic acid and ester doesn’t reacts with phenol. Aspirin has the chemical formula of C9H8O4.
Absorption A drug wouldn’t be effective if the human body doesn’t breakdown and absorb the drug easily. When the aspirin enters the stomach some of it absorbs within the stomach as the aspirin is acetylsalicylic acid and the stomach contains acid. Anthony (2002). In the stomach (pH 2) the hydrolysis rate is lower than at pH 9-11 that is found in the upper G.I tract as the rate goes up significantly. Not all aspirin is absorbed in the stomach as it is a weak acid, but most of the absorption occurs in the upper part of the small intestine by passive diffusion. Aschenbrenner and Samantha (2009). The reason that less absorption occurs in the stomach is due to the surface area of the mucosa in the stomach and the coating layer that is on the tablet. Rainsford (2004). In the stomach about 24% of aspirin is ionised. About 10 minutes and after in the stomach the mass of the aspirin roughly about 12% is absorbed from a solution that is un-buffered. Cooke and Hunt. (1970). If the pH of gastric has risen up to pH 6 there would be a decrease about 1% of the area of absorption as the majority of aspirin would then be in a less permeable ionised form. Slower gastric absorption which is due to increased pH isn’t reflected in the overall slower absorption. This is because the solution that is buffered is rapidly removed into the upper part of the gastrointestinal tract and here the rate of absorption is fast. Dotevall and Ekenved (1976). The rate of absorption of aspirin salts is quick in a man on an empty stomach having a half life of absorption about 5-16 minutes. Rowland et al. (1972).
In the small intestine the aspirin solubility is improved, where the lower down you go through the small intestine the higher or increased the pH will be and by having a large surface area the absorption of aspirin would be increased. Karsten (2009). About 70% of the unchanged aspirin is absorbed in both stomach and in the upper intestine with 30% of salicylate. Quinn (2008). Also the skin can absorb aspirin, but it would be a slow process, but can be beneficial when treating herpeszoster. Rougier et al. (1987). Normally about 30 minutes he absorption of aspirin takes places, but there are many factors that can affect the absorption of aspirin like pH of gastrointestinal (GI) lumens, time of intestinal transit, the time of, taken with food and gastric emptying. Ling et al. (2001) and Aschenbrenner and Samantha (2009). There are also factors that can reduce gastric empting like having a meal that has high fat and having drinks that are acid. To maximize the absorption rate aspirin should be taken on an empty stomach with enough cold water. Williams and Schleader (2003). However it is not recommended to take aspirin with alcohol as it will increase the effect of alcohol. Caffeine increases the pain relief effect of aspirin.
Distribution After the uptake of aspirin from the G.I tract it goes into the portal venous system that enters the first pass, which is the liver, where drug metabolism occurs. Part of the aspirin is hydrolyzed into saclicylate by action of carboxylesterases. Rainsford (2004). Aspirin is distributed throughout the body, which may last about 15 to 20 min. Quinn (2008). Aspirin has a molecular weight of 180.15, which is low. Rainsford (2004). This makes aspirin easier to leave the bloodstream and enter the capillaries. Page et al. (2006). The lipid solubility of a drug can effect the diffusion that will occur across the membrane. Aspirin is quite lipid soluble having a log P value, which is 1.19. Salicyclic acid on the other hand is more soluble in lipid and will have a quite high distribution It has a log P value of 2.26. Drayton (1990). Also it is non-ionized, so it can pass through the lipid membrane of the cell. King and Mary (2009). Aspirin bounds to a plasma protein like albumin through reversibly and irreversible. Rainsford (2004). 50% of aspirin is bounded to plasma protein. Anthony (2002). An acetyl group is joined to the plasma protein when binding irreversible. Acetylsalicylic acid has an half life of 15 minutes, but it is longer for salicylate that has a half life of 2 hours. Aschenbrenner and Samantha (2009).
Mode of administration Drugs are available in different forms. Before aspirin tablets were available the first aspirin was in the form of a power. In 1915 aspirin was no longer in powder form, but now produced in tablet form that was white in appearance and round shaped. Ament (2007). At that time prescription weren’t needed if someone wanted aspirin. Later in 1952 a chewable aspirin was now available making it easier for children to take the drug or haven’t learnt to swallow yet. Ament (2007). There are other advantages like it can be taken with water, the stability is better and portability and palatability. The mode of administration was taken further as toleraid was added to aspirin. This is a thin coating of aspirin tablets or to granules that makes the tablet easier to consume. Rainsford (2004). Today Bayer aspirin are in the form of tablets that are taken orally.
Tablets contain drugs that are mixed with excipients, which are inactive substance that carrier the active ingredients of the drug. Enteric coating is added to Bayer aspirin as this will hold the aspirin together when it in the stomach, but dissolves when it reaches the intestine. King and Mary (2009). This reduces stomach irritation and prevents the enzymes and acid in the stomach to reduce the effectiveness of the drug. Rainsford (2004). This is why aspirin tablets aren’t scored meaning that there isn’t a thin line in the middle of the tablet, so it can be halved. It should also not be crushed or chewed, but the whole of the tablet should be swallowed with water. Enteric coating doesn’t break down at low pH, but will dissolve at higher pH that is found in the intestine. Due to this it would take longer for the aspirin to be absorbed. Tablets are relatively slow compared to liquid and powder forms of drug and take about 1-3 hours delay before effect can take place. Also the drug hasn’t got an unpleasant taste making it easier for people to get it. There are also micro fined aspirin that is absorbed ever more quickly.
When taking the aspirin e.g. aspirin regimen Bayer it is recommended for adults and children over the age of 12 to take 1-2 caplets every 4 hours with full glass of water. Also 3 caplets can be taken, but for every 6 hours. During the 24 hours an individual shouldn’t take more than 12 caplets. A doctor should be consulted before giving aspirin to children under the age of 12, pregnant or breast-feeding. The carton should be kept, so directions and warnings of aspirin can be known and should be store at room temperature.
Mechanism of action One of the benefits of aspirin is that it can reduce the risk of having cardiovascular diseases. When aspirin is in the body it targets the enzyme cyclooxygenase, where it irreversibly prevents the inactivating platelet cyclo-oxygenase. There are two types of cyclooxygenase; COX-1 and COX-2. COX-1 is found in many cells and COX-2 is in places of inflammation. Anthony (2002). Platelets in the human body give out COX-1 and not COX-2. Platelets are found in the blood and are involved it blood clot. When aspirin is present it stops arachidonic acid being converted to prostaglandin H2 and reduces TXA2 from being produced. Anthony (2002). The aspirin effect last for 5 to 7 days, which is the life of the platelets. King and Mary (2009). Platelets can still stimulate through ADP, thrombin and epinephrine. Page et al. (2006). In endothelial cell the platelets inhibitor PGI2 is also block by aspirin.
When there isn’t aspirin in the body this makes the enzyme cyclooxygenase easier to convent arachidonic acid to thromboxane A2. This diffuses across the platelet membrane that then binds to the receptor onto another platelet. King and Mary (2009). This cause the platelets to stick together in the wall of the artery and as they slowly build up in the artery of the heart or the brain, therefore increasing the risk of arterial thrombotic disorders.
Mechanism of action. Platelet cyclooxygenase is inhibited by aspirin, therefore less production of TXA2. Activation and aggregation of platelets occurs when thromboxane A2 starts reactions. Acetylsalicylic acid works as a strong anti-platelet agent and the aspirin effects lasts the life of the platelets, which is about 5 to 7 days.
Elimination Metabolism and excretion are the process that takes place to eliminate drug. Page et al. (2006). Aspirin forms polar metabolites in the liver as it is quickly glucuronidated. Anthony (2002). Part of the aspirin is hydrolyzed into saclicylate by action of carboxylesterases in the liver. Rainsford (2004). Before aspirin is converted to salicylate it goes through enzymatic and spontaneous hydrolysis. However, in the body the spontaneous hydrolysis has little or no importance as this can be seen by the half life of 15.5 hours in buffered saline. Rowland et al., (1972). There should be a slight different in the half life in any point inside 1.2-8.0 Ph range. (Edwards 1952). In tissue like the G.I tract, kidney, liver, blood and hind limbs the enzymatic hydrolysis of acetylsalicylic acid happens. (Cossum et al., 1986) and (gaspari et al., 1989). In human plasma the cholinesterases, which is a main enzymes may hydrolyses acetylsalicylic acid. Rainsford et al., (1980). In proteins especially albumin an acety group is introduced by aspirin and therefore let go of salicylate. Rainsford et al., (1980). The thermal breakdown of acetylsalicylic acid will form acetyl-salicylsalicylic acid, salicylsalicylic acid and cyclic polymers of the salicylic acid as well as salicylic and acetic acids. Rainsford (2004).
Acetylsalicylic acid is excreted by the body in the kidney in the form of urine. Renal excretion of aspirin involves filtration that happens in glomerulus of the kidney, reabsorption and secretion along the nephron. Page et al. (2006). Passive diffusion and carrier mediated of un-ionised species takes place in the proximal tube There will be small quantity of unaffected aspirin in urine due to quick hydrolysis, but >98% happens fully as salicylic acid and its metabolites. The metabolites are gentritic acid, which is about 10%, salicylic acid (10%) and 5-10% of salicylic acid glucuronides. Rainsford (2004). There are factors that control the elimination of salicylate like urinary pH, corticosteroids, circadian pattern and age. However, one factor that may affect the elimination of aspirin is sex. Once aspirin has been in the body for some time there has been lower plasma concentration of the unaffected aspirin in males. Rainsford (2004).
Conclusion As we came to know more about aspirin over the years we understand what happens to aspirin when it enters in human body and how it is removed. There is clear advantage of the use of excipients and when aiding the absorption rate certain factors should be avoided. There is still more to explore from aspirin. Since aspirin is absorbed from the skin aspirin patch preparation may be produced in the future that could be placed on the skin. This may help to ease the pain of shingles. Also aspirin could help individual who have Alzheimer’s disease, but further trials are being performed. WF et al. (1997).