Saliva is secreted by the salivary glands which is an exocrine gland. There are three types of salivary glands, mainly parotids, submandibulars and sublinguals glands. There are also the presences of hundreds of minor salivary glands around the mouth cavity.
Acini which is a cluster of cells found inside the salivary glands will secrete a fluid containing enzyme, water, electrolytes and mucus. Saliva contains the enzyme, lysozyme which is use to breakdown microbes. Salivary amylase is use to convert complex carbohydrates into disaccharides. The autonomic nervous system controls the saliva secretion in terms of volume and types (serous or mucous). The autonomic nervous system is divided into two groups mainly the parasympathetic and sympathetic innervations. In addition, external stimuli can also affect the secretion of saliva such as presence of food, exercising, irritating substances in the mouth. This is because secretion of saliva is controlled by the brain.
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Taste
Taste is one of the five senses which is used to detect the flavor of the food. There are four types of basic tastes on the tongue which are sweet, bitter, salty and sour. All the basic tastes are localized at a specific area on the tongue. Taste is received through the sensory organ which is the taste bud which has the different receptors such as ion channels for the sour and salty taste and G protein coupled receptors which is the sweet and bitter taste. These taste receptor cells are grouped in clusters known as the taste buds. The taste receptor cells in a bud are arranged in a way that the taste pore is situated near the oral cavity.
Aims of the experiment
One of the aims of the experiment is to find out the different factors that will help in increasing or decreasing salivary secretion. The other aim is to find out the location and functions of the different quantities of taste (Sour, Bitter, Sweet and Salty) on the taste buds.
Method
Please refer to the Laboratory Manual unless otherwise stated of changes made.
Results from the experiment on salivary secretion
Overview of results
1. Chewing Movement
Increased in chewing movement will increase the saliva secretion rate.
2. Acid Substance
Increased in acidity of the substance will increase the saliva secretion rate.
3. Exercising
Increased in exercising will decrease the saliva secretion rate.
Table 1: Results of the salivary secretion rate of my group
Resting Rate
12ml/h
Rate during chewing
22ml/h
Rate following application of acid substance
63ml/h
Rate during exercise
9ml/h
Table 2: Results of the mean salivary secretion rate of the class
Resting Rate
(37+29+20+12+13)/5 = 22.2ml/h
Rate during chewing
(57+45+30+22+30)/5 = 36.8ml/h
Rate following application of acid substance
(91.5+90+90+63+90)/5 = 66.9ml/h
Rate during exercise
(33+22.5+18+9+3) = 17.1ml/h
Table 3: Results of the standard deviation of the saliva secretion rate
Resting Rate
10.71
Rate during chewing
14.02
Rate following application of acid substance
23.56
Rate during exercise
11.70
Discussion
Resting secretion is to constantly allow the saliva to come in contact with the oral tissues so that it can aids as a lubricant to prevent the oral cavity from drying up. Hence, protecting against the oral cavity from thermal, mechanical and chemical irritation. It can also help in speech and swallowing. In addition, the resting secretion maintains the oral microflora at a safe level by different mechanisms. Therefore, it is important to have saliva secreting even during resting as it acts as the first line of defense of the immune system. 70% of the saliva is produced by the submandibular glands and 20% from parotid glands.
The chewing movement is a stimuli for the salivary glands to secrete more saliva and thus, resulting in more saliva secretion than the resting rate in Table 1 and 2. The action of chewing will compresses the teeth into the peridodontal ligament in which the mechanoreceptor is found there. Hence, this will activates the mechanoreceptors which will bring the impulses to the salivation center in the brain by the trigeminal nerve. As a result of the sensory input, the parasympathetic fibers will then bring the response to the salivary glands which mainly the parotid glands. Since parotid glands produce saliva which is serous, it can easily digest the food being chewed as it contains digestive enzymes such as amylase, maltase and lysozyme. Apart from digestion of starch to disaccharides, the presence of lysozyme also helps in the killing of bacteria which enters the mouth, hence, increasing the immune system of the individual.
The rate after acid application shows a significant increase in both Table 1 and 2 because more saliva secretion is produced to increase the pH value in the oral cavity due to acid substances. Since saliva contains hydrogen bicarbonate which is alkaline in nature, it can help in increasing the pH value of the acidity of the lemon juice. In addition to that, the action of chewing also help in stimulating more saliva. Since the normal taste of lemon juice is sour, there will be depolarization of the receptor potential and generation of action potentials. Thus, leading to the release of neurotransmitters, acetylcholine. This acetylcholine will then activates the nerve fibers which bring the taste impulses to the brain by the parasympathetic nerve. The parasympathetic fibers will then bring the response to the salivary glands to produce bicarbonate ions. With acid stimulation, both the submandibular and parotids gland produce 45% each out of the total saliva content.
The rate of salivary secretion during exercising is lower as compared to the resting rate. This is because during exercise, there is a need for more blood to transport the oxygenated red blood cells to the different tissues such as muscle tissue. Therefore, the sympathetic autonomic nerve system will increased which will cause a deviation of blood flow from several organs such as salivary glands to the muscle tissue. Therefore, due to this sympathetic stimulation, the salivary volume output decreased.
In addition to table 1 and 2, the standard deviation was also calculated in table 3. The higher the deviation number is, it means that the salivary secretion rate for our group differs a lot as compared to result of the class mean. For resting rate, chewing and exercising rate, the standard deviation is about the same. This could be due to the fact that salivary secretions differ due to external factors such as gender. Male have a higher saliva secretion rate as compared to female. Also, this may be due to the fact that our group did not follow the instructions on the module handbook properly, for example, our group did not undergo vigorous exercise as compared to the rest of the group. For the acid substance application, there is a bigger deviation from our group to the class mean, this is because for our group, we did not undergo vigorous chewing which resulted in lesser amount of saliva produced.
Results from the experiment on taste
Table 4: The sensation, intensity and location of the respective solution
Solution
Sensation (Intensity)
Location
1
No sensation
–
2
Salty (3)
Back and side
3
Bitter (2)
Salty (2)
Bitter at the back
Salty at the side and tip
4
Bitter (4-5)
Side and tip
More intensity at the back
5
Bitter (5)
Side and tip
More intensity at the back
6
No sensation
–
7
Sweet (3)
Back, tip and side
8
Sweet (2)
Back, tip and side
9
Sour (5)
Back and side
10
Sweet (3)
Sour (3)
Sweet at the tip
Sour at the side and back
11
Sour (5)
Back, tip and side
Legend:
The lowest intensity is 1
The highest intensity is 5
Solution 1
From table 4, there is that no taste is perceive on the different location (back, tip and side) of the tongue. The actual composition is water. Therefore, the result is matching.
Solution 2
From table 4, the salty taste is perceive at the side and the back of the tongue. The actual composition is 2% sodium chloride which has the normal salty taste as they are often use as common/table salt. Therefore, the result is matching.
Solution 3
From table 4, the bitter taste is perceive at the back of the tongue while the salty taste is perceive at the side of the tongue. The intensity for both tastes are the same. The actual composition is 2% potassium chloride which has the normal taste of both salty and bitter. Therefore, the result is matching.
Solution 4
From table 4, the bitter taste is perceive at the back and side of tongue. However, the intensity of the bitter taste is higher at the back of the tongue. The normal taste of the 8% Epsom salt is bitter which corresponded with our results.
Solution 5
From table 4, the bitter taste is perceive at the back and side of tongue. However, the intensity of the bitter taste is higher at the back of the tongue. The normal taste of the 2% coffee is bitter which matched with our results.
Solution 6
From table 4, no taste is perceive on the different location (back, tip and side) of the tongue. The actual composition is tap water. Therefore, the result is matching.
Solution 7
From table 4, the sweetness is perceived at the different locations on the tongue. The actual composition is sucrose which has the normal taste of sweetness. Hence, the result is matching.
Solution 8
From table 4, the sweetness is perceived at the different locations of the tongue. The actual composition is glucose which has the normal taste of sweetness. Hence, the result is matching.
Solution 9
From table 4, the sour taste is perceive at the back and side of the tongue. The actual composition is lemon juice which has the normal taste of sourness which corresponded with our results.
Solution 10
From table 4, the sour taste is perceive at the back and side of the tongue while the sweet taste is perceive at the tip of the tongue. The actual composition 5% sucrose in lemon juice which has both the sweet and sour taste. Hence, the result is matching.
Solution 11
From table 4, the sour taste is perceive at the different locations on the tongue because the intensity of the taste is very high. The actual composition is 1% tartaric acid which has very sour taste. Hence, the result is matching.
Discussion
For solution 2 and 3, the intensity of saltiness is higher in solution 2 than 3. For solution 2 which is sodium chloride, it is commonly known as table salt which has the normal taste of saltiness. However, for solution 3 which is potassium chloride, there is the taste of both bitter and salty, hence bringing the intensity of the saltiness below than that of sodium chloride.
For solution 7 and 8, the intensity of sweetness is higher in solution 7 as compared to solution 8. Sucrose is a disaccharides from is formed from glucose and fructose. Therefore, sucrose which is solution 7 is much sweeter as compared to glucose which is a monosaccharide.
For this experiment, the intensity of different sensation/taste is subjective. Different people have different sensitivity to the different taste. Some of us might be more prone to sour stuffs. Therefore, for better accuracy, it is better to let the same individual to try the different range of sensation such as sweetness instead of each individual trying one of the solutions.
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Also, there are some taste perceived at the different locations of the tongue (Back, Side and Tip) which does not correspond to the normal “taste mapâ€Â that everyone knows in Figure 4 . This is because different taste buds are more receptive to specific sensation. For example, that taste bud at the tip of the tongue is more sensitive to sweet flavours, however, sour taste can also be detected.
Question 1
The control of salivary secretion is though the autonomic nerves system which is further divided into two groups, the parasympathetic and sympathetic nervous. The different neurotransmitters and hormones will activate the different receptors on the different salivary glands, hence, producing different types of saliva (Mucous or Serous).
During the presence of stimuli such as food in the mouth or the anticipation of food and the mechanical breakdown of food (chewing), impulses will be send to the salivation centre in the brain by the afferent nerve. In parasympathetic nervous system, impulses will be send to the salivary glands by the cranial nerve which is nerves that emerge directly from the brain stem. In the control of the saliva secretion, there are two types of cranial nerves which is the glossopharyngeal nerve (CN IX) and the facial nerve (CN VII). The glossopharyngeal nerve will supply the parasympathetic impulses to the parotid gland via the otic ganglion. On the other hand, the faical nerve will supply the parasympathetic impulses to the submandibular and sublingual glands by the submandibular ganglion. These nerves will release the neurotransmitter, acetylcholine which will bind to the receptor on the different salivary glands to secrete the type of saliva needed which is normally serous.
On the other hand, in the sympathetic nervous system, the nerve involved in the stimulation of th salivary secretion is the preganglionic nerve which is found on the thoracic segments T1-T3. Norepinephrine will be released which will then activate the acinar and duct cells in the salivary glands. Therefore, this will help in the production of the saliva secretion in the respective salivary glands. In addition, the sympathetic nervous system can affects the production of the amount of salivary glands by sending impulses to the blood vessels that supply the salivary glands. If vasoconstriction of the blood vessels is present, there will be a decrease in salivary secretion and vice versa.
In the control of pancreatic secretion, it is controlled by both hormonal (predominantly) and nervous system. The vagus nerve will send impulses to the pancreas which will produce a small amount of secretion in response to anticipation of a meal. However, the hormonal regulation is the main stimuli of the pancreas. There are two hormones involved which are the secretin and cholecystokinin. The secretion of pancreatic juice is triggered by the chyme which enters into the small intestine from the stomach after digestion in the stomach. This chyme is very high in acid content in which it must be neutralised in the duodenum before proceeding further into the small intestine. Therefore, pancreatic juice which is alkaline in nature will be able to increase the pH value.
When the chyme enters the duodenum, secretin will be secreted in the response to the high pH value in the duodenum. Secretin will be release by the cytoplasmic secretory granules of S-cells in the duodenal mucosa. Secretin will activate the acini duct to release the bi-carbonate rich fluid from the pancreas.
On the hand, cholecystokinin (CCK) will be secreted in response when they chyme which enters the duodenum has the presence of peptides and fats. CCK will stimulate the acinar cells in the pancreas to release enzyme rich fluid so as to digest the fat, proteins and carbohydrates. CCK will also inhibit the gastric emptying phase in stomach digestion so that the small intestine can digest the fats effectively. When the level of the peptides and fats concentration decreases, the release of CCK will also decreases.
Question 2
Taste buds are structures that are found around the oral cavity such as tongue, soft palate, upper esophagus and epiglottis. Taste buds enable individual to know the taste of the food that they eat. Each taste bud contains 50 to 80 taste receptor cells in which they are bundled together to form the taste pores whereby the food which is digested by the saliva will come into contact with the taste receptors. When food enters, the taste receptor cells will receive the information and send them to the brain by the seventh, ninth and tenth cranial nerves. The seventh cranial nerve is the facial nerve which will receive the special sense of taste from the anterior of the tongue and send impulses to the pons of the brain stem. The ninth cranial nerve is the glossopharyngeal nerve which will receive taste from the posterior side of the tongue and send impulses to the medulla of the brain stem. Lastly, the tenth cranial nerve which is the vagus nerve which will receive the taste from the epiglottis and send impulses to the posterolateral sulcus of medulla.
Conclusion
Saliva is the first digestion process of the whole digestive system which is important as it facilitates the efficiency of the digestion in the later part because in the mouth, mechanical and chemical digestions occurs. Mechanical digestion not only stimulate chemical digestion but also help to break down the food into smaller pieces for easy digestion. Furthermore, the taste buds found on the tongue help to differentiate the different tastes which enhances the whole process of eating.
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