Salivary Secretion and Taste - Lab Report Example

Salivary Secretion & Taste One of the main functions of the tongue is to help in mixing the food with saliva. Saliva is a liquid substance secreted by salivary glands. There are three pairs of salivary glands in human beings (Pati et al., 2003). They open themselves in to mouth cavity by ducts. They are as follows: A pair of parotid glands situated in front of the base of the external ears. A pair of sub-maxillary or sub-mandibular glands situated at the base of the lower jaw, one on either side. A pair of sub-lingual glands situated in the lower part of the mouth, one on either side of the tongue. These are the smallest of the three types of salivary glands. The secretions of all salivary glands are collectively called saliva. The saliva contains an enzyme called salivary amylase or ptyalin that helps in breaking the starch to maltose, dextrin and limit destrin. However, the secretion of saliva is influenced by several factors. The differential rates of secretion rates of saliva were reported by some investigators (Marketta Hormia, 1993). It was reported that epidermal growth factors (EGF) of tongue influence the secretion rate. The elevated rate of salivary EGF secretion in juvenile periodontitis patients was found and was associated with the pathogenetic mechanisms of juvenile periodontitis. At the same time, the taste of any substance is decided by taste buds located on tongue. For example, the tip of tongue gives sweet taste, sides give sour taste, salty at edges near tip and bitter at distal end gives taste. Keeping these in view, the present experiment was conducted with the following objectives. Aim / Objectives To study and analyze the factors affecting the secretion of saliva at different times and To study the mechanism of the functional aspects of taste receptors in our mouth Methods As the saliva secretion is said to be influenced by chewing, acid and exercise, one male subject, who stood 5 foot 9 inches tall, was selected for the study and was tested under four different conditions. The saliva was collected from the subject during the times of rest, chewing water, chewing 1 crystal of citric acid and exercise. The saliva was collected in a beaker, and then this was transferred to a measuring cylinder, by a syringe, to measure how much saliva was collected. The way the measurement was taken was by measuring under the froth of the saliva was. In order to keep the accuracy of observations on actual quantity of saliva secreted, both the beaker and the measuring cylinder were cleaned using distilled water after the measurement was recorded so that no saliva was left in order for the next set of results to be accurate. Similarly, for the study of effect of taste receptors, eleven solutions (tap water, 2 % NaCl, 2 % KCl, 8 % Mg SO4, 0.01 % Quinine sulphate, 5 % sucrose, 5 % glucose, lemon juice, lemon juice in 5 % sucrose, phenyl thiourea) were tested on the same subject for evaluating their effect. The results were noted and analyzed with the help of a graph. Results Experiment on saliva secretion rate: The experimental results revealed that the secretion of saliva is regulated by salivary glands and they are in turn influenced by some external factors like chewing, acid treatment and exercise (Table 1). The saliva collected under different treatments were for either 4 minutes or 6 minutes and hence they were converted to secretion rate per unit time i.e. one hour. Rest 3.4ml x (60 /6) = 34ml/hr Chewing water As 1ml of water was used, 1ml was deducted to get correct result, hence: 4ml – 1ml of water = 3ml. 3ml x (60/4) = 45ml/hr Chewing a crystal of citric acid 8.2ml x (60/4) = 123ml/hr Exercise 1.5ml x (60/4) = 22.5ml/hr Table 1: The amount of saliva collected at different treatments State Saliva collected (ml) Saliva collected / hour (ml) Rate of increase over control (%) Rest 3.4 ml in 6 minutes 34 ---------- Chewing water 4 ml in 4 minutes* 45 32.2 Chewing a crystal of citric acid 8.2 ml in 4 minutes 123 261.7 Exercise 1.5 ml in 4 minutes 22.5 -33.8 * 1 ml of water was added and hence it was deleted for calculation purpose The effect of citric acid on secretion rate of saliva was found to be the highest compared to any other factor in the present experiment (Graph1). It is confirmed through 261 % enhancement in secretion rate of saliva relative to rest phase when the subject chewed the crystal of citric acid. The differential rates of salivary secretion with different chemicals was also reported by Aps and Martens (2005). Similarly, the chewing of water also enhanced the secretion rate of saliva by 32 % compared to resting period. However, the exercise has negative effect on the secretion rte of saliva. In the present experiment, the exercise has resulted in –33.8 % decrease in secretion rate when subject undergone exercise compared to that of control treatment (resting). Graph 1: Rate of salivary secretion as affected by different processes Experiment on taste receptors: The results revealed that tap water has no taste when used twice in the experiment. Similarly, phenyl thiourea also resulted in tastelessness (Table 2). Interestingly, 5 % glucose produced sweetness where as 5 % sucrose resulted in bitter taste. 8 % Mg So4 also gave bitter taste to subject. However the extent of bitterness was very high when 0.01 % quinine sulphate solution was tasted by the subject. Lemon juice (alone) and lemon juice in 5 % sucrose produced sour taste. 2 % KCl also resulted in sour taste where as 2 % NaCl resulted in saltiness along with sourness. Let us examine the taste transmission process. Taste buds are composed of groups of between 50 and 150 columnar taste receptor cells bundled together like a cluster of bananas. The taste receptor cells are present within a bud and are arranged such that their tips form a small taste pore, and through this pore extend microvilli from the taste cells. The microvilli of the taste cells contain taste receptors. Interwoven among the taste cells in a taste bud is a network of dendrites of sensory nerves called "taste nerves" (Figure 1). When taste cells are stimulated by binding of chemicals to their receptors, they depolarize and this depolarization is transmitted to the taste nerve fibers resulting in an action potential that is ultimately transmitted to the brain. One interesting aspect of this nerve transmission is that it rapidly adapts - after the initial stimulus, a strong discharge is seen in the taste nerve fibers but within a few seconds, that response diminishes to a steady-state level of much lower amplitude. Hence the different substances used in the experiment tasted differently. The taste and salivary secretion rate arte also interdependent. Once taste signals are transmitted to the brain, several efferent neural pathways are activated that are important to digestive function. Hence, tasting food is followed rapidly by increased salivation and by low level secretory activity in the stomach. At the same time, the extent of taste may vary with person. Therefre, among humans, there is substantial difference in taste sensitivity. Roughly one in four people is a "supertaster" that is several times more sensitive to bitter and other tastes than those that taste poorly. Such differences are heritable and reflect differences in the number of fungiform papillae and hence taste buds on the tongue. Similarly, the taste would be affected by sense of smell. For example, one may realize how tastes are blunted and sometimes different when our sense of smell is disrupted due to a cold. The concentration of substance also changes the extent of taste. Figure 1: Process of tranmission of taste from tongue to brain Table 2: The taste of different solutions used in the experiment S.No. Name of solution Taste 1 Tap water --------- 2 2 % NaCl Salty, sour 3 2 % KCl Sour 4 8 % Mg S04 Bitter 5 0.01 % Quinine sulphate Very bitter 6 Tap water --------- 7 5 % sucrose Bitter 8 5 % glucose Sweet 9 Lemon juice Sour 10 Lemon juice in 5 % sucrose Sour 11 Phenyl thiourea No taste Conclusion: The secretary rate of saliva is positively influenced by chewing with water and chewing with citric acid solution. However it is negatively influenced by exercise. Different substances taste differently and is also decided by the concentration of the substance. References: Aps, J.K.M. and Martens, L.C. 2005. Review: The physiology of saliva and transfer of drugs into saliva. Forensic science International. 150 (2-3): 119-131. Bowen, R. 2006. Physiology of taste. Pregastric digestion. http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html. Marketta Hormia, Irma Thesleff, Jaakko Perheentupa, Kristiina Pesonen and Leena Saxén. 1993. Increased rate of salivary epidermal growth factor secretion in patients with juvenile periodontitis. European Journal of Oral Sciences. 101 (3) : 138-144. Pati,S., Nanda,R.R. and Ghosh,K.K. 2003. Text book of Zoology. Kitab mahal publication. P: 772. ISBN-81-86472-09-6. Read More