EXPERIMENT NO. 12
DIGESTION IN THE STOMACH
ABSTRACT____________________________________________________________________________ Digestion refers to the mechanical and chemical breakdown of food into smaller components that can undergo absorption. The objective of this experiment is to investigate mainly the process of digestion in the stomach. The conditions at which the enzymes responsible for the digestion process were determined. Also, the total and free acidity of gastric juice of the sample were calculated. The procedure was divided into three main parts: (1) peptic digestion, (2) rennin test and (3) gastric analysis. Separate preparations were made in each part. In analysis of peptide digestion, determination of the presence of polypeptide chains and the extent of digestion through the hard-boiled egg white was performed. All of the test tubes were positive for Biuret test which indicates presence of polypeptide chains while for the rennin test, curd formations were observed in test tubes 3 and 4 only. In gastric analysis, the values for free acidity and total acidity were computed. The free acidity is 20.83 N NaOH/ 100 ml sample while the total acidity is 20.0 N NaOH /100 ml sample. Lactic test was also performed in in relation with the gastric analysis. Addition of gastric juice to FeCl2 was done to determine the presence of lactic acid, in which a distinct canary yellow color gives a positive result for the test. The colors obtained were dark yellow (gastric juice) and pale yellow (FeCl3) which indicates a positive result. Though the values gathered were acceptable, errors were inevitable. Inaccuracy in burette reading may be the most contributing factor of the errors obtained (in gastric analysis). Errors due to the experimenter’s skills and techniques in performing were taken into consideration based on the values acquired.
DISCUSSION OF DATA AND RESULTS______________________________________________________
The stomach is a saclike portion of the digestive tract. Its inner surface is highly convoluted, enabling it to fold up when empty and open out like an expanding balloon as it fills with food. The stomach of carnivorous and omnivorous vertebrates is typically a U-shaped muscular tube provided with glands that produce a proteolytic enzyme and a strong acid. The latter is an adaptation that probably arose for killing prey and checking bacterial activity (Hickman et. al, 1993).
The stomach contains an extra layer of smooth muscle for churning food and mixing it with gastric juice, an acidic secretion of the tubular gastric glands of the mucosa. These exocrine glands contain two kinds of secretory cells: parietal cell, which secret HCl, and chief cells, which secrete pepsinogen, a weak protease (protein-digesting enzyme) which requires a very low pH to be active. This low pH is provided by the HCl. Specific sites, producing a much more active protease, pepsin. This process of secreting a relatively inactive enzyme that is then converted into a more active enzyme outside the cell prevents the chief cells from digesting themselves (Raven et. al, 2005).
Pepsin is a protease (protein-splitting enzyme) that acts only in an acid medium – pH 1.6 to 2.4. The combination of pepsin and hydrochloric acid begins the complex process of protein. It is a highly specific enzyme that splits large proteins by preferentially breaking down certain peptide bonds scattered along the peptide chain of the protein molecule. Although pepsin, because of its specificity, cannot completely degrade proteins, it effectively breaks them up into a number of small polypeptides. Protein digestion is completed in the intestine by other proteases that can together split all peptide bonds. Pepsin is present in the stomachs of nearly all vertebrates’ digestion (Miller & Levine, 2003).
Rennin (not to be confused with rennin, an enzyme produced by the kidney) is a milk-curdling enzyme found in the stomach of ruminant mammals and...
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