GENBIO2 Lab Module 7 Worksheet PDF

Page 1 of 6 The digestive system is concerned with the conversion of food into basic nutrients for energy, growth, development, and repair. It is involved in the (1) ingestion of food,...

Page 1 of 6 The digestive system is concerned with the conversion of food into basic nutrients for energy, growth, development, and repair. It is involved in the (1) ingestion of food, (2) physical and chemical digestion of food, (3) absorption of nutrient molecules, and (4) elimination of undigested remains. MODULE The system includes the digestive tract or alimentary 7 canal and the accessory organs. The tract includes the mouth, oral or buccal cavity, pharynx, esophagus, stomach, small intestine, large intestine, and anus/cloaca. The accessory organs are the teeth, PART A tongue, salivary glands, liver, gall bladder, and pancreas. They aid in the digestion process. DIGESTIVE Objectives SYSTEM At the end of the activity, the student should be able to: 1. Identify the sections of the digestive tract. 2. Identify the accessory organs and structures necessary in the process of digestion. Materials Preserved toad Dissecting pan Dissecting materials Procedure Gross Anatomy of the Digestive Tract 1. Get a preserve toad and a dissecting tray/pan. 2. With a probe, pry open the mouth and cut the angle of the jaw. 3. The buccal cavity or the mouth will be studied first.  Page 2 of 6 a. The skin folds in the margin of the upper jaw and lower jaw are called upper and lower lip folds, respectively. b. Feel the margin of the upper jaw. The row of small teeth located along the margin is the maxillary teeth. Another set of teeth is found on the roof of the mouth. These are the vomerine teeth. c. Insert the probe into the external nares and trace the canal into the roof of the mouth cavity. These antero-lateral openings are the internal nares. d. Note the bulging regions at the posterior half of the roof of mouth. These are the eyeball prominences. On the posterolateral side of the eyeballs, medial to the angles of the jaw is a pair of openings, the openings of the Eustachian tube. Where do these openings lead to? e. The tongue is attached to the floor of the mouth cavity near the anterior end by a short pedicle. f. Behind the mouth is the pharynx that leads into the opening of a short distensible tube, the esophagus. Ventral to the esophagus is the laryngeal prominence with a vertical slit-like opening called glottis. This will not be traced here since it is a part of the respiratory system. Label the illustration in the Activity Sheet. 4. With the forceps, gently pick up the skin at the mid-posterior region of the abdomen. Holding the skin up, make a small opening using scissors. Insert the scissors into the opening and make a straight incision forward up to the tip of the lower jaw. Make a transverse incision going to the armpits and base of the trunk. Expose the muscles of the abdomen and chest by peeling the skin with a blunt probe. 5. Locate the mid-ventral line or the linea alba. From the posterior end of the trunk to the right of the mid-ventral line, make an incision in the rectus abdominis muscle. Be careful not to cut the anterior abdominal vein running beneath the linea alba. Continue the incision up to the chest area, cutting through the pectoral girdle. From the incision made in the chest area, make a transverse incision cutting through the middle pectoralis, and the sternum. Slowly pull open the muscle flaps to the sides to expose the body cavities.  Page 3 of 6 6. The cavities revealed are the anterior small pericardial cavity containing the heart and a large posterior pleuroperitoneal cavity housing the lungs and other internal organs or viscera. Examine the inner side of the muscular body wall. A glistening membrane, called the parietal peritoneum lines the body wall. This extension of the parietal peritoneum forms the covering layer of the intestine and other viscera. This extends to the visceral organs as the visceral peritoneum or serosa. 7. The digestive tract is suspended by mesenteries which are extensions also of the parietal peritoneum. The part that attaches the digestive tract for most of its length to the median dorsal line is the dorsal mesentery. This can be seen by gently moving the organs away from the median line. The ventral mesentery, which attaches the organs to the midventral line is usually lost except in the region of the liver and the urinary bladder. 8. Examine the organs in the pleuroperitoneal cavity. a. The liver is a large, trilobed brownish organ occupying the anterior half of the pleuroperitoneal cavity. Separate the left and middle lobes of the liver and locate a greenish, spherical sac, the gallbladder. The gallbladder stores the bile secreted by the liver. Hepatic ducts from the liver and cystic ducts from the gallbladder join to form the common bile duct. The common bile duct enters the duodenum of the small intestine. b. Raise the left side of the liver, the stomach will be seen dorsal to the liver. The portion of the dorsal mesentery supporting the stomach is the mesogaster. Examine the stomach. It is a sac-like organ with three regions. The area nearest the esophagus is the cardiac region. The next region that bulges anteriorly is the fundus. Follow the stomach posteriorly to the pyloric region, the area closest to the small intestine. Gently lift the stomach and locate in the mesogaster a round dense body– the spleen. The spleen has no digestive function. Using the scalpel, make a longitudinal slit into the walls of the fundus to the pyloric region of the stomach. Empty its content. Observe the longitudinal folds in the inner wall of the stomach. These are called rugae. c. From the pylorus, the small intestine begins and makes an abrupt angle to the right. This short, straight, anterior-most segment of the small intestine is the duodenum. In the mesentery between pylorus and duodenum, find a yellowish gland, the pancreas that extends up to the dorsal surface of the liver. The pancreas provides the digestive enzymes and bicarbonates that are secreted into the small intestine. The small intestine proceeds posteriorly as coiled structure, the ileum. The ileum terminates into a short straight tube, the large intestine. The part of the dorsal mesentery supporting the small intestine and the large intestine is the mesentery proper and the mesorectum, respectively.  Page 4 of 6 d. The anterior region of the large intestine is the rectum where it leads into a narrow region, the cloaca. The cloaca is a chamber that serves as a common passageway to the outside for both digestive and urogenital systems. It terminates at the cloacal aperture. e. Label the photograph in the Activity Sheet. References Aceret, T., Lannu, A. 1988. A Laboratory Manual in General Zoology. 2nd ed. Academe Publishing House. San Juan Metro Manila. 69-72. Bailey, P.C., Hollman, D.C. Quarles, T.S. and Waits, E.D. 1970. Laboratory Guide for an Introduction to Modern Biology. International Textbook Co., 111-118. Feldman, S. 1965. Experiments in Biological Design. Holt, Rinehart and Winston, Inc., USA. 95-96. Hymann, L. H. 1965. Comparative Vertebrate Anatomy. University of Chicago Press, Chicago, 270-274.  Page 5 of 6 The exchange of gases is termed respiration. Oxygen is obtained from the environment because it is needed for metabolism. The resulting carbon dioxide produced as a by-product of metabolism is in turn released to the environment. Respiration process PART B consists of two stages: external respiration, which is the exchange of gases between the environment and the respiratory organs, and internal respiration, which is the RESPIRATORY exchange of gases between body fluids and tissue cells. SYSTEM Frogs and toads utilize various respiratory organs such as the lungs, skin, and mucous lining of the mouth. These organs are characterized by semi- permeable membrane through which gases can readily diffuse. Objectives At the end of the activity, the student should be able to: 1. identify the organs involved in respiration. 2. describe the flow of air during the frog’s respiration. Materials preserved toad dissecting pan dissecting set Procedure A. Gross Anatomy of the Respiratory System 1. Obtain a preserved toad (may utilize the same toad from the previous activity). 2. Place the toad, ventral side up, on the dissecting pan. 3. Study again the oral cavity:  Page 6 of 6 a. Locate a pair of openings at the antero-lateral part of the snout. These are the nostrils, also called external nares. As noted in the previous activity (#8), these openings lead into the internal nares. b. At the roof of the oral cavity, near the angle of the jaw, observe the openings of the Eustachian tube. The tube connects the mouth cavity with the cavities of the middle ear. Probe these openings and find out if this will lead to the tympanum. 4. Find the glottis, the slit-like opening at the posterior region of the pharynx mentioned in the previous activity (#8). Notice that the glottis opens downward into the cavity of the larynx or voice box. The larynx is supported or stiffened by cartilages. If possible, locate the anterior pair of arytenoid cartilages and a posterior pair of cricoid cartilages. 5. Elastic bands are found in the larynx. These are the vocal cords. 6. The larynx is connected to the lungs through an extremely short tube, the bronchus. This is quite difficult to locate. 7. Examine the toad’s lungs. It is collapsed in the preserved toad and egg shaped in a living toad. Feel the texture of the lungs. Notice that the lungs are membranous sacs lined by small air pockets called alveoli (alveolus, singular). Gas exchange takes place in the alveoli. References Aceret, T., Lannu, A. L. 1988. A Laboratory Manual in General Zoology. 2nd ed. Academe Publishing House, San Juan Metro Manila. 69-72. Bailey, P.C., Hollman, D.C., Quarles, T.S. and Waits, E.D. 1970. Laboratory Guide for an Introduction to Modern Biology. International Textbook Co., 111-118. Feldman, S. 1965. Experiments in Biological Design. Holt, Rinehart and Winston, Inc. USA. 95-96. Hymann, L. H. 1965. Comparative Vertebrate Anatomy. University of Chicago Press. Chicago 270-274.