Answers-2, BIO 3220, Digestive System


1. Discuss the four overall processes occurring in digestion.
Ingestion – functions in receiving ingested food, eating
Digestion – stores food temporarily then reduces it physically and chemically
Absorption – absorbs the products of digestion
Waste elimination – eliminates the undigested waste

2. Characterize the development of the digestive system, including parietal peritoneum, visceral peritoneum, dorsal mesentery, and ventral mesentery.
The primitive gut is formed as a result of the head-tail and lateral folds of the embryo and the resulting incorporation of the dorsal aspect of the yolk sac into the intra-embryonic coelum. The primitive gut is enveloped by a mesentery that has a dorsal and a ventral aspect. The ventral mesentery degenerates during development with the exception of the foregut ventral mesentery, which develops into specialized structures. The dorsal mesentery has different names according to its position along the gut: mesoesophagus, mesogastrium, mesoduodenum, mesentery proper (distal duodenum, jejunum and ileum), mesocolon and mesorectum. The dorsal mesentery is formed by a double layer of mesothelium that suspends the gut from the dorsal wall of the foregut to the hindgut. A layer of mesothelium lines the whole coelomic cavity (future peritoneal cavity) forming the parietal peritoneum, that lines the somatopleure (body wall), and the visceral peritoneum, that lines the splanchnopleure (gut wall composed of mucosa, submucosa and two muscle layers).

3. Define peristalsis and segmentation.
The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. Segmentation is a stationary mixing contraction.

4. List the four layers of a typical gut wall.
Mucosa, submucosa, muscularis, serosa

5. Discuss the anatomy and physiology of the following:
Oropharyngeal cavity – part of the throat at the back of the mouth between the soft palate and the epiglottis; oropharyngeal isthmus is the opening from oral cavity to pharynx bordered by velum, faucial pillars and tongue
Oral cavity – (mouth) – the mouth extends from the lips to the floor of the mouth to the roof is the hard palate
Tongue – can be divided into an anterior 2/3 and posterior third; the anterior (oral) portion has a variety of papillae for holding food for chewing and taste buds; the posterior third (pharyngeal) is smooth for swallowing
Oral (Paraoral) glands – three paired major salivary glands and numerous minor ones in the tongue and palate; major glands are parotid (more serous secretions), (sub)mandibular (mucinous secretions) and sublingual (mucinous secretions)
Teeth – each tooth has four main parts, including the following: enamel – the outer layer of the tooth, dentin – the inner layer and the main part of the tooth, pulp – part of the inside of the tooth that contains the nerve, root – the part of the tooth that secures it into the jaw.

6. Define the following dental terms:
Dentin – The main, hard bone-like part of a tooth, beneath the enamel and surrounding the pulp hamber and root canals
Enamel – The hard, calcareous substance covering the exposed portion of a tooth.
Pulp cavity – The central hollow of a tooth containing the dental pulp and including the root canal
Pulp – The soft tissue forming the inner structure of a tooth and containing nerves and blood vessels
Cementum – A bonelike substance covering the root of a tooth
Ameloblast – A cell of the inner layer of the enamel organ of a developing tooth that is involved in enamel formation
Odontoblast – One of the cells forming the outer surface of dental pulp that produces the dentin of a tooth
Acrodont – Having teeth attached to the edge of the jawbone without sockets
Pleurodont – Having the teeth attached by their sides to the inner side of the jaw, as in some lizards
Thecodont – Having the teeth inserted in sockets in the alveoli of the jaws
Polyphydont – Having several or many sets of teeth in succession
Diphydont – Having two successive sets of teeth, deciduous and permanent
Monophydont – Having but one set of teeth of which none are replaced at a later stage of growth
Homodont – Having or being teeth that are all of similar form
Heterodont – Having the teeth differentiated into incisors, canines, and molars
Incisor – A tooth adapted for cutting or gnawing, located at the front of the mouth along the apex of the dental arch
Canine tooth – Any of four teeth having a thick conical crown and a long conical root, adjacent to the distal surface of the lateral incisors, pointed for piercing and tearing
Premolar – One of eight bicuspid teeth located in pairs on each side of the upper and lower jaws behind the canines and in front of the molars; grinding teeth with 1-2 roots
Molar – A tooth with a broad crown used to grind food, located behind the premolars; grinding teeth with 3 roots

7. Examine the evolution of teeth.
The development of heterodont teeth is linked to chewing and to high activity. Although some fish do use teeth to process food, most non-mammals use teeth primarily for securing and holding food, which is quickly swallowed. Mammals also secure and hold their food, but in addition they usually shear, crush, or grind their food. These new functions are important because they speed digestion and greatly increase the diversity of foods that can be eaten. Mammals have thecodont teeth, which increases the strength of the teeth for chewing. These dental changes (and many other changes in oral structures) are associated with the increased activity of mammals: they needed more energy more quickly, so the rapid intake and digestion of food was advantageous. Homology between placoid scales (dermal) and teeth is evident.

8. Give the dental formula of a cow, cat and human.
Cow: 0-0-3-3/3-1-3-3 = 32
Cat: 3-1-3-1/3-1-2-1 = 30
Human: 2-1-2-3/2-1-2-3 = 32

9. Discuss the location and function of the pharynx and esophagus.
Pharynx – located in the throat; passageway of food into esophagus (and air into larynx/trachea);
swallowing mechanism (deglutition): chew food & mix with saliva into bolus at back of pharynx;
swallowing reflex triggered (involuntary)
Esophagus – passageway for food from pharynx to stomach; location: mediastinum; behind
trachea; many mucous glands; movement of food: gravity; peristaltic waves from esophagus meet gastro-esophageal sphincter muscle, sphincter muscle relaxes, food moves into stomach all at once

10. Define crop.
A crop is a pouchlike enlargement of a bird’s gullet in which food is partially digested or stored for regurgitation to nestlings.

11. Describe the anatomy of the stomach, including pylorus, pyloric sphincter, greater curvature, lesser curvature, proventriculus, and gizzard.
Parts of Stomach: cardiac region – around esophagus; fundic region – large ballooned area; pyloric region – near duodenum: the pyloric region narrows into pyloric canal, the pyloric sphincter muscle lies between pylorus & duodenum; greater curvature – the boundary of the stomach that forms a long usually convex curve on the left from the opening for the esophagus to the opening into the duodenum; lesser curvature – the boundary of the stomach that forms a relatively short concave curve on the right from the opening for the esophagus to the opening into the duodenum; body; stomach in two parts – the proventriculus produces digestive enzymes; the gizzard may be muscular for grinding food; these two regions least distinctive in carnivorous birds, most distinct in granivorous species

12. List the four parts of the stomach for a typical ruminant.
Rumen, reticulum, omasum, abomasum

13. Discuss the overall gastric function. Define chyme.
The overall function is to receive, store, liquefy, and mix food. Chyme is the thick semifluid mass of partly digested food that is passed from the stomach to the duodenum.

14. Explain the function of gastric zymogenic, parietal and goblet cells.
Zymogenic cells – stomach cells that produce pepsinogen for the breakdown of protein
Parietal cells – stomach cells that produce HCl for protein breakdown and pepsinogen activation; are antimicrobial
Goblet cells – stomach cells that secrete mucus for stomach lining protection

15. Discuss the overall function of the small intestine.
The small intestine functions in chemical digestion. Most absorption occurs in the small intestine.

16. Identify the purpose of the typhlosole, coil, ceca, and villi.
The purpose of typhlosole, coil, ceca, and villi is to increase surface area for more efficiency in digestion.

17. List the three pars of a tetrapod small intestine.
Duodenum, jejunum, ileum

18. Name the parts and discuss the function of the large intestine.
Parts of Large Intestine: cecum – nearest ileum of small intestine; (appendix is a blind pouch in this region); colon – majority of length; rectum – distal region of colon in pelvic cavity; anal canal – narrowing of rectum & opening to outside; the large intestine functions in the formation and storage of feces, some water absorption, and fermentation in some herbivores

19. Examine the development of the liver and gall bladder.
The liver and gallbladder develop from foregut and midgut pouches

20. Locate the falciform ligament, bile duct, and lesser omentum.
The falciform ligament is a fibrous ventral band that separates the medial and lateral segments of the liver’s left lobe.
Bile ducts are the excretory passages in the liver that carry bile to the hepatic duct, which joins with the cystic duct to form the common bile duct opening into the duodenum.
The lesser omentum is a fold of the peritoneum joining parts of the stomach and duodenum to the liver.

21. Locate and discuss the exocrine function of the pancreas. What are acinar cells?
The pancreas is located posterior to stomach on the left side. Acinar cells in the pancreas produce pancreatic juice. The enzymes secreted by the exocrine tissue in the pancreas help break down carbohydrates, fats, proteins, and acids in the duodenum. These enzymes travel down the pancreatic duct into the bile duct in an inactive form. When they enter the duodenum, they are activated. The exocrine tissue also secretes a bicarbonate to neutralize stomach acid in the duodenum (the first section of the small intestine).

22. Compare the cloaca of placental versus nonplacental animals.
The cloaca is the common posterior chamber of most vertebrates into which the digestive, urinary, and reproductive tracts all enter. A cloaca is found in most reptiles, birds, and amphibians; many fishes; and, to a reduced degree, marsupial mammals. Placental mammals, however, have a separate digestive opening (the anus) and urinogenital opening. The cloaca forms a chamber in which products can be stored before being voided from the body via a muscular opening, the cloacal aperture.