Question

1. A. Discuss the process of the chloride shift in both the respiratory and the digestive systems.

B. Why are HCl and intrinsic factor necessary in the digestive system?

C. Briefly explain the roles of the GI hormones – CCK, VIP, GIP and secretin.

2. A. In order, list the components of the digestive system along with its associated glands/organs.

B. List and describe the 3 methods of propelling and mixing food utilized in different segments in the digestive tract and where they occur.

C. Describe where digestive and absorption of carbohydrates, proteins and fats occurs in the digestive tract.

D. Name the six sphincters found in the digestive tract and where they are specifically located.

Answer 1

1 A: Chloride shift (also known as the Hamburger shift) is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3−) and chloride (Cl−) across the membrane of red blood cells (RBCs).

Bicarbonate in the red blood cell (RBC) exchanging with chloride from plasma in the lungs.

The underlying properties creating the chloride shift are the presence of carbonic anhydrase within the RBCs but not the plasma, and the permeability of the RBC membrane to carbon dioxide and bicarbonate ion but not to hydrogen ion. Continuous process of carbonic acid dissociation and outflow of bicarbonate ions would eventually lead to a change of intracellular electric potential because of lasting H+ ions. Inflow of chloride ions maintains electrical neutrality of a cell. The net direction of bicarbonate-chloride exchange (bicarbonate out of RBCs in the systemic capillaries, bicarbonate into RBCs at pulmonary capillaries) proceeds in the direction that decreases the sum of the electrochemical potentials for the chloride and bicarbonate ions being transported.

B :Intrinsic factor is a glycoprotein necessary for the absorption of vitamin B₁₂ in the small intestine. Chief cells—Located primarily in the basal regions of gastric glands are chief cells, which secrete pepsinogen, the inactive proenzyme form of pepsin. HCl is necessary for the conversion of pepsinogen to pepsin.

C : CCK : Cholecystokinin (CCK or CCK-PZ; from Greek chole, "bile"; cysto, "sac"; kinin, "move"; hence, move the bile-sac (gallbladder)) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, officially called pancreozymin, is synthesized and secreted by enteroendocrine cells in the duodenum, the first segment of the small intestine. Its presence causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively, and also acts as a hunger suppressant.

VIP : Vasoactive intestinal polypeptide (VIP) is a neuropeptide that functions as a neuromodulator and neurotransmitter. It is a potent vasodilator, regulates smooth muscle activity, epithelial cell secretion, and blood flow in the gastrointestinal tract.

GIP : Gastric inhibitory polypeptide, or gastric inhibitory peptide, also known as glucose-dependent insulinotropic polypeptide, is an inhibiting hormone of the secretin family of hormones. While it is weak inhibitor of gastric acid secretion, its main role is to stimulate insulin secretion.

2A : The organs associated with the digestive tract include the major salivary glands, the pancreas, the liver, and the gallbladder. Products of these organs facilitate transport and digestion of food within the gastrointestinal tract.

The main functions of the salivary glands are to moisten and lubricate ingested food and the oral mucosa, to initiate the digestion of carbohydrates and lipids with amylase and lipase, and to secrete innate immune components such as lysozyme and lactoferrin.

The pancreas secretes digestive enzymes that act in the small intestine and hormones important for the metabolism of the absorbed nutrients. Bile, whose components are necessary for digestion and absorption of fats, is made in the liver but stored and concentrated in the gallbladder. The liver also plays a major role in carbohydrate and protein metabolism, inactivates many toxic substances and drugs, and synthesizes most plasma proteins and factors necessary for blood coagulation.

Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = “to nourish”) is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost. The main function of the organs of the alimentary canal is to nourish the body. This tube begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body. Both the mouth and anu.s are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space.”

ACCESSORY STRUCTURES

Each accessory digestive organ aids in the breakdown of food. Within the mouth, the teeth and tongue begin mechanical digestion, whereas the salivary glands begin chemical digestion. Once food products enter the small intestine, the gallbladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue. Together, these are called accessory organs because they sprout from the lining cells of the developing gut (mucosa) and augment its function; indeed, you could not live without their vital contributions, and many significant diseases result from their malfunction. Even after development is complete, they maintain a connection to the gut by way of ducts.

HISTOLOGY OF THE ALIMENTARY CANAL

Throughout its length, the alimentary tract is composed of the same four tissue layers; the details of their structural arrangements vary to fit their specific functions. Starting from the lumen and moving outwards, these layers are the mucosa, submucosa, muscularis, and serosa, which is continuous with the mesentery.

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