Digestive Tract Hormones

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

Figure 6.1 Acids and bases exist in the human body and are necessary for its proper function, including the function of the digestion process. When food is swallowed, it is attacked by stomach acids. The stomach acids need to be neutralized before food can continue down the digestive tract. A hormone called secretin monitors the pH balance in the small intestine and sends chemical signals to other parts of the body, thereby regulating pH balance.

Glucagon is a single-chain polypeptide of 29 amino acid residues and a molecular mass of 3500 Da. It is synthesized by the A-cells of the islets of Langerhans, and also by related cells found in the digestive tract. Like insulin, it is synthesized as a high molecular mass from which the mature hormone is releases by selective proteolysis. 

The control of gut function involves interplay between neurones and peptide hormones. Information from a variety of receptors along the digestive tract is processed by a network of nerves, the enteric nervous system, which also receives input from the brain. 

While these steroids can be extracted directly from human tissue, in most instances they can also be synthesized chemically. Direct chemical synthesis methodology has also facilitated the development of synthetic steroid analogues. Many such analogues exhibit therapeutic advantages over the native hormone, e.g. they may be more potent, be absorbed intact from the digestive tract, or exhibit a longer duration of action in the body. The majority of sex steroid hormones now used clinically are chemically synthesized. 

De Castiglione, R., In Hormonal Receptor in Digestive Tract Physiology, Bonfils, S. Fro-mageot, P. Rosselin, G., Eds. Elsevier/North-Holland Amsterdam, (1977) p 33. 

Release of zymogens The release and activation of the pancreatic zymogens is mediated by the secretion of cholecystokinin and secretin, two polypeptide hormones of the digestive tract (see p. 174). 

Protein and peptide hormones must be administered more frequently if used therapeutically. They cannot be administered by mouth since they would be degraded in the digestive tract. Hence, diabetics must regularly inject with insulin. 

I have spent at least 8 years, and millions of dollars of research funds, working on ways to deliver insulin, growth hormone, and other peptide drugs into the body without using a syringe. Any pharmaceutical company that could accomplish this feat would capture a multibillion-dollar market. There is a clear financial incentive to produce a peptide pill. However, the conclusions from this research, which are published throughout the world, remain to this day that peptides are destroyed when they enter the hostile environment of the human digestive tract. They just become another protein meal. Their constituent amino acids are absorbed for a nutritional benefit just like any other food source. 

The human immune system is complex and involves the digestive tract, the blood and lymph systems, hormones, and many other specialized cells that enable the human body to respond to exogenous substances that may come in contact with the body. This ranges from fighting off an E. coli infection to healing a small cut. 

Arachidonic acid (20 4n - 6) is one of two major PUFA synthesized by the D6D/D5D pathway (Fig. 4). In many tissues and cell types, 20 4n - 6 is esterified to the sn-2 position of membrane PL, and is used for the eicosanoid-mediated signaling to perform specialized cell functions. Arachidonic acid esterified in PL is a storage form of this fatty acid and is hydrolyzed from the PL by phospholipases prior to enzymatic conversion into eicosanoids (Chapter 13). Eicosanoids are autocrine/paracrine hormones that mediate a variety of localized reactions, such as inflammation, homeostasis, and protection of digestive tract epithelium. D6D deficiency in humans leads to severe food intolerance and growth retardation (J. Nwankwo, 2003). These symptoms are reversed by arachidonic acid supplementation to the diet, which supports the essential role of eicosanoids in the protection of digestive tract mucosa in humans. 

Increased milk production. Much controversy exists over providing cows with supplemental bovine somatotropin (BST), also called growth hormone, a hormone that increases metabolism and milk production in dairy cows. Tbe controversy centers on human consumption of the hormone. However, BST is a peptide hormone, so it is hydrolyzed in the digestive tract and is not absorbed directly into the human bloodstream (Section 24.2). Furthermore, aU milk must contain some of this hormone, because the cow cannot produce milk without it. A more soundly based concern about BST supplementation in dairy cows is that the cows given extra BST often develop mastitis, an inflammation of the udder caused by bacterial infection. Mastitis is frequently treated with high doses of antibiotics, and some of these antibiotics could end up in tbe mUk, causing problems for people with certain food sensitivity. 

Lehy T, Accary JP, Dubrasquet M, et al. Growth hormone-releasing factor (somatocrinin) stimulates epithelial cell proliferation in the rat digestive tract. Gastroenterology 1986 90 646-653. 

Control of the Digestive Tract Neurological Control Hormonal Control... 

CONTROL OF THE DIGESTIVE TRACT. Like any system in the body, control is exerted over the functioning of the digestive tract in an effort to maintain the status quo of the body. The digestive tract is under neurological and hormonal control. 

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