Digestive hormones

Figure 16.13 Structures of glucagon and the digestive hormones, indicating their homologies. (Asterisk indicates amidation of C-terminal amino acid residue, which occurs with some gut hormones.) (Reproduced by permission from Tietz NW, Rinker AD, Henderson AT. Gastric, pancreatic, and intestinal function. In Tietz NW, ed. Textbook of Clinical Chemistry. Philadelphia WB Saunders, 1986, p. 1439.)...

Another factor that may be beneficial is physical activity, since it affects the immune function and antioxidant defenses, transit time of digestion, hormones, and body fat, and it improves energy balance. Therefore, it may have a protective effect on prostate cancer and it may even slow progression and metastasis (G14, H8, K7, 02, 03). In a 9-year follow-up study performed by Hartman et al., the relative risk for physical exercise in prostate cancer was compared with sedentary workers and found to be 0.6 (Cl = 0.4-1.0), 0.8 (Cl = 0.5-1.3), and 1.2 (Cl = 0.7-2.0) for occupational workers, walker/lifters, and heavy laborers, respectively. Except for heavy laborers, an inverse association was observed (RR = 0.7, Cl = 0.5-0.9) compared to men who were sedentary at work and leisure (H8). However, other studies indicate a positive association between vigorous exercise and prostate cancer Cl), and therefore further study is necessary to provide an activity optimum. Frequency, duration, intensity, type of exercise, and the period during a man s lifetime when exercise may be beneficial, must be investigated (02, 03). 

Dietary triglycerides, 226, 319-320, 366-367 Digestion, see also AbsorpOon Digestive hormones Digestive molecules Digestive system carbohydrates, 10(3-116 control, 58,88 Cephalic phase, 66-68 chemical phase, 69 innerv ation, 58,66-69 dietary bbers. 143 lipids, 93-103... 

As we have seen in this chapter steroids have a number of functions in human physiology Cholesterol is a component part of cell mem branes and is found in large amounts in the brain Derivatives of cholic acid assist the digestion of fats in the small intestine Cortisone and its derivatives are involved in maintaining the electrolyte balance in body fluids The sex hormones responsible for mascu line and feminine characteristics as well as numerous aspects of pregnancy from conception to birth are steroids... 

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. 

A dmg-dedicated osmotic implant for human and veterinary use has been developed to dehver hormones, peptides, and proteins that are digested or rendered inactive after oral adrninistration (106). 

Mammals, fungi, and higher plants produce a family of proteolytic enzymes known as aspartic proteases. These enzymes are active at acidic (or sometimes neutral) pH, and each possesses two aspartic acid residues at the active site. Aspartic proteases carry out a variety of functions (Table 16.3), including digestion pepsin and ehymosin), lysosomal protein degradation eathepsin D and E), and regulation of blood pressure renin is an aspartic protease involved in the production of an otensin, a hormone that stimulates smooth muscle contraction and reduces excretion of salts and fluid). The aspartic proteases display a variety of substrate specificities, but normally they are most active in the cleavage of peptide bonds between two hydrophobic amino acid residues. The preferred substrates of pepsin, for example, contain aromatic residues on both sides of the peptide bond to be cleaved. 

Candidate protease inhibitor drugs must be relatively specific for the HIV-1 protease. Many other aspartic proteases exist in the human body and are essential to a variety of body functions, including digestion of food and processing of hormones. An ideal drug thus must strongly inhibit the HIV-1 protease, must be delivered effectively to the lymphocytes where the protease must be blocked, and should not adversely affect the activities of the essential human aspartic proteases. 

Biochemistry is carbonyl chemistiy. Almost all metabolic pathways used by living organisms involve one or more of the four fundamental carbonvl-group reactions we ve seen in Chapters 19 through 23. The digestion and metabolic breakdown of all the major classes of food molecules—fats, carbohydrates, and proteins—take place by nucleophilic addition reactions, nucleophilic acyl substitutions, a substitutions, and carbonyl condensations. Similarly, hormones and other crucial biological molecules are built up from smaller precursors by these same carbonyl-group reactions. 

In general, the sterols perform a structural function, for example as components of the lipid layers of membranes. The Cis, C19 and C21 steroids mainly perform an endocrine function. In other words they are hormones. The bile salts (C24-steroids) fulfil a functional role in digestion in animals. 

AQP10 has only been identified in the small intestine so far and is thought to play a role in hormonal secretion. AQP11 is expressed in kidney, liver, testis and brain, but no function has been found so far. AQP12 has been identified in pancreatic acinar cells, where it is thought to facilitate the release of digestive enzymes into the pancreatic duct. 

The serine proteases are the most extensively studied class of enzymes. These enzymes are characterized by the presence of a unique serine amino acid. Two major evolutionary families are presented in this class. The bacterial protease subtilisin and the trypsin family, which includes the enzymes trypsin, chymotrypsin, elastase as well as thrombin, plasmin, and others involved in a diverse range of cellular functions including digestion, blood clotting, hormone production, and complement activation. The trypsin family catalyzes the reaction ... 

The administration of drugs to ease disease and chronic, severe pain or to provide benefits such as hormone replacement therapy is difficult because drugs taken orally may lose much of their potency in the harsh conditions of the digestive system. In addition, they are distributed throughout the entire body, not just where they are needed, and side effects can be significant. Recently, however, techniques have been developed to deliver drugs gradually over time, to the exact location in the body where they are needed, and even at the time when they are needed. 

Messenger RNAs exist in the cytoplasm as ribonu-cleoprotein particles (RNPs). Some of these proteins protect the mRNA from digestion by nucleases, while others may under certain conditions promote nuclease attack. It is thought that mRNAs are stabihzed or destabilized by the interaction of proteins with these various structures or sequences. Certain effectors, such as hormones, may regulate mRNA stability by increasing or decreasing the amount of these proteins. 

Nielsen, R. G., Riggin, R. M., and Rickard, E. C., Capillary zone electrophoresis of peptide fragments from trypsin digestion of biosynthetic human growth hormone, /. Chromatogr., 480, 393, 1990. 

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.

Explain how the following mechanisms regulate activity of the digestive system intrinsic nerve plexuses, extrinsic autonomic nerves, and gastrointestinal hormones... 

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