Stomachs

Food is stored in the body of the stomach, which may expand to hold as much as 11 of chyme. As food enters the stomach, it undergoes a reflex relaxation referred to as receptive relaxation. It enhances the ability of the stomach to accommodate an increase in volume with only a small increase in stomach pressure. The fundus does not typically store food because it is located above the esophageal opening into the stomach. Instead, it usually contains a pocket of gas. 

Gastric motility. In addition to the circular and longitudinal layers of smooth muscle, the stomach contains an extra layer of smooth muscle. Beginning at the UES, the oblique layer of smooth muscle fans out across the anterior and posterior surfaces of the stomach and fuses with the circular layer in the lower region. This extra layer of muscle enhances gastric motility and therefore mixing and mashing of food. 

It may take many hours for the contents of the stomach to be processed and moved into the small intestine. Several factors influence gastric motility and therefore the rate of gastric emptying. These include  

The major gastric factor that affects motility and the rate of emptying is the volume of chyme in the stomach. As the volume of chyme increases, the wall of the stomach becomes distended and mechanoreceptors are stimulated. This elicits reflexes that enhance gastric motility by way of the intrinsic and vagus nerves. The release of the hormone gastrin from the antral region of the stomach further contributes to enhanced motility. 

The most important factors that regulate gastric motility and the rate of emptying of the stomach involve the volume and chemical composition of chyme in the duodenum. Receptors in the duodenum are sensitive to  

A bilinear equation applies in this special situation where phospholipid and glyco-calyx layers preceed the lipoidal membrane. As in colon and small intestine there 

Even when no food is present in the mouth, saliva is secreted to keep the mouth moist and facilitates speech. Saliva also has some antibacterial action. Patients with xerostomia (dry mouth) exhibit higher than normal incidence of dental caries. Saliva maintains the oral cavity at a pH of about 7.0. The teeth do not lose calcium to oral fluids because of the high concentration of calcium in the saliva at pH 7.0. 

Like the thyroid gland (Chapter 33), salivary glands (and the gastric mucosa) can take up iodide ions against a concentration gradient. 

The mouth is the normal point of entry of food and drink. There, solid food is reduced in size by mastication, blended with saliva, and temperature-moderated before being swallowed. Conditions that interfere with any of these processes (e.g., tooth loss) can affect food choice and hence the nutritional status and health of the individual. The esophagus is a muscular tube through which masticated food is transported from the mouth to the stomach. It consists of both striated muscle (upper one third) and smooth muscle (lower two thirds). These muscles undergo periodic contractions in the form of peristaltic waves that push the swallowed boluses toward the stomach. The esophagus has no digestive function but secretes mucus to protect the esophageal mucosa from excoriation. 

The stomach stores food temporarily, retards its entry into the small intestine, and secretes pepsin to begin the digestion of protein. Hydrogen ions in the stomach activate pepsinogen to form pepsin and aid in maintaining 

A proteolytic enzyme secreted by gastrie mueosa of infants is chymosin (rennin), which functions to clot milk and promote its digestion by preventing rapid passage from the stomach. Chymosin hydrolyzes casein, a mixture of several related milk proteins, to paracasein, whieh reacts with Ca + to yield the insoluble curd. Pepsin performs the same funetions as chymosin. Chymosin is found in the fourth stomach of ruminants. Calf stomach is a source of this enzyme, which is used in the manufacture of cheese. Chymosin has been synthesized by recombinant DNA techniques and successfully used in the produetion of cheese. 

---

Aldrin is insecticidally active as a contact and stomach poison against a wide range of soil pests. It is non-phytotoxic and does not cause taint. Aldrin is toxic to humans and animals and is now less used. 

The vitamin deficiency is often due to failure to absorb B12 from the stomach and can be alleviated by giving mg doses with extracts of hog s stomach which contains the intrinsic anti-pernicious anaemia factor (a muco-protein), which promotes the absorption. 

The activity of an enzyme varies considerably with acidity and there is generally a marked optimum pH for each enzyme. Thus pepsin of the stomach has an optimum pH of 1 4, i.e., it works best in a decidedly acid medium. It is inactive in neutral or alkaline solutions and the latter rapidly destroy it. 

In any case, I eventually recovered (and so did Jerry), but my immune system must have suffered serious damage, which manifested itself three years later, when I collapsed in my office one day and was found to be bleeding internally from a form of rare stomach cancer, which necessitated major surgery but was fortunately localized. I again recovered and have had no further difficulties since. Whether weakening and knocking out my immune system to overcome the previous problems had any effect is not clear, but it could have been a factor. Despite my health problems I was able to continue my work without much interruption, and the scientific productivity of my group has not... 

Simple life forms, such as bacteria, consist of single cells, whereas, at the other extreme, complex life forms such as animals, contain many types of cell, each having a specific function (cells in eyes, limbs, stomach, etc.). 

A small amount of acrolein may be fatal if swallowed. It produces bums of the mouth, throat, esophagus, and stomach. Signs and symptoms of poisoning may include severe pain in the mouth, throat, chest, and abdomen nausea vomiting, which may contain blood diarrhea weakness and dizziness and coUapse and coma (99). 

Swallowing acryhc monomers may produce severe irritation of the mouth, throat, esophagus, and stomach, and cause discomfort, vomiting, diarrhea, dizziness, and possible coUapse. 

Health and Safety Factors. The low solubiUty of calcium fluoride reduces the potential problem of fluoride-related toxicity. Water saturated with calcium fluoride has a fluoride concentration of 8.1 ppm as compared to the recommended water fluoridation level of 1 ppm fluoride ion. However, because the solubiUty of calcium fluoride ia stomach acid is higher, continued oral ingestion of calcium fluoride could produce symptoms of fluorosis. The adopted TWA limit for fluorides as F is 2.5 mg/m (68,69). 

Mild exposure to HF via inhalation can irritate the nose, throat, and respiratory system. The onset of symptoms may be delayed for several hours. Severe exposure via inhalation can cause nose and throat bums, lung inflammation, and pulmonary edema, and can also result in other systemic effects including hypocalcemia (depletion of body calcium levels), which if not promptly treated can be fatal. Permissible air concentrations are (42) OSHA PEL, 3 ppm (2.0 mg/m ) as E OSHA STEL, 6 ppm (5.2 mg/m ) as E and ACGIH TLV, 3 ppm (2.6 mg/m ) as E. Ingestion can cause severe mouth, throat, and stomach bums, and maybe fatal. Hypocalcemia is possible even if exposure consists of small amounts or dilute solutions of HE. 

Epidemiologic studies in Japan indicate an increased risk of stomach cancer owing to consumption of broiled fish and meats (116). In the United States, stomach cancer incidence has steadily declined since the 1940s, whereas consumption of broiled food has increased (108). In addition, the average human intake of PAHs is only 0.002 of that required to produce cancer in half of animals fed. Test results are often contradictory (117) and many components of food, such as vitamin A, unsaturated fatty acids, thiols, nitrites, and even saUva itself, tend to inhibit the mutagenic activity of PAHs (118—120). Therefore, the significance of PAHs in the human diet remains unknown (121,109). 

The smallest sequence possessing most of the neurotensin spectmm of activities and its high potency is the hexapeptide C-terminus (1). [D-Trp ]-Neurotensin acts like a neurotensin antagonist in perfused heart preparations, but acts like a full agonist in guinea pig atria and rat stomach strips (122). 

Hydrogen chloride in air can also be a phytotoxicant (88). Tomatoes, sugar beets, and fmit trees of the Pmnus family are sensitive to HCl in air. Exposure of concentrated hydrochloric acid to the skin can cause chemical bums or dermatitis. Whereas the irritation is noticed readily, the acid can be water flushed from the exposed area. Copious use of miming water is the only recommended safety procedure for any external exposure. Ingestion is seldom a problem because hydrochloric acid is a normal constituent of the stomach juices. If significant quantities are accidentally swallowed, it can be neutrali2ed by antacids. 

In experimental animals and in vitro, DHBs show a variety of biological effects including binding of metaboHtes to various proteins. Clastogenic effects have been observed in vitro and in some in vivo studies with the three compounds. No reproductive effects have been shown by conventional studies with either hydroquinone, catechol, or resorcinol (122). Hydroquinone has been shown to induce nephrotoxicity and kidney tumors at very high doses in some strains of rat (123) catechol induces glandular stomach tumors at very high dose (124). Repeated dermal appHcation of resorcinol did not induce cancer formation (125). 

Rya.nia., The root and stem of the plant yania speciosa family Flacourtiaceae, native to South America, contain from 0.16—0.2% of iasecticidal components, the most important of which is the alkaloid ryanodine [15662-33-9] C25H250 N (8) (mp 219—220°C). This compound is effective as both a contact and a stomach poison. Ryanodine is soluble ia water, methyl alcohol, and most organic solvents but not ia petroleum oils. It is more stable to the action of air and light than pyrethmm or rotenone and has considerable residual action. Ryania has an oral LD q to the rat of 750 mg/kg. The material has shown considerable promise ia the control of the European com borer and codling moth and is used as a wettable powder of ground stems or as a methanohc extract. Ryanodine uncouples the ATP—ADP actomyosia cycle of striated muscle. 

Mitex [2385-85-5] is l,2,3,4,5,5,6,7,8,9,10,10-dodecachloro-octahydro-l,3,4-metheno-2JT-cyclobuta-p,<7 -pentalene (37) (mp 485°C). The rat LD s are 306, 600 (oral) and >2000 (dermal) mg/kg. Mirex is extremely resistant to biodegradation and was once considered the perfect stomach poison iasecticide for use ia baits to control imported fire ants. However, even at doses of a few milligrams per 10 m it was found to bioaccumulate ia birds and fish and its registrations were canceled ia the United States ia 1976. 

---