Secretions pancreas

Diastase or amylase is formed when malt is produced by the germination of barley grains. Malt is therefore a good source of the enzyme. Diastase is also secreted by the salivary glands (when it is known as ptyalin), and also by the pancreas. Its function is to hydrolysef starch to a mixture of maltose and dextrin ... 

Control of secretion of anterior pituitary hormones also includes inhibition by hormones produced by target organs. For example, CRH stimulates the anterior pituitary to secrete ACTH, which in turn stimulates the adrenal cortex to secrete corticosteroids. Corticosteroids then feed back to inhibit the secretion of ACTH. Feedback mechanisms are important for the control of most hormones. For example, insulin (qv) secretion from the pancreas increases in response to increased blood glucose resulting from ingestion of a meal. Insulin increases tissue uptake and metaboHsm of glucose, which lowers blood glucose and in turn reduces insulin secretion. 

The classic experiments of Von Meting and Minkowski in 1889 first impHcated the pancreas in regulating blood glucose levels removal of a dog s pancreas led directly to the development of hyperglycemia. Then in the early 1920s it was shown that an internal secretion of the pancreas could be isolated... 

In the treatment of diseases where the metaboUtes are not being deUvered to the system, synthetic metaboUtes or active analogues have been successfully adrninistered. Vitamin metaboUtes have been successfully used for treatment of milk fever ia catde, turkey leg weakness, plaque psoriasis, and osteoporosis and renal osteodystrophy ia humans. Many of these clinical studies are outlined ia References 6, 16, 40, 51, and 141. The vitamin D receptor complex is a member of the gene superfamily of transcriptional activators, and 1,25 dihydroxy vitamin D is thus supportive of selective cell differentiation. In addition to mineral homeostasis mediated ia the iatestiae, kidney, and bone, the metaboUte acts on the immune system, P-ceUs of the pancreas (iasulin secretion), cerebellum, and hypothalamus. 

P-Adrenoceptors have been subdivided into P - and P2-adrenoceptors. A third subset called nontypical P-adrenoceptors or P -adrenoceptors have been described but are stiU the subject of debate. In terms of the interactions with various subsets of P-adrenoceptors, some antagonists are nonselective in that they antagonize the effects of activation of both P - and P2-adrenoceptors, whereas others are selective for either P - or P2-adrenoceptors. P - and P2-adrenoceptors coexist in almost all organs but generally, one type predominates. The focus herein is on the clinically relevant P -adrenoceptor-mediated effects on heart and on P2-adrenoceptor-mediated effects on smooth muscles of blood vessels and bronchioles, the insulin-secreting tissue of the pancreas, and skeletal muscle glycogenolysis for side effects profile (36). 

Insulin is a peptide hormone, secreted by the pancreas, that regulates glucose metabolism in the body. Insufficient production of insulin or failure of insulin to stimulate target sites in liver, muscle, and adipose tissue leads to the serious metabolic disorder known as diabetes mellitus. Diabetes afflicts millions of people worldwide. Diabetic individuals typically exhibit high levels of glucose in the blood, but insulin injection therapy allows diabetic individuals to maintain normal levels of blood glucose. 

The primary hormone responsible for conversion of glucose to glycogen is insulin (Figure 6.36). Insulin is secreted by special cells in the pancreas called the islets of Langerhans. Secretion of insulin is a response to increased glucose in the... 

FIGURE 24.3 (a) A duct at the junction of the pancreas and duodenum secretes pancreatic juice into the duodenum, the first portion of the small intestine, (b) Hydrolysis of triacylglycerols by pancreatic and intestinal lipases. Pancreatic lipases cleave fatty acids at the C-1 and C-3 positions. Resulting monoacylglycerols with fatty acids at C-2 are hydrolyzed by intestinal lipases. Fatty acids and monoacylglycerols are absorbed through the intestinal wall and assembled into lipoprotein aggregates termed chylomicrons (discussed in Chapter 25). 

Blood sugar (blood glucose) in human beings is controlled by the secretion of (—>) insulin by the beta (B- or (3-) cells of the islands of Langerhans in the pancreas. Loss of insulin synthesis leads to (—>) diabetes. Type 1 diabetes (insulin dependent diabetes mellitus, EDDM) begins in juveniles as an organ-specific autoimmune reaction, the destructive insulitis. 

Pituitary Adenylyl Cyclase-activating Polypeptide (PACAP) is a 38-amino acid peptide (PACAP-38), which is widely expressed in the central nervous system. PACAP is most abundant in the hypothalamus. It is also found in the gastrointestinal tract, the adrenal gland and in testis. Its central nervous system functions are ill-defined. In the periphery, PACAP has been shown to stimulate catecholamine secretion from the adrenal medulla and to regulate secretion from the pancreas. Three G-protein coupled receptors have been shown to respond to PACAP, PAQ (PACAP type I) specifically binds PACAP, VPACi and VPAC2 also bind vasoactive intestinal peptide (VDP). Activation of PACAP receptors results in a Gs-mediated activation of adenylyl cyclase. 

VIPoma stands for vasoactive intestinal polypeptide-secreting tumour. VIPomas are rare neuroendocrine tumours located in the pancreas. 

Zollinger-Ellison syndrome (ZES) is characterized by the development of a tumor (gastrinoma) or tumors that secrete excessive levels of gastrin, a hormone that stimulates production of acid by the stomach. In most cases, the tumor or tumors arise within the pancreas and/or the upper region of the small intestine (duodenum). 

The enzymes pancreatin and pancrelipase, which are manufactured and secreted by the pancreas, are responsible for the breakdown of fats, starches, and proteins. These enzymes are necessary for the breakdown and digestion of food. Both enzymes are available as oral supplements. 

The human pancreas secretes about 40—50 units of insulin daily, which represents about 15—20% of the hormone stored in the B cells. Insidin and the C-peptide (see Figure 42—12) are normally secreted in equimolar amounts. Stimuh such as glucose, which provokes insidin secretion, therefore trigger the processing of proinsidin to insidin as an essential part of the secretory response. 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

---