GASTROINTESTINAL BLOOD FLOW
The hepatic portal system serves as a vital conduit for blood originating from the gastrointestinal tract, spleen, and pancreas, directing it exclusively to the liver before it enters systemic circulation.
This selective routing enables the liver to fulfill its pivotal role as a metabolic regulator and detoxi- fier. By subjecting blood borne substances to hepatic processing prior to their dissemination throughout the body, this mechanism ensures that potentially harmful agents, such as bacteria and toxins absorbed from the gastrointestinal tract, are intercepted and neutralized before they can exert systemic effects, thereby safeguarding overallDOI: 10.1201/9781003426851-15
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TABLE 15.1
Endocrine Activity of the GIT
| Stimulus for | ||||
| Name of the hormone | Source | secretion | Biological action | Reference |
| Gastrin | G-cells in pyloric glands | Peptides and amino acids in stomach | Stimulation of gastric secretion and mucosal growth | Duan et al., 2022 |
| Cholecystokinin (CCK) | I-cells in the mucosa of duodenum and jejunum | Fats, Fatty acids and amino acids | Stimulation of Pancreatic enzyme secretion, Gall bladder contractions, and small intestinal secretion and moderate inhibition of gastric motility | Wang et al., 2019 |
| Secretin | S-cells in the mucosa of the duodenum | Acid chyme | Stimulation of Pancreatic electrolyte secretion and small intestinal secretions and mild inhibition of gastric motility and secretion | Ma & Lee, 2020 |
| Gastric inhibitory peptide | Upper and lower | Glucose, amino | Inhibition of gastric motility and secretion and | Reimann et al., 2020 |
| (GIP) | intestine | acids and fatty acids | stimulation of intestinal secretion and insulin | |
| Enteroglucagon | Upper and lower intestine | Glucose and fatty acids | Stimulation of blood flow and mitotic activity | Nightingale & Spiller, 2023 |
| Motilin | Upper and lower intestine | variable | Stimulation of MMC in antroduodenum | Deloose et al., 2019 |
| Neurotensin | Upper and lower intestine and colon | Fat | Stimulation of vasodilatation and inhibition of smooth muscles | Janig, 2022. |
| Pancreatic poly peptide Vasoactive intestinal polypeptide (VIP) Neuropepetide Y | Pancreas | Protein | Stimulation of pancreatic secretion Moderate inhibition of gastric secretion Stimulates feeding | Chandra & Liddle, 2020 Iwasaki et al., 2019 Assan et al., 2021 |
| Somatostatin | D cells in the gastric glands | Inhibits the release of gastrin and hydrochloric acid | Chen et al., 2023 | |
| Incretin | Duodenum | Glucose | Stimulates insulin secretion | Holst et al., 2021 |
| Ghrelin | Stomach | Stimulates feeding | Davis, 2018 | |
physiological integrity. Majority of non-fat, water-soluble nutrients absorbed from the gastrointestinal tract are transported via the portal venous system directly to the liver sinusoids.
Consequently, both the reticuloendothelial cells and the parenchymal cells of the liver play pivotal roles in the absorption and temporary storage of approximately 50-75% of these absorbed nutrients.Moreover, blood flow within various segments and layers of the gastrointestinal tract fluctuates in response to physiological activity. During heightened activity, such as digestion, blood flow to the gastrointestinal tract increases. This augmentation is mediated by a complex interplay of gastrointestinal hormones including cholecystokinin (CCK), vasoactive intestinal peptide (VIP), gastrin, and secretin, alongside vasodilatory agents like kinins (kallidin and bradykinin), diminished oxygen levels, and the release of adenosine. These factors collectively induce vasodilation, thereby facilitating enhanced blood flow to the gastrointestinal tract, which is essential for optimal digestive and absorptive processes (Wyatt & Haugk, 2018).
15.4