Gastrointestinal physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
In the small intestine, which is a major site for both digestion and absorption, chyme is mixed with bile, pancreatic juice and intestinal secretions. The folded mucosal surface and the villi of the small intestine provide a large surface area for nutrient absorption. The brush-border membranes of the mucosal epithelial cells house enzymes. Simple tubular glands called the crypts of Lieberkuhn lie between the villi. The epithelia of both the villi and the crypts of Lieberkuhn contain mucus-secreting goblet cells, phagocytes and endocrine cells. Losses of small intestinal epithelial cells (which are replaced and renewed every 6 days) at the tips of the villi release enzymes such as enterokinase from the brush border of enterocytes into the lumen. Enterokinase activates pancreatic trypsin, which then activates other proteolytic enzymes. The crypts of Lieberkuhn secrete 2 to 3 L of isotonic fluid per day. Chloride is transported out of the cell, and sodium and water follow passively via paracellular spaces. Brunner’s glands in the duodenum secret alkaline fluid, which neutralizes the acidic chyme arriving form the stomach. Secretion of the small intestine is stimulated by vagal activity, and by CCK, secretin, gastrin and prostaglandins.
The stomach and gastric function
Paul Ong, Rachel Skittrall in Gastrointestinal Nursing, 2017
The presence of certain nutrients in the small intestines triggers the release of hormones from enteroendocrine cells directly into the lamina propria which are then absorbed into the blood circulation and further contribute to suppression of gastric activity. Lipids and carbohydrates stimulate the release of cholecystokinin (CCK) and gastric inhibitory peptide (GIP). CCK and GIP inhibit the release of acids and enzymes and GIP also slows down gastric motility. As chyme enters the duodenum it will bring with it acid which will lower the pH in the duodenum. This stimulates enteroendocrine cells to release secretin which has the effect of inhibiting the release of acid from the parietal cells and pepsinogen from the chief cells. Secretin also triggers the release of a bicarbonate-rich secretion from epithelial duct cells lining pancreatic and biliary ducts. This bicarbonate-rich secretion has a pH of 7.5–8.8 which travels along the pancreatic and biliary ducts and enters into the duodenum via the hepatopancreatic ampulla. It serves to dilute and buffer the acids within the chyme that enter into the duodenum. This provides the right pH for enzyme activity in the small intestine.
Bolus death
Burkhard Madea in Asphyxiation, Suffocation,and Neck Pressure Deaths, 2020
Approximately 70 per cent of bolus fatalities take place in the home, with the remainder mainly in restaurants, old people's homes, care facilities and hospitals [1]. A link can generally be identified between the onset of death and the ingestion of food. Cases have been reported in kiosks, fast food restaurants and canteens. Geriatric patients or those with neurological disorders are particularly vulnerable as they are more likely to suffer from dysphagia [6]. In these categories of patient, sudden deaths while eating must always indicate the possibility of a bolus mechanism. The hurried feeding of elderly or handicapped patients evidently contributes to this type of incident. In most cases there are no indications of any vomiting as may be repeatedly observed in the aspiration of chyme. Occasionally, the circumstances of the demise or the anamnesis may provide evidence of alcoholization.
Impact of in vitro digestion on gastrointestinal fate and uptake of silver nanoparticles with different surface modifications
Published in Nanotoxicology, 2020
Ashraf Abdelkhaliq, Meike van der Zande, Anna K. Undas, Ruud J. B. Peters, Hans Bouwmeester
A volume of 1 mL, with a concentration of 500 mg/L of AgNPs suspensions or 95 mg/L AgNO3 solution, was mixed with 3 mL of saliva (pH 6.8 ± 0.1) and incubated (head-over-heals at 55 rpm) for 5 min at 37 °C to simulate the digestion in the mouth. Subsequently, 6 mL of gastric juice (pH 1.3 ± 0.1) was added to the mixture and the pH was checked and adjusted to 5 ± 0.5 with NaOH (5 M) to simulate the digestion in the stomach. The samples were further incubated while rotating at head-over-heals at 37 °C for 2 h. Lastly, 6 mL of duodenal juice (pH 8.1) and 3 mL of bile (pH 8.2) were added to the mixture and the pH was checked and adjusted to 6.5 ± 0.5 with NaOH (1 M) or HCl (37%) to simulate the digestion in the small intestine. Again, the samples were incubated while rotating head-over-heals at 37 °C for 2 h. The complete mixture of all the digestive juices is further referred to as chyme.
High internal phase Pickering emulsions stabilised by ultrasound-induced soy protein-β-glucan-catechin complex nanoparticles to enhance the stability and bioaccessibility of curcumin
Published in Journal of Microencapsulation, 2023
Xutao Chen, Junrong Huang, Linlin Chen, Xiaona Chen, Danxia Su, Bei Jin
An in vitro gastrointestinal model was used to evaluate the performance of HIPPEs as a nutraceutical delivery vehicle based on a previous study (Zhang et al.2022d) with some modifications. Briefly, 20 ml Curcumin-loaded HIPPEs samples were mixed with an equal volume of SSF (containing 0.298 g/L NaCl, 0.896 g/L KCl, 0.2 g/L KSCN, 1.694 g/L NaHCO3, 0.888 g/L NaH2PO4, 0.57 g/L Na2SO4, 0.6 g/L amylase, 0.2 g/L urea, and 0.015 g/L uric acid). The pH was adjusted to 6.8 using 1.0 mol/l HCl or 1.0 mol/l NaOH. The mixed solution was incubated at 37 °C for 5 min in a constant-temperature incubator. Subsequently, 20 ml of oral digestion mixtures were transferred into 100 ml simulated gastric fluid (SGF), which contained 3.2 mg/mL of pepsin and 2.0 mg/mL of NaCl. Then the mixture was incubated in a shaking water bath at 37 °C for 120 min after adjusting the pH to 2.0. After the simulated gastric digestion, 30 ml chyme samples were mixed with 30 ml of SIF (containing 8 mg/mL of bile salt, 1.11 g/L CaCl2, 7.01 g/L NaCl, and 1 mg/mL of pancreatin, pH 6.8). The mixture was shaken at 37 °C for 4 h. Average droplet size (d4,3) and microscopic observation for HIPPEs before and after the oral, gastric, and intestinal phases were performed.
Targeting the intestinal lymphatic system: a versatile path for enhanced oral bioavailability of drugs
Published in Expert Opinion on Drug Delivery, 2018
Renuka Suresh Managuli, Sushil Yadaorao Raut, Meka Sreenivasa Reddy, Srinivas Mutalik
Small intestine consists of four tissue layer: i) innermost mucosa layer which is involved in nutrients absorption from partly digested food (chyme); ii) middle submucosa layer consists of nerves, blood, and lymphatic vessels which transport nutrients from intestine to rest of the body; iii) down to submucosa layer exists the muscularis layer consisting of several layers of smooth muscle tissues which aids in contraction of small intestine, and iv) outermost is the serosa layer which along with the mesentery surrounds the intestine. The interior wall of the small intestine is in the form of circular folds and the epithelial lining of the mucosal layer is protruded into finger like projections known as villi (singular: villus). Around 20,000 villi are present per square inch of mucosa [13]. The epithelial cells in the small intestine comprising enterocytes (absorptive cells), goblet cells, paneth cells, enteroendocrine cells, and tuft cells are held together by tight junctions forming a barrier and they possess a brush border surface onto them known as microvilli [14]. The circular folds and projections (villi and microvilli) increase the intestinal surface area thereby offering maximum contact between epithelial cells and chyme for optimum absorption of nutrients.
Related Knowledge Centers
- Digestive Enzyme
- Ph
- Pylorus
- Sphincter
- Small Intestine
- Stomach
- Duodenum
- Bolus
- Hydrochloric Acid
- Nutrient