The gastric epithelium forms a protective barrier against acidic and peptic luminal contents by secreting HCO3 − and mucus, which create a gel-like mucosal barrier.
The basic electrical rhythm, also known as the slow wave, refers to cyclic changes in membrane potential in the smooth muscle of the gut wall.
The frequency of the slow wave is determined by the interstitial cells of Cajal, which act as pacemakers in the gut wall.
The proximal part of the stomach undergoes a gradual change in tone to accommodate its storage function.
The distal part of the stomach experiences varying strength of phasic contractions.
Gastric emptying is regulated by vagovagal reflexes.
According to Sanders KM et al. in their publication "Regulation of gastrointestinal smooth muscle function by interstitial cells" (2016), and Schubert ML in their articles "Functional anatomy and physiology of gastric secretion" (2015) and "Regulation of gastric acid secretion" in the book "Physiology of the GI Tract" (2012), the student should be able to answer the following questions after completing this chapter:

1. How are the various components of a mixed meal digested and absorbed in the small intestine?
2. What are the constituents and functions of pancreatic juice, and how is their secretion controlled?
3. How do bile acids assist with digestion and assimilation of lipids?
4. What are the mechanisms that provide for appropriate levels of fluidity of the intestinal contents?
5. What are the motor patterns of the small intestine in the postprandial period as well as during fasting, and what functions do these patterns subserve?

The small intestine plays a critical role in the assimilation of nutrients. It mixes the meal with various secretions for digestion and absorption, while motility functions ensure adequate mixing and exposure of the chyme to the absorptive surface. The small intestine has specialized structures to efficiently perform its functions, such as the substantial surface area of the mucosa achieved through folds, villi, and microvilli on the epithelial cells' apical surface. The key characteristic of the small intestinal phase in response to a meal is the controlled delivery of chyme from the stomach to match the digestive and absorptive capacity of the intestine. This phase also stimulates pancreatic and biliary secretion, as well as their emptying into the small intestine. Therefore, the function of this region is tightly regulated by feedback mechanisms involving hormonal, paracrine, and neural pathways.
The gastric epithelium secretes HCO3 − and mucus to form a gel-like mucosal barrier that protects it against the acidic and peptic luminal contents.
7.
The smooth muscle of the gut wall undergoes cyclic changes in membrane potential, termed the basic electrical rhythm or the slow wave.
8.
The interstitial cells of Cajal are pacemakers in the gut wall, and they set the frequency of the slow wave.
9.
The proximal part of the stomach undergoes a slow change in tone compatible with its storage function.
10.
The distal part of the stomach undergoes phasic contractions that can vary considerably in strength.
11.
Gastric emptying is regulated by vagovagal reflexes.
Sanders KM, et al. Regulation of gastrointestinal smooth muscle function by interstitial cells. Physiology (Bethesda). 2016;31:316-326.
Schubert ML. Functional anatomy and physiology of gastric secretion. Curr Opin Gastroenterol. 2015;31:479-485.
Schubert ML. Regulation of gastric acid secretion. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Upon completion of this chapter the student should be able to answer the following questions: 1.
How are the various components of a mixed meal digested and absorbed in the small intestine?
2.
What are the constituents and functions of pancreatic juice, and how is their secretion controlled?
3.
How do bile acids assist with digestion and assimilation of lipids?
4.
What are the mechanisms that provide for appropriate levels of fluidity of the intestinal contents?
5.
What are the motor patterns of the small intestine in the postprandial period as well as during fasting, and what functions do these patterns subserve?
he small intestine is the critical portion of the intestinal tract for assimilation of nutrients. In this site the meal is mixed with a variety of secretions that permit its digestion and absorption, and motility functions ensure adequate mixing and exposure of the intestinal contents (chyme) to the absorptive surface. The small intestine has many specializations that enable it to perform its functions efficiently. One of the most obvious specializations is the substantial surface area of the mucosa; this is achieved in a number of different ways. The small intestine is essentially a long tube that is coiled inside the abdominal cavity, there are folds of the full thickness of the mucosa and submucosa, the mucosa has finger-like projections called villi, and finally, each epithelial cell has microvilli on its apical surface. Thus a large surface area exists over which digestion and absorption occur.
The main characteristic of the small intestinal phase of the response to a meal is controlled delivery of chyme from the stomach to match the digestive and absorptive capacity of the intestine. In addition there is further stimulation of pancreatic and biliary secretion and emptying of these secretions into the small intestine. Therefore the function of this region is highly regulated by feedback mechanisms that involve hormonal, paracrine, and neural pathways.