The Physicochemical Environment of the Neonatal Intestine

Objectives

After completing this article, readers should be able to:

1. List the three primary components from which the intestinal environment is derived.

2. Delineate the specific regions between the bulk phase of the intestine and the epithelial cell apex.

3. Discuss the effect of mucus on the acid microclimate of the intestine.

Introduction

The intestinal lumen is topologically outside the living organism. The physicochemical environment of the intestine determines how nutrients are absorbed and controls potential pathogens. The body regulates the composition of the lumen, and the ability of the intestine to dominate this space is critical to life. The key evolutionary event in the development of multiorgan animals was containment of this external environment into a tube to gain effective control over it. This allowed the intestine to select from this area those factors that were beneficial while leaving behind those that were of no benefit or even harmful. Unicellular organisms, sponges, and other collections of cells cannot regulate their absorptive surfaces. They, therefore, have not solved the essential problem of allowing other cells in the body to specialize into organs whose environment is bathed in more consistent surroundings than are found in nature. The evolution of the intestine led to the appearance of many different organ types, including muscles and nerves, which ultimately resulted in intelligent life. This review examines how the intestinal environment is regulated, with particular reference to neonates.

The environment of the intestine is derived from three primary components: dietary intake, bacterial ecology, and factors such as peristalsis and glandular secretions that are intrinsic to the intestine. Regulation of the physicochemical environment, therefore, depends on the body’s ability to control each of these areas effectively. Dietary intake is controlled by active ingestion. As gut development led to the evolution of complex organisms, so also the appearance of coordination in …