Small Intestine Research Paper

The small intestine consists in four layers: serosa, muscolaris, submucosa and mucosa; this last one consists of three different sublayers: muscolaris mucosa, lamina propria and epithelium. The lamina propria forms the supporting layer of the epithelium and is populated by extracellular matrix producing cells, neurons, smooth muscle fibres and immune cells.

The epithelial layer is made up of a single-layered epithelium consist of four cell types: enterocytes, goblet cells, Paneth cells and enteroendocrine cells.

The enterocytes are the most abundant cell-type present in the gastrointestinal tract, covering the whole luminal surface of the intestine, and they have an absorptive function. They’re joined together by tight junction (TJ) which

The length of villi increases from the duodenum to the mid-jejunum and then decreases again towards the terminal ileum. This reflects the various functions of the different segments of the small intestine. Crypts also vary in size and composition along the intestine, they are deepest in the proximal small intestine (duodenum and jejunum) and shorter distally in the ileum (E. R. Miller et al. 1991). In the small intestine, apoptotic absorptive enterocytes are continuously sloughed off into the lumen completely renewing the epithelium every 5-7 days.

The intestinal epithelium has three major functions:

• the digestion and absorption of nutrients;

• the adsorption and secretion of water and electrolytes to maintain the viscosity of the luminal content and the flush out noxious components;

• serving as a barrier against pathogens. The single layer of columnar epithelial cells acts as a mechanical barrier, and, in addition, throughout the whole digestive tract, the epithelium is covered with a highly viscous mucus layer that both trap antimicrobial peptides and neutralizing secretory IgA antibodies.

Impaired intestinal barrier function or an increased intestinal permeability may promote the translocation of bacteria and the entering of allergenic compounds from the gut into the body (Wijtten et al.

This also has strong repercussions at later age (Smith et al. 2010). Consequently, the importance of maintaining a healthy mucosa and a selective gut barrier is crucial for a long-life pig performance.

The post-weaning syndrome is one of the main causes of economic losses associated with pig production. This situation is caused by many stress factors associated with the weaning period, such as removal from the sow, adapting to a new environment, mixing of pigs from different farms, dietary changes, and histological changes in the small intestine. All this stress factor may negatively affect the response of immune system and lead to an intestinal gut dysfunction and cause a decrease in absorptive capacity, diarrhoea onset, and, eventually, growth retard (J.-P. Lallès et al. 2007; McCracken et al. 1999). This could eventually result in delayed growth performance associated with an increased susceptibility to infections (Boudry et al. 2002; Moeser et al. 2007).

Physiological and metabolic