**11. Stomach of goat**

Like other ruminants, a goat's stomach has four compartments, including rumen, reticulum, omasum, and abomasum (**Figure 4**). Feed undergoes microbial digestion in the fore stomach followed by acidic digestion in the abomasums (true stomach). The larger portion of the fore stomach, the rumen, is regarded as a fermentation vat having the boundless hovering of plant particles related with microbes that are affixed to the mucosal lining cells of the rumen. The inner surface of rumen is coated with minuscule ridge called papillae, which enhances the contact surface area and facilitates improved absorption of digested food ingredients. The inner of the reticulum is honeycomb like in appearance which further adds to the nutrient contact surface area extension [48]. Some of the bacterial digested feed material is absorbed *via* ruminal mucosa and the remaining byproducts are advanced toward omasum containing firm lamellae-like leaves for advanced digestion. Acidic digestions then take place in the abomasums [53]. In addition to mechanical digestion, the rumen presents other valuable properties like the production of Vit-B, synthesis of amino

*Alimentary System of Native Goat Breeds of Pakistan DOI: http://dx.doi.org/10.5772/intechopen.111936*

**Figure 4.** *Digestive system of goat.*

acids, and detoxifying anti-nutritional factors like tannins. The fore stomach comprising rumen, reticulum, and omasum is lined by nonglandular keratinized stratified squamous epithelium. The rumen has propria submucosa. And the true stomach has glandular columnar epithelium lining. There are three layers of tunica muscularis– inner oblique, middle circular, and outer longitudinal layer. The lamina muscularis is thicker and has three separate layers. Gastric glands are present in the lamina propria of the mucosal layer in the pyloric region [48, 54–57]. Pylorus is the terminal portion of the stomach, which is characterized by secretions that are largely mucus in nature. This region is separated from the duodenum by a thick circular layer of muscles. At the junction with duodenum, the gastric pits become broader and irregular [58].

The small intestine of most domestic species is quite similar morpho-physiologically. Some of the structural and functional differences in specific regions of the small intestine impart differential functional capabilities to these segments. The small intestine is divided into the following three distinct segments: duodenum, jejunum, and ileum. The major functions of the small intestine are digestion, secretion, and absorption [59, 60]. The small intestinal mucosa has several anatomic adaptations that serve to create an immense surface area to digest and absorb nutrients. These include the plicae circulares (intestinal folds), villi, and microvilli. The villi are the most important area for digestion and absorption of intra-luminal nutrients [61]. It is more elongated in the anterior portion of the gut getting broader toward the ileum. Number of mucous-producing goblets cells increases anterior to posteriorly. The columnar epithelium has a brush border on the top and the mucosa has crypts of Lieberkuhn [62–64]. Columnar cells, Paneth cells, and goblet cells are present in the crypts [24]. Fibrous connective tissue (FCT), blood and lymph vessels are present in

the lamina propria and submucosa. Few of the aggregated lymphoid tissues called Payers patches are present and increase in number toward ileal region. The thickness of the smooth muscles in the muscular mucosa is variable and arranged in thin continuous inner circular and outer longitudinal arrangements. The tunica submucosa is formed by CT, mononuclear cells, having fine blood capillaries along with CT cells, elastic, collagen, and reticular fibers. In duodenum, there are Brunner's glands present in the submucosa which secrete alkaline mucus secretions protecting the intestinal mucosa from the acid released out from the stomach and the viscous mucus lubricates the gut contents [61, 63, 65]. Tunica muscularis thick layer comprising smooth muscle layers similar to the layers present in the mucosa. Mesenteric plexus is present between these layers. Tunica serosa is the last layer containing CT cells, fibers, small capillaries, and flat mesothelial cells. This layer represents the peritoneum and continues with mesentery. The main function of duodenum is to accomplish the initial phase of digestion and mixing of the stomach contents with pancreatic and bile secretions.

Because of the larger surface area of the jejunum, it plays an important role in the absorption of amino acids, fatty acids, sugar, water, minerals, and vitamins. The word ileum means eiliein (Greek word) and is the last part/section of the small intestine in higher vertebrates followed by jejunum. This has fewer diameters than other parts. This portion has smaller circular folds or is even absent in the terminal part and the final absorption of vit. B12, bile salts, and all the remaining important products that are not absorbed in the anterior segments are absorbed in the ileum. These compounds are then absorbed into the bloodstream. The capacity of the small intestine of goats is approximately 2.5 gallons [66].
