Final answer:
The capillaries that nourish the epithelium and are involved in the absorption of digested nutrients are located in the lamina propria. This layer is part of the mucosa and contains both blood and lymphatic vessels, as well as lymphoid tissue MALT for nutrient transport and immune defense.
Step-by-step explanation:
The capillaries that nourish the epithelium and absorb digested nutrients lie in the lamina propria. The lamina propria is part of the mucosa, which is the innermost layer of the gastrointestinal (GI) tract, and it is responsible for nutrient absorption and immune functions. In addition to providing the structural support to the epithelial layer, the lamina propria is rich in blood and lymphatic vessels facilitating the transport of nutrients throughout the body. These vessels, alongside lymphoid tissue known as mucosa-associated lymphoid tissue (MALT), play a key role in both nourishing the epithelial cells and in defending against pathogens that may be present in the alimentary canal.
The submucosa lies immediately beneath the mucosa and is also involved in nutrient transportation; however, it is not the layer that directly houses the capillary networks responsible for nutrient uptake from the digested material. It primarily serves to connect the mucosa to the underlying muscularis, contains blood and lymphatic vessels, and supports a nerve plexus that regulates the digestive process.