Two muscle groups that oppose the action of each other include flexors and extensors, like the biceps and triceps. these muscle groups are known as:

Circular folds, villi, enterocytes, microvilli, brush border, lacteal, capillaries, duodenum, jejunum and ileum.

Explanation:

1. The three structural features of the small intestine that increase its surface area are the circular folds, the villi, and the microvilli.

2. The finger-like projections that cover the circular folds of the small intestine and contribute to the increased surface area of the small intestine are called villi.

3. The absorptive cells that line the wall of the intestine are called enterocytes.

4. The hair-like projections that cover the surface of an enterocyte and contribute to the increased surface area of the small intestine are called microvilli.

5. The collective term for the carpet of microvilli that covers the enterocytes of the small intestine is the brush border

6. Each villus contains a lymphatic vessel called a lacteal that absorbs fat-soluble nutrients into the lymph fluid.

7. The tiny blood vessels located in each villus that absorb water-soluble nutrients into the bloodstream are capillaries.

8. The first section of small intestine, receiving chyme from the stomach, is called the duodenum .

9. The middle portion of the small intestine is called the jejunum.

10. The last portion, or segment, of the small intestine is called the ileum

All these describes the components/features of the small intestines and their functions in the body system.