Question

The finger-like projections which increase the surface area in the small intestine are called_
A. Pseudopodia
B. Villi
C. Lumen
D. None of the above

Answer 1

Hint: The innermost lining of the alimentary canal is the mucosa which encloses the lumen. Pseudopodia are not associated with the human body. It is the cytoplasmic projection of Amoeba which is used for locomotion or engulfing the food.

Complete answer: The wall of the alimentary canal is composed of four layers that are serosa, muscularis, submucosa, and mucosa. This wall extends from the oesophagus to the rectum. The four layers have certain modifications in different parts of the alimentary canal.
The serosa is the outermost layer and it is made up of thin mesothelium which is the epithelium of the visceral organ. Serosa also possesses some connective tissues. Muscularis is the second layer from outside and it is made up of smooth involuntary muscles. It is arranged as an inner circular and outer longitudinal layer. Sometimes an outer oblique muscle layer is present in some regions.
The submucosa layer is the third layer from outside which is formed of loose connective tissue. This layer contains nerves, blood, and lymph vessels. The duodenum part of the small intestine contains Brunner’s gland in this layer.
The innermost layer of the alimentary canal is the mucosa which encloses the lumen of the alimentary canal. In the stomach part, this layer forms irregular folds called rugae. In the small intestine, this layer forms small finger – like foldings called villi. The cells which line the villi produce numerous microscopic projections called microvilli. It gives a brush border appearance. These increase the surface area for absorption.
These villi contain a network of capillaries and lacteal which is a large lymph vessel that helps to absorb fat from the digested food. There is the presence of crypts between the bases of the villi in the intestine called the crypts of Lieberkuhn. The crypts of Lieberkuhn contain paneth cells and argentaffin cells. Paneth cells secrete lysozyme enzyme which is an antibacterial enzyme. Argentaffin cells secrete hormones and serotonin.
Hence, the correct answer is option B.

Note: Gastric glands also contain parietal or oxyntic cells which secrete hydrochloric acid and intrinsic factor which plays an important role in the absorption of vitamin B12 . Hydrochloric acid provides acidic pH which activates the proenzyme pepsinogen .