question_answer 3)

Answer briefly (a) Why are villi present in the intestine and not in the stomach? (b) How does pepsinogen change into its active form? (c) What are the basic layers of the wall of alimentary canal? (d) How does bile help in the digestion of fats?  

Answer:

(a) The mucosa layer of alimentary canal forms small finger-like folding called villi in the small intestine. The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance. These modifications increase the surface area enormously. Villi are supplied with the network of capillaries and large lymph vessel called the lacteal mucosai. (b) The inactive form of enzyme pepsinogen is activated by HCI. (c) The wall of alimentary canal from oesophagus to rectum possesses four layers namely serosa, muscularis, sub-mucosa and mucosa. Serosa is the outermost layer, followed by muscularis, sub-mucosa and mucose. (d) Bile salts help in emylsification of lipids and activate the lipases.