Question

why complex digestion done in small intestine ​

Answer 1

The small intestine is lined with finger-like projections, called villi, which provide a very large surface area facilitating the absorption of nutrients, including carbohydrates, proteins and fats, into the bloodstream. The small intestine also plays a key role in regulating blood glucose levels.

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Answer 2

$\textbf{Olá User!!}$
$\textbf{Here's your answer.}$

$\color{red}{Small \: Intestine:}$
• It is about 6 meters (20 feet) long tube around 2.5 cm (1 inch) diameter. It is differentiated into three parts :-

~ Duodenum : It is C-shaped first part of intestine which is 25 cm long. The descending limb of duodenum recieves openings of bile duct and pancreatic duct.

~ Jejunum : It is about 2.5 meters (8 feet) long and narrower than duodenum.

~ Ileum : It is about 3.5 meters (12 feet) long.

• Complex digestion done in small intestine ​because : Basically, it has small finger like projections called villi, which increases surface area for absorption. The the digestive juices, secreted by these glands, is called succus entericus. the digestive enzymes present in bring about complete digestion of carbohydrates, proteins and lipids.

$\textbf{Hope it helps!!}$
$\textbf{@charlie16}$