Question

Why are our intestines so long?

Answer 1

Because of a diet derived mostly from plants: such a plant based diet includes our common foods like fruits, vegetables, grains, legumes and tubers.

Explanation:

Herbivores possess an intestine at least 10 times longer than their body, though in case of human the value is not more than 7 times.

It takes time to disintegrate and ultimately digest fibrous plant parts, most of which takes place in intestine. Many herbivores have also evolved facilities to digest cellulose abundantly available in plant based diet.

Human also eats plant based food and needs a considerably long intestine but at the same time, it must be remembered that,

1. we can digest only cooked starch, we are not ruminants
2. we do not have the ability to digest cellulose, caecum vestigeal
3. we are omnivores, so there's supply of nutrients from animal source as well (for which we have a robust stomach)

In human, starch digestion starts in oral cavity by action of salivary amylase but it discontinues in highly acidic environment of stomach.

Our daily breakfast cereals, and breads and rice, etc are digested completely once food enters small intestine. Here pancreatic amylase and intestinal amylase enzymes mix with food and complex carbohydrates are broken down to maltose, isomaltose, etc.

Digestive juice of intestine also contains enzymes like maltase, isomaltase, sucrase, lactase-- all these enzymes break disaccharides into absorbable monosaccharides.

Maltase acts on maltose
Isomaltase acts on isomaltose
Sucrase acts on sucrose/cane sugar
Lactase acts on lactose/milk sugar.

Simple nutrients are absorbed in body from small intestine. Surface area of absorption is increased due to presence of villi and microvilli on the inner lining.

So small intestine plays an important role in human physiology by being significantly long. It helps to draw maximum benefit from food that we eat by facilitating complete digestion and subsequent absorption.

Small intestine is about 20 feet long in adults and large intestine is about 5 feet in length. No digestion takes place in large intestine, only some water is absorbed. Length of intestine in human is moderate due to his omnivorous food habit ; it is comparatively longer than that in carnivores but much shorter and less complex when compared to intestine of herbivores.