Small Intestine: Structure & Adaptations

Small intestine

Long, coiled organ where digestion is completed and nutrients are absorbed

Duodenum

First part of the small intestine where enzymes and bile act

Ileum

Second part of the small intestine where absorption occurs

Villi

Finger‑like projections that increase surface area for absorption

Microvilli

Tiny folds on villi cells that further increase surface area

Capillaries

Blood vessels inside villi that absorb glucose and amino acids

Lacteal

Lymph vessel inside villi that absorbs fatty acids and glycerol

Thin epithelium

One‑cell‑thick layer allowing fast diffusion

Long length

Provides large surface area and time for absorption

Muscular walls

Move food by peristalsis

Rich blood supply

Maintains steep concentration gradients for absorption

What is the main function of the small intestine?

To complete digestion and absorb nutrients

What happens in the duodenum?

Enzymes and bile break down food

What happens in the ileum?

Absorption of digested nutrients

Why does the small intestine have villi?

To increase surface area for absorption

Why do villi have microvilli?

To further increase surface area

Why is the epithelium of villi one cell thick?

To allow fast diffusion of nutrients

What do capillaries in villi absorb?

Glucose and amino acids

What does the lacteal absorb?

Fatty acids and glycerol

Why does the small intestine have a rich blood supply?

To maintain steep concentration gradients

Why is the small intestine very long?

To increase surface area and time for absorption

What process moves food along the small intestine?

Peristalsis

Why is a steep concentration gradient important?

It speeds up diffusion of nutrients into the blood

Which enzyme products are absorbed into the blood?

Glucose and amino acids

Which enzyme products are absorbed into the lacteal?

Fatty acids and glycerol

Why is the small intestine folded?

To increase surface area for absorption