The structure of the small intestine and its involvement in digestion (pH, segments, villi/microvilli, absorption, chemical breakdown of nutrients)

Question 1

Structure of the small intestine

Duodenum

D.U.D.E.S

Answer 1

Duodenum: U-shaped, first 30 cm.
Unique function: Primary digestion site.
Ducts: Common duct for bile and pancreatic juice.
Enzymes: Peptidase (peptides to amino acids), disaccharidases (disaccharides to monosaccharides).
Secretions: Bile and pancreatic juice enter the duodenum.

Question 2

Structure of the small intestine

Jejunum

Answer 2

• next 3m; additional digestion and absorption of small molecules

Question 3

Structure of the small intestine

Ileum

Answer 3

• last 4m; most absorption occurs by diffusion and active transport

Question 4

Size of small intestine

Answer 4

The small intestine is 7m long and 2.5cm in width

Question 5

Villi

Answer 5

• finger-like projections attached along the walls of the small intestine that increase surface area.
• Capillary networks inside each villus will absorb monosaccharides and amino acids.

Question 6

Microvilli

Answer 6

• cells lining the villi, appear thread-like. Further increase surface area for absorption

Question 7

Enzymes of the small intestine help break down food molecules into subunits that can be absorbed and used for energy:

Answer 7

→ Carbohydrase
Maltase, sucrase and lactase break down the carbohydrates maltose, sucrose and lactose into glucose

→ Trypsin
Continues digestion of proteins

→ Peptidase
Breaks down polypeptides (proteins) into amino acids.

→ Lipase
Secreted by the pancreas, breaks down fats into fatty acids and glycerol.

Question 8

Difference between digestion and absorption

Answer 8

• Digestion and absorption are NOT the same thing. - - - - - Digestion is the breaking down of molecules into their smallest parts (i.e. amino acids, glucose, fatty acids and glycerol).
• Absorption is the body’s way of using these molecules for energy and storage. Most of these molecules are absorbed in the small intestine.