Human Bio T2 W7

Small intestine structure

Smaller in diameter, 6-7m long

Where does the small intestine receive materials from

materials are pushed through pyloric sphincter from the stomach

Regions of small intestine

Duodenum, Jejunum and Ileum

Duodenum region

First part, only 25cm, most chemical digestion occurs here

Jejunum region

Middle section, most carbohydrates and proteins absorbed here

Ileum region

Final section, remaining products of digestion absorbed here

Small intestine function

2 major functions:

1. Complete digestion of nutrient macromolecules.

2. Absorption of these nutrient molecules across the wall of the intestines into the blood and lymph.

Digestion key structures

Pancreatic juices, Bile and intestinal juices

Where are pancreatic juices secreted

secreted by pancreas via pancreatic duct

Bile

produced by liver but stored in gall bladder. Secreted into small intestine via bile duct. Contains bile salts to emulsify lipids.

Intestinal juices

secreted by glands in the lining of small intestine.

Mechanical digestion in small intestine

Larger pieces of food broken down into smaller pieces of food.

Mix food with digestive juices: pancreatic juice and intestinal juice.

2 processes:

1. Bile salts emulsifying fat droplets

2. Segmentation

emulsification

Bile breaks down large fat droplets into smaller droplets.

Why deos emulsification occur

Fats (lipids) will clump together into larger clumps when in contact with each other and will slow down chemical digestion of lipids by lipases. Therefore bile is needed to break down the clumps into fat droplets.

Why do fat droplets have a large surface area

So the lipases can more efficiently chemically digest lipid molecules. Bile doesn’t contain enzymes therefore it isn’t a chemical digestion process.

Peristalsis

•During peristalsis, contraction of circular and longitudinal muscles move food along the oesophagus toward the stomach.

⚬Circular - contracts from behind food to propel food forward

⚬Longitudinal - contracts ahead of food to shorten pathway for food to travel

Segmentation

•Mechanical digestion

•Contractions of the circular muscles narrow the intestine which helps to break up the bolus and mix it with the intestinal and pancreatic juices, and the bile.

•This also aids the process of absorption.

small intestine - chemical digestion

•Larger nutrient molecules --> small nutrient molecules.

•Involves the use of digestive enzymes:

⚬Amylases - break down carbohydrates

⚬Proteases - break down proteins

⚬Lipases - break down lipids (fats)

Where pancreatic juice is secreated

•Pancreatic juice is produced by the pancreas.

•It has a pH of 8 and is secreted into the duodenum via the common pancreatic duct.

Pancreatic juice digestion enzymes

⚬Pancreatic amylase breaks down any remaining polysaccharides into disaccharides.

⚬Pancreatic protease (or trypsin) breaks down any remaining polypeptide chains into shorter peptide chains.

⚬Pancreatic lipase breaks down lipids into fatty acids and glycerol.

Where intestinal juice is secreted

Intestinal juice is secreted by the intestinal glands and has a pH of 8.

Intestinal juice digestive enzymes

•It contains the digestive enzymes:

⚬Intestinal amylase (or maltase, sucrase, lactase) breaks down disaccharides into monosaccharides.

⚬Intestinal protease (or peptidase) breaks down peptides into amino acids.