The Digestive System

Digestion

The breaking down of the nutrients we eat into simpler organic compounds that can be absorbed by the body.

Mechanical digestion

The physical process that reduces the size of the molecules (increasing surface area)

Chemical digestion

The breaking down of complex molecules into less complex molecules.

Chewing (mastication)

Teeth break food down to increase the amount of surface area. A mechanical digestive process in the mouth.

Swallowing

Tongue shapes food into a lump known as a bolus. The tongue then pushes the bolus down the pharynx to the oesophagus. A mechanical digestive process in the mouth.

Salivary amylase

An enzyme secreted by the salivary glands that breaks down large starch molecules (complex carbohydrates) into maltose (simpler sugars). A chemical digestive process in the mouth.

Incisors

• Chisel shaped

• Cutting

• 4

Canines

• Pointed and sharp

• Tearing and ripping

• 2

Premolars

• Broad and flat

• Crushing and grinding

• 4

Molars

• Broad and flat

• Crushing and grinding

• 6

Oesophagus

• Long tube connecting the pharynx to the stomach.

• Contains double layer of muscle that is able to constrict and push the bolus into the stomach.

• These wave like constrictions are known as peristalsis.

Churning in the stomach

Due to the extra oblique layer of muscle, the stomach is able to churn and mix the food and gastric juices to create Chyme. Mechanical process in the stomach.

Hydrochloric acid

Activates pepsinogen to form pepsin. First step of chemical digestion in the stomach.

Pepsin

Digests proteins into polypeptides. Second step of chemical digestion in the stomach.

Pyloric sphincter

Controls the movement of chyme from the stomach to the small intestine.

Small intestine

A small diameter tube, roughly 7m long, that consists of three parts:

1. Duodenum

2. Jejunum

3. Ileum

Three substances are secreted into the tube:

1. Pancreatic juice

2. Bile

3. Intestinal juice.

1. Duodenum

Section of the SI responsible for most of the chemical digestion of the small intestine.

2. Jejunum

Section of the SI responsible for absorption of carbohydrates and proteins.

3. Ileum

Section of the SI responsible for the absorption of vitamins, Bile salts, and any other remaining nutrients.

Pancreatic juice

Secreted from the pancreas into the duodenum. Works to neutralise the acidic environment of from the stomach, and contains:

1. Pancreatic amylase: Digests starch and disaccharides into glucose and maltose.

2. Pancreatic lipase: Digests fats into fatty acids and glycerol.

3. Trypsin: Digests polypeptides into peptides.

Bile

Emulsifies fat, breaking it into smaller droplets and increases surface area, making it mechanical digestion.

Produced in the liver, stored in the gal bladder, and secreted into the duodenum.

Intestinal Juice

Secreted throughout the small intestine, mostly into the jejunum. Contains:

1. Maltase, sucrase, and lactase: break down disaccharides (maltose, sucrose, and lactose) inro monosaccharides (galactose, glucose, and fructose).

2. Intestinal lipase: breaks down fatty acids and glycerol.

3. Peptidase: breaks down peptides into amino acids.