1. Human Biology Digestive system
Senior Lecturer
Talib F. Abbas
Collage of Pharmacy
University of Muthana

2. Stomach
From the oesophagus the food enters the stomach which has a j-shape. When empty the stomach lies in longitudinal folds known as a rugae.
The stomach lining is made up of mucosa which is specialized for the secretion of gastric juice. Gastric juice is secreted by gastric glands located in gastric pits in the mucosa.

4. stomach digestion
Gastric juice contains HCl, mucus and digestive enzymes which are secreted by different cells in gastric pits. The stomach has an oblique muscle layer allowing it to contract in a variety of ways to churn food and mix it with gastric juice.
• The food is then converted to a thick 'soupy' liquid called chyme.
• Most of the chemical digestion in the stomach deals with the start of protein digestion.
• The enzyme pepsin (gastric protease) breaks the bonds between certain amino acids, forming smaller polypeptides.
• Pepsin is secreted in an inactive form (pepsinogen) before it is activated when it comes into contacted with HCl (low pH)
• Protein stays in the stomach longer which leads to more efficient protein digestion.
• The low pH kills bacteria entering the stomach with food.

5. small intestine
The small intestine is approximately 6 meters long, the longest part of the alimentary canal (6m long) It receives the cyme pushed through by the pyloric sphincter form the stomach.

6. Duodenum
The first part of the small intestine is the duodenum; which is 25cm long and extends from the bottom end of the stomach in a curve around the pancreas.
Digestion continues in the small intestine by the influence of: -
1. intestinal juice which is secreted by the lining,
2. pancreatic juice which is secreted by the pancreas.
3. bile which is secreted by the liver but is stored in the gall bladder.

7. Enzyme s of intestine digestion

8. Small Intestine: Absorption
Most of the absorption occurs in the small intestine. After food is mechanically and chemically digested in the mouth, stomach and intestine, it is in the form that can move through cells lining the villi and into the blood and lymph. This movement is known as absorption.
Nutrients are absorbed through the internal surface of the small intestine; this is because absorption requires a large surface area. The structure of the villus is ideally suited for its function of nutrient absorption.

9. Small Intestine: Absorption
• Monosaccharides such as glucose, fructose and galactose are actively absorbed. They pass through cells on outside of the villi and into the blood capillaries.
• Amino Acids are actively absorbed as well.
• Fatty acids and glycerol are absorbed by simple diffusion. In the cells of villi, glycerol and fatty acids recombine to form triglycerides, which are coated in protein. They enter lacteals as tiny droplets of chylomicrons.
• Fat-soluble vitamins are absorbed in association with the fatty acids and glycerol.
• Water-soluble vitamins are absorbed by simple diffusion into the blood capillaries.
• Water is absorbed by osmosis.

10. The Large intestine
The large intestine (colon)n is about 1.5 m long and is named 'large' as it has a wider diameter than the small intestine. It is arranged in an inverted 'U' shape.
There are no villi in the large intestine and no digestive juices are secreted however the lining secretes large amounts of mucus.
Structure: At the part where ileum joins large intestine, there is a blind pouch called caecum. The caecum is about 6cm long and ends in a tube- the appendix.
The final part of the large intestine (colon) is the rectum which opens to the exterior at the anus. Around the anal opening is a circular muscle, the anal sphincter.

11. Large intestine