1. The digestive system

2. Your stomach doesn't do most of the digestion
Random Fact
Your stomach doesn't do most of the digestion

3. What starts digestion?
The mouth:
Enzymes?

4. Human Digestive System

5. The Stomach
doesn’t depend on gravity
Physical digestion

6. Enzymes in digestion
Digestive enzymes are classified based on their target substrates:
Proteases and peptidases split proteins into small peptides and amino acids.
Lipases split fat into three fatty acids and a glycerol molecule.
Amylases split carbohydrates such as starch and sugars into simple sugars such as glucose.
Nucleases split nucleic acids into nucleotides.

7. Enzymes in the mouth Lingual lipase: Salivary amylase:
Salivary glands secrete enzymes and substances that aid in digestion and also disinfection.
Lingual lipase:
Lipid digestion starts in the mouth.
Starts the digestion of the lipids/fats.
Salivary amylase:
Carbohydrate digestion starts initiates in the mouth.
Breaks complex carbohydrates to smaller chains

8. Pepsin - the main gastric enzyme
Protein digestion first starts in the stomach
Chief cells produce pepsinogen – inactive form of pepsin
Activated by the stomach acid  pepsin.
Breaks down the protein in the food into smaller particles
Peptide fragments and amino acids.

9. Hydrochloric acid (HCl)
Stomach acid produced by parietal cells.
Functions to denature the proteins ingested, to destroy any bacteria or virus that remains in the food, and also to activate pepsinogen into pepsin.

10. Intrinsic factor (IF) Produced by the parietal cells of the stomach.
Is used to bind Vitamin B12, for absorption at the terminal portion of the ileum.

11. Mucin & Gastrin
Mucin and bicarbonate are secreted by mucous cells to protects the lining of the stomach from HCl
Gastrin is a hormone produced by the G cells of the stomach in response to stomach stretching occurring after food enters it, and also after stomach exposure to protein.
It is an endocrine hormone that enters the bloodstream and eventually returns to the stomach where it stimulates parietal cells to produce hydrochloric acid (HCl) and Intrinsic factor (IF).

12. Gastric lipase
Acidic lipase secreted by the gastric chief cells in the fundic mucosa in the stomach.
pH optimum of 3–6.
Gastric lipase & lingual lipase = the two acidic lipases

13. Cells and their function summary
Parietal cells: Produce hydrochloric acid and intrinsic factor.
Gastric chief cells: Produce pepsinogen.
Chief cells are mainly found in the body of stomach
Mucous neck and pit cells: Produce mucin and bicarbonate to create a "neutral zone"
G cells: Produce gastrin in response to distention or protein
stimulate parietal cell secretion
Located in the antrum of the stomach