1. The digestive system

2. Random Fact
Stomach growling is called borborygmic and happens all the time, but it is just louder when your stomach is empty because there is no food to muffle it.

3. 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.

4. 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

5. 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.

6. 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.

7. 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.

8. 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).

9. 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

10. 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

11. Words to know Enzymes Hormone Lingual lipase Salivary amylase Pepsin
Pepsinogen
Intrinsic factor
Bicarbonate
Parietal cell
Gastric chief cell
Mucous neck and pit cells
G cells
Gastrin
Esophagus
Hydrochloric acid
Peristalsis
Bicarbonate
Bolus
Parietal cell
Upper and lower esophageal sphincters
Gastric chief cell
Fundus
Body
Muscle layers
Mucous membrane
Antrum
Pyloric sphincter

12. Using the information provided…
With a partner, draw the digestive system from the mouth to the stomach on a window
Stages 1 & 2
Make sure to label the parts of the body we have discussed (words to know at the end of both PowerPoints)
Include all of the enzymes and hormones in these areas

13. Questions to think about
How do the layers in the stomach contribute to digestion?
What factors may alter how digestion takes place?

14. Small intestine Named for its small diameter
It is very long (avg. 6 m – 18 ft.)

15. Duodenum Most of digestion takes place here
Ducts from liver, gallbladder and pancreas join to form the pancreatic duct (controlled by sphincter of Odi)
Bile from liver & gallbladder - emulsifies fat
Pancreatic juices from pancreas – has sodium bicarbonate  slightly basic environment that neutralizes chime

16. Digestive enzymes & hormones
From pancreas and liver - enter by the pancreatic duct.
Pancreatic enzymes and bile from the gallbladder = a response to the hormone cholecystokinin (produced in response to the presence of nutrients).
Secretin (hormone) promotes the release of bicarbonate from pancreas
Gastrointestinal inhibitory peptide (GIP) (hormone) believed to stimulate insulin secretion

17. Digestion of Proteins
Degraded into small peptides and amino acids before absorption.
Proteolytic enzymes (trypsin and chymotrypsin): secreted by the pancreas and cleave proteins into smaller peptides.
Proteo – protein
Lytic – break apart
Carboxypeptidase: pancreatic brush border enzyme
Splits one amino acid at a time.

18. Lipid digestion Lipids degraded into fatty acids and glycerol.
Pancreatic lipase breaks triglycerides into free fatty acids and monoglycerides.
Help from bile secreted by the liver and stored in the gall bladder.
Bile salts attach to triglycerides to help emulsify them

19. Carbohydrate digestion
Pancreatic amylase: breaks down starch into oligosaccharides.
Brush border enzymes:
Sucrase, maltase and lactase
Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria.

20. Carbohydrates that go undigested
Lactase is absent in some adult humans
lactose is not digested
Some carbohydrates (cellulose) are digested
Humans lack the enzyme for splitting the bonds between the glucose molecules.

21. Jejunum & Ileum Jejunum: 2nd part Ileum: 3rd part
Area where the majority of absorption takes place
Ileum: 3rd part
Absorption of vitamins
Small Intestine: Structure, Digestion, Absorption

22. Villi Increase surface area (SA) Absorb nutrients
Outer wall of epithelial cells
Each cell has thousands of microvilli (brush border)
Increase surface area (SA)
Absorb nutrients
Sugars and amino acids enter the blood capillaries
Glycerol and fatty acids enter epithelial cells. They are packaged as lipoprotein droplets and enter the lacteal.

23. Words to know Enzymes: Hormones: Gastrin Secretin GIP CCK Duodenum
Jejunum
Ileum
Chime
Bile
Villi
Microvilli
Brush border
Blood capillaries
Lacteal
Emulsification
Pancreatic amylase
Maltase
Lactase
Sucrase
Pepsinogen
Pepsin
Trypsin
Carboxypeptidase
Gastric lipase
Lipase
Nuclease
Nucleosidase
Gastrin
Secretin
GIP
CCK