1. Digestive System

2. Organisms Organ systems Organs Tissues Cells Molecules Atoms
tree
human
Organ systems
Organs
leaf
stem
brain
heart
Tissues
leaf tissues
cardiac
tissue
Cells
nerve cell
Molecules
DNA molecules
Atoms

3. Functions of the Digestive System
Disassemble large organic molecules into smaller component molecules
Transfer these to circulatory system for distribution to rest of body
Get rid of indigestible material

4. Steps of digestion
1. Break down food
Mechanical Digestion: Grinding large food particles into smaller clumps
Reduces the number of molecules per clump
Increases total surface area of ingested food
Chemical Digestion: Breaking larger molecules into smaller component molecules, by means of a chemical reaction, using enzymes
2. Absorption: Smaller component molecules transported across wall of digestive tract and into blood vessels 
3. Elimination : getting rid of undigested food

5. Organs involved in digestion
Two types of organs:
Digestive Tract Organs
- Food travels through these organs
Accessory Organs
- Organs that secrete products to help digestion

6. Digestive Tract Organs
Accessory Organs
Oral Cavity
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Salivary Glands
Liver
Gall Bladder
Pancreas

7. Oral Cavity: Mechanical processing- chewing
Chemical Digestion- saliva secretion: carbohydrate digestion
 Epiglottis:
“Lid” that closes over opening to trachea - Prevents food entering airway

8. Why is mechanical processing important?
Enzymes must bind to their substrates, but can not access these molecules inside large clumps of food
Mechanical processing:
increases surface area of food particles
Exposes more molecules to enzymes, increases efficiency.

9. Swallowing:

10. Pharynx and Esophagus:
No mechanical processing, digestion, or absorption, merely conducts food to stomach.
If you stand on your head, will the food still move to your stomach?
YES: Peristalsis is a series of muscle contractions that moves food down the esophagus

12. Stomach:
1. Stores food and releases small amounts into small intestines
2. Mechanical digestion: churning
3. Chemical digestion: protein digestion begins
Stomach wall cells secrete:
enzymes
hydrochloric acid - Lowers pH to kill pathogens (disease-causing organisms) and activate protein enzymes

13. Small Intestine: Most chemical digestion occurs
lipids, nucleic acids, carbohydrates, and proteins are broken down
Absorption of nutrients
Helped by secretions of accessory organs

14. Small Intestine: From Accessory Organs: Liver Bile: produced in liver
stored in gall bladder
emulsifies lipids so they can be digested
Pancreas
Pancreatic juices:
Enzymes that digest all types of food molecules
Chemicals to neutralize pH of chyme

15. Small Intestine: Digestion Mechanical: Emulsification of Lipids
Lipids are not water soluble, but enzymes are –
Bile breaks up large groups of lipid molecules into smaller droplets so enzymes can act on them
Bile enters the small intestine through the bile duct
Chemical - Carbohydrate, protein, lipid & nucleic acid digestion
enzymes are secreted from the pancreas and the intestinal wall

16. Small Intestine:
Absorption - Component molecules diffuse across intestinal wall into circulatory system
Villi (fingerlike projections)

17. Pancreas structure increases surface area for absorption:
1. Intestinal wall - folded
2. Villi - Fingerlike projections of intestinal wall;
3. Microvilli - Projections of plasma membrane of intestinal cells

18. Amino acids, glucose, other water soluble nutrients absorbed into the capillaries

19. What are lacteals? vessels of the lymphatic system
found Inside the villi
absorb fatty acids and glycerol

20. Blood leaving intestines is transported to the liver via the hepatic portal vein for processing [molecules modified, toxins removed]

21. Large Intestine (colon): - Absorbs water;
Responsible for elimination of undigested food (feces)-
Contains lots of bacteria (mostly E. coli), which
digest some remaining food
produce vitamins (K)

22. Accessory Organs

23. The liver
Removes
unwanted or harmful chemicals (detoxification) including chemicals produced in the body,
unwanted chemicals taken into the body (e.g. carcinogens), and medications.
Hepatocytes - Liver cells - the liver's main functional units.

25. Pancreas
Main enzyme producing organ of digestive system

26. Pancreas
Pancreatic duct enters the small intestine to deliver fluid (pancreatic juice) through a small hole in the wall of the second part of the duodenum
Pancreatic juice contains enzymes capable of digesting all food types - protein, fat and carbohydrates