1. Digestive System
A closer look

2. Digestive Processes
In order for our bodies to use the food we eat to grow, energize, and repair our cells, 5 digestive processes have to occur.
These include:
Ingestion
Movement
Digestion
Absorption
Egestion (excretion)

3. Digestive Processes
These processes occur at different locations along the digestive tract, which is a continuous tube from mouth to anus.
We are going to discuss what happens at each site as we go through the stages.
It will be useful to copy the following concept map and to keep adding to it as we add more details to help you stay organized.

4. NOTE: This should be a straight line in your notes
Small
Intestine
Stomach
Large
Intestine
Esophagus
Tongue
Rectum/
Anus
Mouth/
Throat
Teeth
Salivary Glands

5. Digestive System Includes organs which perform digestion tasks:
Digestive Tract (Gastrointestinal Tract, G. I. Tract) includes: mouth, esophagus, stomach, small intestine, large intestine or colon, and anus.
Accessory Structures include:, tongue, salivary glands, liver, gall bladder and pancreas.

6. Digestion
The process in our bodies that breaks down food for use by our cells. This is done in two ways:
Mechanical: our teeth chewing through the food
Chemical: enzymes breakdown food into absorbable molecules.

7. Mouth (where it all begins)
Hard Palate
Four main parts of the mouth
Teeth
Tongue
Salivary Glands
Hard and Soft Palates
Uvula

8. Mouth Teeth (Chewing) How many teeth in adult humans?
Mechanical Digestion
Are covered by enamel, the hardest structure of the body
Their movements slice, tear, grind and mix food
Incisors: snap off pieces of food
Canine: tearing pieces apart
Premolars & molars: grind food to a paste
How many teeth in adult humans?

9. Tongue Floor of oral cavity
Composed of voluntarily controlled muscle tissue
Role: Guides food during chewing and swallowing
Major taste buds are embedded here.
Salty, sweet, sour, bitter

10. Salivary Glands
Release saliva in response to the smell, taste, and thought of food
First example of chemical digestion:
Contains Amylase: an enzyme that begins breakdown of starch into simple sugars, like glucose or table sugar.
Interesting Fact: We secrete about 1-2L of saliva per day!

11. Hard & Soft Palates Separate mouth from nasal
cavity, so food doesn’t go up your nose!
Located at the roof of your mouth.
Uvula (dangles)
Just beneath the soft palate
Prevents food from entering nasal passages by raising up.

12. Soft Palate
Hard Palate
Tongue
Uvula
Epiglottis
Trachea

13. Recap (Mouth) Food enters
Teeth rip, tear, and chew into smaller pieces to swallow
At the same time, Salivary Glands are stimulated to release saliva which contains amylase.
Tongue pushes bolus to back of pharynx (throat) and the uvula elevates, closing off the nasal passage. The bolus now pushes the epiglottis which closes the opening of the larynx, preventing the food from entering the wrong tube, which results in choking

14. Esophagus
Muscular tube which extends from pharynx (throat) to the stomach
Swallowing initiates peristalsis, a wave of contraction which initiates just above the “bolus” (substance) and moves it towards the stomach.
This movement also occurs in the stomach and in the intestines.

15. Esophagus Secretes mucus (along with the rest of the digestive tract)
This lubricant decreases the likelihood of the esophagus getting damaged by any sharp edges from the food entering.
Mucus also protects esophagus from acid and enzymes in gastric juice if reflux were to occur.

16. NOTE: This should be a straight line in your notes
Small
Intestine
Stomach
Mechanical: Peristalsis
Large
Intestine
Esophagus
Tongue
Rectum/
Anus
Mouth/
Throat
Mechanical: Chewing
Chemical: Starch/Amylase
Teeth
Salivary Glands

17. Stomach Separated from esophagus by the Gastro esophageal sphincter
Expandable muscular J-shaped sac that can hold up to 2-4 liters of food and liquid
Secretes mucous to protect lining cells
Contents are held in the stomach by the pyloric sphincter, ring of circular muscle, which separates the stomach from upper small intestine

18. Stomach
3 Functions
Stores food and releases it gradually into the small intestine
Assist in mechanical breakdown of food by peristalsis and contractions of muscular walls
Chemical breakdown of food by enzymes and other substances.

19. Stomach Secretions (continued)
Gastrin: hormone that stimulates secretion of Hydrochloric acid (HCl)
Pepsinogen: inactive form of enzyme is activated by HCl and transformed into pepsin which helps breakdown proteins into amino acids (smaller units).

20. Stomach
Food is gradually converted into a thick liquid called chyme which consists of partially digested food and digestive secretions.
Chyme is propelled towards small intestine
The Pyloric sphincter lets a teaspoon of chyme into the small intestine during each contraction
Takes around 2-6 hours to empty stomach

21. NOTE: This should be a straight line in your notes
Mechanical: Muscle Contractions
Mechanical: Peristalsis
Small
Intestine
Stomach
Mechanical: Peristalsis
Chemical: Pepsin (Proteins), HCl
Large
Intestine
Esophagus
Tongue
Rectum/
Anus
Mouth/
Throat
Mechanical: Chewing
Chemical: Starch
Teeth
Salivary Glands

22. Small Intestine (S. I.) Narrow tube (1-2 inches in diameter)
Longest part of digestive tract
Split into three parts: duodenum, jejunum, and the ileum
Function: to digest food into small molecules and absorb into blood stream and lymph vessels.

23. Small Intestine (S. I) Helped by three other sources:
1. Liver: Has many functions in our bodies. In digestion, it produces bile which is stored in the gall bladder, then released in the S. I.
Bile is made up of bile salts, water, and other salts and assist in the breakdown of lipids.

24. Small Intestine (S. I.)
2. Gall Bladder stores bile until it’s needed for digestion

25. Small Intestine (S. I.) Located between stomach and S. I.
3. Pancreas
Located between stomach and S. I.
Cells produce pancreatic juice which neutralizes the acidic chyme it receives from the stomach
Digests carbohydrates, proteins, and lipids
Contains water, sodium bicarbonate, and many enzymes
YouTube - Pancreas - "Weird Al" Yankovic

26. Small Intestine (S. I) Pancreas (cont’d) Enzymes include:
Amylase Carbohydrates
Lipase Lipids
Proteases Proteins and peptides

27. Small Intestine (S. I.)
Specialized cells within the wall complete the process. At the same time, nutrients are absorbed into the blood stream.
The numerous folds and projections, called villi, give the internal surface area a much larger surface for absorption.

28. Small Intestine (S. I.)
The area of absorption is also increased by the millions of microvilli.

29. NOTE: This should be a straight line in your notes
Mechanical: Peristalsis
Bile emulsifies lipids
Alcohol absorbed
Chemical: Amylase-CH2O
Lipase-Lipids
Proteases-Proteins
Mechanical: Muscle Contractions
Peristalsis (3 layers)
Small
Intestine
Stomach
Macro & micronutrients absorbed
Mechanical: Peristalsis
Chemical: Pepsin-Proteins
HCl: pH-2
(gastric juices)
Large
Intestine
Esophagus
Tongue
Rectum/
Anus
Mouth/
Throat
Mechanical: Chewing
Chemical: Amylase-Starch
Teeth
Salivary Glands

30. Are We There Yet? Almost…
While the nutrients are being absorbed by these cells, chyme is being mixed back and forth by segmentation movements within the small intestine.
When absorption is complete, undigested material moves into the large intestine.

31. Large Intestine (L. I.) Is about 5 feet long and 3
inches in diameter in adults
Two parts:
Colon
(for most of its length)
Rectum: the final 6”
Receives leftovers of digestion: water mixture, undigested fat and proteins, indigestible fibers

32. Large Intestine (L. I.)
Contains large populations of bacteria that thrive on the unabsorbed nutrients and are also responsible for synthesizing important vitamins for the body (B12, riboflavin, K).
Remaining water, salts, and vitamins are reabsorbed by cells in the L. I.

33. NOTE: This should be a straight line in your notes
Mechanical: Peristalsis
Bile emulsifies lipids
Mechanical: Muscle Contractions
Peristalsis (3 layers)
Chemical: Amylase-CH2O
Lipase-Lipids
Proteases-Proteins
Small
Intestine
Stomach
Macronutrients absorbed
Mechanical: Peristalsis
Chemical: Pepsin-Proteins
HCl: pH-2
(gastric juices)
Large
Intestine
Esophagus
Tongue
Remaining water, salts and vitamins absorbed
Rectum/
Anus
Mouth/
Throat
Mechanical: Chewing
Chemical: Amylase-Starch
Teeth
Salivary Glands

34. Large Intestine (L. I.)
Leftover material is condensed into semisolid feces which are transported to the rectum by peristaltic movements.
Expansion of the rectum stimulates the urge to defecate which is initiated voluntarily after age 2.

35. The Facts About Poop
The Facts About Poop