1. The Digestive System
The Anatomy

2. Anatomy We have what we call an alimentary canal
This means we have 2 holes
One for import, one for export
This is in contrast to organisms such as jellyfish who have a gastrovascular cavity
You guessed it…..just one hole for both in AND out
Moral of the story: be glad you have 2 holes!!

3. Anatomy
Connecting our 2 holes we have a series of tubes PLUS a bunch of accessory organs that assist in the digestion of foods

4. The Tubes
Our alimentary canal, aka our gastrointestinal (GI) tract, consists of a continuous, coiled, hollow, muscular tube
Organs
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine

5. Let’s Draw a Picture!

6. 1) Mouth Lined with a mucous membrane Important components
Question: What type of membrane is that?
Epithelial membrane
Means it is comprised of epithelial tissue and connective tissue
Important components
Tongue
Teeth
Salivary glands

7. Ms. Mueller’s Teeth

9. 2) Pharynx Passageway for food, fluids, and air
Muscular passageway to propel food
Called peristalsis

10. CAREFUL!! Do NOT confuse this structure with the larynx
The pharynx is for phood (food) and air
The larynx is for voice (we will talk about this in the respiratory system)
Food should NOT be found here!!

11. True or False
Food passes through the larynx on the way to the stomach.

12. 3) Esophagus Runs from the pharynx to the stomach
4 layers (innermost to outermost) called tunics
Mucosa
Moist membrane that lines the lumen (the hollow part of the tube)
Epithelial tissue, connective tissue, smooth muscle layer
Submucosa
Connective tissue
Blood vessels, nerve endings, lymph organs

13. 3) Esophagus Muscularis externa Serosa
Inner circular layer and outer longitudinal layer of smooth muscle
Serosa
Outermost layer consisting of flat serous fluid-producing cells
Visceral peritoneum and parietal peritoneum

14. Question What are the 4 tunics, in order, from external to internal?
Serosa, muscularis externa, submucosa, mucosa

15. Location Matters
Notice the location of the esophagus to the trachea

16. Question What prevents our food from “going down the wrong tube”?
Answer: the epiglottis!!
Flap of cartilage that directs food to the stomach and air to the lungs

17. 4) Stomach C-shaped organ Has the same 4 tunics as the esophagus
What were those again?
Mucosa, submucosa, muscularis externa, serosa

18. 4) Stomach Has 2 sphincters Let’s add to our picture!
These acts as gatekeepers letting things in and out of the stomach
Cardioesophageal sphincter connects the cardiac region of the stomach (closest to the heart) with the esophagus
the pyloric sphincter connects the stomach to the small intestine
Let’s add to our picture!

19. 4) Stomach Contains large folds of mucosa called rugae
This enables it to be flexible in its diameter
When full, it can hold up to ONE GALLON of food

20. Surgery: Gastric Bypass
Treatment for obesity
Involves decreasing the size of the available storage space of the stomach
Intended to make you feel full faster so that way you can eat less
Surgery Squad!

21. 4) Stomach: Microscopic
Pitted appearance called gastric pits that lead to gastric glands
There is also a variety of cells that assist in digestion
(We will get to those when we get to the physiology of digestion )

22. 5) Small Intestine Connects to the stomach via the pyloric sphincter
Coiled tube
Average length: 8-18 feet!!
Same 4 tunics of the stomach and esophagus
3 subdivisons
Duodenum (5% of length)
Jejunum (40% of length)
Ilium (55% of length)

23. 5) Small Intestine Contains ducts that connect to accessory organs
Both ducts merge into 1 duct
Pancreatic duct
Connects the pancreas to the small intestine
Common bile duct
Connects the liver/gall bladder to the small intestine
The gall bladder, liver, and pancreas are accessory organs to the GI tract

24. 5) Small Intestine: Microscopic
The small intestine has folds in it, just like the stomach
Called circular folds
Difference: these folds are not for stretching like the rugae of the stomach
These folds are for increased surface area

25. 5) SI: Microscopic
More microscopically, villi are fingerlike projections of mucosa found facing the lumen of the SI on the circular folds
Again, these function to increase the surface area

26. 5) SI: Microscopic
Even more microscopically, there are a series of microvilli on each villus
Projections of the plasma membrane of the mucosa cells
Often referred to as the “brush border”

27. Let’s Draw a Picture
Circular folds
Villi
Microvilli

28. Question Which of the following has the 4 tunics? A) esophagus B) SI
C) stomach
D) LI
E) all except D

29. 6) Large Intestine
Larger in diameter than the SI, but shorter in length
Frames the SI on 3 sides
Subdivisions
Cecum attaches the SI to the LI
The appendix hangs off of this structure
Called vermiform appendix because it looks like a rat tail
Colon
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal

30. Interesting….. Your anus is a sphincter
That is, it has a muscular gatekeeper
It has both voluntary and involuntary muscle so technically you can’t always control your elimination
Elimination=defecating=going #2

31. Let’s draw a complete picture putting it all together!

32. Quiz Yourself
Put the following organs in order: pharynx, mouth, small intestine, large intestine, stomach, esophagus
Mouth, pharynx, esophagus, stomach, SI, LI
Where does food pass through first: the cardioesophageal sphincter or the pyloric sphincter?
Cardioesophageal and then pyloric
What are the three accessory organs and how are they connected to our GI tract?
Liver, gall bladder, and pancreas; SI
What allows our stomach to expand?
Rugae folds
What is the purpose of the circular folds, villi, and microvilli? What organ contains these structures?
Increase surface area; SI