The Digestive System
The 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!!
Anatomy
Connecting our 2 holes we have a series of
tubes PLUS a bunch of accessory organs that assist in the digestion of foods
Anatomy
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
The Tubes
Let’s Draw a Picture!
Lined with a mucous membrane
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
1) Mouth
Ms. Mueller’s Teeth
Passageway for food, fluids, and air Muscular passageway to propel food
Called peristalsis
2) Pharynx
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!!
CAREFUL!!
Food passes through the larynx on the way to the stomach.
True or False
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
3) Esophagus
Muscularis externa
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
3) Esophagus
What are the 4 tunics, in order, from external
to internal? Serosa, muscularis externa, submucosa,
mucosa
Question
Location Matters
Notice the location of the esophagus to the trachea
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
Question
C-shaped organ Has the same 4 tunics as the esophagus
What were those again? Mucosa, submucosa, muscularis externa, serosa
4) Stomach
Has 2 sphincters
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!
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
4) Stomach
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! http://
www.surgerysquad.com/surgeries/rny-gastric-bypass-surgery/
Surgery: Gastric Bypass
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 )
4) Stomach: Microscopic
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)
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
5) Small Intestine
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
5) Small Intestine: 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
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”
5) SI: Microscopic
Circular folds Villi Microvilli
Let’s Draw a Picture
Which of the following has the 4 tunics?
A) esophagus B) SI C) stomach D) LI E) all except D
Question
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
6) Large Intestine
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
Interesting…..
Let’s draw a complete picture
putting it all together!
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
Quiz Yourself
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