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