1. The digestive system

2. Digestive System Basics:
Digestive system:  Your digestive system is a group of organs that work together to breakdown the food that you eat physically as well as chemically into nutrient molecules, that are then absorbed into your bloodstream.  Your digestive system then rids your body of indigestible remains (waste).  
The organs of your digestive tract are divided into two major divisions, the alimentary canal and the accessory digestive organs.
1.  Alimentary canal
- A continuous coiled hollow, muscular tube that winds through the central body cavity and is open at both ends.
-It is composed of the following organs:  mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
2. Accessory Digestive Organs
-Help to assist the process of digestive breakdown
-Made up of the salivary glands, teeth. tongue, and several large digestive glands.

3. Order of Digestive Tract (Alimentary Canal) :
The Mouth:
- Is composed of the lips (which protect its anterior opening), the cheeks (from mouths lateral walls), the hard plate (which forms its anterior roof, and the soft plate (which forms the posterior roof).
-The uvula is a projection on the soft plate
-The tongue takes up the floor of the mouth
-From the mouth your food travels to the pharynx
The Pharynx:
- From the mouth your food passes through the oropharynx and laryngopharynx.
- Food travels down the laryngopharynx to the esophagus via muscles that line its walls.  

4. Esophagus:
- Runs from the pharynx through the diaphragm and into the stomach.
-Conducts food to the stomach.  
*There are four layers of tissue in the walls of the alimentary canal organs going from the esophagus to the large intestine, and they are...
1. mucosa (innermost layer)
2. submucosa (just beneath the mucosa)
3. muscularis externa (muscular layer after the submucosa)
4. serosa (the outermost layer of the wall)
Stomach:
- Food enters the stomach via the esophagus
- Once the food enters the stomach it secretes a solution called gastric juice, and the chief cells produce the protein-digesting enzymes ( makes stomach filling acidic).  
- Most digestive activity occurs in the pyloric region of the stomach

5. Small Intestine:
- Is the body's major digestive organ, and is where your food goes once it leaves the stomach.  
-  The small intestine is divided into three subdivisions,
1. The duodenum-curves around head of the pancreas (25cm long)
2. The jejunum-extends from the duodenum to the ileum (8ft long)
3. The ileum-leads to the large intestine (12ft long)
-Most of the chemical digestion of food takes place in the small intestine
-Can only process a small amount of food at one time
-Pancreatic ducts release enzymes which complete the chemical breakdown of foods in the small intestine.
- Bile formed by the liver also enters into the small intestine
- Nearly all food absorption occurs in small intestine.  
- Three structures in the small intestine help it to absorb food
Microvilli-tiny like projections of the plasma membrane, that
sometimes give the cell a fuzzy looking appearance.  
2. Villi- finger like projections of mucosa that give the cells
a velvet like feel.
3. circular folds- help to increase surface area for absorption.

6. Large Intestine:  
-Larger in diameter than small intestine, but shorter in length.
- Major function is drying up indigestible food absorbing all of the water from the waste so that it can leave the body as feces.
- Has four subdivisions
1. Cecum- first part of the large intestine
2. Appendix- hangs from the cecum ( easily infected)
3. Colon-many different parts, runs through the pelvis
4.Rectum/anal canal- all lie within the pelvis
-At the end of the large intestine is the anus which is where  waste leaves the body.  

7. Order of Digestive Tract (Accessory Digestive Organs)
Salivary glands:
-Empty their secretions into the mouth.
-saliva helps to protect against bacteria, but also helps to release the chemicals that allow you to taste your food.  
Teeth:
- your teeth's major function is to chew/grind your food to break it down physically.
Pancreas:   
-Soft pink triangular gland that extends across your abdomen.
- Produces enzymes  into the duodenum that help to break down all digestible foods.    

8. Liver and Gallbladder:
- The liver is the largest gland in the body, located under the diaphragm.
- Most important function is its production of bile.
- Bile does not contain enzymes but its major function is the breakdown of fats during digestion via its fats.
-The gallbladder is a small thin-walled sac that lays within the inferior surface of the liver.
- Its main function is the storage of bile when it backs up, until it can be broken down and removed with water.  

9. Functions of Digestive System:
- Main function of the digestive tract can be thought of as two things, absorptions, however there are other functions not covered by these terms.
-The key functions of the digestive tract can be summarized in six ways.
1. Ingestion- occurs when food enters the mouth so that the digestion process can begin to occur.
2. Propulsion- The movement of food from one body organ to the next, i.e. swallowing.  Peristalsis is the involuntary contraction of muscles in the organ walls, segmentation is another way for food to move through the tract, and it is the squeezing of muscles.  
3. Food breakdown: mechanical digestion- Mechanical digestion (grinding in stomach, break down of food by the tongue) all further prepare your food for chemical digestion.
4. Food breakdown: chemical digestion- The process by which large food molecules are broken down by enzymes.
5. Absorption- Transport of digested end products from the GI tract to the blood (small intestine is a major absorptive site).
6. Defecation- The elimination of waste or indigestible food from the body via the anus.  

10. More Diagrams to know:
The Stomach