1. Mouth

   • Ingestion

   • Chemical digestion with the salivary amylase.

   • Mechanical digestion due to teeth grinding

   • Saliva:

     • Salivary amylase.

     • Counter acts acidity avoiding tooth decay.

     • Lubricates food, which with the tongue shaping becomes bolus

2. Esophagus

   • Carries food from the mouth towards the stomach.

   • Carries a movement called peristalsis, which can be classified as mechanical digestion.

3. Stomach

   • Produces gastric juiced and acids to break down the bolus into smaller nutrients. This is considered chemical digestion.

   • Does mechanical digestion through its churning.

   • Has hydrochloric acid, which is very acidic providing the correct environment for the stomach’s enzyme, and denatures proteins from some bacteria.

   • The stomach’s cells produce mucus to protect it from the acidic internal environment.

   • After the stomach’s processes, what is left is called chyme.

4. Small Intestine

   • Absorption of most nutrients.

   • Some chemical digestion occurs too.

   • Parts:

     • Duodenum: Last part of chemical digestion in the pathway using bile.

     • Jejunum: Transition between the other parts

     • Ileum: More villi, therefore more absorption.

5. Large intestine

   • Also called after “Colon”

   • Absorbs water and salts

   • Parts:

     • Ascending colon

     • Transverse colon

     • Descending colon

6. Rectum

   • The chyme becomes feces, since only undigested content is in there.

   • Stores the feces until it sends a signal to the anus.

7. Anus

   • Excretes feces.

Accessory organs:

1. Appendix: Useless at the moment.

2. Liver: In charge of detoxification, processing substances to eliminate them. It also produces enzymes for digestion. Produces bile.

3. Pancreas: Produces insulin, which breaks down glucose, and pancreatic juices.

4. Gall Bladder: Stores bile.

Types of digestion

• Chemical digestion: Break down of food due to chemical reactions, with enzymes or other substances.

• Mechanical digestion: Break down of food through physical processes such as chewing, stomach-churning, and peristalsis.

Teeth types

1. Incisors: They break down soft foods.

2. Molars and pre-molars: They grind food into a bolus.

3. Canines: They tear meat

   1. Carnivores: Pointy and sharp teeth.

   2. Omnivores: Neither sharp nor smooth.

   3. Herbivores: Falts and smooth teeth.

Tooth decay

Occurs when the hard and outer enamel of the tooth is damaged when bacteria in the mouth convert sugars into acids that react with the enamel, entering the softer and more delicate dentine, on the inside of the tooth.

Enzymes

Bile

The enzymes in the small intestine work best in alkaline environments, but the chyme is acidic after the stomach.

Bile is an alkaline substance produced by the liver and stored by the gall bladder.

Functions:

1. Neutralizes the acidic chyme, providing the required alkaline conditions.

2. Emulsifies the fats, dividing the lipid into smaller with higher surface area droplets to ease absorption.

Absorption

The movement of digested food molecules through the wall of the intestine into the blood and lymph.

The small intestine is the region where digested food is absorbed.

Most absorption happens in the ileum (third part of the small intestine) which is the largest part, therefore providing more surface area.

Villi

Its function is to increase the surface area of the lining in the small intestine.

Characteristics:

1. One cell thick provides a small distance for nutrients to pass through diffusion and active transport.

2. Network of blood capillaries that transport glucose and amino acids through the blood.

3. Lacteal is an internal structure that transports fatty acids and glycerol into the lymph.

Assimilation

The movements of digested food into the cells of the body where they are used are mediated by the liver.

Egestion

The large intestine absorbs most of the water and, by the end of all intestines, most food has been absorbed

The remaining material consists of:

→ Water

→ Bacteria (beneficial)

→ Fiber and undigested materials.