1. Digestion & Digestive Systems
Animal Anatomy & Physiology
Digestion & Digestive Systems

2. Introduction
The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in the body.

3. DIGESTION 4 main steps in digestion:
Ingestion - the taking in of nutrients
Digestion - the physical and chemical breakdown of complex food molecules into smaller molecules
Absorption - (the transfer of digested nutrients from the digestive system to the bloodstream
Egestion - the removal of waste food materials from the body

4. Digestive Sac
Some simple animals, such as flatworms or jellyfish, have a digestive sac with a single opening into a gastrovascular cavity.
Nutrients are absorbed by cells lining the cavity and diffuse into all other cells

5. Earthworm Digestive System

6. Alimentary Canal (GI Tract)
The human digestive system is also a complete digestive system. Unlike that of the earthworm, the digestive tract of humans is much longer than the body
Often referred to as the gastrointestinal tract (GI tract), the human digestive tract is approximately 7 m to 9 m long, depending on the age and size of the individual.

7. Human Digestive Tract Begins when food enters the mouth.
It is physically broken down by the teeth.
It is begun to be chemically broken down by amylase, an enzyme in saliva that breaks down carbohydrates.

8. Taste The myth of the tongue map; that 1 tastes bitter, 2 tastes sour,
3 tastes salt, and
4 tastes sweet.

9. The Mouth
In humans, digestion begins in the mouth. Food is broken down into smaller pieces by the teeth (physical digestion). Enzymes, like amylase begin chemical digestion in the mouth
Flat for grinding and crushing food
Sharp for grabbing and cutting food

10. Herbivore or Carnivore?

11. After Ingestion
The tongue moves the food around until it forms a ball called a bolus.
The bolus is passed to the pharynx (throat) and the epiglottis makes sure the bolus passes into the esophagus and not down the windpipe!

12. Sending food down the right tube!

13. Down the Esophagus
The food stretches the walls of the esophagus, activating the smooth muscles to undergo rhythmic, wave-like contractions called peristalsis
sphincter the circular muscle that
contracts to close an opening in the body

14. The Stomach

15. In the Stomach
The stomach has folds called rugae and is a big muscular pouch which churns the bolus (Physical Digestion) and mixes it with gastric juice, a mixture of stomach acid, mucus and enzymes.
The acid kills off any invading bacteria or viruses.
The enzymes help break down proteins and lipids. Chemical Digestion.
The mucus protects the lining of the stomach from being eaten away by the acid.

16. Chyme The stomach does do some absorption too.
Some medicines (i.e. aspirin), water and alcohol are all absorbed through the stomach.
The digested bolus is now called chyme and it leaves the stomach by passing through the pyloric sphincter.

17. The Structure of the Small Intestine
S.I. is where most digestion and absorption of nutrients takes place
S.I. is a tube only about 2.5cm in diameter but can be 7m long.
Made up of three sections: the duodenum, the jejunum, and the ileum
absorbed in the ileum

18. Villi and Microvilli Up Close

19. Absorption of nutrients
Within each villus is a network of tiny blood vessels called capillaries. All nutrients, except digested fats, enter the bloodstream through the capillaries.

20. Liver and Pancreas

21. The Structure of the Large Intestine
The large intestine is approximately 1.5 m in length but is two to three times larger in diameter than the small intestine, about 7.6 cm.
The large intestine consists of the cecum, colon, rectum, and anus

22. The Function of the Large Intestine
The large intestine (or colon) is used to absorb water from the waste material leftover and to produce vitamin K and some B vitamins using the helpful bacteria that live here.
All leftover waste is compacted and stored at the end of the large intestine called the rectum.
When full, the anal sphincter loosens and the waste, called feces, passes out of the body through the anus.