1. 4.4 Digestion in the Mouth and Stomach

2. 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

3. Specialized Digestive Systems
Each animal species has unique adaptations that enable it to obtain and digest food.
The mosquito, for example, has specialized mouth structures and a digestive system that may be used for sucking blood to obtain nutrients

4. Animal Planet - Mosquito

5. Specialized Digestive Systems
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

6. Specialized Digestive Systems
More complex animals have a digestive tract that has two openings—one for food intake and another for waste elimination.
Ex. Earthworm
food ingested in mouth travels through the pharynx and into the esophagus.
The esophagus then pushes the food into the crop for temporary storage.
Physical breakdown of the food is carried out by the gizzard.
The food particles pass into the intestine and are chemically broken down into smaller molecules to be absorbed by the cells lining the intestine
Any undigested wastes eliminated through the anus.

7. Earthworm Anatomy

8. The Structure of the Human Digestive System
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 (Figure 4).
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.

9. The Structure of the Human Digestion System
Every organ system depends on the digestive system for nutrients, but the digestive system also depends on other organ systems.
Muscle and bones, for example, enable animals to catch and ingest food.
The circulatory system transports oxygen and other materials to the digestive organs, and carries digested foods from the digestive system to the tissues of the body.
The nervous system and endocrine system regulate the actions of the digestive organs. Digestion involves interaction among several body systems.

10. Taste
Make a hypothesis about the evolutionary origin of taste in humans?

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

13. 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

14. Herbivore or Carnivore?
The type of teeth an animal has is directly related to its diet.
Mammalian herbivores have many molars for chewing plant matter
Mammalian carnivores have canine teeth that allow them to grab and kill prey.

15. Herbivore or Carnivore?

17. Sending food down the right tube!

18. 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

19. More About Sphincters….
There are more than 50 sphincters in the human body, and several of these are in the digestive tract. The gastroesophageal sphincter is located where the esophagus joins the stomach. This sphincter keeps food and acid from moving up the esophagus, preventing acid reflux
The pyloric sphincter is located between the exit point of the stomach and the first part of the small intestine (duodenum)

20. The Stomach

21. In the Stomach
The stomach is an organ where food is temporarily stored and chemical digestion continues.
Gastric juice (2 L per day) provides the necessary acidic environment for enzymes to function. It also kills most of the bacteria or other micro-organisms that enter the stomach. Gastrin is the major hormone that regulates acid secretion in the stomach.
Mucus present in gastric juice helps protect the stomach from acid damage.
Food in the stomach activates nerves which release signals that cause an increase in muscular contractions, which mixes the food with gastric juice.

22. Pepsinogen becomes pepsin
Pepsinogen is secreted in the stomach and is converted to pepsin, a protein digesting enzyme, when exposed to the acid present in gastric juice.
Pepsin begins the breakdown of proteins into separate amino acids. Secreting the inactive enzyme pepsinogen prevents damage to the stomach tissue. If gastric glands were to make pepsin instead of pepsinogen, the stomach would digest itself.

23. ULCERS
Stomach acid is strong enough to kill most bacteria that enter the stomach.
An ulcer is an open sore in the lining of the stomach caused by the presence of H. pylori bacteria in the stomach.
These bacteria prevent mucus-producing cells from producing enough mucus to protect the stomach lining
H. pylori may be transmitted through food or water, but the bacteria have also been found in the saliva of people with ulcers. H. pylori is usually successfully eliminated with antibiotics.