1. The Digestive System
Section 30.3

2. What is the main purpose of the digestive system?
The digestive system converts food into small molecules, that can be used by the cells of the body
There are four stages
Ingestion - eating
Digestion – Mechanical and chemical
Absorption – occurs in intestines, absorbed into circulatory system
Elimination – all waste material removed as feces

3. Why is the mouth important?
Teeth do most of the mechanical digestion
Incisors, cuspids and bicuspids grind at food
Molars grind and crush food
Tonuge moves food around
Saliva triggered by the scent of food (controlled by nervous system)
Contains Amylase – breaks down starch
Also contains Lyzosome – helps prevent infection by breaking down bacteria
Tongue and throat muscles force clumps of food (bolus) down into throat
Flap of connective tissue – (epiglottis) prevents food entering trachea

4. What is the esophagus? The esophagus connects the mouth to the stomach
Does gravity force food down?
If so, how would astronauts eat in space?
Peristalsis provides the force that drives food into the stomach
Cardiac Sphincter closes the esophagus from the stomach
What is heartburn?

5. What is the pH of the stomach? What is it designed to digest?
Very acidic due to hydrochloric acid
Enzyme pepsin breaks down proteins
Glands produce mucus which protects the stomach wall - if it fails, can lead to a peptic ulcer
Stomach also causes mechanical digestion due to alternating contractions – essentially churning
Chyme produced (oatmeal conistency)
After a few hours, the pyloric valve opens up, and chyme is released into small intestine

6. What are the roles of the pancreas, liver and gallbladder in digestion?
The pancreas produces hormones that regulate blood sugar level,
It also produces enzymes to help break down carbohydrates, proteins, lipids and nucleic acids
It also produces a sodium bicarbonate – a base. Why do you think a base is needed at this stage of the digestive system?
Enzyme would be destoryed by stomach acid – it needs to be neutralized
The Liver assists in fat digestion
Liver produces bile, a fluid loaded with lipids and salt, which is stored in the gallbladder
When fat is present in the duodenum, the gallbladder releases bile into the small intestine
Fat globs together, making digestion difficult. Bile breaks up these globs

7. So where are different enzyme found in the digestive system
So where are different enzyme found in the digestive system? What do they do?

8. How does absorption from the small intestine work?
Most nutrients from food are absorbed through the small intestine
After leaving the duodenum, most chemical digestion is finished
Small intestine designed for absorption of food – how?
Villi and microvilli move move and absorb food particles
Products of carbohydrates and proteins absorbed by capillaries in the villi
Fats and fatty acids are absorbed by lymph vessels
At the end of the small intestine, only water, cellulose and other indigestible substances are left behind

9. What does the large intestine do?
Before entering the large intestine, material passes by the appendix. What is the role of an appendix?
Chyme then enters the large intestine/colon
Primary function is to remove water from undigested material - this process happens quickly
Colonies of bacteria help produce compounds that the body can use, such as vitamin K
Antibiotics can inadvertently destroy these colonies
Feces eliminated through the anus
Issues with water removal can lead to diarrhea or constipation

10. Key points What is the function of the digestive system?
What is the difference between mechanical and chemical digestion?
What structures does food travel through during digestion? What are their functions?
What would happen if your stomach could not contract and churn food?
How are nutrients absorbed?
Why are villi folded?