Grade 11 Biology Digestion. Ontario curriculum. Describes how digestion occurs in the human body and compares it with other organisms.

1. Digestion
Chapter 6.4

3. The Stomach
• Consists of three layers of smooth muscle
making it one of the strongest organs
• The stomach can be divided into three parts:
–Fundus (top) Body (middle), Pylorus (end)

4. Stomach Sphincter
• Sphincter: circular ring of muscles
which closes and opens tubes.
• Two in the stomach:
• Cardiac: prevents food from reentering
the esophagus
• Pyloric: closes off stomach from small
intestine, allowing food to stay in the
stomach longer (up to 8 hours)

5. Cardiac sphincter
(found in the rugae)

6. Rugae in a Dog’s Stomach (relaxed)

7. Gastric Juices
• Rugae = folds in lining of stomach
secrete gastric juices
• Gastric juices include:
1. Hydrochloric acid (HCl)
2. Pepsinogens
3. Mucus
4. Rennin (curdles milk to allow for longer
digestion in infants)

8. Functions of the Stomach
• The stomach has several functions:
1.Storage bin  holding food in the fundus &
releasing slowly into lower portion for
processing
enabling you to eat two or three meals a day
adult stomach stretches up to 1.5 L & produces
same amount of gastric juices every 24 hours
Humans would eat every 20 minutes if no
storage available

9. 2. Food mixer strong muscles contract &
mash food into sticky, slushy mass called
chyme
3. Sterilizer HCl kills pathogens (germs) in
food
4. Protein Digestion produces protein
enzymes
 Hydrochloric acid (pH of 1-3) converts
pepsinogen into an active protein enzyme
called pepsin
 Pepsin breaks proteins into polypeptides

10. What is an Ulcer?
• Why doesn’t the stomach destroy itself
since it is made up of proteins?
• Mucus provides a protective coating to
prevent self digestion
• Ulcer a surface lesion
• when the mucous lining of stomach is too
thin, it is exposed to HCl & pepsin,
irritating the stomach

11. Peptic (stomach) Ulcer

12. What Causes Ulcers?
• Linked to a bacterium called Heliobacter
pylori
• Can detect with H. pylori with a breath
test, treatment requires strong antibiotics
• Diet, Aspirin and stress can cause or
added to the ulcer irritation

13. Heliobacter pylori

14. Endoscopes
• An endoscope can be used to
diagnose ulcers
• Used to view interior of the body
• A light-emitting glass fibre and
forceps can be fitted on an
endoscope for tissue biopsy (to be
tested)

15. Endoscope Used in Diagnostics

16. Endoscope Treating an Ulcer