1. Human Digestive System
Digestion is the process by which organisms break large molecules into smaller ones
For example, breaking down carbs, fats, proteins
Digestion must take place so that molecules will be small enough to pass through cell membranes

2. Mouth Food enters here Mechanical breakdown occurs
Teeth bite and grind food
Tongue moves and shapes food

3. The digestive juice called saliva is added
Wets the food
Sticks food together into a bolus
Contains a digestive enzyme called salivary amylase
Salivary amylase breaks down starch (a polysaccharide) into maltose (a disaccharide)
Food is pushed into the throat
Food is kept from entering the larynx and trachea by a flap of tissue called the epiglottis

4. Esophagus
No mechanical or chemical breakdown occurs here
Food is pushed to the stomach by the muscular walls of the food tube ~ peristalsis
Food enters the stomach when a ring of muscle – the cardiac sphincter lets it through
Reverse peristalsis – cardiac sphincter opens and stomach contents are forced out – vomiting

5. Esophagus
Heartburn – when the cardiac sphincter relaxes causing stomach juices containing hydrochloric acid to come into contact with the esophagus

6. Stomach
a thick-walled muscular sac
Mechanical breakdown is completed here
Solid food is reduced to a thin soupy liquid called chyme (2-6 h)
Liquids pass through in 20 min. or less
Stomach has pyloric glands
Secrete mucus to protect the stomach from being “digested”

7. Stomach
Stomach has gastric glands
Secrete gastric juices
Gastric juices contain hydrochloric acid and the digestive enzyme called pepsin
Pepsin can only break down proteins in an acidic environment
When acid is present it changes the proteins into shorter chains of amino acids called polypeptides
When stomach is empty only small amount of juice is present

8. All stimulate gastric juices
Stomach
When food is eaten gastric juice increases
Thought, sight, smell, taste of food
Food touching the stomach lining
Food mass stretching stomach walls
Food exits through the pyloric sphincter into the small intestine
All stimulate gastric juices

9. Stomach
Ulcers can occur when the mucous layer breaks down and part of the stomach is “digested”

10. Small intestine About 6.5 m long, 2.5 cm in diameter Coiled tube
Three sections:
a. duodenum (25 cm)
b. jejunum (several metres)
c. ileum (largest section)
Chemical digestion is completed here
Absorption of nutrients is completed here

11. Small intestine
When food is present the small intestine is in constant motion (peristalsis)
Four main effects:
Squeezes chyme through
Mixes chyme with digestive enzymes
Breaks down food
Speeds up absorption
Small intestine fluids are alkaline (pH > 7)

12. Small intestine Three juices mix with the chyme Bile Made by liver
Stored by gallbladder
Emulsifies fats (breaks them into smaller drops to make it easier to break them down later)
Contains no enzymes
Neutralizes the acids from the stomach

13. Contains several enzymes:
2. Pancreatic juice
when acidic chyme enters the small intestine it stimulates hormones which signal the pancreas to release juice and enzymes into the upper part of the small intestine
Contains several enzymes:
Amylase ~ continues to breakdown starch to maltose)
Trypsin (protease) ~ breaks down the polypeptides called peptones and proteoses, into peptides
Lipase ~ breaks down fats and oils into fatty acids and glycerol

14. Intestinal juice contains the enzymes
Peptidase ~ breaks down peptides into amino acids
Maltase ~ finishes carbohydrate digestion by breaking down maltose into glucose
Now all nutrients have been broken down:
carbohydrates glucose (monosaccharides)
fats fatty acids and glycerol
proteins amino acids

15. Small intestine (cont’d)
Absorption of these nutrients takes place through finger-like projections called villi that line the intestinal walls
Each villus has a network of capillaries and a lacteal
Through diffusion and active transport the nutrients are absorbed
Monosaccharides, amino acids, vitamins, minerals are all absorbed into the capillaries
Fatty acids and glycerol are absorbed into the lacteal and into the lymphatic system

17. Large intestine No digestion here About 1.5 m long and 6 cm diameter
Small pouch called appendix situated where the small intestine joins the large intestine
Has no function but can cause problems

18. Large intestine (3 main functions):
Re-absorption of water (about ¾ of it)
Too much water absorbed = constipation
Too little absorbed = diarrhea
Absorption of vitamin K and some B vitamins that are produced by bacteria that live in the large intestine
Elimination of undigested and indigestible materials like plant cell walls, bacteria, bile, mucus, worn-out cells

19. Large intestine
As the material travels through it becomes feces or stool
Feces stored in the rectum (last part of colon) before being eliminated through the anus

20. Label diagram of respiratory system in resource booklet!!!