1. The Digestive System Lab1

2. Organs of the Digestive System
Gastrointestinal tract (GIT) – continuous passageway which contains the food from the time it enters the body until it leaves; organs include:
mouth (oral cavity), pharynx (oropharynx & laryngopharynx), esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum), anal canal, anus
Accessory organs - participate in digestive processes; organs include:
teeth, tongue, salivary glands, liver, gall bladder, pancreas 2

3. Function of the Digestive System
To break down food into a “usable” (absorbable) form – occurs through mechanical processing & chemical digestion
To supply our cells with the nutrients they need for energy, growth & repair 3

4. Classes of Nutrients: carbohydrates – including
polysaccharides (“complex” carbohydrates )
starch
disaccharides (“simple” sugars)
maltose, sucrose, lactose
proteins
fats (lipids/triglycerides)
vitamins
minerals
water
No digestive processes necessary, just absorption

5. Digestive processes
Mechanical processing – physical breakdown of food; e.g. mastication, emulsification, mixing waves, segmentation
Chemical digestion – chemical breakdown of food; disassembling of organic molecules into their component parts; requires enzymes
carbohydrates (polysaccharides)  disaccharides  monosaccharides
proteins  amino acids
lipids (triglycerides)  fatty acids & glycerol (monoglycerides)

6. Mouth (oral cavity)
Digestion (mechanical & chemical) begins within the oral cavity –
mastication
production of saliva by salivary glands
Parotid gland
Sublingual gland
Submandibular gland
saliva – made of H2O, salts & salivary amylase; moistens foods to create “bolus” to help with deglutition, & begins chemical digestion of starch
Starch (polysaccharide)
Maltose (disaccharide)
amylase 6

7. Stomach
Mechanical digestion – mixing waves to change bolus of food to “chyme”
Chemical digestion - secretions from cells of stomach to begin protein digestion: Peptic (chief) cells – pepsinogen
Parietal cells – hydrochloric acid (HCL)
Pepsinogen + HCL  Pepsin
Pepsin
Proteins
polypeptides
HCL

8. Small intestine Fats + bile  emulsified fats
Chyme from stomach (with partially digested starch & proteins) + Bile from liver & gall bladder + Pancreatic juice from pancreas – released into duodenum of small intestine
Segmentation mixes chyme with other secretions
Fats + bile  emulsified fats
bile

9. Pancreas proteases (trypsin, chymotrypsin, carboxypeptidase)
Pancreatic juice – mixture of enzymes & buffers (sodium bicarbonate) secreted by acinar cells into pancreatic duct & released into duodenum
pancreatic amylase
Starch maltose
lipase
Lipids (triglycerides) fatty acids + monoglycerol
proteases (trypsin, chymotrypsin, carboxypeptidase)
Proteins & polypeptides small peptides (tripeptides & dipeptides)
nucleases – digest RNA & DNA
Stomach
Head
Body
Tail
sodium bicarbonate – neutralizes acidic chyme because enzymes in small intestine need an alkaline pH 9

10. Small intestine
Cells in jejunum and ileum produce peptidases and disaccharidases for final digestion of proteins and sugars
small polypeptides, tripeptides, dipeptides
peptidases
amino acids
maltose
maltase
glucose + glucose
sucrose
sucrase
glucose + fructose
lactose
lactase
glucose + galactose

11. Absorption
Absorption of monosaccharides (glucose, fructose, galactose), amino acids and fatty acids (as well as vitamins/minerals) occurs in small intestine (into blood or lymph (fatty acids)
Absorption of water (and some vitamins) occurs in large intestine