Bio 102: Fundamentals in Animal Biology. This is a handout for the digestive system.

2. Functions:
• Takes in food (ingests it)
• Breaks it down physically and chemically
into nutrient molecules (digests it)
• Absorbs the nutrients into the
bloodstream
• It rids the body of the indigestible
remains (defecates)
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Chapter IV. The Digestive System

3. • The digestive tube can be organized into
specialized regions
• That carry out digestion and nutrient
absorption in a stepwise fashion
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4. 4

5. 5

6. Types of animal body plans
• Sac-like plans
– are found in many invertebrates
– have a single opening for food intake
and the discharge of wastes
• Tube-within-a-tube plan
– found in vertebrates
–food entering through one opening (the
mouth) and wastes leaving through another
(the anus)
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7. Types of Digestion
• Intracellular digestion
–occurs in sponges, coelenterates (corals, hydras
and their relatives) and most protozoans
• Extracellular digestion
–occurs in chordates, annelids, and crustaceans
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8. Stages in the Digestive Process
• movement: propels food through the
digestive system
• secretion: release of digestive juices in
response to a specific stimulus
• digestion: breakdown of food into
molecular components small enough to
cross the plasma membrane
• absorption: passage of the molecules
into the body's interior and their passage
throughout the body
• elimination: removal of undigested
food and wastes 8

9. The Mammalian Digestive System
• Each organ has specialized food-
processing functions
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• Alimentary canal/
GI tract
- mouth
- pharynx
- esophagus
- stomach
- small intestine
- large intestine
• Accessory organs
- salivary glands
- teeth
- pancreas
- liver
- gall bladder

10. Components of the Digestive System
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11. Mechanics of Swallowing
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12. 12
Peristalsis- rhythmic waves of contraction
of smooth muscles in the wall
of the canal

13. • Liver- regulation of amino acids in blood, production
of glycogen (storage molecule) and bile
• Pancreas- secretion of amylase and insulin (lack of
insulin may cause diabetes)
• Gallbladder- storage of bile
Accessory Digestive Organs
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14. The Stomach
• Large muscular storage organ; function in storage,
mixing, and secretion of gastric juice, which
converts a meal to acid chyme
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15. 15
Small intestine
– is the major organ of digestion and absorption

16. • The enormous microvillar surface
– Is an adaptation that greatly increases the rate of
nutrient absorption
16

17. 17
• Hormones help coordinate the secretion of digestive
juices into the alimentary canal

18. • reabsoption of water
• Bacteria in colon produce vitamin K
• The wastes of the digestive tract, the
feces
–Become more solid as they move
through the colon
–Pass through the rectum and exit via
the anus
The large intestine, or colon
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19. 19

20. Chemistry of Digestion
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Hydrolysis- digests foods:
1. Carbohydrates (starches) - become
simple sugars
2. Proteins - become amino acids
3. Fats - become fatty acids & glycerol
4. Nucleic acids (RNA, DNA) - become
nucleotides

21. Carbohydrate Digestion
21
• Begins in mouth - salivary amylase breaks down
starch
• Mostly occurs in small intestine aided by following
enzymes:
a. Pancreatic enzymes - breaks starch into maltose
b. Maltase - breaks maltose into 2 glucoses
c. Sucrase - breaks sucrose into 1 glucose and 1
fructose
d. Lactase - breaks lactose into 1 glucose + 1 galactose
• Last 3 enzymes produced by small intestine. Following
absorbtion, glucose, fructose, & galactose transported
to the liver where they are converted to glycogen.

22. Fat Digestion
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• Gastric lipase of stomach breaks down some
fats.
• Most fat digestion occurs in small intestine.
• bile emulsifies fat, exposing more fat to
enzymes
• Bile salts link fat molecules to water
molecules; (normally fats are hydrophobic)
• Pancreatic lipases continues fat digestion
• subunits now cross into microvilli
• subunits are reassembled into triglycerides,
combined with cholesterol, and transported to
the circulatory system

23. Protein Digestion
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• Stomach - pepsinogen converted to pepsin in
the presence of HCL. Pepsin breaks some of
the peptide bonds of some proteins
• Small intestine - Pancreatic enzymes trypsin
& chymotrypsin break proteins into smaller and
smaller units. The pancreatic enzyme
carboxypeptidase breaks peptides into free
amino acids. Several enzymes produced by the
small intestine further break peptides into
amino acids.

24. • Amino acids- absorbed and transported to the
liver.
− used directly by the liver to make liver
proteins
− others converted to acetyl coenzyme A
(used in citric acid cycle)
− other amino acids sent to various parts of
the body for protein synthesis
• Proteases must be activated before being used
− Prevents them from breaking down pancreas
(where they’re made & stored)
− Activation occurs when they come in contact
w/ certain chemicals found in the small
intestine 24

25. Nucleic Acid Digestion
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• Enzymes called nucleases break down
nucleic acids such as RNA (ribonucleic
acid) and DNA (deoxyribonucleic acid)
into nucleotide chains.
• The pancreas produces ribonuclease and
deoxyribonuclease
• small intestine produces nucleases that
break down nucleotides into smaller
subunits.

26. Integration & Regulation of Digestive
Processes
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• Mechanical - act of chewing causes release of
salivary amylase.
• Neural - food in stomach stimulates vagus
nerve, signal sent to brain, brain sends another
signal down vagus nerve for stomach to release
gastric secretions.
• Hormonal - e.g. the stomach releases the
hormone gastrin when a protein concentration is
detected; gastrin circulates in blood, target cells
are gastric glands which release gastric
enzymes; similar in small intestine and pancreas.

27. Importance of Nutrition
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• provides food for fuel
• provides food for fabrication
• provides food to obtain essential
nutrients, water, minerals