1. Digestion
AP Biology
Unit 6

2. General Steps Ingestion = food is taken in (eating )
Digestion = Food is broken down into smaller pieces /molecules
Absorption = Nutrient molecules are absorbed into body cells
Elimination = undigested material exits the body

3. Types of Digestion
There are two kinds of digestion – mechanical and chemical
Mechanical = Food is broken down into smaller pieces (chemical structure not changed)
Chemical = Food is broken down into smaller molecules (chemical structure changed)

4. Intracellular Digestion
In the animal kingdom, only sponges (Phyla Porifera) do this exclusively.
Steps:
Cells engulf food via phagocytosis or pinocytosis, forming food vacuole.
Lysosomes fuse with food vacuoles; hydrolytic enzymes break down food.

5. Extracellular Digestion
All animals (except sponges) perform this mode of digestion
Digestion begins in a compartment continuous with the outside of the animal’s body (gut).
What is the advantage of extracellular digestion?
animal can take in a lot of food at once and slowly digest it

6. Extracellular Digestion
Enzymes are secreted to break food into smaller molecules.
After the food has been broken down, many animals continue digestion intracellularly.
Animals that perform extracellular digestion can have a variety of different digestive systems.

7. Gastrovascular Cavity
Gastrovascular cavity = digestive sac with a single opening
Animals that have a gastrovascular cavity = Hydra
Phyla Cnidarian (also includes jellyfish, anemones, corals)

8. Digestion in Gastrovascular Cavities
Tentacles sting prey and stuff it into opening
Digestive enzymes are secreted to allow for extracellular digestion
Nutritive muscular cells then engulf food particles and complete digestion intracellularly
Undigestible material leaves through mouth (no anus)

9. Complete Digestive Tracts
Complete digestive tract = digestive tube running throughout body (alimentary canal)
Organisms with a complete digestive tract have both a mouth and an anus

10. Question…
Why would having a separate entry and exit point be beneficial?
digestion can be broken down into steps
there can be specialization of digestive tissues for these steps

11. Specialized Digestive Structures
Certain organisms have specialized digestive structures
Crop
Function = Store and moisten food
Who has it?
Earthworms (Phylum Annelida)
Grasshoppers (Phylum Arthropoda)
Birds (Phylum Chordata)

12. Specialized Digestive Structures
Gizzard
Function = Contains sand and stones; As the muscles around it move, food is ground up (mechanical digestion)
Who has it?
Earthworms (Phylum Annelida)
Cockroaches (Phylum Arthropoda)
Birds (Phylum Chordata)

13. Specialized Digestive Structures
Gastric ceca
Function = Extend from midgut to help with absorption
Who has it?
Grasshoppers (Phyla Arthropoda)

14. Human Digestion
Where do the four steps in food processing occur?

15. Human Digestion Ingestion = mouth
Digestion = mouth, Stomach, Small Intestines
Absorption = Small Intestines, Large Intestines
Elimination = End of large intestines

16. Oral Cavity, Pharynx, Esophagus
Participate in ingestion and digestion
Mechanical Digestion
By teeth and tongue (chewing)
Forms mass of food = bolus
Chemical Digestion
Salivary amylase begins digestion of carbohydrates (starch)

17. Oral Cavity, Pharynx, Esophagus
Epiglottis moves during swallowingto cover the trachea, so food travels down “right pipe” to the esophagus
Peristalsis (muscle contractions) will involuntarily continue movement of the bolus

18. Stomach Important in storage & digestion
What advantage do folds in the stomach tissue provide?
Allows the stomach to expand to hold more food
Tissue is also very elastic so that it can stretch

19. Stomach
Gastric glands produce gastric juice from a combination of 3 cells:
Mucus Cells secrete mucus (protects stomach lining)
Chief Cells secrete pepsinogen (inactive enzyme)
Parietal Cells secrete HCl

20. Stomach
Gastric juice is churned with bolus to break down food and kill bacteria
HCl converts pepsinogen into pepsin (active enzyme)
Pepsin hydrolyzes (breaks down) protein.
Halfway done!

21. Stomach: Pepsin What kinds of bonds are broken by pepsin?
Peptide bonds
What kind of reaction is this?
Hydrolysis

22. Protection of the stomach
Stomach protects itself from self-digestion by
keeping pepsinogen stores away from HCl until pepsin is needed
lining stomach with mucus
Food leaves stomach as acid chyme, squirting slowly through the pyloric sphincter

23. Small Intestine Participates in digestion and absorption
Peristalsis allows for movement of chyme and digestive juices down the small intestine.

24. Digestion in the Small Intestine
Digestion is usually completed in the duodenum (first section) with the help of digestive juices

25. Digestive Juices
Digestive juices come from 4 sources, entering the duodenum:
Pancreas
produces digestive enzymes
produce basic bicarbonate solution (buffer)

26. Digestive Juices Lining of duodenum Liver Gallbladder
produces digestive enzymes
Liver
Produces bile
Gallbladder
Stores bile

27. Bile contains bile salts
breaks up fat droplets into very small pieces called micelles
micelles are then absorbed and taken up by the lymph vessel (lacteal)

28. Question… Does bile perform mechanical or chemical digestion?
Mechanical– breaking it up into smaller pieces

29. Protection of Small Intestine
Small intestine and adjacent organs are protected from digestive enzymes by producing inactive forms that are only activated in the duodenum.

30. Absorption of Nutrients
Occurs in the jejunum (mid-small intestine) and ileum (end-small intestine)
The surface area in these regions is very large because of the villi and microvilli.
Villi and microvilli are projections of the lining

31. Absorption of Nutrients
Some nutrients are absorbed into the lymph vessel (lacteals).

32. Absorption of Nutrients
Most nutrients are absorbed into the blood vessels
capillaries  hepatic portal vessel  liver
the liver converts many nutrients and regulates blood sugar and other nutrient levels
Water is also absorbed here.

33. Digestion Summary Biomolecule Where Digested Key Enzymes Carbohydrates
Mouth, Small Intestine
Amylase, Maltase, Lactase, Sucrase
Lipids
Small Intestine
Bile, Lipase
Proteins
Stomach, Small Intestine
Pepsin, Peptidases, Trypsin
Nucleic Acids
Nucleases

34. Large Intestine responsible for water recovery from digested material
Feces = Waste of digestive tract
Bacteria live here (including E. coli) that live on feces and produce vitamins B and K () and stinky gases

35. Large Intestine End of colon = rectum End of rectum = anus
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36. Ruminant Digestion
Ruminants (ex. Cows) eat plants with tough-to-digest cellulose.
In order to improve digestion efficiency, Ruminants have symbiotic relationships with microbes.
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37. Ruminant Digestion Steps
Microbes in the rumen help digest the cellulose (products are fatty acids and “cud” (partially digested food)
Cud is regurgitated and rechewed
Water is removed in the omasum
Digestive enzymes in the abomasum complete digestion
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38. Control of Digestive System
The actions of the digestive system are regulated by hormones as well as it's own nervous system.
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39. Lower pH inhibits gastrin release CCK slows movements of stomach down
Food in the stomach
Stomach cells release GASTRIN
Increased secretion of:
HCl
Pepsin
Increased movement in stomach
Faster delivery of chyme to small intestine
small intestine cells release CHOLECYSTOKININ (CCK)
small intestine cells release SECRETIN
gallbladder releases bile
pancreas releases digestive enzymes
pancreas releases sodium bicarbonate to neutralize acid
Digestion of food
Lower pH inhibits gastrin release
CCK slows movements of stomach down
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40. Diabetes
Diabetes mellitus is a condition in which insulin is not produced or cells are insulin resistant
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