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

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

13. Oral Cavity, Pharynx, Esophagus
Participate in ingestion and digestion
Mechanical Digestion
By teeth and tongue (chewing)
Chemical Digestion
Salivary amylase begins digestion of carbohydrates (starch  glucose)

14. Oral Cavity, Pharynx, Esophagus
Epiglottis = flap that covers the trachea during swallowing, so food travels down “right pipe” (the esophagus)
Peristalsis (muscle contractions) will involuntarily continue movement of the mass of food (bolus)

15. 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

16. Stomach Gastric juice continues digestion:
HCl converts pepsinogen into pepsin (active enzyme)
Pepsin hydrolyzes (breaks down) protein.
Gastric juice is churned with bolus to break down food and kill bacteria

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

18. Protection of the stomach
Stomach protects itself from self-digestion by
keeping pepsinogen stored away from HCl until pepsin is needed
lining stomach with mucus

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

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

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

22. Digestive Juices also come from
Lining of duodenum
produces digestive enzymes
Liver
Produces bile
Gallbladder
Stores bile

23. Bile contains bile salts
breaks up fat droplets into very small pieces (emulsification)
Increases surface area for lipase to digest into micelles
micelles are then absorbed

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

25. 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.

26. Absorption of Nutrients
Occurs in the jejunum (mid-small intestine) and ileum (end-small intestine)
Nutrients are absorbed into the blood vessels and lymph vessel (lacteals).
Water is also absorbed here.

27. Absorption of Nutrients
Villi and microvilli
Projections of the lining of the small intestine
Benefit?
Increases the surface area in these regions  increases amount of nutrient absorption

28. Digestion Summary Biomolecule Where Digested Key Enzymes Carbohydrates
Mouth, Small Intestine
Amylase, Maltase, Lactase, Sucrase
Lipids
Small Intestine
Bile (not an enzyme but helps process), Lipase (from pancreas)
Proteins
Stomach, Small Intestine
Pepsin (stomach), Peptidases, Trypsin
Nucleic Acids
Nucleases

29. 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
End of colon = rectum
End of rectum = anus

30. Control of Digestive System
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

31. Nervous System Control of Digestion
The Autonomic Nervous System controls the internal environment by controlling muscles in various organ systems
Sympathetic division (“fight or flight”): inhibits digestion, promotes release of glucose from liver
Parasympathetic division (“rest and digest”): stimulates digestion
Enteric division: neurons that control the secretions of the digestive organs.

32. Diabetes
Blood sugar levels are controlled by hormones

33. Diabetes (continued)
Diabetes mellitus is a condition in which insulin is not produced or cells are insulin resistant
Type 1 –
can’t produce insulin
Type 2
cells no longer respond to insulin
End result: glucose cannot be used by cells  blood sugar is too high (homeostasis not maintained)