1. 6.1 Digestion and Absorption

2. Skill: Create an annotated digestive system diagram.
Alimentary Canal = food tube, from mouth to anus
Function of digestive system = to break down large carbon molecules into smaller ones that can be absorbed into bloodstream
Digest = “break down”
Practice drawing: x0KLbCPE&list=PLb1wF0xa6WI9nnb-yE_rjY2h4DX8ZI7R0&index=2

3. Digestive System

4. Digestive system structures & functions

5. Skill: Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.

6. Predict what cross-section of intestinal wall would look like!

7. Description of tissue layers in small intestine
Serosa (serous membrane) = outer lubricating coat
Muscle layers = longitudinal muscle and circular muscle
Sub-mucosa = contains blood & lymph vessels
Mucosa = line of small intestine, with epithelium that absorbs nutrients on inner surface

8. Identify tissue layers in transverse section of small intestine micrograph

9. Answers to previous slide:
A = mucosa (contains villi)
B = goblet cell (secrete mucous to line lumen)
C = submucosa
D = muscle layer (inner circular & outer longitudinal)

10. Identify tissue layers in transverse section of small intestine micrograph

11. Stomach is similar…

13. Understanding: The contraction of circular & longitudinal muscle layers of small intestine mixes food with enzymes and moves it along the gut.
Circular & longitudinal muscles are SMOOTH muscles.
Outer longitudinal muscles contract in front of bolus, and intestines shorten.
Inner circular muscles contract behind bolus, intestines narrow, pushing the food along.

14. Peristalsis
= wave-like muscle contractions in esophagus, stomach, small & large intestines that move the food along, while mixing food with enzymes and
Wwwwwwwwwww * Wave-like muscle contractions
* Occurs in esophagus, stomach, sm & L intestines
* Speeds digestion
* Only occurs in ONE DIRECTION
* Speaking of which, what muscles are used when vomiting?
Abdominal muscles
* Through which organ does peristalsis move food the slowest?
Small intestine
(Allows time for digestion & absorption)

15. Understanding: The pancreas secretes enzymes into lumen of small intestine.
Pancreatic amylase – digests starch
Pancreatic lipase – digests triglycerides & phospholipids
Pancreatic proteases (trypsin, chemotrypsin, aminopeptidase, carboxypeptidase) – digests polypeptides
What organelle in pancreatic gland cells synthesize these enzymes?
Ribosomes on the rough ER
What organelle processes these proteins before they are secreted?
Golgi apparatus
By what process are the enzymes secreted by the pancreatic gland cells
Exocytosis

16. Understanding: Enzymes digest most macromolecules in food into monomers in small intestine
Digestive enzyme Chart Activity!
What is the substrate and product of each of these enzymes? 
Pancreatic amylase
Pancreatic lipase
Phospholipase
Pancreatic protease
Nuclease
Maltase
Lactase
Sucrase
Carboxypeptidase
Aminopeptidase
Dipeptidase
Cellulase

17. What is Cellulose? We don’t have an enzyme to digest it, so it passes to the large intestine. AKA “fiber” or “roughage”.

18. Whiteboard Activity: State the source, substrate, product, and optimum pH for one named amylase, protease, & lipase. (a chart would be ideal!)

19. U: Villi increase surface area of epithelium over which absorption is carried out
Absorption = process of taking substances into cells & the blood
Site of absorption = small intestine
Rate of absorption depends on surface area of epithelium
Adult Sm intestine = 7m (23ft) long; mm (1in) wide
Villi (villus, singular) = small finger-like projections of mucosa
Villus = 0.5 – 1.5mm long (40 villi/mm2)
Function of folds & villi = increase surface area for absorption by 10X

20. U: Villi absorb monomers formed by digestion as well as mineral ions & vitamins
Single epithelium layer is semipermeable
Allows in products of digestion (monomers): monosaccharides, amino acids, fatty acids, monoglycerides, glycerol, nitrogen bases
Also allows in substances not needing digestion:
Mineral ions (e.g. Ca+2, K+, Na+)
Vitamins (e.g. A, B, C, D, E)
If harmful substances get through, detoxified by liver
Unwanted, harmless substances get through (e.g. food coloring & flavoring), pass in urine
Small amt of bacteria get through, removed by phagocytes in liver

21. U: Different methods of membrane transport are required to absorb different nutrients
Different methods of moving nutrients into & out of villi:
Simple diffusion
Facilitated diffusion
Active transport
Exocytosis

22. Exocytosis (requires effort & energy by cell, therefore ACTIVE transport)

23. Absorption TRIGLYCERIDES GLUCOSE
Triglycerides digested into fatty acids & monoglycerides
Fatty acids & monoglycerides absorbed into epithelial by simple diffusion (fatty acids also absorbed by facilitated diff)
Inside epithelium cells, fatty acids combine with monoglycerides to make triglycerides again
Triglycerides combine w/ cholesterol to form droplets, coated in phospholipids & protein (“lipoproteins”)
Lipoproteins released by exocytosis through membrane on inner side of epithelial cells
Lipoproteins enter lacteal and carried away in lymph or enter blood capillaries in villi
Starch digested into glucose
Glucose can’t pass by simple diffusion because it’s polar/hydrophilic
Active transport: Na+/K+ pumps pump Na+ from cytoplasm to interstitial spaces inside villus, and K+ in opposite direction  creates low conc of Na+ inside epithelial cells
Facilitated diffusion: Na+/glucose co-transporter proteins in microvilli transfer a Na+ and glucose molecule together from lumen to cytoplasm of epithelial cells
Glucose channels allow glucose to move by facilitated diffusion from cytoplasm to interstitial spaces inside villus and into blood capillaries in villus

24. Absorption of triglyerides
Absorption of glucose

25. App: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver
Starch = many α-glucose monomers linked by condensation rxns in plants (Bread, potatoes, pasta, rice, cereal, oatmeal)
Must be digested because too large to be absorbed
Starch digestion = exothermic (releases heat) & enzymes speed it up
Digestion of 1,4 bonds: Amylase breaks 1,4 bonds (if at least 4 glucose), leaving mixture of maltose (2 glucose) & maltotriose (3 glucose)
Digestion of 1,6 bonds: fragments with 1,6 bonds = “dextrins”.
What enzyme breaks down these sugars ?
Maltose?
Maltase
Dextrins?
Dextrinase
Maltotriose?
Glucosidase (HA, tricked you!)

26. NOS: Use models as representations of the real world: Dialysis tubing can be used to model absorption in the intestine
Experiments on living systems are complex and involve many variables.
If you did your IA using a living thing, you understand this!
Sometimes it’s better to experiment on PARTS of a system (cells rather than whole organisms)
… or use a MODEL to represent part of a living system
Example: Dynamic Gastric Model = computer-controlled model of human stomach that carries out mechanical and chemical digestion of real food!
Can test effects of diet, drugs, alcohol, etc on digestion
Example: dialysis tubing made from cellulose (semipermeable due to size of pores) – mimic small intestine to model absorption by passive diffusion and osmosis
Can test effects of different factors on diffusion of molecules into or out of tubing
Disadvantage: cannot model active transport or exocytosis

27. App: Use of dialysis tubing to model absorption of digested food in intestine.
Whiteboard Activity: (10 minutes)
Investigation 1: Predict what will happen
Experiment: (30 minutes)
Investigation 2: Set up and carry out experiment.
Turn in:
Research Question
Hypothesis
Qualitative & Quantitative data
Conclusion

28. TOK Application Which is the normal human condition…
Lactose-tolerant or lactose intolerant?
3 arguments:
Humans are only mammals who continue to drink milk into adulthood
High proportion of humans are lactose-intolerant
Ancestors were probably lactose-intolerant & tolerance evolved