1. 6.1 Digestion and Absorption

2. Understandings
The contraction of circular and longitudinal muscle layers of the small intestines mixes the food with enzymes and moves it along the gut.
The pancreas secretes enzymes into the lumen of the small intestines.
Enzymes digest most macromolecules in food into monomers in the small intestines.
Villi increase the surface area in epithelium over which absorption is carried out.

3. Understandings
Villi absorb monomers absorbed by digestion as well as mineral ions and vitamins.
Different methods of membrane transport are required to absorb different nutrients.

4. Applications
Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.
Use of dialysis tubing to model absorption of digested food in the intestines. (Nature of Science- models are representations of the real world)

5. Skills Production of an annotated diagram of the digestive system.
Identification of tissue layers in transverse sections of the small intestines viewed with a microscope or in a micrograph.

7. 6.1.S1 Production of an annotated diagram of the digestive system.

9. Peristalsis in the Digestive System The contraction of circular and longitudinal muscle layers of the small intestines mixes the food with enzymes and moves it along the gut.
Peristalsis is the wave of involuntary smooth muscle contraction along the digestive system.
It involves the interaction of both the circular and longitudinal muscles of the digestive system.
The contraction of circular muscles behind the food prevents the food from being pushed back towards the mouth and pushes food down.
The contraction of longitudinal muscles where the food is located moves the food forward along the gut.

10. Smooth Muscle Contraction

11. Peristalsis can only occur in one direction, away from the mouth.
FYI: Reverse Peristalsis aka PUKING uses the abdominal muscles to return food to the mouth NOT the circular and longitudinal muscles.
Food moves quickly down the esophagus to the stomach in one continuous peristaltic movement.
In the intestines the food is only moved a few centimeters at a time so progression is MUCH SLOWER which allows for more time for DIGESTION.
The main function of peristalsis in the small intestines is for CHURNING of the semi- digested food to MIX with digestive ENZYMES which speed up the rate of reaction of digestion.

12. ENZYME REVIEW

13. Pancreatic Juices The pancreas secretes enzymes into the lumen of the small intestines.
The pancreas synthesizes and secretes digestive ENZYMES directly into the gut in response to eating a meal.
About a liter of PANCREATIC JUICES are secreted from the gland cells into smaller ducts that merge into one pancreatic duct and is released into the lumen of the small intestines. (EXOCRINE GLAND)

14. Larger macromolecules need to be digested before they can be absorbed.

15. 6.1.U3 Enzymes digest most macromolecules in food into monomers in the small intestine.

16. Macromolecules ,Polymers, and their Monomers
Form Ingested
Polymers
Form After Digestion
Monomers
Protein
Dipeptides or amino acids
Lipids
Triglycerides
Fatty acids and monoglyceride
Carbohydrates
Ex) Starch and Glycogen
Poly-, di-, and/or monosaccharide
Monosaccharide
Ex)glucose
Nucleic acids
DNA, RNA
Nucleotides

17. POLYMERS
MONOMERS

18. PANCREATIC JUICES hydrolyze (add water break apart) the following reactions:
AMYLASE- digest starch (amylose) into maltose
LIPASE- digest lipids or TRIGLYCERIDES into fatty acids and glycerol or monoglycerides.
PROTEASE (endopeptidase)- digest proteins and polypeptides into shorter peptides.

19. The pancreas synthesizes the three main types of digestive enzyme:
6.1.U2 The pancreas secretes enzymes into the lumen of the small intestine.
The pancreas synthesizes the three main types of digestive enzyme:
amylase to digest carbohydrates, e.g. starch
lipases to digest lipids, e.g. triglycerides
proteases to digest polypeptides
Pancreatic juice containing the enzymes is released into the upper region of the small intestine (duodenum) via the pancreatic duct
The small intestine is where the final stages of digestion occur.

20. Digestion in the Small Intestines Enzymes digest most macromolecules in food into monomers in the small intestines.
Macromolecules are only partially digested in the small intestines by the PANCREATIC JUICES.
The WALL of the SMALL INTESTINES produces a variety of other enzymes (Intestinal Juices) which further digest more substances.

21. Intestine Facts
The small intestines are about 7 meters long and about 30 mm wide have folds which increase the surface area.
Food takes hours to pass through. (slooooow peristalsis)
The greatest amount of DIGESTION of MACROMOLECULES takes place here.
We do not synthesize the enzyme necessary to digest CELLULOSE so it passes through as dietary fiber.

22. Structure of the Wall of the Small Intestines (From the outside to the inside)
Serosa- an outer coat
Muscle layer- longitudinal muscle with circular muscle inside it for peristalsis.
Sub- mucosa- tissue layer containing blood and lymph vessels.
Mucosa- the lining of the small intestines with epithelium that absorbs nutrients on its inner surface.

24. 6.1.S2 Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.
The small intestine contains four distinct tissue layers from the lumen
Mucosa – inner lining, includes villi
Submucosa – connective tissue (between the mucosa and muscle)
Muscular layer – inner circular and outer longitudinal muscle perform peristalsis
Serosa – protective outer layer
Epithelial cells – single outer layer of cells on each villus (see 6.1.U4)
Muscular layer
circular
longitudinal

25. Villi and the Surface Area for Digestion Villi increase the surface area in epithelium over which absorption is carried out.
The small intestines are ALSO the main sight of the ABSOPTION (the taking in of substances into the cells and blood) of nutrients.
VILLI are small finger-like projections of the MUCOSA that increase the surface are of the small intestines by about 10X.

26. a. Villus which increase the surface area for absorption of the products of digestion
b. Microvilli border of the epithelial cell further increases the surface area for absorption.
c. Lacteals are connect to the lymphatic system for the transport of lipids.
d. In the wall of the small intestine are the blood vessels to transport absorbed products to the general circulation.
There is also muscle to maintain peristalsis

27. Adaptations to Absorption
6.1.U4 Villi increase the surface area of epithelium over which absorption is carried out.
Adaptations to Absorption
Getting digested food molecules into the blood from the lumen of the ileum.
Many villi protrude into the lumen, greatly increasing the surface area for absorption.
Single-cell layer of epithelial cells
Short path for diffusion.
Microvilli on the surface of each cell increase surface area even further.
Lacteals (lymph vessels)
Allow for rapid absorption and transport of lipids.
Capillaries close to epithelium
Short path for diffusion, rich supply of blood.
Rich blood supply
Maintains concentration gradients between lumen and blood.
Images from:

28. Absorption by Villi Villi absorb monomers absorbed by digestion as well as mineral ions and vitamins.
Villus cells absorb these products of digestion of macromolecules in food:
Monosaccharides including glucose, galactose, and fructose
Amino acids from the digestion of proteins.
Fatty Acids, monoglycerides, and glycerol from the digestion of lipids.
Nitrogenous bases from the digestion of nucleotides.
Minerals including calcium, potassium, and sodium.
Vitamins including ascorbic acid (Vit. C) and thiamin, riboflavin, and niacin  (Vit B).

29. TRANSPORT REVIEW

30. Methods of Absorption Different methods of membrane transport are required to absorb different nutrients
To be ABSORBED into the body, nutrients must pass from the lumen of the small intestines to the CAPPILLARIES or LACTEALS in the VILLI.
The nutrients must first be absorbed by the micro-villi on the exposed part of the plasma membrane that increase the SURFACE AREA of the EPITHELIUM CELLS of the VILLI and is then passed through to the other side facing the capillaries and lacteal.

31. Membrane Transport of Triglycerides http://www. wiley
TRIGLYCERIDES emulsified (increased surface are by making smaller droplets) by BILE SALTS. (made by liver but stored and concentrated in the gall bladder)
They are then digested into FATTY ACIDS AND MONOGLYCERIDES by lipase.
FATTY ACIDS and MONOGLYCERIDES can be absorbed by SIMPLE DIFFUSION (HL concentration, no energy used) through the villus epithelium. (Like absorbs Like- Both are NONPOLAR)
Once the Monoglycerides and Fatty Acids are inside the epithelium they recombine to form TRIGLYCERIDES.

32. Triglycerides join with cholesterol to form droplets that are coated with proteins and phospholipids.
These lipoprotein particles are released by exocytosis (fuse with cell membrane and EXIT the cell) through the plasma membrane.
They will then enter the LACTEAL and are carried away in the lymph to then enter the blood stream.

34. Membrane Transport of Glucose
Glucose cannot pass directly through the plasma membrane by simple diffusion because it is POLAR (hydrophilic).
Na+/ K+ pumps- pumps Na+ OUT of the epithelial cells of the villi into the interstitial space around the lacteal and capillaries and K+ IN. (PUMPS- active transport LH using energy)
Na+ is LOW in the epithelial cells.
Na+/Glucose CO- transporter proteins move a Na+ and a glucose TOGETHER into the epithelial cell of the villi.

36. Glucose channels now allow glucose to move by FACILITATED DIFFUISION (HL) to the capillaries inside the villus.

37. 6.1.A1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.
Starch consists of amylose (by 1,4 bonds) and amylopectin (by 1,4 bonds and occasional by 1,6 bonds)
Amylase breaks 1,4 bonds in chains of four or more monomers producing maltose
Maltase digests maltose into glucose monomers.
Dextrinase breaks the 1,6 bonds that amylase cannot deal with forming glucose monomers

38. Dialysis (visking) tubing can be used to model absorption
6.1.A2 Use of dialysis tubing to model absorption of digested food in the intestine.
Dialysis (visking) tubing can be used to model absorption
The tubing is semi-permeable and contains pores typically ranging 1 – 10 nm in diameter
Predict what will happen to the glucose and starch after 15 minutes.
Initially contains a mixture of starch and glucose
Test the solutions inside and outside the dialysis tubing for starch and glucose before and after at least 15 minutes have elapsed (see the Practical Biology link for details).

39. Dialysis (visking) tubing can be used to model absorption
Nature of Science: Use models as representations of the real world - dialysis tubing can be used to model absorption in the intestine. (1.10)
Dialysis (visking) tubing can be used to model absorption
The tubing is semi-permeable and contains pores typically ranging 1 – 10 nm in diameter
Predict what will happen to the glucose and starch after 15 minutes.
The model is the most basic element of the scientific method. It is any simplification, substitute or stand-in for what you are actually studying or trying to predict. Evaluate the usefulness of dialysis tubing as a model for absorption by considering:
How is the function of dialysis tubing similar to the small intestine?
What features of a real gut are missing from this model?
Initially contains a mixture of starch and glucose
Test the solutions inside and outside the dialysis tubing for starch and glucose before and after at least 15 minutes have elapsed (see the Practical Biology link for details).