1. Digestion
Option D.2

2. U: Nervous & hormonal mechanisms control the secretion of digestive juices.
Nerves and hormones activate digestion only when needed
Conserves energy!
During “rest and digest”, digestion activated only after eating
During “fight or flight”, digestion is inactivated so all energy can go to muscle use
Video clip: Sympathetic vs parasympathetic control of digestion

3. U: The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.
Sight or smell of food causes vagus nerve from medulla to send impulse to stomach to cause it to secrete gastric juice.
Impulses sent back to brain if chemoreceptors in stomach detect peptides or if stretch receptors detect expansion.
Vagus nerve sends impulse to stomach and duodenum to secrete hormone gastrin.
Gastrin stimulates stomach to secrete HCL acid and pepsin.
Hormones secretin (from duodenum) and somatostatin (from stomach) inhibit gastrin if stomach pH falls too low
Animation: Three phases of gastric secretion

4. U: Exocrine glands secrete to the surface of the body or the lumen of the gut.
Alimentary canal = food tube from mouth to anus
Exocrine glands secrete digestive juices along the way
Exocrine glands secrete into ducts. (Endocrine secrete directly into bloodstream.)
Examples: salivary glands, pancreas, gland cells in stomach wall and small int. wall

5. Electron micrograph of pancreatic cell
rER  for synthesis of enzymes
Mitochondria  synthesis of ATP
Vesicles  carry enzymes

6. U: The structure of cells of the epithelium of the villi is adapted to the absorption of food.
Cells adhere to each other through “tight junctions”  so most molecules pass into blood vessels
Microvilli (a.k.a. “brush border”)  to increase surface area for absorption
Lots of mitochondria to produce lots of ATP
Lots of vesicles for endocytosis
Apical surface has different proteins than basal surface

7. Skill: ID of exocrine gland cells that secrete digestive juices & villus epithelium cells that absorb digested foods from electron micrographs (DBQ p674)
1 a) Identify the structures colored green. [1]
b) Explain the function of these structures. [2]
2 a) Identify which structures are mitochondria. [1]
b) Explain the need for many mitochondria in villus epithelial cells. [2]
3 a) Many vesicles are visible in the cytoplasm of the cells. State the name of the process used to form these vesicles. [1]
b) Predict the contents of the vesicles. [2]
4 a) Part of the junction between the 2 cells has been colored blue. State the name of this structure. [1]
b) Explain its function. [2]

8. NOS: Serendipity and scientific discoveries: the role of gastric acid in digestion was established by William Beaumont while observing the process of digestion in an open wound caused by gunshot.
1822, Alexis St. Martin – Canadian fur trader, gunshot wound to side
Bullet left small hole in his side and stomach
William Beaumont, army surgeon, paid Alexis room, board & $150/yr to study his stomach
studied digestion by tying food to a string and watching how it was digested
Investigated over 11 year period and published results
Before this, digestion in stomach thought to be only physical
Beaumont provided evidence that it also involves chemical digestion

9. U: Acid conditions in the stomach favor some hydrolysis rxns and help to control pathogens in ingested food.
Stomach releases HCl acid
What does HCL do?
Denatures protein in food, so pepsin can break the bonds easier
Converts inactive pepsinogen  pepsin
Breaks up cells
Inactive pepsinogen released first, so cells producing it are not digested at he same time as protein in your food!

10. App: Helicobacter pylori infection as a cause of stomach ulcers.
Stomach ulcer = open sore caused by partial digestion of lining by HCl & pepsin
Stomach cancer = tumor growth
Traditionally, stress and excess gastric juice (spicy foods) were believed to cause ulcers
Today, Helicobacter pylori is a bacteria known to cause ulcers (maybe factor in stomach cancer)
H. pylori attacks lining acid gets through leads to ulcer
Get H. pylori through food, water, utensils, saliva
Symptoms of ulcer: bloating, heartburn, nausea, vomiting, pain

11. Stomach Ulcers!

12. App: The reduction of stomach acid secretion by proton pump inhibitor drugs.
Acid reflux (a.k.a. “heartburn”) = stomach acid leaks into esophagus because cardiac sphincter doesn’t close
H+, K+-ATPase = proton pump that produces stomach acid
Proton Pump Inhibitors (PPIs) can bind to pump to stop acid production
Not permanent
Consumed in inactive form
Good for ulcers and acid reflux

13. U: Materials not absorbed are egested.
Fiber = edible part of plants that are resistant to being digested, and not absorbed
Made of cellulose (cell wall), lignin (xylem), & pectin (fruit)
Some substances are secreted INTO intestines
Excretory products, like bilirubin from breakdown of red blood cells
A lot of water from saliva, stomach and small intestine, reabsorbed by large intestine
Feces = undigested fiber, unabsorbed water, excretory products
Egested = defecated = “to carry outside”

17. Foods made from cultured fungi (mycoprotein) has fiber!

18. U: The rate of transit of materials through the large intestine is positively correlated with their fiber content.
Soluble Fiber
Insoluble Fiber
oatmeal, nuts, beans, apples, blueberries
Lowers cholesterol & reduces risk of CHD
Reduces risk of obesity (fiber fills you up!)
Soaks up water, bulks up stool, prevents constipation (the higher the water content in intestine, the faster the movement of feces!)
Reduces risk of type II diabetes (slows absorption of sugar)
fruit skins, whole wheat bread, brown rice
Reduces risk of obesity (fiber fills you up!)
Soaks up water, bulks up stool, prevents constipation
Reduces risk of bowel cancer, hemorrhoids, appendicitis

19. App: Dehydration due to cholera toxin.
Cholera = intestinal disease caused by bacteria Vibrio cholera
V cholera releases toxin that binds to receptor on intestinal cells
Toxin enters via endocytosis
Toxin leads to efflux of Cl- and HCO3- from cell into intestine
Water follows by osmosis, leading to diarrhea
Water is drawn from blood into cells to replace fluid loss from intestinal cells
Dehydration results
Can be fatal due to dehydration

20. TOK: what role does conservatism play in science?