Download Topic D.2 Digestion - Cougar science rocks!

Option D.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
U: The volume and content of gastric secretions are
controlled by nervous and hormonal mechanisms.
1.
Sight or smell of food causes vagus nerve
from medulla to send impulse to stomach
to cause it to secrete gastric juice.
2.
Impulses sent back to brain if
chemoreceptors in stomach detect
peptides or if stretch receptors detect
expansion.
3.
Vagus nerve sends impulse to stomach and
duodenum to secrete hormone gastrin.
4.
Gastrin stimulates stomach to secrete HCL
acid and pepsin.
5.
Hormones secretin (from duodenum) and
somatostatin (from stomach) inhibit
gastrin if stomach pH falls too low
•
Animation: Three phases of gastric secretion
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
Electron micrograph of pancreatic cell
•
rER  for synthesis of enzymes
•
Mitochondria  synthesis of ATP
•
Vesicles  carry enzymes
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
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]
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
•
http://www.huffingtonpost.com/2012/07/13/weird-science-experiments_n_1672414.html
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!
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
Stomach Ulcers!
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
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”
Foods made from cultured fungi
(mycoprotein) has fiber!
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
•
fruit skins, whole wheat bread, brown rice
•
Lowers cholesterol & reduces risk of CHD
•
Reduces risk of obesity (fiber fills you up!)
•
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!)
Soaks up water, bulks up stool, prevents
constipation
•
Reduces risk of bowel cancer, hemorrhoids,
appendicitis
•
Reduces risk of type II diabetes (slows
absorption of sugar)
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
TOK: what role does conservatism play in science?
p677