Audesirk, Audesirk & Byers Part of Chapter 34, Selections from other
Today's musical selection
Weird Al Yankovic Eat
break down long chain proteins, polysaccharides and nucleic acids into monomers
recall hydrolysis (opposite of dehydration synthesis) (hydro-water lysis-break
if not broken down, proteins which are non-self would make a big antigen
Starch (glycogen, animal starch , is much like this)
Cellulose (also a polymer of glucose, but not digested, "fiber"
contributres to bulk and "regularity")
In sponge, Collar cell
In Hydra and flatworm, gastrovascular - digestive and circulatory
systems are combined
Rumen - bacteria - ruminants - chew cud not acid - pensive "ruminate"
fermentation then feed to other chambers
Input - output
Tube - Alimentary canal
One emphasis will be on how the human digestive system invests many juices
(hydrolases = enzymes which catalyse hydrolysis)
Some glands have ducts and these are called exocrine glands.
This is in contrast with endocrine glands (ductless, for hormones, which
are also involved in digestion)
Sources and sites of secretions
(from mouth to stomach)
Mouth - teeth,
birds have gizzard - stones to break up seeds, sort of a lapidary device
(this is why you give pet bird gravel),
gizzard is near the stomach and near the bird's center of gravity -- not
only do birds need to be light to fly but also balanced, and teeth, which
are heavy and in the mouth, would upset the center of gravity
Crop is used for storage in birds
lubrication, salivary amylase to disaccharide maltose - starch tastes sweet
(only starch in mouth)
Esophagus - bolus, peristalsis
Lower esophagesl sphincter
Stomach - gastric mucosa - mucus protect
HCl kill bacteria, stop amylase
From chief cell: pepsinogen ---(HCl, pepsin))--> pepsin (proteolytic)
Heartburn, antacids, ulcer (although it is now known that a specific bacterium,
Helicobacter pylori, is associated with ulcer)
very little absorption in stomach - exceptions: aspirin, alcohol
The optimum pH for pepsin (proteolytic enzyme in stomach) is acidic while
for trypsin (proteolytic enzyme in intestine) is slightly basic. And for
salivary amylase, it is neutral.
Figure 34-12 (again)
Pyloric sphincter regulates emptying of acidic gastric juice to duodenum.
In duodenum, bile from liver and bicarbonate and enzymes from pancreas add
to enzymes from small intestine
Gastric bypass and band
enzymes - lactase, maltase, sucrase, others
mitosis - since cells digest themselves
absorption - food and water
Villi (big) increase surface area. Mitoses in crypts.
Here is a micrograph
from our histology
course dramatizing the tremendous increase in apical surface area of
intestinal cells caused by the microvillar brush border.
The microvilli in the intestines have a special name, the brush border.
Pancreas is responsible for dumping in many of the enzymes
"pro..." as in "procarboxypeptidase and "...ogen"
as in "chymotrypsinogen" --a peptide fragment is cut off from
a larger precursor protein to make active enzyme; there are many examples
like this in biology, for instance prohormones cleaved to make active peptide
Pancreas puts out bicarbonate (alkaline) to neutralize stomach acid.
Optimum pH for for trypsin is 8.
Pancreas and common bile duct (from liver and gall bladder) dumping into
When I took organic chemistry lab (1966-7) we used gall stones for a cholesterol
Note: Islets of Langerhans (endocrine tissue) in pancreas where alpha cells
make glucagon and beta cells make insulin.
Liver contributes to fat digestion via bile salts, salts of cholesterol,
that emulsify fats
Very few enzymes.
Emulsify fats (salts of cholesterol)
Eliminate some wastes to feces.
Portal blood veins (circulatory system "wired" in series is unusual,
another famous example being the hypothalamus of the brain which feeds to
the pituitary gland and kidney cortex to medulla). Via hepatic portal vein
pick-up from small intestine is first delivered to liver cels. There, "microsomal
fraction" (how biochemists view the smooth endoplasmic reticulum) has
enzymes to detoxify. Enzymes like those that detoxify drugs like barbiturates
are increased on exposure to toxins (inducible). Alcohol -(alcohol dehydrogenase
(ADH) )-> aldehyde - (aldehyde dehydrogenase)-> acetic acid. With
AcetylCoA, acetic acid can add to fatty acid chains 2 carbons at a time.
There is a fatty metamorphosis of the liver from one binge. Continued heavy
drinking leads to scarring and cirrhosis.
Erythrocyte iron recycling, bile pigment (bilirubin) ->urobilinogen turns
Also colors urine.
Hepatitis (disorder which spills bile into blood) - turns skin yellow (jaundice)
(feces are not as dark, urine is darker)
Local hormones control digestion - Many found later in other places
food stimulates gastrin which, in turn, stimulates gastric juice until there
is a low (acidic) pH
Cholecystokinin (CCK) - liver and pancreas
Secretin for bicarbonate release
Gastric inhibitory peptide to slow gastric emptying and stimulate insulin
Questions used in 2007 & 2008 relating to this outline
Which is NOT a function of the liver?
*(a) providing digestive enzymes
(b) emulsifying fats
(c) recycling erythrocytes
(d) detoxifying what intestines absorb
(e) eliminating wastes through feces
Which is NOT true of the pancreas?
(a) Insulin-secreting cells are located there.
(b) Its exocrine secretions go into the small intestine.
(c) It makes bicarbonate to neutralize acidity of what the stomach sends
to the intestines.
(d) It makes precursors for digestive enzymes.
*(e) It is the source of salts of cholesterol.
Why do birds have a gizzard?
(a) the site of collar cells, since they have no tissues or organs
*(b) instead of teeth, for grinding
(c) manufacture of bilirubin
(d) alcohol metabolism, the microsomal fraction
(e) to house symbiotic bacteria, for cellulose digestion
The word for the apical surface of intestinal cells
(b) pyloric sphyncter
(c) Helicobacter pylori
*(d) brush border
The pH optimum for pepsin is
(b) a higher number that that for salivary amylase or trypsin.
*(c) about 2.
(d) why it stops working once it reaches the stomach.
Which comes from the pancreas?
(e) vitamin K
A disorder involving iron recycled in the liver:
In addition to being the organ where insulin is made, the pancreas also
*D) precursors of digestive enzymes.
The rumen of a ruminant
*A) has microbes that help in cellulose digestion.
B) is the site of action of the famous enzyme gastrin.
C) grinds up hard seeds with the aid of gravel.
D) was the first prototypical cell.
E) is lined with rings of cartilage that keep this windpipe from collapsing.
The largest variety of digestive enzymes comes from the
A) large intestine.
What is the hepatic portal vessel?
A) It is inside an embryonic membrane.
B) It is the true body cavity for animals above the flat worm.
*C) It carries blood from the intestines to the liver.
D) It is the valve between the atria and the ventricles.
E) after gastrulation, it will become the gut.
*A) the precursor of an enzyme that comes from the pancreas.
B) the term for smooth muscle contractions that moves food through the gut.
C) the cause of ulcers.
D) what endocytosed (phagocytosed) food particles merge with in the sponge's
E) a hormone that stimulates gastric secretions.
The liver's contribution to digestion is that its secretions
A) break down cellulose.
B) include pepsin.
C) include insulin.
D) are involved in acid reflux.
*E) emulsify fats.
Cirrhosis is caused by
A) grinding action in the gizzard.
D) Helicobacter pylori.
E) symbiosis with microorganisms that digest cellulose
Starch is digested by
A) the gall bladder.
C) beta cells in the islets of Langerhans.
The optimum pH for pepsin is
A) referred to as "peristalsis."
E) the way it is because it preserves the brush border.
Questions used in 2003 relating to this outline
Famous for its function at low pH.
The largest variety of digestive enzymes function in the
(a) large intestine.
*(d) small intestine.
Cellulose looks most like
What is the hepatic portal vessel?
(a) It is what defines the chordate.
(b) It is the gastro-vascular cavity of the flat worm.
(c) after gastrulation, it is the cavity that will become the gut.
(d) It connects the gall bladder to the duodenum.
*(e) It carries blood from the intestines to the liver.
The liver bile salts that are secreted into the intestines are most closely
(b) membrane glycolipids.
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