Digestion

Assignment
Audesirk, Audesirk & Byers Part of Chapter 34, Selections from other chapters

Today's musical selection
Weird Al Yankovic Eat it

Chemistry

Figure 3-2
break down long chain proteins, polysaccharides and nucleic acids into monomers
recall hydrolysis (opposite of dehydration synthesis) (hydro-water lysis-break apart)
if not broken down, proteins which are non-self would make a big antigen invasion

Figure 3-8
Starch (glycogen, animal starch , is much like this)

Figure 3-9
Cellulose (also a polymer of glucose, but not digested, "fiber" contributres to bulk and "regularity")

Comparative biology

Figure 34-4
In sponge, Collar cell

Figure 34-5
In Hydra and flatworm, gastrovascular - digestive and circulatory systems are combined

Figure 34-6
Rumen - bacteria - ruminants - chew cud not acid - pensive "ruminate"
fermentation then feed to other chambers

Input - output

Figure 34-9
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)

Table 34-4
Sources and sites of secretions

Overall anatomy
(from mouth to stomach)

Figure 34-7
Mouth - teeth,

Figure 34-8
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)
-ase enzymes

Figure 34-10
Pharynx swallowing

Figure 34-11
Esophagus - bolus, peristalsis

Figure 34-12
Lower esophagesl sphincter

Stomach

Figure 34-12
Stomach - gastric mucosa - mucus protect
HCl kill bacteria, stop amylase
From chief cell: pepsinogen ---(HCl, pepsin))--> pepsin (proteolytic)

Figure E34-2
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

Figure 6-19
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

Figure E34-1
Gastric bypass and band

Intestine:

enzymes - lactase, maltase, sucrase, others
mitosis - since cells digest themselves
absorption - food and water

Figure 34-14
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.
Protease

Pancreas

Figure 34-13
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 hormones.
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 duodenum.
When I took organic chemistry lab (1966-7) we used gall stones for a cholesterol extraction.
Note: Islets of Langerhans (endocrine tissue) in pancreas where alpha cells make glucagon and beta cells make insulin.

Liver

Figure 34-13
Liver contributes to fat digestion via bile salts, salts of cholesterol, that emulsify fats
Very few enzymes.
Emulsify fats (salts of cholesterol)
Iron recycling.
Eliminate some wastes to feces.
Detoxify.

Detoxification

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 feces dark.
Also colors urine.
Hepatitis (disorder which spills bile into blood) - turns skin yellow (jaundice) (feces are not as dark, urine is darker)

Hormones

Table 34-5
Local hormones control digestion - Many found later in other places

Figure 34-16
from stomach:
food stimulates gastrin which, in turn, stimulates gastric juice until there is a low (acidic) pH

Also:
from duodenum:
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
(a) peristalsis
(b) pyloric sphyncter
(c) Helicobacter pylori
*(d) brush border
(e) cholecystokinin

The pH optimum for pepsin is
(a) neutral.
(b) a higher number that that for salivary amylase or trypsin.
*(c) about 2.
(d) why it stops working once it reaches the stomach.
(e) alkaline.

Which comes from the pancreas?
(a) thyroxin
*(b) chymotrypsinogen
(c) pepsin
(d) bile
(e) vitamin K

A disorder involving iron recycled in the liver:
*(a) jaundice
(b) ulcer
(c) scurvey
(d) diabetes
(e) malaria

In addition to being the organ where insulin is made, the pancreas also secretes
A) bile.
B) surfactant.
C) ozone.
*D) precursors of digestive enzymes.
E) antigens.

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.
*B) pancreas.
C) stomach.
D) mouth.
E) liver.

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.

Chymotrypsinogen is
*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 collar cells.
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.
B) hydrolysis.
*C) alcoholism.
D) Helicobacter pylori.
E) symbiosis with microorganisms that digest cellulose

Starch is digested by
A) the gall bladder.
B) pepsin.
C) beta cells in the islets of Langerhans.
D) bile.
*E) amylase.

The optimum pH for pepsin is
A) referred to as "peristalsis."
B) neutral.
C) basic.
*D) acidic.
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.
*(a) pepsin
(b) ethylene
(c) bile
(d) amylase
(e) kinase

The largest variety of digestive enzymes function in the
(a) large intestine.
(b) mouth.
(c) stomach.
*(d) small intestine.
(e) liver.

Cellulose looks most like
*(a) glycogen.
(b) octane.
(c) hemoglobin.
(d) tRNA.
(e) triglyceride.

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 related to
(a) cellulose.
(b) membrane glycolipids.
(c) ATP.
*(d) cholesterol.
(e) antibodies.


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