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DIGESTIVE PHYSIOLOGY
Mastication – the act of chewing
Deglutition- the act of swallowing
Bolus- a mass of chewed food
Peristalsis- involuntary contractions of smooth
muscle to propel food through GI tract
Chyme: yellow fluid which leaves stomach for
duodenum – consists of partially digested food
and secretions
• Chemical vs mechanical digestion
a) mechanical – chewing, mixing ,
churning
b) chemical – adding water via enzymes
= H Y D R O L Y S I S (see handout)
Organic molecules (food)
A) Carbohydrates (C H2O)
-sugars, fibers, sweeteners
1) polysaccharides –
cellulose(fiber), starch
2) disaccharides
sucrose, lactose , maltose
3) monosaccharides
glucose, fructose, galactose
*you can only absorb monosaccharides
B) Proteins (C H O N)
all proteins are polypeptides composed of
combinations of 20 types of amino acids
*you only absorb amino acids
C) Lipids (CHO)
fats, oils, cholesterol, waxes, some steroids
1) triglycerides – common food lipid
composed of 3 fatty acids + glycerol
2) phospholipids – cell membranes
composed of 2 FA, glycerol, phosphate
*You can only absorb fatty acids, glycerol, etc
FOOD LABEL BASICS
1) Calories = kilocalories
# grams X 4(carbs,proteins) or 9 (lipids)
2) Vitamins
a)water soluble - B, C,
b) fat soluble – A D E K
3) Minerals – think periodic table – needed in
trace amounts – Ca, K, Fe, etc
Enzymes of Digestion
A) Mouth (saliva)
1)salivary amylase- targets starchesresults in smaller saccharides and
disaccharides
2) Lipase – minimal effect? –targets lipids
B) Stomach- enzymes produced by “chief cells “
in gastric pits1) Pepsin –targets proteins- results in
smaller peptide chains
2) Lipase – minimal effect?- targets lipids
* HCl is produced by “parietal cells” in gastric
pits
C) Pancreas - enzymes are produced by acini
(acinar cells)
1) protease – targets proteins – results in
smaller peptides
2) lipase – targets lipids – most effective
*enters small intestine with bile
Pancreas (continued)
3) Amylase – targets carbohydrates – results in
disaccharides
D) Small intestine brush border (duodenum)
1) Peptidase – targets peptides(protein) –
finalizes their breakdown to amino acids
2) Amylases (specific)
a)sucrase – targets sucrose – results in
one glucose and one fructose
b)lactase-targets lactose-results in one
glucose and one galactose
Sm. Int. (continued)
c)maltase – targets maltose – results in two
glucose
B I L E
Bile emulsifies lipids (forces them into water soluble
droplets) so that they can be more readily hydrolyzed
Bile is not an enzyme or hormone.
Bile is made by the liver, stored in the gall bladder
Bile consists of cholesterol, pigments *, bile salts,
water
Absorption of nutrients
A) Proteins
1) absorbed as amino acids
2) enter into capillaries of villi then to the
liver via the hepatic portal vein
3) amino acids can be converted to
monosaccharides or fatty acids upon removal
of the amine (NH2) group (see handout)
B) Carbohydrates
1) absorbed as monosaccharides
2) enter into capillaries of villi, then to liver
via hepatic portal vein
3) can be converted to fatty acids or even
some amino acids
C) Lipids
1) absorbed as fatty acids/glycerol
2) absorbed into lymph in lacteals (usually in
ileum)and enter blood stream near heart
3) Must be transported in blood as
lipoproteins – why?
4) can be converted to some amino acids or
even monosaccharides in the liver
LDL vs HDL
LDL (low density lipoprotein)
-Mainly travel from liver to body cellsespecially adipose cells
-contain a lot of lipid and little protein
- can leave deposits in blood vessels
* known as bad cholesterol*
HDL (high density lipoprotein)
-Mainly travel from cells back to liver
-contain a lot of protein and little lipid
- can pick up deposits in vessels
- the liver often excretes these lipids as part
of the bile
***known as good cholesterol***
Assorted terms
a) Diarrhea - too much water lost in feces
b) Constipation – too little water in feces
Diabetes
1. Insulin – decreases blood glucose levels
“tells” cells to take glucose from blood
Glucagon – increases blood glucose levels
“tells” liver to break down
glycogen stores
2. Pancreatic Islets of Langerhans
Beta cells- insulin
Alpha cells – glucagon
Early signs of Diabetes
3. a) frequent urination
b)dehydration
c) acidosis (low blood pH) from metabolizing
fatty acids—fruity breath type I
d)thirst
4. Type I - IDDM- 20%
insulin dependent diabetes mellitus
a) destruction/loss of beta cells
5. Type II – DM (NIDDM) – 80%
non-insulin dependent diabetes mellitus
a) cells don’t respond effectively to insulin
b) can lead to type I
Prolonged diabetes
6. a) necrosis –tissue death
b) cardiovascular disease
c)retinal degeneration
d)loss of nerve function
e)kidney damage
f) serious infections
7. Pancreas
a) endocrine gland – produces hormones –
Islets (Islets of Langerhans) are cells to
produce pancreatic hormones- 1% of
pancreatic cells
insulin, glucagon
b) exocrine gland- releases products to ductsacini are cell clusters to produce digestive
enzymes – 99% of pancreatic cells
protease, lipase, amylase