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The
Digestive
System
Features of the Generalized
Vertebrate Gut
Oral Cavity - Origin
1. Origin Heterostomes - most of
the invertebrate phyla
Mouth originates from the
blastopore
2. Deuterostomes - not formed
early, but breaks through later
in development; anus
originates from the blastopore
Teeth
1. Origin - dermal denticles
2. Structure
Enamel - hardest substance in
the body,
Enamel
Dentin
occurs above the gum line
Pulp
• Cementum - continuation of
enamel
below the gum line
Cementum
• Dentin-matrix
Blood vessels• Pulp-living portion of tooth
•
and nerves
Glands of the mouth

Salivary glands secrete
saliva
mucin - lubricant
 salivary amylase converts starch to
glucose

Esophagus
1. Length-short in fish,
longer in tetrapods to
bypass lungs
2. Muscles
Upper end- striated
Lower 2/3 - smooth
3. Modifications of the
esophagus - crop in
birds for storing food
Stomach
1. Occurrence
 Present in
invertebrates with
complete digestive
tract
 Absent in most lower
chordates, even fish
2. Regions
Functions of the stomach


Little absorbtion by stomach water and alcohol
secretes
HCl - very acid pH
 mucin - lubricant
 pepsin - digests proteins to shorter
peptides
 gastrin - hormone which regulates
HCl secretion

Specialized stomachs
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Muscular gizzard of ground birds
4 chambers of grazing mammals ruminants
rumen is specialized for storing
food to be chewed later
Small Intestine
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Primary site of digestion
Digested food absorbed here absorbtion
Enzymes
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peptidases - peptides to amino acids
lactase - lactose (milk sugar) to simple
sugars
maltase - maltose to glucose
sucrase - sucrose to simple sugars
Absorbtion in the
Small Intestine
Pancreas - enzymes
for digestion
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lipase - fats to triglycerides
trypsin - proteins to shorter
peptides
nucleases - DNA & RNA
secretin - hormone which
stimulates buffering of HCl
Caecum

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
large sac at junction of small and large
intestines
contains symbiotic bacteria that digest
cellulose
our appendix is a rudimentary caecum
Colon

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
no digestion
reabsorbs H20 and ions
contains bacteria that synthesize
Vitamin K
Fermentation of gases by bacteria
Liver
A. Development - outpocket of the
gut - tube that remains is the
common bile duct
B. Digestive function - produces bile
that emulsifies fats
 Bile is stored in the gall bladder for
secretion into the small intestine
Other function of the liver
C. Other functions  stores glycogen
 stores fats - cholesterol
 filters and stores toxic
materials
 destroys red blood cells
Circulation and the Liver
Pancreas
A. Origin - outpocket of the gut
B. Functions
1. Exocrine - produces digestive
enzymes
2. Endocrine - produces insulin
that regulates blood glucose
levels
The
fate of
food
NUTRITION

Nutrient - specific substance that must
be taken into the body in sufficient
quantities to meet the body’s needs


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Essential Nutrient - required preformed;
body cannot make it or cannot make
enough to meet needs
Nonessential nutrient - body can make
IF raw materials are available
Body needs BOTH to function
Nutrient Classes

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
Water (H2O)
Carbohydrate (CHO)
Protein (Pro)
Lipid (Fat)
Amount of energy??
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calorie - energy needed to raise 1 gm of
H2O 1 degree Centigrade
Kilocalorie (kcal) - 1000 calories; energy
needed to raise 1 liter of H2O 1 deg. C
Direct Calorimetry - measuring the heat
(energy)
Indirect Calorimetry - measuring the CO2
& O2 and “deriving” the energy
Energy from Nutrients
Nutrient Class
Calories/gram
CHO
4
Pro
4
Fat
9
Alcohol
7
Phytochemicals (plant)


Only few of 10,000’s studied
associated with
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decrease CVD & cancer risk
decrease infections
increase immune function
examples - flavonoids; carotenoids (>
600); isoflavones; plant sterols

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Best to get from food NOT supplements
** soy; tomatoes, garlic, onions,
legumes, green tea; cruciferous
vegetables, red wine, grapes
I.e., EAT MORE AND WIDER VARIETY
OF FRUITS & VEGETABLES
Water & Micronutrients

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Functions
Intake Sources
Losses
Dehydration
Balance
Maintaining Hydration
Water Functions

Regulates body temperature
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Environment for cells & chemical reactions
Transport (blood)

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cools body temperature AND evens heat
throughout body
blood pressure fxn of volume of H2O
secondary lubrication of joints
takes part in chemical reactions
Body Water (45 liters)
INTERCELLULAR
(12)
BLOOD/LYMPH (3)
intracellular
intercellular
blood/lymph
INTRACELLULAR (30)
Sources of Water

Fluids Foods Metabolic H2O -

Total
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550 - 1500 ml
700 - 1000 ml
200 - 300 ml
1450 - 2800 ml
Carbohydrates
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Introduction to CHO
Terminology
 Simple/sugars
 Complex/Starch
Digestion
Metabolism Overview
Carbohydrates....
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First link in the food chain
Photosynthesis - plants store some of sun’s
energy (0.1%) in chemical bonds of CHO
CO2 + H2O -----> CHO
ALL PLANT foods have CHO
Only significant animal sources of CHO are
milk and some milk products
Energy source for man - 8% Eskimos; >70%
some non-industrialized countries
CHO Functions
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Energy - all cells use
Some cells (RBC, brain) can use
only CHO until starvation sets in
Needed for effective burning of fat
Spares protein from use for energy
Fiber, alternative forms of CHO,
provides a number of benefits
CHO Terminology

Saccharide = building block

Simple CHO = “sugars”
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Complex CHO = Starch or Amylose
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(1-3 saccharides)
mono (1), di (2), tri (3)
(many saccharides) - poly
Complex CHO = Fiber

Different bonding than starches
Monosaccharides

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Glucose (Glu) - most abundant CHO;
part of table sugar; “blood” sugar
Fructose (Fru) - found in fruit &
honey; part of table sugar
Galactose (Gal) - part of milk sugar;
generally not found free in nature
Disaccharides

Sucrose = Glu + Fru
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Maltose = Glu + Glu
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Table sugar
product of amylase digestion; beer;
sprouts
Lactose = Glu + Gal

Milk sugar
Polysaccharides
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multiple glucose (usually) units bound
together
Starch/Amylose = many Glu
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Storage form of energy in plants
Fiber - # different kinds; some are
multiple Glu units but different chemical
bonding from Amylose

examples - cellulose; pectin
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Fiber (cont.) - often the structural CHO
in plants
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ONLY FOUND IN PLANTS
Glycogen = storage form of CHO in
animals (many Glu units)
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very highly branched to aid release
Major Hormones of Digestion
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Insulin - made in pancreas; lowers
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Glucagon - made in pancreas; raises

Epinephrine (adrenaline) - made in
blood glu; increases all energy stores
blood glu; decreases adipose fat &
liver glycogen stores
adrenal glands; raises blood glu;
decreases all energy stores
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CHO Health Issues
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Fiber
Abnormal CHO Metabolism
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Lactose Intolerance
Hypoglycemia
Diabetes Mellitus
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Type 1 diabetes
Results from the body's failure to produce insulin, the hormone that "unlocks"
the cells of the body, allowing glucose to enter and fuel them. It is estimated
that 5-10% of Americans who are diagnosed with diabetes have type 1
diabetes.
Type 2 diabetes
Results from insulin resistance (a condition in which the body fails to properly
use insulin), combined with relative insulin deficiency. Most Americans who are
diagnosed with diabetes have type 2 diabetes.
Gestational diabetes
Gestational diabetes affects about 4% of all pregnant women - about 135,000
cases in the United States each year.
Pre-diabetes
Pre-diabetes is a condition that occurs when a person's blood glucose levels are
higher than normal but not high enough for a diagnosis of type 2 diabetes.
There are 41 million Americans who have pre-diabetes, in addition to the 20.8
million with diabetes.
Syndrome X –
 insulin resistance (the inability to properly deal with dietary
carbohydrates and sugars), abnormal blood fats (such as elevated
cholesterol and triglycerides), overweight, and high blood pressure.
Sources of Sugar
Processed
45%
Beverages
29%
Home Use
26%
Beverages
Home Use
Processed
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Take 12 oz H2O
add 10 tsp sugar
drink
~ 160 empty calories, i.e.,
A soda
Proteins

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Structure
Digestion
Absorption
Roles in Body


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Tissue maintenance & Growth
Regulation & Control
Energy
Distribution of Body Proteins
Skin
10%
Other
20%
Muscle
Bone
Skin
Other
Bone
20%
Muscle
50%
Protein Structure
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Made up of carbon, oxygen, hydrogen
& nitrogen (C, O, H, N)
Amino acids (aa) are building blocks
9 essential
11 nonessential (can be made from
other aa or carbon skelton (“glucose”) if
N available
AA differ by side chain (R group)
Regulation & Control Functions

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Enzymes
Hormones (some)
Antibodies; immune system
Transport
Acid-base balance (buffers in blood)
Fluid & electrolyte balance
Protein Sources (US)
Vegs
7%
Grains
19%
Meats
Legumes
Dairy
Vegs
Grains
Dairy
21%
Legumes
5%
Meats
48%
Protein in Foods
“Food”
M Meat
M Dairy
Vegetable
Grain
Legume
Serving
3 oz
1cup or 1 oz
1/2 cup
gm Pro
21 gm
8 gm
2 gm
1 sl or 1/2 cup 3 gm
1/2 cup
7-8 gm
Lipids
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Classes
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Triglycerides (TG)
Phospholipids (PL)
Sterols
Class Functions
Terminology
Digestion
Transport - Lipoproteins
Lipid Classes

Triglycerides
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Phospholipids
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made of 3 fatty acids (fa) & 1 glycerol
fa 4-22 Carbons long; mostly 16-20
95% of dietary lipids (fats & oils)
1 fa replaced by a phosphate group
Sterols
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
complex ringed structures; noncaloric
ex. cholesterol & Vit D
TG Functions
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Concentrated energy (diet and main storage
form)
Provides essential fatty acids (linoleic;
linolenic)
Carrier of Fat Soluble Vits (A,D,E,K)
Body Insulation & padding around organs
Cell membranes
Adds flavor & texture to foods
Contributes to satiety
Phospholipid Functions
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Cell membranes
Help transport other fats in blood
Precursor for some neural transmitters
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Lecithin ----> Acetyl Choline
emulsifier in foods
Cholesterol Functions
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Cell membranes
Precursor for Vit D & some hormones
(estrogen, testosterone)
Major component of bile
ONLY FOUND IN ANIMALS; NEVER
FOUND IN PLANTS
not an essential nutrient since man
makes
Saturated Fats
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maximum # of Hydrogen atoms
usually solid at room temp.
mostly from animal sources
Exceptions - tropical oils (palm,
coconut) are very saturated
raise blood cholesterol
Unsaturated Fats
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fewer H atoms; double bonds b/t Carbons
usually liquid at room temp.
mostly plant and fish sources
more chemically active (turn rancid faster)
lower blood cholesterol
Monounsaturated fat acid (MUFA) - 1
double bond (minus 2 H)
Polyunsaturated fat acid (PUFA) - 2 or
more double bonds
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Dietary fats (TG) really mix of saturated
and unsaturated fats
Classified by predominate type
Fatty acids can differ by 1) degree
of saturation or 2) length (# carbons)
BUT NOT by calories (all 9
kcals/g)
Essential Fatty Acids

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Linoleic (Omega 6/n-6) - found mostly in
plant oils
Linolenic – (n-3) found mostly in cold-water
fish and some plant oils (canola oil, nuts,
seeds)
Deficiency leads to poor growth, liver
problems, dermatitis
O-6 to O-3 ratio MUCH higher than in Hunter
Gatherers - inc risk # diseases or adverse
outcomes (CVD, pregnancy, learning, bone
health)
Lipoproteins
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
Transport lipids
mixture of protein and lipids
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packaged so water soluble cpds on
outside and insoluble cpds on inside
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Pro & phospholipids are water soluble
like homogenized milk
LP have different forms, functions, &
effects on CVD risk
Low Density LP (LDL)
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remnant of VLDL after most TG removed
very HIGH in Cholesterol

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not always effectively cleared by liver so
other tissues remove including artery
walls
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major component of total blood cholesterol
esp when cholesterol has been modified
risk of “high blood cholesterol” is from LDL,
i.e., increases risk of CVD
High Density LP (HDL)

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made by liver & intestine & then altered
in blood
carries cholesterol from tissues
(including arteries) & other LP to Liver
Reduces risk of CVD
Ratio of LDL/HDL may be better
predictor of CVD risk than any single LP
or total blood cholesterol level
Levels of LP & CVD Risk

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HDL > 60mg/dl
= Low risk
HDL < 35 mg/dl
= High risk
LDL/HDL ratio < 4 = Low risk
men’s HDL run from high 30’s to high
40’s
women’s from low 50’s to low 60’s
(estrogen effect)
Sources of Fat
Grains
10%
Sweets/Frt
10% Vegetables
6%
Dairy
18%
Meats
22%
Fats/oils
34%
Meats
Fats/oils
Dairy
Grains
Sweets/Frt
Vegetables
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~50% fat from animal sources
~ 75% Saturated fat from animal sources
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6 foods foods provide 1/2 sat. fat
cheese; beef (esp ground), milk, baked
goods, margarine, butter
Trend towards less animal & more plant fat
lower % of fat 42% (60’s) -> 36% (80’s) ->
34% now BUT
> amount of fat
Excretory System
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Among vertebrates the #1 Apparatus in the
Excretory System is the KIDNEY
Filters 2000L of blood/day
3 Functions
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Filtration – Blood Filter
Reabsorption – Selective – take back the good stuff – leave
the waste
Secretion and Excretion– secretion of foreign molecules and
waste across membranes of capillaries and kidney tubules –
opposite of reabsorption
Excretion of waste - Urine
Basic Structure of Kidney
Units
The Mammalian Kidney
Route of waste

In the nephron tubule,


filtration occurs from glomeruli into Bowman's
capsule The filtrate passes from Bowman's
capsule through the PCT (proximal convoluted
tubule), the loop of the nephron (loop of Henle),
the DCT (distal convoluted tubule), before
reaching a collecting duct.
Now, just dumping out the filtrate would be a
waste (literally) and would not address issues of
osmoregulation.
Functional Unit of Kidney Nephron
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Glomerulus
Bowman’s capsule
Proximal convoluted
tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
2 types – Juxtamedullary
and cortical
Nephron - Filtration
•Filter is non-selective except for
size ( <70,000 MW; 7 nm in
diameter).
•Blood cells and proteins do not
pass through the filter.
•Fluid in Bowman's capsule much
like plasma without the proteins.


Large amounts of
water are necessary
for filtration.
Most of this water is
reabsorbed back
into the circulation
through the tubules
- proximal & distal
conv. tubules and
Henle’s loop.
Reabsorption

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Need to reabsorb stuff (H20, ions, nutrients)
or animal literally urinate itself to death
180L of water leave the blood in filtrate
Water, selected ions, glucose, and other
items must be reabsorbed
This reabsorption most typically involves the
use of energy to reclaim sodium (and other
items tagging along with it)