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The Digestive System
Or…What happens to that “Big Mac”
once you take a bite!
What makes up a “Big Mac”?
• The six basic groups of nutrients are:
1. Water
2. Carbohydrates
3. Fats
4. Proteins
5. Minerals
6. Vitamins
• Water is the most basic nutrient
• You die first without it
• If you lose 10% of your body water you are in
danger of dying –dehydration.
• Water makes up 70% or more of your body
(depending on your age).
• You are dehydrated before you actually
experience thirst.
• Made of carbon, hydrogen, and oxygen in the
proportion of [CH2O]n.
• Nutritional carbs are of plant origin.
• Function: provide energy.
1. Simple sugars
-Monosaccharides (glucose, fructose,
galactose, and mannose) C6H12O6
-Dissaccharides (2 monosaccharides
combined by dehydration synthesis)
Sucrose (glucose + fructose)
Lactose (glucose + galactose)
Maltose (glucose + glucose)
2. Complex Carbohydrates (polysaccharides)
-Starches (amylose, amylopectin, glycogen)
-Cellulose -mammals have no cellulase –
not digestible = FIBER
Isomers: same empirical formula,
different structural formula
Something to think about!!!
Lipids (Fats)
• Made of carbon, hydrogen, and oxygen.
• Functions: stored energy, cell membranes,
insulation and padding, steroid hormones
• Calorically dense. 2.54 calories / gram more
that carbs or protein
• Triglycerides (LDL and HDL), Cholesterol
• Basic component is fatty acids
– Saturated –each carbon fully hydrated
– Unsaturated –some double bonds
Generalized triglyceride structure
• Cylomicrons
– Form of fat absorption from the intestines
– More about it later
• HDL: High density lipoproteins
– Good Cholesterol
– Increased by cardiovascular exercise
• LDL: Low density lipoproteins
– Bad Cholesterol
Essential Fatty Acids
• Essential: required in the diet for
health, not made in adequate
amounts by the body to sustain
• Linoleic acid
• Linolenic acid
• Aracadonic acid
• Structure: chains of amino acids coded for on
DNA -C, H, O, N, and sometimes S.
• Functions: structural, enzymatic, antibodies,
regulatory (some hormones), energy
• Essential Amino Acids: PVT MATT HILL
• Non-essential –made by the body.
• Complete proteins –have the right combination
of essential amino acids
• Incomplete proteins have an imbalance of
essential amino acids –at least one limiting aa.
Meat, milk, eggs, soy.
Which is the best protein?
What is protein quality?
How is protein evaluated?
What about vegetarians?
What is the difference between ouevolacto and vegan?
• What is a complementary protein?
• Fat Soluble: ADEK
1. Vitamin A -retinoic acid –eyesight (night
vision), epithelial tissue health
2. Vitamin D –calcitrol –calcium absorption and
bone health. Deficiency disease =Rickets
3. Vitamin E –α-tocopherol –antioxidant in fat
soluble tissues.
4. Vitamin K – part of the clotting cascade.
Made by gut bacteria.
Water Soluble Vitamins
B vitamins:
B1 =thiamine TPP
B2 =riboflavin FAD -carries hydrogens
B3 =niacin NAD -carries hydrogens
B5 =Pantothenic acid
B6 =Pyridoxine transfers amino acids
B9 = Folic acid
B12 =carboxycobalamine -only one stored!
Animal products only
Vitamin C
Ascobic acid
Water soluble
Deficiency disease is scurvy
Only required by primates (including humans),
guinea pigs, and fruit bats.
• Important in the conversion of proline to
hydroxyproline to make collegen
• Important in immune response. Increase
turnover in disease.
• Anti-oxidant
• Macro-minerals: required in percentage
amounts in the diet
–structural: calcium, phosphorus,
-electrolytes: sodium, potassium, chlorine
Micro-minerals: trace elements –ppm (1mg/kg)
-iron, copper, fluoride, iodine, selenium,
Back to the “Big Mac”
• What is in a “Big Mac”
• Dissect your burger into its
• Explain the caloric effect of fat in the
burger or any food?
• Now what happens!!!
What is digestion?
• Digestion is the sum of the mechanical and
chemical processes that convert food
elements into small enough particle to be
absorbed into the body.
• There are 2 basic aspects of digestion:
• Chemical Processes –enzymatic
• Physical process –mechanical like chewing and
Mouth: Processes
Mechanical digestion:
Prehension: food gathering –lips, hands,
• Mastication: chewing, breaks food into smaller
pieces (greater surface area) to facilitate
enzyme breakdown.
• Ensalivation: coats food particles with saliva to
facilitate swallowing -lubrication
Chemical digestion
• Salivary amylase: breaks down starch (amylose)
into dextrins (6 carbon sugars).
• Dental Formula
– Set up like a fraction = ½ of the mouth
– Numerator = the top of the jaw
– Denominator = bottom jaw
– Numbers are given in the following order
– Incisors/canines/premolars/ molars
– Human permanent teeth =
– 2123/2123 X 2
Permanent teeth
Do all animals have the same teeth?
• Food is swallowed
• Moves through the pharynx
• Past the epiglottis
What is the purpose?
– Enters esophagus
– Moves by peristalic movement (wave-like
Stomach: gastric phase
Gastric Activities
• Mixing movements
• Gastric secretions: pH=2-3
– Pepsinogen
– HCl
– mucous
• Hormone release: (gastrin and intrinsic factor)
• Absorption
alcohol and water
• Chief cells -secrete pepsinogen
• Parietal cells –secrete HCl
• HCl converts pepsinogen to pepsin
Functions of the Stomach
• 1. Break down of proteins into peptides
• 2. Absorption of water –especially if
dehydration exists.
• 3. Absorption of alcohol
• 4. Absorption of acidic drugs (due to pH)
• 5. Secretion of “rennin” in babies causes milk
proteins to form “curds” for digestion.
Intestinal Digestion
Small Intestine
• Parts: No distinct bounderies.
• Duodenum
-first 25 cm (10 inches)
-primary area of digestion and absorption
• Jejunum
– Continued digestion and absorption
• Ileum
mostly water
• Ileocecal junction: where SI joins the cecum and
Intestinal lining
Intestinal “juices”
• Sodium bicarbonate -neuralizes pH pancreas
• Mucous –
Brunner’s glands
goblet cells.
• Chyme has a pH of____7_________.
Enzymes (all enzymes are proteins –
coded for on DNA)
• Peptidase 1
breaks down proteins
• Dissaccharidases convert dissacharides
to monosaccharides
• Lipase
breaks down triglicerices
SI & P
• Enterokinase
breaks down proteins
• Amylase
Breaks down amylose
SI & P
• Chyme passes through the ileocecalvalve into the Large
• Cecum
-in some animals (rabbits and horses)
is very large and provides a fermentation vat.
• Vermiform appendix – function is a lymph node
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Rectum
• Anus has 2 sphincters.
Lots of distance –little function
• The digestive function of the large intestine is
• Only mucous is secreted
• Absorption of water.
• Intestinal bacteria make: vitamin K, some
amino acids.
LI problems
• Diverticula: balloon like projections
that form in the large intestine due
to strain and weakness of the
intestinal wall.
• Diverticulitis= inflammation of the
Digestion of Fat:
• Bile emulsifies fat: O (droplets) + Bile  o o o o o o
• Emulsify means: the mixture of immiscible liquids
(like oil and water).
• Lipase attaches to the glycerol of the triglyceride and
breaks off the fatty acids 1 and 3.
Glycerol is absorbed into the blood
Fatty acids pass through mucosal cells are combined
with protein as cylomicrons the lymph system.
–transport of fat coated with protein from
intestines in lymphatics to thoracic duct.
-Dumped into the vena cava.
-Can go directly to muscle and adipose tissue or
to the liver to be reprocessed.
• LDL and HDL made by liver and
transport of fat in blood. HDL –
happy cholesterol.
Largest gland in the body.
Many important functions:
Carbohydrate metabolism
-maintains blood glucose level
-converts excess glucose to glycogen for
• -gluconeogenesis- breaks down glycogen to
glucose when blood sugar is low.
Lipid Metabolism
-oxidation of fat
-converts cylomicrons to VLDL, LDL, and HDLs.
-bile formation and release.
Protein Metabolism
-deamination of amino acids
-formation of urea
-vitamins A, D, and B12