1
THE DIGESTIVE SYSTEM
Food for Energy and Growth

The food animals eat provides both a source of
energy and essential molecules that the animal
body is not able to manufacture for itself
 an
optimal diet contains more carbohydrates than fats
and also a significant amount of protein
Figure 31.1 The pyramid of nutrition
Food for Energy and Growth

Carbohydrates are obtained primarily from cereals,
grains, and breads
on the average, carbohydrates contain 4.1 calories per
gram
 the body uses carbohydrates for energy


Dietary fats are obtained from oils, margarine, and
butter and are abundant in fried foods, meats, and
processed snack foods
fats contain 9.3 calories per gram
 the body uses fats to construct cell membranes, to insulate
nervous tissue, and to provide energy

Food for Energy and Growth

Proteins can be obtained from many foods,
including poultry, fish, meat, and grains
 proteins
have 4.1 calories per gram
 proteins are used for energy and as building materials
for cell structures, enzymes, hemoglobin, hormones, and
muscle and bone tissue
Animation: Energy for Activity
Food for Energy and Growth

In wealthy countries, being significantly overweight
is common
 this
is due to habitual overeating and high-fat diets, in
which fats constitute over 35% of the total caloric
intake
 the standard measure of appropriate body weight is
the body mass index (BMI), estimated as your body
weight in kg, divided by your height in meters squared
Figure 31.3 Are you overweight?
66% of Americans are overweight with a BMI of 25 or
more
Animation: Body Mass Index
Food for Energy and Growth

One essential characteristic of food is its fiber
content
 fiber
is the part of plant food that cannot be digested
by humans
 diets that are low in fiber result in a slower passage of
food through the colon
 low fiber is thought to be associated with incidences of
colon cancer
Food for Energy and Growth

Over the course of evolution, many animals have
lost their ability to manufacture certain substances
they need
 many
vertebrates are unable to manufacture one or
more of the 20 amino acids used to make proteins
 humans
are unable to synthesize eight amino acids, which
must be obtained from proteins in food
 these are called essential amino acids
Food for Energy and Growth

In addition to supplying energy, food must also
supply essential minerals, such as calcium and
phosphorous


some minerals are required in very small amounts and are
called trace elements
Essential organic substances that are used in trace
amounts are called vitamins

many vitamins are required cofactors for enzymes
Digestion
13


Processing of food
Types

Mechanical (physical)






Chew
Tear
Grind
Mash
Mix
Chemical


Catabolic reactions
Enzymatic hydrolysis



Carbohydrate
Protein
Lipid
Types of Digestive Systems

Heterotrophs are divided into three groups on the
basis of their food sources
herbivores eat plants exclusively
 carnivores are meat eaters
 omnivores eat both plants and animals



Single-celled organisms, as well as sponges, digest
their food intracellularly
All other animals digest their food extracellularly,
within a digestive cavity
Digestion
15

Phases
 Ingestion
 Movement
 Digestion
 Absorption
 Further
digestion
Digestive System Organization
16

Gastrointestinal (Gl) tract (Alimentary canal)
Tube within a tube
 Direct link/path between organs
 Structures












Mouth
Oral Cavity
Pharynx
Esophagus
Stomach
Duedenum
Jejenum
kIleum
Cecum
Ascending colon
Transverse colon
Digestive System Organization
17





Descending colon
Sigmoid colon
Rectum
Anus
Accessory structures


Not in tube path
Organs






Teeth
Tongue
Salivary glands
Liver
Gall bladder
Pancreas
The Mouth and Teeth

Many vertebrates have teeth, and chewing
(mastication) breaks up food into small particles and
mixes it with fluid secretions

mammals have heterodont dentition, teeth of different
specialized types

the general pattern of dentition is modified in different mammals
depending on their diet


in carnivorous mammals, the canines are prominent, and other teeth are
more bladelike and sharp
in herbivorous mammals, incisors are well-developed for snipping,
canines are reduced or absent, and molars are large and flat, with
complex ridges well suited to grinding
The Mouth and Teeth

Humans are omnivores and human teeth are
specialized for eating both plant and animal
material
 humans
are carnivores in the front of the mouth and
herbivores in the back
 children have only 20 teeth but these are lost during
childhood and replaced by 32 adult teeth
Figure 31.9 Human teeth
The tooth is a living
Anatomy of the Mouth and Throat
21
Human Deciduous and Permanent Teeth
22
Dorsal Surface of the Tongue
23
The Major Salivary Glands
24
Deglutition (swallowing)
25

Sequence

Voluntary stage


Push food to back of mouth
Pharyngeal stage

Raise




Soft palate
Larynx + hyoid
Tongue to soft palate
Esophageal stage



Contract pharyngeal muscles
Open esophagus
Start peristalsis
Deglutition (swallowing)
26

Control

Nerves




Glossopharyngeal
Vagus
Accessory
Brain stem

Deglutition center



Medulla oblongata
Pons
Disorders


Dysphagia
Aphagia
The Esophagus and Stomach

The esophagus is a muscular tube that connects the
pharynx to the stomach
 the
upper third is enveloped in skeletal muscle for
voluntary control of swallowing
 the lower two-thirds is surrounded by involuntary smooth
muscle
 rhythmic waves of contractions, called peristalsis,
propel food towards the stomach
Esophagus
28


Usually collapsed (closed)
3 constrictions
Aortic arch
 Left primary bronchus
 Diaphragm


Surrounded by
SNS plexus
 Blood vessels


Functions
Secrete mucous
 Transport food

Peristalsis and Segmentation
29
Esophagus
30

Sphincters
Upper
 Lower


Abnormalities
Achalasia
 Atresia
 Hernia
 Barret’s esophagus
 Esophageal varices

The Esophagus and Stomach

The movement of food from the esophagus into the
stomach is controlled by a ring of circular smooth
muscle, called a sphincter
contraction of the sphincter prevents food in the stomach
from moving back into the esophagus
 in humans, stomach contents can be brought back out during
vomiting
 the relaxing of the sphincter may lead to acid reflux, which
is when stomach acid moves into the esophagus


this produces a burning sensation known as heartburn
The Esophagus and Stomach

The stomach is a saclike portion of the digestive
tract
 the
stomach contains an extra layer of smooth muscle
for churning food
 gastric juice is released by gastric glands in the lining
of the stomach
 parietal
cells secrete hydrochloric acid (HCl)
 chief cells secrete pepsinogen

pepsinogen requires a low pH to be activated into pepsin, a
protease that begins the digestion of proteins
Stomach
33



Usually “J” shaped
Left side, anterior to the spleen
Mucous membrane
G cells – make gastrin
 Goblet cells – make mucous
 Gastric pit – Oxyntic gland – Parietal cells – Make HCl
 Chief cells – Zymogenic cells



Pepsin
Gastric lipase
Anatomy of the Stomach
34
Stomach
35

3 muscle layers




Regions







Oblique
Circular
Longitudinal
Cardiac sphincter
Fundus
Antrum (pylorus)
Pyloric sphincter
Vascular
Inner surface thrown into folds
– Rugae
Contains enzymes that work best
at pH 1-2
Stomach
36

Functions



Mix food
Reservoir
Start digestion of







Protein
Nucleic acids
Fats
Activates some enzymes
Destroy some bacteria
Makes intrinsic factor – B 12
absorption
Destroys some bacteria
 Absorbs
 Alcohol
 Water
 Lipophilic
B
12
acid
The Small and Large Intestines

The small intestine is the true digestive vat of the
body
 only
relatively small portions of chyme are introduced
into the small intestine at one time
 this
allows time for acid to be neutralized and enzymes to
act
 in
the small intestine, carbohydrates, protein, and lipids
are broken down and absorbed into the bloodstream
Small Intestine
38

Absorbs





80% ingested water
Electrolytes
Vitamins
Minerals
Carbonates



Active/facilitated transport
Monosaccharides
Proteins


Di-/tripeptides
Amino acids
 Lipids
 Monoglycerides
 Fatty
acids
 Micelles
 Chylomicrons
1.6 The Small and Large Intestines

While some enzymes necessary for digestion are
secreted by the cells of the intestinal wall, most are
made in the pancreas
 the
pancreas is an exocrine gland, meaning it secretes
through ducts
 the pancreas sends it products via a duct that empties
into the first part of the small intestine, the duodenum
The Small and Large Intestines

Much of the food energy the vertebrate body
harvests is obtained from fats
 fat
digestion involves bile salts that are secreted into
the duodenum by the liver
 bile salts act like detergents and combine with drops of
fat to form microscopic droplets
 this
process is known as emulsification
 this increases the surface area for the enzyme lipase to
work on in order to breakdown the fat
Small Intestine
41

Secretes digestive enzymes

Peptidases







Sucrases
Maltase
Lactase
Saccharidases




AminoDiTri-
DiTri-
Lipase
Nucleases
Small Intestine
42


Control
Requires pancreatic
enzymes & bile to
complete digestion
Large Intestine
43


Extends from ileocecal valve to anus
Regions
Cecum – Appendix
 Colon




Ascending
Transverse
Descending
Rectum
 Anal canal

Anatomy of the Large Intestine
44
Large Intestine
45

Histology
 No
villi
 No permanent circular folds
 Smooth muscle
 Taeniae
coli
 Haustra
 Epiploic
appendages
 Otherwise like rest of Gl tract
Large Intestine
46

Functions

Mechanical digestion



Haustral churning
Peristalsis
Reflexes



Gastroileal
Gastrocolic
Chemical digestion –
Bacterial digestion


Ferment carbohydrates
Protein/amino acid
breakdown
– Absorbs
•More water
•Vitamins
–B
–K
– Concentrate/eliminate
wastes
Feces Formation and Defecation
47


Chyme dehydrated to form
feces
Feces composition






Water
Inorganic salts
Epithelial cells
Bacteria
Byproducts of digestion
Defecation


Peristalsis pushes feces into
rectum
Rectal walls stretch

Control
 Parasympathetic
 Voluntary
Liver
48

Location
R. Hypochondrium
 Epigastric region


4 Lobes
Left
 Quadrate
 Caudate
 Right


Each lobe has lobules – Contains hepatocytes –
Surround sinusoids – Feed into central vein
Liver
49

Functions

Makes bile


Detergent – emulsifies fats
Release promoted by:




Vagus n.
CCK
Secretin
Contains






Water
Bile salts
Bile pigments
Electrolytes
Cholesterol
Lecithin
Liver
50

Detoxifies/removes



Stores








Drugs
Alcohol
Gycolgen
Vitamins (A, D, E, K)
Fe and other minerals
Cholesterol
Activates vitamin D
Fetal RBC production
Phagocytosis
Metabolizes absorbed food
molecules



Carbohydrates
Proteins
Lipids
Liver
51

Dual blood supply
 Hepatic
portal vein
 Direct
input from small
intestine
 Hepatic
 Direct
artery/vein
links to heart
Animation: Impact of Alcohol
Vitmins
53
• organic compounds that the body uses for
metabolic purposes but is unable to produce in
adequate quantity
Nutrient
Vitamin A
RDA
Men: 3,000 IU
Women: 2,300 IU
Beta carotene (as
mixed
carotenoids)
Vitamin D
N.D.
Vitamin E
Vitamin K
Vitamin C
9-50 years: 200 IU
51-70 years: 400 IU
> 70 years: 600 IU
osteoporosis: 1,000 IU
22 IU
M: 120 mcg
W: 90 mcg
M: 90 mg
W: 75 mg
smokers add 35 mg
Potential toxic effects
Main function
Best food sources
Liver toxicity, dry rough skin and
Healthy immune barriers and
Foods high in beta
cracked lips, irritability, headache,
epithelial tissue, growth,
carotene, fortified
birth defects
foods, liver
reproduction, bone and red blood
cell formation, vision
Possibly increased lung cancer in Antioxidant, source of vitamin A, Orange, yellow, red
smokers, harmless orange skin
immune booster, possible cancer and green vegetables
colour
prevention, vision
and fruits
Fortified
milk, fatty fish
Heart/liver/kidney toxicity,
Calcium metabolism, bone
hypercalcemia (excess calcium in
mineralization, possible cancer
the blood)
prevention
Possible increase in heart disease,
excess bleeding
Antioxidant, anticoagulant,
protection from heart disease,
possible cancer prevention
Interaction with blood thinners
Bone mineralization, blood
clotting
Pro-oxidant, excess iron absorption, Antioxidant, immunity, antiviral
diarrhea
in test-tubes, cancer prevention,
increases iron absorption
Thiamine (B1)
M: 1.2 mg
W: 0.9 mg
Very high doses may promote
tumour growth
Riboflavin (B2)
M: 1.3 mg
W: 1.1 mg
M: 16 mg
W: 14 mg
N.D.
Niacin (nicotinic
acid)
Itching, skin flushing,
Liver toxicity, insulin resistance
Vitamin B6
M: 1.3-1.7 mg
W: 1.3-1.5 mg
Nerve damage (neuropathy)
Folate
0.4 mg
High dose can mask B12 deficiency
leading to nerve damage
Vitamin B12
(cobalamin)
2.4 mcg
Rare cases of eye damage
Energy metabolism, mood,
nervous system
Wheat germ, vegetable
oils, nuts
Green leafy vegetables
Fruits and vegetables,
especially peppers and
citrus fruits
Whole grains, brown
rice, fortified foods,
legumes, pork, oysters
Energy metabolism, antioxidant, Dairy products, leafy
possible migraine prevention
greens, oysters
Energy metabolism, lowers LDL Poultry, red meat, fish,
cholesterol and triglycerides,
legumes, peanut
raises HDL cholesterol
butter, nuts
Protein metabolism, immunity,
Meat, fish, poultry,
neurotransmitter synthesis (e.g.
eggs, potatoes,
serotonin and dopamine), treats
fortified cereals,
peripheral neuropathy and PMS
peanuts, soybeans
Cell division, prevents neural Leafy greens, legumes,
tube defects and perhaps other
oranges, broccoli,
cauliflower
birth defects, lowers
homocysteine, possible cancer
prevention
Cell division, amino acid
Fish, shellfish, meat,
metabolism, nervous system,
fortified soy and rice
mental function
milk, fermented soy
products
Minerals
55



Major and trace minerals
Major minerals are essentials of cells
and body fluids and are structural
components of tissues
Trace minerals are for support for
larger molecules to function
Minerals (table 8.5 in book)
56
Calcium
1,000-1,200 mg
Magnesium
M: 400 mg
W: 320 mg
Iron
Zinc
Selenium
M: 8 mg
W: 18 mg
Calcium deposits in soft
tissues
Bone mineralization,
muscle contraction
Bone mineralization,
Diarrhea, decreased calcium active in more than 300
absorption
chemical reactions in the
body
Dairy products,
fortified soy and
rice milk, fish
bones
Whole grains,
nuts, green
vegetables,
legumes
Makes hemoglobin which
Meat, legumes,
Iron overload disorders,
carries oxygen, makes
tofu, leafy greens,
heart disease, liver cirrhosis
energy in the
breakfast cereals
mitochondria
M: 11 mg
W: 8 mg
Immune suppression,
nausea, metallic taste,
copper deficiency
Growth, immunity, wound
healing, taste, sperm
production, antioxidant,
prostate health
Oysters, meat,
poultry, fish
55 mcg
Brittle hair and nails,
irritability, garlic breath,
fatigue, nausea
Antioxidant, immunity,
possible cancer
prevention, viral infections
Whole grains from
selenium-rich
soils, poultry,
meat, dairy
Class homework
57



Keeping a food diary for 1 full week (7 days)
Track all food and beverage consumption
Use websites to track calories
 Fitwatch.com




Use measuring cups/spoons
If you work-out; track your calorie outtake
Also want 1 pg of what you learned over the week
Due via email in table format by NOV 18th
 Worth:
50 points
Example:
58
DATE: 10/16
Food Items:
Calories
Breakfast:
1 egg sandwich (egg, bread, cheese, and ketchup)
1 apple
270
50
Snack:
Hand full of almonds
150
Lunch:
2-Mc Donalds hamburgers with no cheese & NO PICKLE
Diet coke
400
0
Snack:
Green tea with splenda
Animal crackers (20 of them)
0
250
Dinner:
Chicken breast (med size) with sweet potato, butter, and corn
2 cups of milk
Glass of green tea sweetened with splenda
Piece of pumpkin pie with cool whip
630
Activity:
Walked the dogs around the neighborhood for 30 mins
-250
Other notes:
Had no energy when I got up this morning but by the afternoon I
was feeling pretty good.
Total: 2530-250=2280
200
0
580