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Food and
Nutrition
Big Questions



1. How do the different parts of the
digestive system help the body
breakdown and absorb nutrients?
2. What features does the digestive
system have to maximize the speed at
which certain nutrients are absorbed by
diffusion?
3. What are the different ways in which
nutrients are absorbed?
Big Questions Cont’d



What determines the movement of
food through the system?
Why do children with Kwashiorkor
have distended bellies?
How does the small intestine protect
itself from the contents of the
stomach and why can’t it protect
itself the same way the stomach
does?

Heterotrophs
•obtain nourishment
from the organic
molecules man. by
other organisms

Nutrients used to
•Run the systems
of the body
•Make compounds
for metabolic
processes
•Grow and repair
tissue

Food processing
•Ingestion -food into the
digestive cavity
•Digestion -breaking down
food mechanically and
chemically
•Absorption -Nutrients pass
lining of the digestive tract
and into the blood

Food processing,
cont.
•Egestion or
elimination
Food that is not
digested and
absorbed is
discharged from
the body
Credit: © Fritz Polking/Visuals Unlimited
Rocky Python (Python sebae) eating an Impala.
133544

In cnidarians and
flatworms
•Food is digested in
the gastrovascular
cavity
•The gastrovascular
cavity serves as
both mouth and
anus

In more complex
invertebrates and in all
vertebrates
•The digestive tract is a
complete tube with an
opening at each end
•Digestion takes place
as food passes through
the tube
Various parts of the
digestive tract are
specialized to perform
specific functions
 Food passes in sequence
through -mouth,
pharynx, esophagus,
stomach, small intestine,
large intestine, and anus

Mechanical and enzymatic
digestion of carbohydrates
begin in the mouth
•Mammalian teeth include
incisors for biting,
canines for tearing, and
premolars and molars for
crushing and grinding
•Three pairs of salivary
glands secrete saliva

As food is swallowed, it
is propelled through the
pharynx and esophagus
•A bolus of food is
moved by peristalsis
•The mixing and
propulsive movements
of the digestive tract
are known as motility

In the stomach
•Food is mechanically
digested by churning
•Proteins are enzymatically
digested by pepsin
•Rugae are stomach folds
that expand with food
•Gastric glands secrete HCl
and pepsinogen
Credit: © Dr. Fred Hossler/Visuals Unlimited
Stomach surface.
212339
stomach lined with
columnar epithelium
cells that secrete mucus
 as stomach fills Gastrin
is released that
stimulates release of
pepsinogen

pepsinogen becomes active
pepsin in presence of HCl
 pepsin hydrolyzes proteins
into polypeptides
 peptic ulcers results when
mucus is absent;
Helicobacter pylori is
causative factor in decrease
mucus secreting cells


Into the small intestine
•Chyme leaves the
stomach through the
pylorus (sphincter) and
enters the small
intestine
•Most enzymatic digestion
takes place in duodenum
•The liver produces bile,
which emulsifies fats
Credit: © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited
The small intestine seen here in cross-section shows the numerous villi that greatly increase
the surface area for the digestion and absorption of nutrients. SEM X30.
166828
Credit: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
900025
Microvilli on simple columnar epithelium from intestinal cells. SEM X5125.
acidic chyme triggers
release of secretin from
duodenum (signals
 secretion of sodium
bicarbonate from
pancreas and bile from
liver)


presence of fatty acids
and partially digested
protein triggers release of
cholecystokinin (CCK)
from duodenum (signals
release of pancreatic
digestive enzymes and
release of bile from gall
bladder)

Presence of fatty acids
and partially digested
protein triggers release
of Gastric inhibitory
peptide (GIP) which
reduces churning in
stomach

BASICALLY….The
pancreas releases
enzymes that digest
protein, lipid, and
carbohydrates, as
well as RNA and DNA

The large intestine
reclaims H2O,
eliminates undigested
waste and incubates
bacteria that produce
Vitamin K and certain
B vitamins
Credit: © Mediscan/Visuals Unlimited
Colored X-ray showing barium ingestion.
16998
Credit: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
Transverse section of the colon, the largest portion of the large intestine. The colon is divided
into ascending, descending, and transverse segments. Shown in this photo is the large
central cavity (lumen), the tubular glands (Crypts of Lieberkuhn) that make up the inner layer
of the colon (the mucosa), and the smooth muscle that forms the muscularis layer or outer
layer. SEM X45.
900023

Dig.of-carbs, protein, lipid
•Nutrients in chyme are
enzymatically digested as
they move through the
digestive tract
•Polysaccarides are
digested into
disaccharide maltose by
salivary and pancreatic
amylases
-Maltase splits maltose into
glucose
•Proteins are split by pepsin
and by proteolytic enzymes
into amino acids
•Lipids are emulsified by
bile salts and then
hydrolyzed by pancreatic
lipase

Structural adaptations
that increase the surface
of the digestive tract
•The surface area of the
small intestine is
greatly expanded by
Folds in its wall
Intestinal villi
Intestinal microvilli
villi contain capillaries and
lacteals (lymphatic
vessel)
 glucose and amino acids
absorbed by secondary
active transport coupled to
sodium-potassiun pumps
 fructose enters by
facilitated transport

Credit: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
Close up of the tongue-shaped villi of the small intestine (jejunum) as viewed from the lumen.
The lining of the small intestine has a large surface area made up of large, circular folds of
epithelium. The epithelium is lined with villi that project outwards from each of the many folds.
Extensive networks of capillaries directly supply each villi and allow for the absorption of
nutrients into the vascular system. SEM X80.
900049
Absorption – A closer look

How are the different nutrients
absorbed including lipids, calcium
and iron?
Absorption of Carbohydrates


Fructose – Relying only on diffusion
(passive transport)
Glucose – Relying on pumps and
diffusion (termed secondary active
transport)
Transport of Amino Acids

Similar mechanism to glucose – using
pumps with diffusion (secondary active
transport)
Transport of Calcium
- Involves passive and active transport
- Active transporters require a vitamin to be
built ….can you guess which?
Transport of Lipids and
Cholesterol

A lipoprotein is a biochemical
assembly that contains both proteins
and lipids, bound to the proteins, which
allow fats to move through the water
inside and outside cells
Lipids/Cholesterol need to be
packaged
Iron Absorption

In general, the digestive system is set up to
maximize absorption; there is no regulation
of the amounts of substances absorbed into
the body. A notable exception is iron, in
which daily dietary absorption is regulated
so that it matches daily iron loss. The
reason that absorption must be carefully
regulated is that the body does not possess
a physiological mechanism for regularly
eliminating iron from the body.

Lipid absorption incl.
cholesterol
•Nutrients are absorbed
through the thin walls
of the intestinal villi &
enter lacteals
(lymphatic sys.)
•The hepatic portal vein
transports amino acids
and glucose to the liver
How the
body uses
fat
Absorption of other
nutrients
 Fat products pass through
intestinal lining
•They are packed into
chylomicrons
•The lymphatic system
transports chylomicrons
to the blood circulation


Carbohydrates
•Most carbohydrates are
ingested in the form of
complex carbohydrates
•Fiber is a mixture of
cellulose and other
indigestible carbohydrates
•Carbohydrates are used
mainly as an energy
source
Lipids are used as
•An energy source
•Components of cell
membranes
•To synthesize steroid
hormones and other
lipid substances
 Most lipids are ingested
in the form of
triacyglycerols

Proteins
•Serve as enzymes
•Are essential structural
components of cells
 The best distribution of
essential amino acids is
found in the complex
proteins of animal foods

How the
body
uses
protein

Vitamins
•Organic compounds
required in small
amounts for many
biochemical
processes
•Many serve as
components of
coenzymes

Vitamins, cont.
•Fat-soluble vitamins
include A, D, E, and
K
•Water-soluble
vitamins are the B
and C vitamins
Minerals are
inorganic nutrients
ingested as salts
dissolved in food and
water
 Trace elements are
minerals required in
amounts less than
100 mg per day

Basal metabolic rate
(BMR)
•The body’s cost of
metabolic living
 Total metabolic rate
•BMR plus the energy
used to carry on daily
activities


Energy input and output
•When energy
(kilocalories) input
equals energy output,
body weight remains
constant
•When energy input
exceeds energy output,
body weight increases

Current hypotheses
regarding the reg. of food
intake/energy
homeostasis
•Researchers are id.
signaling molecules
The hormone leptin
The neuropeptite Y
(NPY), neurotransmitter
prod. in hypothalamus
Credit: © Dr. Daniel Eitzman/Visuals Unlimited
Normal mice (left) and obese mice without the gene for leptin (right).
350882
DISORDERS / DISEASES
Colon Cancer
 Diarrhea
 Constipation
 Protein
deficiencykwashiorkor

Figure 45-12
Page 886
Transverse
colon
Ascending
colon
Cancer
Descending
colon
Protein deficiency
Figure 45-15
Page 891
Diseases/Disorders continued
 Cardiovascular diseases 
avoid sat. fats and trans
fats as they raise LDL
(bad) cholesterol
 Ulcers  H.pylori
 Food poisoning  ie
salmonella
166821
Credit: © RDF/Visuals Unlimited
Salmonella bacteria showing its peritrichous flagella used in locomotion. TEM X13,250.
350692
Credit: © Veronika Burmeister/Visuals Unlimited
Helicobacter pylori (formerly Campylobacter) on the digestive tract lining. TEM X40,000.
Q and A
1. Place the following in order:
Gastrin
Bile
Pepsin
Lipase
Water reabsorption
Sodium bicarbonate
Salivary amylase
Secretin
Sodium-Glucose transporter

2. What symptoms would you
expect from a deficiency in
a) Calcium
b) Iron
c) Iodine
d) Sodium or Potassium
e) Vitamin B’s (NAD+ and FAD
prod.)