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The Digestive
System and
Nutrition
Miller/Levine - Chap 38 (Sections 1&2)
Learning Standard

MA BIO 4.1 Explain generally how the
digestive system (mouth, pharynx, esophagus,
stomach, small and large intestines, rectum)
converts macromolecules from food into
smaller molecules that can be used by cells
for energy and for repair and growth.
Definitions



Nutrition – process by which the body obtains
raw materials from food
Nutrients – the source of raw materials that
the body uses to build tissues and
provide energy for cellular work
Essential nutrients – those that must be
supplied in diet because the
body cannot make them
Organic Nutrients
Proteins
2. Carbohydrates
3. Lipids (fats)
4. Vitamins
1.
Vitamins are water soluble or fat soluble
organic compounds which help enzymes do
their jobs (sometimes called coenzymes)
Inorganic Nutrients
Minerals
2. Water
1.
Minerals are inorganic ions used as cofactors
that helps enzymes & other protein
molecules do their job.
Four Stages of Processing Food
1.
2.
3.
4.
Ingestion – taking food in
Digestion – process of breaking down
food into molecules small enough to be
absorbed
Absorption – digested food leaves
digestive system and taken in by cells
Elimination – removal of undigested
food from digestive system
Types of Digestion:
Mechanical digestion – physical
break down of food to
increase surface area
 Chemical digestion – chemical
breakdown of large molecules into
molecules small enough to enter cells

End Result of Digestion
 Carbohydrates
become
monosaccharides or simple
sugars
 Proteins become amino acids
 Lipids become fatty acids &
glycerol
Human Digestive System
Mouth
 Ingestion
 Digestion
– mechanical & chemical
 Mechanical digestion – teeth,
tongue
 Chemical – starch digestion begins
 Saliva
– liquid secreted by the
salivary glands that contains
amylase & mucus.
 Amylase- enzyme that starts
starch digestion.
 Typically, about one liter of saliva is
secreted each day.
Pharynx
 Upper
part of throat
 Junction of digestive system &
respiratory system.
 Bolus- chewed clump of food that
leaves the mouth
Esophagus
 Muscular
tube that connects the
pharynx and the stomach
 Peristalsis
– rhythmic series of
smooth (involuntary) muscle
contractions that push food
through digestive system
Stomach
 Elastic,
muscular sac capable of
stretching to hold up to 2 liters of
food.
 Gastric juice – “stomach juice”
which is a mixture of mucus,
hydrochloric acid and pepsin
Function of HCl
1.
2.
Breaks apart the cells in food
Kills bacteria that is swallowed
with food
 Pepsin
- enzyme that starts the
chemical digestion of proteins.
 Chyme
– acidic liquid into which
bolus is turned in the stomach
Small Intestine

1.
2.
Long (6 m – 20 ft), narrow (2.5 cm – 1
in) tube where
Chemical digestion is completed
Digested food is absorbed into the
bloodstream.
Duodenum
 first
10 inches of small intestine
where chemical digestion of carbs,
proteins and lipids are completed
with the aid of the liver and
pancreas
Villi
Villi
Villi - fingerlike projections or folds in
the lining of the last 19 feet of small
intestine to increase surface area for
absorption of food.
 Total surface area of all villi = surface
area of a tennis court.


Digested food passes through the lining
of the small intestine into the
circulatory system which transports
nutrients to all cells of the body.
Large Intestine
Also called the colon which is involved in:
1. Absorption of water
2. Elimination of feces (rectum)

Feces – undigested food, bacteria and
other wastes
Human Digestive System can be
divided into 2 parts:
1.
2.
Alimentary canal – those organs that
food passes through as it is being
digested
Accessory organs – organs that aid
digestive process but food doesn’t
pass through (liver & pancreas)
Liver & Digestion
Produces bile which is:
1. not an enzyme.
2. stored in the gallbladder
3. used in small intestine where it
emulsifies fats (mechanical
digestion)
Pancreas & Digestion
Makes pancreatic juice which:
1. is secreted into small intestine.
2. neutralizes stomach acids
3. Contains enzymes that helps small
intestine complete digestion.
Assignment

Reading a food label
Citations


Human Body Systems: The Digestive System. United
Learning. 1997.
unitedstreaming. 11 November 2006
<http://www.unitedstreaming.com/>
Managing Your Health: The Digestive System.
Discovery Channel School. 2004.
unitedstreaming. 29 July 2008
<http://streaming.discoveryeducation.com/>