Chapter 3 7digestion metabolism

Digestion & Absorption &
Transport and Metabolism
of Nutrients


Digestion
• The process of physically &
chemically changing the
composition of food in the
gastrointestinal tract
• The process by which food is broken
down into absorbable units


Absorption
• The process of assimilating the
products of DIGESTION into the
body.


Absorption


Anatomy of Absorption


Anatomy of Absorption
• Folds in the small intestinal wall
• Villus - fingerlike projections on the
folds
• Microvilli - hair like projections on

each cell of the small intestine
• Increases the surface area


Vessels in the Villi
• Capillaries in the villi
– carry water soluble nutrients to
liver
– amino acids
– monosaccharides


Vessels in the Villi
• Capillaries in the villi
– water soluble vitamins
– minerals
– water
– glycerol


Vessels in the Villi
• Lymph vessels in the villi
– carry fat soluble nutrients
– triglycerides
– fat soluble vitamins
– cholesterol


Small intestine - villi

Enzymes
• Are very specific for
– substrate
– environment
• temperature
• pH


Enzymes
• Are complex protein molecules
• Enable a chemical reaction to take
place but do not change during the
reaction


Digestive or gastrointestinal system


Esophagus


The Muscular Action of
Digestion
• Peristalsis
• Segmentation


Peristalsis
• Gastrointestinal(GI) tract muscular

• Movement of food/chyme through
the GI tract
• Food moves ahead of the
constriction


Stomach Muscles


The Muscular Action of
Digestion


pH Changes in GI Tract
•
•
•
•

7 = neutral
14 = very basic
1 = very acid
Major changes
– between esophagus and stomach
– between stomach and small
intestine


pH
of

Common
Substances


pH Changes in GI Tract
• Neutral pH in mouth & esophagus
• Stomach pH is very acid
– Inactivates some salivary enzymes
– Activates some enzymes
– Bacterioside
• Shift back to neutral in the small
intestine


Metabolism
• Occurs within individual cells
• It includes the use of basic nutrients
for the work of the cell & chemical
changes are involved
• Building new compounds
• Breaking down compounds


THE CELL
Inside the cell membrane lies the
cytoplasm

Nucleus.

Inside the nucleus are

the chromosomes,
that contain the
genetic material DNA.

The Mitochondria (power houses)
house all the enzymes involved in
the conversion of pyruvate to
acetyl CoA, fatty acid oxidation,
the TCA cycle, and the electron
transport chain.b

The cell membrane
encloses each cell’s
contents and regulates
the passage of molecules
in and out of the cell.

The ribosomes
assemble AA into
proteins.


Metabolism
• Work of the cell includes:
– Anabolism: building new compounds
– Catabolism: breaking down compounds for
energy


Anabolism