Download Digestion, Absorption, and Transport

Digestion, Absorption, and
Transport
Chapter 3
Prepared by
L.Nicholle Clark DTR, MS
Digestion
• The body’s process of breaking down foods into
nutrients in preparation for absorption.
• Anatomy of the Digestive Tract
• Gastrointestinal (GI) Tract- a flexible muscular
tube that extends from the mouth, through the
esophagus, stomach, small intestine, large
intestine, and rectum to the anus. The body
surrounds the GI tract. Figure 3-1.
Anatomy of the Digestive Tract
• Lumen- The enter space within the GI tract.
Substances must penetrates the GI tract’s wall to
enter the body proper.
• Mouth-Digestion begins here –four basic tastesweet,salty, sour, bitter.
• Pharynx – short tube that is shared by both the
digestive system and the respiratory system. Food
passes through, and the epiglottis closes off your
air passages so you do not choke.
Anatomy of the Digestive Tract
• Bolus-after a mouth full of food has been
swallowed it is called a bolus.
• Esophageal sphincter- the esophagus has a
sphincter muscle at each end. At the top the
bolus slides down through the sphincter to
the stomach.The lower sphincter closes so
the bolus proceeds forward and does not
slip back into the esophagus.
Anatomy of the Digestive Tract
• The stomach adds liquids and grinds the food in
to a semi-liquid mass called chyme.
• Phloric sphincter- opens and the chyme passes
through to the small intestine.
• Small intestine (appro 10 ft)- has three segmentsthe duodenum, the jejunum, and the ileum.
• Ileocecal valve- opens and the remaining contents
enter the colon.
Anatomy of the Digestive Tract
• Large Intestine(lg,colon)- water is removed from
the contents as it passes out of the lg into the
rectum.Strong muscles of the rectum and the anal
canal hold back waste until it is time to defecate.
• The muscular Action of Digestion
• Peristalsis- the relaxing and contracting of the
circular and longitudinal muscles of the GI tract
that work opposite each other to push the intestinal
contents along.
The Muscular Action of
Digestion
• Stomach Action- has a third layer of
diagonal muscles that work to force the
chyme downward.
• Segmentation-The rhythmic contractions of
the intestines that mix the chyme and
promote close contact with the digestive
juices & the absorbing cells of the intestinal
walls.
The Muscular Action of
Digestion
• Sphincter Contractions-muscles periodically open
and close to allow contents to move along at a
controlled pace.
• The Secretions of Digestion- The breakdown of
food into nutrients requires secretions from 5
different organs:Salivary glands,the stomach, the
pancreas, the liver and the small intestine.These
secretions, contain water & enzymes enter the GI
tract at various points along the way.
Secretions of Digestion
• Enzyme- is a protein that facilitates a chemical
reaction. It is often identified by the organ they
come from and the compounds they work on. Ex.
Gastric lipase-stomach enzymes that work on
lipids. Pancreatic lipase-comes from pancreas
works on lipids. It is a catalyst as the enzyme it
self remains unchanged.
• The digestive enzymes facilitate a chemical
reaction known as hydrolysis = the addition of
water.
Secretions of Digestion
• Salivary Glands-squirt just enough saliva to
moisten each mouthful of food so it can pass
easily down the esophagus.
• Gastric Glands- secrete gastric juice which acts
primarily in protein digestion.The strong acidity of
the stomach prevents bacterial growth and kills
most bacteria that enter the body with food.
Mucus is secreted from the stomach cells to
protect itself from gastric juices.
Secretions of Digestion
• Pancreatic juice- contains enzymes that act
on all three energy nutrients. This juice also
contains sodium bicarbonate which is an
alkaline, it neutralizes the acidic chyme
arriving in the small intestine from the
stomach.The cells of the intestinal wall also
possess digestive enzymes on their surfaces.
Secretions of Digestion
• Bile from the liver flows into the duodenum. Bile
is an Emulsifier it brings fats into suspension in
water so that enzymes can break then down into
their components parts.
• The Final Stage- At this point, the three energyyielding nutrients have been disassembled.
• In the colon intestinal bacteria ferment some fibers
producing water, gas, and small fragments of fat
that provide energy for the cells of the colon.
Absorption
• Most absorption takes place in the small intestine.
A rush of circulating blood continuous washes the
underside of the surface carrying the absorbed
nutrients away to the liver and other parts of the
body.
• Anatomy of the Absorptive System
• The small intestine surface under a microscope
appears to be wrinkled into hundreds of folds or
projections called villi each villi is covered with
its own microscopic hairs called microvilli.
Anatomy of the Absorptive
System
• In the crevices between the villi lie the the crypts
which are glands that secrete the intestinal juices
into the small intestine.
• Any nutrient molecule small enough to be
absorbed is trapped among the microvilli that coat
the cells and then draw into the cells.
• A closer look at the Intestinal Cells-Successive
portions of the intestinal tract are specialized to
absorb different nutrients.
A closer look at the Intestinal
Cells
• The myth of “Food Combining”.
• Preparing nutrients for Transport- When a
nutrient molecule has crossed the cell of a
villus, it enters either the bloodstream of the
lymphatic system.Water soluble nutrients
and smaller products of fat digestion are
released directly into the bloodstream.
A closer look at the Intestinal
Cells
• Larger fats and fat-soluble nutrients called
chylomicrons are released into the lymphatic
system enter the bloodstream at a point near the
hear.
• The circulatory Systems-The circulatory system
deliver nutrients wherever they are needed.
• Vascular System/ blood circulatory- is a closed
system of vessels through which blood flows
continuously, with the heart serving as the pump.
The circulatory Systems
• As the blood circulates through this system, it
picks up and delivers materials as needed.
• Blood travels Heart to arteries to capillaries to
veins to heart.
• Lymphatic System-Provides a one-way route for
fluid from the tissue spaces to enter the blood.No
pump, lymph circulates between the cells of the
body and collects into tiny vessels. The fluid
moves from one portion of the body to another as
muscles contract and create pressure and there.
The Health & Regulation of the
GI Tract
• GI tract health depends on adequate nutrition.
• Gastrointestinal Bacteria-An estimated 10 trillion
bacteria representing some 400 or more different
species & subspecies live in a healthy GI
tract.Most of these bacteria normally do the body
no harm and may actually do some good.Diet is
one of several factors that influence the body’s
bacterial population.Yogurt contains probiotics.
• Gastrointestinal Hormones &Nerve Pathways
Gastrointestinal Hormones
&Nerve Pathways
• Homeostasis-survival depends o body conditions
staying about the same; if they deviate too far
from the norm the body must do something to
bring them back to normal.The body regulates its
temperature, digestion, blood pressure etc.
• The system at its best-To maintain health &
promote the functions of the GI tract, you should
make balance, moderation, variety, & adequacy
features of every day’s menus.
Summary
• References
• Whitney, E., Rolfes, S.,. Understanding
Nutrition. Belmont, CA:ThomsonWadsworth