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The Science of Digestion
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What is Digestion?
Organisms need nutrients in order to survive and thrive.
The act of absorbing food and delivering it to the
individual cells in a useable form is the basis for
digestion.
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What is Digestion?
In single celled organisms the primary mode of food absorption is
pinocytosis. Food is absorbed into the cell and then broken down
to be used to produce energy.
In multi celled organisms the process is much more complex
individual cells are specialized and unable to absorb food in the
same fashion as single celled organisms. Instead they use a
specialized digestive system that breaks down food and relies onthe circulatory system to deliver useful substances to individual
cells to be absorbed.
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The digestive system
There are several processes and anatomical structures involved in
digestion. In order to fully understand digestion we must first
examine these processes
The pathway by which food travelsthe digestive tract
The mechanical movement of this food through this tract
The chemical digestion of food
The rolls of the digestive organsdigestive tract, liver, pancreas
and gall bladder
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Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
The Human Digestive System
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The Tube System
This digestive model functions on what can be
simplified as a large tube arrangement.
This Tube system is separated by a series of
sphincterswhich are essentially openings
controlled by muscles through the system.
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The Tube System
There are four main sphincter muscles along the alimentary
canal that aid in digestion:
The cardiac sphincter, between the esophagus and thestomach, opens at the approach of food, which is then swept
into the stomach by rhythmic peristaltic waves
The pyloric sphincter controls the opening from the stomach
into the duodenum. It is usually closed, opening only for amoment when a peristaltic wave passes over it.
Two anal sphincters, internal and external, control the anus,
allowing the evacuation of feces.
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The Tube System
This system functions on the idea of compartmentalization,where different compartments are capable of specificfunctions allowing concentration gradients of biologicalsubstances for digestion.
For Example The concentration of HCl in the Stomachwhich if allowed to flow through the system would ultimately
break down much of the bodies tissues.
Compartmentalization allows the concentration of these fluidsin one compartment and the neutralization of them in anotherin order to efficiently process ingested foods.
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7/29/2019 The Science of Digestion
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Structure & Function
of the Human
Digestive Tract
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The Mouth
Type a detailed list of the items you needed to complete your
experiments.
Be specific about the amounts used.
Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
Food enters the body through the mouth. Here it is shredded by the teeth
and mixed with salivary amylase and lingual lipase to commence starch
and fat digestion.
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The Esophagus
Food passes from the mouth to the stomach
via the esophagus which is about 24 cm long.
The esophagus is lined with longitudinal and
circular muscles along its length which is
lubricated with Mucin, secreted by tubular
glands found in the back of the throat.
These muscles work to push the food into the
stomach after swallowing.
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The Stomach
The stomach is a muscle lined sack
that contains glands that secrete
gastric juices that aid in the
physical and chemical breakdown
of food.
The stomach contains an oblique
layer of muscles that work to
physically break down food into a
thick liquid known as chyme
Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
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The Small Intestine
Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
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The Small Intestine
Type a brief summary here of what you discovered based on the
results of your experiments. You need to indicate whether or not the
data supports the hypothesis and explain why or why not.
Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
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The Small Intestine
Vili in the small intestine have a
fine layer of microvili designed to
further increase the surface area, and
thus the rate of nutrient absorption.
Intestinal glands are found between
the vili which are designed to secrete
intestinal juices keeping the
intestinal environment ideal for
absorption by the body.
Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
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The Large Intestine
The Large intestine transports
undigested food and water and
dissolved minerals are absorbed
aided by intestinal bacteria.
The bacterias by products are
vitamin B-12 and K along with
various amino acids, which are all
beneficial and absorbed by the
body.
The remaining digested food, also
known as feces passes into the
rectum and is passed through the
anus.Reproduced with permission from http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/scenario1GITlecture.htmMarch 28th 2005
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Food Movement - Peristalsis
Food is not simply pushed through the digestive
system, instead the various forms of food are moved
through muscle contraction.
This muscle contraction in tubular compartments is
called peristalsis and describes a contraction wave
type movement.
Peristalsis is not only used to mechanically movefood forward but also to churn and mix digestive
juices into the chyme.
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The Living Model
Image Source: http://www.sdmesa.sdccd.net/~bbrothers/Pages/Digestive_Flat_model.htm March 28, 2005
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The Living Model
Image retrieved from http://library.thinkquest.org/15401/learn_idiagram_dig.html March 28, 2005
Diaphragm
Gallbladder
Liver
Pancreas
Small
Intestine
Stomach
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The Science of DigestionSenior Biology
Appleby College
C. Watt
V1. 2005-03-29