Download Overview of the digestive system

Block 2 Notes
Digestive System
Overview of the digestive system
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There are three main
functions of the digestive
system:
1. it ingests (takes in)
food
2. breaks the food down
so nutrients can be
absorbed
3. eliminates what
cannot be digested
Overview cont.
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Types of digestion:
1. mechanical – involves chewing
food to break it down into smaller
pieces (also uses the smooth
muscles of the stomach to help
churn the food)
Chemical digestion – breaks down
large molecules of food into
smaller substances using enzymes
(the smaller stuff can be absorbed
into the body’s cells more easily)
Remember – enzymes are proteins
(a macromolecule) that speed up
reactions (amylase is an enzyme
found in saliva that starts the
process of chemical digestion by
breaking starches down)
Organs that are part of the digestive
system
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Tongue, esophagus,
several sphincters,
stomach, small intestine,
large intestine, pancreas,
liver, gall bladder, colon
The path food takes during digestion
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Starts in the mouth with saliva
(enzymes begin breaking down the
food)
The tongue pushes chewed food to the
back of the mouth which stimulates
swallowing reflexes
Food is forced into the upper part of
the esophagus (which is a muscular
tube that connects the pharynx – or
upper throat – to the stomach)
The wall of the esophagus is lined with
smooth muscles that contract to move
the food through the digestive system
(this is called peristalsis) – even if you
were upside down, food would still
move toward your stomach
When you swallow, your epiglottis
covers the trachea to prevent choking
Path of food cont.
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When food leaves the esophagus, it
passes through a round muscle called a
sphincter, and into the stomach.
The walls of the stomach are made of 3
overlapping layers of smooth muscle
that help digestion by contracting,
which breaks down the food and mixes
it with secretions of gastric glands that
line the inner wall of the stomach
The gastric glands secrete (release) an
acidic solution (if the sphincter allows
any of this through, it causes
heartburn)
Cells in the lining of the stomach
secrete mucus to help prevent damage
from the acid
Not much is absorbed in the stomach
The muscular walls of the stomach
contract and push food farther along
the digestive tract (at this point your
food is the consistency of tomato
soup), through another sphincter to the
small intestine
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Path of food cont.
Your small intestine is about 7 meters
long; the first part is called the
duodenum
The smooth muscles in the walls of
your small intestine continue to push
food farther through the digestive tract
The pancreas, liver and gallbladder all
help with chemical digestion here
The pancreas produces enzymes that
digest carbohydrates, proteins, and fats.
It also releases a fluid that raises the
pH to a little above 7 (this helps the
intestine enzymes survive)
The liver is the largest organ of the
body and makes bile, which helps
break down fats (you make about 1 L
of bile each day).
Extra bile is stored in the gallbladder
Digestion is completed here and most
of the nutrients are absorbed in the
small intestine, into the bloodstream
through fingerlike structures called villi
The remaining food, now in a semiliquid form called chyme, moves to the
large intestine – this is the stuff that
couldn’t be digested or absorbed
Path of food cont
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The large intestine is the end of the
digestive tract
It’s about 1.5 meters long and includes
the colon, the rectum, and the
appendix
The colon absorbs water from the
chyme
The indigestible material gets more
solid and becomes your feces (poop)
Peristalsis continues to move feces
toward the rectum, causing the walls of
the rectum to stretch.
This initiates a reflex that causes the
final sphincter muscle to relax, and
eliminate the feces through the anus
This entire process usually takes about
12-24 hours (most of the time is spent
in the large intestine)
Assignment
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Love letter: Students will write a five paragraph
love letter to their digestive system. (20 min)
Introduction
3 reasons why they love their digestive system
Conclusion/summary
Diagram: Students will spend the remaining
time coloring and labeling a digestive system
diagram hat will go into their notebooks. (20
min)