Download THE HUMAN DIGESTIVE SYSTEM

THE HUMAN DIGESTIVE SYSTEM
Label the following diagrams.
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PARTS OF THE HUMAN DIGESTIVE SYSTEM
STRUCTURE
FUNCTION
MOUTH
A) teeth
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number of teeth arranged along the upper and lower jaws
used in physical digestion
B) uvula
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hangs from the middle of the back edge of the soft palate
prevents food from entering the pharynx when swallowing
C) salivary
glands
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there are three sets of salivary glands: parotid glands (largest), the
sublingual glands (smallest) and submaxillary glands
these glands produce saliva that enters the mouth through a duct
the saliva assist in the chemical digestion of starch and glycogen, it also helps
to lubricate the food before passing into the next part of the digestive system
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D) tongue
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the upper surface of the tongue is covered with tiny pimple-like structures called
papillae which contains a number of taste buds that has the ability to
determine if something is sweet, sour, bitter, salty, or some combination
thereof
the tongue also aid in mixing the food and saliva to together to form the bolus
which is pushed to the back of the pharynx
EPIGLOTIS
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when swallowing the esophagus and trachea move up causing the trachea to
come in contact with the epiglottis which prevents liquids and solids (food) from
entering the trachea
ESOPHAGUS
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a muscular structure that receives the bolus from the mouth
contains a number of small tubular glands that secrete mucin which is used
to lubricate the bolus as it moves from the mouth to the stomach
the esophagus contains circular and longitudinal muscles which are used to
move the food in a forward direction through a process called peristalsis (is a
series of wave like contractions.
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STOMACH
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at the top of the stomach is a ring like structure called the cardiac sphinster
which allow the bolus to pass into the stomach and prevent partially digested
food from entering the esophagus
stomach is a muscular, J-shaped, sac-like organ
the stomach lining is packed with millions of gastric glands which secrete
gastric juice which start to digestion of proteins
the stomach contain three muscular layers; circular, longitudinal and oblique
layer which work together to break food physically into smaller pieces and
mix it with the gastric juices, rendering it into a thick liquid called chyme
gastric juice cause the chyme to become acidic
at the end of the stomach is a muscular valve called the pyloric sphincter
which controls the movement of chyme into the small intestine
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SMALL
INTESTINE
A) duodenum
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subdivided into three regions
contains only circular and longitudinal muscles
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is generally U-shaped, and is the shortest and widest of these regions.
the pancreatic and bile ducts open into the duodenum, to further aid in the
digestion of carbohydrates, proteins and fats
carbohydrates are broken down into monosaccharides (glucose, fructose
and galactose
proteins are broken down into amino acids
fats are broken down into glycerol and three fatty acids
the neutralization of the acidic chyme
the absorbing surface area of the duodenum is increased by
i) a number of folds in the mucous membrane ( SA 3X)
ii) a number of tiny projections called villi (sing. villus) ( SA 30X)
iii) each villi contains a fine brush like boarder called microvilli ( SA 600X)
between the villi are intestinal glands that secrete intestinal juices
the villi will absorbs the nutrients produced by chemical digestion and passes
them into the circulatory system
inside the villi is a lacteal that absorbs large fat molecules from the intestine
the lacteal is connected to the lymphatic system which will connect to the
circulatory system
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B) jejunum
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is about 2.5 m long
contains more folds and intestinal glands than the duodenum
its function is to break down remaining proteins and carbohydrates so the
end products can be absorbed
C) ileum
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is about 3 m long
contains fewer and smaller villi
its function is also to absorb nutrients,
to push remaining undigested material into the large intestine.
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LARGE
INTESTINE
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 At about 1.5 m long
The large intestine consists of the caecum, colon, rectum, and anal canal
A) caecum
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The sac-like caecum is the blind end of the large intestine.
B) appendix
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hangs suspended from the caecum
an organ that plays no role in digestion but which may play some role in
fighting infection
C) colon
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the main portion of the large intestine
undigested food moving up, along, and down the colon
water and dissolved minerals are absorbed from the undigested food,
intestinal bacteria help to
i) break the undigested food down further to provide more nutrients
ii) produce vitamins B-12 and K and some amino acids
the damp mass of indigestible material that remains at the end of this process
is called feces
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D) rectum
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is the last 20 cm of the large intestine
feces is passed into the rectum and anal canal
E) anus
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the feces passes out of the body through the anus, which has rings of circular
muscle called the anal sphincters.
these sphincters allow the body to control the timing of elimination of waste
to some extent.
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The Roles of Related Organs
Three other organs associated with the digestive tract are the liver, pancreas, and gall bladder. These
organs play vital roles in the digestive process. The liver also carries out many other functions
essential to the body's general good health, some of which have an impact on the digestive process.
LIVER

largest organ in the body and has been identified as having over 500 different
functions.
In digestion:
 produces bile salts from cholesterol.
 bile salts are released into the small intestine as needed
 bile is used to break up fat globules into tiny fat droplets (emulsifies the
fat)
 the emulsified fat is broken down by an enzyme called lipase which is
activated by bile
 the resulting fatty acid and glycerin molecules are engulfed through
pinocytosis by the epithelial cells of the villi.
 once inside the villi, the fatty acid and glycerin molecules enter the lacteal
vessels, where they frequently reunite to make fat molecules.
 these molecules are then transported by the lacteal vessels through the
lymphatic circulatory system and into the main bloodstream near the left
shoulder.
GALL
BLADDER
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PANCREAS
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serves as the storage warehouse for bile produced in the liver.
bile contains a number of chemicals that include cholesterol and the bile salts
so important to the digestion of fats.
the bile to enter the duodenum via the bile duct.
as lipids are absorbed by the intestine, so are the components of bile which are
carried back to the liver to be recycled back into bile
the pancreas is the source of several enzymes that act on carbohydrates,
fats, and peptides (smaller units of proteins)
produces and releases a basic solution that changes the pH of chyme (from a
strongly acid mixture to a weakly basic one) after it enters the duodenum.
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The Movement of Food
The movement of food is accomplished by a series of wavelike muscular contractions and
relaxations known as peristalsis.
Peristalsis involves the circular and longitudinal muscles that surround the various parts of the
digestive tract.
To move food,
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the circular muscles over a food mass relax while the longitudinal muscles immediately in front
of it contract.
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the circular muscles immediately behind the food mass then contract while the longitudinal
muscles over the food mass relax.
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As succeeding muscular regions relax and contract, the food is pushed along
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