DIGESTIVE SYSTEM
DIGESTIVE TRACT
• Tube in which digestion occurs
• Also called alimentary canal,
gastrointestinal tract (GI)
• Entire canal is about 9 meters along (30
feet) in a cadaver. Shorter in a live person
FUNCTIONS
• Ingest food
• Break down nutrients to a form that can
cross plasma membranes
• Absorb nutrients
• Eliminate undigested parts
PARTS
ORAL CAVITY
• Mouth - receives food
• Lips (labia) protects opening
• Tongue – taste buds,
pushes food to back of throat
fermium – a fold of mucous membrane that
secures the tongue to the floor of the mouth
• Roof of mouth – contains made up of:
1. hard palate -anterior portion is bone
2. Soft palate posterior portion is muscle
Parts continued
• Uvula – finger-like projection that closes off
nasopharynx
keeps food from entering the nasal cavity
• Tonsils – protects against injection
SALIVARY GLANDS
• 3 pairs
• secrete saliva
• contains enzyme salivary amylase
starts digestion of starch
feel flaps under tongue and cheeks – where ducts
are located
• Contains substances that inhibit bacteria growth
• Dissolves food chemicals so they can be tastes
• Teeth – mechanical digestion
PHARYNX – region that
receives food and air
• Trachea – also called windpipe
lies in front of esophagus
• Swallowing is a reflex
• Glottis – opening to the larynx
• Epiglottis – spoon shaped tissue covering a
piece of cartilage
covers
glottis so food/liquids do not enter trachea
ESOPHAGUS
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Muscular tube
Connects to stomach
Remains collapsed until bolus enters
Peristalsis – rhythmic contractions that push
food along digestive tract
• No chemical digestion occurs
LAYERS OF GI TRACT
• Mucosa – inner most – moist membrane
that lines the lumen
• Submucosa- beneath mucosa- made up of
connective tissue, and lymph vessels
• Muscularis external - smooth muscles
• Serosa – outermost layer
Esophagus continued
• Sphincters – muscles that encircle a tube act
as valves
• located at point where stomach and
esophagus meet
• when open – food passes into stomach
• closed – keeps acid from entering
esophagus
STOMACH
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Thick muscular wall
Wall has deep folds called rugae
Holds 4 liters when full
Stores food
Empties in 2/6 hours
Mechanical digestion – churns and mixes food
with gastric juices
• pyloric sphincter connects to small intestine
• Cardioesophageal sphincter – connects to
esophagus
REGIONS OF STOMACH
• Fundus – expanded part of the stomach
• Body – the midportion
• Pylorus – terminal part of stomach
GASTRIC JUICES
• Pepsin – digests protein
• HCL – hydrochloric acid
pH 2
kills bacteria
breaks down connective tissue of meat
activates pepsin
• Mucus
• Intrinsic factor – substance needed for the
absorption of vitamin B12 in the small intestine
MUCUS
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Thick layer of mucus
Protects stomach from HCL
Produced by goblet cells
Ulcer – open sore in wall of stomach
exposed to gastric juices
bacterial infection interferes with mucus
production
STOMACH CONTINUED
• Chyme – contents of stomach thick soupy
liquid enters small intestines in small squirts
• No absorption of food occurs in stomach
• Alcohol absorption only
SMALL INTESTINE
• Major site of digestion
• Has small diameter
• About 3 meters (9 feet) long
THREE PARTS OF SMALL
INTESTINE
• Duodenum – 1st part of small intestine
– sphincter muscles control chyme entering
– receives enzymes from liver and pancreas
• Jejunum
• Ileum – terminal part of intestine
– Ends with the ileocecal valve
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WALL OF SMALL INTESTINE
• Fingerlike projections called villi
• Microscopic microvilli absorb sugars and
amino acids directly into blood stream
• Components of fats enter smooth ER where
they are rejoined and enter the lacteal (small
lymphatic vessels)
LARGE INTESTINE
• 1.5 Meters
• Absorbs water, salts, and vitamins
• Parts: cecum
colon
rectum
CECUM
• Lind end of large intestine
• Appendix – small projection
may help fight infection
subject to inflammation
COLON
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Ascending
Transverse
Descending
Sigmoid colon – enters rectum
RECTUM
• 20 cemeters
• Anus – opening to outside
expels feces
• Stretching of rectal wall sends nerve
impulses to spinal cord causing relaxation
of anal sphincters
• Bacteria found in some feces produce
vitamins that are reabsorbed by our body
PANCREASE
• Endocrine functions involves insulin and
glucagon
• Exocrine function involves the secretion of
pancreatic juices
PANCREATIC JUICES
• Sodium bicarbonate
– NaHCO3
– Neutralizes chyme
• Pancreatic amylase
– Digest starch
• Trypsin
– Digest proteins
• Lipase
– Digest fats
LIVER
• Responsible for maintaining homeostasis of
blood
• Removes poisonous substances
• Removes Fe and stores it
• Removes Vitamins A,D,E and K and stores
them
• Makes plasma proteins to maintain osmotic
pressure
LIVER CONTINUED
• Makes cholesterol and regulates amount in
blood
• Maintains blood glucose levels
• Produces bile which emulsifies fat
• Produces fact
GALL BLADDER
• Sac attached to undersurface of liver
• Stores bile until needed in the duodenum
• Gall stones - cholesterol comes out of bile
solution forming crystals
Feces – more or less solid
product delivered to the rectum
• Resident bacteria of large intestine
metabolize the remaining material
• Gases are released
• Methane and hydrogen sulfide produce the
odor – more gas is produced when food is
high in carbohydrates
• Bacteria make vitamin K and some B
vitamins
DISEASES OF THE GI TRACT
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Acid reflux
Appendicitis
Cirrhosis
Colorectal cancer
Colostomy
Constipation
Diarrhea
Gallstones
Hemorrhoids
Hepatitis
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Hernia
IBS
Jaundice
Lactose intolerance
Mumps
Peritonitis
Ulcer
Vomiting