Digestive System
Chapter 17
Functions of Digestive System
• Ingestion
• Secretion
• Movement
• Digestion
• Absorption
• Excretion
Digestion Types:
Mechanical or Chemical
Mechanical – muscular actions or
movement to tear, grind and mix
Chemical – enzymes used to breakdown
nutrients.
Tissue Layers
1.Serosa:Visceral
Peritoneum
2.Muscularis:
smooth muscle,
circular and
longitudinal layers
3.Submucosa
4.Mucosa:epithelial
(strat.simple or
simple columnar)
and areolar tissue
Specialized Tissues…
• Peritoneum – lines cavity wall (parietal) and
covers abdominal organs (visceral).
- Retroperitoneal: positional term for behind
peritoneum.
• Mesentary – thick peritoneal sheets that
suspend digestive tract, stabilizing organs,
prevents intestine tangling.
• Greater Omentum “Fatty apron”– Large folded
tissue containing adipose and lymph nodes.
Protects, insulates and provides energy reserve.
What organs compose the
Digestive Tract or
Gastrointestinal Tract?
What is the direction of transport
through the tube from start to finish?
What structures are help with digestion
but are not part of the GI Tract?
Which regions do mechanical
and/or chemical digestion?
The Oral Cavity
• Sensory analysis of
material.
• Mechanical digestion by
teeth and tongue.
• Chemical digestion by
enzymes.
• Lubrication by mucus
and saliva
• Bolus is formed at end.
• 32 adult teeth, 20
deciduous
Halitosis – Bad breath
Salivary Glands
• Types: Parotid,
submandibular, and
sublignual.
• Function: Releases
enzymes to digest
carbohydrates
(starches) into tri-&
disarccharides with
Salivary amylase.
• Small amount of
Lingual Lipase
starts fat breakdown.
• “Mumps”- virus
attacks usually
parotid glands
Pharynx
• Common
passageway for
solid food, liquids
and air.
• Regions:
1. nasopharynx
2. oropharynx
3. layrngopharynx
• Uvula – blocks
food from going
into nasophayrnx
Uvula
Epiglottis flap is pushed down by
food to cover tracheal opening
Esophageal
Cancer
Human esophagus – 10 inches
long
Giraffe esophagus – 6 feet long
Esophagus
• Muscular tube that
moves bolus to the
stomach by
PERISTALSIS.
• Mucus secretions
keep tube lubed
• “Swallow reflex”
controlled by
medulla.
• Heartburn and
GERD can be
problems
Hiatal Hernia
•Part of the stomach
moves up through an
opening (hiatus) in
the diaphragm.
•The presence
increases the risk for
GERD.
Stomach
•
•
•
•
J-shaped organ
Muscular rugae to churn food.
Sphincter doors at both ends.
Gastric Glands:
Mucous (Goblet) cells – secrete
mucus
Chief cells – secrete pepsinogen
Parietal cells – secrete HCl and
intrinsic factor (helps small intestine
to absorb Vitamin B12)
• Pepsin = Pepsinogen + HCl
*This begins digestion of proteins
into polypeptides and smaller
peptides.
Stomach Continued…
• Absorption of nutrients:
NONE! Only certain drugs and
alcohol can be absorbed here.
• Hormones regulating stomach:
Gastrin – increases gastric
secretion
Cholecystokinin(CCK) and
Gastric Inhibitory Peptide
(GIP) - slows gastric motility
and secretions
Secretin – inhibits gastric
secretions
Animation
• Bolus is turned into CHYME
before leaving
Carbs pass through quickest and
lipids take the longest due to CCK
release.
Peptic Ulcers
*Erosion of the digestive tract
layers. Can affect any part of tract.
Causes: “Helicobacter pylori”
Bacteria (80%), stress, cancers,
other disorders
Gastric Bypass Surgery
• Restricts appetite
• Restricts stomach size
significantly
• Limits absorption of
nutrients, fat, and
calories.
• Allows patients to achieve
rapid loss.
• Side effects: nausea,
weakness, sweating,
faintness, and,
occasionally, diarrhea
after eating, anemia,
calcium absorption, and
gallstones.
Lap Band Procedure
A ‘gastric band’ with a small
balloon inside is attached
around the top portion of your
stomach, forming a smaller
‘gastric pouch’. The placement
of the band creates a small
pouch at the top of the stomach
that holds up to approximately
30 ml, which works out to about
1/8 cup. You are inclined to eat
less because the pouch holds
less food than the whole
stomach. As the upper part of
the stomach registers itself as
being full, it sends a message to
the brain saying that the entire
stomach is full.
Small Intestine
• Function: digestion and absorption (90%)
• 3 sections: duodenum, jejunum, ileum
• Mesentary stabilizes/holds intestine, provides
access for blood vessels.
• Intestinal villi – fingerlike projections, absorbs
nutrients; increases surface area. (There are
microvilli on the villi too!)
• Ileocecal valve – sphincter muscle; door to
cecum of large intestine.
• Peristalsis moves chyme through tube.
• Bicarbonate ions (from pancreas) increase pH
of chyme released at duodenum.
Small Intestine
• Intestinal enzymes:
(peptidase, sucrase,
maltase, lactase, lipase,
enterokinase)
• Lacteals: structures
within villi that take in
fat/protein complexes;
connects with lymphatic
system.
• Chylomicrons:
fatty/protein structures
formed by intestinal cells.
Video
Video 2
Video 3
Small Intestine Disorders
•
•
•
Inguinal Hernia: protruding
through a weak point or tear in
the thin muscular abdominal
wall.
Can restrict blood supply to the
bowel herniated through the
defect, creating a medical
emergency. Gangrene!
Causes: for adults - heavy lifting,
straining bowel movements,
coughing.
Celiac Disease: Autoimmune, body
attacks villi of small intestine. Can
be environmentally triggered.
Pancreas
• Exocrine function: chemical digestion
• Released into the duodenum via pancreatic duct
that connects with common bile duct.
• Enzymes: amylase, lipase, nuclease, trypsin,
chymotrypsin, carboxypeptidase.
• Trypsin = trypsinogen + enterokinase
• Secretes Bicarbonate ions to increase pH of
chyme.
• Hormone Regulation: (secreted by small intestine)
1. Secretin- increase pancreatic secretion
2. Cholecystokinin (CCK)- slows down stomach
release of chyme, stimulates pancreatic
secretion
Pancreatitits:
inflammation of
pancreas; blockage of
duct leads to enzymes
destroying pancreas.
Nutrients are broken down into
basic units for absorption
LIVER
Liver
• Bi-lobed, reddish brown
organ
• All blood from digestive
organs stops here first.
• Functions:
1. Carbohydrate, protein,
and lipid metabolism
2. Detoxification of blood
3. Removes damaged/old
blood cells
4. Produces bile
5. Stores vitamins, minerals
and glycogen.
6. Participates in formation
of vitamin D.
•Falsiform Ligament –
holds liver to anterior wall
•Regeneration capabilities
•Hepatocytes – liver cells
Liver
• Kupffer cells - phagocytize
pathogens and old RBC’s
• Blood from the hepatic
artery and hepatic portal
vein carry blood into the
liver to be serviced.
• Serviced blood leaving the
liver exits the hepatic vein
which connects with inferior
Vena Cava.
• Hepatitis – Inflammation of
the liver, causes can be viral
or chemical.
Gall Bladder
•
•
•
•
Green muscular sac; 10cm
Ventral surface of liver
Stores bile made from liver.
Bile consists of: cholesterol,
salts, bilirubin, & other lipids.
• Bile emulsifies fats (breaks
down into smaller droplets),
helping digestion &
absorption of fat-soluble
molecules.
• Released into Cystic duct
and travels to bile duct.
Fat droplet
Bile
Fat droplets
coated with bile
Micelles formed: fatty
acids, monoglycerides
and bile
Absorption of
lipid material into
villus and
chylomicrons
formed, moving
into the lacteal.
Gall Stones
Formed from the crystallization of bile salts or cholesterol
in the gall bladder.
Blockage of cystic duct…PAINFUL!
Removal of gall bladder or other ways to break up
crystals is the treatment.
Diet will have to be careful with fat and cholesterol intake.
Large Intestine
• Functions: Reabsorbs water; absorbs certain vitamins
and electrolytes; forms semi-solid feces; stores feces
• Suspended inside cavity by peritoneum but rectum is
retroperitoneal.
• Sections:
a. Cecum: pouch-like part; appendix is posterior end
b. Colon: ascending, transverse, descending, sigmoid
c. Rectum: anal canal and anus located at end
• Ecoli bacteria break down cellulose, make vitamin K,
vitamin B5, and GAS! Break down bilirubin giving fecal
colors.
• No villi but tons of goblet cells for lubrication.
• Colon pouches are called “Haustrum” or haustra.
Large Intestine…Defecation!
• Distension of rectal wall
triggers defecation reflex.
• Internal anal sphincter
(involuntary control)
Relaxes on stool entrance
• External anal sphincter
(voluntary control)
Relaxation results in
defecation
• Hemorrhoids:
distended, swollen veins in
anal canal
Bowel Issues
• Diarrhea: not enough water absorbed, food is
hurried through.
Causes: microbes, stress, food intolerances
Problems: dehydration and malnutrition
• Constipation: feces remain too long in tract,
drying too much.
Causes: lack of fiber, dehydration, stress, failure
to relieve
Problems: Hemorrhoids, hernias, diverticulitis
Colitis – inflammation of the colon
Diverticulosis – formation of colon
pouches, weakening of wall
Polyps – bumps on colon wall,
precancerous
Colon Cancer
• 3rd leading cause of cancer related deaths
• Standard screening: stool checks and
colonoscopy
Digestion Animation
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