DIGESTIVE SYSTEM CHAPTER 24
I.
Introduction
A. Alimentary canal
(GI tract)
1. mouth
2.
pharynx
3.
esophagus
4.
stomach
5.
small intestine
6.
large intestine
7.
anus
B.
Accessory organs
1.
tongue
2.
salivary glands
3.
teeth
4.
liver
5.
gallbladder
6.
pancreas
C.
Processes
1.
ingestion
a. take in food
2.
mechanical breakdown
a. decrease size of
particles
b. churning in stomach
3.
chemical digestion
a.
enzyme action to degrade to smaller units
4.
absorption
a.
simple units from digestion taken into blood or lymph from lumen of GI
tract
5.
propulsion
a. to move contents of lumen
b.
occurs entire length of GI tract
c. tongue pushes food
into esophague
d. perstalsis
(1)waves of
contraction/relaxation
6.defecation
a.
excretion of indigestables
II. ANATOMY
A.peritoneum
1.membrane of abdominal
cavity
a. visceral over
surface of organs
b. parietal near wall
of cavity
2.
peritoneal cavity
a.
serous fluid
3.
mesentery
a.
double membrane of peritoneum
b.
contains:
(1)blood vessels
(2)lymphatics
(3)nerves
c.
positions organs in abdominal cavity
B.
circulation
1.
arterial:
a.abdominal
aorta
b.splanchnic
circulation
(1)celiac
trunk
(2)hepatic
(3)splenic
(4)gastric
(5)mesenteric
c.hepatic portal circulation
(1)venous blood from GI to
liver -first pass
C.
Histology
1.
mucosa
a.columar
epithelial membrane lining the lumen
b.
functions:
(1)absorption
(2)secretion
(a)mucus
(b)hormones
(c)digestive enzymes
and HCl
(3)protection
c.
specialized for specific sites in GI
d.
contains underlying lamina propria of loose
connective tissue and blood vessels
e.
muscularis mucosae
2.
submucosa
a.
dense CT
b.
vascular network
c.
submucosal plexus
(1)
intrinsic nerve supply (autonomics)
(a)glands
(b)smooth muscle of
mucosa
3.
Muscularis Externa
a.
circular layer of smooth muscle
b.
longitudinal layer of smooth muscle
c. myenteric plexus (autonomic) to
control motility of GI tract
How
do sympathetic and parasympathetic fibers differ
in
regulation of GI motility?
4.
Serosa
a.
areolar connective tissue
b.
mesothelium
(1)simple
squamous epithelium
c.
certain areas may contain adventitia in place of serosa
(1)esophagus
(2)rectum
D.
Organs of the alimentary canal
1.Mouth
a.oral
or buccal cavity
b.oropharynx
c.
lips(labia)
d.labial frenulum
e.palate(roof)
(1)hard
(a)palatine and
palatine process of maxillae
(2)soft
(a)skeletal muscle
(b)uvula
(c)fauces
i)contain platine tonsils
ii)opening to pharynx
(3)tongue
(a)taste buds
(b)moves food
(c)forms bolus
(d)muscles
i)intrinsic
a)unattached to bone
ii)extrinsic
a)from bones of skull
or soft palate
(e)lingual frenulum
f.salivary glands
(1)serous fluid
(2)salivary amylase
(3)3 pairs
(a)parotid
i)anterior to ear
ii)superficial to masseter
iii)mumps - viral infection
(b)submandibular gland
(c)sublingual
i)under tongue
(4)parasympathetic control
g.teeth (dentitions)
(1)deciduous teeth
(a)primary or baby
teeth
(b)20
(2)permanent teeth
(a)32 including wisdom
teeth (3rd molars)
(b)impacted if remains
in jaw
(3)types
(a)incisors
i)cutting
ii)central and lateral
(b)canines
i)tearing
(c)premolars
i)1st and 2nd set-
grind/crush
(d)molars
i)1st,2nd, and 3rd
-grind/crush
(4)structure
(a)crown
i)enamel - calcium salts
(b)gingiva
i)gums
(c)root
i)within jaw
ii)outer portion covered in
cementum
a)calcified CT
(d)periodontal ligament
(e)dentin
i)under enamel
ii)bonelike
iii)surrounds pulp cavity
iv)pulp cavity in root is
root canal
v)odontoblasts
a)cells secreting
dentin
(5)dental diseases
(a)dental caries
i)dental plaque
a)sugar, bacteria
b)calculus
(i)calcified
plaque
(b)gingivitis
i)inflammation of gums
(c)peridontal disease
i)tooth loss
(6)functions in digestion
(a)mastication
i)chewing
ii)mechanical breakdown of
food
(b)lubrication of food
(c)deglutition
i)swallowing
(d)CHO breakdown by salivary amylase
2.Pharynx
a.oropharynx and
laryngopharynx
b.stratified squanous
epithelium
(1)friction
c.skeletal muscle in outer layer
3.Esophagus
a.carries food to
stomach
b.located in
mediastinum
c.esophageal hiatus
(1)where esophagus passes
through diaphragm
(2)enters stomach at
cardiac orifice
d.skeletal muscle in superior portions of muscularis
externa
e.hiatal hernia
(1)portion of stomach or SI
enters thoracic cavity at esophageal hiatus
f.esophagus and pharynx function in deglutition
4.Stomach
a.empty 50ml volume
b.stretch to 4L
c. rugae
(1)folds of mucosa and
submucosa when empty
d.regions
(1)cardiac
(2)fundus
(3)body
(4)pylorus
(a)joins duodenum at
pyloric sphincter
e.layers
(1)muscularis externa
(a)has additional
oblique layer
(b)churning function as
well as movement
i)creates CHYME
a)semi-liquid
f.simple columar epithelium
(1)goblet cells
(a)secrete mucus
g.gastric pits
(1)lead to gastric glands
(a)secrete gastric
juice
h.cells
(1)parietal cells
(a)HCl
(b)intrinsic factor
i)vitamin B12 absorption in
SI
(2)chief cells
(a)pepsinogen
(3)enteroendocrine cells
(a)hormones of
digestion
i)gastrin
a)stimulated by
proteins
b)stimulates gastric
gland secretions
c)stimulates movement
of food through GI
ii)serotonin
a)stimulated by food
b)stimulates
contraction of Smooth muscle
iii)histamine
a)stimulated by food
b)stimulates secretion
of HCl
iv)somatostatin
a)stimulated by food
b)inhibits secretion
of stomach and pancreas
i.digestive functions of the stomach
(1)protein digestion
(2)pepsinogen converted to
pepsin
(3)Phases of gastric
secretion
(a)Cephalic phase
i)triggered by senses
ii) increase secretions
(b)Gastric phase
i)presence of food in
stomach
ii)stimuli for secretions
a)stretch
b)peptides or other
foodstuffs
c)pH- proteins act as
buffers
and tie up H ions to increase pH
d)histamine stimulates
HCl
e)Cloride ions in HCl come
from plasma and H ions from carbonic acid in parietal cell.. bicarobonate ions
are returned to capillaries and makes blood from stomach more alkaline - ALKALINE TIDE
(c)intestinal phase
i)excitatory
ii)inhibitory
iii)movement of food
through tract
(4)Motility
(a)peristalsis
(b)relaxing,
contraction of valves
(5)Vomiting reflex
(a)reverse emptying of
stomach
(b)irritants, toxins
(c)extreme stretch
5.Small Intestines
a.most digestion and
absorption occurs here
b.pyloric sphincter to
ileocecal valve
c.1 inch diameter and
20 feet long (cadaver)
d. divisions
(1)duodenum
(a)around pancreas, 10
inches
(b)hepatopancreatic ampulla
i)bile and pancreatic juice
enters
ii)regulated by sphincter
of Oddi
(2)jejunum
(a)8 feet
(3)ileum
(a)12 feet
(b)suspended by
mesentery
e.modified for absorption
(1)plicae circulares
(a)circular folds of
mucosa and submucosa
(b)mixing of chyme
-spiral
(2)villi
(a)fingerlike
projections of mucosa
(b)absorptive columnar
cells
(3)microvilli
(a)projections from
each epithelial cell
(b)increases surface
area
(c)brush border
(d)brush border enzymes
i)to complete SI digestion
of
carbohydrates
and proteins
(4)pits to intestinal glands
(a)intestinal crypts
(glands)
i)secrete intestinal juice
a)watery, mucous
ii)Paneth cells
a)lysozyme
(5)submucosa
(a)Peyer's Patches
i)lymphoid tissue
ii)more in LI
(b)Duodenal glands
i)alkaline mucus to
increase pH
(6)intestinal juice
(a)1 to 2 liters/day
(b)6.5 -7.8 pH
f.digestive processes
(1)bile and pancreatic
enzymes act on food in
duodenum
(3-6 hrs transit)
(2)peristalsis
(a)moves food through
(b)segmentation
i)slow, waves
6.Large Intestine
a.ileocecal valve to
anus
b.functions to absorb
water
c.elimination of feces
d.regions
(1)cecum
(a)first saclike
section
(b)vermiform appendix
(c)appendicitis
(2)colon
(a)ascending (up right
side)
(b)transverse colon
(c)descending colon
(down left)
(d)sigmoidal(s-shaped)
(e)mesentery sheets
i) anchor Transverse and
sigmoid
ii)called mesocolons
(3)rectum
(a)at 3rd sacral
vertebra
(4)anal canal
(a)external anal
sphincter
(b)internal anal
sphincter
(c)open with defecation
(5)teniae coli
(a)muscularis muscle
layer is three bands of smooth muscle
(b)allow for pockets
i)HAUSTRA
ii)but not in rectum
e.Bacteria
(1)dead and alive
(2)normal
(a)bacterial flora
(b)Escherichia coli
i)makes Vitamin K
(c)some produce gas
f.transit time
(1)motility through GI
(2)12 to 24 hours through
the LI
(3)dietary fiber decreases
time
(4)haustral contractions
(a)slow movement
(5)mass movement
(a)specialized
peristalsis
(b)forces contents to
rectum
g.diverticulitis
(1)formation of outpockets
in LI
(2)left sided appendicitis
h.defecation
(1)parasympathetic reflex
(2)close epiglottis
(3)contract diaphragm and
agdominal muscles
(4)this increases
intraabdominal pressure
(5)Valsava's Manuever
i.diarrhea
(1)water stools - rushes
through GI
(2)constipation- too much
water absorbed
B. Accessory
Organs
1.Liver
a.3 pounds - largest
organ
b.four lobes
(1)right (largest
(2)left
(3)caudate lobe (posterior)
(4)quadrate lobe
c.falciform ligament
(1)separates right and left
lobes
(2)attaches to diaphragm
d.ligamentum terez
(1)remnant of umbilical
vein
e.hepatic artery
f.hepatic portal vein
g.hepatic duct
(1)bile leaves liver
(2)fuses with cystic duct
from gallbladder
(3)forms common bile duct
h.hepatocytes
(1)functional liver cells
(2)functional units called
liver lobules
i.Kupffer cells
(1)hepatic macrophages
j.hepatitis
(1)inflammation of liver by
virus
k.cirrhosis
(1)chronic inflammation of
liver
(2)liver becomes fibrotic
and small
l. production of bile
(1)yellow-green solution
(2)bile salts
(a)function to emulsify
dietary fats
(b)chendeoxycholic and
cholic acids
i)made from cholesterol
ii)recycled
a) enterohepatic
circulation
b)reabsorbed in blood
via
ileum
c)back to liver via
hepatic portal vein
(3)bile pigments
(a)bilirubin
i)waste product of heme
ii)urobilinogen metabolite
that
gives
feces brown color
2. Gallbladder
a.in fossa on ventral
surface of liver
b.stores bile
c.contraction empties
bile into SI
d.cholecystokinin
(CCK)
(1)hormone that stimulates
bile release
(2)made in duodenum
e.gallstones
(1)crystallizing
ofcholesterol
(2)obstruct bile flow
(3)may be associated with
high fat diets
3.Pancreas
a.Functions in
production of digestive enzymes
as an exocrine function
b.pancreatic juice
drains form pancreatic duct
c.fuses to common bile
duct form liver and gallbladder and enters duodenum at hepatopancreatic ampulla
d.acini
(1)clusters of secretory
cells
(2)zymogen granules
(a)contain digestive
enzymes
e.pancreatic juice
(1)1200 ml/day
(2)pH 8 by pancreatic duct
epithelial cell secretion of bicarbonate ions
(a)neutralizes chyme
(3)enzymes secreted
(a)trypsinogen (trypsin)
(b)chymotrypsinogen
(chymotrypsin)
(c)procarboxypeptidase(carboxypeptidase)
(d)pancreatic amylase
(e)pancreatic lipases
(4) regulation by
(a)CCK
(b)Secretin
III. Chemical
Digestion and Absorption
A.Carbohydrates
1.hydrolysis to simple
units
CARBOHYDRATES TO
GLUCOSE BY SALIVARY AMYLASE
SUCROSE
FRUCTOSE PANCREATIC
AMYLASE LACTOSE
GALACTOSE BRUSH
BORDER ENZYMES: MALTOSE MALTASE
STARCH SUCRASE
GLYCOGEN LACTASE
2.
absorbed
a.facilitated
diffusion by carriers on microvilli
b.in SI
c.
may be coupled to active transport of glucose
B.Proteins
1.hydrolysis to amino
acids
2.
pepsin in stomach
3.
pancreatic enzymes
4.
brush border enzymes
5.
most in SI - digestion and absorption
6.
active with sodium, glucose
C.Lipids
1.need bile for
emulsification
a.form micells in
water
2.digestion in SI
3.pancreatic lipase
4.hydrolyze to glycerol
and fatty acids
5.absorbed via lacteals
6.inside epithelial cells
of intestinal villi
a.reorganize into
triglycerides
b.combine with
phospholipids and cholesterol to form CHYLOMICRONS
(1)processed by golgi and
released to lacteals (lymphatic vessels in villi)
(2)into thoracic duct to
venous blood
(3)fasting before blood
drawn
D. Water
1.95% SI by osmosis
2.
water and electrolytes in LI
E.Vitamins
1.diffusion
2.fat soluble with lipids
F.electrolytes
1.from GI secretions and
foodstuff
2.Sodium
a.active with glucose
and amino acids
b. Cl follows sodium
c. Cl actively
reabsorbed when bicarbonate is
secreted in ileum
3.Potassium
a.diffusion
4.Iron
a.actively transported
into mucosal cells
(1)binds to ferritin
(carrier)
(2)carried in blood on
transferrin
5.Calcium
a.absorption from SI
regulated by Vitamin D
b.balanced with
phosphorus
c.PTH stimulates Vit D
activation
G.
Nucleac acids
1.
nucleases break down to components
2.
pancreatic nucleases
3.
brush border nucleases
IV. Disorders
A.malabsorption
1.various causes
a.adult
celiac disease
(1)gluten protein in grains
damages villi
(2)diarrhea
B.Cancers
C.Diarrhea
D.Colitis
E.Enteritis
F.Pyloric Stenosis
1.narrowed pyloric sphenic
(birth)