Gut Tube and Digestion
Path of Food
Esophagus
Stomach
Small intestines
Large intestines
Rectum and anus
Liver and Pancreas
Digestion function
Role in glucose metabolism
Path of Food
Mouth--chewing
Pharynx--conscious swallowing
Esophagusu--transport to stomach
Stomach--mechanical
and chemical breakdown
Small Intestines-chemical digestion and absorption
Large Intestines-resorb water, form feces
Rectum---collect and expel feces
Esophagus
Pharynx to stomach
Smooth muscle (conscious swallowing is in
pharynx)
Passes through esophageal hiatus in diaphragm,
stomach against inferior diaphragm
Cardiac orifice, with esophageal hiatus guard
opening to stomach, prevent regurgitation
GERD--gastroesophageal reflux disease
Sometimes due to hiatal hernia
Lower esophagus becomes ulcerous and precancerous
Treat with antacids and other acid-reducing drugs
Stomach
STRUCTURE
J-shaped but varies from “steerhorn” (high and horizontal)
to vertically elongate (down to pelvis on tall, thin people)
From esophagus (cardiac orifice) to small intestine
(pyloric sphincter)
Greater, lesser curvatures
FUNCTION
Mechanical breakdown of food--smooth muscle in wall
Protein breakdown--pepsin secreted by epithelial lining
Acidic conditions--for pepsin to work and to kill bacteria
Absorption of water, ions and some drugs (e.g., aspirin,
alcohol)
Digestive Tract (adult gut tube)
Wall
Internal = Mucosa
Epithelium
Lamina propria
Muscularis mucosae
Middle = Submucosa
CT w/ elastic fibers, nerves, vessels
Outer = Muscularis Externa
Inner circular layer
Outer longitudinal layer
Internal Anatomy of Stomach
Mucosa
Rugae: mucosal folds
allow expansion
Typical Submucosa
Muscularis externa
Oblique layer
Circular layer
Pyloric sphincter
Longitudinal layer
Serosa
pg 648
Small Intestines
Duodenum
C-shaped initial piece (5% of total)
Entries for pancreatic, bile ducts
Jejunum
Fan-shaped coil (40% of total) at superior left
abdomen
Ileum
Inferior right part of coil
End of appendix at lower right quadrant
Location of Duodenum
Small Intestine: Modifications for
absorption
Length
Increase surface area
Plicae circularis
Transverse ridges of mucosa
Increase surface area
Slow movement of chyme
Villi
Move chyme, increase contact
Contain lacteals: remove fat
Microvilli:
Increase surface area
Modifications decrease distally
pg 653
Large Intestines
Frame around rest of gut
Ascending, transverse, descending
Starts at cecum/appendix
Ends at rectum, anal canal
Teniae coli
“ribbons” or strips of muscle along length of colon
(three around tube)
Tension in teniae coli forms haustra or sacs
Little continuous movement, but mass
peristaltic movement several times daily to
force feces towards rectum
Resorption of water from food
Rectum +
Anal Canal
Rectum
descends into pelvis
no teniae coli
longitudinal muscle
layer complete
rectal valves
Anal Canal (more with
pelvis)
passes through levator
ani muscle
releases mucus to
lubricate feces
Internal anal sphincter
involuntary, smooth m.
External anal sphincter
pg 655
voluntary, skeletal m.
Blood supply--ventral branches off of aorta
Celiac a.--to
stomach, liver,
pancreas, spleen,
duodenum
Superior (cranial
mesenteric a.--to
small intestines and
most of colon
Inferior (caudal)
mesenteric a.--to
descending colon,
rectum
Innervation of gut
Parasympathetic
What nerve? VAGUS
With aorta
Where does it run?
Sympathetic
Only thoracic output from spinal cord
Splanchnic nerves from thorax lateral to vertebral
bodies bring posteriorly to abdominal cavity and gut
Synapse in celiac and superior mesenteric ganglia
Both Para- and Sympathetic follow aa. out to
organs
High level of local control with network of
synapses within ganglia and around gut
Liver
STRUCTURE
Large ventral organ of abdominal cavity
with multiple lobes (learn them!!)
Sets against inferior surface of diaphragm
on left side
Forms as outpocketing of gut--common
bile duct is left as connection
Bile duct is two-way street (bile from
hepatic duct is stored in gall bladder and
later expelled to common bile duct to
duodenum)
FUNCTION
Digestion--bile is digestive enzymes plus
RBC breakdown product
Removes nutrients and toxins from blood
(hepatic portal system brings gut blood
directly to liver)
Glucose metabolism (with pancreas--see
below)
Gallbladder
Muscular sac
Between right +
quadrate liver lobes
Bile is stored +
concentrated
Bile: breaks down fats
= emulsification
Bile
Produced by liver
Stored in gallbladder
pg 659
Bile Ducts
Cystic duct
carries bile from
gallbladder
Hepatic duct
carries bile from
liver
Common Bile
duct
joins cystic and
hepatic
carries bile into
duodenum
pg 652
Movement of Bile
pg 652
Bile secreted by liver
continuously
Hepatopancreatic
(Vater) ampulla
common bile + main
pancreatic duct meet
and enter duodenum
Sphincter of Oddi
around it
closed when bile not
needed for digestion
Bile then backs up into
gallbladder via cystic
duct
When needed
gallbladder contracts,
sphincters open
Liver: External Features
Diaphragmatic surface
Right lobe (larger)
Left lobe
Falciform ligament between
Fissure between
Visceral surface
Quadrate lobe
Caudate lobe
Both part of left lobe
pg 659
Liver: Blood Supply
Hepatic Vein
from inferior vena cava
Hepatic Artery
from abdominal aorta
Hepatic Portal Vein
Carries nutrient-rich
blood from stomach +
intestines to liver
Portal system = 2
capillary beds!
pg 660
Hepatic Portal System--concept
Fig. 19.22,
M&M
Directs blood that has already been through gut
capillaries into liver capillaries (or sinusoids)
Allows nutrients and toxins to be removed from
blood
Hepatic Portal System--anatomy
Pancreas
STRUCTURE
Smaller, diffuse gland
Head in C of duodenum
Tail extends towards
spleen
FUNCTION
Digestion--produces
most digestive enzymes
Glucose metabolism-Islets of Langerhans
make insulin
Glucose metabolism
Liver receives blood from intestines (don’t forget hepatic portal system
After meal, in response to insulin from pancreas, glucose stored as complex
carbohydrate--glycogen--in liver
Between meals, in response to glucagon from pancreas, glucose is released
Pancreas releases insulin when sugar levels in blood go up
Inadequate or zero insulin production results in hyperglycemia or high blood
sugar
Overproduction or over-dosing of insulin results in hypoglycemia or low blood
sugar--insulin shock
Diabetes is insufficient production of insulin
Type I--juvenile onset with elimination of Islets of langerhans and zero
insulin production
Type II--adult onset with gradual loss of insulin production
“How Stuff Works”
Diabetes:
http://www.howstu
ffworks.com/diabet
es1.htm