Gut Tube and Digestion

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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

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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
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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

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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)

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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

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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
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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

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Location of Duodenum
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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
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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

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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
• voluntary, skeletal m.

pg 655
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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

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Innervation of gut

• Parasympathetic
• What nerve?
• 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

VAGUS
With aorta
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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)

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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
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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
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Movement of Bile

• 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

pg 652
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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
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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
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Hepatic Portal System--concept
Fig. 19.22, MM

• Directs blood that has already been through gut
  capillaries into liver capillaries (or sinusoids)
• Allows nutrients and toxins to be removed from
  blood

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Hepatic Portal System--anatomy
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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

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Glucose metabolism

• Liver receives blood from intestines (dont
  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

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