Gut Tube and Digestion
Path of FoodEsophagus
Stomach
Small intestines
Large intestines
Rectum and anus
Liver and PancreasDigestion function
Role in glucose metabolism
Path of FoodMouth--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
EsophagusPharynx 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 diseaseSometimes due to hiatal hernia
Lower esophagus becomes ulcerous and precancerous
Treat with antacids and other acid-reducing drugs
Stomach
STRUCTUREJ-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
FUNCTIONMechanical 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 = MucosaEpitheliumLamina propriaMuscularis mucosae
Middle = SubmucosaCT w/ elastic fibers, nerves, vessels
Outer = Muscularis ExternaInner circular layerOuter longitudinal layer
Internal Anatomy of Stomach
MucosaRugae: mucosal folds allow expansion
Typical SubmucosaMuscularis externa
Oblique layerCircular layer
Pyloric sphincter
Longitudinal layer
Serosa
pg 648
Small Intestines
DuodenumC-shaped initial piece (5% of total)
Entries for pancreatic, bile ducts
Jejunum Fan-shaped coil (40% of total) at superior left abdomen
IleumInferior right part of coil
End of appendix at lower right quadrant
Location of Duodenum
Small Intestine: Modifications for absorption
Length Increase surface area
Plicae circularisTransverse ridges of mucosa
Increase surface area
Slow movement of chyme
VilliMove chyme, increase contact
Contain lacteals: remove fat
Microvilli: Increase surface area
Modifications decrease distally
pg 653
Large IntestinesFrame around rest of gut
Ascending, transverse, descendingStarts at cecum/appendixEnds 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 rectumResorption of water from food
Rectum + Anal Canal
Rectumdescends into pelvisno teniae colilongitudinal muscle layer completerectal valves
Anal Canal (more with pelvis)
passes through levator ani musclereleases mucus to lubricate feces Internal anal sphincter
involuntary, smooth m.
External anal sphinctervoluntary, skeletal m.pg 655
Blood supply--ventral branches off of aorta
Celiac a.--to stomach, liver, pancreas, spleen, duodenumSuperior (cranial mesenteric a.--to small intestines and most of colonInferior (caudal) mesenteric a.--to descending colon, rectum
ParasympatheticWhat nerve?
Where does it run?
SympatheticOnly 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
Innervation of gut
VAGUS
With aorta
Liver
STRUCTURELarge ventral organ of abdominal cavity with multiple lobes (learn them!!)Sets against inferior surface of diaphragm on left sideForms as outpocketing of gut--common bile duct is left as connectionBile duct is two-way street (bile from hepatic duct is stored in gall bladder and later expelled to common bile duct to duodenum)
FUNCTIONDigestion--bile is digestive enzymes plus RBC breakdown productRemoves 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 ductcarries bile from gallbladder
Hepatic ductcarries bile from liver
Common Bile duct
joins cystic and hepatic
carries bile into duodenum pg 652
Movement of Bile Bile secreted by liver continuouslyHepatopancreatic (Vater) ampulla
common bile + main pancreatic duct meet and enter duodenumSphincter of Oddi around itclosed when bile not needed for digestion
Bile then backs up into gallbladder via cystic ductWhen needed gallbladder contracts, sphincters open
pg 652
Liver: External FeaturesDiaphragmatic surface
Right lobe (larger)Left lobeFalciform ligament betweenFissure between
Visceral surfaceQuadrate lobeCaudate lobeBoth part of left lobe
pg 659
Liver: Blood SupplyHepatic Vein
from inferior vena cava
Hepatic Artery from abdominal aorta
Hepatic Portal VeinCarries nutrient-rich blood from stomach + intestines to liverPortal system = 2 capillary beds!
pg 660
Hepatic Portal System--concept
Directs blood that has already been through gut capillaries into liver capillaries (or sinusoids)
Allows nutrients and toxins to be removed from blood
Fig. 19.22, M&M
Hepatic Portal System--anatomy
Pancreas
STRUCTURESmaller, diffuse glandHead in C of duodenumTail extends towards spleen
FUNCTIONDigestion--produces most digestive enzymesGlucose metabolism--Islets of Langerhans make insulin
Liver receives blood from intestines (don’t forget hepatic portal systemAfter meal, in response to insulin from pancreas, glucose stored as complex carbohydrate--glycogen--in liverBetween meals, in response to glucagon from pancreas, glucose is releasedPancreas releases insulin when sugar levels in blood go upInadequate or zero insulin production results in hyperglycemia or high blood sugarOverproduction or over-dosing of insulin results in hypoglycemia or low blood sugar--insulin shockDiabetes is insufficient production of insulin
Type I--juvenile onset with elimination of Islets of langerhans and zero insulin productionType II--adult onset with gradual loss of insulin production
Glucose metabolism
“How Stuff Works” Diabetes:http://www.howstuffworks.com/diabetes1.htm