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