anatomy 403 GI 1

what is the purpose of the digestive system

• takes chemically complex foods that we eat and breaks them down into molecules that our body can use at a cellular level

• body absorbs or metabolizes molecules for energy, healing, and growth

what are the molecules that are body can use

• fatty acids

• amino acids

• glycerol

• glucose

what are the functions of the digestive system

• ingestion

• secretion

• mixing and propulsion

• digestion

  • mechanical

  • chemical

• absorption

• defecation

what are the two groups of the digestive organs

• gastro-intestinal tract organs

• accessory digestive organs

list the gastro-intestinal tract (alimentary canal) organs

• mouth

• pharynx

• esophagus

• stomach

• small intestine

• large intestine

list the accessory digestive organs

• teeth

• tongue

• salivary glands

• liver

• gallbladder

• pancreas

describe the development of the gut

• single embryological gut tube

• rotates in abdomen as it lengthens

• produces characteristic loops of bowel

what are the regions of the gut

• foregut

• midgut

• hindgut

which digestive organs are included in the foregut

• esophagus

• liver and gallbladder

• stomach

• spleen

• pancreas

• first half of duodenum

which digestive organs are part of the midgut

• second half of duodenum

• ileum

• cecum (appendix)

• asending colon

• proximal 2/3 of transverse colon

which digestive organs are part of the hindgut

• distal 1/3 of transverse colon

• descending colon

• sigmoid colon

• rectum

• anus

how is regional anatomy useful in describing GI anatomy

• relationships maintained in fully developed gut

• no matter how loopy gut gets during development, areas of gut are going to hold on to their neurovascular supply

what artery supplies the foregut

• celiac trunk

what artery supplies the midgut

• superior mesenteric a.

what artery supplies the hindgut

• inferior mesenteric a.

what are the branches of the celiac trunk

• L. gastric a.

• splenic a.

• common hepatic a.

what does the splenic artery branch into

• L. gastro-omental a.

what does the common hepatic artery branch into

• gastro-duodenal a.

  • R. gastro-omental a.

• R. gastric a.

• proper hepatic a.

what does the superior mesenteric artery branch into

• jejunal branches

• ileal branches

• colic branches

what does the inferior mesenteric artery branch into

• colic branches

• superior rectal a.

what is the hepatic portal vein

• all venous blood from gut processed in liver before returning to systemic circulation

what is the portal-caval anastomoses

• small connections between portal vein tributaries

• exist where there are overlaps in the veins that drain digestive organs and are typically within the wall of the organ

• very small so inefficient routes for normal circulation

• help prevent stagnation of blood flow in gut

  • in cases of liver disease, passage of blood back into systemic circulation can be blocked

what vein does most of the foregut drain into

• splenic v.

what vein does most of the midgut drain into

• superior mesenteric v.

what vein does the hindgut drain into

• inferior mesenteric v.

what type of neurons contribute to the enteric nervous system

• autonomic motor

  • sympathetic

  • parasympathetic

• visceral sensory

describe the organization of the enteric nervous system

• submucosal (meissner’s) plexus

  • in submucosa

  • for mucosal glands

• myenteric (auerbach’s plexus)

  • in muscularis (muscular layer)

  • for gut motility

what is the sympathetic supply of the gut

• thoracic splanchnic nerves innervate the foregut and midgut

• lumbar splanchnic nerves innervate the hindgut

describe the pathway for sympathetic innervation of the gut

• all sympathetic innervation originates from spinal cord and travels into sympathetic chain

• pre-ganglionic fibers in the splanchnic nerves

• synapse in prevertebral ganglia

• post-ganglionic fibers in aortic and peri-arterial plexuses

  • use mesentery arteries as a guide to reach organs

• synapse in the gut viscera

what is the parasympathetic supply of the gut

• posterior (and anterior) vagal trunks innervate the foregut and midgut

• pelvic splanchnic nerves (S2-4) innervate the hindgut

describe the pathway of parasympathetic innervation of the gut

• pre-ganglionic fibers in aortic and peri-arterial plexuses

• synapse in enteric gangia within the walls of the organ

• post-ganglionic fibers in myenteric/submucosal plexuses

• synapse in gut viscera

sensory innervation of the gut

• dull and hard to pinpoint

• enteric reflex loops without the need for central nervous system

• some sensory impulses follow sympathetic and parasympathetic pathways back to spinal cord

  • synapse in same region as somatic sensory

  • referred pain

what is referred pain

• visceral pain felt as somatic pain in body wall

  • foregut: epigastric

  • midgut: peri-umbilical

  • hindgut: hypogastric

identify the layers of the gastrointestinal tract

• serosa/adventitia

• muscularis

• submucosa

• mucosa

what are features of the mucosa layer

• deepest layer of GI tract

• 3 divisions

  • epithelial layer

  • areolar connective tissue

  • smooth muscle

describe the epithelial layer

• mouth/pharynx/esophagus: stratified squamous epithelium (protection)

• stomach/intestines: simple columnar epithelium (tight seal)

  • replaced 5-7 days

describe the areolar connective tissue

• blood and lymphatic vessels (MALT)

describe smooth muscle

• folds mucosa

• expose absorptive cells to GI contents

what are the features of the submucosa layer

• connective tissue layer

  • collagen

  • nerves

  • blood vessels

• submucosal plexus

describe the submucosal plexus

• part of enteric nervous system

  • autonomic neurons

  • enteric neurons

• regulates

  • mucosal movement

  • vasoconstriction

  • secretory glands of mucosa

what are the features of the muscularis

• upper GI tract

• lower GI tract

• myenteric plexus

describe the upper GI tract

• mouth, pharynx, and proximal 2/3 of esophagus

  • skeletal muscle (swallowing)

describe the lower GI tract

• smooth muscle

  • longitudinal fibers (superficial)

    • breakdown GI contents

  • circular fibers (deep)

    • propel GI contents

describe the myenteric plexus

• part of enteric nervous system

  • autonomic neurons

  • enteric neurons

• controls gut motility

what are the features of the serosa

• serous membrane surrounding GI organs

  • areolar connective tissue

  • epithelium (= visceral peritoneum)

    • lubricates surface of GI organs

what are the features of the adventitia

• single layer of areolar connective tissue

  • no epithelium

  • found in esophagus and rectum

why do the esophagus and rectum not have epithelium

• majority of their length is not within the abdominal cavity so as they grow, they don’t push into the peritoneal sac like the other abdominal organs do

what is the peritoneum

• largest serous membrane in the body

  • makes serous fluid (lubricant)

• lines the cavities, organs, and neurovasculature

what are the functions of the peritoneum

• supports abdominal organs

  • surrounds and adheres to surface

  • tethers to posterior abdominal wall

• allows contraction of smooth muscle without gross movement

  • prevents twisting and knots

what are the divisions of the peritoneum

• visceral peritoneum

  • walls of organs

• parietal peritoneum

  • abdominal wall

• mesentery/ligament

  • tethers wall to organ or organ to organ

how does mesentery form

• all GI organs begin developing posterior to the peritoneal sac

• organs move anteriorly and press into the sac during development

• peritoneum pinches closed posterior to advancing organs

• organs rotate and mesenteries may fuse during development

• organs may move posteriorly after developing a mesentery and become secondarily retroperitoneal

identify the 5 major folds within the abdominal cavity

• the mesentery

• mesocolons

• greater omentum

• lesser omentum

• falciform ligament

what is the mesentary

• small intestine - posterior wall

• superior mesenteric artery, portal vein tributaries

what are the mesocolons

• transverse mesocolon

  • transverse colon - posterior wall

  • superior mesenteric artery, portal vein tributaries

• sigmoid mesocolon

  • sigmoid colon - posterior wall

  • inferior mesenteric artery, portal vein tributaries

what is the greater omentum

• greater curvature of stomach - transverse colon

• many lymph nodes

  • combat GI infections

what is the lesser omentum

• lesser curvature of stomach - liver

  • hepato-gastric ligament

• duodenum - liver

  • hepato-duodenal ligament

• celiac trunk branches, portal vein tributaries

• bile duct

what is the falciform ligament

• liver - anterior wall

  • pathway of obliterated umbilical vein

  • inferior end at the umbilicus

what are intraperitoneal organs

• organs that protrude into peritoneal cavity

• walls covered by visceral peritoneum

• has mesentery

what are retroperitoneal organs

• organs posterior to peritoneal sac

• mostly organs that are deep and laterally positioned

what are secondarily retroperitoneal organs

• organs that were initially intraperitoneal during early development, but later become retroperitoneal

• keep the same blood, nerve, and lymph supply during their intraperitoneal period

list the intraperitoneal organs

• stomach

• liver

• gallbladder

• spleen

• proximal ¼ duodenum

• jejunum

• ileum

• cecum

• appendix

• transverse colon

• sigmoid colon

• “sally loathes getting stuck picking junk in corners and taking stairs”

list the retroperitoneal organs

• kidneys

• ureters

• suprarenal glands

• aorta

• IVC

• esophagus

• rectum

• anal canal

• “kids understand sharing and inviting everyone receives awards”

list the secondarily retroperitoneal organs

• distal ¾ duodenum

• pancreas

• ascending colon

• descending colon

• “don’t pause a drama”