Introduction to the Digestive System For student copy

Digestive system & homeostasis Digestive system contributes to homeostasis of body by breaking down food into forms that can be absorbed & used by body cells. also: – absorbs : water, vitamins, minerals – eliminates: wastes

2 groups of organs: GI TractAccessory Organs aka Alimentary Canal continuous tube mouth  anus mouth most of pharynx esophagus stomach small & large intestine teeth tongue salivary glands liver gallbladder pancreas

vocabulary Ingestion: eating Secretion: ~7 liters water, acids, buffers, & enzymes into lumen of GI tract Motility: contraction/relaxation of smooth muscle in wall of GI tract mix & propel food & secretions  anus Mechanical Digestion: physically breaking down food Chemical Digestion: Absorption Defecation: wastes leave body/ material defecated called feces/ gas called flatus

Layers of the gi tract (inner  outer) 1.mucosa 2.submucosa 3.muscularis 4.serosa

Mucosa: 3 layers 1.epithelium – mouth  esophagus: stratified sq. epith for protection – stomach  intestines: simple columnar – cells slough off q 5-7 d – exocrine mucus glands (mucus & water) & several types endocrine glands called enteroendocrine cells interspersed

Mucosa: 2 nd layer: lamina propia areolar CT rich in blood & lymph vessels contains most of MALT (mucosa- associated lymphatic tissue)

Mucosa: 3 rd layer: muscularis mucosa thin layer of smooth muscle creates small folds in epithelium  increases surface area for digestion & absorption

submucosa areolar CT that binds mucosa to muscularis rich blood & lymphatics, glands submucosal plexus: extensive network of neurons

Muscularis skeletal muscle in mouth, pharynx, superior & middle parts of esophagus, external anal sphincter – voluntary swallowing & defecation 2 sheets smooth muscle in rest of GI tract with myenteric plexus between them 1.outer longitudinal 2.inner circular

Serosa parts of GI tract suspended in abdominopelvic cavity have this superficial layer = visceral peritoneum esophagus lacks a serosa; has adventitia a single layer of areolar CT

Innervation of the gi tract

Enteric Nervous System (ENS) 100 million neurons that extends from esophagus  anus 2 plexuses: 1.myenteric plexus (plexus of Auerbach) – motor neurons of longitudinal & circular muscle 2.submucosal plexus (plexus of Meissner) – w/in submucosa supplying the secretory cells

ANS parasympathetic fibers via X to most of GI tract (not to 2 nd ½ large intestine: gets it from sacral spinal cord) – increase secretions & motility sympathetic fibers from thoracic & upper lumbar spinal nerves – decrease secretions & motility

Peritoneum largest serous membrane of body simple squamous epithelium with underlying areolar CT divided: 1.parietal peritoneum 2.visceral peritoneum

Peritoneal Cavity space between parietal & visceral peritoneums – contains serous fluid: decreases friction – Ascites: excess serous fluid ass’c w/ some diseases

Retroperitoneal “behind peritoneum” kidneys & most of pancreas, end of sigmoid colon under parietal peritoneum

5 Major Peritoneal Folds 1.greater omentum 2.falciform ligament 3.lesser omentum 4.mesentery 5.mesocolon

Greater Omentum largest peritoneal fold “fatty apron” drapes over transverse colon & coils of sm intestine extends downward anterior to sm intestine contains adipose cells, macrophages, plasma cells; function to combat & contain infections

Greater omentum

Falciform Ligament attaches liver to anterior abdominal wall & diaphragm – liver only organ in abdominopelvic cavity attached to anterior abd wall

Lesser Omentum arises as 2 folds in serosa of stomach & duodenum

Mesentery fold of peritoneum that attaches small intestine to posterior abdominal wall – posterior wall  wraps around sm intestine  reflects back to posterior abd wall – route of bld supply to sm intestine

Mesocolon binds large intestine to posterior abd wall route of blood supply, lymphatic drainage

Peritonitis acute inflammation of the peritoneum: contamination by infectious microbes – from punctures of abdominal organs trauma surgical wounds