introduction to the digestive system for student copy
TRANSCRIPT
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 Tract Accessory 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. mucosa2. submucosa3. muscularis4. 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: 2nd layer:lamina propia
• areolar CT• rich in blood &
lymph vessels• contains most of
MALT (mucosa-associated lymphatic tissue)
Mucosa: 3rd 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 longitudinal2. 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 thegi 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 2nd 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 peritoneum2. 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 omentum2. falciform ligament3. lesser omentum4. mesentery5. 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– starts @ 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