GI Structure Flashcards
Digestion Def
Mechanically and enzymatically breaking down food into simpler chemical components for absorption
6 Digestive Processes
Ingestion (Voluntary), motility (peristalsis), mechanically (chewing, churning, mixing), chemically (enzymatic degredation), absorption/secretion (kidney) and defecation (voluntary)
4 layers of intestine
Mucosa (innermost), submucosa, mucosa propria and serosa (outermost)
Mucosa Outline
Innermost layer, surrounding lumen. Has 3 layers
3 layers of mucosa
epithelium (innermost, function absorption), lamina propria (connective tissue, regulates epithelium) and muscularis mucosa (smooth muscle, controls local movement and optimises epithelium and lamina propria contact)
Submucosa Outline
Connective tissue containing blood + lymph vessels (nutrient transport), nerve fibers (absorption and secretion) and lymphoid vessels (immune system)
Muscularis Outline
Controlling intestinal motility (peristalsis and segmentation). 2 layers: inner circular and outer longitudinal. At different points the circular layer thickens and thins creating sphincters that control food passage
Serosa Outline
Connective tough tissue lubricated in mucus. Prevents abrasive contact with other organs periodontal cavity via lubricants
GI Tract Thickness (thinnest to thickest)
Small intestine, colon and esophagus. Esophagus thickness is useful for peristalsis
Epithelium Outline
Innermost cell sheet (continuous). Transports nutrients and forms a protective barrier. Characterized by tight junctions and functional polarity. 4 types
4 Types of Epithelial Cells
Enterocytes, Goblet Cells, Paneth and enteroendocrine
Stratified squamous characteristics
Sectretes mucus (protects against abrasion + wear and tear). Found in eosophagus, mouth and anal canal
Simple Columnar
Allow absorption and secretion to occur
How does secretion/absorption occur with large molecules
Protein transporters. Substances transported include: amino acids, peptides, water, sugars, fatty acids, cholesterol, water soluble vitamins and ions. Activity controlled by hormones and nurotransmitters
Epithelial Barrier Outline
Lipid. Only allows lipophilic molecules through, hydrophilic must pass through transporter proteins
Epithelial Tight Junctions Outline
Proteins that anchor cells together towards luminal (apical) side, creates a strong barrier as cells are continuos. Comprised of occulin, claudin and junctional adhesion molecule. Permeability controlled by signalling proteins
Functional Polarity Outline
The control of the rate of absorption/secretion. Protein channels respond to changes in the enviorment opening/closing
Goblet Cells Function
Secret mucus. Prevents abrasion and pathogen contact with organ surface. Thickness varies in intestines
Enteric Tear Mechanism
Colloquial: diahorrea. Removes pathogens without causing infection
Paneth Cells Outline
Secrete alpha defensins, destroying pathogens in the small intestines
Enterocytes Outline
Secrete beta defensins, in the colon
Immune Cells in Lamina Propria
Mast cells, neutrophils, macrophages, monocytes and dendretic cells. Engulf and breakdown pathogens. Release cytokines to stimulate bigger immune response
What causes coeliac disease, IBS and intolerences
Incorrectly regulated immuno-epethelial reactions (over active immune system)
2 types of intestinal smooth tissue in muscarinic
Circular (controls segmentation mixing and peristalsis) and longitudinal (peristalsis)
Enteric Nervous System Components
Submucosal plexus (regulating epithelial functions) and myenteric plexus (regulates smooth muscle contractions). Connected to CNS via autonomic nervous system fibres (sensory, motor and internuerons)
Parasympathetic Gut Innervation Outline
Vagus (upper GIT) and pelvic (lower GIT) nerves carry signals from ganglia within myenteric and submucosal plexuses. Stimulate GIT
Sympathetic Gut Innervation Outline
thoraco-lumbar spine region carries signal from synampse in ganglia within myelinic and submucosa plexuses. Inhibit epithelial transport and motility
Enteroendocrine Cells Outline
Type of epithelial cell that sense changes in enviorment. Release paracrine (local) and endocrine (far acting) hormones
G cells outline
enteroendocrine cells in stomach. Release gastrin = increase in pepsinogen/HCl = increased motility
S cells Outline
Enteroendocrine cells in intestine. Release secretin in response to HCl in lumen = decreased gastrin= increased luminal HCO3- secretion
I cell Outline
Enteroendocrine cells in duodenum. Release cholyecytocholeton in response to nutrient = bialiary secretions = incraese pancreatic secretions
L cells outline
enteroendocrine cells in ileum and colon. Release GLP1 = increase insulin secretion
Cephalic Pase Outline
Autonomic Nervous Cells. Salivary, Gatric and pancreayiovc secretions. Enetro nervouis nsystem relaxing mescles in GI and increasing secretions
