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How the gut protects itself (Attack v Defense: STOMACH (Mucosal…
How the gut protects itself
Attach v Defense
: GUT
Acid and pepsin
Ingested drugs
Refluxed bile
Smoking
Microorganisms
Ischemia
Food allergens
Mucus- HCO3-
Cell membrane
Cell migration and renewal
Mucosal blood flow
Prostaglandins
Immune system
Acid inhibition
Programmed cell death
Attack v Defense
: STOMACH
Mucus-HCO3- barrier slows H+ diffusion
Cell migration and regeneration
Tight junctions between cells, slow H+ diffusion
Mucosal blood flow:
Blood supply carries H+ away, helps antioxidant function
Cell surface phospholipids
Mucosal prostoglandins
Inhibit H+ secretion. Stimulate mucous and HCO3-
Exocrine pancreas produces bicarbonate to neutralize acidic stomach chyme
Stomach chyme sensed by stretch receptor, VAGUS nerve
HCO3- stimulant
VIP
Secretin
Stimulate pancreas, digestive fluids HCO3-
Neutralise stomach chyme
Enzymes stimulant
Inhibited
ACH
CCK
Stimulates acinar cells of pancreas
:
Pancreatic digestive enzymes (fat, protein and carbs)
(inhibits gastric emptying)
Increased blood flow in response to penetrating acid
Hyperaemia:
Excess of blood in vessels
Afferent nerve fibres
CGRP/NO releasing efferent fibres : vasodilators
Blood provides mucosa with oxygen and HCO3-, removes H+
Restitution
Rapid repair mechanisms
30 mins. Epithelium thinner, but restored
Prostaglandins
Gastrin
Growth Factors
Regenerating protein (Reg)
Trefoil peptides
Damaged surface epithelial cells shed, form layer that protects restituting mucosa
Viable epithelial cells: flattened and migrate to basal lamina
Superficial epithelium re-established when migrating cells touch, form new tight junctions and repolarise their organelles
Stomach, colon, duodenum and rectum
Gastrin stimulates migration
Peyor's patches
Aggregate of lymphoid cells: ILEUM, projected to lumen: initiation of immune response
subepithelial dome (separated from lumen by follicle associated epithelium): Large number of B cells follicles with its germinal centre
T cells areas between them in a smaller number + dendritic cells
FAE: conventional intestinal epithlial cells: small number of M cells: folded luminal surface, no digestive enzymes and lack thick glycocalix
Antigens from microbes in gut are absorbed via endocytosis (by microfold cells lining surface)
Antigens passed onto lymphoid tissue, absorbed by macrophages, presented to T & B cells
Immune response + migration through lymph nodes
Enterocytes
Intestinal absorptive cells: columnar epithelial cells in SI
Glycocalyx surface coat contains digestive enzymes
Microvilli on apical surface increase SA for digestion and transport
Villi
are projections into the lumen covered predominantly with mature, absorptive enterocytes
Crypts
: invaginations of epithelium around villi: secretion: base of crypt: stem cells
Stem cells divide to form daughter cells
One daughter cell retained, other differentiate: enterocyte
'Born ' at bottom of crpts, make their way up to absorptive 'adulthood' on villi
Maintenance of tight junctions during cell shedding
Vom reflex
Vomiting centre
: Medulla oblongata
Efferent fibres: phrenic and vagus nerve
Afferent fibres: Pain, bloating, inflammation, irritants and toxins
LOS, UOS and pharynx relaxed
Diaphragm fixed for inspiration
Contraction of duodenum, pylorus and antrum
intercostal muscles contracted (Huge abdominal muscular pressure)