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Overview of Digestion: LEARNING POINTS (Describe function of regions of…
Overview of Digestion:
LEARNING POINTS
Describe function of regions of gut tube (mouth to anus) + associated secretory organs
Region & fucntion
Stomach
Gastrin and Somatostatin
Storage, H+ peptic digestion + intrinsic factors
SI
(upper): CCK, Secretin, GIP, motilin
Jejunum
Water and electrolyte transport
Ileum
Bile salt and vit B12 trasnport
Duodenum
Fat, protein, carb digestion and absorption, Ca2+/Fe2+
Oesophagus
Transit
LI
(GLP-1, PYY, neurotensin)
Colon
Storage + Water and electrolyte trasnport
Rectum and anus
Defaecation
Secretory organs
Synthesis + secretion
Exocrine pancreas
Proteases, lipase, amylase, HCO3- and water
Liver
Bile salt synthesis, bile secretion
Salivary glands
Amylase, mucus, water and electrolyte
Gallbladder
Storage and concentration of bile
Motility patterns in fasted and fed state
MMC (migrating myoelectric complex)
Contractions down GI tract
Start at antrum (heart of stomach): motilin, ghrelin and vagus nerve
Duodenum: somatostatin, serotonin and xenin
Phases of ocntraction
Quiescence
Random contractions
Burst of contractions
Rapid decrease contractions
Distal SI
Peristaltic reflex
Caudad
Contraction
Excitatory motor neurons: ACh and tachykinin
Intrinsic primary afferent neurons
Relaxtion
Inhibitory motor neurons: Vasoactive intestinal polypeptide and nitric oxide
Differentiate between involuntary and voluntary muscle control + context to GI motility (swallowing, peristalsis)
Nerves
Intrinsic
Nerves from CNS (parasymp)
Myenteric plexus
Submucosal plexus
Extrinsic
Afferent and efferent nerves
Hypogloassal nerve XII and pudendal nerve
Vagal X and pelvic splanchnic trunks (ANS)
Sympathetic
Noradrenaline
Salivary glands, gut blood vessels, gut wall sphincters and adrenal medulla
Parasympatheitc
Ach
7,9 and 10
Salivary glands, gut wall, gut sphincters, gut secretions, pancreas and rectum
ICC
BER
Motility in small and large intestine
Segemntation
Alternate contraction and relaxation of adjacent segments causes thorough mixing of contents
Remove indigestible matter
Peristalsis in Rectum
duodenal colic reflexes: shift matter from sigmoid colon to rectum
Distension reflex:
Colon contract ACh
Relax anal shnicter VIP
Voluntary control pudendal nerve