GIT phys

• What are the functions of the GIT system?

  1. Nutrition

  2. Excrete waste product

  3. Fluid and electrolyte regulation

  4. Immune function
• Definition of motility

  Propulsion of food through the gut
• What happens when the gut circular and longitudinal muscle layers contract?

  Circular muscle contraction will cause gut tube to become constricted(long and skinny)

  Longitudinal muscle contraction will cause shortening of gut tube
• Oesophageal peristalsis causes the movement of the bolus from the pharynx to the stomach.
• What are the muscle sphincters that control the passage of food along the gut?

  upper oesophageal, lower oesophageal, pyloric, oddi (hepatopancreatic) ileocecal, internal anal, external anal
• A sphincter is a thickening of smooth and skeletal muscle that prevent the back flow of food and regulate passage of food from one section to another.
• What type of nerves innervate different parts of the gut?

  Sensory-chemoreceptors(pH), stretch/mechanoreceptors

  Autonomic-glands, sm in gut wall and blood vessels

  Enteric-glands, smooth muscle in motility
• What sphincters in the GIT are skeletal muscle?

  upper oesophageal, external anal
• What sphinters in the GIT are smooth muscle?

  Lower oesophageal, pyloric, oddi (hepatopancreatic), ileocecal, internal anal
• What happens if the autonomic nerves innervating the gut are damaged?

  The gut brain(enteric nervous system)can control gut functions independently of the central and autonomic nervous systems
• Myenteric plexus

  Between layers of SM(circular and long sm layer)

  Along entire length of gut, controls motility
• submucosal plexus

  In submucosal connective tissue, not along entire length only in discrete portion of gut secretion from glands and absorption of nutrients
• Excitatory enteric neurotransmitters

  Acetylcholine

  Motility and glandular secretion
• Inhibitory enteric neurotransmitters

  Mainly nitric oxide(NO), relaxation of SM
• neuronal control of the smooth muscle sphincters in the gut

  Rings of circular smooth muscle in a constant state of contraction(constriction)

  Innervated by intrinsic(enteric) and extrinsic(autonomic) nerves

  Sympathetic activation contracts circular muscle, keeping sphincter closed

  Relaxation results from activation of parasympathetic nerves and intrinsic inhibitory nerves in the myenteric plexus(NO)
• Three sections of the small intestine are duodenum, jejunum and ilium
• What are the sphincters at the start and end of the small intestine?

  pyloric and ileocecal sphincter
• Digestive processed in the small intestine

  Chyme mixed with digestive juices and slowly moved along the SI

  Chemical digestion is completed

  Nearly all nutrient absorption occurs in the walls of SI

  Moves undigested remains to LI
• Segmenting contractions/segmentations


  Localised constrictions of SI

  not much downward propulsion, allows time for chyme to mix with digestive enzymes, chemically broken down to form nutrients
• Peristaltic contractions


  When most of the meal has been absorbed segmenting (or mixing) contractions are replaced by peristaltic contractions called the migrating myoelectric complex

  Moves undigested remains to large intestine, stops when meal enters stomach
• Initiation of MMC


  Initiated by increased ph of chyme(alkaline) or increased concentration of motilin (hormone triggering motility), and modulated by ENS and ANS
• Digestive processes in the large intestine

  Mixing contractions

  Chemical digestion by enteric bacteria

  Absorption of h2o and electrolytes

  Propulsive actions

  Excretions
• Haustral contractions


  Formed by localised activation of myenteric nerves and activation of circular SM
• Mass movements in LI

  Simultaneous contraction large segments from caecum to sigmoidal colon

  constrictive ring and loss of haustra
• What facilitates mass movements?

  Gastrocolic and duodenalcolic reflexes

  Activated by distension of stomach or duodenum

  Mediated via ANS
• Poor motility causes greater absorption, hard feces in transverse colon causes constipation
• Excess motility causes less absoption and diarrhoea or loose faeces
• What are the three extrinsic buccal salivary glands?

  parotid, submandibular and sublingual
• Composition of saliva


  H2o(97-99.5%)

  Ions eg na,k,ca,mg,po4

  Salivary amylase(starts carbohydrate/starch digestion)

  Mucin(glycoprotein that lubricants food we ingest)

  Immunoglobulins(limit ability for microbes to infect mouth)
• Functions of saliva


  Lubrication - via mouth

  Digestion - salivary amylase

  Protection - protection of teeth and gums

  Control of h2o intake

  Speech - movement of tongue in mouth aided by saliva

  Absorption - sublingual

  Taste sensation - b/c chemicals in food need to be dissolved in fluid(saliva)
• What type of medication would decrease salivation?

  Muscarinic receptor antagonist

  Low dose bc a high dose would inhibit gut motility, systemic effects
• Main causes of dry mouth

  Drugs, radiotherapy, dehydration, shock, renal failure
• Diagnosis of dry mouth

  citric acid, dry crackers
• Treatment of dry mouth

  Muscarinic receptor agonist, withdraw offending drug
• What are the three phases of swallowing?

  1. Voluntary or buccal phase
  2. Pharyngeal phase
  3. Oesophageal phase
• Voluntary/buccal phase


  Initiates swallowing

  Presence of bolus at back of throat, or top of pharynx activates touch sensors and mechanoreceptors in the wall of the pharynx and become involuntary
• Pharyngeal phase


  Initiates swallowing

  Presence of bolus at back of throat, or top of pharynx activates touch sensors and mechanoreceptors in the wall of the pharynx and become involuntary
• Oesophageal phase


  Bolus travels down oesophagus-stomach

  Longitudinal muscles contract, shortening passageway ahead of bolus.

  Circular muscles contract, constricting passageway and pushing bolus down
• What controls oesophageal peristalsis?

  Somatic motor nerves-skeletal

  Autonomic(parasympathetic) nerves and the myenteric plexus
• Common cause of dysphagia

  -diseases of mouth, tongue or salivary glands

  -neuromuscular disorders

  -outpouchings on pharyngeal/oesophageal wall

  -seen frequently after stroke and with Parkinson’s disease