Gastro-intestinal Physiology General Prof. K. Sivapalan.

2013GIT Grneral2 Why Eat? Hunger. Taste and satisfaction. Passing time Energy. Growth. Socialization. Health.

2013GIT Grneral3 Functions of GIT Tranquility [oral activity] Ingestion. Digestion. Absorption Excretion. Protection- immunity

2013GIT Grneral4 Gastro-Intestinal Tract

2013GIT Grneral5 General Organization of GIT Serosa. Longitudinal muscle. Myenteric [Auerbach’s] plexus Circular muscle Sub mucus [Meissner’s] plexus Sub mucus muscle Sub mucosa Mucosa Mesentery Glands: Goblet cells Mucosal Sub mucosal Glands outside. Dorsum

2013GIT Grneral6 Smooth muscle in GIT Smooth muscles in intestine form a syncytium with tight junctions and gap junctions. Membrane potential shows slow waves. More in pace makers. (Basic electrical rhythm (BER) of gastrointestinal smooth muscle) When the waves reach threshold level, spike potentials occur. Muscle tension increases or decreases depending on the number of spikes. Acetylcholine increases and adrenaline reduces tension.

2013GIT Grneral7 Innervation Sub mucus [Meissner’s] plexus is mainly sensory - stimulated by, irritation, distention or chemicals. Autonomic afferents from tissues [vagal (80 %) and sympathetic] and Meissner’s plexus go centrally. Myenteric [Auerbach’s] plexus is motor. Parasympathetic [Vagus] end on cells of Myenteric plexus. Sympathetic fibers end on Myenteric plexus, muscles and glands. Sensory neurons

Gut Reflexes Coltroll within the gut- secretions, peristalsis, mixing, local inhibitions etc. Coordinated in para vertibral sympathetic ganglia- enterogastric reflex, colonoilial reflex Coordinated in brain stem- stomach to stomach: motor and secretary, pain inhibiting entire GIT function, defecation 2013GIT Grneral8

2013GIT Grneral9 Peristalsis. Coordinated by myenteric plexus Contraction of circular muscles proximal to the stimulus and relaxation distally. Longitudinal muscles contract and pull over the contents. The relaxed circular muscles contract. The sequence is propagated in oral to caudal direction.

Migrating Motor Complex Cycles of motor activity, initiated by motilin, migrate from the stomach to the distal ileum during fasting at 90 minute intervals at 5 cm/min Clear the stomach and small intestine of luminal contents in preparation for the next meal Quiescent period (phase I), irregular electrical and mechanical activity (phase II), burst of regular activity (phase III) 2013GIT Grneral10

2013GIT Grneral11 Voluntary and Involuntary Aspects Searching, cooking, serving, placing in the mouth, mastication- voluntary. Swallowing- begins as voluntary and ends as involuntary. Gastric functions- involuntary but affected by moods. Small intestinal functions- fully involuntary. Storage of feces- involuntary. Defecation- starts as involuntary and ends as voluntary.

2013GIT Grneral12 Regulation of the functions Voluntary actions are generally conditioned reflex. Intrinsic plexus coordinates local reflexes. Sympathetics inhibit [stimulate sphincters]. –Nerve endings on muscles and glands Parasympathetic- stimulate [inhibit sphincters]. –Nerve endings on Myenteric plexus [preganglionic] Pace makers in GIT.