1. Functional Anatomy of GIT and Movements Lecture by Dr Sandeep 07-04-08 8:30 – 9:30 am

2. The function of GI tract are digestion and absorption of nutrients To serve these functions, there are 4 major activities 1) Motility, 2) Secretion, 3) Digestion, 4) Absorption The GI tract is arranged in linear sequence

4. The wall of GI tract has two surfaces, mucosal and serosal A mucosal layer consists of a layer of epithelial cells, a lamina propia, and a muscularis mucosae The epithelial cells are specialized to carry out absorptive and secretory function The lamina propria consists primarily of connective tissue, but it also includes blood and lymph vessels

5. The muscularis mucosa consists of smooth muscle cells, which helps in contraction Beneath this, submucosal layer is, which consists of collagen, elastin, glands and blood vessels The motility is provided by two layers of muscle, circular and longitudinal muscle The two plexus, submucosal and myentric plexus, contain the nervous system of the GI tract. The submucosal plexua lies between submucosa and circular muscle. The myentric plexus between circular and longitudinal muscle

6. Structure and innervations of GI tract

7. GI motility Motility is a general term that refer to contraction and relaxation GI wall All of the contractile tissue of the GI tract is smooth except for pharynx and 1/3 of upper esophagus and external anal sphincter, which are skeletal muscle The smooth muscle of GI tract is unitary smooth muscle, in which cells are electrically coupled via low resistance pathways called gap junctions

8. The circular and the longitudinal muscles have different functions When circular muscle contracts, it results in shortening of a ring of smooth muscle, which results in decrease the diameter of the segment When longitudinal muscle contracts, which results in shortening in longitudinal direction, in turn decreases length of that segment

9. Contraction of GI smooth muscle can be either phasic or tonic Phasic contractions are periodic contractions followed by relaxation – seen in, esophagus, gastric antrum, and small intestine, helps in mixing and propulsion Tonic contraction maintain constant level of contractions without regular relaxation – found in orad (upper) region of stomach, lower esophageal, ileocecal, and internal anal sphincter

10. Slow waves: Like all muscle, contraction in GI smooth muscle is preceded by electrical activity Slow waves are not action potential rather oscillating depolarization and repolarization of membrane potentials These slow waves if they reach threshold they burst into action potentials Frequency of slow waves vary between 3-12 waves/min. Stomach has lowest ~3 and duodenum has ~12 waves

11. Origin of slow waves believed to that slow waves originate in the interstitial cells of Cajal, which are abundant in the myenteric plexus

12. Chewing and swallowing Chewing and swallowing are the 1 st step in processing of ingested food 1) It mixes food with saliva 2) It reduces the size of the food particles 3) It mixes ingested carbohydrates with salivary amylase It has both voluntary and involuntary component

13. Swallowing: Is initiated by voluntary action in mouth once swallowed it becomes involuntary or reflex, controlled by swallowing center, located in medulla It has 3 pahses Oral phase is initiated when tongue forces a bolus of food towards pharynx which contains high density somatosensory recptors – activation of these receptors initiates the involuntary swallowing reflex Pharyngeal phase The soft palate is pulled upwards

15. Creating a narrow passage for food to move into the pharynx The epiglottis moves to cover the glottis Upper esophageal sphincter relaxes allows food to pass from pharynx to esophagus A peristaltic wave of contraction is initiated in the pharynx propels food through the open sphincter

16. Esophageal phase is controlled in part with swallowing reflex and in part with enteric nervous system A primary peristaltic wave, travels down the esophagus propels food forward but does not clear the esophagus A secondary peristalsis will help in clearing of the food from esophagus to stomach

18. Gastric motility has 3 components 1) Relaxation of orad (upper) region to receive food from esophagus 2) Contractions that reduce the size of the bolus and mix it with gastric secretions to initiate digestion 3) Gastric emptying that propels chyme to small intestine Small intestinal motility Segmental and persistaltic contractions

20. Large intestinal motility Segmental contracitons Mass movements occur in colon – basically to move food in to large distance. This occur anywhere between 1-3 times/day

21. Reference Physiology by, Linda S. Costanzo 3 rd Edition. Page no 335 - 342