Functional Anatomy of GIT Functional Anatomy of GIT and Movementsand Movements

Lecture byLecture byDr SandeepDr Sandeep

07-04-0807-04-088:30 – 9:30 am8:30 – 9:30 am

The function of GI tract are digestion and absorption The function of GI tract are digestion and absorption of nutrientsof nutrients

To serve these functions, there are 4 major activities To serve these functions, there are 4 major activities

1)1) Motility, 2) Secretion, 3) Digestion, 4) AbsorptionMotility, 2) Secretion, 3) Digestion, 4) Absorption

The GI tract is arranged in linear sequenceThe GI tract is arranged in linear sequence

The wall of GI tract has two surfaces, mucosal and The wall of GI tract has two surfaces, mucosal and serosalserosal

A mucosal layer consists of a layer of epithelial cells, A mucosal layer consists of a layer of epithelial cells, a lamina propia, and a muscularis mucosaea lamina propia, and a muscularis mucosae

The epithelial cells are specialized to carry out The epithelial cells are specialized to carry out absorptive and secretory functionabsorptive and secretory function

The lamina propria consists primarily of connective The lamina propria consists primarily of connective tissue, but it also includes blood and lymph vesselstissue, but it also includes blood and lymph vessels

The muscularis mucosa consists of smooth muscle The muscularis mucosa consists of smooth muscle cells, which helps in contractioncells, which helps in contraction

Beneath this, submucosal layer is, which consists of Beneath this, submucosal layer is, which consists of collagen, elastin, glands and blood vesselscollagen, elastin, glands and blood vessels

The motility is provided by two layers of muscle, The motility is provided by two layers of muscle, circular circular and and longitudinal musclelongitudinal muscle

The two plexus, The two plexus, submucosal submucosal and and myentric plexus, myentric plexus, contain the nervous system of the GI tract. The contain the nervous system of the GI tract. The submucosal plexua lies between submucosa and submucosal plexua lies between submucosa and circular muscle. The myentric plexus between circular muscle. The myentric plexus between circular and longitudinal muscle circular and longitudinal muscle

Structure and innervations of GI tract Structure and innervations of GI tract

GI motilityGI motility

Motility is a general term that refer to contraction and Motility is a general term that refer to contraction and relaxation GI wallrelaxation GI wall

All of the contractile tissue of the GI tract is smooth All of the contractile tissue of the GI tract is smooth exceptexcept for pharynx and 1/3 of upper esophagus and for pharynx and 1/3 of upper esophagus and external anal sphincter, which are skeletal muscleexternal anal sphincter, which are skeletal muscle

The smooth muscle of GI tract is unitary smooth The smooth muscle of GI tract is unitary smooth muscle, in which cells are electrically coupled via low muscle, in which cells are electrically coupled via low resistance pathways called resistance pathways called gap junctionsgap junctions

The circular and the longitudinal muscles have The circular and the longitudinal muscles have different functionsdifferent functions

When circular muscle contracts, it results in When circular muscle contracts, it results in shortening of a ring of smooth muscle, which results shortening of a ring of smooth muscle, which results in decrease the diameter of the segment in decrease the diameter of the segment

When longitudinal muscle contracts, which results in When longitudinal muscle contracts, which results in shortening in longitudinal direction, in turn decreases shortening in longitudinal direction, in turn decreases length of that segmentlength of that segment

Contraction of GI smooth muscle can be either phasic Contraction of GI smooth muscle can be either phasic or tonicor tonic

Phasic contractions are periodic contractions followed Phasic contractions are periodic contractions followed by relaxation – seen in, esophagus, gastric antrum, and by relaxation – seen in, esophagus, gastric antrum, and small intestine, helps in mixing and propulsionsmall intestine, helps in mixing and propulsion

Tonic contraction maintain constant level of Tonic contraction maintain constant level of contractions without regular relaxation – found in orad contractions without regular relaxation – found in orad (upper) region of stomach, lower esophageal, ileocecal, (upper) region of stomach, lower esophageal, ileocecal, and internal anal sphincterand internal anal sphincter

Slow waves:Slow waves: Like all muscle, contraction in GI Like all muscle, contraction in GI smooth muscle is preceded by electrical activitysmooth muscle is preceded by electrical activity

Slow waves are not action potential rather Slow waves are not action potential rather oscillating depolarization and repolarization of oscillating depolarization and repolarization of membrane potentialsmembrane potentials

These slow waves if they reach threshold they burst These slow waves if they reach threshold they burst into action potentialsinto action potentials

Frequency of slow waves vary between 3-12 Frequency of slow waves vary between 3-12 waves/min. Stomach has lowest ~3 and duodenum waves/min. Stomach has lowest ~3 and duodenum has ~12 waves has ~12 waves

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

Chewing and swallowingChewing and swallowing

Chewing and swallowing are the 1Chewing and swallowing are the 1stst step in step in processing of ingested foodprocessing of ingested food

1)1) It mixes food with salivaIt mixes food with saliva

2)2) It reduces the size of the food particlesIt reduces the size of the food particles

3)3) It mixes ingested carbohydrates with salivary It mixes ingested carbohydrates with salivary amylaseamylase

It has both voluntary and involuntary componentIt has both voluntary and involuntary component

Swallowing: Swallowing: Is initiated by voluntary action in mouth Is initiated by voluntary action in mouth

once swallowed it becomes involuntary or reflex, once swallowed it becomes involuntary or reflex, controlled by swallowing center, located in medullacontrolled by swallowing center, located in medulla

It has 3 pahsesIt has 3 pahses

Oral phaseOral phase is initiated when tongue forces a bolus of is initiated when tongue forces a bolus of food towards pharynx which contains high density food towards pharynx which contains high density somatosensory recptors – activation of these somatosensory recptors – activation of these receptors initiates the involuntary swallowing reflexreceptors initiates the involuntary swallowing reflex

Pharyngeal phasePharyngeal phase The soft palate is pulled upwards The soft palate is pulled upwards

Creating a narrow passage for food to move into the Creating a narrow passage for food to move into the pharynxpharynx

The epiglottis moves to cover the glottisThe epiglottis moves to cover the glottis

Upper esophageal sphincter relaxes allows food to Upper esophageal sphincter relaxes allows food to pass from pharynx to esophaguspass from pharynx to esophagus

A peristaltic wave of contraction is initiated in the A peristaltic wave of contraction is initiated in the pharynx propels food through the open sphincterpharynx propels food through the open sphincter

Esophageal phaseEsophageal phase is controlled in part with is controlled in part with swallowing reflex and in part with enteric nervous swallowing reflex and in part with enteric nervous system system

A primary peristaltic wave, travels down the A primary peristaltic wave, travels down the esophagus propels food forward but does not clear esophagus propels food forward but does not clear the esophagusthe esophagus

A secondary peristalsis will help in clearing of the A secondary peristalsis will help in clearing of the food from esophagus to stomachfood from esophagus to stomach

Gastric motilityGastric motility has 3 components has 3 components

1)1) Relaxation of orad (upper) region to receive food Relaxation of orad (upper) region to receive food from esophagusfrom esophagus

2)2) Contractions that reduce the size of the bolus and Contractions that reduce the size of the bolus and mix it with gastric secretions to initiate digestionmix it with gastric secretions to initiate digestion

3)3) Gastric emptying that propels chyme to small Gastric emptying that propels chyme to small intestine intestine

Small intestinal motilitySmall intestinal motility Segmental and persistaltic Segmental and persistaltic contractions contractions

Large intestinal motilityLarge intestinal motility

Segmental contracitonsSegmental contracitons

Mass movements occur in colon – basically to Mass movements occur in colon – basically to move food in to large distance. This occur move food in to large distance. This occur anywhere between 1-3 times/dayanywhere between 1-3 times/day

ReferenceReference

Physiology by, Linda S. CostanzoPhysiology by, Linda S. Costanzo

33rdrd Edition. Page no 335 - 342 Edition. Page no 335 - 342