1. Ingestion Taking in food through the mouth Propulsion (movement of food) Swallowing Peristalsis propulsion by alternate contraction &relaxation Mechanical digestion Chewing Churning in stomach Mixing by segmentation Chemical digestion Complex food molecules (carbohydrates, proteins and lipids) broken down into chemical building blocks (simple sugars, amino acids, and fatty acids and glycerol) Carried out by enzymes secreted by digestive glands into lumen of the alimentary canal Absorption Transport of digested end products into blood and lymph in wall of canal Defecation Elimination of indigestible substances from body as feces

2. Four main layers. From inside (the lumen) to outside the are:o Mucosao Sub mucosao Muscularis (external)o Serosa ( visceral peritoneum) 3. is the innermost, moist, epithelial membrane thatlines the entire digestive tract. (1) It secretes mucus, digestive enzymes, and hormones;(2) absorbs digestive end products into the blood; and(3) protects against infectious disease. Consists of a lining epithelium, a lamina propria, and aMuscularis mucosa. Epithelium - simple columnar epithelium and goblet cells Lamina propria - areola C.T. with capillaries and lymphoidfollicles Muscularis mucosa - thin layer, produces local movements of themucosa is a moderately dense connective tissue layercontaining blood and lymphatic vessels, lymphoid follicles, andnerve fibers.typically consists of smooth muscleand is responsible for peristalsis and segmentation. Contains the my enteric plexus of Auerbach, the other majorintrinsic nerve plexus. Located between the two layers ofsmooth muscle, controls motility of the G.I. tract. , the protective outer layer of the intraperitonealorgans, is the visceral peritoneum 4. Two types: Slow waves or basic electrical rhythm (BER) Spike Potentials BER BER 5. These are slow, undulating changes in restingmembrane potential of GIT smooth muscle.Slow, undulation of the pumping activity ofNa-K Pump. The basic electrical rhythm (BER) is a slow spontaneousdepolarized wave in the GI. BER of smooth muscle cells form the basis (actionpotential) of stomach contractions. The ability of BER to induce smooth muscle contraction isaltered by the activity of extrinsic nerves andhormones, brought into play by stomach and intestinereceptors. Slow waves are not true action potential, but showundulating changes in the resting membrane potential. 6. These are true Action Potentials that occur when RestingMembrane Potential of GIT smooth muscle rises above-40mV Opening of slow Ca-Na channels.Ca++ ions that enter GIT smooth muscle fiber during spike potential, cause GIT smooth muscle to contract (i.e. Peristalsis). 7. Under normal conditions, the resting membranepotential averages about -56 mill volts, but multiplefactors can change this level. When the potentialbecomes less negative, which is called depolarization ofthe membrane, the muscle fibers become moreexcitable. When the potential becomes more negative,which is called hyper polarization, the fibers become lessexcitable. 8. (1) stretching of the muscle, (2) stimulation by acetylcholine, (3) stimulation by parasympathetic nerves that secreteacetylcholine at their endings, and (4) stimulation by several specific gastrointestinalhormones. (1) the effect of nor epinephrine or epinephrine on thefiber membrane and (2) stimulation of the sympathetic nerves that secretemainly nor epinephrine at their endings. 9. Smooth muscle contraction occurs in response to entry ofcalcium ions into the muscle fiber. Calcium ions, actingthrough a calmodulin control mechanism, activate themyosin filaments in the fiber, causing attractive forces todevelop between the myosin filaments and the actinfilaments, thereby causing the muscle to contract. The slow waves do not cause calcium ions to enter thesmooth muscle fiber (only sodium ions). Therefore, theslow waves by themselves usually cause no musclecontraction. Instead, it is during the spikepotentials, generated at the peaks of the slow waves, thatsignificant quantities of calcium ions do enter the fibersand cause most of the contraction. 10. Some smooth muscle of the gastrointestinal tract exhibitstonic contraction as well as or instead of rhythmical contractions. Tonic contraction is continuous, not associated with the basicelectrical rhythm of the slow waves but often lasting severalminutes or even hours. The tonic contraction often increases ordecreases in intensity. Tonic contractions (continued)- Caused by: Continuous repetitive spike potentialHormonal effects Continuous entry of Ca 11. 1. Enteric Nervous System2. Autonomic Nervous System3. Sensory Nervous System 12. It is Intrinsic system of GIT extending fromesophagus up to anus. Division Two: Lies between longitudinal and circular musclelayer. Functions: Control GIT movements. Lies in submucosa. Functions: Control GIT secretions and blood flow. Sub serves sensory functions by receiving signalsfrom GIT Epithelium and from stretch receptorsof GIT wall. 13. Activity is control by sympathetic and parasympathetic nervous system.Vagus Nerve innervates GIT from esophagus up toproximal 2/3 of transverse colon.Pelvic Parasympathetic Nerve:(S2-S4)Innervates GIT fromdistal 1/3 of transverse colon.Increase peristalsis and tone.Relaxes Sphincters.Increase digestive secretions. 14. : Preganglionic sympathetic originate in T5 TO L2 segment ofspinal cord, Pass thru sympathetic chain, synapse with post ganglionic neuron in celiac and mesenteric and hypogastric ganglia. Postganglionic fibers innervates in GIT. Decrease peristalsis and tone Contract sphincters Decrease digestive secretion 15. Sensory nerve endings originate in the gastrointestinalepithelium or gut wall and send afferent fibers to bothplexuses of the enteric system, as well as(1) to the prevertebral ganglia of the sympathetic nervoussystem,(2) to the spinal cord, and(3) in the Vagus nerves all the way to the brain stem. These sensory nerves can elicit local reflexes within thegut wall itself and still other reflexes that are relayed tothe gut from either the prevertebral ganglia or the basalregions of the brain. 16. Two types of movements occur in the gastrointestinal tract:1. Mixing movements: ( Segmentation Contraction)2. Propulsive movements: (Peristalsis) 17. First the intestinal wall is in relaxing state when it is distended with chyme(food which is mixed with secretion) The distension of intestinal wall causes contraction in intestine and thesecontraction divides the intestine into segments Each segment is 1-2cm long As one set of segmentation contraction relaxes, anew set often begins but the contraction this time appears at new sitesbetween the previous contraction. These contraction help in chopping of chyme and promotes mixing of foodparticles with the secretion of small intestine. Segmentation contraction occurs 12time/min in duodenum and 8time/min inthe ileum. These contraction last for 5-6sec, they occur through out the digestive period. These segmentation contraction are controlled by the Myenteric plexuses ofAutonomic Nervous System. 18. Chyme is propelled or pushed through small intestine byperistaltic waves. These waves are produced and response to stretch .This iscalled Myenteric Reflex. They occur in any part of small intestine and move at avelocity of 0.2-2cm/sec. They usually dies off after travel thisdistance. From here it starts a new peristalsis state and move a chymein forward direction, thus several peristaltic waves occur oneafter the other and push the small intestine contents at thedistal end of the small intestine. Therefore due to the slow movement of peristalsis wavesusually 3-5hours are required for passage of chyme frompyrolysis to the ileocecal valve. These peristaltic wave dont occur alone but aresuperimposed upon segmental movement of small intestine.Thus both segmental and peristalsis movements occurssimultaneously.