Surfing the Digestive System Donald George MD Nemours Children’s Clinic Jacksonville, Florida Potential source of bias: Pediatric Gastroenterology “Cover the relationships of biology, anatomy, normal physiology, pathophysiology, digestion, absorption, hormones, nerves and and immune function on cellular and bodily function, nutrition and growth” And do it in under 20 minutes •Largest organ in surface area •Largest and most diverse endocrine organ •Home of 70% of our immune cells •There are more nerve cells in the gut than in the spinal cord •Has it’s own pacemaker The function of the system as a FunctionFunction whole is processing food in such a Individual parts way that high energy molecules can function in: be absorbed and residues ingestion eliminated. mechanical digestion chemical and enzymatic digestion secretion absorption compaction excretion and elimination DigestiveDigestive SystemSystem consists of: Muscular, hollow tube (= “digestive tract”) + Various accessory organs ThreeThree pairspairs ofof SalivarySalivary GlandsGlands 1-1.5 l / day for digestion (enzymes) lubrication (swallowing) moistening (tasting) Parotid – Submandibular – Sublingual – LiverLiver On right under diaphragm, largest organ made up of 4 lobes (left and right, caudate, and quadrate) Extremely versatile: Detoxifies, makes a wide variety of proteins including clotting factors, makes digestive juice, stores nutrients including Vitamins, iron, and energy (fat and carbohydrate) Gall bladder: stores digestive juice (bile) and releases in response to food PancreasPancreasPancreas Very active gland Endocrine and exocrine function Makes hormones (insulin and glucagon) as well as digestive enzymes OrganizationOrganizationOrganization ofofof thethethe gutgutgut 1 Tube made up of 2 four layers. Muscularis Modifications 3 externa along its length as needed. 4 StomachStomach Stores ingested food Churns (mixes and liquefies) Regulates how quickly nutrient is released into the small bowel Makes acid (good news and bad) Initiates mixing with fluid and digestive enzymes (pepsin) Receives signals from the lower small bowel SmallSmallSmall IntestineIntestineIntestine (longest(longest(longest partpartpart ofofof tube)tube)tube) Duodenum (short, 12 inches) – Fixed shape & position – Mixing bowl for food, bile and pancreatic juice Jejunum Most of digestion – Rich in digestive enzymes Ileum Most of absorption, – Lots of reserve capacity – Secretes hormones that slow the stomach Ileocecal valve – slit valve into large intestine (colon) LargeLarge IntestineIntestine CecumCecum –– pocket at proximal end with Appendix ColonColon Absorption of water and electrolytes Storage of stool until Fig 25-17 expellation RectumRectum ––terminal end is anal canal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter Colonic Secretion and Absorption In Out Ingestion ~ 1,500 ml Most is absorbed in Saliva 1,000 ml the ileum Stomach 1,500 ml Pancreas 1,000 ml 1.5 liters reaches the Bile 1,000 ml colon Small Bowel 1,800 ml 100-200 ml out in the Brunner’s glands 200 ml stool Colon 200 ml Total 8-9 liters Why is this important? The area of bowel injured or resected Influences the symptoms, complications, therapies and prognosis. GallstonesGallstones IncreasedIncreased incidenceincidence ofof gallstonesgallstones –– 8484 adultadult patientspatients withwith severesevere SBS:SBS: asymptomaticasymptomatic gallstonesgallstones inin 4444 %% –– 44 ofof 2424 childrenchildren whowho hadhad ilealileal resectionresection inin thethe newbornnewborn periodperiod RiskRisk factors:factors: –– IlealIleal resectionresection –– AbsenceAbsence ofof anan ileocecalileocecal valvevalve –– HigherHigher numbernumber ofof abdominalabdominal operationsoperations –– LongerLonger durationduration ofof parenteralparenteral nutritionnutrition LikelihoodLikelihood ofof adaptationadaptation LengthLength ofof remainingremaining smallsmall bowelbowel RemainingRemaining segmentssegments ofof smallsmall bowelbowel IntestinalIntestinal continuitycontinuity PresencePresence ofof thethe coloncolon IntactIntact ileocecalileocecal valvevalve AgeAge SiteSite ofof IntestinalIntestinal Resection:Resection: JejunumJejunum AnatomyAnatomy – Long villi – Large absorptive surface – High concentration of digestive enzymes and transport proteins – Primary digestive and absorptive site for most nutrients ResectionResection -->> temporarytemporary reductionreduction inin absorptionabsorption ofof mostmost nutrients:nutrients: – Evidence of jejunal adaptation: limited and inconsistent – Transient nature of the malabsorption: compensatory process of ileal adaptation IlealIleal AdaptationAdaptation Ileum:Ileum: reducedreduced surfacesurface areaarea CapableCapable ofof undergoingundergoing massivemassive adaptationadaptation – significant growth in length, diameter, function GradualGradual improvementimprovement inin macronutrientmacronutrient absorptionabsorption occursoccurs afterafter jejunaljejunal resectionresection asas ileumileum adaptsadapts LengthLength ofof villivilli andand intestinalintestinal absorptiveabsorptive areaarea increasesincreases ++ digestivedigestive andand absorptiveabsorptive functionfunction graduallygradually improveimprove SiteSite ofof intestinalintestinal Resection:Resection: IleumIleum Jejunum is a “leaky” organ – Marked fluid secretion in response to any hypertonic feeding – Most fluid subsequently reabsorbed: primarily in ileum and colon – If substantial part of ileum resected, fluid and electrolyte loss will occur Primary site of absorption of vitamin B12 and bile acids – Resection of 60 cm of ileum (adults) significantly impairs B12 and bile acid absorption for life – B12 deficiency and impaired absorption of fat and fat soluble vitamins because of loss of bile acid absorptive function and persistent bile acid insufficiency – Delivery of unabsorbed bile acids to the colon causes more diarrhea LossLoss ofof ICIC valvevalve Important effects > in patients with ileal resection: – Major barrier to reflux of colonic material from colon into SB – Regulating exit of fluid and nutrients from ileum into colon Small bowel bacterial overgrowth: – Progressive dilation, decreased motility -> enhance degree of overgrowth – Failure to thrive in children, malabsorption of fats, B12, and bile salts, gross and histologic bowel inflammation, GI bleeding, bacterial translocation, liver injury, and D-lactic acidosis Preservation of the colon – Water absorption can be increased to as much as 5 x normal capacity following small bowel resection – Metabolizes undigested carbohydrates into short chain fatty acids It can absorb up to 500kcal daily Used as an energy source Summary The digestive system is complex and uniquely designed for efficient digestion and absorption Derangement of any part can have profound and varied effects Therefore there is no “one size fits all” approach, therapy is highly individualized Thank You Questions? Normal Pathophysiology Term neonates have 240cm of small bowel and 40cm of colon The length of the jejunum, ileum & colon all double during the 3rd trimester of pregnancy LengthLength ofof remainingremaining smallsmall bowelbowel Difficult in predicting Cases < 20 cm of SB remaining: full enteral feedings Estimation of length at time of surgery fraught with error – Should not be used as sole determinant of ability to feed enterally Length influences duration of dependence upon PN – review of 44 children, neonatal small bowel resection – small bowel length after initial surgery – percent of daily energy intake received by the enteral route at 12 weeks adjusted to age predicted duration of dependence on TPN Predicting the duration of dependence on parenteral nutrition after neonatal intestinal resection. Sondheimer JM; J Pediatr 1998 Jan;132(1):80-4. ChronicChronic complicationscomplications WATERYWATERY DIARRHEADIARRHEA CATHETERCATHETER RELATEDRELATED COMPLICATIONSCOMPLICATIONS HEPATOBILIARYHEPATOBILIARY DISEASEDISEASE – Liver disease – Gallstones ESOPHAGITIS/PEPTICESOPHAGITIS/PEPTIC ULCERULCER DISEASEDISEASE ANASTOMOTICANASTOMOTIC ULCERSULCERS BACTERIALBACTERIAL OVERGROWTHOVERGROWTH – D-lactic acidosis NUTRIENTNUTRIENT DEFICIENCIESDEFICIENCIES – Osteoporosis HYPEROXALURIAHYPEROXALURIA SBS: Intestinal Adaptation Process of upregulation of nutrient absorption following small bowel resection Stimulation of adaptation should be a goal of any successful medical management strategy Highly dependent on enteral nutrition Food Refusal This is want you want But, this is what you get Food Refusal: Causes Unpleasant history with oral stimulation – Intubation and suctioning – Nasogastric and/or orogastric feeding tubes Discomfort associated with feeding – Gastroesophageal reflux – Gaging/Vomiting Oral-motor immaturity – Suck/swallow/breath pattern – Weak flexion and muscle strength – Poor endurance for full oral feeds Disruption of hunger-satiety cycle .