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

Function Individual parts function in:

The function of the system as a whole is processing food in such a way that high energy molecules can be absorbed and residues eliminated.

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ingestion

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mechanical digestion

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chemical and enzymatic digestion

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secretion

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absorption

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compaction

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excretion and elimination

Digestive System

consists of:

Muscular, hollow tube (= “digestive tract”) + Various accessory organs

Three pairs of

Salivary Glands

1-1.5 l / day for digestion (enzymes) lubrication (swallowing) moistening (tasting)

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Parotid –

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Submandibular –

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Sublingual –

Liver 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

Pancreas „

Very active gland

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Endocrine and exocrine function

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Makes hormones (insulin and glucagon) as well as digestive enzymes

Organization of the gut Tube made up of four layers. Modifications along its length as needed.

1 2

Muscularis

3 externa

4

Stomach „ „ „

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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

Small Intestine (longest part of 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)

Large Intestine Cecum – pocket at proximal end with Appendix

Colon Absorption of water and electrolytes Storage of stool until expellation

Fig 25-17

Rectum – 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 Saliva 1,000 ml Stomach 1,500 ml Pancreas 1,000 ml Bile 1,000 ml Small Bowel 1,800 ml Brunner’s glands 200 ml Colon 200 ml Total

8-9 liters

Most is absorbed in the ileum 1.5 liters reaches the colon 100-200 ml out in the stool

Why is this important? The area of bowel injured or resected Influences the symptoms, complications, therapies and prognosis.

Gallstones „

Increased incidence of gallstones – 84 adult patients with severe SBS: asymptomatic gallstones in 44 % – 4 of 24 children who had ileal resection in the newborn period

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Risk factors: – Ileal resection – Absence of an ileocecal valve – Higher number of abdominal operations – Longer duration of parenteral nutrition

Likelihood of adaptation „

Length of remaining small bowel

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Remaining segments of small bowel

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Intestinal continuity

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Presence of the colon

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Intact ileocecal valve

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Age

Site of Intestinal Resection: Jejunum „

Anatomy – – –

Long villi Large absorptive surface High concentration of digestive enzymes and transport proteins – Primary digestive and absorptive site for most nutrients „

Resection -> temporary reduction in absorption of most nutrients: – Evidence of jejunal adaptation: limited and inconsistent – Transient nature of the malabsorption: compensatory process of ileal adaptation

Ileal Adaptation „

Ileum: reduced surface area

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Capable of undergoing massive adaptation – significant growth in length, diameter, function

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Gradual improvement in macronutrient absorption occurs after jejunal resection as ileum adapts

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Length of villi and intestinal absorptive area increases + digestive and absorptive function gradually improve

Site of intestinal Resection: Ileum „

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

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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

Loss of IC valve „

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

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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

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The length of the jejunum, ileum & colon all double during the 3rd trimester of pregnancy

Length of remaining small bowel „

Difficult in predicting

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Cases < 20 cm of SB remaining: full enteral feedings

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Estimation of length at time of surgery fraught with error – Should not be used as sole determinant of ability to feed enterally

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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.

Chronic complications „ „ „

WATERY DIARRHEA CATHETER RELATED COMPLICATIONS HEPATOBILIARY DISEASE – Liver disease – Gallstones

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ESOPHAGITIS/PEPTIC ULCER DISEASE ANASTOMOTIC ULCERS BACTERIAL OVERGROWTH – D-lactic acidosis

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NUTRIENT DEFICIENCIES – Osteoporosis

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HYPEROXALURIA

SBS: Intestinal Adaptation „

Process of upregulation of nutrient absorption following small bowel resection

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Stimulation of adaptation should be a goal of any successful medical management strategy

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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

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Discomfort associated with feeding – Gastroesophageal reflux – Gaging/Vomiting

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Oral-motor immaturity – Suck/swallow/breath pattern – Weak flexion and muscle strength – Poor endurance for full oral feeds

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Disruption of hunger-satiety cycle