11- Digestion and Absorption of Biomolecules

Iron & Folate

Carbs, Proteins, & Fats

Lose absorption of THESE when the duodenum is removed.

Loss of Na+ Coupled transport of gluc/AA’s

Loss of pancreatic secretions allowing absorption of fats/lipids

NEC MOA

1. PAMPs/MAMPs bind TLR

2. Initiates transcription of pro-inflammatory/apoptotic genes

Note: there’s more bacterial infections with NEC

Transporters that increase in function post-SI resection:

• SGLT1

• PepT1

• NHE3 7 DRA

SGLT1

Glucose and Na Symport

PepT1

Di/Tri peptides & H Symport

NHE3 & DRA

Na and Cl absorption

Vitamin B12 (cobalamin)

Lose absorption of THIS when Ileum is removed.

It’s only absorbed in the ileum!

2 methods for apoptosis:

• Intrinsic

  • Mitochondria & Cytochrome C

• Extrinsic

  • TLR mediated

  • Capase 8

• Both affect Capase 3 → apoptosis

50

60

100

Chance of weaning parenteral nutrition:

• 30 cm of bowel remaining means _% chance

• 60 cm of bowel remaining means _% chance

• 100 cm of bowel remaining means _% chance

Length of SI left over

Determining factor for a pt having NEC and SI resection will be able to be taken off TPN is THIS.

Na

Water

Fat-Soluble Vitamins

Ca

Mg

Phosphate

Iron

Lab values that need to be closely watched when losing a duodenum and proximal jejunum

SI Adaptations Post-Resection

1. Better absorption (adaptive mucosa)

2. Hypertrophy/Hyperplasia

3. Bowl lengthens/dilates

4. Functional changes (where transport happens, where enzymes are)

Duodenum & Jejunum

Where most hormones of the SI are secreted.

An issue when NEC causes resection of this region.

Bacterial Overgrowth Syndrome

Consequence of losing the ileocecal valve.

Causes lactic acidosis!

Ileum

Consequences of losing THIS:

• Vitamin B12 Deficiency

• Steatorrhea (lose bile salts)

• Diarrhea (bile salts/acids not absorbed anymore)

NF-Kappa B Pathway

The signaling pathway associated with NEC that leads to signaling of apoptosis and pro-inflammation.

Released from TLR, acts as transcription factor for pro-inflammatory and apoptotic genes.

Apoptosis

death of cell that doesn’t affect nearby tissues really

Necrosis

more inflammatory and damaging to nearby tissues

Water & SCFA (short chain fatty acids)

Lose absorption of THESE when you lose the colon.

Ileum (paracellular) or Distal Colon (active)

Loss of K absorption can happen when THIS or THIS are removed.

Sx of NEC (necrotizing enterocolitis)

• bloody diarrhea

• distended abdomen

• penumatosis intestinalis

Mechanism of NEC

• Bowel ischemia → damaged mitochondria → necrosis/apoptosis

• No ATP production → loss of:

  • Na/K pump (ER swelling, loss of microvili)

  • Decreased pH (increased anaerobics)

  • Decreased protein synthesis

Pneumatosis Intestinalis

Gas bubbles/cysts in abdomen

Caused by bacterial colonization (fermentation byproducts)

Risk Factors of NEC

• Prematurity

• Intestinal Ischemia

• Bacterial Colonization

• Enteral feeding

Why premature babies are more at risk of NEC:

Immature intestinal barrier

Weak tight junctions

Bacterial colonization

Repeat infections, uncontrolled inflammation