GI Enzymes Note

GI enzymes (very exam-relevant):

1. Lactase Deficiency (Lactose Intolerance)

Problem

↓ Lactase at brush border

Result

Lactose not digested → stays in lumen

Symptoms

• Bloating

• Gas

• Osmotic diarrhea

• Abdominal cramps

Why?

Undigested lactose → fermented by bacteria → gas + osmotic load

Key Point

✔ Not an allergy
✔ Very common
✔ Worse with age / post-infection

2. Pancreatic Insufficiency

Seen in:

• Chronic pancreatitis

• Cystic fibrosis

• Pancreatic cancer

Problem

↓ Pancreatic enzymes (lipase most important)

Symptoms

• Steatorrhea (fatty stools)

• Weight loss

• Fat-soluble vitamin deficiency (A, D, E, K)

Why fat first?

Lipase is most vulnerable enzyme

Stool

• Bulky

• Pale

• Floating

• Foul-smelling

3. Acute Pancreatitis

Key Enzymes

• Lipase (most specific)

• Amylase

Diagnosis

↑ Serum lipase

Mechanism

Premature activation of trypsin → autodigestion

Clinical Clues

• Epigastric pain → radiates to back

• Nausea/vomiting

4. Enteropeptidase (Enterokinase) Deficiency

Problem

Cannot activate trypsinogen → trypsin

Effect

↓ Activation of ALL pancreatic proteases

Symptoms

• Severe protein malabsorption

• Failure to thrive (infants)

Rare but classic test question

5. Pepsin / Achlorhydria

Seen in:

• Pernicious anemia

• Chronic gastritis

• PPI overuse (mild effect)

Problem

↓ HCl → ↓ pepsin activation

Result

↓ Protein digestion

Also affects

• Iron absorption

• B12 release from food

6. Cystic Fibrosis

Problem

Thick secretions block pancreatic ducts

Effect

↓ Enzyme delivery

Symptoms

• Steatorrhea

• Malnutrition

• Fat-soluble vitamin deficiency

7. Lipase vs Amylase (Exam Favorite)

Enzyme	Clinical Value
Lipase	More specific for pancreatitis
Amylase	Less specific (also ↑ in salivary disease)

8. Brush Border Damage

Seen in:

• Celiac disease

• Gastroenteritis

Problem

↓ Disaccharidases (especially lactase)

Symptoms

Secondary lactose intolerance

9. Trypsin’s Central Role

Trypsin activates:

• Chymotrypsinogen

• Procarboxypeptidase

• Proelastase

Clinical Relevance

Premature trypsin activation → pancreatitis

10. Fat Malabsorption Consequences

Due to ↓ lipase / bile / mucosal disease:

Deficiencies

• Vitamin A → night blindness

• Vitamin D → osteomalacia

• Vitamin E → neuropathy

• Vitamin K → bleeding

Exam Memory Tricks

✔ Lipase = Pancreatitis
✔ Steatorrhea = Fat digestion problem
✔ Lactase = Most easily lost enzyme
✔ Trypsin = Master activator