EBL W1 - Structure/basic function of GI tract and GI directed formulation Flashcards
pH, enzymes and chemical environments of the mouth
- pH: ~6.5–7.5 (slightly acidic to neutral)
- Enzymes:
o Salivary amylase: Begins starch → maltose
o Lingual lipase: Starts fat digestion (more active in stomach) - Other chemicals: Mucus (lubrication), bicarbonate (buffer), lysozyme (antibacterial)
pH, enzymes and chemical environments of the oesophagus
- pH: ~7 (neutral)
- Other chemicals: Mucus (lubrication)
- Function: No digestion; transports bolus to stomach
pH, enzymes, chemical environments and key cells of the stomach
- pH: ~1.5–3.5 (highly acidic due to HCl)
- Enzymes:
o Pepsin: Proteins → peptides (from pepsinogen via HCl)
o Gastric lipase: Begins lipid digestion - Other chemicals:
o Intrinsic factor: Vitamin B12 absorption
o Mucus: Protects stomach lining - Key cells:
o Parietal cells: Secrete HCl and intrinsic factor
o Chief cells: Secrete pepsinogen
pH, enzymes and chemical environments of the small intestine
- Sections: Duodenum, Jejunum, Ileum
a. Duodenum
* pH: ~6–7.5 (neutralized by pancreatic bicarbonate)
* Enzymes (from pancreas):
o Amylase: Starch → maltose
o Trypsin & Chymotrypsin: Protein digestion
o Carboxypeptidase: Protein digestion
o Lipase: Fats → fatty acids + glycerol
o Nucleases: DNA/RNA digestion
* Other chemicals:
o Bile (from liver/gall bladder): Emulsifies fats
b. Jejunum & Ileum
* pH: ~7–8 (slightly alkaline)
- Enzymes:
o Disaccharidases: Maltase, sucrase, lactase
o Peptidases: Peptides → amino acids
pH, enzymes and chemical environments of the large intestine
- pH: ~5.5–7 (neutral to slightly acidic)
- Function: Water & electrolyte absorption
- Other chemicals: Mucus (lubrication)
Accesory organs
- Pancreas: Secretes digestive enzymes and bicarbonate into duodenum
- Liver: Produces bile for fat emulsification
- Gall Bladder: Stores and releases bile into duodenum
Cells in GI Tract
- Chief cells: Secrete pepsinogen (inactive form of pepsin)
- Parietal cells: Secrete HCl and intrinsic factor
Movement Through the GI Tract
Peristalsis
* Involuntary wave-like muscle contractions and relaxations of the muscularis layer
* Moves food along the tract (oesophagus → rectum)
GI Tract Physical Structure (4 Layers)
- Mucosa: Innermost; secretion & absorption
- Submucosa: Connective tissue with blood vessels, nerves
- Muscularis: Smooth muscle for peristalsis
- Serosa: Outermost protective layer
Digestion & Absorption in GI Tract
- Nutrients must be broken down before absorption:
o Carbs → Monosaccharides
o Proteins → Amino acids & small peptides
o Fats → Fatty acids & monoglycerides
Absorption Sites & Mechanisms
- Small Intestine: Major site of absorption (villi & microvilli ↑ surface area).
o Water-soluble nutrients → Bloodstream → Hepatic portal vein → Liver
o Fat-soluble nutrients → Lymphatic system → Bloodstream
Nutrient Absorption Details - Vitamins
- Vitamins:
o Lipophilic (A, D, E, K): Absorbed with fats via micelles
o Hydrophilic (C, B): Passive/facilitated diffusion
Nutrient Absorption Details - proteins
o Digested in stomach (begins) → small intestine (continues)
o Amino acids: Active transport (Na⁺-dependent)
o Peptides: PEPT1 transporter → broken into amino acids intracellularly
Nutrient Absorption Details - Fats
o Emulsified by bile salts → micelles
o Passive diffusion → Repackaged into chylomicrons → Lymphatic system
Nutrient Absorption Details - Carbs
Carbs (Monosaccharides):
o SGLT1: Glucose & galactose via active transport (Na⁺-dependent)
o GLUT5: Fructose via facilitated diffusion
o GLUT2: All monosaccharides eventually enter hepatic portal vein (basolateral side)
- GLUT2 plays a major role in exporting monosaccharides from enterocytes into the portal blood, it’s not involved in their initial uptake into the cells, and not the only transporter involved overall
Nutrient Absorption Details - Water
o Osmosis via Na⁺-glucose transport (SGLT1) in small intestine
o Also absorbed in large intestine (Na⁺ transport → water follows)
Drug Absorption - factors affecting it, routes, mechanisms, sites
- Factors: Ionisation, solubility, pH
- Routes: Oral, rectal
- Mechanisms:
o Lipophilic drugs: Passive diffusion
o Amino acid/vitamin-based drugs: Facilitated diffusion
o Analogues of nutrients (e.g., Levodopa): Active transport
o Large molecules (e.g., B12): Endocytosis - Sites:
o Stomach (pH 1.5–3.5): Weak acids
o Small Intestine (pH 6–7.4): Most drugs
o Large Intestine: Water, electrolytes, slow-release drugs
Acute GI Conditions
- Gastroenteritis: Infection of the stomach and intestines, usually caused by an infection → Vomiting, diarrhea, abdominal pain
- Acute Pancreatitis: Premature enzyme activation → Pancreatic autodigestion
- Appendicitis: Blocked appendix → Inflammation, potential rupture
- Others:
o Mesenteric Ischemia: Reduced blood flow to intestines
o Cholera - acute diarrheal disease, causes severe dehydration -
Colitis - inflammation of the colon (large intestine)
o Gallbladder Inflammation: Often infection-related
Oral Liquid vs Solid Drug Formulations
- Advantages (Liquid):
o Easier to swallow, faster absorption, adjustable dosing - Disadvantages (Liquid):
o Shorter shelf life, higher cost, taste/measurement issues - Examples:
o Liquid: Omeprazole suspension
o Solid: Gaviscon tablets
Suspensions & Emulsions vs Solutions
- Why use: Poor solubility, better taste, stability, controlled release
- Examples:
o Suspension: Pepto-Bismol, Calpol
o Emulsion: Neoral (Cyclosporine) - Additives: Surfactants, wetting agents enhance solubility
Activated Charcoal & Paracetamol Overdose
- Mechanism: Adsorbs drug in GI tract → Prevents absorption
- Best for: Non-ionised, poorly water-soluble toxins
- Must be given within 1 hour
- Ratio: Ideal AC:Toxin = 10:1
- Structure: Porous → Large surface area for binding
Gaviscon Advanced (Chewable Tablets) – Counselling Points
- How to Take: Chew after meals/bedtime, no water needed
- Function: Forms barrier against acid reflux
- Storage: Cool, dry place
- Side Effects: Rare – bloating, nausea; safe in pregnancy (confirm use)
