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How the GI Tract Is Specialized for Its Function: (Organized and Manifold…
How the GI Tract Is Specialized for Its Function:
Cellular Structures
Efficient absorption of materials (small intestine)
Maximization of SA : Volume
Plica
Villi
Microvilli
Layers and layers of surface area maximization means very efficient absorption of materials via diffusion
Blood and lymph vessels in every villus
Lymph vessels take objects too large for capillaries
Efficient distribution of materials throughout body
Blood is the main transport system
Efficient distribution of materials throughout body
Immunity
GI Tract is on the frontline of potential pathogen exposure
Mouth
Keratinized stratified squamous ET
Barrier to abrasion and pathogen entry
Stomach
Very low pH
Breaks down pathogens
Receives mucus from respiratory tract (which may contain pathogens)
Mucus lining stomach walls
Barrier to entry
Small intestine
Lymph vessels in every villus
Better pathogen detection
Organized and Manifold Methods of Chemical Breakdown
Oral cavity
Salivary Glands
Some breakdown via enzyme activity
Amylase secretion
Mechanical breakdown of food via mastication
Compaction into a bolus
Stomach
Significant mechanical and chemical breakdown of food
Very little absorption
Enzymes and acid secreted from gasrtic glands
Parietal cells
HCl
Activates proteolytic enzymes
Stomach acid
Ghrelin
Chief cells
Pepsinogen
Inactive form of pepsin
Small intestines
Nearly all absorption happens here
Enzymes from pancreas for final breakdown
Amylases
Carbohydrates
Lipases
Lipids
Proteases
Proteins
Nucleases
Nucleic acids (RNA and DNA)
Bile salts from liver
Concentrated in gall bladder
Released to small intestine to emulsify fats
Increases surface area for enzyme activity
Large intestine
Reabsorption of important materials
Water
Bile salts
Absorption of bacteria-generated vitamins
Compaction of indigestible materials for defecation
How the stomach protects itself, from itself
Mucus
Mucus covers stomach lining
Protection against acidity
Gastric pits produce alkaline mucus (pH above 7)
Neutralization of acids above cells offers additional protection in hostile envronment
Enzymes
Chief cells secrete inactive form of pepsin in gastric glands
It's activated by low pH
Becomes active once it leaves the gastric pit, thus protecting the glandular cells from being broken down
Tissue arrangment
Folded epithelium
Gastric pits
Folds protect cells, glands in gastric pits from acidic environment above
High mitotic rate
Quick replenishment of lost cells (very hostile environment)
