Intestinal Villi

• The small intestine is where absorption of nutrients into the blood happens
• The small intestine also releases digestive enzymes to ensure the complete hydrolysis of food molecules
• Villi: Thin, finger-like projections that increase the surface area of the small intestine
• Villi have several features that promote the absorption of digestive products: microvilli, rich blood supply, single layer epithelium, lacteals, intestinal glands, membrane proteins (MR SLIM)
• Microvilli – Ruffling of epithelial membrane further increases surface area
• Rich blood supply – Dense capillary network rapidly transports absorbed products
• Single layer epithelium – Minimises diffusion distance between lumen and blood
• Lacteals – Absorbs lipids from the intestine into the lymphatic system
• Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
• Membrane proteins – Facilitates transport of digested materials into epithelial cells
• The epithelial lining of villi has structural features which optimise its capacity to absorb digested materials: tight junctions, microvilli, mitochondria, pinocytotic vesicles
• Tight Junctions: create an impermeable barrier, keep digestive fluids separated from tissues, and maintain a concentration gradient by ensuring one-way movement
• Microvilli: allow for more absorption, embedded with immobilised digestive enzymes and channel proteins to assist in material uptake
• Mitochondria: epithelial cells have them to provide ATP for primary active transport (against gradient), secondary active transport (co-transport) or pinocytosis
• Pinocytotic Vesicles: for the non-specific uptake of fluids and dissolved solutes