Tissues & Organs

• Tissue


  An amalgamation of cells that all perform the same function.
• Organ


  A body part composed of several tissues grouped together to perform an overall function.
• Layers of the ileum ( Outer -> Inner )

  • Serosa
  • Muscularis externa (circular & longitudinal)
  • Submucosa
  • Muscularis mucosa
  • Mucosa
• Columnar epithelium 


  Secretes copius amounts of mucus that acts as a lubricant and prevents digestion of the gut by its own enzymes.

  Mucus produced by goblet cells.
• Crypts of Lieberkuhn


  Each crypt contains paneth cells which are specialised for the secretion of antimicrobial peptides and lysozyme to protect stem cells at the bottom of the crypt which actively divide to replenish epithelial cells further up the villi.
• Capillaries


  Monossaccharides, dipeptides and amino acids are absorbed into the capillaries.

  Help to maintain a concentration gradient.
• Lacteal


  fatty acids and glycerol pass into the lacteals and are transported away as fats in the lymphatic system.
• Microvilli


  Each epithelial cell possesses many microvilli.

  The microvilli forma brush border and serve to further increase the surface area.
• Mitochondria


  Each epithelial cell has many mitochondria to provide the ATP necessary for active uptake.
• Absorption of monosaccharides and amino acids

  Absorbed via sodium linked active transport.

  Once in the cell their conc. increases and they exit via facilitated diffusion into the tissue fluid before diffusing into the capillary.
• Absorption of lipids


  Diffuse into the epithelial cell where they reform as triglycerides.
• Some substances are absorbed by pinocytosis
• Muscularis Mucosa

  • layer of smooth muscle
  • allows mucosa to stretch and contract with the movements of the digestive system
  • allows the maintenance of a concentration gradient between the contents of the ileum lumen and cells of the villi.
• Submucosa


  Layer of tissue containing blood and lymphatic vessels. It also contains connective tissue that supports the mucosa.
• Muscularis externa

  • Layer of circular and a layer of longitudinal muscle.
  • Coordinated movement provides:
  • Peristalsis which moves food along the gut
  • Local constrictions churning and mixing food in the gut
  • Pendular movement throwing food and therefore mixing it.
• Serosa


  Composed of loose fibrous connective tissue.

  Role: support and protection.
• Mesophytic leaf layers

  • upper epidermis
  • palisade mesophyII
  • spongy mesophyII
  • xylem
  • phloem
  • lower epidermis
  • stomata
• Waxy cuticle


  Forms a waterproof layer over the leaf preventing excessive water loss.
• Palisade mesophyII 


  Packed arrangement of columnar cells that are filled with chloroplasts.

  Maximises photosynthesis
• Spongy mesophyll


  Loosely arranged spherical cells

  Intercellular air spaces facilitate gas exchange - carbon dioxide entering stomata can readily diffuse through our spaces and reach photosynthesising cells.
• Leaf lamina


  very thin and has a large surface area.

  mesophyll cells are closer to the surface reducing the diffusion distance of carbon dioxide.
• Xylem


  Brings water and minerals from the roots into the leaf.