BS Mod 1 Lecture 1 PDF

Neural Crest • Entire nervous system arises from ectoderm • Neural plate forms in midline and expands in cranial to caudal direction • Neural crest induced at boundary between neural plate and non-neural ectoderm • Neural crest develops at edges of neural plate • Neural plates invaginate to form neu...

Neural Crest • Entire nervous system arises from ectoderm • Neural plate forms in midline and expands in cranial to caudal direction • Neural crest induced at boundary between neural plate and non-neural ectoderm • Neural crest develops at edges of neural plate • Neural plates invaginate to form neural groove flanked by neural folds • Neural folds approach each other in dorsal midline • Neural folds fuse to form neural tube • Neural tube and neural crest separate from overlying ectoderm, and developing skin overlies original site of neurulation Connective tissue • Mostly derived from mesoderm • Some parts within head and neck derived from neural crest – Ectomesenchyme • Functions – Structural support – Exchange of nutrients, metabolic waste and signaling molecules – Helps in defense, protection and repair – Fat storage Two types of connective tissue • Connective tissue proper – Loose connective tissue – Dense connective tissue • Specialized connective tissue – Reticular connective tissue supporting lymphoid organs – Bone – Cartilage – Ligaments – Adipose – Blood Cellular components of Connective tissue • Fixed cells develop and remain in place – Fibroblasts – Myofibroblasts – Adipocytes – Pericytes – Mast cells – Macrophages • Transient cells (originate in bone marrow) and come from blood stream – Neutrophils – Eosinophils – Basophils – Monocytes – Macrophages – Lymphocytes – Plasma cells Fixed connective tissue cells Fibroblasts • Most abundant but least specialized cell • Synthesize – Collagen fibers – Reticular fibers – Elastic fibers • Quiescent fibroblasts are fibrocytes Myofibroblasts • Transiently modified fibroblasts • Characteristics similar to fibroblasts and smooth muscle cells – Contractile properties • Abundant during wound healing • Can also be derived from other cell types Pericytes • Surround endothelial cells of capillaries • Contractile • Regulate capillary blood flow Adipocytes Synthesize, store and release fat Fully differentiated cells – Do not divide Unilocular adipocytes with large lipid droplet – Form white adipose – Abundant form of fat Multilocular adipocytes with multiple small lipid droplets – Form brown adipose – Abundant in newborns Mast cells Derived from bone marrow likely from myeloid stem cells Mediate inflammation and immediate hypersensitivity reactions Primary mediators found in granules – Heparin – Histamine Secondary mediators (newly synthesized) – Cytokines derived from arachidonic acid precursors – Other cytokines not derived from arachidonic acid precursors **toluidine blue stains granules purple ** Mast cells Connective tissue proper mast cells – Concentrated around blood vessels – Rich in heparin Mucosal mast cells in digestive / respiratory tracts – Rich in chondroitin sulfate NOT found in central nervous system Macrophages - Derived from stem cells in bone marrow - Enter circulation as monocytes - Mature into macrophages in connective tissue Macrophages Fixed (resident) and transient Different names in different places – Phagocytes and antigen-presenting cells – Kupffer cells in liver – Langerhans cells in skin/mucosa