How tissues make organs

===Lecture Details===
Jeff Kerr; Week 7 MED1011; Anatomy
===Lecture Content===
Kidney grows from the mesoderm, one part of the growing organ induces another to turn into a special component. Both parts grow together then unite to become the filtration and excretory parts of the kidney. Is called reciprocal induction of development. Development of kidney begins in the pelvis arising within mesoderm tissue; metanephrogenic mesenchyme will form the bulk of the nephrons, the mesonephros will begin the duct system. Inside developing kidney is extensive branching morphogenesis. Buds lengthen and branch, will become duct drainage system inside the kidney. The primitive ureteric bud which is epithelium induces the mesenchyme to become epithelium itself. This works by growth factors being secreted and responded to by receptors, biological change leads to new tissue development. The collecting duct is the part that branches and connects to the developing mesenchymal nephron.
In special regions of bone the developing cartilage cells degenerate leaving behind a scaffold of cartilage matrix, which allows osteoblasts to lay down bone and mineralise into. Cartilage does not transform into bone. Cartilage is invaded by cells capable of producing bone in the embryo, immature bone is deposited on the surfaces of cartilage tissue. Hypertrophic chondrocytes are the ones that die and are replaced by bone. At the apical ectodermal ridge the limb grows, condensed mesenchyme is formed in the middle and cartilage is laid down in bone-like models, bone ossifies into it. Bits of cartilage become calcified as bone is deposited so bone replaces cartilage.
Zones of cartilage slowly move apart by continuous cell proliferation and death allowing gradual lengthening of the growing bone. Cartilage is no longer required in these areas.
===Readings===
====Kerr; 240-246, 373-378====