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Ebook Embryology at a glance: Part 2

(BQ) Part 2 book "Embryology at a glance" presents the following contents: Skeletal system (ossification), skeletal system, muscular system, respiratory system, digestive system - Gastrointestinal tract, urinary system, endocrine system, central nervous system, peripheral nervous system,. | Skeletal system ossification Figure 21.1 Mesenchymal cells condense and form a model of the future bone Hypertrophic chondrocytes Perichondrium Figure 21.2 Mesenchymal cells differentiate into chondrocytes and the matrix becomes calcified in the future diaphysis Osteoblasts Primary centre of ossification ----Periosteum bone forming beneath Figure 21.3 Blood vessels invade bringing progenitor cells that become osteoblasts and haematopoietic cells Bony spicules Diaphysis Epiphysis Figure 21.4 The diaphysis becomes ossified but the epiphyses remain cartilaginous Secondary centre of ossification Figure 21.5 Later the epiphyses also begin to ossify Figure 21.7 Mesenchymal cells form a condensation between 2 developing bones Figure 21.6 With the epiphyses and diaphysis ossified the bone continues to grow in length from the growth plates. Eventually the growth plates also ossify and growth ceases Stages of endochondral ossification Figure 21.8 Mesenchymal cells become organised into layers and differentiate into different cell types in this case the tissues of a synovial joint Joint development Embryology at a Glance First Edition. Samuel Webster and Rhiannon de Wreede. 50 2012 John Wiley Sons Ltd. Published 2012 by John Wiley Sons Ltd. Time period week 5 to adult Introduction Mesodermal cells form most bones and cartilage. Initially an embryonic loosely organised connective tissue forms from mesoderm throughout the embryo referred to as mesenchyme. Neural crest cells that migrate into the pharyngeal arches are also involved in the development of bones and other connective tissues in the head and neck see Chapters 39-42 . Bones begin to form in one of two ways. A collection of mesenchymal cells may group together and become tightly packed condensed forming a template for a future bone. This is the start of endochondral ossification Figure 21.1 . Alternatively an area of mesenchyme may form a hollow sleeve roughly in the shape of the future bone. This is how .