Biology: Skeletal structure ch.11

• Hormones are chemical messengers secreted by one cell or group of cells to influence another cell's behavior.
• There are 2 types of skeleton: exoskeleton and endoskeleton
• Humans have endoskeleton
• Exoskeleton must shed and regrowth to accomodate growth. Endoskeleton re much better to accomodate the growth of a larger organisms.
• Endoskeletal is divided into axial and appendicular.
• The axial skeletal consists of the skull, vertebral column, and rib cage, and hyoid bone.
• The appendicular is made of other sections of the body
• Both have muscle, connective tissue, and vasculature.
• The skeletal is made of bone and cartilage.
• Bone is a connective tissue derived from embryonic mesoderm.
• Bone is much harder than cartilage but more lightweighted.
• Bones could be compact bone, dense and strong, or spongy/ cancellous bone
• The lattice structure of spongy bone is visible under microscope and consist of bony spicules (points) known as trabeculae.
• The cavities btw trabeculae are filled with bone marrow
• Bone marrow can be red or yellow
• If bone marrow is red, it is filled with hematopoietic stem cells that are responsible for the generation of all the cells in our blood
• If we have yellow bone marrow, it is comp[osed of fats and are inactive
• Bones in appendicular skeleton are typically longer bones that are characterized by cylinderical shafts called diaphyses that swell at each end to form metaphysis and terminatin gin epiphyses
• The outer portion of bone is made of compact bone and internal core is made of spongy bone.
• The long bone diaphyses and metaphyses are full of bone marrow
• The epiphyses use their spongy core more effectove dispersion of force and pressure at the joints.
• At the edge of the epiphyses is epiphyseal (growth) plate which is cartilaginous and the site of longitudinal growth.
• Prior to adulthood, the epiphyseal plate is filled with mitotic cells that contribute to growth
• During puberty, the epiphyseal plates close and vertical growth is halted
• A fibrous sheath called periosteum surrounds the long bone to protect it and serve as site for muscle attachment.
• Some periosteum cells are capable of differentiating into bone forming cells, a healthy periosteum is necessary for bone growth and repair.
• Tendons attach muscles to bones
• Ligaments hold bones together at joint
• The strength of compact bone comes from bone matrix, which has both organic and inorganic component
• Strong bone requires uniform distribution of organic and inorganic materials
• Bone matrix is ordered into structural units known as osteons or haversian systems.
• Each of theses osteons/harversians systems contains concentric circles of bony matrix called lamellae surrounding a central microscopic channel.
• Longitudinal channels are known as harversian canals.
• The transverse channel (axis perpendicular to the bone) are known as Volkmann's channel.
• These canals contain blood vessel, nerve fibers, lymph vessel that maintain the health. of the bone.
• Btw the lamellar rings are small spaces called lucunae which house mature bone cells known as osteocytes.
• The lacunae are interconnected by tiny channels called canaliculi that allows the exchange of nutrient & waste btw osteocytes, harversian, and Volkmann's canals.
• Two cell types that are largely responsible for building and maintaining strong bones: Osteoblasts and Osteoclasts.
• Osteoblasts build bone
• Osteoclasts macrophages of bone, reabsorb it.