The Skeletal System v=yENNqRJ2mu0

Introduction The functions of the skeletal system are: 1.the support of soft tissues, 2.protection by enclosing vital organs, 3.aid in movement (with aid of muscles), 4.blood cell formation within red marrow called hematopoiesis), 5.storage of minerals (calcium and phosphate)

Bone Structure There are four main types of bone: Long bones  greater in length than width (femur) Short bones  about equal in length and width (carpals or tarsals) Flat bones  thin and flat (scapula or sternum) Irregular bones  variable shapes that do not fit above (mandible)

Parts of Long Bone Diaphysis—long thin part of the bone Epiphyses—the extreme ends Medullary cavity—central chamber of diaphysis Periosteum—dense CT covering Endosteum—membrane lining inner wall of medullary cavity Articular cartilage—hyaline cartilage at the end surfaces

Parts of Long Bone Compact bone—forms the walls of the diaphysis Spongy bone—fills the center of the epiphyses Red marrow—CT within spongy bone: site of blood cell formation Yellow marrow—fills the medullary cavity: fat storage

Parts of a Long Bone Red marrow Yellow Marrow Compact Bone

Microscopic Structure of Bone Compact bone is made of a concentric structure of osteons, allowing little space between layers of matrix. Nourishment of cells is by way of blood vessels that course through the central osteonic canal and canaliculi. Spongy bone has thin plates of bone with spaces in between filled with red marrow. chttps:// c

Microscopic Structure of Bone The material that makes up bone tissue is part collagen and part inorganic salts. Collagen gives bone its strength and resilience. Inorganic salts make it hard and resistant to crushing.

Microscopic Structure of Bone The bone matrix is composed of an organic part (osteoid) and an inorganic part (hydroxyapatite). Osteoid is made of protein and collagen that gives bone its tensile strength…pliable but tough. Hydroxyapatite is a calcium phosphate (Ca 10 (PO 4 ) 6 (OH) 2 ) crystal which give bones their hardness and density.

Microscopic Structure of Bone There are three main types of bone cells: osteoblasts, osteocytes and osteoclasts. Osteoprogenetor cells (immature osteoblasts) which are differentiated stem cells. Osteoblasts make collagen and the proteins osteocalcin and osteopontin. Together these make up osteoid. Osteoblasts also make alkaline phosphatase, an enzyme to make hydoxyapatite.

Microscopic Structure of Bone When osteoblasts mature, they are called osteocytes that live in lacunae (little lakes). Osteocytes...the little braches of the lacunae allow for communication with other bone cells.

Microscopic Structure of Bone Osteoclasts are known as bone eaters. They produce tartrate resistance acid phosphatase which breaks down bone. After they eat bone they form little empty spaces called Howships lacunae where they live.

Microscopic Structure of Bone Recall that the main bone cells are called osteocytes and are located in very small bony chambers called lacunae. Lacunae form concentric circles around central canals (Haversian Canals)—the circle itself is called a lamella. Osteocytes communicate with nearby cells by means of cellular processes (arms) passing through called canaliculi.

Microscopic Structure of Bone In compact bone, the osteocytes and layers of intercellular material concentrically clustered around a central canal form a cylindrical-shaped unit called an osteon. Many of these units cemented together form the substance of compact bone. Each central canal contains blood vessels and nerve fibers surrounded by loose CT.

Microscopic Structure of Bone Central canals extend longitudinally through bone and transverse canals (perforating canals) connect them. Spongy bone is composed of osteocytes as well. They do not form around central canals. Instead, substances diffusing into canaliculi that lead to the surface of these thin, bony plates nourish the cells.

Bone Composition Organic component of bones are collagen which provides flexibility and strength to the matrix. Inorganic components are calcium phosphate and calcium carbonate that form crystals of hydroxyapatite that makes bones hard and brittle. Maintaining sufficient blood calcium levels is important in muscle contraction, nervous impulse conduction and blood clotting.

Bone Composition When the blood is low in calcium, parathyroid hormone stimulates osteoclasts to break down bone tissue. This releases calcium into the bloodstream. A high blood calcium level inhibits osteoclast activity while the thyroid stimulates osteoblasts to form bone tissue—storing excess calcium in the matrix. Bone is always being remodeled by osteoblasts and osteoclasts. HoEhttps:// HoE

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– Thigh Bone

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Parts of a Long Bone Red marrow Compact Bone Epiphyseal Line / Plate Articular Cartilage Periosteum Red Marrow Spongy Bone Compact Bone Medullary Cavity