Skeletal System Bones and Joints

Function of the Skeletal System Five basic functions of the skeletal system: (1) Support- framework that supports body and cradles its soft organs (2) Protection- for delicate organs, heart, lungs, brain, spinal cord, reproductive organs (3) Movement- bones act as levers for muscles (4) Mineral and lipid storage- calcium & phosphate (5) Blood cell formation- hematopoiesis

Types of Bones Long Bones- metacarples, metatarsals, phelangies, humerus, ulna, radius, tibia, fibula Short Bones- carpals, tarsals Flat Bones- rib, scapula, skull, sternum Irregular Bones- vertebrae, some facial bones Sesamoid- patella

Bone Classification

Organization of Bones Total of 206 bones make up the adult skeleton Divided into: (1) Axial – includes the head, neck, and trunk (2) Appendicular – includes limbs and bones connecting the limbs to the pelvic girdle (coxal bones – lower limbs) and pectoral girdle (scapula and clavicle- upper limbs)

Axial Skeleton

Appendicular Skeleton

275 bones 12 weeks (6-9 inches long) Fetal Skeleton 275 bones 12 weeks (6-9 inches long) Why so many more bones than an adult?

Anatomy of Long Bone (Typical) Consists of several major parts: (1) Epiphysis – expanded ends of the bone (2) Diaphysis – shaft of the bone (3) Articular Cartilage – hyaline cartilage at both ends of the bone (4) Periosteum – tough membrane-like covering over the entire bone, except for the articular cartilage. Connects with tendons and ligaments and forms bone tissue.

Anatomy of Long Bone (Typical) The Medullary cavity is the hollow chamber found inside the diaphysis that connects to spaces in spongy bone. The cavity is filled with soft specialized tissue called bone marrow. *Red Marrow – found in spongy bone in adults and produces blood cells. Contains mature and immature red blood cells, white blood cells, and the stem cells that produce them *Yellow Marrow – fat storage that replaces the red marrow in the diaphysis throughout childhood. Important energy reserve. Endosteum – lining of the medullary cavity

Anatomy of a Long Bone spongy bone Proximal compact bone epiphysis Endosteum diaphysis epiphyseal line yellow marrow Sharpey’s fibers Distal epiphysis periosteum hyaline cartilage

Bone Tissue Compact Bone Two types of bone tissue: (1) Compact (cortical) bone – walls of diaphysis that are solid and strong (2) Spongy (cancellous) bone – found in epiphysis and covered with a thin layer of compact bone. Has many branching, bony “plates” Spongy Bone

Microscopic Bone Structure Osteocytes are mature bone cells. Recall bone histology slide… Osteon

Microscopic Bone Structure Several components: Osteocytes enclosed in tiny chambers called lacunae and form a concentric ring (layers) around a passageway called the haversian canal. Thin layers of bone matrix are called lamellae Osteocytes connected by minute branches called canaliculi that allow nutrient transfer and osteocyte communication Haversian canals are connected by passages called Volkmann’s canals, that contain blood vessels and nerve fibers. Except at joints, the outer surfaces of bones are covered by a periosteum layer. Circular layers of matrix and osteocytes along with the haversian canal make up a unit called the osteon (haversian system)

Microscopic Bone Structure

Bone Development and Growth Two types of bone based on the way that bone forms: (1) Intramembranous bones – broad, flat bones of the skull that form from membrane-like sheets of connective tissue (2) Endochondrial bones – all other bones

Bone Development and Growth Bones first form as hyaline cartilage. The cartilage gradually changes into bone tissue, a process called OSSIFICATION. Ossification begins near the middle of the diaphysis in an area called the PRIMARY OSSIFICATION CENTER. Later the bone begins to ossify in the epiphysis – these areas are called SECONDARY OSSIFICATION CENTERS.

Bone Development and Growth As long as growth is occurring, a “band” of cartilage (called an epiphyseal disk, or growth plate) remains between the diaphysis and the epiphysis. Bones increase in length as these cartilage cells continue to reproduce and ossify. Cartilage cells form cells called OSTEOBLASTS. Osteoblasts produce new bone matrix by making and releasing proteins and organic components of the matrix. They also assist in elevating local concentrations of calcium phosphate and promote the deposition of calcium salts in the matrix. Once the osteoblast is completely surrounded by bone matrix, it now becomes an osteocyte.

Bone Development and Growth Appositional growth describes an increase in the width of the bone. Growth in thickness of the bone occurs as osteoblasts from beneath the periosteum produce bone matrix and build compact bone just beneath the periosteum. Bone tissue is constantly replaced as OSTEOCLASTS dissolve bone tissue from within the medullary cavity, a process called resorption. At the same time, new bone is added to the outside of the bone, increasing the width.

Bone cells that aid in remodeling Osteoblast Builds new bone Osteocyte Mature bone cell Osteoclast Eats/dissolves bone

Bone Remodeling Mineral and organic components of bone matrix are constantly being recycled and renewed through the process of bone remodeling. Continues throughout your adult life as part of normal bone maintenance Remodeling can replace bone matrix and therefore change the bone, or can change the bone shape, internal structure, and mineral content of the bone

Bone Remodeling Through the remodeling process older mineral deposits are removed from bone and released into circulation at the same time that circulating minerals are being deposited. The interplay between osteocytes, osteoblasts, and osteoclasts is required for bone modeling to occur. Turnover rate of bone is high: young adults about 1/5 of the entire skeleton is recycled and replaced every year. Not every part of every bone is changed; EX: spongy bone in femur head replaced 1-2 times/year versus compact bone remain unchanged.

Bone Remodeling Because of their similarity to calcium, heavy metals like uranium or plutonium can be incorporated into bone matrix. Over many years, the continual turnover of bone can have detrimental health effects. EX: Chernobyl in 1986 deposited radioactive compounds into bones of exposed individuals. Over time, radiation released by their bones resulted in cancer.

Effects of Exercise on Bone The high turnover rate gives bone the ability to adapt to new stresses. Because bones are adaptable, their shapes reflect the forces applied to them. EX: bumps and ridges on bone reflect muscle attachments. If muscles are more powerful, the corresponding attachment sites become more prominent/larger to withstand greater force Muscle attachment more pronounced in archer’s bone than normal radius.

Exercise Effects on Bone Exercise encourages bone growth and strength. Skeletal muscles pull against the bone, making the bone remodel to become stronger and more dense.

Joints Three basic joints (articulations): 1. Synarthrotic joints 2. Amphiarthrotic joints 3. Diarthrotic joints

Synarthrotic Joints Synarthrotic joints are immoveable joints that have junctions called SUTURES. Examples of synarthrotic joints include the bones in the skull.

Amphiarthrotic Joints Amphiarthrotic joints are slightly moveable joints. Examples include the vertebrae.

Diarthrotic Joints Diarthrotic joints are freely moveable joints, like the shoulder, knee, elbow, wrists, fingers, etc. These joints are enclosed within a fibrous capsule that contains a lubricating fluid called SYNOVIAL FLUID. These are also known as SYNOVIAL JOINTS.

Ligaments VS Tendons Ligaments connect BONE TO BONE Tendons connect MUSCLE TO BONE