Skeletal system

A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the organs of the body, produce red and white blood cells, store minerals, help regulate acid-base homeostasis, provide structure and support for the body, and enable mobility and hearing. Bones come in a variety of shapes and sizes and have complex internal and external structures.

bony structure found in vertebrates

long, thin, tubular structure made up of nervous tissue

In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs, heart, and other vital organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.

A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole. They are constructed to allow for different degrees and types of movement. Some joints, such as the knee, elbow, and shoulder, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit very little movement (only during birth) in order to

Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and the bronchial tubes, and the intervertebral discs. In other taxa, such as chondrichthyans and cyclostomes, it constitutes a much greater proportion of the skeleton. It is not as hard and rigid as bone, but it is much stiffer and much less flexi

cells and soft materials in the hollow space of long bones

internal framework of the human body

Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.

A tendon or sinew is a tough band of dense fibrous connective tissue that connects muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tension.

A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have ligaments.

one of the group of foot bones forming the lower part of the ankle joint

bones of hand

The stapes or stirrup is a bone in the middle ear of humans and other tetrapods which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the footplate (or base) to transmit sound energy through the oval window into the inner ear. The stapes is the smallest and lightest bone in the human body, and is so-called because of its resemblance to a stirrup ().

cartilage of spine

set of bones which connects the arm to the axial skeleton on each side

bone of the carpus

bone of the wrist

Osteoblasts (from the Greek combining forms for "bone", ὀστέο-, osteo- and βλαστάνω, blastanō "germinate") are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.

bone in the hand

An osteoclast () is a type of bone cell that removes bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium. An odontoclast (/odon·to·clast/; o-don´to-klast) is an osteoclast associated with the absorption of the roots of deciduous teeth.

bone in the wrist

thumb|300 px|right|Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, IGF) signalling. Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue: Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilag

bone embedded within a tendon or muscle

The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartilage", a type of hyaline cartilage.) Endosteum lines the inner surface of the medullary cavity of all long bones.

bone of the ankle

bone of the wrist

An osteocyte, an oblate-shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. The adult human body has about 42 billion of them. Osteocytes do not divide and have an average half life of 25 years. They are derived from osteoprogenitor cells, some of which differentiate into active osteoblasts (which may further differentiate to osteocytes). Osteoblasts/osteocytes develop in mesenchyme.

thumb|upright=1.2|Endoskeleton of a swordfish

An epiphysis (; : epiphyses) is one of the rounded ends or tips of a long bone that ossify from one or more secondary centers of ossification. Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). During formation of the secondary ossification center, vascular canals (epiphysial canals) stemming from the perichondrium invade the epiphysis, supplying nutrients to the developing secondary centers of ossification. At the joint, the epiphysis is covered with articular cartilage; below that covering is a zone s

the part of the skeleton that consists of the bones of the skull and trunk of a vertebrate

part of a long bone where growth takes place

right|371x371px|thumb|Diagram of a typical long bone showing both compact (cortical) and cancellous (spongy) bone. thumb|Osteons on cross-section of a bone

right|250px

type of cartilage found on many joint surfaces

the portion of the skeleton of vertebrates consisting of the bones or cartilage that support the appendages

thumb|right|Closeup of a Heloderma|helodermatid's skin, revealing the osteoderms thumb|Armadillo skeleton, with shell made of osteoderms (displayed at the Museum of Osteology) Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amphibians), various groups of dinosaurs (most notably ankylosaurs and stegosaurians), phytosaurs, aetosaurs, placodonts, and hupehsuchians (marine reptiles with possible ichthyosaur a

The perichondrium (from Greek and ) is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two separate layers: an outer fibrous layer and inner chondrogenic layer. The fibrous layer contains fibroblasts, which produce collagenous fibres. The chondrogenic layer remains undifferentiated and can form chondroblasts. Perichondrium can be found around the perimeter of elastic cartilage and hyaline cartilage.

Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of cartilage that contains type I collagen in addition to the normal type II.

unit of the skeleton of some marine invertebrates, made of carbonate calcium or silica

A condyle (; , from ; κόνδυλος knuckle) is the round prominence at the end of a bone, most often part of a synovial joint – an encapsulated articulation with another bone. It is one of the markings or features of bones, and can refer to: On the femur, in the knee joint: Medial condyle Lateral condyle On the tibia, in the knee joint: Medial condyle Lateral condyle On the humerus, in the elbow joint: Condyle of humerus (Condylus humeri) On the mandible, in the temporomandibular joint: Mandibular condyle On the occipital bone, in the atlanto-occipital joint: Occipital condyles

thumb|upright=1.2|Fossil skeletal parts from extinct Belemnitida|belemnite cephalopods of the [[Jurassic – these contain mineralized calcite and aragonite.]]

midline joint between the parietal bones of the skull

dense, fibrous connective tissue joint on the posterior aspect of the skull

connective tissue joint of the skull

series of microscopic tubes in the cortical bone

piece of bone in the breathing passage of humans and other animals

cartilaginous precursor of the jaw

Osteosclerosis is a disorder characterized by abnormal hardening of bone and an elevation in bone density. It may predominantly affect the medullary portion and/or cortex of bone. Plain radiographs are a valuable tool for detecting and classifying osteosclerotic disorders. It can manifest in localized or generalized osteosclerosis. Localized osteosclerosis can be caused by Legg–Calvé–Perthes disease, sickle-cell disease and osteoarthritis among others. Osteosclerosis can be classified in accordance with the causative factor into acquired and hereditary.

bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax

The metaphysis (: metaphyses) is the neck portion of a long bone between the epiphysis and the diaphysis. It contains the growth plate, the part of the bone that grows during childhood, and as it grows it ossifies near the diaphysis and the epiphyses. The metaphysis contains a diverse population of cells including mesenchymal stem cells, which give rise to bone and fat cells, as well as hematopoietic stem cells which give rise to a variety of blood cells as well as bone-destroying cells called osteoclasts. Thus the metaphysis contains a highly metabolic set of tissues including trabecular (spo

extra bone piece that can occur within a suture (joint) in the skull

bones that are as wide as they are long

cartilaginous bone development that forms the long bones

Midline joint in the frontal bone of the forehead

area inside a bone where marrow is stored

Hypochondroplasia (HCH) is a developmental disorder caused by an autosomal dominant genetic defect in the fibroblast growth factor receptor 3 gene (FGFR3) that results in a disproportionately short stature, micromelia and a head that appears large in comparison with the underdeveloped portions of the body. It is classified as short-limbed dwarfism.

Channels in bones for blood vessels

An epicondyle () is a rounded eminence on a bone that lies upon a condyle (epi-, "upon" + condyle, from a root meaning "knuckle" or "rounded articular area"). There are various epicondyles in the human skeleton, each named by its anatomic site. They include the following:

bone of the index finger