THE SKELETAL SYSTEM & JOINTS

cells

There are four major types of ___: Osteoprogenitor (Osteogenic) Osteoblasts Osteocytes (the most common type of cell in mature bone tissue.) Osteoclasts

Osteocytes

are known as "mature bone cells" and are the principal cells of bone tissue. They maintain the daily cellular activities of bone tissue.

compact bone

compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name implies, cortical bone forms the cortex, or outer shell, of most bones.

endosteum

—thin epithelial membrane that lines medullary cavity

medullary cavity

(or marrow) cavity Tube-like, hollow space in diaphysis Filled with yellow marrow in adult

epiphyses

-Both ends of a long bone, made of cancellous bone filled with marrow -Bulbous shape -Function is to provide attachments for muscles and give stability to joints

diaphysis

-Main shaft of long bone -Hollow, cylindrical shape and thick, compact bone -Function is to provide strong support without cumbersome weight

Q- Describe the functions of bones, and know the classifications of bones.

-Support - structural support for the entire body. -Protection - for example, ribs protect the heart, ribs, liver; skull protects the brain; vertebral column protects the spinal cord. -Leverage & Movement -Storage - calcium, phosphate and fat. - Blood cell production

Q Parathormone:

A hormone that is made by the parathyroid glands and is critical to maintaining calcium and phosphorus balance.

resorption ( Q)

Bones grow in diameter by the combined action of osteoclasts and osteoblasts Osteoclasts enlarge the diameter of the medullary cavity Osteoblasts from the periosteum build new bone around the outside of the bone

osteoclasts + osteoblasts

Bones grow in diameter by the combined action of osteoclasts and osteoblasts Osteoclasts enlarge the diameter of the medullary cavity Osteoblasts from the periosteum build new bone around the outside of the bone During breakdown of bone, osteoclasts release calcium into blood and increase circulating levels Osteoclasts which are known as "bone breakers." These cells develop from circulating monocytes. Their function is resorption (degradation) of bone. They play a very important role in bone development, growth, and repair of bone.

spongy bone

Compared to compact bone, cancellous bone has a higher surface area to mass ratio because it is less dense. This gives it softer, weaker, and more flexible characteristics. Cancellous bone is typically found at the ends of long bones, proximal to joints and within the interior of vertebrae. Cancellous bone is highly vascular and frequently contains red bone marrow where haematopoiesis, the production of blood cells, occurs Trabeculae appear and join in a network to form spongy bone

epiphyseal plate

Epiphyseal plate is composed of four layers: "Resting" cartilage cells—point of attachment joining the epiphysis to the shaft Zone of proliferation—cartilage cells undergoing active mitosis, causing the layer to thicken and the plate to increase in length Zone of hypertrophy—older, enlarged cells undergoing degenerative changes associated with calcium deposition Zone of calcification—dead or dying cartilage cells undergoing rapid calcification

epiphyseal line

The EPIPHYSEAL LINE is located at the junction of the epiphysis and diaphysis (a region called the "metaphysis") in adult bone. The epiphyseal line is a remnant of the EPIPHYSEAL PLATE, which is a cartilage plate that serves as a growth area for long bone lengthening. The epiphyseal plate allows the diaphysis of the bone to increase in length until early adulthood. When growth stops, the epiphyseal plate cartilage is replaced with bone, then becoming the epiphyseal line.

Q -1 Endochondral ossification http://study.com/academy/lesson/bone-growth-development-factors-endochondral-ossification.html

Most bones begin as a cartilage model, with bone formation spreading essentially from the center to the ends Periosteum develops and enlarges, producing a collar of bone Primary ossification center forms In long bones the blood vessels enter the cartilage model at the midpoint of the diaphysis Bone grows in length as endochondral ossification progresses from the diaphysis toward each epiphysis Secondary ossification centers appear in the epiphysis, and bone growth proceeds toward the diaphysis Epiphyseal plate remains between diaphysis and each epiphysis until bone growth in length is complete Epiphyseal plate is composed of four layers: "Resting" cartilage cells—point of attachment joining the epiphysis to the shaft Zone of proliferation—cartilage cells undergoing active mitosis, causing the layer to thicken and the plate to increase in length Zone of hypertrophy—older, enlarged cells undergoing degenerative changes associated with calcium deposition Zone of calcification—dead or dying cartilage cells undergoing rapid calcification

osterprogenitor cells

Osteoprogenitor cells are types of cells that work in the growth or repair of bones. These cells originate from stem cells and are created by progenitor cells. Also known as preosteoblasts, osteoprogenitor cells are found in the bone marrow. The bone marrow is comprised of several cellular layers, and it is one of these layers that house these preosteoblast cells.

Q- CALCINOTIN + PARATHROMONE . Describe how calcitonin and parathromone (PTH) influence blood calcium levels.

Protein hormone produced in the thyroid gland Produced in response to high blood calcium levels Stimulates bone deposition by osteoblasts Inhibits osteoclast activity Far less important in homeostasis of blood calcium levels than parathyroid hormone -Calcitonin is involved in helping to regulate levels of calcium and phosphate in the blood, opposing the action of parathyroid hormone. This means that it acts to reduce calcium levels in the blood. Calcitonin reduces calcium levels in the blood by two main mechanisms: It inhibits the activity of osteoclasts, which are the cells responsible for breaking down bone. When bone is broken down, the calcium contained in the bone is released into the bloodstream. Therefore, the inhibition of the osteoclasts by calcitonin directly reduces the amount of calcium released into the blood. It can also decrease the resorption of calcium in the kidneys, again leading to lower blood calcium levels.

Q - 1. Know the difference between (1) intramembranous ossification and (2) endochondral ossification. Give example of which bones form from each of the two process.

_______Occurs within a connective tissue membrane Most skull bones and the clavicles form by intramembranous ossification Flat bones begin when groups of cells differentiate into osteoblasts Osteoblasts are clustered together in centers of ossification where they secrete matrix material and collagenous fibers Large amounts of ground substance accumulate around each osteoblast Collagenous fibers become embedded in the ground substance and constitute the bone matrix Bone matrix calcifies when calcium salts are deposited Trabeculae appear and join in a network to form spongy bone Apposition growth occurs by adding of osseous tissue