Skeletal System TEST #2 Flashcards
How does compact (dense) bone differ from cancellous (spongy) bone?
Compact bone: tissue that is dense, hard, and forms the protective exterior portion of all bones; has bone cells embedded in extracellular matrix that is primarily collagen and inorganic salts; resists compressive forces
Cancellous bone: tissue inside compact bone which is very porous (full of tiny holes); has bone cells embedded in mineral salts and collagen fibers; has trabecular (branching, bony plates with irregular spaces between them); is on ends (and insides) of long bones; is strong and light; is subject to compressional forces
What is osteology?
The study of bones
What is an osteocyte?
Mature bone cell encased with body extracellular matrix
What is an osteoblast?
Cell which deposits (makes or builds) bone
What is an osteoclast?
Cell which resorbs (breaks down or cuts up) bone
Describe and locate the microscopic structures of compact bone
Osteocytes are located in tiny, bony chambers called lacunae
Osteocytes can communicate with one another through tiny channels known as canaliculi
Osteocytes and layers of extracellular materials are clustered around a central canal (housing blood vessels and nerves) to form a cylinder-shaped unit called the osteon
Each osteon (also called a Haversian system) is the structural and functional unit of compact bone
Many osteons cemented together form compact bone
How does the microscopic structure of spongy bone differ from that of compact bone?
Spongy bone doesn’t have central canals around which bones cells aggregate; instead, cells lie within bony ridges called trabeculae and get nutrients from substance diffusing through canaliculi that lead to the surface of the trabeculae.
Which of the four major tissue types (epithelial, connective, muscular, nervous) are found in bone?
Primarily connective and nervous: connective (dense fibrous connective–tendons; supportive connective–bone and cartilage; fluid connective–blood), nervous (nerve fibers)
When do bones first begin to form?
The first two weeks of prenatal development
How do intramembranous bones differ from endochondral bones?
Intramembranous bones: are mostly broad, flat bones like the skull bones
Endochondral bones:include most of the bones of the skeleton
How does the origin of intramembranous bones differ from the encochonfral bones?
Intramembranous bones: originated with sheet-like layers of connective tissue.
Endochondral bones: begin as masses of hyaline cartilage that act as a model upon which bone is later formed
What are the first steps involved in long bone development?
Hyaline cartilage acts as a model for long bone development that starts during the first weeks of prenatal development
Hyaline cartilage tissue breaks down and the periosteum (with osteoblasts and blood vessels) develops
Osteoblasts first form spongy bone in the primary ossification center (space previously occupied by the cartilage). Osteoblasts next deposit a thin layer of compact bone around the spongy bone. This will eventually become the diaphysis
Developing bone thickens as compact bone is deposited on the outside.
As compact bone forms on the outside, osteoclasts erode tissue on the inside, creating the medullary cavity
The epiphysis remain cartilaginous and grow. Secondary ossification centers appear in the epiphysis and spongy bone forms in all directions from them
A band of cartilage known as the epiphyseal plate remains between the primary ossification centers of the diaphysis and the secondary ossification center of the epiphyses.
How does the long bone increase in length? When does it stop lengthening?Growth at the epiphyseal plate causes the bone to grow in length
Actively dividing cartilage cells (nearer to the end of the plate than to the end of the bone) lay down layer upon layer of new cartilage cells which extend out from the epiphyseal plate
The cartilage cells become calcified.
Osteoblasts break down the calcified matrix
Osteoblasts deposit bone tissue in place of calcified cartilage
A long bone continues to lengthen as long as the cartilaginous cells of the epiphyseal plate are active
Once the ossification centers of the diaphysis (primary ossification center) and epiphysis (secondary ossification center) meet and the epiphyseal plates ossify, lengthening stops. The epiphyseal plates of children are very well defined, while those of adults whose bone growth has ceased are indistinct
What is meant by the phrase “homeostasis of bone tissue”?
Resorption (breaking down of bone by osteoclasts) and deposition (making bone by osteoblasts) are regulated so the total mass of bone tissue within an adult skeleton remains relatively constant throughout life
What organ system regulates bone resorption and deposition?
The endocrine system. Resorption occurs when parathyroid hormone stimulates osteoclasts to break down bone. Deposition occurs when calcitonin hormone from the thyroid gland stimulates osteoblasts to form bone. A negative feedback system is involved.
