Module 5 Flashcards
Hyaline Cartilage
Bones start as Hyaline Cartilage then converts to bone. Growth plates & articular ends of long bones are lined and are composed of it.
Chondroblasts: make new matrix on surface of cartilage
Chondrocytes: Once chondroblast is surrounded by matrix it becomes a chondrocyte
Hyaline Cartilage: perichondrium
Perichondrium surrounds the cartilage.
Outer fibrous layer: dense fibrous connective tissue
Inner chondrogenic layer: contains chondroblasts
Articular cartilage lacks perichondrium
Appositional growth
Interstitial growth
Appositional growth occurs on the surface of the cartilage as chondroblasts lay down new layers of matrix.
Interstitial growth occurs within the cartilage as chondrocytes proliferate & create new matrix
Axial skeleton
Bone & skull, vertebral column & rib cage
Appendicular skeleton
Upper & lower limbs, shoulder & hip bones
Hydroxyapatite
Bone is made up of extracellular matrix composed of (65%) calcium phosphate crystals-Hydroxyapatite- which surrounds collagen fibers (35%)
Calcium phosphate provides the weight bearing strength
Collagen fibers provide tensile strength-allowing bending but not breaking (excessive bending =decrease hydroxyapatite to collagen)
Increased fractures = more hyrdroxyapatite to collagen
Compact bone/ cortical bone
Densely packed aversion systems (osteons). Minimal pores
Spongy bone
Composed of a network of boney charts (trabeculae) with spaces between them. Has pores to make it light
The outer surface of all bones is compact bone and the innermost layer of all bones is cancellous bone
Mesenchymal cells become bone marrow
Yellow marrow
Red marrow
Yellow marrow: fat cells serve as a storage reservoir as it can be converted back to red marrow under severe blood loss. At birth red marrow is converted to yellow with age
Red marrow is mesenchymal cells known as hematopoietic tissue. Red blood cells, platelets & most white blood cells are produced by red marrow. Red marrow in adults-Flat bones like ribs, vertebrae & pelvic bones
Osteoclast
Bone destroying, remodeling, reabsorption. Large, multinucleated cells located on the outer & inner surfaces of bone.
Osteoblast
Bone forming, building
Osteocytes
Entrapped osteoblasts which have secreted the portein mixture of osteoid, which mineralizes to become bone= mature bone cells= osteocyte
Structure
Lacunae
Spaces entrapped osteocytes form in mineralized bone
Canaliculi
osteoblasts start to harden and send out multiple processes that reach out & join with other osteoblasts that are becoming entrapped
Lamellae
Osteocytes are trapped in concentric layers called lamellae that surround a central canal containing blood & nerves
Osteon
concentric layers combined with the central canal form an osteon which is the functional unit of compact bone. Osteoblasts are stimulated to increase the production of osteoid (bone growth) by the actions of growth hormones, thyroid hormones & sex hormones
Describe bone breakdown/resorption
Osteoclasts form pits called resoption pits. pits are left behind as the osteoclast breaks down bone & moves along the surface. Pits are filled with new bone matrix by osteoblasts.
1) Liberation of minerals
2) enzymatic digestion of the collagen.
Osteoclast resorption
Osteoclasts secrete lysosomal enzymes to digest the organic matrix & protons (h+), donated from citric & latic acid to create an acidic environment which frees the minerals. The “digested” bone matrix is endocytosed into the osteoclast & into the blood.
This is homeostatic in maintaining blood Ca++ level
Activation of osteoclasts
Parathyroid hormone releases PTH when Ca++ is low
Inactivation of osteoclasts
Osteoprogerin secreted by osteoblasts & calcitonin secreted by parafollicular cells of the thyroid gland inactivate it
Factors that induce osteoporosis
hormonal imbalances, smoking, petite body forms, lack of exercise, poor diet, overuse of meds
