Endochondrial Ossification occurs in 6 steps (which do not only occur in long bones):
a. Development of a cartilage model: this occurs in the early weeks of embryonic development as mesencymal cells cluster and differentiate into chondroblasts and secrete matrix to make a template. The model is made of avascular hyaline cartilage surrounded by a perichondrium of BV and nutrients.
b. Growth of the cartilage model: template grows in length by interstitial growth and diameter by appositional growth. As the chondrocytes grow, they rupture and die increasing the pH of the cartilage matrix and results in beginning of calcification. This persists quickly as positive feedback takes hold and more cells die (due to lack of nutrients) and more cartilage is calcified. Some tissues descintergrate and create air pockets
c. Development of the primary ossification center: This primary ossification center is located along the diaphysis of the bone model in the perichondrium where an increase in vascularity triggers mesenchymal cells to become osteogenic cells. Before all cells in perochondrium were chondrocytes but now the perichondrium convert to a periosteum as osteoblasts differentiate and secrete osteoid to form the bone collar. The bone collar is a ring of firm stable bone tissue which stabilizes the diaphysis. This forms after the matrix starts to calcify.
d. Invasion of the periosteal bud: is located ___________________________________________. The periosteal bud is a collection of structures atht invaginates into the central cavity containing a nutrient artery, vein, lymph vessels, nerve fibers, osteogenic cells, osteoblasts/clasts, and hematopoetic stem cells. These vessels begin to branch and spread longitudinally as osteoclasts work to hollow out the cavity by phagocytosis of cartilage matrix that remains. Osteoblasts secrete spongy bone on the internal surface of the bone collar; the medullary cavity forms at the ossification center and hematopoetic stem cells form the red marrow. Anything that remains cartilage can technically still grow.
e. Development of the secondary ossification center forms at the epiphyses of the bone and with this ossification center, no medullary cavity forms and ossification starts internally and moves outward. Forms at or around the time of birth in most bones of the body. It *At birth babies have: bony diaphysis, growing/widening medullary cavity, and a cartilage epiphysis
f. Formation of the articular cartilage and epiphyseal plates: the region between the epiphysis and diaphysis at either end is called the metaphysis. This region contains cartilage that can grow in length after birth (interstitial, stops in adolesence and early 20s). the edges of bones which articulate with other bones do not have periosteum on their outside but rather articular cartilage which is a thin layer atop compact bone which covers the red marrow.
Three general types of movement possible at a synovial joint:
a. Gliding→linear motion in which bones slip and slide past each other, occurs in flat bone surfaces that articulate together, not a planar movement because there is no rotation around an axis (ex. Sacroiliac joints, intercarpal/tarsal, vertebralcostal)
b. Angular movements→occur at hinge joints and can measure ROM at these joints, monoaxial (ex. Knee, elbow, ankle, interphalangeal joints)
c. Rotation→occurs at pivot joints, monoaxial rotation (ex. Between atlas and axis, proximal radioulnar joint (pronation and supination)
Six types of synovial joints:
a. Planar joints—gliding joints whose articular surfaces are flat (ex. Sacroilliac joint)
b. Hinge joints—concave articulates with convex (socket), monoaxial, movement in one plane (knee and elbow)
c. Pivot joints—rotate, the rounded end of one bone articulates with a ring formed by another bone or ligament, monoaxial, (proximal radioulnar joint)
d. Condyloid joints (ellipsoid joints)—the oval surface on the end of one bone fits into an oval depression on another, bi-axial (bones rock against eachother) and can measure angles of joints and ROM, (wrist, knuckles)
e. Saddle joints—modified condyloid joint in which concave and convex surfaces on each bone fit closlet (complementary joints), biaxial, (thumb)
f. Ball and socket joints—angular joint that allows movement in three planes (triaxial), most freely movable synovial joint (shoulder and hip joint)
Types of arthritis:
a. Osteoarthritis (OA): most common with aging women due to wear and tear on joints, enzymes destruct cartilage to the point where they become dry and cracked and friction causes pain and stiffness, bones inflame and enlarge
b. Rheumatoid arthritis (RA): autoimmune disease common in 40-50 year old women, not as common as OA but more destructive, can be triggered by bacterial or viral infection, S/S are tenderness and sstiffness of joints, affects batient bilaterally always, synovial membrane thickens and swells releasing more synovial fluid, (cartilage not affected first), overtime this fluid adheres to the articular cartilage and destroys it. The articular cartilage tries to repair itself and scarring occurs which fuses bones and therefore there is no movement at the joint (scaring and fusing = ankalasois which results in bent, stiff, immovable joints), destruction occurs during periods of active inflammation (flares) and not during calms therefore the course is variable. It is treated by trying to limit inflammation with steroids and anti-inflammatory drugs
c. Gouty arthritis: more common in men due to their higher levels of blood UA than women. It is caused by an accumulation of uric acid at a joint. Uric acid is the metabolic by product of nucleic acids and is normall removed from the blood when filtered through the kidneys and excreted out in urine. If blood uric acid levels rise, UA is deposited as crystals in joint. It can accumulate because of over production or under excretion. It is first deposited at the base of the big toe and if not treated can damage the cartilage at a joint. To treat in less severe cases, limit alcohol and red meat.