Bone Physiology Flashcards
What is bone histogenesis?
Bone formation and growth
What is ossification?
The appearance of osteoblasts and the laying down of osteoid/the matrix.
What is calcification?
Deposition of hydroxyapatite.
What are the two kinds of ossification?
Intramembranous (inside membrane) and endochondral (inside cartilage)
Where does intramembranous ossification take place? Examples?
Takes place within membranes of connective tissue. Bones of skull, growth of short bones, thickening of long bones.
Where does endochondral ossification take place? examples?
Takes place within a piece of hyaline cartilage whose shape is a small version of the bone to be formed. Formation of long and short bones.
What is the process of endochondral ossification?
Growth of cartilage, calcification of cartilage, destruction of chondrocytes, leaving cavities, invasion by osteoblasts, synthesis of osteoid, calcification of bone.
How does formation of long bones take place?
They start out as hyaline cartilage with no blood supply, dying chondrocytes leave spaces for osteoblasts and secrete osteoid, then the primary ossification center is formed in the middle of diaphysis - this later becomes the marrow cavity - as it becomes larger, secondary ossification centers are formed in flared portions of epiphyses. By birth, only site of cartilage is at epiphyseal plates.
How is a bone fracture repaired?
When a bone is fractured, hemorrhage results in clot. Destruction of bone matrix and death of bone cells. Macrophages remove debris. Fibroblasts from periosteum and endosteum invade area and differentiate into chondroblasts. Cartilage replaced by intramembranous and endrochondral ossification, resulting in immature bone temporarily bridging fracture site (callus).
What is Wolff’s Law?
“Every change in the form and function or function alone of a bone produces change in the architecture and external form of the bone”
How is bone changed by different stressors?
Pressure causes bone resorption and pulling/tension causes bone formation
What is calcium important for?
Muscle contraction, transmission of nerve impulses and in ECF, coagulation of blood.
How is blood calcium levels maintained at a constant 10 mg/dl?
Blood and bone calcium are in continuous interchange.
If blood calcium drops, what is the rapid mechanism to reach constant level?
Transfer of ions from hydroxyapatite crystals to interstitial fluid and then to blood. Cannot accommodate large demands.
What is the slow mechanism?
The parathyroid hormone activates and increase the number of osteoclasts which resorb bone and liberate calcium. The “C” cells of the thyroid release calcitonin which inhibits osteoclasts.
What are the three effector sites that aid in slow mechanisms to fill blood calcium levels?
The GI tract increases calcium absorption from diet, the bone is resorbed via activation of osteoclasts that release calcium, and the kidney holds on to calcium and dumps more potassium
What is the Law of Mass Action?
The Law of Mass Action says that the levels of blood calcium and phosphorus automatically change with each other to maintain an overall constant. Because of this law, there is not a hormone to regulate phosphorus in the body.
What does a nutritional deficiency of calcium lead to?
Nutritional deficiency of calcium causes secondary hyperparathyroidism. This can be from not consuming enough calcium, too much phosphorus or if kidney is not doing its job.
What is primary hyperparathyroidism?
The disease of overstimulated parathyroid gland or parathyroid tumor
How do growth hormones effect bones?
Growth hormone effects epiphyseal cartilage. Too little=dwarfism, too much during growth years=gigantism, too much in mature bone=acromegaly, increased bone width
How do sex hormones effect bones?
Sex hormones stimulate bone formation, precocious presence results in small stature because epiphyseal cartilage replaced by bone too soon. Horses are castrated early to gain taller stature because epiphyseal cartilage remains longer.
