Bone Formation Begins as cartilage or fibrous membranes in embryos – ossification replaces it with bone.

Fetal Skeleton at 12 Weeks

Bone Growth and Remodeling Bones increase in length epiphyseal plate epiphyseal line is left behind when cartilage gone Bones increase in width = appositional growth osteoblasts lay down matrix in layers on outer surface and osteoclasts dissolve bone on inner surface Bones remodeled throughout life architecture of bone determined by mechanical stresses action of osteoblasts and osteoclasts greater density and mass of bone in athletes or manual worker is an adaptation to stress

Control of Growth & Remodeling Growth hormone from pituitary gland and sex hormones control long bone growth PTH (parathyroid hormone) activates osteoclasts to break down bone and release Ca+2 ions to blood if levels too low. When Ca+2 level is too high, deposits in bone matrix where mechanical stress is high.

Dwarfism Achondroplastic Pituitary long bones stop growing in childhood normal torso, short limbs spontaneous mutation during DNA replication failure of cartilage growth Pituitary lack of growth hormone normal proportions with short stature

Ion Imbalances hypocalcemia hypercalcemia Changes in calcium can be serious hypocalcemia causes excitability of nervous system if too low muscle spasms, tremors or tetany laryngospasm and suffocation hypercalcemia depresses nervous system muscle weakness and sluggish reflexes, cardiac arrest

Hormonal Control of Calcium Balance Calcitriol, PTH and calcitonin maintain normal blood calcium concentration.

Calcitriol (Activated Vitamin D)

Calcitonin Secreted by thyroid gland when calcium concentration rises too high Functions reduces osteoclast activity as much as 70% increases the number and activity of osteoblasts Can be used to treat what condition???

Correction for Hypercalcemia

Correction for Hypocalcemia Increased absorption from intestines Calcitriol

Other Factors Affecting Bone Hormones, vitamins, and growth factors Growth rapid at puberty hormones stimulate osteogenic cells, chondrocytes and matrix deposition in growth plate girls grow faster than boys and reach full height earlier (estrogen stronger effect) males grow for a longer time and taller Growth stops (epiphyseal plate “closes”) teenage use of anabolic steroids = premature closure of growth plate and short adult stature

Fractures and Their Repairs

Fractures and Their Repair Stress fracture caused by trauma car accident, fall, athletics, etc Pathological fracture in bone weakened by disease bone cancer or osteoporosis Open (simple) vs closed (compound) fractures Reduction is realignment of broken bone ends Immobilization to allow healing.

Fibrocartilage Callus Healing of Fractures Hematoma Bony Callus Fibrocartilage Callus Remodeling 3-4 months 6 weeks

Joints (Articulations) Classified two ways: Function – degree of movement Structure – fibrous tissue, cartilage, or joint cavities separate the bones

Functional Synarthroses Amphiarthroses Diarthroses Structural Fibrous Cartilaginous Synovial

Synarthroses/ Fibrous joints

Amphiarthroses/ Cartilaginous Joints

Diarthrotic/Synovial Joints Condyloid

Synovial Joint Structure

Quiz 1. _______________ is secreted by the parathyroid gland when calcium blood levels are low. It increases osteoclast population, promotes calcium resorption by the kidneys, & promotes calcitriol synthesis in the kidneys. It also inhibits collagen synthesis and bone deposition by osteoblasts. ____________ is secreted by thyroid gland when calcium concentration rises too high. It reduces osteoclast activity as much as 70% and increases the number and activity of osteoblasts. 3. ________ is made by the skin, liver, and kidneys, and behaves as a hormone that raises blood calcium concentration by: -increases intestinal absorption and absorption of calcium from the skeleton -increasing osteoclasts -promoting urinary reabsorption of calcium ions