BONE CELLS BONE DEVELOPMENT Directed Notes Osteogenic cells

BONE CELLS & BONE DEVELOPMENT Directed Notes

Osteogenic cells osteoblast osteocyte

BONE CELLS: Osteoprogenitor (Osteogenic) Cells • Embryonic cells that divide to produce osteoblasts o Are located in inner endosteum o Assist in fracture repair

Osteoblasts o Immature bone producing cells that secrete matrix compounds § not yet calcified to form bone § Osteoblasts surrounded by osseous tissue become osteocytes

Osteocytes o Mature bone cells that maintain the bone matrix o Do not divide o OSTEON = one unit of bone tissue

SUMMARY o Osteogenic cells osteoblast osteocyte

Osteoclasts = “break bone” o Breaks down bone § Dissolve bone matrix and release stored minerals which is taken up by the blood § Causes osteoporosis (loss of bone tissue) if bone is unable to repair

Osteogenesis: n bone formation Ossification: nthe process of replacing other tissues with bone

The 2 main forms of ossification: 1) Intramembranous ossification ( dermal ossification) n occurs in the dermis n Produces bones such as mandible and clavicle 2) *Endochondral ossification n Bone replaces cartilage n Most bones formed this way n Observed easily in long bones

ENDOCHONDRAL OSSIFICATION STEP 1) Chondrocytes in the center of hyaline cartilage enlarge, calcify, and die, leaving cavities in cartilage

STEP 2) Blood vessels grow around the edges of the cartilage and cells begin to change to osteoblasts Produces layer of superficial bone around shaft which becomes compact bone

STEP 3) Blood vessels enter the cartilage spongy bone develops at the primary ossification center in the shaft where bone tissue replaces cartilage creates a marrow cavity

STEP 4) Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers

STEP 5) Epiphyses fill with spongy bone and there is no cavity in this region of the bone On the ends; hyaline cartilage that remains is ARTICULAR CARTILAGE

o At the Epiphyseal plate (between the diaphysis and epiphysis) the bone grows lengthwise as bone tissue replaces cartilage

Epiphyseal Plates become Epiphyseal Lines § When long bone stops growing, after puberty, epiphyseal cartilage disappears at the growing epiphyseal plate and an epiphyseal line is visible on X-rays.

BONE METABOLISM Directed Notes But first let’s see if this helps… Bob and Claude? ? ? http: //www. youtube. com/watch? v=5 gpysd. G 1 Ho. E

Bone Metabolism o Bone stores 99% of total calcium in body o Calcium ions involved with many body systems n nerve & muscle cell function n blood clotting n enzyme function in many biochemical reactions

Bone Homeostasis/Metabolism

Details… that you don’t have to know… G-protein activates adenylate cyclase to convert ATP to c. AMP in the cytosol G proteins (guanine nucleotid -binding proteins) Proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell They communicate signals from many hormones, neurotransmitters, and other signaling factors

Bone Metabolism Background only… o The thyroid gland is located in the front of the neck and wraps around the trachea; has a shape that is similar to a butterfly formed by two wings (lobes) and helps to regulate metabolism

Bone Metabolism Hormones o *Parathyroid hormone (PTH) is secreted if Ca+2 levels falls n n PTH gene is turned on and more PTH is secreted from gland osteoclast activity increased kidneys retain Ca+2 so it is not all lost in urine and produces calcitriol *Calcitriol is a hormone that works with PTH & promotes absorption of calcium in digestive tract & blood

Bone Metabolism Hormones o *Calcitonin is a hormone that produces the - opposite effects: if calcium level gets too high less absorption in the digestive tract, increased excretion by the kidneys, movement of calcium from the blood into the bones n n inhibits osteoclast activity increases bone formation by osteoblasts

Important Bone Metabolism Vitamins o Vitamin A: Necessary for osteoclast activity o Vitamin C: Needed to build durable bone matrix (osteoid) o Vitamin D: Calcitriol is formed from vitamin D

Bone Homeostasis Bone Tissue and Exercise o Pull on bone by skeletal muscle and gravity is mechanical stress. o Lack of mechanical stress results in bone loss n reduced activity while in a cast or bedridden person o Weight-bearing exercises build bone mass

Osteoporosis Prevention (or decrease in severity) o Calcium supplements, weight-bearing exercise, & hormone replacement therapy (including a form of calcitonin) n behavior when young may be most important factor!

Bone Remodeling o Ongoing process o Osteoclasts secrete enzymes and acids to break down bone n This releases calcium and other minerals of bone for resorption by blood o Osteoblasts rebuild osteons

Bone Remodeling o Continual remodeling of bone matrix along lines of mechanical stress n The distal femur is fully remodeled every 4 months

Fracture Repair A fracture is break in a bone o STAGE 1 Inflammation) Repair starts with formation of fracture hematoma: damaged blood vessels produce clot, bone cells die n new capillaries grow into damaged area o STAGE 2 Repair) Callus (healing tissue) formation: n n fibroblasts lay down collagen fibers chondroblasts produce cartilage to span the broken areas of the bone

Fracture Repair o Bone Formation: n osteoblasts secrete spongy bone that joins the broken areas of bone n lasts 3 -4 months o Bone remodeling: n compact bone replaces the spongy in the callus n surface is remodeled back to normal shape

Video Clip o Principles of Fracture Healing o http: //www. youtube. com/watch? v=VZF 3 x ic. Lt. Tw