Osseous Tissue (Bone Tissue)

Classification of Bone by Tissue Type Two basic types of Tissue 1. Compact bone Homogeneous Looks “smooth” 2. Spongy bone Small needle-like pieces of bone Many open spaces (like sponge) Keep bones light Figure 5.2b

Review: Bone is a type of connective tissue 2 Parts: 1. Cells (living) 2. Matrix (nonliving substance released by cells) A. Fiber B. Ground Substance

Formation of the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints

Bone Growth (Ossification) Epiphyseal Plate: epi- above physean- to grow plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Enclosed cartilage is digested away, opening up a medullary cavity Bone replaces cartilage through the action of osteoblasts

Bone Growth (Ossification) Bones are remodeled and lengthened until growth stops Bones are remodeled in response to two factors Blood calcium levels Pull of gravity and muscles on the skeleton Bones grow in width (called appositional growth)

1. Cells 2. Matrix Osteocytes— mature bone cells Osteoblasts— bone-forming cells (germ cells or “bud” cells) Osteoclasts —bone-destroying cells (“breakers”) A. primarily collagen fibers flexibility tensile strength (the strength to endure stretching forces) B. calcium salts (hardness) contain calcium and phosphorus great compressional strength (the strength to endure squeezing forces) 2. Matrix

About 10% of bone is replaced every year in an adult skeleton Bone Remodeling constant balance of bone deposit and removal that occurs throughout your life bone deposit occurs at a greater rate when bone is injured bone resorption allows calcium of degraded bone matrix to move into the blood. About 10% of bone is replaced every year in an adult skeleton

osteoblasts osteoclasts Maintenance of Bone bone formation bone reabsorption osteoblasts osteoclasts

Control of Remodeling Hormonal  Rising blood Ca2+ levels trigger the thyroid to release calcitonin   Calcitonin stimulates calcium salt deposit in bone   Falling blood Ca2+ levels signal the parathyroid glands to release Parathyroid hormone (PTH)   PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood 

Hormonal effects osteoblasts osteoclasts Calcitonin (CT) from thyroid bone formation bone reabsorption osteoblasts osteoclasts Calcitonin (CT) from thyroid Parathyroid hormone (PTH) from parathyroid

Before age 25 osteoblasts osteoclasts Increase bone mass bone formation bone reabsorption osteoblasts osteoclasts Before age 25

bone formation bone reabsorption osteoblasts osteoclasts Age 25-50

Age 50-on osteoblasts osteoclasts Decrease bone mass bone formation bone reabsorption osteoblasts osteoclasts Age 50-on

Stress increases bone density Stress effects bone formation bone reabsorption osteoblasts osteoclasts Stress increases bone density

Increasing bone stress can reduce or eliminate age-related bone loss

http://www.youtube.com/watch?v=yFJ4iswRiu4&feature=related