7-1

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

7-2

Fetal Skeleton at 12 Weeks

7-3

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.

7-4

7-5

Dwarfism

• Achondroplastic– 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

7-6

Ion Imbalances• Changes in calcium can be serious

hypocalcemia causes excitability of nervous system if too

lowmuscle spasms, tremors or tetanylaryngospasm and suffocation

hypercalcemia depresses nervous

systemmuscle weakness and sluggish reflexes, cardiac arrest

7-7

Hormonal Control of Calcium Balance

Calcitriol, PTH and calcitonin maintain normal blood calcium concentration.

7-8

Calcitriol (Activated Vitamin D)

7-9

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???

7-10

Correction for Hypercalcemia

7-11

Correction for Hypocalcemia

CalcitriolIncreased absorption from intestines

7-12

Other Factors Affecting Bone

• Growth stops (epiphyseal plate “closes”)– teenage use of anabolic steroids = premature

closure of growth plate and short adult stature

• 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

7-13

Fractures and Their Repairs

7-14

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.

7-15

Healing of Fractures

Hematoma Fibrocartilage Callus

Bony Callus

Remodeling

6 weeks3-4

months

Joints (Articulations)

7-16

Classified two ways: 1)Function – degree of movement2)Structure – fibrous tissue, cartilage, or joint cavities separate the bones

7-17

Functional

Synarthroses

Amphiarthroses

Diarthroses

Structural

Fibrous

Cartilaginous

Synovial

Synarthroses/ Fibrous

joints

7-18

Amphiarthroses/ Cartilaginous

Joints

7-19

7-20

Diarthrotic/Synovial Joints

Condyloid

Synovial Joint Structure

7-21

7-22

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

2. ____________ 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.

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.

Quiz