Transcript 7-1 Bone Formation - Rock Hill High School

Bone Formation
Begins as cartilage or fibrous membranes in embryos –
ossification replaces it with bone.
7-1
Fetal Skeleton at 12 Weeks
7-2
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
7-3
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
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
7-5
Ion Imbalances
• 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
7-6
Hormonal Control of Calcium Balance
Calcitriol, PTH and calcitonin maintain
normal blood calcium concentration.
7-7
Calcitriol (Activated Vitamin D)
7-8
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???
7-9
Correction for Hypercalcemia
7-10
Correction for Hypocalcemia
Calcitriol
Increased absorption
from intestines
7-11
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
7-12
Fractures and Their Repairs
7-13
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.
7-14
Healing of Fractures
Hematoma
Fibrocartilage
Callus
Bony
Callus
6 weeks
Remodeling
3-4
months
7-15
Joints (Articulations)
Classified two ways:
1) Function – degree of movement
2) Structure – fibrous tissue, cartilage,
or joint cavities separate the bones
7-16
Functional
Structural
Synarthroses
Fibrous
Amphiarthroses
Cartilaginous
Diarthroses
Synovial
7-17
Synarthroses/
Fibrous
joints
7-18
Amphiarthroses/
Cartilaginous
Joints
7-19
Diarthrotic/Synovial Joints
Condyloid
7-20
Synovial Joint Structure
7-21
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.
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.
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
7-22