Bone Tissue chapter 7

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Dr Beth Cohen Broward College anatomy and phsio

Bone Tissue

Dynamic tissue that continually remodels itself
-connective tissue with a matrix hardened by minerals
bones make up the skeletal system

skeletal system

includes bones of the skeleton, cartilages, ligaments and other connective tissue that stabilize and connect

Functions of the skeletal system

support, protection, movement, blood formation, mineral reservoir, electrolyte balance - calcium and phosphate ions, acid-base balance - buffers blood against excessive pH changes

skeletal system

Shapes of Bones

Long bones

longer than wide
rigid levers acted upon by muscles
eg- humurus, femur, ulna, radius, tibia, fibula,

Short bones

equal in length and width
glide across one another in multiple directions
designed for strength and compactness
carpals and tarsals-little short pieces of bone

Flat bones

protect soft organs
curved but wide & thin and flat
skull(pariatal bone), sternum(breast plate), scapula(shoulder blade),

Irregular bones

elaborate shapes that don't fit into the other categories
vetebrae

Structure of a Long Bone

Parts of a long bone are the:
Epiphysis (ends)
Diaphysis (shaft)
Medullary (marrow) cavity
Endosteum - contains osteoprogenitor cells
Periosteum - membrane around the bone
fibrous layer
osteogenic layer
Articular cartilage - hyaline cartilage covers the surface of joints

Epiphysis

ends of the bone
epi means on top

Diaphysis

shaft of the bone

Medullary

marrow cavity filled with red and yellow marrow

Endosteum

contains osteoprogenitor cells

Periosteum

membrane around the bone
fibrous layer
osteogenic layer

Articular cartilage (at joints)

hyaline cartilage covers the surface of joints
cover the tip of the epiphyses for the femur at the hip and and the knee

HISTOLOGY OF BONE

Bone consists of widely separated cells surrounded by large amounts of matrix
Four principal types of cells:
1. osteoprogenitor cells - unspecialized can divide
2. osteoblasts - form bone, secrete collagen
3. osteocytes - former osteoblasts, strain sensors that detect stress in the bone and talk to osteoblasts on the bone surface
4. osteoclasts - reabsorb bone
Matrix contains some calcium carbonate, calcium phosphate but mostly hydroxyapatite, which is the PRIMARY salt that makes bone hard.
Matrix is deposited in a framework of collagen fibers, - calcification or mineralization
salts confer hardness on bone
collagen fibers give
tensile strength
Matrix (Bone) composition =
25% water, 25% protein fibers
and 50% minerals

osteoprogenitor cells

unspecialized can divide

osteoblasts

form bone, secrete collagen

osteocytes

what bone is largely made up of
-a mature bone cell
-accounts for the majority of bone cell
-they do not divide
-maintain the protein and mineral content in the matrix which keeps the bones strong and rigid

former osteoblasts, strain sensors that detect stress in the bone and talk to osteoblasts on the bone surface

osteoclasts

reabsorb bone when there is a fracture or when the calcium ion in the blood is too high

hydroxyapatite

the PRIMARY salt that makes bone hard

Matrix (Bone) composition

25% water, 25% protein fibers
and 50% minerals
made of calcium (mineral) and collagen(protien fiber)
the combination is very tough. the collagen helps the bone be less brittle and the calcium allows it to be less rubbery

Compact Bone

Dense bone tissue consists of osteons (Haversian systems) = basic structural unit
cylinders of tissue formed from layers (lamellae)
central canal holding a blood vessel
osteocytes connected to each other and by tiny canals called canaliculi

Spongy Bone

Sponge like appearance called trabeculae
spaces filled with red bone marrow
Provides strength with little weight
trabeculae develop along bone's lines of stress
Spongy bone have few osteons, why?
Also known as, "cancellous" bone

Bone may be categorized as

compact or spongy

Intramembranous Ossification

Forms FLAT BONES (skull, sternum, mandible, and clavicle).
Multipotent mesenchymal cells differentiate directly into osteoblasts and bone is formed.
Mesenchyme  Bone
Produces flat bones of skull and clavi

Endochondrial Ossification

Goes through a cartilage model on its way to being bone.
Intramembranous ossification does not.
Endochondral ossification (cartilage model replaced by bone) is involved in: embryonic bone formation, growth in length of long bones, and fracture healing
Cartilage  Bone

Bone Growth and Remodeling

Grow and remodel themselves throughout life
athletes or history of manual labor have greater density & mass of bone
Most bone is formed by Endochondral ossification (IN- outward)
Step 1 = Cartilage forms
Step 2 = Cartilage grows
Step 3 = Bone replaces the cartilage from the inside center outward.

Stages of Endochondral Ossification

Produces most of the bones in the body

bone markings

characteristic for each bone and each person
everyone has
elevations and projections
depressions are like valleys like fossas
grooves and tunnels like a canal

Mineral Resorption

Bone is the major reservoir for calcium (Ca++)
Blood level of calcium ions is very important in cardiac, nerve, enzyme, and blood
If blood Ca ion levels get to low, the body will pull Ca ion from the bones

calcium ion concentration is too high in blood

calcitoniin is released in the blood causing
1. kidneys allow urination of calcium
2. allows more output of ca in the waste from the GI tract
3. stops osteoclast action and initiates osteoblast action to lock calcium into the bone matrix instead of being in the blood

Hormonal Bone Growth

Hormonal Regulation of Bone Growth
Human Growth Hormone (GH) stimulate bone deposition, in addition to thyroid hormone, parathyroid hormone, and calcitonin
variation of these hormones can lead to either gigantism or dwarfism
At puberty the sex hormones stimulate sudden growth and modify the skeleton
thyroid hormone - promotes growth and maturity
calcitonin - thyroid gland - promotes bone formation, inhibits osteoclast activity
parathyroid hormone - promotes bone resorption, increase activity of osteoclasts

Human Growth Hormone (GH)

stimulate bone deposition, in addition to thyroid hormone, parathyroid hormone, and calcitonin
variation of these hormones can lead to either gigantism or dwarfism

sex hormones

At puberty the sex hormones stimulate sudden growth and modify the skeleton

thyroid hormone

promotes growth and maturity
calcitonin - thyroid gland - promotes bone formation, inhibits osteoclast activity

parathyroid hormone

promotes bone reabsorption, increase activity of osteoclasts

name 3 ways that PTH increases ca concentration

1. increasing intestinal absorbtion-intestine absorbs more ca instead of letting it come out in the waste
2. kidneys will retain ca instead of urinating it out
3.osteoclasts will disolve ca from the bone and putting it into the blood

BONE HOMEOSTASIS

Remodeling
Replacement of old bone tissue with new bone tissue
Destroyed by osteoclasts (clubbed) and is constructed by osteoblasts (built)
Increased _____ activity/ decreased _____ activity causes bone loss
Increased _____ activity/ decreased _____ activity causes bone creation

Example of Bone Remodeling

Dental braces reposition teeth, creating greater pressure on the bone on one side of the tooth and less on the other side
increased pressure stimulates osteoclasts; decreased pressure stimulates osteoblasts to remodel jaw bone

Fractures

Stress fracture is a break caused by abnormal trauma to a bone
car accident, fall, athletics, etc




Pathological fracture is a break in a bone weakened by some other disease
bone cancer or osteoporosis = is #1 Cause of Fx

Stress fracture

a break caused by abnormal trauma to a bone
car accident, fall, athletics

Pathological fracture

a break in a bone weakened by some other disease
bone cancer or osteoporosis = is #1 Cause of Fx

Types of Bone Fractures

Healing of Fractures

Normally healing takes 8 - 12 weeks (longer in elderly)
Stages of healing
1. fracture hematoma-is formed that is a large blood clot to stop the bleeding that occurs when there is a fracture

2. granulation tissue
3- callus formation-internal callus forms- as a netwerk of spongy bone unites the inner suraces. external callus forms-of cartilage and bone to stabilize the outer ridges. this cartilage of the external callour gets replaced by spongy bone that unites the broken ends
4. remodeling occurs over next 6 months
-swelling on the surface of the bone marks the place of the fracture

Electrical stimulation is used on fractures that take longer than 2 months to heal

Silica- Horsetail herb, repairs fractures
swelling on the surface of the bone marks the place of the fracture

Bone Diseases

Abnormal softness of the bones is called rickets in children and osteomalacia in adults
Paget's disease = massive osteoclastic resorption and extensive bone formation
Osteoporosis: most common bone disease
Pathophysiology: estrogen maintains density in both sexes inhibits resorption by osteoclasts
Testes and adrenals produce estrogen in men
In women, rapid bone loss after menopause since estrogen blood level drop
Bones lose mass & become brittle
Risk of fracture of hip, wrist & vertebral column
Leads to fatal complications such as pneumonia, why?
Widow's (dowager's) hump is deformed spine

rickets

Abnormal softness of the bones in children

osteomalacia

Abnormal softness of the bones in adults

Paget's disease

massive osteoclastic resorption and extensive bone formation

Osteoporosis

most common bone disease
loss of spongy bone mass
29% of women over age 45 get this when
18 % of men get this
the bone can fracture easily and can just crumble
ways to prevent it- weight lift
Pathophysiology: estrogen maintains density in both sexes inhibits resorption by osteoclasts
Testes and adrenals produce estrogen in men
In women, rapid bone loss after menopause since estrogen blood level drops
Bones lose mass & become brittle
Risk of fracture of hip, wrist & vertebral column
Leads to fatal complications such as pneumonia, why?

Widow's (dowager's) hump

deformed spine

osteopenia

inadequate osefication or a reduction in bone mass because osteoblast acticity declines

Nutrition for good bones

Vitamins
A - controls activity of osteoblasts and osteoclasts, rarely toxic
D - promotes removal of Calcium from the bone (1,500 mg maximum)
C - maintains the matrix
AVOID SODA DRINKS
Minerals
calcium and phosphorus - make matrix hard
magnesium - deficiency inhibits osteoblast
manganese - inhibit formation of new bone, supports ligaments (Boneless chickens

EXERCISE AND BONE

Response to mechanical stress increases deposition of mineral salts and production of collagen fibers (aids osteoporosis)
Removal of mechanical stress weakens bone through demineralization
Weight-bearing activities help build and retain bone mass

Function of skeletal system

support-
storage of minerals and lipids
blood cell production- bones produce the blood by the bone marrow
protection- main organs and tissues are covered by skeletal tissue
leverage- muscles use the bone as levers to move the body.

main mineral in the bones

calcium

skull

protects the brain

pelvis

protects the reproductive organs

vetebral column

protects the spine

rib cage or thorasic cage

protects the heart and lungs

sutural bones

bones that form within a suture
eg-the back of the skull

sessmoid bone

form in a place of stress
an example of an extra bone that has formed
patella is the biggest sessmoid bone in the body
we are actually born without knee caps (patella) and as we start to crawl, we develop the patella to handle the stress

2 types of bone

compact dense bone
spongy bone(cancellous)

metaphyses

middle of the bone- between the epiphyses and the diaphysys

matrix

main parts that make up any type of tissue is the matrix. it is what the cells are suspended in

2 parts of the matrix
ground substance
fibers

matrix of bone

calcium and collagen
the combination is very tough. the collagen helps the bone less brittle and the collagen less rubbery

cells in the bones

...

calcium

extremely brittle
about 2/3 is Ca

collegen

very elastic and rubbery
1/3 is collegen

bone

is very vascular
if you break a bone, there is lots of bleeding which is why you see bruising

central canal

where the artery and vien are located in the bone

lacunae

a pocket in the matrix that is the housing for each osteocyte cell

cananiculae

cytoplasmic extension of the osteocytes that connect the osteocytes together and to the central canal so they can recieve the oxygen and nutients. The osteocytes are nurished by via the cananiculae highways from the central canal

lamellae

layers of matrix or rings that surroung the central canal

osteon

unit of compact bone that houses the central canal, osteocytes, lacunae, canaiculi and the lamallae

osteoblast

immature bone cell that participates in osteogenesis
osteo=bone
genesis=creation
osteoblasts helps grow our bones or heal an injured bone

osteoclasts

dissolves bone matrix or breaks down the bone

osteolysis

the process of dissolving bone

osteoprogenitor

stem cells that pump osteoblasts
-very important in bone repair

compact bone

located on the ourside of the bone
located where stress is limited in direction
great at handling weight

spongy

located on the inside of the bone
located where stresses are weaker and multi directional
takes stress from multiple directions
because it is so porous, it makes the bone much lighter but still incredible tough

compact bone makeup

basic unit of compact bone is an osteon
osteocytes arranged around a central canal
perforating canals extend between adjacent osteons

spongy bone makeup

trabeculae
lots of pores and struts

perioteum

covers the nome

endosteum

inside lining of the bone. like the pereosteum but inside the bone

bone development and growth

ossification and calcification

ossification

convert another tissue into bone

calcification

depositing calcium within a tissue

intramenbranous ossification

this happens in utero
part of the fetal development of dermal bones such as the skull is developed

endochondral ossification

how the rest of the fetus skeleton is formed
bones are intact but are soft and elastic when birth occurs; they have to harden
this is the production of the rest of the skeletal system
hyaline cartilage

Epiphyseal cartilage

growth plate
the gap in the metathaisis
when the growth plate disappears, growth is finished

epiphysial line

a faint line that shows in adults that represents where the growth used to be

exercise

can increase bone mass

things that effect bone mass

bones change constantly through
remodeling
exercise- increases bone mass
hormone level- growth hormone and thyroxine can increase bone mass
calcitonin- decrease blood ca
PTH- parathyroid- increase blood ca

Calcitonin

decrease blood ca

PTH- parathyroid hormone

when ca ion is too low, our body takes calcium from the bones to compensate for the low blood ca by releasing PTH
the parathyroid increases blood calcium by :
increasing intestinal absorbtion-intestine absorbs more ca instead of letting it come out in the waste
kidneys will retain ca instead of urinating it out
osteoclasts will disolve ca from the bone and putting it into the blood

99% of body's calcium is in the

bones

calcium ion concentration is maintained by

bones
GI tract
Kidneys

calcitonin and PTH regulate

blood calcium

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