Lecture 7Osseous Tissue

Bio-11

JPHubbard

• Dynamic and ever-changing throughout life• Skeleton composed of different tissues

– cartilage, bone tissue, epithelium, nerve, blood forming tissue, adipose, and dense connective tissue

Functions:

• Support • Movement and leverage

• Protection

• Storage of minerals (Ca especially) and fat

• Blood cell production

Types of Bones – ShapeKnow some examples:

• Long Bone• Flat Bone• Irregular Bone• Short Bone• Two additional types – vary with individuals:

– Sutural Bones– Sesamoid Bone

Gross Anatomy of Long Bone• _______________ tough connective tissue layer

covering boneattachment of tendons and ligaments

blood vessels in periosteum• ______________- ends

spongy bonecompact bone, articular cartilage

• ______________- middlecompact bonemedullary cavity- contains yellow marrow (fat)lined with endosteum (squamous epithelium)

Bone = Osseous tissue • a type of connective tissue – What characterizes connective tissue?

– Cells? – Vascular– matrix

What differentiates bone from other connective tissues?

Bone Cells

• _____________ – build bone, lay down matrix• _____________ – mature bone cells• Osteoprogenetor – mesenchyme cells which

differentiate into osteoblasts, largely inner layer of periosteum

• _________________ – large cells, destroy bone• Activity of osteoblasts, osteoclasts impacted by

hormones from thyroid/parathyroid

Matrix

• Collagen fibers –– Protein– like reinforcing rods – What would be the effect of lack of collagen?

• Minerals: provide rigidity – Calcium salts

Bone Micro-Anatomy – Osseous Tissue• Two types:

– 1. Compact bone• Osteon – Basic organizational unit• Diaphysis long bone, outer layers at

epiphysis and of flat bone– 2. Spongy Bone – no osteons

• Trabeculae provide bracing effect• Red Marrow produces blood cells• Ends of long bones + inside flat bones

Compact Bone – Osteon basic unit

• Central canal: blood vessels at center of osteon

• Lamella: Concentric layers of matrix

• Lacunae: contain osteocytes between layers of lamella

• Canaliculi: canals which connect lacunae

Trabeculae of Spongy Bone• oriented along lines of stress - Latticework• Harbor and protect red marrow ( blood cells

develop)

No true Osteons.

Bone Development Prenatal : (embryonic and fetal) skeleton is mostly cartilaginous

Ossification – the process of mineralization of tissue (hyaline cartilage, fibrocartilage) resulting in formation of bone

Cartilage cells and then osteoblasts start to deposit minerals

Bone Formation – 2 ways:1) Intramembrannous ossification – Flat Bones - bone

formed between sheets of connective tissue

2) Endochondral ossification –Long Bones - formed from hayaline cartilage model– increase in length until puberty at epiphyseal

plate– increase in diameter due to activity of cells

under periosteum– Control from growth hormone (GH) + other

endocrine hormones

Rickets and Osteomalacia• Disorders resulting in abnormal/poor ossification• Rickets:

– Vitamin D deficiency– Bowed limbs– Pain– Limbs easily broken

• Osteomalacia– Failure of adult bone to ossify– hip fractures are common

Growth hormone regulates skeletal growthstimulates cell division in epiphyseal disksin long bones

Growth stops when epiphyseal disks are converted to bone

When excess growth hormone is produced inchildhoodgigantism

In adulthood- acromegaly. Bones can’t growbut soft tissue can

Fracture & Repair of Bone• Healing is faster in bone than in cartilage due

to lack of blood vessels in cartilage• Healing of bone is still slow process due to

vessel damage• Clinical treatment

– closed reduction = restore pieces to normal position by manipulation

– open reduction = surgery

Bone Repair – Similar to Development

6-8 hours Hematoma forms

~ 3 weeks Fibrocartilaginous callus develops

~3-4 months Bony callus and spongy bone formed

Future Osteoblasts form compact bone

Bone Remodeling• Continuous Process

– distal femur is fully remodeled every 4 months• Osteoblast build - stimulated by

– Weight bearing activity– Blood Ca levels via endocrine hormones

(calcitonin stimulates)– Numbers increased by estrogen/testosterone

• Osteoclasts– Stimulated by dropping blood Ca level via

parathyroid hormone– Calcitonin inhibits

Small changes in blood levels of Ca+2 can be deadly:(plasma level maintained 9-11mg/100mL)

cardiac arrest if too high

respiratory arrest if too low

This is an example of a _____________ feedback loop.

Aging & Bone Tissue• Bone is being built through adolescence, holds its own in

young adults, but is gradually lost in aged.• Demineralization = loss of minerals

– very rapid in women 40-45 as estrogens levels decrease

– in males, begins after age 60• Decrease in protein synthesis

– decrease in growth hormone– decrease in collagen production which gives bone its

tensile strength– bone becomes brittle & susceptible to fracture

Osteoporosis• Loss in bone density• Affected by age, sex, race, nutrition, exercise• Particular problem for women after menopause

due to decreased estrogen• Diet factors with negative impact: alcohol,

caffeine, certain antibiotics and other drugs• Positive: Exercise increases bone mass, Fosamax,

vitamin D, hormone replacement therapy, calcium fluoride