Bone Tissue

Lecture 5

Bone (osseous tissue)

hard, rigid material made of mineralized collagen and is hardened by calcium phosphate

Cartilages

tough, flexible connective tissue

Ligaments

fibrous band of tissue that holds bones together

Features of Bone

Outer shell is:

• compact

• dense

• cortical bone the encloses marrow

Spongy / Cancellous bone

Loosely organized bone tissue with ends of the bone (epiphyses)

Diaphysis

the middle of the bone

Epiphysis

the ends of the bone

Epiphyseal plate

a line of cartilage that separates the marrow of the epiphysis and diaphysis

• is only present in kids and adolescents

Diploe

the spongy bone in the skull

Osteogenic cells

stem cells that give rise to osteoblasts

Osteocytes

former osteoblasts that get trapped in the matrix

• they stay in the lacunae

• they help detect stress in the bone

Osteoblasts

bone building cells, promotes mineralization

Osteogenesis: the action of osteoblasts building the bones

Osteclasts

Bone crushing/dissolving macrophages in the endosteum and osteogenic layer of periosteum

They secrete HCl onto bone to dissolve the minerals

Osteolysis: the bone breaking action that osteoclasts do

Matrix of bone

made of 1/3 organic stuff and 2/3 inorganic stuff

organic stuff: collagen, glycoproteins, anything with -glycan

inorganic stuff: hydroxyapatite (calcium phosphate salt)

Compact bone features

• concentric lamellae

• osteon

• circumferential lamellae

• interstitial lamellae

Spongy bone features

• spicules

• trabeculae

Bone marrow

soft material inside the marrow of a long bone, spaces within spongy bone, and largest of central canals

Red bone marrow

Myeloid or hematopoietic tissue that makes blood

Yellow bone marrow

adipose tissue that eventually replaces red bone marrow

• in kids and babies, every bone has red bone marrow, but in adults, red bone marrow is only in the skull, spine, sternum, ribs, pelvis, and humerus and femur

Intramembranous Ossification

makes flat bones of the skull, part of the mandible, and clavicle

Endochondral ossification

makes other bones such as vertebrae, ribs, scapulae, pelvic girdle, limb bones. has 2 step process

1. Chondrification: mesenchyme becomes hyaline cartilage model of a future bone

2. Ossification: when cartilage is broken down and replaced by bone

Structure of Metaphysis

• Zone of reserve cartilage: resting hyaline cartilage

• Zone of cell proliferation: chondrocytes multiply

• Zone of cell hypertrophy: chondrocytes enlarge, lacunae walls thin

• Zone of calcification: minerals go into matrix walls

• Zone of bone deposition: chondrocytes die and osteocytes dissolve cartilage

Wolff’s law of bone

structure of a bone depends on the mechanical stress put on it

Ex. pro tennis players get thick arm bones

Calcium and phosphate

materials for mineralization

Vitamin A

promotes glycosaminoglycan synthesis

Vitamin C

promotes collagen cross-linking

Vitamin D

helps calcium absorption from food/diet

Calcitonin

helps osteoblast activity

Growth hormone

promotes cartilage growth at epiphyseal plates

Bone resorption stimulated by 1 hormone

Parathyroid hormone (PTH): helps osteoblasts make osteoclasts resorb bone

maintain good level of blood calcium

Osteoporosis

when you lose so much bone that your physical activity gets impacted (like when you age)

Osteopenia

Net loss of bone