Skeletal Tissues
Compact vs. Spongy
 Compact
bone is dense and solid in
appearance.
 Cancellous,
or spongy, bone is
characterized by open space partially
filled by an assemblage of needle-like
structures.
Compact
and
Spongy Bone
Four Bone Types

Long bones – extended longitudinal axis
and expanded and often uniquely shaped
articular ends.
 Examples

are the femur and humerus
Short Bones – cube- or box-shaped
structure, which are about as broad as they
are long.
 Examples
include the wrist (carpals) and ankle
(tarsal) bones
 Flat
bones – generally broad and thin
with a flattened and often curved
surface.
 Examples
include some skull bones, scapulae,
ribs, and sternum
 Irregular
Bones – often clustered in
groups and come in various shapes
and sizes.
 Examples
include the vertebral bones that
form the spine and facial bones
Parts of a Long Bone

Diaphysis – main shaftlike portion

Epiphyses – both ends of a long bone have a
bulbous shape that provides generous space near
the joints for stability and muscle attachment.

Articular Cartilage – thin layer of hyaline
cartilage that covers joint epiphyses and acts as a
cushion.

Periosteum – Dense, white fibrous membrane
that covers bone except at joint surfaces

Medullary (marrow) cavity – tubelike hollow
space in the diaphysis of a long bone. In adults
it is filled with fatty yellow marrow.

Endosteum – thin epithelial membrane that lines
the medullary cavity of long bones.
Bone (Osseous) Tissue


Connective tissue
Consists of cells, fibers, and extracellular matrix

Extracellular components are hard and calcified

Matrix is more abundant that the bone cells
Composition of Bone Matrix

Inorganic Salt are responsible for the hardness
of bone.

Hydroxyapatite – composed of calcium and
phosphate

Organic Matrix – composite of collagenous
fibers and a mixture of protein and
polysaccharides called ground substance.
Osteoporosis

Age related skeletal disease that is characterized
by loss of bone mineral density, increased bone
fragility, and susceptibility to fractures

More common in women

May lose 4% - 8% of their bone density on a
yearly basis
Microscopic Structure of Bone

Compact bone contains many cylinder-shaped
structural units called osteons, or Haversian
systems.

Each osteon surrounds a canal that runs
lengthwise through the bone.
Main Structures of the Osteon

Lamellae – concentric, cylinder shaped layers of
calcified matrix.

Lacunae – small spaces containing fluid and
bone cells

Canaliculi – ultrasmall canals radiating in all
directions from the lacunae that connects them
to each other and the Haversian canal

Haversian canal – Extends lengthwise through
the center of each Haversian system; contains
blood vessels, lymph vessels and nerves

Volkmann’s canals – run perpendicular to
Haversian canals
Structure of Compact and
Cancellous Bone
Section of Flat Bone
Cancellous Bone

There are no osteons in cancellous bone

Consists of needle-like bony spicules called
trabeculae.

Bone cells are found within the trabaculae

Nutrients are delivered and wastes removed by
diffusion
Orientation of Trabeculae
Types of Bone Cells

Osteoblasts – synthesize and secrete a
specialized organic matrix called osteoid, that is
an important part of the ground substance of
bone. (bone forming cells)

Osteoclasts – giant multinucleate cells that are
responsible for the active erosion of bone
minerals. (bone reabsorbing cells)

Osteocytes – mature, non-dividing osteoblasts
that have become surrounded by matrix and
now within a lacunae.
Osteoblasts and Osteocytes
Osteoclast
Bone Marrow

Soft, diffuse connective tissue called myeloid
tissue.

Site of blood cell production

Found in medullary cavities of certain long
bones and in the spaces of some spongy bones.
Red Marrow & Yellow Marrow

In a child’s body, virtually all of the bones
contain red marrow.

Red marrow produces red blood cells.

As an individual ages red marrow is replaced by
yellow marrow.

Yellow marrow has become saturated with fat
and is no longer active in blood cell production.
Active Marrow in Adults
Functions of Bone

Support – supporting
framework of body

Protection – protect
delicate structures such
as the brain

Movement – joints act as
levers and allow
movement in conjuction
with muscular system

Mineral Storage – major
reservoir for calcium,
phosphorus, and certain
other minerals

Hematopoiesis – blood
cell formation
Regulation of Blood Calcium Levels

98% of body calcium is stored in bone

Osteoblasts remove calcium from blood

Osteoclasts break down bone and calcium levels
in the blood increases

Calcium is important for normal blood clotting,
nerve impulses, and muscle contraction
Calcium in the Body

Calcium that is consumed is
absorbed through the
intestines

Calcium is stored and released
from bone tissue

The kidneys eliminate extra
calcium and absorb calcium
from urine if blood calcium
levels get too low.
Parathyroid Hormone

When calcium levels fall below their “set point,”
osteoclasts are stimulated to increase the rate of
bone matrix breakdown.

Calcium is released into the blood until the level
returns to normal.
Vitamin D (Calcitriol)

Acts to increase blood calcium levels

Facilitates the absorption of calcium in the small
intestines
Calcitonin

Functions to reduce blood calcium levels

Enhances excretion of calcium in urine

Inhibits osteoclasts
Calcium Deprivation
Development of Bone

Before birth, the skeleton consists of cartilage
and fibrous structures shaped like bones.

Cartilage is replaced with calcified bone matrix

The combined action of osteoblast and
osteoclasts to make bone is known as
osteogenesis
Intramembranous Ossification

Takes place within a connective tissue
membrane
Endochondral Ossification

Bone forms from cartilage models

Forms from the center to the ends
Endochondral Ossification
Epiphyseal Fracture
Bone Growth and Resorption

Bone growth is from the combined action of
osteoclasts and osteoblasts

Osteoclasts break down bone to enlarge the
diameter of the medullary cavity.

Osteoblasts from the periosteum build new bone
around the outside of the bone
Bone Fracture Repair