Bones' Anatomy: Compact & Spongy Tissue, Haversian System, Osteons, & Growth, Study notes of Biochemistry

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B.Sc. (H) Biochemistry

IInd Year, IVth Sem

Human Physiology

Bone Structure and Formation

Lecture-2 & 3

Dr. Prabha Arya Assistant Professor Deshbandhu College

Compact Bones and Spongy Bones

 Bone is not completely solid but has many

small spaces between its cells and

extracellular matrix components.

 Some spaces serve as channels for blood

vessels that supply bone cells with nutrients.

 Other spaces act as storage areas for red

bone marrow. Depending on the size and

distribution of the spaces, the regions of a

bone may be categorized as compact or

spongy.

 Overall, about 80% of the skeleton is

compact bone and 20% is spongy bone.

Compact Bone structure

Martini and Nath, 11 edition th

Haversian System

 In an osteon, the osteocytes are arranged in concentric layers around a central canal, or Haversian canal. This canal contains one or more blood vessels (normally a capillary and a venule, a very small vein) that carry blood to and from the osteon. Central canals generally run parallel to the surface of the bone.  Other passageway known as perforating canals of Volkmann’s canal, extend perpendicular to the surface.  Blood vessels in these canals supply blood to osteons deeper in the bone and to tissues of the medullary cavity

Types of lamellae in Compact Bone

 Interstitial Lamellae fill in the spaces

between the osteons in compact bone.

These lamellae are remnants of osteons

whose matrix components have been almost

completely recycles by osteoclasts.

 Circumferential lamellae are found at

the outer and inner surfaces of the bone,

where they are covered by the periosteum

and endosteum, respectively

 These lamellae are produced during the

growth of the bone.

 Compact bones is thickest where the

stresses arrive from a limited range of directions

 The Osteons in the diaphysis of a long

bone are parallel to the long axis of the shaft. Thus the shaft does not bend, even when extreme forces are applied to either end.

Spongy bone….

 Nutrients reach the osteocytes by

diffusion along canaliculi that open onto

the surfaces of trabeculae.

 Red bone marrow is found between the

trabeculae of spongy bone, and blood

vessels within this tissue deliver nutrients

to the trabeculae and removes waste

generated by the osteocytes.

Location of spongy bone

 Spongy bone is located where bones are not heavily stressed or stress arrive from many directions.

 Being lighter in weight spongy bone reduces the weight of the skeleton

 Spongy bone houses the red bone marrow in the epiphyses in long bones

 At the other sites, spongy bone may contain yellow bone marrow-adipose tissue important as energy reserve. Martini and Nath, 11th^ edition

Martini and Nath, 11th^ edition

Endosteum

 An incomplete cellular layer, lines the medullary cavity. This layer, which is active during bone growth, repair, and remodelling, covers the trabeculae of spongy bone and lines the inner surfaces of the central canals. The endosteum consists of a simple flattened layer of osteoprogenitor cells that covers the bone matrix, generally without any intervening tissue fibers.

 Where the cellular layer is not complete, the matrix is exposed. At these exposed sites, osteoclasts and osteoblasts can remove or deposit matrix components. The osteoclasts generally occur in shallow depressions called osteoclasts crypts that have eroded into the matrix.

Types of ossification

 Ossification occurs in two ways: endochondral

and intramembranous. In endochondral

ossification , bone replaces existing cartilage.

Then bone growth occurs through interstitial

growth (in length) and appositional growth (in

width).

 In intramembranous ossification , bone develops

directly from mesenchyme (loosely organized

embryonic connective tissue) or fibrous

connective tissue.

 The bony skeleton begins to form about six weeks after fertilization, when the embryo is approximately 12 mm (0.5 in.) long. (At this stage, the existing skeletal elements are made of cartilage.) During fetal (beyond the eighth week) development, these cartilages are then replaced by bone, by either endochondral or intramembranous ossification. Endochondral ossification occurs mostly in long bones, while intramembranous ossification occurs mostly in flat bones.  During development after birth, the bones undergo a tremendous increase in size. Bone growth continues through adolescence, and portions of the skeleton generally do not stop growing until about age 25.

Growth in Length:

 This process involves the development of

secondary ossification centers.

 The completion of epiphyseal growth is

called epiphyseal closure. The timing of

epiphyseal closure differs from bone to

bone and from individual to individual. The

toes may complete ossification by age 11,

but parts of the pelvis or the wrist may

continue to enlarge until about age 25.