Human Physiology Bone Structure and Formation, Schemes and Mind Maps of Biochemistry

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B.Sc. (H) Biochemistry

IInd Year, IVth Sem

Human Physiology

Bone Structure and Formation

Lecture- 1

Dr. Prabha Arya Assistant Professor Deshbandhu College

Functions of skeletal system

1. Support : Structural support for entire body

and framework to support organs

2. Storage of minerals and lipids : Calcium and

phosphate stores, yellow bone marrow ahs

lipid as energy reserves

Classification of bones

 There are typically 206 bones which can be categorized into 6 categories according to their shapes  1. Sutural bones , or wormian bones, as they name suggest they are for the connection between two bones. Basically found in between of flat bones of skull. Their borders are irregular and are like jigsaw puzzle and have variable size Fig: 6.1, Martini and Nath

2. Irregular bones

 They have irregular shapes with short, flat, notched or ridged surfaces. Exaples are spinal vertebrae, bone of pelvis and skull bones Fig: 6.1, Martini and Nath

4. Flat bones

 They have thin parallel surfaces. They form room of the skull, the sternum, the ribs and the scapulae. Provide protection and attachment surface for the skeletal muscle Fig: 6.1, Martini and Nath

5. Long bones

 These bones are long and slender. They are located in arms, forearm, thigh, leg, palms, soles, fingers and toes. Femur is the largest and heaviest bone of the body Fig: 6.1, Martini and Nath

Bone structure

Fig: 6.1, Martini and Nath

Bone structure……

 A typical bone for example femur has one elongated tubular shaft called diaphysis which is having at both ends on expanded are known as epiphysis. Epiphysis is connected to diaphysis at both ends with a narrow zone called as metaphysis.  Diaphysis has a wall made up of compact bone or dense bone which surrounds medullary (marrow)cavity. Fig: 6.1, Martini and Nath^ Fig: 6.1Tortora and Grabowski

Flat bones

 Found in skull such as parietal bones

 It is having sandwich like structure, compact

bone covering a core of spongy bone. This

spongy layer in cranium is called diploe (two

fold). Bone marrow is present in spongy bone

but there is no medullary cavity like diaphysis

of long bones

Fig: 6.1, Martini and Nath

Bone composition

Ref: https://commons.wikim edia.org/wiki/File:Com position_of_bone.png

 Hydroxiapatite crystals combine with other

calcium salts like calcium corbonate (CaCO

and ions such as sodium, magnesium and

fluoride.

Calcium phosphate (2/3) Collagen (1/3) Cells (2%)

 Crystals are very hard, but relatively inflexible and

quite brittle. They can withstand compression, but

likely to shatter when exposed to bending, twisting

or sudden impacts.

 Collagen fibers are relatively quite strong and

when subjected to tension are relatively strong

(stronger than steel).

 The composition of the matrix in compact bone is

the same as in spongy bone. The collagen fibers

provide an organic framework on which

hydroxyapatite crystals can form

Osteocytes…..

 Canaliculi contain cytoplasmic

extensions of osteocytes.

Neighbouring osteocytes are

linked by gap junctions, which

permit the exchange of ions and

small molecules like ntrients

and hormones between the

cells.

 The interrstitial fluid that

surrounds the osteocytes and

their extensions provides an

additional route for the

diffusion of nutrients and waste

products.

Fig: 6.3, Martini and Nath

Functions of osteocytes

1. Maintenance of protein and mineral content of

the surrounding matrix

 Osteocytes secrete chemicals that dissolve the

adjacent matrix, and minerals released enter

the circulation.

 Osteocytes then rebuild the matrix, stimulating

the deposition of new hydroxyapatite crystals.

The turn over rate varies from bone to bone.