Top Banner
HISTOLOG Y OF BONE BY DR. MUDASSAR ALI ROOMI (MBBS, M. Phil.)
8

1st Lec on Histology of Bone by Dr Roomi

Apr 06, 2018

Download

Documents

Mudassar Roomi
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 1/8

HISTOLOGY OF

BONE

BY

DR. MUDASSAR ALI ROOMI (MBBS, M. Phil.)

Page 2: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 2/8

FUNCTIONS OF BONE

Definition of bone : Bone isa specialized supportingconnective tissuecomposed of calcifiedintercellular material,

the bone matrix, andthree cell types.

1. Support & Protectionfor soft body parts

2. Points of attachmentsfor muscles (Makesmovement possible)

3. Red & Yellow marrow ->Blood cell production

Page 3: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 3/8

Bone cells

1. Osteocytes (Gr. osteon, bone+ cytos, cell), which arefound in cavities (lacunae)between layers (lamellae) of bone matrix

2. Osteoblasts (osteon + Gr.blastos, germ), whichsynthesize the organiccomponents of the matrix

3. Osteoclasts (osteon + Gr.clastos, broken), which aremulti-nucleated giant cellsinvolved in the resorptionand remodeling of bonetissue.

Page 4: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 4/8

OSTEOBLASTS (Bone forming cells)

Synthesize and secrete osteoid

Osteoid= organic components of bone

matrix, consisting of type I collagen fibers,

proteoglycans, and several glycoproteins

including osteonectin.

Deposition of the inorganic components

of bone also depends on them via

secretion of ALP enzyme.

located at the surfaces of bone matrix, in a

layer somewhat resembling a simple

epithelium.

When active, they have a cuboidal to

columnar shape and basophilic cytoplasm

(RER).

When their activity declines, they flatten

and cytoplasmic basophilia is reduced.

stimulated by PTH

Page 5: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 5/8

osteocytes (mature bone cells)

Individual osteoblasts are graduallysurrounded by their own secretion and

become osteocytes

enclosed singly within spaces called lacunae.

In the transition from osteoblasts to

osteocytes the cells extend many long

cytoplasmic processes, which also becomesurrounded by calcifying matrix.

An osteocyte and its processes occupy each

lacuna and the canaliculi radiating from it .

maintain matrix, if they die matrix is

resorbed

Processes of adjacent cells make contact viagap junctions.

they are flat and almond-shaped cells

Cytoplasm: reduced RER and Golgi apparatus

Nucleus: more condensed nuclear chromatin

.

Page 6: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 6/8

Osteoclasts (bone resorbing cells)

very large (dia=150 um), motile cells with

multiple nuclei.

Origin: from the fusion of monocytes.

osteoclasts lie within depressions in the bone

matrix known as resorption bays (Howship

lacunae).

In active osteoclasts, the surface against the

bone matrix is folded into irregular projections,

which form a ruffled border.

Surrounding the ruffled border is a clear

cytoplasmic zone rich in actin filaments which is

the site of adhesion to the bone matrix.

This circumferential adhesion zone creates a

microenvironment between the osteoclast andthe matrix in which bone resorption occurs .

Into this subcellular pocket the osteoclast

secretes collagenase and other enzymes and

pumps protons, forming an acidic environment

locally for dissolving hydroxyapatite and

promoting the localized digestion of collagen.

Page 7: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 7/8

Osteoclasts (bone resorbing cells)

Page 8: 1st Lec on Histology of Bone by Dr Roomi

8/2/2019 1st Lec on Histology of Bone by Dr Roomi

http://slidepdf.com/reader/full/1st-lec-on-histology-of-bone-by-dr-roomi 8/8

Functions of osteoclasts

1. Remodeling of the bone during bone repair

and bone growth.

2. Calcium homeostasis:

maintenance of constant calcium ions in blood.