Bone Histogenesis & Histology BSM

Question 1

Ossification / Osteogenesis

Answer 1

. The process by which bones form

Question 2

How many germ layers are there in an embryo? Name them?

Answer 2

3 germ layers in an embryo
. The ectoderm, mesoderm and the endoderm

Question 3

Which of the embryonic layers is used to form bones?

Answer 3

. The mesoderm - the mesoderm forms the mesenchyme and the mesenchymal stem cells are capable of differentitaing into different types of cells like chondroblasts which can form chondrocytes (both are cartilage cells)
& osteoblasts can form osteocytes (both are mature cells)

Question 4

How many types of cartilage are there? Name them?

Answer 4

. 3 different types of cartilage
- Hyaline cartilage, elastic cartilage and fibrocartilage

Question 5

Which type of cartilage do bones have ?
Outline the structure + type of collagen in this cartilage

Answer 5

• Hyaline cartilage
• It has cells in ECM - the cells are chondrocytes, which are located in spaces called lacunae (either singly or in groups).
  Matrix = consists of collagen, mainly Type 2 collagen & a well hydrated ground substance - both are synthesised by the chondroblasts

Question 6

Where are chondroblasts located in hyaline cartilage?

Answer 6

. In the perichondrium
. Perichondrium = connective tissue layer which covers the catilage

Question 7

What are osteoprogenitor cells?

Answer 7

. Osteoblasts develop from mesenchymal stem cells called osteoprogenitor cells

Question 8

What do osteoblast cells do?

Answer 8

. Synthesise the bone matrix which is then calcified

Question 9

Osteoblast to osteocyte

Answer 9

Some of the osteoblasts get trapped in the matrix and differentiate into osteocytes which are located in spaces called lacuna - one osteocyte in each lacuna

Question 10

Appearnce & Function of osteoclasts

Answer 10

. Multinucleated giant cells
. Resorb bone - digest the bone matrix

Question 11

3 different types of cells found in bone & state their function in 2 words.

Answer 11

1 - Osteoblasts = forms bones (bone formation)
2 - Osteocytes = maintain bone
3 - Osteoclasts = destroy bone (bone resorbtion)

Question 12

Compact bone versus cancellous bone

Answer 12

Compact bone = dense
Cancellous bone = spongy - has trabeculae - spaces between trabeculae are filled with bone marrow

Question 13

What is the middle portion of a long bone called? What does it contain?

Answer 13

Cross-section of a shaft (diaphysis) of a long bone
Central portion of diaphysis
- medullary cavity filled with marrow

Question 14

What are the ends of a long bone called? What are the expanded ends of the diaphysis called?

Answer 14

• Epipysis
• Metaphyses

Question 15

What is the periosteum

Answer 15

• Surface of compact bone is covered with connective tissue called periosteum and it has an inner cellular layer which has osteoprogenitor cells, osteoblasts and osteoclasts

Question 16

What are the marrow cavities lined with?

Answer 16

. lined by endosteum which also has the 3 bone cells

Question 17

How many different types of ossification are there? Name them & state their fundamental difference?

Answer 17

2 different types of ossification
1- Endochondral ossification - involves cartilage as indicated by chondro in the name. The mesenchyme forms cartilage first, which serves as a template and that cartilage gets REPLACED by bone. How most bones form such as long bones like humerus and femur are formed.
2- Intramembranous ossification - bone is going to directly form from the mesenchyme with osteoblasts forming osteoid - examplee most bones of the skull vault & the facial bones. In short, most CRANIOFACIAL bones

Question 18

Intramembranous Ossificaton Info - Just read

Answer 18

• No cartilage template
• Bone directly forms from mesenchyme
• The mesenchyme in the area where bone is going to be condenses - the condensed mesenchyme has stem cells which differentiate into osteoblasts (the bone matrix forming cells)
  . Osteoblasts start synthesising osteoid - which is the matrix before mineralisation happens ( so just the collagen and the ground substance)
  . The matrix then gets calcified
  . As the osteoblasts form this matrix some get trapped forming osteocytes in the lacunae - the osteocytes have cytoplasmic processes that sit in canaliculi - this is an ossification centre and multiple ossification centres form and fuse
  . The bone matrix organises into rods and plates forming the trabeculae of the cancellous bone
  . Between the trabeculae = hematopoietic tissue - here mesenchymal cells become bloof-forming cells (marrow)

Question 19

What is immature woven bone

Answer 19

. Bone that forms first in any process of ossification = immature woven bone
- it is irregular & not very strong
- so the immature woven bone gets remodelled to form lamellar bone

Question 20

Geography of a bone

Answer 20

Periosteum - underneath the periosteum = compact bone forms - and then on the inside = cancellous bone

Question 21

Endochondral Ossification Stages

Answer 21

• Mesenchyme first forms the chondroblasts, which synthesize the cartilage matrix (type 2 collagen & the ground substance)
• Cartilage forms in the shape of the bone which is going to replace it - this cartilage is hyaline cartilage and it has chondrocytes in lacunae
• The cartilage is surrounded by perichondrium which is the scaffold for the formation of bone

Question 22

Learn

Answer 22

Osteoblasts -> Osteoid -> Gets calcified to form IMMATURE WOVEN BONE -> gets remodelled to form MATRUE LAMELLAR BONE

Question 23

What does the surface of epiphysis have?

Answer 23

. Articular cartilage - becuase they articulate with other bones forming joints
. Articular cartilage = stays for life

Question 24

What is the epiphyseal growth plate responsible for?

Answer 24

. Longitudnal growth of bones

Question 25

Longitudnal Bone Growth
(Epiphyseal Growth Plate)

Answer 25

Complete