Lecture 8 - General principles of bone 1

Question 1

What features of connective tissue give it its unique qualities?

Answer 1

Connective tissue depends on the type of cells, their number and arrangement. The ECM of the connective tissue depends on the arrange of the fibers, and the type of fiber (collagen, reticular, elastic) and the composition of the ground substance

Question 2

Why doe the ECM of connective tissue vary between tissues?

Answer 2

The composition of the ECM and types of fibers vary because the ECM is tissue specific

Question 3

What are the constituents of a collagen fiber?

Answer 3

Triple helix of 3 intertwined polypeptide chains (alpha chains) -> Collagen molecule -> Bundle of collagen fibrils -> Collagen fiber

Question 4

What makes up types l and ll collagen?

Answer 4

Type l is made of 2 α1 chains and 1 α2 chains Type ll is made of 3 identical α chains

Question 5

What gives collagen its banded appearance?

Answer 5

Its due to the arrangement of the collagen molecules

Question 6

In histology, do the light or dark areas have more molecules?

Answer 6

Light areas have more molecules, since more light is reflecting

Question 7

What does the ground substance in ECM consist of?

Answer 7

Proteoglycans (have a large protein core with GAGs attached) Glycsoaminoglycans (GAGs) (covalently bound to the proteoglyans) Glycoproteins (multiadhesive)

Question 8

In relation to other cells, describe the function of ECM

Answer 8

ECM is a dynamic and interactive system that informs cells of biochemical and mechanical changes in their extracellular environment

Question 9

Desribe the structure of glycosoaminoglycans (GAGs)

Answer 9

GAGs are long chain unbranched polysaccharides of repeated disaccharide units (with sugars + uronic acid)

GAGs are highly negatively charged, this makes them attract water. And it is this negative charge that determines how hydrated the ground substance is, allowing the ECM to resist compression. This enables there to be rapid diffusion of water molecules. The rigidity of GAGs provides a structual framework for the ECM.

Question 10

What role do glycoproteins have in the ECM?

Answer 10

They stabilise the ECM and link it to the cell surfaces (since they are multiadhesive)

Glycoproteins also have binding sites for a variety of ECM proteins

Question 11

Describe bone tissue

Answer 11

Bone is a connective tissue that is specialized for support and protection. It acts as the levers for movement, and as a calcium store for homeostasis.

The ECM in bone CT has been mineralised by hydroxyapatite.

The constituents of bone are cells (osteoblast, osteocyte, osteoclast) and ECM

Question 12

Where do osteoblasts lie when they are remodelling the bone?

Answer 12

Osteoblats lie along the outside edge

Osteoblasts may vary in size because their demands may be different. E.g. a cell producing bone is going to be larger than one that is not

Question 13

Describe how the calcified matrix of bone tissue is produced

Answer 13

Fibroblasts produce vesicles containing alkaline phosphatase. This cleaves phosphate ions from other things in the matrix. The Calcium (which is bound to osteocalcin in the matrix) combines with phosphate to form hydroxyapatite.

Question 14

Where do cells reside within the calcified matrix of bone?

Answer 14

Osteocytes are in lacuna, and have cytoplasmic processes within the cannaliculi

Question 15

Describe an osteoclast

Answer 15

They are large, multinucleate cells. They are mobile, and are in the resorption cavity. They have a ruffled border and release enzymes.

They also secrete MCSF and RANKL

Question 16

In basic terms, describe how a osteoclast breaks down bone

Answer 16

It creates an acidic environment, and then conceals this environment to make an acidic pool so that its enzymes can break down the bone, the constituents are then released and then go into the lymphatics and then into the capillaries

Question 17

Bone is described as a composite structure, what other structures does it contain?

Answer 17

Bone has a periosteum, which is a deep fibrous connective tissue.

It also contains nerves and blood vessels, hemopioetic tissue, hyaline cartialge, adipose tissue, and if they are still growing a cartilage growth plate

Question 18

How is boned arranged?

Answer 18

The cells lie within the lamellae of the calcified matrix.

The bone is arrange as having an outer layer of compact cortical bone (thickness depends on location, and type of bone)

The cancellous (spongy, trabecular) bone lies toward the center near the central marrow cavity

Question 19

Since no diffusion can occur to bone, how does blood get supplied?

Answer 19

There are perforating and central canals that give a blood supply network within the bone

Question 20

What kind of tissue is periosteum?

What is on the inner layer of periosteum?

How does periosteum stick onto bone?

Answer 20

Periosteum is dense FCT, which contains blood vessels, collagen bundles and fibroblats

The inner cellular layer of periosteum are osteoblasts which are laying down new bone for remodelling, and osteoprogenitor cells

The periosteum has sharpey fibers - they go into the bone matrix, and bind the periosteum to the bone

Question 21

What does the periosteum provide for bone tissue?

Answer 21

Periosteum nourishes bone tissue, and it also provides a source of new bone cells for appositional growth/repair

Question 22

What area does the endosteum line?

And what does it provide to bone?

Answer 22

The marrow cavities

The endosteum has a similar inner cellular layer to periosteum, as it also has osteoblasts and osteoprogenitor cells