bones week

Question 1

What are the functions of the skeleton

Answer 1

Structural support for the head
Protection for the brain, uterus and other internal organs
Attachment sites for muscles allowing movement of limbs
mineral recevoir for calcium and phosphorus
defence against acidosis
trap for some dangerous minerals such as lead

Question 2

What are the 2 major types of bones?

Answer 2

Trabecular (compact) and cortical (spongy)

Question 3

What are the 2 categories of bone cells?

Answer 3

Osteoclasts and osteoblasts (including osteocytes)

Question 4

Describe osteoclasts

Answer 4

large cells with many nuclei
they share lineage with blood cells (especially macrophages)
Precursors circulate in bone marrow and blood
Mature osteoclasts are formed from fusion of the precursors
This happens when RANK receptors on the osteoclast precursors are activated by RANK-ligand which is secreted by osteoblasts

Question 5

What is osteoprotegerin (OPG)?

Answer 5

A factor in marrow which also binds to RANK-ligand so it can help to regulate osteoclast activation

Question 6

What do osteoclasts do?

Answer 6

they resorb the bone. They form sealed compartments next to the bone surface and secrete acids and enzymes which degrade the bone. the edge next to the bone is called the ruffled border.
After they finish resorbing bone, they undergo apoptosis. this process is regulated by proteins from other cells.

Question 7

What do osteoblasts look like?

Answer 7

Cuboidal and columnar in shape with a central nucleus found on the bone surface

Question 8

what sort of junctions do osteoblasts form? why?

Answer 8

Gap junctions with neighbouring cells to allow communication with one another

Question 9

where do osteoblasts come from?

Answer 9

Bone marrow precursor cells. These are capable of also differentiating into fat cells and various factors determine the types of cells to be made. One of these is called Cbfa 1.

Question 10

what is the role of osteoblasts?

Answer 10

to make proteins which will form the organic matrix of the bone and also to control the mineralization of the bone.

Question 11

What are examples of hormones that osteoblasts have receptors for?

Answer 11

vitamin d, oestrogen, and parathyroid hormone

Question 12

What is the main factor that osteoblasts secrete to activate osteoclasts?

Answer 12

RANK-ligand

Question 13

What does PHEX do?

Answer 13

its a protein which helps to regulate the amount of phosphate excreted by the kidney

Question 14

What happens to the team osteoblasts when they are finished making new bone?

Answer 14

some become surrounded by matrix and differentiate into osteocytes. others will remain on the surface of the new bone and differentiate into lining cels. the rest undergo apoptosis

Question 15

Describe the structure of osteocytes?

Answer 15

they live inside the bone and have long branches which allow them to contact each other as well as the lining cells of the bone surface

Question 16

What do osteocytes do?

Answer 16

They are in the perfect position to sense any mechanical strain on the bone. They can secrete growth factors which activate the lining cells or stimulate the osteoblasts. Their exact role is still under investigation, but probably they direct bone remodelling to accommodate mechanical strain and repair fatigue damage

Question 17

Where do lining cells come from?

Answer 17

They are former osteoblasts. They become flat and pancake-shaped

Question 18

Where are lining cells found?

Answer 18

They line the entire surface of the bone

Question 19

What do lining cells do?

Answer 19

They are responsible for the immediate release of calcium from the bone if blood calcium levels are too low.
They protect the bone form chemicals in the blood which dissolve crystals (e.g. pyrophosphate)
They have receptors for hormones and factors that initiate bone remodelling.

Question 20

Where are osteoblasts and osteocytes derived from?

Answer 20

Mesenchymal stem cells

Question 21

Where are osteoclasts derived from

Answer 21

Haematopoietic progenitors

Question 22

What are bone morphogenetic proteins (BMPs)?

Answer 22

They are produced in the bone or bone marrow. They bind to BMP receptors that are on mesenchymal stem cells within the bone marrow. This causes the cells to produce Cbfa 1.

Question 23

What does Cbfa 1 do?

Answer 23

It is a transcription factor which causes the cells to differentiate into mature osteoclasts. without cbfa 1, the stem cells would differentiate to fat cells.

Question 24

What are insulin-like growth factors (IGFs?)

Answer 24

These are produced by osteoblastic cells in response to several bone active hormones, such as parathyroid hormone and oestrogen, or BMPs. IGFs accumulate in the bone matrix and are released during the process of bone remodelling by osteoclasts. IGFs stimulate osteoblastic cell replication - they may also induce differentiation.

Question 25

IL-6 is one of the cytokines which is involved in bone cells, what does it do?

Answer 25

It causes stem cells to differentiate into pre-osteoclasts
changes in proliferation and differentiation of osteoblasts
inhibition of apoptosis of osteoblasts

Question 26

What is RANK-L and what does it respond to?

Answer 26

It stays on the surface of an osteoblast in response to systematic hormones (such as 1,25dihydroxyvitaminD3)
and cytokines such as IL-6. Cell contacts between RANK-L expressing osteoblastic cells and RANK expressing osteoclast precursors induces osteoclast development

Question 27

What % of the bone is made up from mineral?

Answer 27

60% mainly calcium and phosphate

Question 28

Other than mineral, what else is the bone made from?

Answer 28

Water and matrix, which is formed before the mineral is deposited, and may be considered scaffolding of the bone.

Question 29

What makes up 90% of the matrix protein?

Answer 29

Type 1 collagen

Question 30

What are other matrix protein in the bones?

Answer 30

Fibronectin
osteonectin
thrombospondin
osteocalcin
matrix-gla-protein

Question 31

What does SIBLINGS stand for?

Answer 31

small integrin binding ligand, N-linked glycoproteins

Question 32

What are the 5 types of bones?

Answer 32

Long bone
short bone
irregular bone
flat bone
sesamoid bone

Question 33

What is the diaphysis?

Answer 33

main shaftlike portion. Its hollow cylindrical shape and the thick compact bone that composes it adapt the diaphysis well to its function of providing strong support without adding cumbersome weight

Question 34

what is the epiphysis?

Answer 34

Both ends of the long bone. Epiphyses have a bulbous shape that provides generous space near joints for muscle attachments and also gives stability to the joints. A soft connective tissue called red marrow fills the spaces of the cancellous bone.

Question 35

What is articular cartilage?

Answer 35

Thin layer of hyaline cartilage that covers the articular joint surfaces of epiphyses. The resiliency of this material cushions jolts and blows

Question 36

What is the periosteum?

Answer 36

A dense, white fibrous membrane that cover all bone except at joint surfaces, where articular cartilage forms the covering. Many of the periosteum fibres penetrate the underlying the bone and well these two structures together. In addition, muscle tendon fibres interlace with peroisteal fibres, thereby anchoring muscles firmly to bone. The periosteum is a critically important membrane that, depending on its location, also contains bone - forming and bone- destroying cells and blood vessels that become incorporated into bones during their initial growth and subsequent remodelling and repair. This membrane is essential for bone cell survival and for bone formation

Question 37

Medullary cavity

Answer 37

a tubelike hollow space in the diaphysis of a long bone, also called a marrow cavity. The adult medullary cavity is filled with connective tissue rich in fat - a substance called yellow marrow.

Question 38

What is the endosteum?

Answer 38

A thin fibrous membrane which lines the medullary cavity of long bones. The endosteum lines the spaces of cancellous bones as well. Like the periosteum, the endosteum has various types of bone cells that produce them

Question 39

What is the structure of a flat bone?

Answer 39

The structure of a flat bone is similar to that of a long bone but simpler. A flat bone in the cranium has outer and inner walls made of compact bone. These are called the internal and external tables. Between them there is a region called the dipole, which is made up of cancellous bone. Other flat bones, such has the ribs and sternum, have a similar overall structure. Like long bones, flat bones are covered in a periosteum and the inner spaces are lined with endosteum.
red marrow fills the spaces of the cancellous bone within many flat bones.

Question 40

What structure do short, regular and sesamoid bones have?

Answer 40

Very similar to that of flat bones

Question 41

What is the function of the organic matrix?

Answer 41

It is composite of collagenous fibres and a mixture of protein and polysaccharides called ground substance. Connective tissue cells secrete the gel-like ground substance. This provides support and adhesion between cellular and fibrous elements and also serves an active role in many cellular metabolic functions necessary for growth, repair and remodelling.

Question 42

What is the structure of compact bone?

Answer 42

It makes up about 80% of the total bone mass in the adult human body. It contains many cylinder-shaped structural units called osteons or haversian systems. Each osteon surrounds a central canal that runs through the bone. Living bone cells within these units are literally cemented together to constitute the structural framework of compact bone. The unique structure of the osteon permits delivery of nutrients and removal of waste from metabolically active, but imprisoned bone cells.

Question 43

What is the structure of cancellous bone?

Answer 43

There are no osteons in cancellous bones. Instead, it consists of needlelike bony branches called trabeculae. Bone cells are found within the traberculae. Nutrients are delivered to the cells and waste products are removed by diffusion thorough tiny canaliculi that extend to the surface of the very thin bony branches.

Question 44

What happens in the early stages of ossification?

Answer 44

Bone tissue develops in a chaotic pattern of mineralised layers. Its crisscross appearance gives this new bone the name woven bone.

Question 45

What is woven bone replaced by?

Answer 45

A stronger, layered bone called lamellar bone, which is characterised by the presence of many osteons.

Question 46

What are the first osteons in lamellar bone called?

Answer 46

primary osteons.

Question 47

How are primary osteons formed?

Answer 47

osteoclasts in the endosteum that surrounds a blood vessel first demineralise a cone or tube around a blood vessel. This leaves a cavelike hollow filled with collagenous fibers and lined with endosteum. Osteoblasts in the endosteum then form layer upon layer (lamellae) along the inside wall of the tube, trapping osteocytes between the lamellae. Eventually the concentric lamella run out of space to mineralise - leaving only the central canal with its tightly packed blood vessels, nerves and lymphatic vessels. As the bone develops, primary osteons are replaced through the same process by secondary osteons through the same process.

Question 48

How do long bones grow in diameter?

Answer 48

Osteoclasts enlarge the diameter of the medullary cavity by eating away the bone and its walls. At the same time, osteoblasts from the periosteum build new bone around the outside of the bone. By this dual process, a bone with a larger diameter and larger medullary cavity.

Question 49

Why is remodelling of bone important?

Answer 49

Homeostasis of blood calcium levels. It also permit bones to grow in length and diameter and change their overall shape and size of the marrow cavity

Question 50

At what age does bone loss start to exceed bone gain?

Answer 50

Between 35 and 40 years

Question 51

What happens to bone under mechanical stress?

Answer 51

Cancellous bone remodels its trabecula in different directions and thicker diameters to better stand stress. Remodelling in compact bone involves the formation of new secondary osteons when bone is stressed. Bones that bear the greatest weight have the narrowest osteons.