Structure and Function of the MSK System – The Skeleton

Question 1

What is the primary cell of the connective tissue and what are their purpose

Answer 1

Fibroblasts

Produces and maintains ECM of connective tissue

Question 2

What can the matrix of the connective tissue be divided into

Answer 2

Ground substance and protein fibres

Question 3

Functions of the bone

Answer 3

Provides the bodies framework – support and protection

Acts as a calcium store for the body

Question 4

Groups of bone

Answer 4

Long bones – consist of a shaft and two ends (tibia)

Short bones – nearly equal in length and diameter (carpal)

Flat bones – thin and plate-like (skull)

Irregular bones – shape that does not fit in above categories

Question 5

Examples of Irregular bone

Answer 5

Complex shape – vertebrae

Bone contains air spaces – ethmoid bone

Question 6

What is the composition of the bone matrix

Answer 6

Three main components:
Organic matrix (osteoid – 25%)
Inorganic mineral content (50%)
Water (25%)

Question 7

Two types of bones and how are they caused

Answer 7

Collagen fibre arrangement leads to two types of bone – woven (immature) and lamellar (mature)

Question 8

What is the organic matrix (osteoid) composed off

Answer 8

Osteoid composed of 90% collagen fibres (primarily type I) and 10% non-collagenous proteins (glycoproteins, osteocalcin) – forms the framework of bones

Question 9

What dies the cortical bone contain

Answer 9

Constitutes the shaft (external layer) of bones

Consists of osteons – composed of haversian canal that is concentrically surrounded by lamellae

Question 10

What are osteons

Answer 10

– cylindrical structures containing a mineral matrix & osteocytes, connected by canaliculi

Osteons are aligned in the same direction along lines of stress and help resist bending/fracture

Question 11

What are Harversian canal

Answer 11

– contains bone’s blood vessels and nerve fibres

Question 12

What is the trabecular bone made up of

Answer 12

Constitutes the inner layer of bones

Consists of trabeculae – arrangement of rods and plates
Trabeculae arranged so that one side of bone bears tension and the other withstands compression

Question 13

What are the characteristics of woven bones

Answer 13

Disorganised fibre organisation
Osteoblasts produce osteoid rapidly
In all fetal bones – later replaced by lamellar bone
Present following fractures – woven bone is initially laid down as healing occurs

Question 14

What are the characteristics of lamellar bone

Answer 14

Created by remodelling of woven bone
Collagen fibres are highly organised and aligned in sheets
Collagen fibres run in opposite directions to provide tensile strength
Contains less osteocytes than woven bone

Question 15

What are osteoblasts and what are their function

Answer 15

Bone building cells

Synthesise and secrete the organic parts of bone ECM (osteoid)

Initiate and control the mineralisation of osteoid via hydroxyapatite

Produce many products including enzymes (alkaline phosphatase), growth factors, hormones (osteocalcin), and collagen

Question 16

Structure of ostoblasts

Answer 16

OBs are cuboidal in shape and become flattened when surrounded by the matrix

Question 17

What are the fucntions of osteoclasts

Answer 17

Bone breaking (resorption) cells
Critical in the maintenance, repair and, remodelling of bones 
Produce enzymes (acid phosphatase) that dissolve the organic and inorganic components of bone

Question 18

Strcuture of osteoclasts

Answer 18

Large, multinucleated cells formed by the fusion of many cells derived from monocytes circulating in the blood

Contain many small projections (microvilli) that extend into the bone’s surface

Question 19

What are osteocytes

Answer 19

Derived from osteoblasts
Most abundant cell type in mature bone

Found within fully formed bone

Occupy a small gap known as a lacuna

Signal other osteocytes in response to bone deformations in bone remodelling process

Question 20

What specialised cell does the cartilage composed of

Answer 20

The chondrocyte

Question 21

Charactersitics of cartilage

Answer 21

Composed of collagen, proteoglycans (aggrecan), glycosaminoglycans (GAGs), and water
Contains one highly specialised cell type – the chondrocyte
Avascular – obtains all nutrients through diffusion
Three types – hyaline, elastic, fibro

Question 22

What are the purpose of chondrocytes

Answer 22

Occupy small cavities in the cartilage known as lacunae

Produce and maintain the cartilaginous matrix

Absorb nutrients via diffusion from the perichondrium

Question 23

What is chondrogenesis

Answer 23

Process of cartilage formation from mesenchymal cell condensation

These then differentiate into chondroblasts and begin secreting molecules to form ECM

Question 24

Where are hyaline cartilage found

Answer 24

Found on joint surfaces of long bones (articular cartilage), trachea, larynx, end of ribs (costal cartilage)

Question 25

What is the most abundant type of cartilage

Answer 25

Hyaline

Question 26

What are hyaline cartilages composed of

Answer 26

Matrix primarily composed of type II collagen along with GAGs and PGs – composition of these is essential to for its function (articular cartilage acts as a shock absorber)
Chondrocytes secrete and modify the extracellular matrix

Question 27

What is the hyaline cartilage matrix composed of

Answer 27

Type II collagen fibrils

Glycosaminoglycans (GAGs) – hyaluronan

Proteoglycans – aggrecan

Water

Question 28

Why is chondrocyte and collagen oreintation important

Answer 28

Different zonal organisation helps tissue withstand sheer and tensile forces

Question 29

Where is elastic cartilage found

Answer 29

Found in the epiglottis (located behind the tongue), external ear (pinna), larynx, and eustachian tubes

Question 30

What is elastic cartilage composed of

Answer 30

Matrix primarily composed of elastic fibres and type II collagen

Chondrocytes are much more abundant and larger than those present in hyaline cartilage

Question 31

Where is fibrocartilage found

Answer 31

Found in the intervertebral discs and pubic symphysis

Question 32

What is fibrocartilage composed off

Answer 32

Matrix primarily composed of type I collagen and several GAGs
Chondrocytes often aligned in alternating parallel rows with bundles of collagen

Question 33

What is collagen

Answer 33

Main structural protein in cartilage – accounts for 2/3 dry mass of articular cartilage
At least 28 different types

Question 34

What twi categories can you divide collagen into

Answer 34

Fibrillar and non-fibrillar

Question 35

What are glycosaminoglycans

Answer 35

Glycosaminoglycans (GAGs) are long polysaccharides composed of repeating disaccharide units
GAGs – hyaluronan, heparin sulphate, chondroitin sulphate – highly negatively charged

Question 36

What are proteoglycans

Answer 36

Proteoglycans are proteins that have been heavily glycosylated – GAGs attached
PGs – aggrecan (major PG in cartilage), perlecan, decorin, biglycan

Question 37

How is ECM able to withstand compression

Answer 37

GAGs are highly negatively charged and as a result are involved in binding cations

Resulting osmotic effect leads to the retention of water in ECM

ECM can now withstand compression/loading

Question 38

What are tendons and ligaments

Answer 38

Soft, collagenous fibrous connective tissue

Composed of parallel rows of fibroblasts surrounded by collagen fibrils

Help withstand tension

Tendons connect muscles to bones

Ligaments connect bones to bones