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Flashcards in Musculoskeletal System Deck (146):

What are the two meanings of bone?

1) Bone the organ
- organs are made up of different types of tissue
2) Bone the tissue
- One of the tissues found in the bones of the skeleton.


What are the 6 functions of the skeletal system?

1) support
2) protection of vital organs
3) movement - muscle must pull on bone
4) Calcium and phosphorous reserve
5) Haemopoiesis
6) Fat storage


Why must calcium be tightly regulated?

It is used for many things, e.g. muscle contraction of heart, hormone and enzyme production.


What percentage of calcium is stored in the bones?

99% in the bones


What is the function of haemopoietic tissue? What colour is it?

Makes RBC's, WBC's and platelets.


What are the two components of bone marrow?

Haemopoietic tissue and fat storage tissue


What is the phosphorous found in bone used for?

To build many substances e.g. ATP


Describe the bone marrow at birth compared to that of an adult.

All bone marrow is red at birth.
In adults, red bone marrow tends to be in the axial skeleton.


What are the two components of the adult skeleton?

Axial and Appendicular


How many bones are in the axial and appendicular skeleton?

80 (some paired)
126 (all paired)


What are the differences in function between the axial and appendicular skeleton?

Axial: support/protection and haemopoiesis
Appendicular: movement and fat storage


Describe the overall sections of a long bone in order.

Epiphysis, metaphysis, diaphysis, metaphysis, epiphysis


Relate the type of forces to the requirement for plates, rods and beams in the epiphysis and diaphysis.

Epiphysis: Forces perpendicular so plates, rods, and beams are needed for support.
Diaphysis: Forces are parallel so no need for plates, rods, and beams.


What are plates, rods and beams formed by?



What are trabeculae covered by?



List the layers of the epiphysis from outside to inside.

Articular cartilage, compact bone, spongy bone


What is another name for spongy bone?

Trabecular bone


Why is there no periosteum covering the articular cartilage?

It would just be sheared off by the other bone.


What is found between trabeculae?

Medullary cavity with bone marrow inside.


Where are blood vessels found in the epiphysis? What is their function?

Inside compact bone and between trabeculae.
RBC's, WBC's and platelets can enter blood.


Give the layers of the diaphysis from outside in.

Periosteum, compact bone, endosteum, medullary cavity


What is the periosteum?

Outer fibro-cellular sheath surrounding the bone. Made up of dense irregular connective tissue, rich with blood vessels and nerves.


Describe the compact bone of the diaphysis.

Forms a cylinder
Very light and strong


How does the compact bone of the diaphysis compare to that of the epiphysis?

D: thick
E: thin


Describe the endosteum of the diaphysis.

Thin, inner fibro-cellular layer lining medullary cavity.


What does the medullary cavity of the diaphysis contain in the appendicular skeleton vs the axial skeleton vs the front of the face?

Appendicular: yellow bone marrow
Axial: red bone marrow
Front of face: air (must be lighter)


What is another name for the perforating fibres between the periosteum and the compact bone? What are they produced by?

Sharpey's fibers - very strong
Collagen produced by periosteum blends with the collagen on the bone.


Where are the blood vessels found in the diaphysis?

In the periosteum and compact bone.


Bone is a type of __________ _________ tissue

Specialised connective


What are the two components of connective tissue?

ECM and cells


What is ECM made up of?

Fibres (organic): 1/3 of the dry weight
Ground substance (inorganic): 2/3 of the dry weight


In bone, what fibres are present? What is their purpose?

Collagen fibres type I and IV.
Resists tension (stretching and pulling)


What is found in the ground substance?

Water and long chain carbs
Hydroxyapatite Ca10(PO4)6OH
Resists compression (squeezing and crushing)


What type of cells are found in bones? What are the functions of each type?

Osteogenic: cell reserve
Osteoblast: bone formation
Osteocyte: bone maintenance
Osteoclast: bone destruction


What does tension plus compression add up to?

Torsion (twisting)


What are osteogenic cells also known as? What is the precursor, location, and function?

Osteoprogenitor cells.
Precursor: unspecialised stem cells (mesenchyme = embryonic connective tissue)
Location: surface of bone in the periosteum and endosteum.
Function: normally dormant, but can divide and supply developing bone with bone-forming cells.


What is the precursor for osteoblasts? What are they located? What is their function?

Osteogenic cell
Location: usually in a layer, under the peri or endosteum. Wherever new bone is being formed.
Function: synthesis, deposition and mineralisation of osteoid.


What is osteoid?

Not a cell.
The organic extracellular matrix (mainly collagen) of bone, synthesised by osteoblasts prior to mineral deposition. Collagen accounts for 70% of osteoid with the remainder consisting of proteoglycans and other proteins.
This precursor matrix is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification. Water is displaced gradually, so it becomes difficult for full calcification.
This makes the bone strong but also dense, thus nutritive fluids cannot diffuse freely through it.


What is the precursor to osteocytes? Where are they located? What is their function?

Location: trapped within lacunae inside bone. Osteocytes can communicate with neighbouring cells through their long cellular processes and canaliculi.
Function: bone tissue maintenance.


How do osteoclasts come about? Where are they found? What is thei function?

Fusion of monocyte (WBC) progenitor cells forming a syncitium.
Location: at sites where bone resorption is occurring.
Function: secretes acid and hydrolytic enzymes to dissolve the mineral and organic components of bone. Exposes collagen using acid and breaks down protein with enzymes.


What is the function of the clear zone?

Stops acids and enzymes from getting out from under the bone.


What must happen for a child's bone to grow into an adult's bone?

Appositional growth: the bone has to be remodelled. This involves appositional growth and bone resorption. We don't want the bone to get too thick and heavy.


How does appositional growth occur? Give an example of when this might occur? What does it occur in response to?

Bone is put down onto an existing layer.
A long bone growing in diameter.
In response to mechanical damage.


Describe the process of bone resorption.

Monocyte precursor cells leave blood vessel and start to fuse on bone surface. Osteoclasts form on surface and start dissolving. A tight seal is formed between the osteoclast and the surface of the bone. Osteoclasts eventually die by apoptosis and resorption stops. They have a short life. Blood vessels grow into new space.


What is Howship's lacuna?

A pit formed when an osteoclast dissolves bone.


What happens when growth of the bone stops?

Osteoblasts can convert back into osteogenic cells or die. Osteoid becomes fully calcified.


Why can't the tissue bone grow by interstitial growth?

It is too rigid


Where does interstitial growth occur? What occurs during interstitial growth?

In softer tissues that can deform.
Involves cells dividing, secreting more extracellular matrix, and growing the tissue from within.


What is appositional growth? Why is this the only way bone can grow?

Adding new bone onto an existing surface.
Bone is designed to resist deformity.


What does bone-remodelling involve?

The two processes, appositional growth and bone resorption, which occur throughout the skeletal system, often completely independent of each other.


What process do long bones grow by?

Endochondral ossification


How does oestrogen affect bones? Why does osteoporosis occur?

It is needed for osteoclast regulation.
Osteoporosis occurs at menopause because of decline in oestrogen. Affects spongy bone first.


As osteoblasts deposit new bone onto a surface, they do so in ________ or _______.
Describe the placement of collagen fibres. What effect does this have?

Layers or sheets
The collagen fibres are typically put down in the same direction within a layer, but can alternate up to 90 degrees out of phase between the layers. This enables bone to withstand forces from different directions, making it significantly stronger. Increases strength without increase of volume.


What are the two forms of lamellar bone?

Spongy and compact


What is another name for mature bone?
What is another name for immature bone?

M: Lamellar bone
I: Woven bone


Describe woven bone.

Wavey collagen, low density, random arrangement, not very strong. Most turns into lamellar bone after 3 years. The only place it is found in the adult skeleton is when a bone is broken.


What is another name for spongy bone?

Cancellous or trabecular bone


What percentage of the skeleton is spongy bone? What does this change depend on?

Changes depending on loads placed on bones throughout the skeleton.


Does spongy bone have osteons?



Where is spongy bone mostly found?

In the epiphysis


What is the size of a trabecula of spongy bone?

Less than 0.4 mm because it is rare to find osteoclasts more than 0.2 mm away from a blood vessel as it will not get enough nutrients


What is the turnover of spongy bone compared to compact bone? Why so?

5 times due to increased surface area over which osteoclasts can move.


What is another name for compact bone?

Cortical bone


What is a by-product of appositional growth in compact bone?

Circumferential lamellae


What is the normal thickness of compact bone? Why is it thicker than spongy bone?

Variable thickness, normally greater than 0.4mm
Able to be thicker because it has a lattice of blood vessels.


Describe the formation of primary osteons.

Primary osteons are formed around an existing blood vessel on the surface of bone (normally in the periosteum). This occurs when the bone is growing and new bone tissue is being deposited onto an existing surface.


Describe the 4 steps required for appositional growth to form a primary osteon.

1) Osteoblasts in the active periosteum either side of a blood vessel put down new bone forming ridges.
2) As the bone continues to grow, these ridges come together and fuse, forming a tunnel around the blood vessel. The tunnel is now lined with endosteum.
3) The osetoblasts in the endosteum build concentric lamellae onto the walls of the tunnel. The tunnel is slowly filled inward toward the centre, forming a new osteon.
4) The bone continues to grow outwards as the osteoblasts in the periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over another blood vessel.


What are secondary osteons created inside?

The existing bone tissue


What is the first step for secondary osteon formation.

1) Osteoclasts form and gather in an area that needs to be remodelled. this group of osteoclasts starts boring its way through the existing bone. This area is called the cutting cone and creates a tunnel inside the existing bone. This is how secondary osteons differ to primary osteons. In primary osteons, the tunnel is created on the surface of a bone as it grows.


What is the second step for secondary osteon formation?

After the tunnel has been created, osteoblasts move in and line the tunnel wall. They form the new active endosteum and start depositing osteoid onto the walls of the tunnel.


What is the third step of secondary osteon formation?

Layer upon layer of new concentric lamellae are put down. A blood vessel will also grow into the tunnel to suppply the active osteoblasts. This area is called the closing cone and moves along behind the cutting cone. Some of the osteoblasts are trapped in the newly deposited bone and become osteocytes.


What is the fourth step of secondary osteon formation?

Eventually, the tunnel is reduced to the size of a typical Haversian canal. The remaining osteoblasts lining the Haversian canal either die or become bone lining cells.


How fast does boring of a tunnel through bone occur?

1mm/20 days


What is the unit of spongy bone vs compact bone?

S: trabecula
c: osteon (Haversian system)


Compare and contrast the process of unit formation in spongy bone and compact bone.

S: grows outwards into the medullary cavity.
C: grows inwards into the Haversian canal.


Where is spongy bone and compact bone found?

S: inside bones, epiphysis of long bones
C: the outer shell of bones, diaphysis of long bones


What is the blood supply for spongy bone and compact bone?

S: Blood vessels in the medullary cavity
C: Blood vessels within the Haversian and Volkmann's canals


What are the differences in function between spongy bone and compact bone?

S: To supprt the outer cortex of compact bone in areas where forces occur from multiple directions. This is to help reduce the weight of the bone. Rapid turnover of Ca and P.
C: To provide a strong dense shell of bone on the outside, thickening in areas that are exposed to large forces.


How can we distinguish between a primary and secondary osteon?

If tunnel is grown, primary osteon
If tunnel is bored, secondary osteon


Define joint.

A joint or articulation is any point at which two or more bones interconnect. This union will be a compromise between the need to provide support and the need to remain mobile.


What is another name for joint?



What are the functions of joints?

1) Movement
2) Force transmission
3) Growth


What is the stiffness of a joint due to?

Abnormal adhesion and rigidity of the bones of a joint.
Ankylosis is due to increased synarthrosis.


Define each of the three joint types based of functional classification. State their stability level, movement, and location.

Synarthrosis: immovable joint, high stability, low movement, axial skeleton, force transmission and growth
Amphiarthrosis: slightly movable, medium stability, medium movement, both axial and appendicular skeleton, support function
Diarthrosis: freely movable, low stability, high movement, appendicular skeleton, injured the most, most abundant.


What is synarthrosis and amphiarthrosis held together by?

A block of tissue


Describe synovial joints.

Most common
Unlike the other types of joints found in the human body, synovial joints are not restricted by the properties of a specific tissue or tissues which hold the ends of the bones tightly together. Apart from the articular capsule, the ends of the articulating bones in a synovial joint are mostly free. This permits a wide range of motion, but can also introduce instability.


What is articular cartilage? What is its function? How thick is it?

A specialised type of hyaline cartilage (a type of connective tissue). Its primary function is to protect the ends of bones that come together to form a joint. This connective tissue forms a thin layer. typically 1-7 mm thick, which is attached to the bone. Articular cartilage can absorb shock, support heavy loads, and provide a smooth, near frictionless surface when combined with synovial fluid.


What causes arthritis?

The degradation of the articular cartilage.


What is meant by CoF?

Coefficient of friction
Higher means lots of friction.


What percentage of the articular cartilage is made up of cells? What type of cells? Describe their function, location and properties.

- Build, repair, and maintain cartilage
- Live in spaces called lacunae
- Depending on the zone, they occur by themselves or in groups called nests


What percentage of the articular cartilage is made up of extracellular matrix? What makes up the ECM?

- Water and soluble ions (75%): the fluid phase that can move in and out of the tissue.
- Fibres (75% dry weight)
- Glycosaminoglycans (GAG)
- Proteoglycans (PG)


What are the functions of the fibers found in the articular cartilage?

- Provides the structural integrity to the tissue.
- Specific zonation patterns
- Part of the solid phase that is fixed inside the tissue.


What type of fibres are present in the ECM of articular cartilage? How are they different to the other type?

Collagen (mainly type II)
They are thinner and more flexible than type I


What makes up the ground substance?

Water and soluble ions, glycosaminoglycans, and proteoglycans.


Give examples of glycosaminoglycans and proteoglycans. Outline their functions.

GAG: Hyaluronic acid, Chondroitin sulphate, keratin sulphate
PG: Aggrecan
Provides the swelling and hydrating mechanism for the proper function of cartilage. Also part of the solid phase that is fixed inside the tissue.


Does cartilage contain blood vessels, nerves or lymphatics? What nourishes chondrocytes?

Chondrocytes are nourished by diffusion only


Describe the loading cycle of articular cartilage.

- Negative charges on the repeating disaccharide units attract positive ions into the cartilage from the joint space. This increases the ion conc. in the matrix.
- Creates osmotic pressure/ gradient, which draws water into the matrix. The cartilage begins to swell with the influx of water.
- As the cartilage swells, the collagen is placed under increasing tension. Eventually, the swelling force = tensional forces, and the cartilage stops swelling. This known unloaded equilibrium.
- When a load is introduced, the fluid phase (water and positive ions) is squeezed out of the cartilage back into the joint space and synovial fluid.
- The loss of the fluid phase reduces the volume of the cartilage (creep). This pushes the negative charges closer together. Eventually, the compressive load will be supported by the solid phase and the repulsion of the negative charges. The cartilage will stop shrinking = loaded equilibrium


Is cartilage hydrophilic or hydrophobic?



Distinguish between the area of contact for loaded and unloaded cartilage.

Unloaded: small area of contact
Loaded: deforms so load is spread out over a larger area


What are all synovial joints surrounded and enclosed by? Why must this be suitably loose? What is it perforated and reinforced by?

A joint capsule
The capsule forms a sleeve around the joint connecting the ends of the contributing bones. Must be suitably loose to permit the joint to function properly. The articular capsule is perforated by vessels and nerves and may be reinforced by ligaments.


Where does the articular capsule become tight?

At the extreme limits of the natural range of joint motion, thereby protecting the joint from damage caused by excessive movement.


What is a ligament?

Dense regular connective tissue connecting bone to bone


What are the two layers of the articular capsule?

An outer fibrous layer and an inner synovial membrane


Describe the fibrous layer.

Outer layer of dense connective tissue. Variable in thickness. The fibrous layer is made up of parallel but interlacing bundles of white collagen fibres that are continuous with the periosteum of the bone. Poorly vascularised but richly innervated, which is why it hurts to sprain joints.


What are capsular or intrinsic ligaments?

Thicker sections of the articular capsule. These ligaments, along with the rest of the capsule, resist tensional forces and are designed to check excessive and abnormal joint movement.


What is the function of the fibrous layer of the articular capsule?

Supports the synovial membrane and protects both the synovial membrane and the whole joint.


Describe the synovial membrane.

Inner layer of loose connective tissue of variable thickness. Lines all non-articular surfaces inside the joint cavity, up to the edge of the articular cartilage.


What can the articular cartilage be further split into?

Two histological layers:
1) Intima
2) Subintima


Describe the intima of the synovial membrane.

Thin and normally only 1-3 cells thick. These cells are loosely called synoviocytes and secrete some of the components found in synovial fluid.


Describe the subintima of the synovial membrane.

Highly vascular and contains macrophages, fat cells and fibroblasts which help maintain and protect the articular capsule during normal movement.


What is the joint cavity? What is it filled with?

The small area between the articulating surfaces, while the peripheral margins of the joint cavity are filled by the collapsing and in-folding of the synovial membrane (villi).This potential space is filled with a fluid called synovial fluid.


What does the amount of synovial fluid not exceed?

The amount of fluid inside a healthy joint cavity rarely exceeds 1 mL, even in large human joints such as the knee.


What is synovial fluid? What is found in it?

A clear or slightly yellowish fluid that is an ultrafiltrate of blood plasma that leaks out of the vessels in the synovial membrane subintima. Other compounds (e.g. hyaluronic acid) not found in the blood filtrate are secreted by the synoviocytes. Free cells are also found in low concentrations. These cells tend to be monocytes, lymphocytes, macrophages, and synoviocytes.


What are the functions of synovial fluid?

Joint lubrication, shock absorption, chondrocyte metabolism, and overall joint maintenance.


What is muscle tissue designed to do?

Specifically to move different parts of the body by pulling on another tissue.


What are the 5 functions of muscles?

1) Movement
2) Stability
3) Communication
4) Control of body openings an passages
5) Heat production


Describe the movement function of muscle.

Movement of bones in skeletal system (skeletal muscle), gut contents and lymph transportation (smooth muscle), and circulating blood (cardiac muscle).


How does muscle pay a role in stabilising joints and maintaining posture?

Muscle is especially important in stabilising those joints that have a wide range of movement. In these joints, stability (normally provided by the ligaments and/or the articular capsule) has been replaced with active contraction of the surrounding muscles.


How is muscle used for communication

Facial expression, body language, writing and speech


How is muscle used for controlling the body openings and passages?

Some ring-like muscles (sphincters) help control the admission of light (eyelids and pupils) and food and drink (muscles around the mouth) that enter our bodies. The elimination of waste is also controlled by the urethral and anal sphincters (smooth and skeletal muscle). Normally, the passage of food and liquid through the gut is also controlled by smooth muscle.


Skeletal muscle can produce as much as ___% of our body heat. What is this heat used to maintain?

Maintains the body at 37 degrees celsius for normal function.


What does the ramp up when cold?

Tonus contraction, which causes shivering


What is a bone avulsion?

A break in the osteotendinous junction


What are tendons made up of?

Dense regular connective tissue


What is epimysium?

Dense irregular connective tissue surrounding the perimysium and the entire muscle. Defines the outer boundary of muscle.


What is perimysium?

Dense irregular connective tissue surrounding the fascicles.


What is endomysium?

Loose irregular connective tissue surrounding myocytes. Contains the nerves and capillaries that supply the myocytes.


What is a myocyte/myofibre? What does it contain? What is its size?

A muscle fibre/cell. A bundle of myofibrils. Has many nuclei, sarcoplasm and sarcolemma. Highly variable in diameter, 10 fold difference.


Describe the sarcoplasm and sarcolemma.

Sarcoplasm: cell cytoplasm, area between myofibrils. Contains mitochondria, glucose, lipids, myoglobin and is therefore highly active and aerobic.
Sarcolemma: cell membrane. Highly conductive. Allows for quick and even conduction and thus uniform contraction.


What are myofibrils? Describe their size.

Contractile organelles made up of many sarcomeres containing z line/band, A band (dark) and I band (light). Striated. 1 micrometer


List the layers of the not muscle and muscle in order

Not muscle: Skin, superficial fascia (subcutaneous layer), deep fascia
Muscle: Epimysium, muscle, perimysium, fascicle, endomysium, myocyte, sarcolemma, sarcoplasm, myofibril


What is deep fascia?

A wrapping of dense connective tissue (regular and irregular) covering the deep structures of the body. It underlies the skin and the subcutaneous tissue.


What is muscle grouped into?

Muscles that are supplied with the same nerves or have a similar action can be found grouped together in regions called compartments.


What is the outer sleeve and walls of the compartments of muscle made up of? What are the walls or septa of muscle compartments referred to as? What happens when investing fascia comes into contact with

Deep fascia
Investing fascia (e.g. intermuscular septa, interosseous membranes)
Where investing fascia comes into contact with bone, it fuses with the periosteum.


Describe the movement of epimysium in different areas.

In most areas, the outer layer of muscle can move and glide under the deep fascia. In other areas, the deep fascia is part of the muscle tendon and can act as an attachment point for the muscle.


What is increase in muscle size due to?

Increase in muscle size is due to increases in the size of fibres (hypertrophy) rather than any increase in fibre numbers (hyperplasia. The myocytes themselves will increase in diameter with more myofibrils packed into each muscle cell. Typically, the effect will be an increase in overall muscle size and strength, but the same number of cells will still contribute to the contraction.


What factors can stimulate skeletal muscle hypertrophy?

- Repetitive contraction of muscles to near maximal tension (heavy resistance training)
- Use of anabolic steroids


What are anabolic steroids?

Variants of the male sex hormone testosterone, which have been synthesised by pharmaceutical companies. These steroids increase protein synthesis through their interactions with specific target tissues that include skeletal muscle and bone.


What are the side effects of anabolic steroids?

Anabolic steroids don't just target muscle and bone tissue, they can also effect other tissues which can have side effects such as: acne, hair loss, excess hair gain in the wrong places, liver failure, shrivelled testes, infertility, increased susceptibility to coronary artery disease (increased absorption of cholesterol), and extreme mood swings (roid rage).


What is meant by atrophy?

Decrease in the size of myocytes. Muscular atrophy occurs when muscles are not used or stimulated by motor neurones. For example, when a limb is immobilised in a cast for a period of time or if a muscle is paralysed. It also occurs as part of the complex pathology in disease such as heart failure, diabetes, cancer and AIDS.


When does normal loss of muscle mass start? When is the rate accelerated? By what age is 40% of muscle mass lost? What happens to the lost muscle?

At the age of 20 years
After the age of 50
By the time we reach 80 years
Muscle is replaced by fat and connective tissue.


What is muscle loss due to? When can atrophy be reversed?

Some of the loss is due to individual fibre shrinkage i.e. atrophy. Some is due to individual fibre loss i.e. hypoplasia. If atrophy is not permitted to proceed too far, it can normally be reversed.


What is another name for satellite cells?



Where are satellite cells found?

They lie beside muscle fibres outside the sarcolemma but within the same basement membrane.


Why aren't myocytes able to divide by mitosis?

Because myocytes are large multinucleated cells, created when myoblasts fused together into a syncitium. They are too large to divide by mitosis.


What are the satellite cells able to do?

They are the only cells in muscle that can divide and fuse with other satellite cells and myocytes to repair any damage that may have occurred. While the number of muscle fibers is more or less set at the time of birth, satellite cells do have a limited ability to replace muscle fibres that die from old age or injury.