MSK histology

Question 1

What are the primary functions of bone in the body?

Answer 1

• Support <br></br> - Levers for effective movement <br></br> - Protection of internal organs <br></br> - Calcium storage <br></br> - Haemopoiesis (blood cell production)

Question 2

Where is more than 95% of the total calcium found in the body?

Answer 2

It is found in bones, and there is a constant exchange of calcium between bone and the blood.

Question 3

How does intramembranous ossification differ from endochondral ossification?

Answer 3

• Intramembranous ossification occurs from fibrous membranes, forming flat bones of the skull, mandible, and clavicles. <br></br> - Endochondral ossification occurs from hyaline cartilage, forming most bones in the body.

Question 4

Which bones are primarily formed through intramembranous ossification?

Answer 4

Flat bones of the skull, mandible, and clavicles.

Question 5

Where does endochondral ossification take place in bone development?

Answer 5

It occurs in the rest of the body’s bones. Cartilaginous bones initially ossify within the diaphysis and secondarily within the epiphysis.

Question 6

How is bone girth increased?

Answer 6

By cells from the periostrum laying down circumferential new bone on the periphery of the existing cortex.

Question 7

How is bone length increased?

Answer 7

Through cartilage proliferation at growth plates between the metaphysis and epiphysis, followed by ossification of the cartilage.

Question 8

When does blood cell production predominantly shift to bone marrow?

Answer 8

Blood cell production begins in the bone marrow well before birth and becomes the primary site of haemopoiesis by the time of birth.

Question 9

At what age does blood production typically involve only the axial and limb girdle skeleton?

Answer 9

By the early 20s, typically only the axial and limb girdle skeleton is involved in blood production.

Question 10

What are the components of bone composition?

Answer 10

• 65% bioapatite (a form of calcium phosphate, mostly hydroxyapatite) <br></br> - 23% collagen <br></br> - 10% water <br></br> - 2% non-collagen proteins

Question 11

What is the function of the periosteum?

Answer 11

It covers the outer surface of all bones, except at the articular surfaces. It has an outer fibrous layer and an inner ‘osteogenic’ layer containing progenitor cells that develop into osteoblasts.

Question 12

What makes up the outer shell of the bone shaft (diaphysis)?

Answer 12

Dense cortical bone.

Question 13

What occupies the ends of the bone (epiphysis)?

Answer 13

Cancellous or trabecular bone.

Question 14

What is the structural difference between compact and trabecular bone?

Answer 14

The main difference lies in the presence of spaces (marrow cavities) adjacent to trabecular bone. Both types are lamellar, made up of layers.

Question 15

What is the functional unit of bone and its structure?

Answer 15

The osteon, consisting of concentric circles of lamellae surrounding a Haversian canal that transmits small vessels. Osteocytes are found between the lamellae within lacunae, interconnected by canaliculi.

Question 16

Where are osteocytes found in bone and how are they interconnected?

Answer 16

Osteocytes are located within lacunae between the lamellae. They are interconnected by a series of interconnecting tunnels called canaliculi.

Question 17

How does the microarchitecture of bone change with age?

Answer 17

At 20 years: strong, healthy bone. At 50 years: a decrease in trabecular thickness, especially for non-load-bearing horizontal trabeculae. At 80 years: a decrease in connections between vertical trabeculae and a decrease in trabecular strength.

Question 18

What are osteoprogenitor cells and where are they located?

Answer 18

They are reserve osteoblasts located on bone surfaces, such as under the periosteum.

Question 19

What is the function of osteoblasts and their origin?

Answer 19

Osteoblasts are bone-forming cells derived from mesenchymal cells in the bone marrow stroma. They have abundant RER (rough endoplasmic reticulum) and prominent mitochondria.

Question 20

What characterizes osteocytes and their role?

Answer 20

Osteocytes are the primary cells of mature bone and are derived from osteoblasts that become buried in the bone matrix. They are believed to sense mechanical strain on the skeleton.

Question 21

Describe osteoclasts and their origin.

Answer 21

Osteoclasts are large, multinucleated cells responsible for bone reabsorption. They are believed to be derived from the macrophage lineage of cells (haematopoietic progenitors), and several osteoclasts can fuse to form a giant cell.

Question 22

What is bone remodeling, and what is the Basic Multicellular Unit (BMU)?

Answer 22

Bone undergoes a continuous remodeling cycle at distinct sites, involving osteoclasts drilling into the bone, followed by osteoblasts lining the tunnel and laying down new lamellar bone. The collection of osteoclasts and osteoblasts at a site is termed the BMU.

Question 23

How does bone mineralization occur?

Answer 23

Osteoblasts secrete osteoid, a matrix of collagen, glycosaminoglycans, and proteoglycans that mineralizes over time in the extracellular space. The principal mineral of bone is calcium phosphate crystals, primarily hydroxyapatite.

Question 24

What distinguishes woven bone from lamellar bone?

Answer 24

Woven bone is the first bone laid down during development or after a break, characterized by haphazardly oriented collagen fibers. It is weaker than lamellar bone and is remodeled into lamellar bone by osteoclasts breaking it down and new osteoblasts reforming it.

Question 25

What are chondrocytes, and where do they reside?

Answer 25

Chondrocytes are cells found in cartilage, and they live in spaces within the extracellular matrix called lacunae. They actively produce and maintain the cartilage’s extracellular matrix.

Question 26

What are the three types of cartilage and their locations?

Answer 26

• Hyaline cartilage: found in articular surfaces, tracheal rings, and costal cartilage. <br></br>- Elastic cartilage: found in the auricle of the ear and most of the epiglottis. <br></br>- Fibrocartilage: found in intervertebral discs.

Question 27

What characterizes the extracellular matrix of hyaline cartilage?

Answer 27

Glassy appearance
Type I collagen
Articular cartilage has perichondrium

Question 28

De

A scribe the characteristics of skeletal muscle fibers.

Answer 28

Skeletal muscle fibers are striated, unbranched, and multinucleated. They are long cylinders, 10-100µm in diameter and 1,000-200,000µm in length, with nuclei positioned at the periphery of the fiber, just beneath the sarcolemma (muscle cell membrane).

Question 29

How are muscle fibers organized in a muscle?

Answer 29

Muscle fibers are grouped into bundles known as fascicles, and a muscle typically contains several fascicles. These are enveloped by the epimysium (connective tissue surrounding the whole muscle), perimysium (surrounding a single fascicle), and endomysium (around a single muscle fiber).

Question 30

What comprises a sarcomere and its role?

Answer 30

A sarcomere is the fundamental unit of contraction in a muscle cell. Thousands of sarcomeres are aligned end-to-end in a myofibril. They extend from one Z line to the next and contribute to the striated appearance seen in skeletal muscle under a light micrograph.

Question 31

Explain the concept of the motor unit and its role.

Answer 31

A motor unit comprises one motor neuron and all the muscle fibers it innervates. The fewer the muscle fibers in a motor unit, the finer the control of movement. The axon of the motor neuron branches, ending in neuromuscular junctions (synapses) with muscle fibers. The fibers within a motor unit are scattered in the muscle but are of the same fiber type.

Question 32

What characterizes Type I muscle fibers?

Answer 32

Type I fibers are relatively slowly conducting fibers that heavily rely on oxidative metabolism. They possess abundant mitochondria and myoglobin, resist fatigue, and produce relatively less force. Also known as “red” fibers.

Question 33

What defines Type IIA muscle fibers?

Answer 33

Type IIA fibers are an intermediate type, relatively fast contracting, and reasonably resistant to fatigue. They are relatively uncommon compared to other types.

Question 34

What are the characteristics of Type IIB fibers?

Answer 34

Type IIB fibers are fast-contracting fibers relying on anaerobic metabolism. They have few mitochondria and less myoglobin compared to Type I, fatigue easily, and produce significant force. Often referred to as “white” fibers.