MSKS Histology Lecture 1_Skeletal System

Question 1

Define woven and lamillar bone

Answer 1

• Woven (immature) — during bone tissue formation, the cells and bone matrix are arranged
randomly, without any obvious pattern.

• Lamellar (mature) — during bone tissue formation, the cells and bone matrix are arranged
into well-organized layers, known as lamellae

Question 2

What is the main cell type at the perifery of the perichondrium

Answer 2

chondroblast

Question 3

describe the function of Parathyroid hormone (PTH) and Calcitonin

Answer 3

• Parathyroid hormone (PTH) — released by parathyroid gland; raises low blood Ca2⁺ by stimulating osteoclast activity indirectly (via RANKL produced by osteoblasts) and osteocytes (directly); both cells resorb surrounding bone matrix and release Ca2⁺ into the blood stream.

• Calcitonin — released by thyroid gland; lowers elevated blood Ca2⁺ by opposing PTH in bone to
decrease osteoclast activity

Question 4

What is the main cell type in the perichondrium?

Answer 4

It is typically a fibroblast

Question 5

What are the 6 steps of Endochondral ossification

Answer 5

see attached

Question 6

Describe Osteoporosis and osteopetrosis

Answer 6

• Osteoporosis — bone resorption exceeds bone formation and leads to a reduced bone mineral density (BMD), not due to a calcium deficiency.
• Osteopetrosis (“marble bones”) — bone resorption is defective and leads to thickening of cortical bone and obliteration of the marrow cavity

Question 7

Deffine Appositional growth

Answer 7

growth occurs at the periphery of the cartilage or deep layer of perichondrium, if present

Question 8

Define Endochondral ossification

Answer 8

hyaline cartilage precursors forms within the mesenchyme initially, which is later replaces by bone deposition and ossification; occurs in nearly all long bones, short bones, and ribs.

Question 9

Define:

• Diaphysis
• Metaphyses
• Epiphyseal line
• Epiphyses

Answer 9

• Diaphysis — shaft
• Metaphyses — widening ends of shaft
• Epiphyseal line — remnant of growth plate
• Epiphyses — proximal and distal ends,
articular surface covered by articular cartilage

(see attached)

Question 10

What is a chondroma and condrosarcoma

Answer 10

Cartilage cell tumors — chondroma (benign) vs. chondrosarcoma (malignant)

Question 11

Why is it difficult for adults to repair cartilage?

Answer 11

avascularity, low metabolic rate, immobility of chondrocytes, and limited proliferation of mature chondrocytes

Question 12

Describe Osteoarthritis and Rheumatoid arthritis

Answer 12

• Osteoarthritis — gradual loss or changed physical properties of the articular cartilage due to physical or pathological damage or old age.
• Rheumatoid arthritis — autoimmune disorder that causes chronic inflammation of the synovial membrane due to the release collagenases and other hydrolytic enzymes by macrophages into the synovial fluid, which degrades the articular cartilage.

Question 13

Define

• Pituitary dwarfism
• Gigantism
• Acromegaly

how is growth hormon related to each of these conditions?

Answer 13

• Pituitary dwarfism — lack of GH during growth period leads to short bones
• Gigantism — excess GH during growth period leads to long bones
• Acromegaly — excess GH after epiphyseal plates have closed leads to wide bones through Appositional Bone Growth

Question 14

What causes Osteogenesis imperfecta (“brittle bone disease”)

Answer 14

deficit in type I collagen fiber, either in the amount or the production of defective fibers (genetic mutation)

Question 15

What cell type is a the cartilage proper, often within a lacunae?

Answer 15

chondrocyte

Question 16

Define Intramembranous ossification

Answer 16

bone deposition and ossification occurs directly within the mesenchymal tissue; occurs in most flat bones of the skull and face, scapula, and clavicle

Question 17

Where is elastic Cartilage typically found?

Answer 17

the ears and the epiglotsis

Question 18

What are the three layers of Periosteum?

Answer 18

• Fibrous layer — outer layer of dense (irregular) CT
• Cellular layer — contains osteoprogenitor cells and is well-defined in bones that are actively growing
• Perforating (Sharpey) fibers — penetration of the periosteum into underlying bone tissue, most dense at attachment sites of tendon and ligaments

Question 19

What is the main difference between hyaline cartilage and elastic cartilage?

Answer 19

the presence of elastic fibers. (see attached)

Question 20

What are the three types of “bone cells”

Answer 20

Osteoblasts, Osteocytes, Osteoclasts

Question 21

Deffine Interstitial growth

Answer 21

chondrocyte proliferation within cartilage gives rise to isogenous groups

Question 22

Hyaline Cartilage is often bound on either side by what?

Answer 22

perichondrium (see attached)

Question 23

What are the 4 steps in cartilage growth?

Answer 23

see attached

Question 24

What are the protein fibers in the Cartilage ECM? What produces them?

Answer 24

• Type II collagen (produced by chondrocytes) is most prevalent, among all three cartilage types • Elastic fibers (produced by chondrocytes) is prevalent within elastic cartilage • Type I collagen (produced by fibroblasts and some chondrocytes) is present only within fibrocartilage

Question 25

Define the calcium deficency for children and adults

Answer 25

Calcium deficiency — insufficient calcium in diet or failure to produce vitamin D
• Rickets — bone growth is impeded and developing bones and epiphyseal plates become deformed
• Osteomalacia — in adults, it leads to deficient calcification of newly formed bone matrix
and partial decalcification of already calcified bone matrix

Question 26

How are chondrocytes typically arranged in fibrocartilage?

Answer 26

axially (see attached)

Question 27

Define compact and cancellous bone

Answer 27

• Compact — bone tissue is highly packed with no medullary spaces; typically found in the
cortical region of bone (underlying the periosteum)

• Cancellous — bone tissue is arranged in thin spicules, or trabeculae, which form an
anastomosing meshwork with spaces between the trabeculae that are lined by endosteum
and filled with bone marrow; typically found within the medullary space of the bone

Question 28

What are two important sub groups of hyaline cartilage?

Answer 28

Articular cartilage, Epiphyseal
(growth) plate

Question 29

What are the 5 steps of Intramembranous ossification

Answer 29

see attacehd

Question 30

Where is fibrocartilage typically found?

Answer 30

It is typically in symphisis joints and in between vertebral disks