Bone formation, cartilage, tendons

Question 1

Answer 1

Fetal bone

Developing trabeculae

Osteoblasts forming a monolayer around trabeculae

Question 2

Answer 2

Active osteoblast with unmineralized osteoid on bottom right

Question 3

Answer 3

Osteocytes

embedded within bone matrix

Flattened cells that occupy lacunae

Osteocytes communicate with osteoblast, pericytes of blood cells and other bone cells

Question 4

Answer 4

Osteocyte in decalcified bone section

Slender cytoplasmic processes sit in places called canaliculi to communicate with other cells via gap junctions

Question 5

Answer 5

Osteoclasts

large multinucleated cells derived from monocyte precursors

Occupy a shallow space called Howship’s lacuna

Question 6

Answer 6

Osteoclasts

Green outline - ruffled border - increased SA for hydrolytic enzymes

Basal zone - nucleus &cytoplasmic organelles, usually away from resorption border

Green space = Howship’s lacuna

Question 7

Answer 7

Epiphyseal plate

From top to bottom:

Zone of reserved cartilage

Zone of active proliferation: cells are larger, organized in columns, actively produce cartilage and matrix

Zone of hypertrophy: greatly enlarged cells with clear cytoplasm (glycogen, lipids, ALP), metabolically active and secrete type I collagen

Zone of calcified cartilage: hypertrophied chondrocytes begin to degenerate and the cartilage matrix becomes calcified - serves as a scaffold for new bone deposition

Zone of resorption: nearest the diaphysis, calcified cartilage in direct contact with marrow. Small blood vessels invade spaces previously occupied by dying chondrocytes, and provide a source for osteoprogenitor cells. Osteoblasts begin to deposit bone onto calcified cartilage

Question 8

Answer 8

compact bone

organized into osteons (yellow circles)

concentric layers of bone matrix surrounding a Haversian canal that contains vascular & nerve supply

Osteocytes reside in lacunae, extend cytoplasmic processes into small canaliculi to communicate with others

HCs connected by Volkmann’s canals. Nerves and blood vessels travel from periosteal/endosteal surfaces to the HC

Interstitial lamellae (red circles) - remants of previously formed osteon

Question 9

Answer 9

Spongy bone

matrix lamellated with lamellae arranged in parallel rather than concentrically organized lamellae found in compact bone

Question 10

Answer 10

Rib - hyaline cartilage

• peripheral: perichondrium

Adipose tissue and skeletal muscle also seen

Question 11

Answer 11

Perichondrium of hyaline cartilage

• outer fibrous layer: flattened cells - fibroblasts, merges with surrounding tissue
• inner chondrogenic layer: chondroblasts, more round in lacunae

Question 12

Answer 12

Hyaline cartilage

Chondrocytes in lacunae

Chondrocytes arranged in isogenous nests

High concentration of sulfated glycosaminoglycans in the territorial matrix (darker)

lighter region outside: interterritorial matrix - contains collagen type II

Question 13

Answer 13

Trachea

C-shaped hyaline cartilage

Question 14

Answer 14

Epiglottis

core of elastic cartilage

Van Gieson - stains elstin dark

trichrome - stains collagen green

Question 15

Answer 15

Elastic cartilage core of epiglottis

perichondrium on left

progressive enlargement of chondrocytes & denser network of elastic fibers towards the middle

Question 16

Answer 16

Elastic cartilage core of the epiglottis

Eosinophilia of the cartilage matrix

Elastic fibers seen

Question 17

Answer 17

Intervertebral disc

fibrous cartilage

Question 18

Answer 18

Intervertebral disc - fibrous cartilgae

Central basophilic nucleus pulposus

outer eosinophilic annulus fibrosis (Fibrous cartilage)

Question 19

Answer 19

Fibrocartilage

directionality in fibrillar matrix and alignment of chondrocytes into rows

Type I collagen predominates matrix

no perichondrium

found in: intervertebral disc, pubic sym, menisci of joints, insertions of tendons into bone

Question 20

Answer 20

Knee joint

synovial hinge

Two areas of hyaline cartilage - articular and epiphyseal plate

Question 21

Answer 21

Knee joint

see hyaline cartilage at epiphyseal plate and articular surface

also see menisci (fibrocartilage)

Question 22

Answer 22

Chondrocyte in lacuna

ECM - type II collagen with proteoglycan aggregates

sister chondrocyte of isogenous nest has popped out during prep

Question 23

Answer 23

Tendon

closely packed parallel arrangements of collagen fiber bundles

mainly type I collagen

Small embedded nuclei within fascicles - fibroblasts

Question 24

Answer 24

Skeletal muscle on top

tendons on bottom

an entire tendon surrounded by epitenon

Question 25

Answer 25

Tendon

Entire tendon surrounded by epitenon

fascicles surrounded by endotenon - conduit for vasculature and nerve supply

Fibroblasts dispersed

Question 26

Answer 26

Tendon

Fascicles surrounded by endotenon

Endotenon - delicate CT that acts as a conduit for blood vessels and nerves

Dispersed fibroblast nuclei

Question 27

Answer 27

Muscle-tendon jxn

Finger-like extensions of the sarcolemma interdigitate with collagen fibers of the tendon

Question 28

Answer 28

Projections of sarcolemma (white arrows) at muscle-tendon junctions