L0: CT supportive

Question 1

What does CT supportive include?

Answer 1

Bone, cartilage

Question 2

Cartilage definition

Answer 2

contains fibers, ground substance and cells. No vascularization; cells receive nutrients via long-range diffusion. Cells are chondroblasts/cytes, which produce ground substance and fibers.

Question 3

Chondrocytes (function, developmental sequence)

Answer 3

produce cartilage ground substance and fibers.

Developmental sequence: mesenchymal cells > fibroblasts > chondroblasts > chondrocytes

Question 4

Describe hyaline cartilag function and location.

Answer 4

Most common cartilage type.
Found covering articular surfaces of most joints, costal cartilages, larger respiratory tubes, nasal cartilages.
Embryonically and in young it provides temporary model for endochondrial bone development.

Question 5

What cells are in hyaline cartilage? How are they arranged?

Answer 5

chondrocytes, young chondroblasts forming isogenous nests of 2-4 cells with secreted layer of matrix around them.

Question 6

Shape difference between chondroblasts and chondrocytes

Answer 6

chondroblasts are at the periphery of cartilage; cytes are enveloped in matrix and more rounded.

Question 7

Hyaline Matrix

Answer 7

appears homogenous, glasslike, stains basophilic.

Matrix is composed of fine collagen fibers (invisible w/o special staining) and amorphous gel of proteoglycans.

Question 8

Hyaline perichondrium

Answer 8

dense irregular CT that surrounds cartilage; composed of 2 cell layers.
Fibrous zone= normal dense irregular CT outer layer.
Chondrogenic zone= inne rlayer, gives rise to chondroblasts.

Question 9

Appositional cartilage growth

Answer 9

adding new layers to outside

Question 10

interstitial cartilage growth

Answer 10

formation of isogenous nests + secretion of matrix around nests (= territorial cartilage)

Question 11

What type of growth(s) do hyaline undergo?

Answer 11

appositional and interstitial

Question 12

Describe elastic cartilage.

Answer 12

Adapted to resist bending.
Found in external ear, epiglottis, some laryngeal cartilages
Similar to hyaline in appearance and composition except that matrix contains extensive network of elastic fibers.
Not prone to undergo degeneration or calcification as sometimes occurs in hyaline cartilage.
Surrounded by perichondrium.

Question 13

Describe fibrocartilage.

Answer 13

Structurally intermediate between dense regular CT and cartilage; contains collagen bundles + chondrocytes with min amount of matrix.
Occurs where tough support or high tensile strength is needed (like intervertebral discs and certain joints).
Functions to attach dense regular CT to cartilage or bone.
Lacks perichondrium
Chondrocytes tend to be grouped in short rows (capsules) between collagen bundles.

Question 14

What is bone?

Answer 14

rigid supportive tissue making up most of the skeleton in evolutionarily advanced vertebrates.
composed of cells and matrix with a dense CT periosteum covering the outside.

Question 15

There are 4 general types of cells in bone. Name them.

Answer 15

Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts

Question 16

What are osteogenic cells?

Answer 16

precursor cells derived from mesenchyme; capable of mitotic division; found near bone surface and in inner portion of periosteum.

Question 17

What are osteoblasts?

Answer 17

deposit bone matrix, found at margins of growing bone.

Question 18

What are osteocytes?

Answer 18

occupy lacunae (holes) in bone matrix.

Question 19

What are osteoclasts?

Answer 19

multinucleated cells acting in dissolution of bone; derived from monocytes which collect at sites of bone resorption and fuse together.

Question 20

Describe bone matrix.

Answer 20

Contains collagen fibers in bundles which act as strengthening frame work, ground substance of matrix becomes impregnated with calcium salts (mainly hydroxyapatite = crystalline calcium phosphate)

Question 21

Bone is ____ _____, unlike cartilage.

Answer 21

Highly vascular.

Question 22

Canaliculi

Answer 22

tiny canals interconnecting osteocyte lacunae; eventually connect lacunae (directly or indirectly) to a fluid surface.

Contain cytoplasmic processes of osteocytes- so allow nourishment and gas exchange for osteocytes.

Question 23

How does bone growth occur?

Answer 23

appositional growth only, since osteocytes become embedded in hard matrix, no interstitial growth is possible.

Question 24

What are the two types of bone structure?

Answer 24

Spongy (cancellous) or Compact.

Question 25

Describe spongy (cancellous) bone

Answer 25

Consists of a latticework of slender trabeculae enclosing a large number of marrow cavities; found in flat bones of the skull, sternum, and epiphysis of long bones.
Blood cells and red bone marrow found in marrow cavities.

Question 26

Describe compact bone.

Answer 26

Lamellar bone made of osteons (haversian system_= concentric layers of bone surrounding central haversian canal; small amount of soft tissue present.

Question 27

Haversian canal

Answer 27

carry nerves, blood and lymph vessels along longitudinal plane of bone

Question 28

Volkman’s canals

Answer 28

carry nerves, blood and lymph vessels between marrow cavity, haversian systems, and periosteum.

Question 29

What are sharpey’s fibers?

Answer 29

direct extensions of dense irregular CT from periosteum into compact bone.
Function to anchor tendon (with fibers penetrating periosteum to bone) to bone.

Question 30

How do sharpey’s fibers form?

Answer 30

Formation by appositional growth around original tendon attachment site.

Question 31

Describe bone appositional growth.

Answer 31

Transition between compact bone and periosteum:
1) outer bone layers = outer circumfrential lamellae, enclose entire bone.
2) periosteum outside of circumrential lamellae - 2 zones:
osteogenic zone = gives rise to osteogenic cells
fibrous zone = dense irregular CT

Question 32

Describe intramembranous bone development

Answer 32

forms spongy bone and eventually may form compact bone.
Forms directly from mesenchyme.
ossification centers form from dense vascular regions of mesenchyme.
Mesenchymal cells > osteoblasts > secrete matrix which eventually becomes calcified (ossified) as thin needlelike spicules.
When osteoblasts become embedded in calcified matrix they are osteocytes.
New osteoblasts on surface of spicules continue to lay down bone by appositional growth, form trabeculae = radiating network of spongy bone.

Question 33

Describe endochondrial bone development.

Answer 33

Bone forms replacing cartilage model.
Sequence: formation of primary ossification center. Expansion of primary ossification center. Formation of secondary ossification center.

Question 34

Describe the formation of the primary ossification center.

Answer 34

Hyaline cartilage model is formed.
Cells in middle of model enlarge, absorb matrix, leaving irregular cartilage spicules which subsequently calcify.
Capillaries and osteogenic cells and mesenchyme cells invade, disintegrating cartilage as osteogenic bud from periosteum (perichondrium).
Simultenous with “c”, osteoblasts form from inner perichondrium and begin laying down a tube of periosteal bone encircling the middle third of the cartilage model. Periosteal bone forms as intramembranous bone but fills in to form compact bone.
Ossification of calcified cartilage spicules internally to form trabeculae and primary marrow from osteogenic bud.
With continued formation of periosteal bone, get trabecular resorption inside leaving primary marrow cavity (osteoclasts involved in resorption).

Question 35

Describe the expansion of the primary ossification center.

Answer 35

As bone increases in size by appositional growth, primary center expands towards ends of bone as adjacent cartilage regions become osteogenic

epiphyses at each end continue interstitial production of cartilage, but epiphyseal regions don’t expand because cartilage is replaced on diaphyseal side by bone at same rate as it is produced.

Epiphyseal plate extends horizontally across bone and is the region where cartilage replacement during expansion occurs.

Question 36

4 regions of the epiphyseal plate

Answer 36

zone of resting cartilage, proliferation, maturation, and calcification.

Question 37

What is the zone of resting cartilage?

Answer 37

chondrocytes are not actively contributing to bone growth, acts to anchor epiphyseal plate to epiphysis

Question 38

What is the zone of proliferation?

Answer 38

chondrocytes proliferate to replace dying chondrocytes from calcification; chondrocytes are stacked into parallel columns

Question 39

What is the zone of maturation?

Answer 39

chondrocytes hypertrophy and accumulate glycogen and lipid, secrete alkaline phosphates, which are involved in formation of calcified cartilage spicules

Question 40

What is the zone of calcification?

Answer 40

hypertrophied cells become surrounded by calcified cartilage and die; trabeculae form as osteoblasts secrete bone onto calcified cartilage spicules.

Question 41

formation of secondary ossification center

Answer 41

Develop in epiphyses of long bones sometime after birth.

Chondrocytes in middle of epiphyseal zone hypertrophy and mature, matrix between them calcifies and disintegrates, osteogenic bud then invades giving rise to osteoblasts which deposit bone on cartilage spicules.

Question 42

What is bone remodeling?

Answer 42

bone growth stops at about 20 years of age in humans. adult bone continuously adapts to prevailing stresses by appropriate deposition and resorption.

Question 43

What are the controls on bone remodeling?

Answer 43

Deposition and resorption are under hormonal control.

Integrated with regulation of blood calcium levels. Parathyroid hormone and calcitonin.

Intense activity increases blood lactic acid levels (decreases pH), causes dissolution of bone and can increase blood calcium levels.

Question 44

parathyroid hormone

Answer 44

promotes resorption, increases blood calcium

Question 45

calcitonin

Answer 45

reduces resorption, decreases blood calcium.