Monday: Histology of Cartilage and Synovium

Question 1

Synovial joints are also called…

Answer 1

Diarthroses

permit free movement

Question 2

What are syndesmoses?

Answer 2

Sutures of young skull

joined together by fibrous tissue

Question 3

What are synchondroses?

Answer 3

In sternocostal joints. Joined together by cartilage.

Question 4

Describe a synovial joint.

Answer 4

Involves two bones.

Each bone has covering of articular cartilage.

Participating ends of two bones and their caps of cartilage project into a space (the synovial cavity).

Synovial cavity is bounded by articular cartilage and synovial membrane. Synovial membrane is innermost portion of sleevelike fibrous capsular ligament extending from one bone to the other.

Question 5

What are three varieties of cartilage matrix?

Answer 5

Hyaline cartilage
Elastic cartilage
Fibrocartilage

Question 6

Hyaline cartilage:

Answer 6

Forms costal cartilage, respiratory tract, articular cartilages, epiphyseal plates, and fetal skeleton that is replaced by bone.

Chondrocytes: Occupy spaces (lacunae) distributed through matrix.

Question 7

Articular cartilage is specialized form of hyaline cartilage: How is it different?

Answer 7

Lacunae and enclosed cells are essentially spherical in the deep portion but are flattened and discoid toward the periphery of the cartilage.

Question 8

More info about chondrocytes of hyaline cartilage:

Answer 8

Peripheral lacuna houses single chrondrocytes. Deeper lacunae contain two or more chondrocytes. Each cell is immediately surrounded by recently formed, territorial matrix that stains more deeply than interterritorial matrix and has higher concentration of proteoglycans.

Young chondrocytes and chondroblasts have rounded nuclei each with one or more nucleoli. Cytoplasm contains ER, mitochondria, Golgi, glycogen, lipid droplets.

Older chondrocytes: ER and Golgi are less prominent. Lipid and glycogen are increased.

Both: Surface is irregular.

Question 9

What percentage of cartilage matrix is water?

Answer 9

75%

Question 10

What is half of dry weight of cartilage?

Answer 10

Collagenous fibrils

Question 11

What is other part of dry weight of cartilage?

Answer 11

Nonfibrous filler material.

Afibrillar components are:

1. Large proteoglycans
2. Small proteoglycans (5% of total)
3. Cell membrane associated proteoglycans

Question 12

What are the main glycosaminoglycans (GAG) of large and small proteoglycans of cartilage?

Answer 12

Chondroitin sulfate and dermatan sulfate

Question 13

What is collagen that makes up hyaline cartilage?

Answer 13

Type II collagen

Question 14

What is collagen in skin and bone?

Answer 14

Type I collagen

Question 15

What is elastic cartilage?

Answer 15

Hyaline cartilage permeated with elastic fibers that confer resiliency upone tissue.

This is in external ear, external acoustic meatus, auditory tube, and arytenoid cartilages and epiglottis.

Question 16

Fibrocartilage?

Answer 16

Does not have surrounding perichondrium.

Composed of bundles of thick collagenous fibers (unicellular islands of chondrocytes arranged singly, in pairs, or in chains between these).

Collagenous fibers are arrayed parallel to tension on tissue.

Fibrocartilage is in tendons subject to frictional pressure, point of insertion into bone, in symphyseal joints, in intervertebral discs, and in articular discs.

Question 17

Articular cartilage: Superficial zones do or do not calcify?

Answer 17

DO NOT calcify

Except in pathologic states like pseudogout

Question 18

Nourish to cartilage comes from?

Answer 18

Diffusion from capillaries in perichondrium and imbibition.

Diffusion ceases when cartilage calcifies and death of chondrocytes ensues.

Large masses of cartilage are reported to have vascular canals that enter from perichondrium. Such vascular canals may cause endochondral ossification.

Question 19

Articular cartilage: free surface has what at periphery?

Answer 19

Perichondrium

Question 20

Cells and lacunae of articular cartilage are arranged in 3 layers. What are they?

Answer 20

Superficial layer: Small and flattened with long axes parallel to surface. No mitotic figures should be here.

Next layer: Larger and rounded and arranged in columns at right angles to surface. Mitotic figures may be seen in this layer during growth.

Depp layer: Progressively replaced by bone while more superficial portions form cartilage that is added nearer the surface.

Question 21

In older adults, what compensates for wear of articular cartilage?

Answer 21

Chondrocytes producing more matrix.

Question 22

Junction of calcified and uncalcified cartilage is called the what?

Answer 22

Tidemark

Question 23

Hyaline cartilage vs articular cartilage nourishment?

Answer 23

Hyaline cartilage: Perichondrium contins capillaries for nourishment of cartilage.

Articular cartilage only has peripheral rim of perichondrium on free surface and calcification of portion of cartilage abutting bone may limit or preclude diffusion of blood vessels from supplying subchondral bone.
SO synovial fluid that bathes cartilage is where nourishment comes from!

Question 24

Regeneration of articular cartilage?

Answer 24

Severely limited except at periphery (where there is perichondrium and attachments of synovial membrane).

Superficial injuries except those near peripheral rim of perichondium/near attachment of synovium remain unhealed for long periods of time.

Question 25

Movable joints between bones form by intramembranous rather than endochondral ossification is what type of cartilage?

Answer 25

Fibrocartilage.

Example: Temporomandibular joint

Question 26

Articular discs: What kind of cartilage?

Answer 26

Fibrocartilage that blends with capsular ligament.

Menisci are crescentic articular discs, wedge-shaped in cross section, projecting between condyles of femur and tibia.

Articular disc adds resilience to that of articular cartilage in cushioning the ends of bones and may assist in maintaining synovial fluid over articular surfaces.

Question 27

What is the synovial membrane?

Answer 27

Innermost portion of capsular ligament of synovial joint. With articular cartilage, it forms walls of synovial cavity.

It is supplied by blood vessels, lymphatics, nerves.

It is sheet of fibrous connective tissue. No epithelial component.

Question 28

What are synovial cells?

Answer 28

Appearance of undifferentiated cells and resemble fibroblasts. Concentrated at inner surface of membrane. Constitute a continuous cell layer.

Question 29

Type A synovial cells

Answer 29

Type A: prominent surface ruffling, many lysosomes, smooth-walled vesicles.

Receptors for Fc portion of IgG molecule and rich in lysozyme.

Question 30

Type B synovial cells

Answer 30

Appear to be fibroblasts with rough-surfaced ER. React positively to Ab against laminin and type IV collagen. May be source of hyaluronic acid and glycoproteins in synovial fluid.

Question 31

Three types of synovial membrane:

Answer 31

1. Fibrous: Rests directly on capsular ligament. Cells are widely separated from each other and larger/more numerous cells deeper in membrane. This type of synovium is present over intraarticulcar ligaments and tendons. Where synovium is subject to pressure.
2. Areolar: Loosely bound to capsular ligament and is found where it must move freely in suprapatellar pouch of knee joint. Superficial cells closely grouped (3-4 rows of cells) and in meshes of collagenous fibers. This membrane contains elastic fibers that form distinct layer.
3. Adipose: Intraarticular fat pads (olecranon fossa) where membrane may appear to be a layer of cells resting on adipose tissue intervening between it and capsular ligament. Cells in thin layer of collagenous fibers.

Question 32

Synovium is capable of repair? True or false?

Answer 32

Synovial cells are undifferentiated and can differentiate into chondrocytes. Synovium is capable of rapid and complete repair/regeneratoin.

Question 33

Nerves entering synovium appear to be distributed primarily to blood vessels (probably vasomotor and vasosensory nerves). Is synovium sensitive to pain?

Answer 33

No. Few of nerve fibers are pain fibers.