HISTOLOGY - Bone & Cartilage Flashcards
What is Cartilage and where does it get its blood supply?
A semi-rigid tissue comprised of cells and ECM that is flexible and resilient
Perfect for mechanical & protective support
blood via surrounding capillaries
What are chondroblasts and chondrocytes?
Chondroblast – cells that give rise to cartilage, secrete cartilage matrix and maitain mitotic capabilities –> BECOME CHONDROCYTES
Chondrocytes - the cells that make up cartilage in mature form
Name refers to cartilage cells during (blast) and after proliferation (cyte)
What distiguishes the subcatagories of cartilage?
The ratio of the cartiklage cells to the composition of the ECM, which is comprised of collagen and elastin fibers
What is perichondrium, what does it arise from and what cartilage is it involved with?
The tissue that envelopes hyaline and elastic cartilage
Important for maintainence and growth
Derives from Superficial mesenchyme
What are the layers of Perichondrium?
1) Outer/Fibrous - type I collagen
2) Inner/Chondrogenic — source of chondroblasts
- responsible for creating new cartilage since it comntains mesenchymal cells and is thus the source for new chrondroblasts
Where are condrocytes housed? What is it called when more than one chondrocyte type is present?
Lacunae – holes in catilage
Isogenous groups
Why is the ECM important and what are it’s components?
-ECM is used during development and for maintanence of the cartilage
Components:
1) Collagen
Type II collagen – MOST COMMON
Type I —- may be present
Elastic cartilage — ONLY in elastic cartilage
2) Ground Substance
- Hyaluronic Acid + Chondroitan sulfate
Explain the process of Chrondrogenesis
Step 1
Embryonic mesenchyme cells differentiate as chondroblasts
Step 2
chondroblasts divide until they reach certain number and start secreting ECM
Step 3
ECM corrals chondroblasts into “islands” without ECM which will develop into the Lacunae
Step 4
Once ECM secretion stops, the chondroblasts begin to mature into true chondrocytes
Differentiation occurs from center -> outward
Central cells = chondrocytes
What type of ECM does hyaline, fibbrocartilage and elastic cartilage secrete?
hyaline = x
fibrocartilage = y
elastic = z
a = perichondrium
b = cartilage
P - perichondrium
C - chondrocyte
Cc - chondrocyte
Cb - chondroblast
M - matrix
What are the three major subcatagories of cartilage?
hyaline, fibrocartilage, elastic
Indicate the following about hyaline cartilage:
1) Location
2) Appearence
3) What it secretes
4) Stain character
5) Perchondrium?
1) MOST COMMON IN BODY — synovial joint articulatimng surfaces, respiratory passages, costal cartilage, epiphyseal plates, portions of embryonic skeleton. ——- in lacunae
2) Glassy, seimitransparent
3) Type II Collagen
4) Basophilic stain (diffuse) — aggrecan, hyaluronic acid, sulfates
5) YES! — Except in joints (articular cartilage)
What limits cartilage growth?
Distance from vascular source
What cartilage type is this?
Hyaline
What are the two division of matrixes, where are they located in relation to the chondrocyte and what are some facts about their arrangement and staining?
Territorial Matrix - immediately surrounding chondrocyte
- Randomly arranged Type II collagen
- Staining is basophilic and dark (due to HIGH [GAG] )
Interterritorial Matrix - surrounds territorial matrix
-Less intensely stained
What cartilage type is this?
Elastic!
Answer the following about Elastic Cartilage:
1) How does it differ from hyaline cartilage
2) What is its function?
3) Perichondrium?
4) Locations in body
5) Stainin character
1) It is essentially hyaline cartilage (has same matrix, Type II collagen, etc.) with abundent network of elastic fibers, MORE FLEXIBLE than hyaline
2) elastic fibers allow for recoil/rebound -> shape retention after deformation
3) YES!
4) Ear: aurical, auditory canal, auditory tubes
Epiglottis
5) elastic fibers stain dark and appear as dark bundles throughout matrix
What cartilage is this? how can we differentiate it from dense CT?
Fibrocartilage!
Note. the singly-arranged chondrocytes!
The nucleus in dense CT is flat while in cartilage it is round, like a penny
Has lacunae as well
Answer the following about Fibrocartilage:
1) What are some of it’s structural characteristic?
2) What is its function?
3) Perichondrium?
4) Locations in body
5) Chondrocyte arrangement
1) mix of hyaline cartilage and dense CT, very tough
2) Cushions bone
3) NO
4) Intervertebral discs, pubic symphysis, selected joint capsules
5) arrange singly in rows of isogenous aggregates
Key: fibers arrange in direction of stress - provides extra tensile strength
How does cartilage grow and repair?
interstitial growth and appositional growth
What is the difference betwen interstitial growth and appositional growth?
Interstitial Growth - mitotic division of prexisiting chondrocytes in lacunae
-occurs in the core/center of the the tissue (increase in cell mass)
Appositional Growth - chondroblast differentiation from progenitor cells in the perichondrium
- Growing from outer periphery
- chondroblasts -> secrete type II collagen + ground substance
What are the differences in cartilage repair between adults and kids
Kids – very fast repair
Adults – slow and incomplete
cells invade perichondrium and produce new cartilage or dense CT
PROBLEM: bone may be created instead which is a problem depending on location
Explain some features of bone (especially its matrix)
- special CT that provides support and protection
- comprised of osteocytes (mature bone cells, housed in lacunae)
- Mineralized matrix (produces extremely hard tissue)
- Calcium phosphate as hydroxyapatite crystals
What are the 4 bone cell types and what are their functions and roles?
Osteoprogenitors/osteogenic cells
-from mesenchymal cells that produce osteoblasts
Osteoblasts
-Initiate and control the mineralization of osteoid via secretion of osteoid
Osteocytes
- mature bone cells housed in lacunae that maintain bone matrix
- Has spider-like processes that extend through multiple layers of bone
Osteoclasts
-Multinucelated cell from monocytes that reabsorbs bone (breaks it down) using its “ruffled border” which secretes H+ and lysosomal proteins (ACID)
What are the two classifications of bone
compact and cancellous
Explain the differences of Compact and Cancellous Bone w/r to:
1) bone type
2) structure
3) where it’s located
Compact (cortical) —- covered by periosteum
1) lamellar bone (mature)
2) solid, dense
3) nexternal surfaces of long and flat bones
Cancellous (spongy)
1) lamellar (mature) or woven (immature) bone
2) Trabecular bone — open lattice of narrow plates
3) Internal layer of bone
Compact encloses Cancellous — MOST BONES HAVE BOTH
Describe characteristics of Woven bone
- Immature/primary bone – will grow into lamellar (mature) bone (ALL BONE WILL START AS WOVEN)
- Characterized by loose arrangement of collagen fibers
- Low mineral content
- Forms during fracture repair and remodling
Where in the body is woven bone permanent?
The jaw - why we can make teeth move around
What are the following parts of a long bone?
Epiphysis - knobby region at ends of bone - contains epiphyseal plate
Diaphysis - shaft/body of the bone
Metaphysis - area between diaphysis and epiphysis (has spongy bone)
Epiphyseal Line — remnant of the growth plate we had as kids (fused epiphyseal plate)
Marrow Cavity – cylindrical space in diaphysis containing bone marrow
What are the two types of bone covering, what are they comprised of, where are they located and other interesting facts?
Periosteum
1) Comprised of Dense Irregular CT (important because tendons and ligaments need to attached)
2) Surround long bones
3) Anchored by perforating fibers and contain osteoblasts
4) HELPS BONE HAVE FLEXIBILITY
Endosteum
1) CT
2) Lining of all trabeculae (lattice of narrow plates in spongy bone) and marrow cavity
3) Contains osteoprogenitor cells, reticular cells of bone marrow and CT fibers
What is the Osteon?
Cylindrical, latered structures that comprise mature bone (betwen the periosteum and spongy bone)
What is the structure of an individual osteon?
1) runs parallel to the diasphysis and the entire length of the bone
2) Consists of concentric lamellae that have a central canal at the center that contain neurovasculature
3) Perforating canals that run parallel to the concentric lamellae, connect central canals together so that if one goes down, the neurovascularture can anastomose with another. Also they allow vasculature to connect with the periosteum (outer surface) and endosteum (inner surface) portions of the bone
Excluding the Concentric Lamellae, what are the other three Lamellae within and around the osteon structure and what are they?
Interstitial Lamellae
- “Half pieces” of osteons with two functions:
1) Fill in gaps - helps maintain strength
2) Left over from bone remodling
Circumferential Lamellae
-Line the INNER (lines marrow cavity) and OUTER (lines shaft of bone, under periosteum) circumference of the diaphysis
What are located between the concentric lamellae? What structure allows these things to interact with one another?
- Osteoclasts
- Interact via Canaliculi - tiny channels between Lacunae
How do osteons form and why is this important for bone strength?
Bone starts as unwoven and then overtime, as the bone grows, osteons form over interstitial lamellae. Overtime, octeoclasts break down (partially) the osteons and new ones are created, staking them on top of one another which will eventually create greater bone strength
1) Where is spongy bone found, 2) what does in house and 3) how is it orientated?
1) Skull bones
2) bone marrow
3) orientated in a way that maximizes strength and minimizes mass
What are the two types of Osteogenesis?
Endochondral and Intramembranous
NOTE: Osteogenesis IS NOT minerilization
WOVEN BONE is produced first in both and then replaced by Lamellar Bone
Describe Endochondral ossification and the bones it forms
- Prexisting “model” hyaline cartilage invaded by osteoblasts, osteoid is secreted and bone begins being made
- Bones of the extremities, pectoral and pelvic girdles, pelvis, vertebrae, end of the clavicle
Describe Intramembranous Ossification
- Bone growth directly from mesenchyme precursors – osteoblasts diferentiate directly from mesenchyme and begin secreting osteoid
- Flat bones of the skull, most facial bones, central part of the clavicle
What are the steps of intramembranous ossification?
1) Mesenchymal cells aggregate and begin dividing
2) After sufficient replication, the cells differentiate and bercome osteoblasts
3) Osteoid is then released by the osteoblasts
4) Osteoid is calcified, creating a calcified bone matrix (“Islands” form)
5) Osteoblasts within the newly calcified bone matrix become osteocytes and house themselves in LACUNAE (These “islands” are know as Primary Ossification Centers)
6) Overtime, the primary ossification centers grow size and eventually connect with one another creating a continuous stretch of bone tissue
7) Trabeculae established first and then compact bone gets layered on top of the outer boundaries
What are the steps of Endochondral Ossification?
1) Fetal hyaline cartilage develops. The center than extpands and begins to die off, recruiting blood vessels to area
2) Cartilage then calcifies and a bone collor forms around the diaphysis after osteblasts come in since vasculature can now supply them.
3) Primary ossification center forms in the dyaphysis (center of bone)
4) Because the epiphyses (ends of bone) need to ossify, cartilage at the ends increase in size and dies off, blood vessels come in and then osteoblasts come in, forming secondary ossification centers
5) Bone replaces cartilage in all places EXCEPT in the areas of articular cartilage (outmost part of epiphyses) and the epiphyseal plates
Why is it important that the epiphyseal plate remains as cartilage?
So it can be manipulated to grow over time – if it ossified, the size of our bones would remains constant from birth. Once we aredone growing, the epiphyseal plate ossifies, creating the epiphyseal line
What are the zones of cartilage in the epiphyseal plate?
What are the various zones of the epiphyseal plate labeled in this photo?
A) Zone of ossification
B) Zone of calcified cartilage
C) zone of hypertrophy
D) Zone of proliferation
E) Zone of reserve cartilage
What is the:
1) Zone of reserve cartilage
2) Zone of proliferation
3) Zone of hypertrophy
4) Zone of calcified cartilage
5) Zone of ossification and reabsorption
1) No active matrix production (closest to epiphysis/articular cartilage)
2) Area where cartilage cells are actively producing collagen (type II & XI) matrix proteins
3) where cartilage cells are increasing in size and recruiting vascular invasion via secretory factors
4) Hypertrophied cells begin to degenerate and the cartilage matrix becomes calcified
5) Connected with diaphysis and marrow cavity — area where bone is established sicne blood vessels and osteoprogenitors invade, differentiating into osteoblasts
KEY!!!! — Diaphysis will grow/get longer, pushing epiphysis away
What happens when you damage growth plate as a kid?
May cease all future growth of bone!
CLINICAL
Achondroplasia
-Autosomal dominant mutation in Fibroblast growth factor (FGFR3)
Clinical manifestations:
1) Dwarfism (most common reason)
2) Small midface
3) Shortening of long bones
4) Altered spinal curvature
What is Appositional Bone Growth and why is it important?
Growth in the circumference of the long bones via osteoblasts in the periosteum (like adding rings to a tree)
-Allows our bones to increase in volume to support our increasing bodyweight overtime
-Begins with formation of bone collar on cartilagenous diaphysis, accompanied by ENLARGEMENT of the marrow cavity by osteoclasts in endosteum
In appositional bone growth, there is a balance of osteoblast and osteoclast action. When osteoclasts begin to be more active than osteoblasts, what happens?
Osteoporosis!!
What can occur when the re is a calcium deficiency in a child’s diet?
- Can lead to ricketts, where the bone matrix does not calcify normally, causing the epiphyseal plate to bocome distorted by the weight of the body and muscular activity
- Bones also grow more slowly and deformed due to the negative impact of the ossification process.
Deficiency commonly due to 1) insifficient calcium in diet or 2) failure to produce vitamin D, which is important fdor absorption of Ca2+ by the small interstine
Osteomalacia
Deficient calcification of recently formed bone & partial decalcification of already calcified matrix
Causes:
1) Dietary vitamin D deficiency
2) Lack of sun exposure (low vit D)
3) Gastrointestinal disease
Can be asymptomatic
Rickets (aka Juvenile Osteomalacia)
Description:
Bone matrix does not calcify normally
Symptoms
1) Epiphysealplate can become distorted by normal strains of body weight & muscular activity
2) Bones to grow more slowly and often become deformed
3) Bowlegged, soft skull bones (Craniotabes)
Cause:
-Vitamin D deficiency, decreased absorption of calcium & phosphorus from bowels
Osteoporosis
- Decrease in bone mass & increased fragility
- Loses ability to produce organic matrix (mainly collagen)
- Loses Ca2+ & other bone salts
- Commonly occurs in the elderly & postmenopausal females
- No clinical manifestations until there is a fracture
Osteoarthritis
Degenerative joint disease with causes unknown but it is related to aging and injury of articular cartilage
Symptoms
- Chronic joint pain
- Various degrees of joint deformity (heberden’s nodes, Bouchards nodes)
- Affect DIP and PIP and weight bearing joints
Early Stage
Superficial layer of articulkar cartilage is disrupted
Late Stage
destruction of cartilage extends to the bone, where the bone now articulates at joint (reduced mobility and pain)
Explain the process of Bone Remodling. How often does bone turn over?
1) Old osteons are reabsorbned by osteoclasts, which create pores/tunnels in the bone
2) Osteoprogenitors go into the tunnels, create osteoblasts who then secrete osteoid to form new bone
3) New osteon forms, trapping osteocysts within its concentric lamellae and overlayer old fragments of osteons while interstitial lamallae remain
5-10% turn over per year in healthy adults
Explain the process of bone fracture repair
1) Blood vessels that were injured during the fracture release blood, which clots and forms a hematoma
2) Hematoma is removed and replaced by a fibrocartilage-like mass known as a soft callus
3) The callus is invaded by 1) blood vessels and 2) osteoblasts, both of which gradually replaced the fibrocartilage with bone woven bone, forming a hard callus
4) Woven bone remodled as compact bone and vasculature is restablished
Explain the key features of a synovial joint
1) Articular cartilage - HYALINE
2) Joint Cavity - space in which fluid resides
3) Articular capsule
- Two Layers: Dense Fibrous CT (outside) amnd Loose Synovial (Inside) —- creates seal withkn joint for fluid
4) Synovial fluid - lubricates joint
5) Reinforcing ligmaments - extra support
6) Nerves and Blood Vessels
What does the synovial membrane do?
1) Lines joint cavity from inside
2) Lubricates cartilage
3) Because it is a vascular membrane, it procvides nutrients to joint
4) PRODUCES SYNOVIAL FLUID
5) Absorbs shock
Describe important features of the Articular Capsule
1) Reduces friction
2) Avascular
3) Comprised of Hyaline cartilage (NO PERIXCHONDRIUM - present in areas where cartilage is not part of a joint)
4) Nourished by synovial fluid
Synovial joint
SM - synovial membrane
A - articular cartilage
E - epiphyseal growth plate
C - articular capsule
What is articular cartilage, where is it found, what are some structural features, describe its zones
- Cartilage present in joints at the ends of bone on the surfaces of movable joints
- Made of hyaline cartilage (remnant of original hyaline template used by developing bone)
- Four zones:
Superficial, Intermediate, Deep, Calcified
What does SZ, IZ, DZ, CZ indicate and what are they?
SZ - Superficial Zone
Contains elongated and flattened chondrocytes
IZ - Intermediate Zone
Contains round chondrocytes
DZ - Deep Zone
Chondrocyes are arranged in short columns
CZ - Calcified Zone
Where the chondrocytes are small and border the subchondral bone (dark stain)
