Connective tissue

Part 1

CONNECTIVE TISSUE

Part II

Skeletal CT

Cartilage Bone

Cartilage

• Specialized form of firm and

resilient CT that can bear

stresses without permanent

distortion

• Consists of cells and

extracellular matrix

• Is covered by perichondrium

• Is an avascular tissue

Cartilage Cells

• chondroblasts – immature cells– In the inner layer of the

perichondrium and right under in the lacunae

– Synthesize the matrix

• chondrocytes –differentiated cartilage cells– In the center of the

cartilage in the lacunae

– form isogenous groups

– Synthesize cartilage matrix

– Synthesize enzymes braking down the matrix -collagenase, elastase, hyaluronidase

Cartilage matrix(95% of cartilage volume)

• Fibers collagen type II

• Ground substance:

- Hyaluranan (hyaluronic acid)

- Proteoglycans:

# Core protein

# GAGs:

* chondroitin sulfate

* keratan sulfate

Perichondrium

• 2 layers:– external – dense CT

– internal – cellular or chondrogenic (loose CT + chondroblasts +blood vessels)

• Function: nutrition, appositional growth, repair

perichondrium

chondroblasts

chondrocytes

Growth of cartilage

• Appositional growth- formation of new cartilage

on the surface of pre-existing

cartilage

* Occurs within inner layer of

perichondrium

* Differentiation of

chondroblasts and

chondrogenic cells into the

chondrocytes

* Growth in girth

• Interstitial growth- formation of new cartilage

within the cartilage mass.

* Existing chondrocytes

divide within lacunae

creating isogenous groups

* New chondrocytes secrete

more matrix

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Types

of cartilage

– HYALINE

– ELASTIC

– FIBROUSE

• The most abundant type of cartilage

• Provides support through resilience

• Extracellular matrix looks translucent with no clearly visible collagen fibers (glassy appearance)

• Chondrocytes lay in lacunae

• Found in: fetal skeleton, trachea, most of the laryngeal cartilages, articular cartilage, ends of ribs, external nose, epiphyseal plates

• Mainly covered by perichondrium (except the articular cartilages!)

Hyaline cartilage

Hyaline cartilage

Elastic cartilage

• Dense network of elastic fibers in

addition to collagen fibers

• More fibers in the center of the

cartilage

• Provides flexible support and

maintains shape

• Surrounded by a perichondrium

• Found in: external ear, epiglottis,

corniculate and cuneiform cartilages

of the larynx

Elastic fibers stained by Weigert

Elastic cartilage – darker staining matrix

• Is a combination of dense regular connective

tissue and hyaline cartilage

• Consists of chondrocytes and their matrix

material in combination with dense connective

tissue

• Chondrocytes are dispersed among the

collagen fibers singularly, in rows, and in

isogenous groups

• Gives support and rigidity

• Found in: pubic symphysis, annulus fibrosus of

the intervertebral disk, menisci of the knee

joint, some tendons insertions

Fibrous cartilage

Fibrous cartilage

• Second to cartilage in ability

to withstand compression

and second to enamel in

hardness

• Consists of extracellular

matrix and cells

• Covered by periosteum from

the outside

• Covered by endosteum from

the inside

Bone tissue

Functions of bone

• Major support of the body

• Protection for internal organs

• Attachment for muscle tendons, creating

lever systems for body movement

• Harbors hematopoietic organs (red bone

marrow)

• Storage for calcium and other essential

minerals

Extracellular bone matrix

• Organic part –

50% of volume (25 % of weight)

• Inorganic part –

50% of volume (75% of weight)

Bone matrix

• It is like reinforced concrete where steel bars are collagen

fibers and cement is hydroxyapatite

• Thus, it is responsible for major functional characteristic of

the bone

• If the mineral is removed, bone is

too flexible

• If the collagen is removed, bone is

too fragile

Organic components

• Are synthesized by osteoblasts

– Fibers: Collagen type I (90-95%)

– Amorphous substance:

*proteoglycans

*glycoproteins

Inorganic part

• Mainly Calcium (35%) and

Phosphate (50%), form

hydroxyapatite crystals

• Which make junctions with

collagen

• Some bicarbonate,

potassium, magnesium

and citrate

Bone Cells

• Osteoprogenitor cells (bone stem cells)

• Osteoblasts (matrix synthesis)

• Osteocytes (maintain matrix)

• Osteoclasts – bone macrophages, bone resorbtion (develop

from blood monocytes)

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Osteoprogenitor cells

• Develop from undifferentiated mesenchyme cells

• Lay in the inner layer of periosteum

• Function – stem cells, they are osteoblasts precursors

Osteoblasts• Differentiate from osteoprogenitor

cells

• Are on the surface of the bone and around blood vessels

• function – bone matrix synthesis

• once surrounded with secreted matrix, it is referred to as an osteocyte.

Osteocytes• Differentiate from osteoblasts

• Have long processes – philopodia by

means of which cells contact and

exchange nutrients

• Cells lay in the lacunae, processe – in

the canaliculi

• Function – bone matrix maintaining

Osteoclasts• Lay in the Howship’s lacunae

• Large multinucleated cells

• Ruffled border – plasma-membrane infoldings on the side facing the matrix, forming many compartments where enzymes are released

• Function – bone matrix resorption

PERIOSTEUM

• 2 layers:– external – dense CT

– internal – loose CT +

osteogenic sells + osteoblasts

– Sharpey’s fibers – collagen

fibers that anchor periosteum to

the bone

• Functions: nutrition, growth

of bone in girth, repair

ENDOSTEUM• Covers inner surface of bones, marrow cavities

• Structure resembles the inner layer of periosteum

• Contains bone and blood cell precursor

• Extends into the Haversian canals

Types of bones

I. - Primary (woven) bones

- Secondary (lamellar) bones

II. - Long bones

- Flat bones

III. - Spongy (cancellous) bones

- Compact bones

Primary bone

• First bone tissue that appears in

embryonic development and

fraction repair

• Collagen fibers are arranged in

irregular arrays

• Many cells, less minerals

• Eventually replaced by secondary

bone, except cranial sutures and

alveolus of maxilla and mandible

Secondary bone

• Mature bone with

collagen fibers that are

arranged in lamellae

• Fiber are well

organized around

vascular canal

Long bones

-diaphysis (compact bone)

-epiphysis (spongy bone)

-medullary cavity (bone

marrow)

Flat bones

-two layers of compact bone

-spongy bone between them

(diploe)

Compact bone Spongy bone

Spongy bone

• 3D lattice of trabeculae with many open spaces

• Slips of bone between spaces – trabeculae, align along the

lines of stress

• Can be primary or secondary bone

Spongy bones

Compact bone

(osteon)

• Series of concentric

lamellae around the

Haversian canal

• Haversian canal –

vessels, nerves

• Collagen fibers in one

lamellae are parallel, in

the adjacent lamellae –

perpendicular

• Osteocytes lay in the

lacunae, their filopodia

– in the canaliculi

• Volkmann’s canals –

vascular connections

between osteons

• Interstitial lamellae –

remnants of old lamellae

Bone formation/

osteogenesis

Intramembranous Endochondral

(mesenchyme) (cartilage model)

Intramembranous bone formation

• Takes place in the embryonic mesenchyme

• Forms flat bones of the scull, mandible,

clavicles

Mesenchyme cells Osteogenic cells

Organic matrix Osteolasts

Calcification Osteocytes

Periosteum Blood vessels

Endochondral bone formation

Bone growth in

length• Epiphyseal plate –

between diaphysis and epiphysis

– Proliferation and growth of cartilage from epiphysis side

– Turnover of cartilage into bone from the diaphysis side

– Growth hormone (pituitary gland)

Growth of bone in width•By the appositional growth on the bone surface

•Periosteal cell differentiate into the osteoblasts and form bony ridges and then

tunnels around vessels

•Concentric lamellae fill in the tunnel to form the osteon

Bone remodeling

• Takes place throughout life

• Osteoclasts – remove old bone

• Osteoblasts – deposit new bone

1. Formation of blood clot at the site of injury

2. Formation of the cartilage callus

3. Formation of woven bone

4. Remodeling and replacing of primary bone by secondary bone

Bone fracture

Hormone regulation

• PTH (parathyroid gland)

level of Ca in blood

• Calcitonin (thyroid

gland) level of Ca in

blood

Factors affecting bone tissue:

• Protein deficiency

• Ca deficiency (defect

matrix calcification-

rickets/osteomalacia)

• VitD deficiency (Ca++ is

not absorbed in the

intestines)

• VitA deficiency (defect

synthesis of GAGs and

bone growth)

• VitA excess (early closure

of epiphyseal plates)

• VitC deficiency (defect

collagen synthesis)