Histology Lecture 4 - Connective Tissue II

What is cartilage a specialized CT for?

bearing weight and spanning spaces

What does cartilage do in the fetus/young

serves as the template for developing bony skeleton

is cartilage vascular?

No!

where is cartilage in adults?

• joints

• resp. tract

• ear

what makes up the cartilage?

cells + ECM

What do chondroblasts do?

actively secrete chondroid matrix

What do chondrocytes do?

Less active (but still active), live in clear little “lacunae”

What do chondroclasts do?

resorb/dissolve cartilage

What makes up ECM?

ground substance and fibers (collagen and elastin)

what determines the type of cartilage?

ratio of ground substance to fibers

What is hyaline cartilage?

few cells embedded in blue matrix.

• usually surrounded by perichondrium (bands of fibrous CT)

• found in

  • tracheal/bronchial rings

  • larynx, nose, ends of ribs

  • growth plates of bones

  • articular surfaces

What are 3 types of cartilage?

hyaline, fibrocartilage, and elastic cartilage

what is fibrocartilage?

orderly bundles of collagen.

• chondrocytes arranged in lines

• located in

  • intervertebral discs

  • menisci

  • symphyses

  • often at ligament or tendon attachments to bone

What CT does vertebrae contain?

2 types: hyaline and fibrocartilage

What is elastic cartilage?

similar to hyaline cartilage except w/ lots of elastin fibers

locations:

• structures that need to be pliable

• external ear (pinna)

• ear canal epiglottis

Is bone hard and static?

No. It is highly dynamic and constantly changing. Your bones constantly remodel in response to changes in weight-bearing and tension

Is bone CT?

Yes

Is bone vascular?

Yes, it is highly vascular

• a fracture can bleed

What cells in are a bone?

osteoprogenitors, osteoblasts, osteocytes, osteoclasts

what are the components of bone?

cells and EC matrix

What’s in the EC matrix of bone?

Inorganic matter (mineral, makes the bone hard), organic matter (collagen, ground substance, water)

What are osteoprogenitor cells?

periosteum and endosteum

• come from mesenchymal stem cells

  • almost impossible to see histologically (thin squamous layer)

What are osteocytes?

• live in lacunae of mature bone (like cartilage)

  • not mitotically active, just hand out

what do osteoblasts do? where are they?

• form osteiod (unmineralized ECM)

  • on surfaces of immature bone

what are osteoclasts?

large, multinucleated cells

• DON’T come from osteoprogenitor cells

  • come from the same cell line as macrophages

how are osteoblasts and osteocytes connected?

interconnected via cell processes

• allows for communication

• Flow of ions between cells → signals for blood calcium levels

what cells are these?

osteoprogenitors

what cells are these?

osteoblasts

what cells are these?

osteocytes

what cells are these?

osteoclasts

What are the channels containing cell processes called?

canaliculi - “small canals”

• single: canaliculus

• plural: canaliculi

what are the cancer cells in bones?

osteoblasts - uncontrolled growth

How do osteoclasts work?

they secrete acids and enzymes → digests and leads to bone absorption

what is going on here?

The scalloped edges are where osteoclasts dissolved bone.

• edges are called Howship’s lacunae

what is the % makeup of bone ECM?

70% inorganic matter, 30% organic matter

What’s the inorganic matter? What’s in it?

Mineral content of bone.

• Various Ca and Phosphate salts

• “hydroxyapatite” is the result

What’s in the organic matter of ECM?

90% collagen, 10% ground substance (water, GAGs, etc.)

What are 2 mechanical properties of bone?

compressive (jumping and landing) and tensile (slight bend)

Where does the compressive property come from?

mineral (hydroxyapatite)

• twice that of the tensile property

where does tensile property come from?

collagen

what are 2 types of bone?

• compact/cortical

• spongy/cancellous

What is compact/cortical bone?

• thick outer wall of diaphysis

• provides mechanical strength

• lots of dense lamellae (layers)

  • thus, compact bone = cortical bone = lamellar bone

What is spongy/cancellous bone?

fills the epiphysis and medullary cavity

• made of trabeculae (thin bony projections)

what’s in the cell component of compact/cortical bone?

• osteocytes in lacunae

• canaliculi contain cell processess

What’s in the ECM component of compact/cortical bone?

Mineralized matrix deposited in layers (lamellae)

What are Haversian canals?

contain blood vessels

• run longitudinally in bone

• concentrically surrounded by lamellae

What is an osteon?

haversian canal + surrounding lamellae

• like the functional unit of bone

compact bone example

what’s in sponge/cancellous bone?

no haversian canals → have trabecular of bony spicules instead

• lined by thin layer of endosteum

  • have some lamellae, but not many

What is the periosteum?

Outer covering of bone (“peri” = ”around”)

What are the 2 layers of the periosteum?

• Outer layer: dense connective tissue, few cells (peri=around)

• Inner layer: cellular

  • Where osteoprogenitor cells (adults) and osteoblasts (juveniles) live

What is the endosteum?

Very thin layer of flat cells, some osteoblasts

• lines all cavities of bone (endo=within)

  • haversian canal

  • sponge/cancellous bony trabeculae

point out the periosteum and endosteum

What one is compact? What one is spongy?