Intro to Histology: Cartilage, Osseous Tissues, Bone Cells, How Bones Grow

Histology

the study of the microscopic structure of tissues.

4 main categories of tissue types

including epithelial, connective, muscle, and neural tissues.

Epithelial Tissue

(lines things. ie, inner layer of skin or heart)

Connective Tissue

bones[a type of connective tissue].

(provides structure, stores energy, transports materials throughout the body)

Muscle Tissues

(contracts)

Neural Tissue

(connects, sends signals)

3 components of connective tissue

cells, fibers, ground substance

3 Connective tissue Fibers 

1. collagen fibers

2. reticular fibers

3. elastic fibers

Supportive Connective Tissue

(dense matrix of collagen and elastic fibers in rubbery ground substance to create support for body.)

Matrix

firm gel, containing chondroitin sulfates

what are these

chondrocytes in lacunae 

perichondrium

dense irregular tissue that surrounds most cartilage.

cartilage is _______

avascular (heals slower than bone)

bone is_______

vascular (heals faster than cartilage)

Antiangiogenesis Factor

chemical produced by chondrocytes

Hyaline cartilage

closely packed collagen fibers. (supports larynx, trochlea, part of nasal septum) provides stiff but flexible support and reduces friction between bony surfaces. 

what is this?

Hyaline Cartilage

Fibrocartilage

little ground substance (between femur and tibia, pubic symphysis, intervertebral disks). resists compression, prevents bone to bone contact, shock absorbtion

What is this?

Fibrocartilage

Elastic Cartilage

numerous elastic fibers. (external ear, auditory canal) provides support but tolerates distortion without damage and can return to its original shape. 

what is this?

elastic cartilage

Osseous tissues meaning…?

bone tissues

Extracellular matrix

1/3 matrix is collagen fibers. 2/3 of matrix is hydroxyapatite

Periosteum

thin membrane on outside of bone

Endosteum 

a membrane that lines the inner surfaces of bone

Perforating Fibers

collagen fibers of periosteum.

• connects with collagen fibers in bone

• connects with fibers of joints

Osteoprogenitor

the “babies.” stem(mesenchymal) cells divide to produce osteoblasts

Osteoblasts

the “teenagers.” immature bone cells that secrete osteoid (which is a matrix that becomes calcified in bone & becomes bone)

Osteocytes

the “adults.” mature bone cells that come from osteoblasts that have been surrounded in calcified bone (inside lacunae chambers)

Osteoclasts

NOT related to osteo progenitor, osteoblasts, or osteocytes. 

 

Giant multi-nucleated cells that dissolve bone tissue to remodel bone and release stored minerals.

ie, the bone dissolving cells!!!

thick line: osteon

a. canaliculi (the little light grey lines that run outward from central canal)

b. central canal

c. concentric lamellae (the layers)

d. lacunae (with osteocytes in them)

e. interstitial lamellae (space between one osteon and another)

EXTRA: circumferential lamellae is the LARGEST ring that is NOT in the osteon. It runs along the periosteum.

1. perforating canals

2. central canals

3. spongy bone

4. Interstitial lamellae

5. concentric lamellae

6. circumferential lamellae

7. canaliculi (the little squiggly lines moving outward from central canal)

collagen fibers in the osteon

Spongy bone

where bones are not heavily stressed or where stresses comes from many directions

• lighter than compact bone

• houses red & yellow marrow

• system of trabeculae. NOT osteons

a. compact bone

b. spongy bone

Red marrow

• blood vessels

• forms blood cells

• supplies nutrients to osteocytes in spongy bone

• found in epiphyses of long bone, interior of large bones

Yellow marrow

• in some bones, spongy bone holds yellow marrow 

• it’s yellow bc it stores fat

Where yellow marrow is located

medullary cavity within diaphysis 

Periosteum outer layer

dense, irregular connective tissue, fibrous layer

Periosteum inner layer

cellular layer, every type of cell except for osteocytes

Bone Development steps

• human bones begin as cartilage

• osteogenesis: bone formation

• ossification: process of replacing other tissues with bone. (2 types. endochondral and intramembrous)

intramembranous ossification

• stem cells cluster & split into osteoblasts

• osteoblasts secrete osteoid

• developing bone grows outward in spicules

• some osteoblasts are trapped inside bony pockets, so they become osteocytes

• **this all happens in the ossification center

• Blood vessels grow into area of ossification

• Spicules fuse together and some blood vessels become trapped in developing bone

• **initially intramembranous bone consists of spongy bone only

• remodeling around blood vessels produces osteons of compact bone

• as growth slows, connective tissue around bone becomes periosteum

collagen fibers

straight, strong

collagen fibers

Areolar tissue (beneath the skin or around organs. Binds them)

Dense connective tissue (tendons and ligaments)

Adipose tissue ( located inside of skin or around organs. insulates, energy storage )

reticular fibers

small, branch

Mesh like network

Reticular fibers

Branching fibers

Elastic fibers

elastic fibers

stretches and returns to original shape after being stretched or compressed

where endochondral ossification occurs

in cartilage

where intramembrous ossification occurs

in deep layers of skin

Endochondral ossification

1. Mesenchymal (stem) cells are split into chondroblasts, which then secretes hyaline cartilage, which is then formed into a ‘model’ of the bone it is going to be

2. chondroblasts turn into chondrocytes, and calcify into  the cartilage model, and more bone calcifies along the diaphysis(shaft) when blood lines the outer sides of it.

3. blood penetrates bone on diaphysis, creating the primary ossification center as the inside of the bone begins to calcify

4. osteoclasts hollow out center of spongy bone in diaphysis, creating medullary cavity. 

5. Blood then penetrates the epiphyses of the bone and calcifies it, creating the secondary ossification centers.

6. A strip of hyaline cartilage called the epiphyseal plate (growth plate) remains between the diaphysis and epiphysis, allowing bone to continue growing in length until adulthood, ie, when the space is completely closed

Endochondral Ossification

1. chondrocytes are near the center of a cartilage model of a future bone grow, causing lacunae to grow too, causing calcification of cartilage. chondorcytes die from lack of nutrients. 

2. since there are no chondrocytes to release Antiangiogenesis Factor, blood vessels grow into perichondrium surrounding the diaphysis with a thin layer of calcified bone.

3. Blood supply to periosteum increases, and blood vessels move to core of bone causing cartilage matrix to break down. osteoids replace matrix with spongy bone. this all occurs in the primary ossification center

4. as bone enlarges, osteoclasts appear and begin to erode trabeculae(spongy bone) in center of diaphysis. appositional growth.

5. centers of epiphysis calcify in secondary ossification center

6. epiphysis filled with spongy bone and remaining is articular cartilage. epiphyseal plate cartilage. remains for bones to continue to grow throughout puberty.

Epiphyseal plate growth at youth

grows at even pace w/ diaphysis bone.

Epiphyseal plate growth at puberty

grows slower than the diaphysis bone, causing the epiphyseal plate (cartilage) growth to be overtaken and the gap is eventually closed. 

nutrient artery and vain

single pair of large blood vessels that enter diaphysis through nutrient foramen.

mataphyseal vessels location

in metaphysis

periosteal vessel location

in periosteum

Calcitonin

• decrease in osteoclast production so that bone preserves calcium

• decrease in calcium absorption in intestine

• increase in amount of  Ca2+ ions peed out

GOAL: decrease amt of calcium

parathyroid hormone (PTH)

• increase in osteoclast production so that bone releases calcium

• increase in calcium absorption in intestine

• decrease in amt of Ca2+ ions peed out

GOAL: increase amt of calcium

3 cartilages

• Hyaline (medium)

• Elastic (soft)

• Fibrocartilage (tough)

all made of fibers, have chondrocytes in lacunae, rubbery ground substance, and antiogenesis factor

Spongy Bone:

TRABECULAE, not osteon