AVS331: Skeletal tissue system

Skeletal tissue

- Comprised of dynamic tissues, lots of cells, has nerves, and blood vessels

- Continually remodels itself

- Composed of cartilages, tendons, ligaments, and bones

Cartilage

A connective tissue that is more flexible than bone and that protects the ends of bones and keeps them from rubbing together

What are the 2 cell types of cartilage?

chondroblasts and chondrocytes

Chondroblasts

Progenitor cells, make matrix, become chondrocytes in lacunae

Chondrocytes

Mature cells, function for remodeling

What are the 3 types of cartilage?

hyaline, elastic, fibrocartilage

Matrix

Glycosaminoglycans containing collagen fibers

Hyaline

- Matrix: fine collagen fibers

- Locations: articular surfaces of bones, costal cartilage (rib cage), trachea, larynx, fetal skeleton

- Functions: eases joint movement, air passage, precursor to bone in fetal skeleton

Elastic

- Matrix: elastic fibers

- Locations: external ear, tip of nose, and epiglottis

- Functions: provides flexible, elastic support

Fibrocartilage

- Matrix: coarse bundles of collagen fibers

- Locations: pubic symphysis, menisci (in the knees), intervertebral discs

Instead of blood vessels, nutrients are transported via _______

diffusion

Tendons

Connect muscle to bone

Ligaments

Connect bone to bone (at the joints)

What are bones (the organs) made of?

Bony tissue, marrow, cartilage, adipose tissue, nervous tissue, fibrous connective tissue

What are the 2 parts of long bone?

Periosteum and endosteum

Periosteum

A dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles

Does the periosteum have a inner osteogenic layer?

Yes, they're bone-forming cells

Endosteum

Connective tissue lining marrow cavity

What is bony tissue?

Osseous tissue (made up of cells and matrix)

How many bone cells are there?

4

What are the types of bone cells?

osteogenic cells, osteoblasts, osteocytes, osteoclasts

Osteogenic cells

Stem cells of inner layer of periosteum and endosteum

Is osteogenic cells mitotic?

Yes, they give rise to most other bone cell types

Osteoblasts

Bone building cells

- Single layer of cells below endosteum and periosteum

What is the function of osteoblasts?

Synthesize soft organic matter of matrix

What is the process of osteoblasts?

Stress on bone -> stimulates osteogenic cells to multiply rapidly -> increase # of osteoblasts = synthesis of more bony matrix

Osteocytes

"Former osteoblasts" trapped within matrix they deposited

Lacuna

Tiny cavity where an osteocyte resides

Canaliculus

Very small tube or channel, found between lacunae (connecting them together) in compact bone

What do cytoplasmic processes of osteocytes do?

reach into canaliculi and contact processes of neighboring cells (nutrient and waste exchange)

What do the "strain sensors" for osteocytes do?

Produce biochemical signals when stressed that regulate bone remodeling (movement = healthy bones)

Osteoclasts

Bone-destroying cells on bone surface (dissolve bone for bone remodeling)

Where does osteoclasts develop from?

Bone marrow stem cells that give rise to blood cells

What is shape/size of osteoclasts?

Very large cells, fusion of several stem cells (have multiple nuclei in each cell and large surface area)

Bone Matrix

Organic matter (1/3) and inorganic matter (2/3)

How is the bone matrix formed?

Osteoblasts

Osteiod

Collagen and carbohydrate-protein complexes (glycosaminoglycans, proteoglycans, glycoproteins)

What is the purpose of an osteiod?

Gives bone flexibility (organic)

Allows bone to support body weight without sagging (inorganic)

What is the inorganic matter for bone matrix?

85% hydroxyapatite (crystallized calcium phosphate salt), 10% calcium carbonate, other (fluoride, sodium, potassium, magnesium)

What are the 2 structures of bones?

Spongy and compact

Spongy bone

Lattice of bone covered with endosteum

- Few osteons and no central canals

Spicules

Slivers of bone

Trabeculae

Thin plates of bone (give porous appearance)

- Develop along bone's lines of stress

What are the spaces of spongy bone filled with?

Red bone marrow (hematopoietic tissue)

What is the purpose of spongy bone?

Provides strength with minimal weight

Where are the osteocytes located in spongy bone?

Close to bone marrow

Compact bone

Hard, dense bone tissue that is beneath the outer membrane of a bone

Where is the matrix deposited?

Concentric lamellae

Concentric lamellae

Onion-like layers around each central canal

Central (haversian) canals

Blood vessels and nerves travel through central canal

Osteon structure

Central canal and its surrounding lamellae

What are the other bone matrixes that surround osteons?

Circumferential lamellae and interstitial lamellae

Circumferential lamellae

a bony lamella that encircles the outer or inner surface of a bone

Interstitial lamellae

remains of old osteons that broke down as bone grew and remodeled itself

Bone marrow

Soft tissue occupying cavities of long bones and small spaces of spongy bone

Red marrow

Produces blood cells

Where is red marrow found?

Young: every bone

Adult: select bones (skull, vertebrae, ribs, sternum, proximal heads of humerus and femur)

Yellow marrow

Fatty marrow that doesn't produce blood

What is can yellow marrow do in the event of chronic anemia?

Transform back to red marrow

Ossification/osteogenesis

Bone formation

What are the types of ossification that occurs in the fetus?

Intramembranous ossification and endochondral ossification

Intramembranous ossification

Produces flat bones of skull and clavicle and thickens long bones throughout life

Endochondral ossification

Elongates long bones

Does ossification continue throughout life?

yes, with growth and remodeling of bones

Interstitial growth

Growth in length

Where does interstitial growth occur?

epiphyseal plate (aka growth plate)

What happens at the epiphyseal plate?

Hyaline cartilage in the middle with transition zones on each side where cartilage is replaced by bone

Metaphysis

Zone of transition that faces the marrow cavity

What are the 5 names of the zones for intersticial growth?

- Reserve cartilage

- Cell proliferation

- Cell hypertrophy

- Calcification

- Bone deposition

Zone of reserve cartilage

typical hyaline cartilage farthest from marrow cavity; shows no sign of transforming into bone

Zone of cell proliferation

chondrocytes multiplying and lining up in rows of small flattened lacunae

Zone of cell hypertrophy

chondrocyte stop dividing and enlarge; matrix between lacunae become very thin

Zone of calcification

temporary calcification of cartilage matrix between columns of lacunae

Zone of bone deposition

breakdown of lacuna walls, leaving open channels; death of chondrocytes; bone deposition by osteoblasts, forming trabeculae of spongy bone

What happens in interstitial growth when the cartilage is gone?

The epiphyses close

Epiphyseal line

remnant of the epiphyseal plate, seen in adult bones

Does interstitial growth continue forever?

No, will occur at different ages in different bones/species

Appositional growth

Occurs at bone surface

Does appositional growth continue forever?

Yes, continual growth in diameter and thickness