Week 5 - Osseous Tissue A+P

Organs of the skeletal system

Bones!

What components make up the skeletal system?

Bones, cartilage, ligaments, tendons, marrow

Bone

Structure, made of osseous tissue

Ligaments

Dense regular CT that anchors bone to bone

Tendons

Anchors muscle to bone

Bone marrow

Red + yellow, soft CT, in bones

Red bone marrow

Hematopoetic (produces RBC’s). Adults usually have it only in the axial and proximal appendicular bones. Often transplanted during transplants (often gotten from hips/pelvis)

Yellow bone marrow

Stores adipose tissue (full of fat). Replaces red marrow as a person ages

Types of osseous tissue

Compact bone + spongy bone

Compact bone

About 75% of osseous tissue/bone. Hard, dense, outer layer of all bones

Spongy bone

About 25% of bone/osseous tissue, inner portion of bone, more airy

Components of compact bone

Osteon, lamellae, central canal, lacuna, canaliculi, volkmann

Osteon

Whole bone circle (a tree ring group)

Lamellae

Rings of the osteon

Osteocytes

Dots or lines on osteon

Central canal

Opening in center of osteon, transports nutrients and other materials

Lacunae

“Lagoons.” Where the functionals osteocytes live after they get mineralized

Canaliculi

Little canals/vertical lines on osteon. Helps with distribution throughout bone

Long bones

Most common shape. Height greater than width (ex. humerus, fingers)

Short bones

Height about equals width (ex. talus, wirst and ankle)

Flat bones

Sternum and scapula

Irregular bones

Vertebrae, sphenoid

Sesamoid bones

Short bones embedded in a tendon (patella)

Functions of skeletal system

Protects internal organs, stores and releases fat, produces blood cells, stores and releases minerals (calcium), facilitates movement, supports the body

Osseous tissue

Supportive CT with a mineralized matrix

1. Cells (osteocytes)

2. Ground substance ((calcium, fluid with a lot of glucosaminoglycans (GAGs, absorbs and retains water))

3. Fibers: collagen fibers (adds strength and flexibility) and minerals (hydroxyapatite, calcium carbonate, Mg, Na, F, SO4, OH)

Osteogenic cells

Stem cells that produce new bone cells - “bone origin”. First bone builder cell

Osteoblasts

2nd builder cell. New bone cells, builds bone tissue, immature, deposit enzymes that make the matrix (mineralizes it)

Osteocyte

3rd stage of osseous tissue builder. Maintained, matured cells

Osteoclasts

Diff cell line from the builders. Bones breakers, reabsorbs bone, break down + recycle bone tissue. Ruffled border, lysosomes

*you turn your skeleton over every 10 years

Lamellae

Collagen fibers arranged in layers of alternating direction. Limits spread of cracks and breaks

Epiphysis

Proximal end of long bones (enlarged sections). Red bone marrow. Covered by hyaline cartilage (glide, not grind)

Diaphysis

Long, middle section of long bones (shaft), yellow marrow, less pronounced, rounded shape

Medullary cavity

hollow, central space within the diaphysis (shaft) of long bones, primarily responsible for storing yellow marrow (fat) in adults and red marrow (blood cell production) in children

Articular cartilage

Covers each epiphysis

Periosteum

Membrane wrapped around bones (osteogenic cells) + osteoclasts

Epiphyseal line

Transitions between epiphysis and diaphysis

Epiphyseal fracture

When epiphysis separates from diaphysis. Tends to occur where cartilage is dying and calcification of the matrix is occurring

Depressed fracture

broken bone portion is pressed inward. Typical of skull fracture

Greenstick fracture

Bone breaks incompletely. Only one side breaks. Common in children (not completely mineralized yet)

Closed fracture

Skin not broken

Open fracture

Skin broken

Complete fracture

Break goes all the way through

Incomplete fracture

Break doesn’t go all the way through

Comminuted fracture

Bone shatters/fragments in 3+ pieces. Common in elderly

Compression fracture

Bone is crushed. more common in elderly.

spiral fracture

Ragged breaks from excessive twisting forces → common in kids (sports and child abuse)

Fracture repair steps

1. Hematoma formation

2. soft callus formation

3. hard callus formation

4. bone remodeling

Hematoma formation

Encase the injury. Hematoma is converted to granulation tissue by invasion of cells and blood capillaries (1)

Soft callus formation

Packing injury. Deposition of collagen and fibrocartilage converts granulation tissue to a soft callus (2)

Hard callus formation

Unite broken pieces. Osteoblasts deposit a temporary bone collar around the fracture to unite the broken pieces while ossification occurs (3)

Bone remodeling

bone is replaced. Small bone fragments are removed by osteoclasts, while osteoblasts deposit spongy bone and then convert it to compact bone

Osteoporosis

Bone holes. Bone is much more porous than normal. Risk factors: lack of calcium, lack of vitamin D, being a woman, small stature. Lighter, less dense bones. Osteoclasts outpace osteoblasts. Taking estrogen can help, more calcium, more vitamin D

Kyphosis

Increased thoracic curvature. “hunchback.” common in elderly people

Paget’s disease (osteitis deformis)

Rare genetic disease. A very specific area. Osteoblasts lay down bone haphazardly because of over-active osteoclasts

Dipole

the spongy, cancellous bone tissue located between the two layers of compact bone (the inner and outer tables) in the cranial bones

Trabeculae

the small, rod-shaped, or plate-like connective tissue struts that form a porous, lattice-like framework within spongy (cancellous) bone. Located at the ends of long bones and in vertebrae

Brittle bone disease

Person cannot lay down collagen properly. No strength or elasticity, bones are fragile and brittle. Bones shatter

Rickets

Childhood vitamin D deficiency. No calcium → bendy bones. Curved, not straight. some genetic causes for vitamin D deficiency

Intramembranous ossification

Inside/within membrane. bone develops from fibrous membrane → membrane gets partially ossified. Flat bones, cranial bones, clavicles

Endochondral ossification

Inside cartilage. Long bones. Bone forms by replacing hyaline cartilage. Most of skeleton. first made of cartilage → gets switched to bone. Bone collar forms around 9 weeks. Active chondrocytes pushes down, lengthening bones

Epiphyseal (growth) plates

Look like “empty” spaces in the bones. Cartilage does not show up on x-rays

Chondrocytes

Cartilage cells

Hematopoiesis

Formation/production of red blood cells

Articulation

the physical point of contact or connection between two or more bones, or between bone and cartilage

Cartilage

a tough, flexible, and resilient connective tissue that cushions joints, provides structural support, and enables smooth movement by reducing friction. 3 types (fibro, hyaline, elastic)

Endosteum

a thin, vascular membrane of connective tissue that lines the inner surface of bony tissue, specifically the medullary (marrow) cavity of long bones and the spaces within spongy bone

Osteoid

the unmineralized, organic portion of the bone matrix secreted by osteoblasts before maturation into hard bone tissue

Perforating canal

also known as Volkmann’s canals, are microscopic, horizontal channels in compact bone that run perpendicular to the long axis, connecting blood vessels and nerves from the periosteum to the central Haversian canals

Fracture

a partial or complete break in the anatomical continuity of a bone, resulting in mechanical instability, caused by forces exceeding the bone's structural integrity

Ossification

the anatomical process of bone formation, where connective tissues like mesenchyme or cartilage are replaced by hardened bone tissue

Skeletal system

BONE