Human Morph & Func ch 7

What are the components of the skeletal system?

• Bones of skeleton

• Cartilage

• Ligaments

• Other CT

Describe bones.

Primary organs of the skeletal system, rigid framework of body

Describe compact bone.

Dense or cortical bone counting as 80% of bone mass

Describe spongy bone.

Cancellous or trabecular bone located internal to compact bone and appears porous, counting as 20% of bone mass

Describe cartilage.

Semirigid CT, more flexible than bone

What are two types of cartilage?

hyaline and fibrocartilage

Describe hyaline cartilage.

Attaches ribs to sternum, covers ends of some bones, within growth plates, model for bone formation

Describes fibrocartilage.

Weight-bearing cartilage that withstands compression found in intervertebral discs, pubic symphysis, meniscis of knee

What structures are composed of dense regular CT?

Ligaments connecting bone to bone and tendons connecting muscle to bone

What are the basic functions of bone?

• Support and protection

• Levers for movement

• Hematopoiesis

• Storage of mineral and energy reserves such as Calcium and phosphate

What is hematopoiesis?

Blood cell production occuring in red bone marrow CT

What kind of tissue is primarily composed in bone?

connective and nervous tissue

Describe connective tissue in bone.

- found in compact and spongy bone

- examples: dense irregular connective tissue, reticular connective tissue, blood

Describe nervous tissue in bone.

detects and monitors sensory stimuli about status of the bone

What are the 4 kinds of bone?

long, short, flat, irregular

Describe long bone.

Greater in length than width; for example femur, humerus

Describe short bone.

Length nearly equal to width; for example carpals and tarsals

Describe flat bone.

Flat, thin surfaces, may be slightly curved; for example cranial bones

Describe irregular bone.

Elaborate, sometimes complex shapes; for example vertebrae

Describe the diaphysis of a long bone.

Compact bone with thin spicules of spongy bone extending inward that is elongated w/ a cylindrical shaft, providing leverage and weight support

Describe the medullary (marrow) cavity of long bone.

Hollow, cylindrical space within the diaphysis containing red bone marrow in children and yellow bone marrow in

adults

Describe the general epiphysis in long bone.

Knobby region at each end of long bone

Describe the proximal epiphysis in long bone.

End of the bone closest to body trunk

Describe the distal epiphysis in long bone.

End farthest from trunk composed of:

• Outer thin layer of compact bone

• Inner region of spongy bone

Describe articular cartilage in long bone.

Thin layer of hyaline cartilage that covers the joint surface to reduce friction and absorbs shock in moveable joints

Describe metaphysis in long bone.

Region where bone widens and transfers weight between the diaphysis and epiphysis

Describe epiphyseal plate in long bone.

Located within metaphysis, thin layer of hyaline cartilage providing for lengthwise bone growth

What is the epiphyseal line of long bone considered in adults?

remnant of the epiphyseal plate

What is the epiphyseal plate also considered?

growth plate

Describe the Periosteum of long bone.

Tough sheath covering outer surface of bone that is attached to bone by numerous perforating collagen fibers

What tissue is located in the outer layer of the periosteum of long bone?

dense irregular CT

What does dense irregular CT in the periosteum of long bones provide?

• Protects bone from surrounding structures

• Anchors blood vessels and nerves to bone surface

• Attachment site for ligaments and tendons

What is the inner layer of the periosteum of long bones composed of?

osteoprogenitor cells and osteoblasts

How is the periosteum of long bone attached to it?

by numerous perforating collagen fibers

Describe the endosteum of long bone.

Covers all internal surfaces of bone within medullary cavity

What does the thin layer of CT of the endosteum of long bone contain?

osteoprogenitor cells and osteoblasts

Describe the blood supply of long bone.

highly vascularized (spongy bone) w/ a nutrient foramen

What is the nutrient foramen of long bone?

Small opening or hole in bone where artery enters and vein exits from

Describe the nerve supply in long bone.

accompanies blood vessels through foramen and Innervates bone, periosteum, endosteum, marrow cavity w/ sensory nerves

How does short, flat, and irregular bones differ from long bones?

External surface composed of compact bone covered by

periosteum and internal surface composed of spongy bone w/ no medullary cavity

Define Diploë.

spongy bone in flat bone of skull

What is bone marrow?

soft CT of bone

- red & yellow

Describe red bone marrow.

hematopoietic, has myeloid tissue, Reticular CT, developing blood cells, and adipocytes

Where is red bone marrow in children?

Located in spongy bone and medullary cavity of long bones

Where is red bone marrow in adults?

Located only in selected areas of axial skeleton such as the skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus and femur

Describe yellow bone marrow.

Fatty substance that is the product of red bone marrow

degeneration as children mature, may convert back to red bone marrow during severe anemia, and facilitates production of additional erythrocyte

What is bone CT also known as?

osseous CT

What is the primary component of bone? What does this mean?

- Bone CT

- Bone is composed of cells and extracellular matrix

What types of cells are found in Bone CT?

1. Osteoprogenitor cells

2. Osteoblasts

3. Osteocytes

4. Osteoclasts

Describe osteoprogenitor cells in bone CT.

stem cells derived from mesenchyme (cell division) that matures to become an osteoblast

Where are osteoprogenitor cells of bone CT located?

in periosteum and endosteum

Describe osteoblasts in bone CT.

form from osteoprogenitor stem cells that synthesize and secrete osteoid and later becomes entrapped within the matrix to differentiate into osteocytes

What are osteioids?

Initial semisolid organic form of bone matrix that later calcifies

Describe osteocytes in bone CT.

Mature bone cells derived from osteoblasts that detect stress on bone and trigger new bone formation

Describe osteoclasts in bone CT.

Large, multinuclear, phagocytic cells derived from fused hematopoietic cells w/ a ruffled border and involved in bone resorption (breakdown of bone)

What is the purpose of a ruffled border in osteoclasts?

increases surface area exposed to bone

What is the purpose of osteoclasts being located within/adjacent to a depression/pit on bone surface?

Resorption lacuna

What is the organic composition of the bone matrix?

Osteoids that contain collagen protein and semisolid ground substance of proteoglycans and glycoproteins

What is the purpose of osteoids in the bone matrix?

• Gives bone tensile strength by resisting stretching

• Contributes to bone flexibility

What is the inorganic composition of the bone matrix?

Salt crystals, calcium phosphate (Ca3(PO4)2) that interacts with calcium hydroxide to form crystals, hydroxyapatite (Ca10(PO4)6(OH)2)

What is the purpose of salt crystals, calcium phosphate, and Ca3(PO4)2 in the bone matrix?

deposits around collagen fibers, hardens matrix, and account for rigidity of bone

What other components are incorporated into crystals?

calcium carbonate, sodium, magnesium, sulfate, fluoride

Describe bone formation.

Begins with secretion of osteoid -> Calcification

• Process requires: Vitamin D, Vitamin C, and Calcium and phosphate for calcification

Describe calcification.

deposition of hydroxyapatite crystals where Calcium and phosphate ions precipitate out, form crystals

Describe the role of vitamin D in bone formation.

enhances calcium absorption from GI tract

Describe the role of vitamin C in bone formation.

required for collagen formation

Describe bone resorption.

- Bone matrix is destroyed by substances released from

osteoclasts and proteolytic enzymes are released from lysosomes

- Calcium and phosphate dissolved by hydrochloric acid and freed calcium and phosphate ions enter the blood

What is the purpose of proteolytic enzymes released from lysosomes?

Chemically digest organic matrix components

When does bone resorption occur?

when blood calcium levels are low

Describe the process of calcification.

osteoblasts produce osteoids, which form a collagen matrix that forms vesicles to concentrate calcium, phosphate, and alkaline phosphatase, which forms hydroxyapatite crystals that deposit around the collagen fibers, mineralizing the bone

What is the function of hydroxyapatite?

contributes to bone hardness and strength

What is the purpose of alkaline phosphatase?

increases local phosphate concentration

What is compact bone composed of?

osteons or haversian systems

How are osteons in compact bone oriented?

parallel to bone diaphysis

How do osteons appear in compact bone?

as bull's-eye target

Describe Central (Haversian) canal in osteons.

Cylindrical channel at center and parallel of osteon w/ blood vessels and nerves extending through channel

Describe Concentric lamellae in osteons.

rings of bone CT that surrounds central canal w/ collagen fibers, 90 degrees from previous and next lamellae, and gives bone strength and resilience

What are osteons composed of?

- canaliculi

- osteocytes

- concentric lamellae

- central (Haversian) canal

Describe osteocytes in osteons.

mature bone cells found in small spaces between concentric lamellae (lacunae) that maintain bone matrix

Describe Canaliculi in osteons.

Tiny, interconnecting channels within bone CT, extending from each lacuna, traveling through lamellae and connecting to lacunae and the central canal

What is the purpose of house projections in canaliculi in osteons?

allow intercellular contact

What is the function of canaliculi in osteons?

Allow exchange of nutrients, minerals, gases, and wastes between blood vessels and osteocytes

What structures in the long bones of compact bone are not part of osteons?

- Perforating (Volkmann) canals

- Circumferential lamellae

- Interstitial lamellae

Describe perforating (Volkmann) canals.

• Perpendicular to central canals

• Connect central canals within different osteons

Describe Circumferential lamellae.

• External—rings of bone run internal to periosteum

• Internal—rings of bone run internal to the endosteum

• Both run the entire circumference of the bone

Describe Interstitial lamellae.

Components of compact bone between osteons or partially resorbed osteons

What is comprised in the anatomy of spongy bone?

Trabeculae & Parallel lamellae

Describe Trabeculae.

Open lattice of narrow rods and plates of bones w/ bone marrow and a meshwork of crisscrossing bars to resist stress

Describe Parallel lamellae.

Bone matrix w/ osteocytes between lamellae and canaliculi radiate from lacunae

Describe hyaline cartilage connective tissue.

cells scattered through a matrix of protein fibers that is embedded in a gel-like ground substance that is avascular, resilient/flexible, highly compressible, and has a high % of water

What does the gel-like ground substance in hyaline cartilage connective tissue include?

proteoglycans but not calcium

What does hyaline cartilage connective tissue contain?

Chondroblasts, Chondrocytes, Perichondrium

What are chondroblasts?

produce cartilage matrix

What are chondrocytes?

chondroblasts encased within the matrix that occupy small spaces, lacunae, and maintain the matrix

What is perichondrium?

dense irregular CT that covers cartilage and helps maintain its shape

Describe ossification (osteogenesis).

- formation and development of bone CT, beginning in the embryo, continuing through childhood and adolescence

- by 8th through 12th weeks of embryonic development, skeleton begins forming from intramembranous ossification or endochondral ossification

Describe Intramembranous (dermal) ossification.

Bone growth within a membrane that produces:

• Flat bones of skull

• Some of the facial bones

• Mandible

• Central part of the clavicle

What are the steps of intramembranous ossification?

1. Ossification centers form within thickened regions of mesenchyme beginning at the eighth week of development

2. Osteoid undergoes calcification

3. Woven bone and surrounding periosteum form

4. Lamellar bone replaces woven bone, as compact bone

and spongy bone form

Describe ossification centers in intramembranous ossification.

Some cells become osteoprogenitor cells while others become osteoblasts secreting osteoid

Describe calcification of osteoids during intramembranous ossification.

Calcium salts deposit onto osteoid and crystallize while entrapped cells become osteocytes