What is osteology?
The study of bone structure and the treatment of bone disorders
Describe the protection function of the skeletal system
The
... [Show More] skeleton protects internal organs from injury
Describe the support function of the skeletal system
The skeleton is a structural framework for the body (it supports soft tissues and provides attachment points for tendons)
Describe the mineral homeostasis (storage/release) function of the skeletal system
Bones store minerals (calcium and phosphorus) that contributes to bone's strength
Bones release minerals into the blood to maintain homeostasis and distribute minerals throughout the body
Describe how the skeletal system aids in movement
Skeletal muscles attach to bones, contract, and pull on bones for movement
Describe the triglyceride storage function of the skeletal system
Yellow bone marrow consists of adipose cells that store triglycerides (a potential chemical energy reserve)
Describe the blood cell production function of the skeletal system
Red bone marrow produces red/white blood cells, and platelets (marrow changes to yellow with age)
What is a long bone?
A bone that has greater length than width
What is the diaphysis?
The shaft of a long bone (body, main portion)
What are the epiphyses?
The proximal and distal ends of a long bone
What are the metaphyses?
Regions between the diaphysis and epiphyses of long bones (in growing bones, each contains a growth plate)
What is an epiphyseal plate/line?
A layer of hyaline cartilage that allows diaphysis of a long bone to grow in length
Once the bone stops growing (age 14-24), cartilage is replaced by bone (creating an epiphyseal line)
What is articular cartilage?
A layer of hyaline cartilage that covers the epiphysis at joints to reduce friction/absorb shocks (avascular, so damage repair is hard)
What is a periostium?
The connective tissue sheath and blood supply that surrounds the remainder of a long bone's surface (has an outer fibrous layer and inner osteogenic layer)
Help protect bone, aids in fracture repair, nourishes tissue, and acts as attachment point (attached to underlying bone by Sharpey's fibres)
What is a medullary (marrow) cavity?
A hollow space in the diaphysis of a long bone that contains fatty yellow bone marrow and blood vessels (helps minimize bone weight)
What is an endosteum?
A thing membrane that lines the medullary cavity in a long bone
Why is bone classified as a connective tissue?
Bone tissue contains an abundant extracellular matrix (contains water, collagen, and crystal mineral salts) that surrounds widely separated cells
Mineral salts combine to form hydroxyapatite crystals which then participate in calcification
What are osteoprogenitor cells?
Unspecialized bone cells that undergo division (develop into osteoblasts), found along periosteum, endosteum, and canals
What are osteoblasts?
Bone-building cells that excrete collagen to build extracellular matrix, initiate calcification (become osteocytes when they are trapped in extracellular matrix)
What are osteocytes?
Mature bone cells (main cells in bone tissue) that maintain metabolism through exchange (cells don't divide, just maintain and monitor tissue)
What are osteoclasts?
Huge osteogenic cells concentrated in the endosteum (plasma membrane is folded)
Participates in resorption (breakdown of extracellular matrix, a normal part of development, maintenance and repair of bone)
What is compact bone tissue?
The strongest form of bone tissue found beneath periosteum of all bones, makes up most of diaphyses of long bones (has few spaces)
What is an osteon (Haversian system)?
A structural unit of compact bone (aligned parallel to diaphysis), helps shaft resist bending or fracture under lots of force
What is a central (Haversian) canal?
Part of an osteon, surrounded by concentric lamellae (mineralized extracellular matrix) that contains blood vessels and nerves
Interstitial lamellae are fragments of old, destroyed osteons
Perforating (Volkmann's) canals: blood vessels/nerves from the periosteum penetrate compact bone through these canals
What are lacunae?
Spaces between concentric lamellae (have osteocytes)
What are canaliculi?
Small channels in compact bone, radiating in all directions from lacunae (filled with extracellular fluid) and connect lacunae to each other/to central canals, provides routes for nutrients/oxygen and waste removal
What is spongy bone tissue?
Interior part of short, flat, sesamoid bones (protected by compact bone) with light tissue (located where stress is applied from many angles)
Also called trabecular/cancellous bone tissue
Trabeculae: lamellae set in an irregular pattern of columns located along lines of stress (support/protect red bone marrow)
Explain the blood/nerve supply of bones
Blood vessels pass into bones from the periosteum (periosteal arteries enter diaphysis through Volkmann's canals)
Nerves accompany blood vessels (periosteum has many that can detect pain)
Explain the nutrient artery/veins
Nutrient artery: passes through nutrient foramen in diaphysis (then branches)
Nutrient veins: veins that carry blood away from the long bones (accompany artery)
Explain the metaphyseal and epiphyseal arteries/veins
Metaphyseal artery: supply red marrow and bone of the metaphyses (veins go opposite direction)
Epiphyseal artery: supply red marrow and bone of the epiphyses (veins go opposite direction)
Explain the process of ossification (osteogenesis)
The process by which bone forms (happens in 4 places)
Initial formation is in an embryo/fetus, then growth happens during infancy, childhood/adolescence until adulthood, then bone remodelling and repair of fractures happen throughout life
What is intramembranous ossification?
A simpler type of bone formation
Bone forms directly within mesenchyme (in flat skull/facial bones, mandible, clavicle, and soft spots)
What are the 4 steps in intramembranous ossifiation?
1. Development of ossification centre: chemical messages tell mesenchyme to cluster (cluster site is centre), cells differentiate into osteoprogenitor cells then osteoblasts (secrete extracellular matrix)
2. Calcification: secretion stops, osteocytes lie in lacunae, extracellular matrix hardens after mineral salts are deposited
3. Formation of trabeculae: extracellular matrix develops into trabeculae, fuse to form spongy bone around blood vessels
4. Development of periosteum: mesenchyme condenses/develops into periosteum (layer of compact bone replaces spongy bone surface layers and bone is remodelled)
What is endochondral ossification?
Bone forms within hyaline cartilage that develops from mesenchyme (cartilage is replaced by bone)
Most bones are formed this way (easiest to see in long bone)
What are the 6 steps of edochondral ossification?
1. Development of the cartilage model: mesenchyme cells cluster into shape of future bone and develop into chondroblasts (secrete extracellular matrix); perichondrium develops around the cartilage model
2. Growth of the cartilage model: chondroblasts become chondrocytes (after burying into extracellular matrix); model grows in length (interstitial/endogenous growth) and thickness (appositional growth)
3. Development of primary ossification centre: bone replaces cartilage (primary ossification proceeds inward, perichondrium forms periosteum, spongy bone trabeculae form)
4. Development of the medullary (marrow) cavity: osteoclasts break down spongy bone and leave a marrow cavity in the diaphysis
5. Development of secondary ossification centre: develop around time of birth, bone formation is similar to primary ossification
6. Formation of articular cartilage/epiphyseal plate: hyaline cartilage becomes articular cartilage
Describe the process of bone growth in length
Involves 2 steps:
1. Interstitial growth of cartilage on the epiphyseal side of growth plate
2. Replacement of cartilage on the diaphyseal side of growth plate with bone by endochondral ossification
What is an epiphyseal (growth) plate?
A layer of hyaline cartilage in the metaphysis of a growing bone
What are the 4 zones in a growth plate?
1. Zone of resting cartilage: small scattered chondrocytes near epiphysis that anchor the plate to the epiphysis (not involved in bone growth)
2. Zone of proliferating cartilage: larger chondrocytes (stacked like coins) undergo interstitial growth
3. Zone of hypertrophic cartilage: consists of large, maturing chondrocytes in columns
4. Zone of calcified cartilage: consists of dead chondrocytes (since extracellular matrix is calcified), becomes the new diaphysis
What is an epiphyseal line?
A bony line left when an epiphyseal plate closes (cartilage is replaced by bone) in adulthood
Describe the process of bone growth in thickness
Called appositional growth (4 steps)
1. Periosteal cells at bone's surface differentiate into osteoblasts (secrete extracellular matrix until it surrounds them), which become osteocytes that form bone ridges
2. Ridges fold/fuse together, the periosteum becomes the edosteum
3. Osteoblasts in endosteum deposit extracellular matrix and form concentric lamellae (fill the tunnel until a new osteon is formed)
4. As the new osteon forms, osteoblasts deposit new circumferential lamellae (increases bone's thickness)
What is bone remodelling?
The ongoing replacement of old bone with new bone (rate is different depending on the place in the body and a person's lifestyle)
New bone is more resistant to fracture than old bone
Describe bone resorption and bone deposition
Resorption involves removal of minerals and collagen fibres from bone by osteoclasts (destruction of extracellular matrix)
Deposition involves addition of minerals and collagen fibres to bone by osteoblasts (formation of extracellular matrix)
What factors affect bone growth and remodelling?
Bone metabolism depends on minerals (calcium/phosphorus), vitamins (A, C, D, K, B12), hormones and sex hormones
What is a fracture?
Any break in a bone [Show Less]