Bone tissue Flashcards
How many bones in human bod?
Largest bone?
Smallest bone?
Skeleton accounts for what percent of body weight?
206
Femur
Stapes (inner ear)
15%
Functions of bone (5)
- Support: framework of bod
- Protection: proved protection to the delicate structures they enclose
- Movement: muscles attach to bone; as the muscles contract, the produce movement at joints
- Mineral storage: calcium, phosphorus, etc
- Hematopoiesis: blood cell formation
5 types of bone
- Long
- Short
- Flat
- Irregular
- Sesamoid
Long bone
Extended longitudinal axes (femur, humerus)
Short bone
Cube or box-shaped (carpals, tarsals, phalanx)
Flat bone
Broad and thin with a flattened surface (scapula, sternum)
Irregular bone
Various sizes and shapes (vertebra, facial)
Sesamoid bone
Usually develop in the tendons close to the joints (patella)
Long bone components
Diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, and endosteum
Diaphysis
- main shaft of long bone
- hollow, cylindrical shape with thick, compact bone surrounding a central cavity
- function is to provide strong support withough cumbersome weight
Epiphysis
- both ends of a long bone, made up of cancellous bone filled with marrow
- bulbous shape
- function is to provide attachments for muscles and give stability to joints
Metaphysis
- meta = between
- regions between the diaphysis and the epiphyses
- in growing bone, contain epiphyseal plate (a thin layer of hyaline cartilage that allows bone to grow in length)
Articular cartilage
- layer of hyaline cartilage that covers the articular surface of epiphyses
- function is to provide some cushioning between bones, reduce friction
Periosteum
- dense, white, fibrous membrane that covers bone
- attaches tendons firmly to bones
- has 2 layers (outer fibrous layers and inner osteogenic layer containing osteoblasts and osteoclasts)
- contains blood vessels important in growth and repair
- essential for bone cell survival and bone formation
Medullary cavity
Tube-like, hollow space in diaphysis
- filled with blood vessels and yellow marrow (rich in fat) in adults
Endosteum
- thin epithelial membrane that lines medullary cavity of long bones
- made up of single layer of bone-forming cells and a small amount of connective tissue
Parts of flat bone
- . Structure similar to long bone
- covered in periosteum
- inner spaces are lined with endosteum
- instead of yellow marrow, the red marrow fills the spaces of the cancellous bone inside many flat bones
- short bones, irregular bones, and sesamoid bones all have features similar to those of flat bones
Bone tissue
- distinctive form of connective tissue
- osseous tissue
- ECM: 2/3 inorganic salts and 1/3 organic matter
- supportive and protective functions
- tensile strength (collagen fibers) is nearly equal to cast iron at less that 1/3 the weight
- contains osteoprogenitor, osteonsblasts, osteoclasts, and osteocytes
Composition of bone matrix
- inorganic salts
- hydroxyapatite crytals: rocklike crystals of Ca++ and phosphate
- calcification: forming the crystals wishing the softer tissue
- 85% of inorganic matrix
- 10% is calcium carbonate, magnesium, sodium, sulfate, fluoride
Composition of bone matrix
- organic matrix
- collagenous fibers
- ground substance: proteins and polysaccharides
- chondroitin sulfate and glucosamine:
Chondroitin sulfate
Large protein molecule that helps cartilage remain compressible and elastic
Glucosamine
Amino sugar important to cartilage formation, maintenance, and repair
Compact bone
- constitutes about 80% of the total bone mass
- contains many cylinder-shaped structural units called osteons, or ha version systems
- osteons surround canals that run lengthwise through bone and are connected by transverse volkmann’s canals
Osteons
- living bone cells are located in these units, which constitute the structural framework of compact bone
- permit delivery of nutrients and removal of waste products
- lamellae
- lacunae
- canaliculi
- central canal
Lamellae
- concentric, cylinder-shaped layers of calcified matrix (tree rings)
- only 8-15 layers thick
- each subsequent layer’s collagen fibers are oriented in the opposite direction
Lacunae
Small spaces containing tissue fluid in which bone cells are located between hard layers of the lamella
Canaliculi
Very small canals radiating in all directions form the lacunae and connecting them to each other and to the haversian canal
Haversian canal
Extends lengthwise through the center of each osteon and contains blood vessels and lymphatic vessels
Lamellae (1)
Layers of calcified matrix
Lacunae (1)
Spaces with tissue fluid and bone cells
Canaliculi (1)
Canals connecting lacunae
Haversian canal (1)
Central canal contains blood and lymph vessels
Cancellous bone
No osteons
- nutrients are delivered and waste products are removed by diffusion through tiny canaliculi
- trabeculae
- orientation of trabeculae along lines of stress, enhancing the bone’s strength
- decreases overall bone weight
Trabeculae
Irregularaly formed lamellae (bony spicules). Lies between two layers of compact bone or near the ends of long bones
Osteoblasts
Build bone
- bone-forming cells found in all bone surfaces
- produce bone matrix and promote deposition of calcium
- blood calcium levels decrease
Osteoclasts
Carve out bone
- bone-reabsorbing, responsible for the active erosion of bone minerals
- lysosomes highly active - secrete enzymes and acids that ‘lyse’ the proteins/minerals of the matrix
- blood calcium levels increase
Osteocytes
- mature, non-dividing osteoblasts that is surrounded by matrix
- lying within lacunae and maintain matrix
- can change into osteoblasts or osteoclasts when needed
Bone marrow
Myeloid tissue
- specialized type of soft, diffuse connective tissue
- site for the production of blood cells
- found in medullary cavities of long bones and in the spaces of spongy bone
- two types of marrow are present during a person’s lifetime: red and yellow marrow
Red marrow
Functions to produce red blood cells
- gradually reduces overtime and is replaced by yellow marrow
Yellow marrow
Replaces red marrow in long bones
- marrow cells become saturated with fat and are no longer active in blood cell production
Adult bone marrow
- red marrow still present in ribs, pelvis, vertebral bodies, and epiphyses of humerus and femur
- yellow marrow can change to red marrow during times of decreased blood supply, such as with anemia, exposure to radiation, and certain diseases
Blood supply
- bone cells are metabolically active and need a blood supply
- medullary cavity has one or more arteries that supply bone marrow and areas of cancellous bone
Spongy bone blood supply
Receives blood supply from the bone marrow in the internal medullary cavity and passage of nutrients through the canaliculi
Compact bone blood supply
Arteries covered in the periosteum and incorporated into the bone itself (transverse canals)
Bone marrow transplant
Red marrow from compatible donor is introduced into recipient intravenously
- goal is to establish a new, healthy colony of bone marrow
Ca++ levels in blood
- bones sever as a storage site for about 98% of the body calcium reserves
- bone plays a key role in maintaining the constancy of blood calcium levels
- it is the balance between deposition of bone by osteoblasts and breakdown and resorption of bone by osteoclasts that helps to regulate blood Ca++ levels
Osteogenesis or ossification
The process by which osteoblasts and osteoclasts work together to transform cartilage into bone
Intramembranous ossification
Skull, facial bones and clavicles develop through this process which starts with fibrous membrane instead of a cartilage model
- occurs within connective tissue membrane
- groups of osteogenic stem cells with the membrane differentiate into osteoblasts
- cluster of osteoblasts are “ossification centers”
Endochondral ossification
Most bones are formed from cartilage models in this process
Endochondral ossification process (1-6…)
- Bone begins as cartilage model
- Formation of periosteum around cart.
- Osteoprogenitor cells differentiate and osteoblasts are formed (spongy bone tissue)
- More trabeculae are formed and fuse into lamellae
- Bone formation spreads from the center to the ends
- Development of cavities (yellow and red marrow)
Endochondral ossification process (…7-9)
- Bone grows in length as osteoblasts form bone in middle and chondroblasts are adding new cartilage to ends of bone
- Bone grows in width by addition of periosteal bone
- After burst secondary ossification centers develop in the ends of long bones to allow for continued growth until end of puberty - epiphyseal plate
Epiphyseal plate
- until bone growth is complete, a layer of cartilage remains between each epiphysis and diaphysis
- when these cells stop multiplying and cartilage becomes ossified, bone growth ends
Epiphyseal plate injury
- esp if overstressed (kids, grandpas)
- when separated from the diaphysis or epiphysis results in a fracture
- these fractures can cause a slowing or cessation of growth in the bone
Bone remodeling
Osteoblasts and osteoclasts activity
- 5% of bone mass is remodeled at any given time in adult
- spongy bone replaced at 20% per year, compact bone replaced 4% per year
Hormones
- parathyroid glands and the thyroid gland are responsible for secreting hormones (PTH and calcitonin) involved in the regulation of blood calcium levels
Parathyroid
Increase calcium into blood
- stimulates osteoclasts
Calcitonin
Decrease calcium in blood
- stimulate osteoblasts
Factors that affect bone remodeling
- Hormones
- Nutrition
- Stress
Nutrition
- Vit D: necessary for Ca++ absorption
- Vit C: collagen synthesis
- Vit A: balances osteoclast and osteoblasts activity
- Ca++, Mg, P: necessary for hardness of bone (inorganic matrix)
Stress
Mechanical and functional forces
- gravitational forces exerted to support the weight of body
- functional forces exerted on bones by contracting muscles
- wolff’s law: bone grows or remodels in response to the forces or demands placed on it
Osteoporosis
Bone breakdown > bone formation
- composition of bone is normal, decrease bone mass
- factors: decreased sex hormaones, insufficient WBing exercise, poor nutritional intake of necessary supplements
Fracture
Break in the continuity of a bone
- tears and destroys blood vessels that carry nutrients to osteocytes
Fracture healing process
- Formation of fracture hematoma
- Soft procallus formation
- Bony callus
- Bone remodeling
Formation of fracture hematoma
- vascular damage initiates repair sequence, early inflammatory phase
- blood clot forms around the fracture site usually 6-8 hours after injury
- nearby cells die, increased activity of osteoclasts and phagocytes to remove debris around hematoma
Soft procallus formation
- fracture hematoma resorbed and callus forms
- fibrocartilaginous callus forms to bridge broken bones - fibroblasts produce collagen and chondroblasts produce fibrocartilage (3 weeks)
- no structurally rigid
- anchors broken ends
- bony callus forms from osteoblasts and replaces soft callus / forms spongy bone (3-4 months)
Bony callus
- osteoblasts continued to resort dead portions fo broken bone
- compact bone replaces spongy bone around periphery of fracture
- injury heals completely and is similar to original unbroken thickened area arund the healed fracture site
Factors that influence bone growth
- Stresses
- Nutrition
- Hormones
- growth hormone
- sex hormone (increased levels facilitate growth spurt and decreased levels facilitate epiphyseal plate closure)
Cartilage
- cells lie in lacunae
- no canals or blood vessels in matrix
- nutrients reach cells through diffusion (perichondrium or synovial fluid)
3 types of cartilage
- Hyaline: most abundant
- elastic: contains elastic fibers and collagenous fibers and has a firm elasticity
- fibrocartilage: has most numerous amoun of collagen fibers and has greatest tensile strength
Hyaline cartilage
- covers articular surfaces of bones
- forms costal cartilages
- forms rings in the trachea
- bronchi of the lungs
- tip of the nose
Elastic cartilage
- forms external ear
- epiglottis
- Eustachian tube
Fibrocartilage
- strong and rigid
- pubic symphyses
- intervertebral disks
- near the point of attachment of some large tendons to bone
Function of cartilage
- sustain great weight
- shock absorption
- strong pliable support structure that resiste deformation or collapse
- permits growth in the length of bones
