Chapter 6 - Skeletal System Flashcards
What are the five functions of the skeletal system?
- Support- bone is hard and rigid; cartilage is flexible yet strong
- Protection- skull around brain, ribs, sternum
- Movement- muscles pull on bones via tendons, ligaments allow restricted movement
- Storage- calcium and potassium are stored and released
- hematopoesis- bone marrow gives rise to blood cells
What are the cell types of tendons and ligaments?
______________
What are the three types of cartilage associated with the skeletal system?
- Hyaline cartilage
- Fibrocartilage
- Elastic cartilage
What is the precursor to bone?
Hyaline cartilage
What is articular cartilage?
Hyaline cartilage at the ends of bone— cartilage only seen on growth plates in youth
What are the two types of cartilage growth?
- Appositional Growth- chondroblasts in perichindrium lay down new extracellular matrix and adds new cells
- Interstitial Growth- chondrocytes in matrix divide and add matrix
What do chondroblasts and chondrocytes do?
Chondroblasts produce matrix; chondrocytes maintain matrix; live in lacunae
What is the perichondrium?
A double layer of connective tissue around cartilage- avascular
What is the composition of bone matrix?
~ 35% organic and 65% inorganic
What is the main organic and inorganic component of bone?
Collagen and proteoglycans (organic portion (1/3) )
Hydroxyapatite (calcium phosphate) (inorganic/mineral component)
What is hydroxyapatite?
Ca10(PO4)6(OH)2, the primary inorganic component of bone
What happens when mineral is removed from bone?
Bones become soft and pliable (vitamin d deficiency- rickets in children or osteomalacia)
What happens when collagen is removed from bone?
Bones become brittle (vitamin c deficiency - scurvy)
What is Osteogenesis Imperfecta?
A disorder characterized by brittle bones- not making enough collagen - bones shatter
Blue sclera
What is Fibrodysplasia Ossificans Progressiva (FOP)?
A disorder causing fibrous connective tissue or muscles to turn into bone
What is Osteopetrosis?
Also known as ‘Marble Bone Disease’, characterized by dense bones
What do osteoblasts do?
Produce collagen and proteoglycans for the matrix. Also secrete calcium and phosphate for mineral portion
What is ossification?
Conversion of a substrate into bone matrix
Collagen produced by ER and Golgi- precursors of hydroxyapatite stored in vesicles and released by exocytosis
What do osteocytes do?
Mature osteoblasts— Maintain the matrix and are less active than osteoblasts
What do osteoclasts do?
Break down matrix using enzymes (degrade organic) and acid (degrade inorganic)
Where are osteoclasts found?
In both the periosteum and endosteum
What are osteochondral progenitor cells?
Stem cells that can become cartilage or bone cells
What are the two types of bone?
- Woven Bone - formed during fetal development and fracture repair
- Lamellar Bone
What is the difference between woven and lamellar bone?
Woven has collagen fibers in many directions and is immature bone; lamellar has fibers in flat sheets and is mature bone
What characterizes cancellous bone?
More space and less matrix, consisting of trabeculae (interconnecting rods or plates)
What is compact bone?
Denser bone with fewer spaces
What is the Haversian System?
Osteon- The structural unit of compact bone
What are Volkmann’s canals?
Transverse canals connecting one Haversian canal to another one or going from a Haversian canal to the periosteum
What is the periosteum?
Dense irregular connective tissue covering bone- becomes continuous with tendons
What is the endosteum?
A single layer of bone cells lining the medullary cavity
What is the epiphyseal plate?
Growth plate in growing children
What type of cartilage is laid down at the epiphyseal plate?
Hyaline cartilage
Becomes the line when it stops growing
What is intramembranous ossification?
Bone development from a fibrous in many skull bones and part of the clavicle
What is endochondral ossification?
Bone development that starts with a hyaline cartilage model
What is the process of bone growth in length?
Endochondral growth at the epiphyseal plate — cartilage is laid down, ossified, then another layer is laid until it becomes the epiphyseal line
What stimulates bone growth at puberty?
Sex hormones
What role does Vitamin D play in bone health?
Important for absorption of Ca++ and PO4- in the intestine
What is rickets?
A condition caused by Vitamin D deficiency in children. Soft bones due to low Ca
What is osteomalacia?
Softening of bones in adults due to Vitamin D deficiency
What is bone remodeling?
The process of replacing old bone with new bone throughout life.
Important for growth, shape, adaptation to mechanical stress, bone repair, and Ca+ regulation
What regulates blood Ca++ levels?
- Calcitonin
- Parathyroid hormone (PTH)
What happens when blood Ca++ levels drop?
PTH is secreted, increasing osteoclast activity
What happens when blood Ca++ levels are too high?
Calcitonin is secreted, decreasing osteoclast activity
What is the first step in bone repair after a fracture?
Formation of a fracture hematoma (clot)
What cells are stimulated to migrate into the fracture site?
Cells of the periosteum and endosteum
What is a callus in bone repair?
A structure formed between broken ends during healing
How long can bone remodeling take after a fracture?
Four months to a year
Manifestations of Osteogensis Imperfecta
Results in fractures, spinal disfigurements, short stature, dental problems, blue tint of eye
Remodeling
Removing old bone and adding new
Woven bone is remodeled into lanellar bone
Done throughout life - oscteoclasts tear down and osteoblasts build new. Higher stress are remodeled more often.
Trabeculae
Interconnecting rods of bone in spongy bone
Arranged along stress lines
Layering of compact bone
An osteon or Haversian system encases :
A blood vessel filled central canal or Haversian canal
Surrounded by concentric lamellae
Circumderential lamellae under periosteum
Interstitial lamella fill empty space between osteons
Structure of a long bone
Diaphysis (shaft) - compact bone
Epiphysis (end) - spongy bone
Epiphyseal plate or line
Medullary cavity
Medullary cavity in children and adults
Contains red marrow and gradually changes to yellow in limb bones and skull (except for epiphyses of long bones)
Only yellow marrow in adults
Sharpey’s fibers
Some periosteal fibers penetrate through the periosteum and into the bone to strengthen tendon bone attachment
Structure of flat bone
No diaphyses or epiphyses
Sandwich of spongy between compact bone
Structure of shirt and irregular bone
Compact bone that surrounds spongy center; similar to structure of epiphyes of long bones
Sinuses
Air filled spaces between Flat and irregular bones in skull lined with mucous membranes
Steps of intramembranous ossification
Forms fibrous tissue over brain
Centers of ossification develop ossifying the bone center to outward fill they meet
Completed at about 2 years
Fontanels
Large membrane covered spaces between developing skull bones
Steps of endochondral ossification
Begins with hyaline cartilage model
Center becomes calcified then ossified, forming the primary ossification center
Primary opens up and osteocytes form medullary cavity
Secondary ossification center opens in each epiphyses, meet at the plate
Continues at plate until 18-20 years
Bone cannot grow by __ but must grow by __
Interstitial
Appositional
Articular cartilage
Persists through life
Appositional growth
Growth in width
Periosteum captures a blood vessel
Osteoblasts lay down matrix rings around the vessel
Blasts become cytes to form rings to make
An osteon
Where does the growth hormone come from
Pituitary gland to stimulate bone growth and other tissues
Too much GH during growing years
gigantism
Too much GH later in life
Acromegaly
Too little GH during growing years
Pituitary dwarfism
What is required for growth of all tissues
Thyroid hormone from the thyroid gland
Too little TH during growing years
Cretinism — no sex
What hormone stimulates ossification of the epiphyseal plate
Sex hormones
Estrogens cause quicker closer
What role does Vitamin C play in bone growth
Necessary for matrix formation and collage synthesis by osteoblasts
Vitamin C deficiency
Scurvy
Ulcers and hemorrhaging due to insufficient collagen in connective tissues. Leads to brittle bones.
How often is the entire Skelton renewed
Every 10 years
Stress causes bone remodeling to
Increase bone mass
Align trabeculae with stress
Sends electric signals that stimulate osteoblasts to secrete new bone
When blood ca levels drop..
PTH is secreted by the parathyroid. PTH increase osteoclast activity, released Ca 8’to the blood
When blood ca levels are too high
Calcitonin is secreted by the thyroid gland which decreases osteoclast activity
callus in bone repair
Within, Cells differentiate into contributes and lay down cartilage
At edges, cells differentiate into osteoblasts and build a buddy if spongy bone to be woven together
Third step in bone relaur
Osteoblasts replace spongy bone with compact bone and the internal and external callus is converted from cartilage to spongy bone
Steps of bone repair
Hematoma
Callus
Callus ossification
Bone remodeling
Effects of aging in skeleton
Bone matrix decreases
More brittle due to lack of collagen
Bone mass decreases
Rate of bone loss increase after menopause
Increased bone fracture
Bone mode causes
Deformity, loss of height, pain, stiffness, stooped poster, loss of teeth
Risk factors of osteoporosis
Menopause (low estrogen related to ca loss)
Poor diet
Lack of exercise
Lack of vitamin D
Smoking
Current treatments for osteoporosis
