Skeletal system

Question 1

2 functional parts of the skeletal system

Answer 1

The axial skeleton: bones of the head(cranium), neck (hyoid bone and cervical vertebrae), trunk (ribs, sternum, vertebrae, and sacrum)
The appendicular skeleton: bones of the limbs and bones forming the pectoral (shoulder) and pelvic girdle.

Question 2

Periosteum (component, functions..)

Answer 2

fibrous connective tissue that surrounds bones except where articular cartilage occurs
Nourish the external aspect of skeletal tissue
Capable of laying down more bone particularly during fracture healing
Provide attachment of tendons and ligaments.

Question 3

Difference between compact and spongy bone

Answer 3

Distinguished by the relative amount of solid matter and by the # and size of the spaces they contain

Question 4

Accessory bones

Answer 4

Accessory bones develop when additional ossification centers appear and form extra bones.

Question 5

Heterotopic bones

Answer 5

Heterotopic bones= bones form in soft tissue where they’re not normally present. Horse riders develop rider’s bones in thigh due to chronic muscle strain resulting in small hemorrhagic areas that undergo calcification and eventual ossification

Question 6

Two models of bone development

Answer 6

Intramembranous ossification (membranous bone formation): mesenchymal models of bone form during embryonic period, direct ossification of the mesenchyme begins in the fetal period.

Endochondral ossification (cartilaginous bone formation): cartilaginous (hyaline cartilage) models of bones form from mesenchyme during the fetal period, and bone subsequently replaces most of the cartilage
Ex: development of long bone and short bone. However, short bones only develop primary ossification center except in the case of the calcaneus bone, which develops a 2nd center.

Question 7

Development of long bone

Answer 7

In embryo: mesenchymal cells condense and differentiate into chondroblasts (diving cells in growing cartilage tissue) cartilaginous bone model. Cartilage is not very vascular, cells eventually die and cartilage gets calcified in the midregion of the model. Then vessels come in , bringing in bone-forming cells (osteogenic)  set up 1st ossification center. AT the primary ossification center, bone tissue formed by osteogenic cells replace cartilage form spongy bone at diaphysis .Diaphysis (b/w growth plates): shaft of the long bone
2nd: necrosis happens at the 2 ends of bone and the 2 ends get calcified vessels bring in osteogenic cells at the two ends of bone bone tissue replace cartilage called epiphyses
During growth of long bone, bone formed in the diaphysis and epiphysis intervened by the cartilaginous epiphyseal plates. These growth plates eventually replaced by bone at each of its 2 sides, diaphysial and epiphysial bone growth ceases, diaphysis and epiphysis fuse (synotosis)

Question 8

General info of joints’ blood supply, innervation

Answer 8

Receive blood supply from articular arteries that arise from vessels around the joints. Articular veins usually located in the synovial membrane.
Have a rich nerve supply: nerve endings in the joint capsule. Articular nerves branch from cutaneous nerves supplying the overlying skin.
Transmit proprioception
Synovial membrane is insensitive.
Pain fibers are numerous in the fibrous layer and assoc. ligament considerable pain when joint injured.

Question 9

Basic classification of joints

Answer 9

Synovial
Fibrous (ex: interosseous membrane, suture in skull)
Cartilaginous (intervertebral disc or growth plate)

Question 10

Subclassification of synovial joints

Answer 10

Synovial joint further classified into pivot joint (atlantoaxial joint)
ball and socket (hip joint), 
plane joint (acromioclavicular joint), 
hinge (elbow joint), 
saddle (carpometacarpal joint)
condyloid (metacarpophlangeal joint).

Question 11

Structure of synovial joint

Answer 11

Fibrous capsule has similar composition to periosteum. Dense, irregular connective tissue( fibrous capsule) And it holds the 2 bones together. Periosteum blends w/ fibrous capsule
Synovial membrane (aka serous synovial membrane) is vascular and innervated, produces synovial fluid to lubricate the joints. This membrane also nutrients the joints. 
Synovial membrane + fibrous capsule= joint capsule
Inside the joint capsule, hyaline cartilage is avascular, covering the bearing surfaces of the bone

If forces applied to certain joints (e.g hinge joint of the inner phalanges. joint here only bend in one plane, not side to side, fibrous capsule thickens to make ligament to resist bend in side-to-side direction

Physical activity stimulates the growth of joint.

Question 12

Subclassification of fibrous joint

Answer 12

Syndesmosis type unites bones with a sheet of fibrous tissue, either a ligament or a fibrous membrane. (ex:
Suture in cranium  partially moveable
Interosseous membrane= sheet of fibrous membrane joints ulnar and radius in a syndesmosis.

Gomphosis (socket) type: aka dentoalveolar syndesmosis= fibrous joint articulates the root of the tooth and the alveolar process of the jaw.

Question 13

sub-classification of cartilaginous joint

Answer 13

Synchondroses: bones united by hyaline cartilage (ex: epiphysial plate permits slight bending in early life)

Symphyses: strong, slightly moveable joint united by fibrocartilage
Ex: intervertebral discs provide shock absorption and flexibility to vertebral column

Question 14

Osteoid

Answer 14

In histology, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific proteins. When the osteoid becomes mineralized, it and the adjacent bone cells have developed into new bone tissue.

Osteoid makes up about fifty percent of bone volume and forty percent of bone weight. It is composed of fibers and ground substance. The predominant fiber-type is Type I collagen and comprises ninety percent of the osteoid. The ground substance is mostly made up of chondroitin sulfate and osteocalcin.

Question 15

Intra-membranous ossification

Answer 15

• Intramembranous ossification is the simpler of the two methods of bone formation.
• The flat bones of the skull and mandible (lower jawbone) are formed in this way.
• Also, the “soft spots” that help the fetal skull pass through the birth canal later harden as they undergo intramembranous ossification, which occurs as follows

1. Development of the ossification center.
   At the site where the bone will develop,
   •specific chemical messages cause the mesenchymal cells to cluster together and differentiate,
   •first into osteogenic cells
   •and then into osteoblasts.
   •( mesenchyme is the tissue from which almost all other connective tissues arise.)
   •The site of such a cluster is called an ossification center.
   •Osteoblasts secrete the organic extracellular matrix of bone until they are surrounded by it.
2. Calcification.
   •Next, the secretion of extracellular matrix stops,
   •and the cells, now called osteocytes,
   • lie in lacunae
   •and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions.
   •Within a few days, calcium and other mineral salts are deposited and the extracellular matrix hardens or calcifies (calcification).
3. Formation of trabeculae.
   •As the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone.
   •Blood vessels grow into the spaces between the trabeculae.
   •Connective tissue that is associated with the blood vessels in the trabeculae differentiates into red bone marrow.

4 . Development of the periosteum.
•In conjunction with the formation of trabeculae, the mesenchyme condenses at the periphery of the bone and develops into the periosteum.
•Eventually, a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone remains in the center.
•Much of the newly formed bone is remodeled (destroyed and reformed) as the bone is transformed into its adult size and shape.

Question 16

Endochondral ossification

Answer 16

•The replacement of cartilage by bone is called endochondral ossification.
•Although most bones of the body are formed in this way, the process is best observed in a long bone.
It proceeds as follows

1. Development of the cartilage model.
   •At the site where the bone is going to form, specific chemical messages cause the mesenchymal cells to crowd together in the shape of the future bone,
   •and then develop into chondroblasts.
   •The chondroblasts secrete cartilage extracellular matrix, producing a cartilage model consisting of hyaline cartilage.
   •A covering called the perichondrium develops around the cartilage model.
2. Growth of the cartilage model.
   •Once chondroblasts become deeply buried in the cartilage extracellular matrix, they are called chondrocytes.
   •The cartilage model grows by continual cell division of chondrocytes accompanied by further secretion of the cartilage extracellular matrix.
   •This type of growth is termed interstitial growth (growth from within)
   •and results in an increase in length.

• The cartilage model also grows by the addition of more extracellular matrix material to the periphery of the model by new chondroblasts that develop from the perichondrium.
• This growth pattern is called appositional growth (growth at the outer surface)
• and results in an increase in thickness.

•As the cartilage model continues to grow, chondrocytes in its mid-region hypertrophy (increase in size) and the surrounding cartilage extracellular matrix begins to calcify.
•Other chondrocytes within the calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix.
•As these chondrocytes die, lacunae form and eventually merge into small cavities.
3. Development of the primary ossification center.
•A nutrient artery penetrates the perichondrium and the calcifying cartilage model through a nutrient foramen in the mid-region of the cartilage model,
•stimulating cells in the perichondrium to differentiate into osteoblasts instead of chondroblasts.

• Once the perichondrium starts to form bone, it is known as the periosteum.
• Near the middle of the model, periosteal capillaries grow into the disintegrating calcified cartilage, inducing growth of a primary ossification center, a region where bone tissue will replace most of the cartilage.

•Osteoblasts then begin to deposit bone extracellular matrix over the remnants of calcified cartilage, forming spongy bone trabeculae.
• Primary ossification spreads toward both ends of the cartilage model.
4. Development of the medullary (marrow) cavity.
•As the primary ossification center grows toward the ends of the bone, osteoclasts break down some of the newly formed spongy bone trabeculae.
•This activity leaves a cavity, the medullary (marrow) cavity, in the diaphysis (shaft).
•Eventually, most of the wall of the diaphysis is replaced by compact bone.

5. Development of the secondary ossification centers.
   •When branches of the epiphyseal artery enter the epiphyses, secondary ossification centers develop, usually around the time of birth.
   •Bone formation is similar to that in primary ossification centers.
   •One difference, however, is that spongy bone remains in the interior of the epiphyses
   •(no medullary cavities are formed here).
6. Formation of articular cartilage and the epiphyseal plate.
   •The hyaline cartilage that covers the epiphyses becomes the articular cartilage.
   • Prior to adulthood, hyaline cartilage remains between the diaphysis and epiphysis as the epiphyseal (growth) plate,
   •which is responsible for the lengthwise growth of long bones

Question 17

Synovial classification and structure

Answer 17

Synovial joint further classified into pivot joint (atlantoaxial joint), ball and socket (hip joint), plane joint (acromioclavicular joint), hinge (elbow joint), saddle (carpometacarpal joint), and condyloid (metacarpophlangeal joint).
Synovial joint layers(superficial to deep) associated lig–> fibrous capsule–> synovial membrane–> hyaline cartilage of the end of 2 bones separated by the articular cartilage.
Fibrous capsule has similar composition to periosteum. Dense, irregular connective tissue( fibrous capsule) And it holds the 2 bones together. Periosteum blends w/ fibrous capsule
Synovial membrane (aka serous synovial membrane) is vascular and innervated, produces synovial fluid to lubricate the joints. This membrane also nutrients the joints.
Synovial membrane + fibrous capsule= joint capsule
Hyaline cartilage is avascular.