Skeletal System Flashcards
Long bone features:
Made of cortical bone (compact) and pockets of cancellous bone (spongy)
Contain: epiphysis, diaphysis, medullary cavity, metaphysics and epiphyseal plate
Cortical bone is ________, while cancellous bone is _________
Compact
Spongy
Epiphyses
Ends of long bones
Converted by articular cartilage because they form synovial joints with other bones
Spongy bone containing red bone marrow on the inside, important for hematopoesis (production of RBCs)
Diaphysis
Long, hollow shaft between the epiphyses
The outside is covered in a membrane called the periosteum, which wraps around the cortical bone itself
Medullary cavity
The “hollow” inside of the diaphysis
Contains cancellous bone that hold yellow bone marrow
Lined by a membrane called the endosteum
Epiphyseal plate
“Growth plate”
Made of hyaline cartilage
Lies between the epiphysis and metaphysics
Grows in the direction of the metaphyses but lengthens the diaphysis
Grows in response to growth factors
Ossifies when pubertal hormones signal for calcification and apoptosis
Metaphyses
Found between the medullary cavity and the epiphyseal plate
Short bones
Cuboidal- as wide as they are long
Provide support without doing a lot of movement
Primarily made up of cancellous bone covered by a very thin layer of cortical bone
Ex: bones in the wrist
Flat bones
Consist of cancellous bone sandwiched between cortical bone
Mainly provide protection
Ex: bones that make up the skull, and the sternum
Sesamoid bone
Embedded within tendons to increase the muscles leverage on the bone (eg. help the muscles pull)
Ex: kneecap/patella
Irregular bone
Irregularly shaped
Made of abundant cancellous interior surrounded by a thin layer of cortical bone
Ex: bones of the pelvis and spine
Cortical bone
The dense outer layer of bone that allows bones to support our weight
Composed of microstructures: Osteons, Haversian canals, lamellae, lacunae, canaliculi, and Volkmann’s canals
Osteons
The functional unit of cortical bone
Haversian canal lies in the center of each osteon (which is why osteons are sometimes referred to as Haversian systems)
Haversian canals
- Lie at the center of each osteon
- Contain blood vessels that supply nutrients to the bone cells living in lacunae
- tunnels burrowed by osteoclasts
Volkmann’s canals
Connect adjacent Haversian canals to one another and to the periosteum which provides the blood and nutrients that the bone needs to grow
Lacunae
Small spaces between lamellae that hold trapped bone cells (osteocytes) and
Connect to each other, as well as the Haversian canal through canaliculi allowing for exchange of nutrients
Lamellae
Layers of osteon
Canaliculi
Small channels that connect lacunae and the Haversian canals of a single osteon
Cancellous bone
The inner network of spongy bone
Soaks up red bone marrow is network of trabeculae
Part of bone where hematopoiesis occurs (production of RBCs)
Cells involved in bone remodeling:
Osteoprogenitors
Osteoblasts
Osteoclasts
Osteocytes
Osteoprogenitors
- Immature precursor cells that differentiate into osteoblasts
- part of mesenchymal stem cell lineage
Osteoblasts
- Build bone
- Mononucleated cells
- Mature into osteocytes after getting trapped inside the bone matrix they create
- Secrete proteins (organic compounds) and collagen that make osteoid
- They make the enzyme that allows calcium, phosphorus and water to crystalize into hydroxyapatite
- incapable of mitosis
Osteoid
Organic component of bone
Contains many proteins and type 1 collagen fibers
Gives bone tensile strength
Hydroxyapatite
Inorganic component of bone
Made up of crystallized calcium, phosphorus and water
Gives bone density and strength
Osteoclasts
- Multinucleated cells
- Derived from monocytes (hematopoietic stem cell lineage)
- Reabsorb bone back to blood and chew through bone
- Can be found in Howship’s lacunae, which are their own lacunae that they create as they chew through bone
- have carbonic anhydrase
Bone remodeling
The process of going back and forth between the processes of ossification (bone formation) and resorption (bone loss)
Mechanisms involved in bone remodeling
Parathyroid hormone, vitamin D, calcitonin
Parathyroid hormone in bone remodeling
Increases blood calcium levels by stimulating osteoclasts and depressing osteoblasts
Secreted by the parathyroid gland
Vitamin D in bone remodeling
Increases blood calcium levels by raising intestinal calcium absorption
Activated by the parathyroid hormone , but provides a negative feedback on PTH production
Calcitonin in bone remodeling
Decreases blood calcium levels by depressing osteoblasts, allowing osteoblasts to build bone without competition
Secreted by parafollicular cells (C cells) of the thyroid gland
Intramembranous ossification
- Bone is created directly within fibrous membranes (undifferentiated connective tissue is replaced by bone)
- Mainly for flat bones, skull, sternum, manidble, clavicles
Intramembranous ossification steps
1) osteoblasts secrete osteoid: ossification center forms within the mesenchyme
2) osteoid hardness (calcification) and encourages osteoblasts to mature into osteocytes
3) osteocytes form trabeculae which gets wrapped by blood vessels, forming the surrounding periosteum
4) cortical bone begins to grow between periosteum and trabeculae; periosteum is now fully formed
Endochondral ossification
- Bone is created indirectly throng a cartilage model
- Mainly for long bones, limbs, fingers, toes
Endochondral ossification steps
1) a cartilage model is created around the 8th week of development and calcification begins at the center
2) at around 12 weeks, primary ossification center forms from osteoblasts invading the calcified center and increased vascularization
3) secondary ossification centers are established at epiphyses and osteoblasts chew out the inside of the diaphysis, creating the medullary cavity
what are the fibrous connective tissues?
Tendons: muscle to bone
Ligaments: bone to muscle
Periosteum: covers diaphysis of cortical bone
Endosteum: lines medullary cavity, between cortical and cancellous bone
Periosteum
Protective fibrous membrane that covers cortical bone at the diaphysis
Has two sublayers:
Outer fibrous layer- contains nerves and is vascularized
Inner “cambium” layer- contains collagen fibers for attachment of the periosteum to cortical bone underneath and osteoprogenitor cells
Endosteum
Lies between cortical and cancellous bone
Lines the medullary cavity of long bones
Surround the cancellous bone of epiphyses
Lines the cavities of Haversian and Volkmann’s canals
Joints
Vascularized, innervated and found between bones
Three types: synarthroses, amphiarthroses and diarthroses
Synarthroses joints
Dense, fibrous joints that do not move
(Stable)
Amphiarthroses joints
Cartilaginous joints between bones that partially move
(Able)
Diarthroses joints
Synovial joints between bones that are fully movable
typically contain hyaline cartilage
(Doable)
what is the cuticle of the exoskeleton?
a non-living layer of the exoskeleton on insects and other annthropods which is composed of hard chitin
hyaline cartilage
- contains relatively few fibers and is soft and flexible
- acts as a cushion to absorb shock and offers smooth surface for movement (reduces friction) in area when bones connect
- provides support and stability to joints
what tissue does cartilage develop from?
mesenchyme tissue: mesenchyme tissue differentiates into chondrocytes which secrete collagen and proteoglycans forming the cartilaginous matrix
what does yellow bone marrow store?
adipose tissue
articular cartilage
a type of hyaline cartilage (thin layer) that covers the epiphyses and function to absorb shock and minimize friction
osteoperosis
- causes bone density to decrease, making the bone easier to break or fracture
- to prevent, high calcium and vitamin D intake and exercise is important
what hormone can help maintain bone density?
estrogen, but it can increase the risk of blood clots, heart disease and cancer in females
fibrous joints
- connect bones without allowing any movement
- ex: skull, pelvis, spinous process, and vertebrae
cartilaginous joints
- bones are attached by cartilage and allow little movment
- ex: spine and ribs
composition of cartilage:
- composed primarily of collagen fibers embedded in chondroitin sulfate, and receives nutrients via diffusion
what surrounds cartilage?
cartilage is surrounded by a dense fibrous connective tissue called perichondrium
what are the functions of bone?
- support soft tissue
- protect internal organs
- assist in body movement
- mineral storage
- blood cell production
- energy storage in the form of adipose cells in bone marrow
what is woven bone?
- immature and weak bone
- first bone to form during development and in fracture repair
- replaced with llamerlar (spongy and/or compact) bone which is srong and mature
osteocytes
- incapable of mitosis
- exchange nutrients and waste material with blood
