2- Skeletal System

define hematopoiesis.

blood cell formation

• occurs in red bone marrow

where in the bone are lipids stored?

yellow bone marrow

what are the major terms used to classify the structure of bone?

long, flat, compact, spongy

what type of bone has a very dense extracellular matrix?

dense/compact bone

what type of bone is hollow on the inside?

long bone

describe the composition of bone tissue.

specialized cells dispersed in a hardened extracellular matrix

describe the composition of the extracellular matrix of bone?

• 1/3 collagen fibers

• 2/3 calcium salts

• fluid: ground substances

what is the function of collagen fibers in the ECMatrix of bone?

provide strength and flexibility

what is the function of calcium salts in the bone?

calcium + phosphate → form hydroxyapatite crystals

• hardness, resist compression by depositing in gaps

• can still break

what is a proteoglycan?

a type of glycoprotein

what is the function of the ground substance in the ECMatrix of bone?

• attracted to and binds to ionic + polar fibers/salts

• fluid in the matrix

  • water w/glycoproteins and proteoglycans

triple helix of ____ strands link to form ____ which bundle to form ____

tropocollagen → fibrils → fibers

what part of the ECMatrix do we see when we view a skeleton?

hydroxyapatite crystals

what percent of the bone is composed of bone cells?

less than 2%

what is an osteocyte?

mature bone cell that maintains the bone matrix

what is the function of the canaliculi?

connects osteocytes

• helps them share resources + expell waste

what are osteoblasts?

immature bone cells that secrete organic components of matrix

what type of bone cell makes up most of the matrix?

osteoblasts

what are osteoprogenitor cells?

stem cells that divide to produce osteoblasts

what are osteoclast cells?

multinucleated cell that secretes acids and enzymes to dissolve bone matrix

• phagocytes

why would the body break down the bone matrix via osteoclasts?

to release calcium

what is the function of compact/dense bone?

to protect, support, and resist stress

describe an osteon.

cylindrical unit of concentric circles of lamellae and osteocytes trapped in lacunae

what is an osteon also known as?

Haversian system

describe the Haversian Canal.

the center of the osteon

• canal for blood vessels

describe the perforating canal.

transvers blood vessel canals which connect Haversian canals

what is the purpose of osteons being cylindrical?

no edges → strength

what’s another name for spongy bone?

cancellous bone

what is the function of spongy bone?

• support

• storage of bone marrow

what are the units of spongy bone?

trabeculae

• thin interconnecting bundles

• lamellae and osteocytes between layers

what differentiates spongy bone from dense bone?

• less dense matrix

• open network

• NO osteons

• found inside the bone (surrounded by dense)

where is red bone marrow located?

in spongy bone

where is spongy bone found?

• long bones: epiphyses

• flat: sandwiched btwn two layers

• irregular + short: inside vertebrae, pelvic bones, hand and feet bones

what is the func. of canaliculi?

communicate with blood to receive stuff + deposit waste

what are the two different types of bone marrow?

red and yellow

what is the function of red bone marrow?

• site of hematopoiesis

• surrounds trabeculae of spongy bone

define hematopoeisis.

process of making new blood cells

where is red bone marrow found?

interior of flat bones and epiphysis of long bones

• and medullary cavity of children

what is the function of yellow bone marrow?

site of storage of adipocytes

where is yellow bone marrow found?

only in the medullary cavity of long bones

how is yellow bone marrow created?

starts as red marrow, converted until finished in adulthood

what are the two skeletal membranes?

periosteum and endosteum

what is the function and composition of the periostium

dense membrane, covers outer layer of bone (except at articular surfaces)

• isolates and protects bone

• muscle attaches to it

describe the two layers of the periosteum.

• inner cellular layer: osteoblasts + osteoprogenitor cells

• outer fibrous membrane: fibroblasts in fibrous matrix

describe the endostium.

incomplete membrane of interior of bone

• covers trabeculae and lines Haversian canals

what is the composition and function of the endostium?

• endothelial (epithelial) cells mixed with osteoprogenitor cells and osteoclasts

• important for growth and remodeling

define ossification.

bone development

what are the two types of ossification?

intramembranous and endochondral

what is the first step of ossification (conducted by both types)?

bone matrix initially laid down as osteoid (collagen) by osteoblasts

• then mineralized into crystals

describe how bone is produced twice.

• produced first in disorganized way → woven bone

• woven bone then remodeled around blood vessels to form more organized bone

which bones are intramembranous?

bones of skull and clavicle (collar bone)

define mesenchyme.

an early embryonic tissue → becomes connective tissue

where do intramembranous bones come from?

sheet-like membranes of mesenchyme

• DIRECTLY FROM MESENCHYME

what is the timeline of intramembranous ossification?

• begins at 8 weeks of gestation

• complete at two yrs

describe fontanels.

fibrous membranes connecting cranial bones

• “soft spots” in skull during first yrs of life

ossification begins in the deep layers of the dermis, forming what?

dermal bones

define spicules.

small, spike-like structures of bone or calcified cartilage

• form a foundational scaffold during bone development, healing, and remodeling

• org around blood vessels

how is spongy bone remodeled after intramembranous ossification?

remodeled forming the diploë and a thin covering of compact bone.

what bones conduct endochondral ossification?

all other bones (excluding skull + clavicle)

in EO, formation of the bone begins with *what which is then transformed into bone?

hyaline cartilage model

describe the formation of a bone in endochondral ossification.

INDIRECTLY from mesenchyme

• mesenchymal cells first deposit cartilage to form model of growing bone

• hyaline cartilage then replaced with bone tissue

in EO, bone grows in length as…

cartilage cells divide and multiply

what is the timeline of endochondral ossification?

• begins 8-12 weeks of gestation

• continues into early adulthood

  • done when we stop growing

what is the bony collar in EO?

a cuff of compact bone that forms around the diaphysis (the middle shaft) of a hyaline cartilage model

____% of skeleton is remodeled each year until 35 y/o.

100%

____ ____ of bone matrix turnover throughout life

continual process

why do bones remodel?

remodels as an adaptive response to stimuli (weight, micro damage, mechanical stress, etc.)

• also helps meet metabolic needs of body (ex. calcium regulation)

what does bone remodeling do?

partially replaces matrix but leaves bone as a whole intact

• replacement of damaged bone as well as adaptive response

• site specific

what type of bones of replaced more often?

bones that experience a lot of friction

• ex: joints

what role does vitamin c play in bone growth?

required for normal collagen synthesis in osteoblasts

what role does vitamin d play in bone growth?

promotes calcium and phosphate absorption from diet

what results from a vitamin deficiency?

fragile bones

what two hormones regulate calcium?

parathyroid hormone and calcitonin

what secretes the parathyroid hormone and what does it do?

parathyroid gland secretes it when not enough calcium in blood

• stimulates osteoclasts

what secretes calcitonin and what does it do?

thyroid gland secretes it when too much calcium in blood

• inhibits osteoclasts

what is the function of the growth hormone?

stimulates cell growth and division at growth plate

what is the function of the thyroid hormone?

stimulates cell metabolism and osteoblast activity

define a fracture.

any crack or break to a bone

distinguish between the two types of fractures.

• closed: completely internal

• open: project through skin