Human Morph Exam 2

Skeletal system

What are the components of the skeletal system?

Bones of skeleton

Cartilage

Ligaments

Other connective tissue

Bones Overview

-primary organ of the skeletal system

-Rigid framework of body

-Bone types: Compact & spongy

Compact bone

Dense/cortical bone

80% of bone mass

Spongy bone

cancellous/trabecular bone

• located internal to compact bone

• looks porous

  • 20% of bone mass

Cartilage

-semirigid CT that is more flexible than bone

• Types: Hyalone cartilage & Fibrocartilage

Hyaline Cartilage

attaches ribs to sternum

covers ends of some bonds

present within growth plates

used as a model for bone formation

Fibrocartilage

weight0bearing cartilage that can withstand compression

composes : intervertebral discs, pubic symphsis (joint where the fibrocatilage connects to allow for a small amount of movement) & menisci of knee

Structures composed of dense regular CT

-Ligaments (connect bones to bone)

-tendons (connect muscle to bone)

Function of skeletal system

-support & protrecting

-levers for movement

-Hematopoiesis (blood cell production that ocurs in red bone marrow CT)

-stores mineral & energy reserves (Calcium & phosphate)

Tissue types in Bone

-Connective (comoact & spoongy bone, dense irregular connective tissue, reticular connective tissued, blood)

-Nervous tissue (detects & monitors sensory stimuli about status of the bone)

Classification of bones

bones are determined by shape

-Long bones

-Short bones

-Flat bones

-Irregular bones

Long Bones

greater in length than width (femur, humerus)

Short Bones

length is almost = to width (carpals & tarsals)

-outside is composed of compact bone that is covered by periosteum; interior is spongy bone & has no medullary cavity

FLat Bones

-flat, thin surfaces that may be curved (cranial bones)

outside is composed of compact bone that is covered by periosteum; interior is spongy bone & has no medullary cavity

• Diploe: spong bone in skull

Irregular bones

elaborate, sometimes complex shapes (vertebrae)

outside is composed of compact bone that is covered by periosteum; interior is spongy bone & has no medullary cavity

Anatomy of the long bone

• Diaphysis

• Medullary Cavity

• Epiphysis

• Metaphysis

• Epiphyseal plate

• periosteum

• Endosteum

Diaphysis (long bone)

-elongated, cylindrical shaft that provides leverage & weight support

-compact bone w/ thin spicules of spongy bone extending inward

Medullary (marrow) cavity- long bone

-hollow, cylindrical space inside the diaphysis

-contains red bone marrow in kids & yellow bone marrow in adults

Epiphysis

-knob region at each end of the long bone

Proximal epiphysis: end of the bone closest to trunk

Distal epiphysis: end fartherst from trunk

• composed of compact bone on the outer thin layer & spongy bone on the inner region

Articular cartilage: covers the joint surface reducing friction and absorbing shock in moving joints.

• It is a thin layer of hyaline cartilage

Metaphysis

Region where the bone widens & transfers weight between the diaphysis & epiphysis

Epiphyseal plate

-located w/in metaphysis

-this is the growth plate; it provides lengthwise bone growth

-has a thin layer of hyaline cartilaage

-for adults the epiphyseal line is the remnant of the epiphyseal plate

Periosteum

-covering & linning of bone

-Tough sheath covering outer surface of bone

-Outer fibrous layer (dense irregular CT that protects bone from surrounding structures, it anchors blood vessels & nerves to bone surface & is an attachment site for ligaments & tendons)

-Inner cellular layer (includes osteoprogenitor cells, osteoblasts)

-Attached to bone by numerous collagen fibers (perforating fibers)

Endosteum

-covers internal surface of bone w/in medullary cavity

-thin later of CT containing osteoprogenitor cells & osteoblasts & osteoclast

Blood supply of the blood

-bone is highly vascularized (spongy bone)

-Nutrient foramen is a small hole in bone that allows artery entrance & vein to exit

Nerve supply of the bone

-blood vessels also go through foramen
-innervate bone, periosteum, endosteum, marrow cavity

• mostly sensory nerves

Bone Marrow

• this is the soft ct of the bone

consists of red & yellow bone marrow

Red Bone Marrow

(myeloid tissue)

• Hematopoietic (forms blood cell)

• Consists of reticular ct, develops blood cells & adipocytes

  • Children: this is found in spongy bone & medullary cavity of long bones

  • Adults: found only in specific areas of axial skeleton (skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus & femur)

Yellow bone marrow

-red bone marrow degeneration as you mature

-fatty substance

-may convert back to red bone marrow during severe anemia or any condition w/ reduced eythrocytes (red blood cells)

-faciliates production of more erythrocytes

Bone CT (Osseous CT)

-primary component of bone

-composed of cells & extraceulluar matrix

Cells of bone

-these 4 types are found in bone CT:

• Osteoprogenitor cells

• Osteoblasts

• Osteocytes

• Osteoclasts

Osteoprogenitor cells

-stem cells come from mesenchyme

-cell division yield stem cell & a committed cell (matures to become an osteoblast)

• cells are located in the periosteum & endosteum

Osteoblasts

-forms from osteoprogenitor stem cells

-they synthesize & secrete osteoid

-is entrapped w/in the matrix

-differentiate into osteocyes

Osteoid

initial semsisolid organic form of the bone matrix from the osteoblasts that calcifies later

Osteocytes

-mature bone cells that come from osteblasts

-detects stress on bone; triggering new bone formation

Osteoclasts

-large, multinuclear, phagocytic cells

-derived from fused hematopoietic cells

-ruffled border increases surface area exposed to bone

-involved in bone resoprtion

-w/in/ adjacent to a depression/pit on bone surface (resoprtion lacuna)

Inorganic componenets of the bone matrix

-Salt cyrstals, calcium phosphate, Ca3(PO4)2

-interacts w/ calcium hydroxide to form crystals, hydroxyapatite, a10(PO4)6(OH)2

-calcium carbonate, sodium, magnesium, sulfate, flouride is incorporate into crystals

-Crystals deposite aorund collagen fibers

-They harden the natrix & account for rigidity of bones

Organic components of bone matrix

-osteoblasts produce osteoid that contains collagen proteins & semisolid ground substance of preteoglycans & glycoproteins

• give bone tensile strength by resisting stretching

  -contributes to bone flexibility

Bone formation

-starts w/ secretion of osteoid

• Calcification occurs bcuz hydroxyapatite crystals (calcium & phosphate ions precipates out) & deposit

Bone formation requires:

• Vit D (to enhance Ca2+ absorption from GI tract)

• Vit C: for collagen formation

• Calcium & phosphate for calcification

Bone resoprtion

• occurs when blood calcium levels are low

• Bone matrix becomes destroyed by substances released from osteoclasts

• Proteolytic enzymes are released from lysosomes w/in osteoclasts to chemically digest organic matrix components

• Calcium & phosphate is dissolved by HCL acid into ions & enter the blood

Process of Calcification

• Osteoblasts produce osteoid

• Osteoid forms collagen matrix

• Hydroxyapatite crystals form

• Crystals depost on collagen fibers

• Mineralized bone matrix is produced

What is the calcification of bone

deposition of hydroxyapitite crystals w/in the osteoid organic matrix

Osteons (compact bone)

small cylindrial strucutes (Haversian systems)

-basic functional & structural unit of mature compact bone

-oritented parallel to bone diaphysis that looks like bull’s eye target

Osteon Components

-Central (Haversian) canal:

-Concentric lamellae

-Osteocytes

-Canaliculi

Central (Haversian) canal

• Cylindrical channel at center of osteon & parallel to it

• Blood vessels & nerves extend through channel

Concentric lamellae

• rings of bone CT

• surrounds central canal

• collagen fibers that give bone strength & resilience; 90 degrees from previous & next lamellae

Osteocytes

-Mature bone cells

-found in small spaces between concentric lamellae (lacunae)

-purpose is to maintain bone matrix

Canaliculi

-Tiny connecting channels w/in bone CT

-extends from lacuna—-lamella & connects to lacunae & central canal

-house osteocyte projections that allow cell contact

-allows exchange of nutrients, minerals, gases & wastes betwween blood vessels & osteocytes

Difference between lacuna & lacunae

-Lacuna: 1 single space/pocked w/in the bone matrix that houses 1 osteocyte

-Lacunae: plural- multiple spaces/pockets throughout the bone tissue that has osteocytes

Structures in long bone (not part of osteon)

-Perforatiing canals

-Circumferential lamellae

-Interstitial lamellae

-Trabeculae

-Parallel Lamella

Parallel lamellae

-bone matrix

-osteocytes are found between these lamellae

-canaliculi radiate from lacunae

Trabeculae

-open lattice of narrow rods & plates of bones

-the bone marrow fills the spaces and theres a meshwork of crisscrossing bars

-purpose: resisting stress

Perforating (Volkmann) canals

-perpendicular to central canals

-connects central canals w/in different osteons

Circumferential lamellae

-External: rings of bun run internal to periosteum

-Internal: rings of bone that go internal to the endosteum

-They run the entire circumference of the bone

Interstitial lamellae

-components of compact bone between osteons

Properties of hyaline cartilage connective tissue

-these cartilage cells are scattered through matrix of protein fibers & embededd in gel-like ground substance (proteoglycans but not Ca2+)

-very resilent & flexible

-high % of H2O

-Avascular & no innervation

-compressible & a good shocks absorber

Hyaline cartilage CT

-Chondroblasts: produce cartilage matrix

-Chondrocytes: chondroblasts encased in the matrix, found in lacunae & they maintain the matrix

-Perichondrium: dense irregular CT that covers cartilage & helps maintain its shape

Ossification (osteogenesis)

is the formation & development of bone CT

-starts in the embryo & continues through childhood & adolescence

~8-12wks of embryonic development: Skeleton starts forming (from intramembranous ossification/endochondral ossification)

What is intramembranous ossification?

bone growth w/in a membrane that produces flat bones of skull, some facial bones, nadible & central part of the clavicle

aka dermal ossification

What are the (4) steps of intramembranous ossification?

-Ossification centers form w/in thickened regions of mesenchyme starting @~8th wk of development

• Some cells become osteoprogenitor cells, or osteoblasts secreting osteoid

-Osteoid Undergoes calcification

• (Ca2+ salts deposit onto osteoid & crystalize & the entrapped cells become osteocytes)

-Woven bone (primary) & surrounding periosteum form

• Bone is immature & poorly organized until the mesenchyme around the woven forms periosteum

-Lamellar bone replaces woven bone, as compact & spongy bone forms

• compact & spongy bone form from trabeculae

• this is the typical structure of a flat cranial bone (2 external layers of compact bone & a layer of spongy bone in between)

Endochondral ossification

starts w/ hyaline cartilage

-produces most bones of skeleton (upper & lower limbs, pelvis, vertebrae, ends of clavicle)

What are the steps of endochondral ossification

-Hyaline cartilage model of bone forms

-Bone 1st replaces hyaline cartilage in the diaphysis

-Bone replaces hyaline cartilage everything except epiphyseal plates & articular cartilage

-By a person’s late 20’s, all epiphyseal plates have ossified & lengthwise bone growth is complete