NCSU BIO 240 Midterm Klesath

osteoclasts

big cells that BREAK DOWN MATRIX
-formed by fusing bone marrow cells
-digests all components of matrix (organic and inorganic)
-calcium is freed from matrix that can then be added to bone

Bones

-primary organs of the skeletal system
-provides framework of body and attachment site for muscles

Cartilage

-component of embryonic, growing, mature bones and joints
-hyaline cartilage is predominant type

Connective Tissue

-bone and cartilage outer membrane
-ligaments connect bones, tendons connect muscle to bone

osteoblasts

MAKE OSTEOID
-found in bone membranes
-secretes osteoid (collagen)

organic bone composition

COLLAGEN
-gives bone tensile strength by resisting stretching, contributes to bone flexibility, can respond to pressure being place on it

inorganic bone composition

CALCIUM AND PHOSPHATE
-deposited around collagen fibers
-accounts for rigidity of bones

Bone deposition

osteoblasts lay down osteoid and add bone tissue, secretes collagen fibers after collagen framework is there mineralization occurs (lay down calcium and phosphate between highly organized collagen)

Bone resorption

Process of osteoclasts breaking down bone, collagen is broken down (organic portion) by proteolytic enzymes. Calcium and phosphate (inorganic portions) broken down by hydrochloric acid, which frees these into the blood, therefore increasing blood levels of calcium and phosphate

Structural unit of compact bone?

osteon

Structural unit of spongy bone?

trabeculae

Compact Bone

located at bone exterior
-appears white, smooth, and solid
-10% of surface area, 80% of bone mass

osteon

functional unit of compact bone composed of concentric lamellae and a central canal

External concentric lamellae

rings of compact bone that surround the entire outer compact bone surface; found immediately internal to bone periosteum

Interstitial lamellae

compact bone remains of a partially resorbed osteon found between newer, complete osteons

internal circumferential lamellae

Rings of compact bone that line the inner edge of compact bone tissue, found immediately internal to the endosteum

Central (Haversian) Canal

opening in the center of an osteon, carries blood vessels and nerves

nutrient foramen

opening in compact bone where vessels and nerves enter and exit through the periosteum

perforating canals

structures through which blood vessels enter and exit the bone shaft.

Osteon structure

-each osteon contains multiple layers of concentric lamellae surrounding the central canal
-each lamellae is composed of inorganic crystals deposited between collagen fibers
-within each concentric lamellae the collagen fibers are parallel
-90 degrees from collagen fibers in adjacent lamellae

Osteocytes

-osteoblasts surrounded by bone matrix become osteocytes
-osteocytes are located between concentric lamellae
-the osteocyte cell body is housed in small open spaces called lacunae
-cellular processes extend from osteocyte cell body and travel within then concentric lamellae through thin, small spaced called canaliculi

Arrangement of osteocytes

-innermost layer of osteocytes extend cellular processes to the central canal blood supply
-these osteocytes connect to adjacent osteocytes through extensions by gap junctions found at their cellular processes
-nutrients and minerals are shared from cell to cell through this system which also allows for cellular communication within the osteon

periosteum

a double layer sheath that covers and protects outer surface of compact bone

Perforating (Sharpey's) fibers

Tufts of collagen that fuse the periosteum to the outer compact bone layer

Outer Fibrous Layer

anchors blood vessels (nutrient foramen) and nerves to bone surface. Attachment site for ligaments and tendons

Inner Cellular Layer

contains osteoprogenitor cells, osteoblasts, and osteoclasts

Endosteum

an incomplete, inner cellular layer that lines the trabecular of spongy bone
-a cellular layer that lines the osteonal canals and larger bone cavities such as the medullar cavity
-cells found here are osteoprogenitor cells, osteoblasts, and osteoclasts
-wherever you have an opening large enough for a blood vessel, you have endosperm, always have it with canals in compact bone

Spongy Bone

found in interior of bones to varying degrees and locations depending upon the size and shape of the bone
-formed by an open lattice of narrow rods and plates of bones called trabeculae
-spaces between trabecular filled with blood vessels and bone marrow
-trabeculae composed of flattened sequential rings of bone matrix called parallel lamellae, osteocytes are found between lamellae
-canaliculi radiate from lacunae to osteocytes and to the outer surface of the trabeculae
-outer surface covered by endosteum

Short, flat, and irregular bones

-periosteum and endosteum are always present
-external surface of compact bone is associated with the periosteum
-inner layer of spongy bone associated with endosteum
-diploe refers to the spongy bone in flat bones of the skull
-bone marrow and blood vessels associated with spongy bone

Medullary canal

central cavity surrounded by a thick collar of compact bone, line by the endosteum and filled with yell marrow (fatty in adults, red in children)

Diaphysis

-central bone shaft (leverage and support)
-compact bone on exterior, spongy on interior
-contains medullary cavity

Epiphyses (proximal and distal)

-knobs at end of bone, thin outer layer of compact bone and inner spongy bone filled with bone marrow
-thin layer of hyaline cartilage that reduces friction and absorbs shock in moveable joints

Metaphysis

-area between epiphysis and diaphysis
-epiphyseal plate (growth plate) consists of several zones including a thin layer of hyaline cartilage (responsible for lengthwise growth in bone)
-the epiphyseal line is a region of mature bone that developed when all of the cartilage is overtake by bone tissue and growth plate is closed

Red Bone Marrow (myeloid tissue)

-hemopoetic tissue containing stem cells for the formed elements of blood
-in children, located in spongy bone and medullary cavity of long bones
-in adults, located in axial skeleton and few areas in appendicular

Yellow Bone Marrow

-fatty substance produced by the degeneration of red bone marrow as children mature
-protective layer found on some bones ends such as where joints occur

Chondroblasts

-produce cartilage matrix
-mature into chondrocytes
-found in shared lacunae

Matrix

Avascular gel-like protein matrix that includes proteoglycans but not calcium

Chondrocytes

-form from chondroblasts, can divide to form chondroblasts
-maintain the cartilage matrix
-found in individual lacunae

Perichondrium

dense, irregular CT that covers cartilage and helps maintain its shape

Appositional Growth of Cartilage

new chondrocytes and new matrix are added on the outside of the tissue.
-growth on outside--> thickening, this growth occurs on the perichondrium
-mesenchymal cells: come from mesenchyme, they can become undifferentiated STEM cells, which have the ability to create chondroblasts
-these dividing cells become chondroblasts and secrete cartilage matrix, lay down newly formed matrix
-the cells are very close together but as they secrete they push themselves apart and become individual lacunae

Appositional growth of cartilage (cont.)

-mitotic activity occurs in undifferentiated stem cells within the perichondrium
-committed cells become chondroblasts and create new cartilage matrix
-as a result of matrix formation, the condroblasts push apart and become chondrocytes

Interstitial Growth of Cartilage

occurs within the internal regions of cartilage- allows for increase in length
-chondrocyte divides and clones self through mitosis
-produces chondroblasts
-they secrete new cartilage matrix, then separate into individual cells in own lacunae

Epiphyseal plate

growth plate, consists of several zones including a thin layer of hyaline cartilage
-responsible for the lengthwise growth in bone
-growth is always pushing towards ends, as cartilage grows and pushes away, it becomes bone
-estrogen is more potent at making bones grow, also creates plates faster

Epiphyseal line

where cartilage ends, epiphyseal plate closes and there is no more cartilage there, just a line

Epiphyses

area where we have mature cartilage attached to it
-epiphyseal line forms once we have no more growth and no more cartilage, all a ratio of cartilage growth and bone growth following it

Zone of resting cartilage

nearest the epiphysis and contains randomly arranged chondrocytes that do not divide rapidly

zone of proliferating cartilage

rapid cell division (stacked coins)

zone of hypertrophic cartilage

This layer consists of large, maturing chondrocytes arranged in columns.
-these cells build up as much as they can because they know they're not in a good environment

zone of calcified cartilage

thin layer of dead cartilage cells and calcified matrix
-only bone cells can live here, cartilage cannot service, bone tissue is starting to take over

zone of ossification

Walls between lacunae break down, forming channels that become invaded with capillaries and osteoprogenitor cells, blood supply comes in to support cells, causes matrix to form

appositional bone growth

adding to exterior
-add bone to periosteum, as bone thickens and grows you need to adjust to have medullary cavity grow as well
-osteoclasts eat away bone to make medullary cavity bigger
-these cells are only found in the bone membranes, so we need endosteum to make cavity bigger
-osteoblasts at periosteum deposit bone matrix in layers parallel to surface
-osteoclasts at endosteum resorb bone matrix along medullary cavity

Endochondral (interstitial) bone growth

bone eventually replaces new cartilage growth in the epiphyseal plate
-occurs only when the materials involved are non-rigid

Development of the skeleton

-at week 4 the embryonic mesoderm layer divides into somites, then develops mesenchyme tissue that is starting material for the skeletal system structures

Two types of ossification

-intramembranous: mesenchyme directly becomes bone (BONES OF SKULL AND FLAT BONES)
-endochondral: cartilage forms, them becomes bone (LONG BONES)

intramembranous ossification

1) Starts in center of mat (ossification center)
-osteoblasts form and secrete osteoid (mineralization)
2) Osteoid undergoes calcification
-osteoblasts become osteocytes, lay down more matrix
3) woven bone and bone membranes begin to form
-woven bone: looks like spongy bone, but lacking lamellae
-super fast, is remodeled into lamella spongy bone (bone repair starts with woven bone)
-mesenchyme around it will form periosteum
4) lamellar bone replaced woven bone
-lamellar compact (with concentric lamellae) and lamellar spongy (with parallel lamellae) bone form
-make it bigger using appositional growth and add to the outside of it
-endosteum and periosteum fully developed

Endochondral ossification

Process of transforming cartilage into bone.
1) Perichondrium forms on outside
2) periosteal bone collar forms- lay down bone here
3) primary ossification center forms
-take cartilage and mineralize it
-bring in osteoblasts and build bone on top of it
4) secondary ossification center forms in epiphyses
-cartilage calcifies
-blood vessels enter with osteoprogenitor cells and osteoblasts forming woven bone
-the medullary cavity forms in the diaphysis region a osteoclasts resorb the bone tissue

Wolff's Law

A bone grows or remodels in response to forces or demands placed upon it

Mechanical Stress

Occurs in weight-bearing movement and exercise, Required for normal bone remodeling, Detected by osteocytes and communicated to osteoblasts, increase synthesis of osteoid, Causes increase in bone strength, Results from skeletal contraction and gravitational forces

Growth Hormone (somatotropin)

-has to do with bone growth, increases length of bone, increases mineralization, improves bone density
-acts as endocrine regulator after baby is born, helps develop skeleton
-sharp drop off in growth hormone as you age
-has direct impact on bone and muscular system and indirect impact
-insulin-like growth factor (IGF) in the liver produces it and stimulates chondrocytes in bone cells
-makes bones longer but doesn't close off plate

gonadal steroids (estrogen/testosterone)

-increases GH secretion
-increases rate of both cartilage growth and bone formation, but bone formation rate is greater, initiating the closing of the epiphyseal plates and formation of the epiphyseal line

cortisol

stress hormone released by the adrenal glands
-triggers resorption and causes bone breakdown therefore lower bone density
-blocks absorption of calcium, leads to lower bone density measurement (increased risk of osteopoerosis)

calcitriol

-active vitamin D that we need, helps body digest and absorb calcium and causes us to produce calcium
-sunlight absorbed by skin, goes to liver and kidney, then released into blood, this allows for calcium resorption to occur
-inhibits calcitonin

calcitonin

encourage calcium deposition from bone to bone
-stimulates osteoblasts in response to increased blood calcium levels (bone deposition), inhibits osteoclasts
-released in response to high blood calcium (excess)
-can be stored for later use in skeletal system
-decreases how much we pull in intestines and decreases how much we resorb in urine

Parathyroid Hormone

-stimulates osteoclasts in response to decreased blood calcium levels (bone resorption)- take calcium and withdraw from bones and move into blood
-released when not enough calcium consumed
-intestines, urinary system do everything they can to absorb maximum calcium

Bone repair steps
1- a hematoma forms

-simple fracture: broken bone but no opening to surface
-first thing that happens is you have a hematoma (giant blood clot), doesn't matter where bone breaks, the first thing we see is we break blood vessels (because bone is highly vascularized)
-bleeding occurs, then clotting to stop the bleeding

Bone repair steps
2- a fibrocartilaginous (soft) callus forms

-we create our own splint
-this is connective tissue (soft callus)- bodies way of splinting and putting back in alignment
-blood vessels come back in, we clear up hematoma, new blood vessels move in and we support growth of bone

Bone repair steps
3- a hard (bony) callus forms

-producing hard callus: this is where we start making bone tissue (we make woven bone tissue first)- looks like spongy bone but is random and unorganized without lamellar rings which provide structure
-doesn't matter what type of bone we eventually want, we patch it with woven bone first

Bone repair steps
4- the bone is remodeled

-process of remodeling bone, depending on what part of bone broke we put tissue we actually want there
-the body adds extra layers here for protection

osteoporosis

women 4x more likely
-decrease in estrogen leads to increased bone remodeling
-porous bone: bone becomes less dense
-biggest effect on spongy bone

Dendrites

receptive regions, short unmyelinated process branching off cell body
-receive input and transfer it to body
-multiple dendrites off cell body

synapse

where axon meets dendrites, can also be on cell body

Neurotransmitters

chemical messengers that cross the synaptic gaps between neurons, they are converted to ions

post synaptic membrane

the cell membrane opposite the terminal button in a synapse; the membrane of the cell that receives the message

ligand (chemical) -gated channels

channel that opens when a neurotransmitter attaches, always move along gradient

sodium-potassium pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell, moves against gradient, 3 Na+ out and 2 K+ in
1) 3 Na from inside bind to pump
2) ATP converts to ADP, released energy changes pumps shape
3) Na+ released to outside of cell
4) 2 K+ from outside bond to pump
5) 2 K+ released inside the cell

gated channels

A protein channel in a cell membrane that opens or closes in response to a particular stimulus. Normally closed but neurotransmitters allow them to open

graded potential

a membrane potential that varies in magnitude in proportion to the intensity of the stimulus

leak channels

channels that are always open and allow ions to move along their gradient

resting membrane potential

-70mV, maintained by sodium potassium pump and leak channels

Depolarization

more positive

Hyperpolarization

more negative

excitability

responsiveness to a stimulus
-stimulus causes change in cells membrane potential
-neurotransmitters are stimulus (chemical signal that turns to electrical channel)

conductivity

ability to propagate electrical signal- electrical current can be produced
-voltage gated channels along membrane open sequentially
-action potential sent in response to information received

secretion

-release of neurotransmitters in response to conductive activity (electrical signal)
-messenger is released from vesicle to influence target cell

extreme longetivity

cell can live throughout persons lifetime, neurons cannot divide

amitotic

After fetal development, mitotic activity is lost in most neurons, don't divide by mitosis

cell body

contains nucleus, perikaryon (cytoplasm), chromotophilic substance made of ribosomes
-receives and initiates some graded potentials, conducts these potentials to axon
-can also receive signals- this is where organelles are held
-this is where we have biosynthesis of materials we need

axon

functions to conduct action potentials and then release neurotransmitters at synaptic knobs
-may be myelinated by neuroglial cells
-1 axon for multi-polar neuron, this is where it "fires" the action potential, run down lengths of axon (some myelinated, some not)
-meylination helps it move faster (conduct more quickly)
-schwann cells (neurolemmocyte) node of ranvier- spot between each cell of axon

Synaptic konbs

terminal ends of axon, where we house neurotransmitters, where synapse is

K+

mostly intracellular

Na+, Cl-, Ca2+

mostly extracellular

receptive segment

chemically (ligand) gated channels
-dendrites are receptive region as well as cell body because chemically/ligand gated channels that respond to neurotransmitters

initial segment

voltage gated channels
-axon hillock
-cell body tapers down into axon hillock- this is important part of integration process
-this is where we determine if were going to fire or not- quantify the signals and if we meet threshold we fire (-55 mV)
-we also have voltage gated channels at this region that make action potential signals- if we reach threshold voltage gated channels are open, and action potential is sent all the way down the axon

conductive segment

voltage gated channels
-axon

transmissive segment

where the action potential released secretion of neurotransmitters
-synaptic knobs

resting neuron

The plasma membrane at rest is polarized
-Fewer positive ions are inside the cell than outside the cell.
-resting membrane potential typically -70 mV
-greater number of K+ leak channels taking K out of cell, smaller Na+ leak channels bringing Na in

Resting Membrane Potential (RMP)

-all gated channels are closed (these are the default that allow us to get to resting membrane potential
-leak channels always open- ions always moving through them
-leak channels are all over membrane

Graded potentials

local, start at one point, ions move in then diffuse away from that spot
-relatively small, short-lived charges in resting membrane potential caused by movement of small amounts of ions across plasma membrane
-has no effect on causing other neurons to open around them

Region of neuron graded potential occurs in

receptive segment

type of channel responsible for graded potential

chemically gated cation channels, chemically gated K+/Cl- channels