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sheet of cells that covers an exposed area or lines an internal cavity
-provide physical protection
-control permeability
-provide sensation
-produce secialized secretions

connective tissues

found throughout body
never exposed to the enviorment outside of body

connective tissue

basic components
-specialized cells
-extracellular protein fibers
-fluid known as ground substance

functions of connective tissue

-structural framework
-transporting fluids
-protection for organs
-energy reserves
defending the body

connective tissue proper

contains ground substance, extracellular fibers

fixed cells

stationary/involved primarily with local maintenance, repair and energy storage

wandering cells

concerned with defense and repair of damaged cells


"fiber building" most abundant fixed cell, always present, maintenance, and maintain matrix

fixed microphages

"eaters" engulf damaged cells or pathogens that enter the tissue


fat cells, enormous liquid droplet

mesenchymal cells

"stem cells" respond to local injury or infection


"skin celss" store brown pigment, give tissue dark color

free macrophages

"wander" thru connective tissue

mast cell

found near blood cells. secretory granules of histamine and heparin, stimulation of local inflammation


"help with infection"


migrate thru connective tissue in small numbers
"mobilize during infection or tissue injury"

collagen fibers

long straight and unbranched
strongest fibers in connective issue proper
wound together like rope
flexible and strong


consist almost entirely of collagen fibers
connect tissue to bone


resemble tendons
connect bone to bone

reticular fibers

thinner than collagen
contain same protien subunites as collagen fiber, interact in different way
tough but flexible, like spiderweb
resist forces in many directions

elastic fibers

contain protien elastic
stretch 150% of resting length
dominated by elastic fibers
relatively rare, interconnect vertabrae

ground substance

fluid in bone
surrounds cellular and fibrous components of connective tissue
like maple syrup

loose connective tissue

"packing material" in body
fill spaces in organs, provide cushion, support epithelia

aeolar tissue

least specialized
contains all cells and fibers in any connective tissue proper
framework allows distortion
ground substance is most volume
elastice fiber makes it resilient
forms layer seperating skin from deeper strucures

adipose tissue

provides cushion, padding, insulator to slow heat loss
"white fat"
brown fat in children

reticular tissue

"spider web of fiber"
reticular fiber, marcrophages, and fibroblasts
-stroma of liver
-lymph nodes
-bone marrow

dense connective tissue

occuoied by fibers
collagenous because collagen fibers are dominated by fiber type

dense regular

collagen fibers tightly packed and aligned parallel to applied forces


muscle to bone


attach superficial muscles to another muscle structure
abs, lumbar region, palmar region
bottom of foot

elastic tissue

found in walls of blood vessels
surround respiratory passageways


bone to bone

dense irregular

strength and support to areas subjected to stress in many directions
internal organs and forms sheath around cartliage and bones


gives skin strength

fluid connective tissue

blood and lymph
watery matrix
suspended protiens

red blood cells

half volume of blood
transport oxygen in blood

white blood cells

immune system, protects the body from infection and disease


function in clotting response


immune system, respond to signs of injury


firm gel contains complex polysaccharides
-chondroitin sulfates, complex with proteins

collagen fibers provide tensile strength
extracellular fibers and ground substance give it flexibility and resillience


carliage cells, only cells found withon cartliage martix (fluid)
live in lacunae (small chambers)




most common type of cartliage
matrix closely packed in collagen fibers
tough, flexible, but weakest
-connections between ribs and sternum
-passageways of repiratory tract

elastic cartliage

elastic fibers
resilient and flexible
-external flap of ear
epiglottis, throat
-auditory tube, airway of ear
-small cartilage of larynx(vociebox)

fibro cartilage

little ground substance
dominated by collagen fibers
-densely interwoven
-durable and tough
-pads between spinal vertabrae
-pubic bones


osseus tissie
-combination of collagen fibers and calcium salts
consists of SPONGY bone and COMPACT bone


matrix of bone tissue
-1/3 consists of collagen fibers
-mixture of calcium salts
strong/flexible bones


small chambers within the matrix contain the osteocytes
-organized around blood vessels that branch through the bony matrix

diffusion cannot

occur through the calcium salts

osteocytes communicate

with blood vessels through long, slender passages in the matrix called CANALICULI


mature bone cells
maintain and monitor protein and mineral of surrounding matrix (recycling)
-directs release of calcium from bone to blood
-directs deposition of calcium salts in surrounding matrix
-occupy small lacunae between layers of calcified matrix
contain cytoplasmic processes and ground substance
route for diffusion of nutrients and waste products

matrix layers

known as lamellae


cuboidal shape
inner/outer surfaces of bone
secrete organic components of bone matrix-oseoid
-later becomes mineralized
if surrounded by martix, differentiates into osteocyte

osteoprogenitor cells

small square shaped cells differentiate from mesenchymal cells
found in innermost layer of periosteum and endosteum lining marrow cavities
divide to produce daughter cells that differentiate into osteoblasts


large multinucleate cells where bone is being removed
secrete acids that dissolve bony matrix and release amino acids and the stored calcium and phosphate ----> osteolysi-increase calcium and phosphate concentration in body fluids

balance between clast/blast

is very important because
-clasts remove calcium salts faster than osteoblasts deposit them->weaker bones
-blast activity predominates -> bones become stronger and more massive

compact bone

dense bone relatively dense and solid
-forms walls

spongy bone

open network of struts and plates
-internal layer of spongy bone surrounds medullary cavity

medullary cavity contains bone marrow

loose connective tissue that may be yellow marrow(dominated by adipocytes) or red marrow (mixture of mature/immature red and white blood cells and the stem cells that produce them

osteocytes are arranged

in concentric layers (circular) around a central canal (haversian system)

central canal

runs parallel to the surface of the bone and contain blood vessels that supply the osteon(bone cell)

perforating canals

run perpendicular to the surface (volmanns canal)
-deliver blood to osteons deeper in the bone and service the interior marrow cavity

concentric lamellae

each osteon are cylindrical and aligned parallel to the long axis of the bone
-form a series of concentric rings around the central canal
-collagen fibers spiral along the length of each lamella, strengthens osteon

interstital lamellae

fill spaces between the osteons "stitches"

circumferential lamella

occur at external and internal surfaces of the bone

spongy bone

parallel lamellae from struts or thin branching plates called traceulae which gives it considerable strength
-genarally no osteons
--nutrients reach osteocytes by duffusion along canaliculi that open into the surfaces of the trabeculae
-frame work = lighter
presence of spongy bone reduces the weight of the skeleton =much easier for muscles to move the bones

compact vs spongy

compact-thickest where stress arrive from limited directions
compact bone surrounds medllary cavity - bone has 2 ends (epiphyses) serperated by tubular diaphysis.connected by narrow metaphysis
osteons run parallel to axis = strength along axis(straw)
spongy- capable of resisting stresses from different directions - abundant in epiphyses
open trabecular framework provides protection for bone marrow
yellow=energy;found in shaft
red=blood cells formation; found in epiphyses


layer of compact bone is covered by the periosteum
-outter fibrous layer of dense connective tissue
-inner cellular layer containing osteoprogenitor cells
does not surround sesamoid bones or where bone surfaces are covered by articular cartilages
near joints peristeum becomes continuous with connective tissue, helps stabilize joint


1 protects the bone
2 circulatory/nervous supply
3 bone growth
4 attaches bone to connective tissue

perforating fibers

collagen fibers incorporated into bone tissue from tendons and superficial periosteum
-powerful pull on tendon will usually break bone rather than snap collagen fibers at bone surface

bone development and growth

determines size and proportion of body
bony skeleton begins to form about 6 weeks after fertilzation and continues during adolescence


process of replacing other tissues with bone
=formation of bone


deposition of calcium salts with in a tissue


bone develops from mesenchyme or fibrous connective tissue
begins when mesenchymal cells differintiate into osteoblasts within embryotic/fibrous connective
occurs in deeper layers of dermis

frontal/parietal bones



lower jaw



sesamoid bones

with in tendons, patella

osteoblasts cluster together and begin to secrete organic components of matrix


endochronal ossification

begins with formation of hyaline cartliage model
initial formation of limb bones are comprimised of cartliage

cartliage models continue to grow

by interstitial growth-expansion of the cartliage matrix
-enlarges cartliage from with in
appositional growth-priduction of more cartliage at the outter surface
-increases dimension of cartilage by adding to its surface

increasing length

during initial stages of osteogenesis osteoblasts move away from the primary ossification center toward the epiphyses but cartliage of the epiphyses continue to grow

cartliage being replaced by bone

shaft side of metaphysis osteoblasts are continually invading the cartilage and replacing i with bone
on the epiphyseal side new cartilage is being replaced at same rate
result:skeletal element continues to grow longer and longer

osteoblasts migrate

secondary ossifiaction center

cartilage growth =

osteoblast invasion = increase in bone length

epiphyseal closure

epiphyseal cartliage gets continually narrower until ultimately disspears

diamerter of bone

enlarges thru appositional growth at the outer surface
adds successive layers of curcumferential lamellae to the outter surface of the bone
over time deeper lamellae are recycled and replaced with the osteons typial of compact bone

osteoprogenitor cells

inner layer of the periosteum differentiate into osteoblasts and add bone martix to the surface

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