AP Exam 2

Cartilage

•a connective tissue

•resiliency, 80 % water

•no innervation or vascularization

Cartilage Structure

Perichondrium surrounds the cell

Chondrocytes in outer shell of perichondrium and cell and within lacunae inside cell

Blood vessels in perichondirum

Collagen fiber and H2O inside cell

Lacunae surrounding chondrocytes inside cell

How does cartilage grow

It grows by cells under perichondrium dividing

Cartilage

Strength and Resiliency

Fetal Skeleton

cartilage and fibrous membranes which are eventually replaced by bones

Adult cartilage

•cartilage remains in regions where more resilient skeletal tissue is needed – skeletal cartilages

–hyaline

–elastic

–fibrocartilage

Cartilage not replaced by bones is found in regions where more resilient skeletal tissue is needed

Three types of skeletal cartilage

1. hylaine

2. Elastic

3. fibrocartilage

Hyaline Cartilage

-provides support with flexibility and resilience.

-it is the most abundant type of skeletal cartilage.

-locations:

-ends of movable joints - articular cartilage.

-connecting the ribs to the sternum - costal cartilage.

-forming the skeleton of the larynx - laryngeal cartilage.

-reinforcing passageways to the respiratory system - tracheal and bronchial cartilages.

-supporting the external nose - nasal cartilages.

Elastic Cartilage

-able to withstand repeated bending.

-found in two skeletal locations: external ear and the epiglottis.

Fibrocartilage

-highly compressible and provides for tensile strength.

-found in skeletal locations that are subjected to heavy pressure and stretch.

-pad-like cartilages of the knee - menisci.

-intervertebral disks.

Appositional Growth

growth from the outside.

-chondrocytes below surrounding perichondrium secrete a new matrix against the existing cartilage.

Interstitial Growth

growth from within.

-lacunae bound chondrocyte divide and secrete new matrix.

Support

–provide the framework of the body and cradle organs

Protection

–provided by the skull, ribs, and the vertebral column

Movement

–muscles attach to the bones and use them as levers to move body parts

Storage

–bone is a reservoir for minerals (calcium and phosphate)

–Adipose tissue storage

Blood Cell Formation

–occurs within certain bone marrow cavities

5 Functions of Bones

1. Support

2. Protection

3. Movement

4. Storage

5. Blood Cell Formation

Organic Components of bone tissue

Cells

Osteoid

Bone flexibility and strength

Cells of Organic component of bones

–osteoblasts, osteocytes, osteoclasts

Osteoid

–organic part of matrix, secreted by osteoblast andosteocyte

•GAG

•glycoproteins

•collagen

–responsible for bone's flexibility and high tensile strength

65% of mass

Inorganic components make up what % of mass

Inorganic components of bone tissue

Hydroxyapatites

Compressional strength

Present as crystals between collagen fibers in the osteoid

Hydroxyapatiti’s

–mineral salts, mostly calcium phosphates, calcium hydroxides; responsible for hardness of bones

Osteoblasts

Make extracellular matrix

–Found in inner and outer surfaces of a bone

–Make and secrete organic components of bone matrix – osteoid

Osteoclasts

Destroy Extracellular Matrix

–Found in inner and outer surfaces of a bone

–Destroy bone, secrete proteases and acids

–Proteases: destroy osteiod

–Acids: dissolve bony matrix, release stored calcium and phosphates

Osteocytes

–Mature bone cells, enclosed by mineralized osteoid

–Maintain matrix – resorptive, synthetic

Periosteum

Outer layer is associated with…

Endosteum

Inner part is associated with….

Inorganic Components

What part of bones are we able to see during lab because calcium salts which makes it harden and withstand compression

Proteases

Destroy osteoid

Acids

dissolve bony matrix, release stored calcium and phosphates

Four classifications of bone shape

Long

Short

Flat

Irregular

Two basic types of osseous tissue

Compact and Spongy bone

Long Bone

(elongated size, not overall size)

-longer than wide

-include most bones of limbs.

-primarily compact bone but can contain spongy bone in the interior

Short Bone

-include bones of the wrist and ankle.

-roughly cube-like.

-mostly spongy bone with a thin compact bone surface layer.

Flat Bone

-include the sternum, ribs, and most skull bones.

-thin, flattened, and slightly curved.

-two, roughly parallel, compact bone surfaces with enclosing a layer of spongy bone.

Irregular Bone

-include the vertebrae and hip bones.

-don't fit in any of the previous classes.

-mostly spongy bone enclosed by a thin layer of compact bone.

Compact Bone

•smooth and homogenous

•dense and solid

Spongy Bone

•open network of struts and plates

•flat, needle-like pieces of bone

•open space between the trabeculae is filled with marrow

Diaphysis

•shaft

–compact bone surrounding the medullary cavity (contains yellow marrow)

Epiphyses

•bone ends

–compact bone on exterior, spongy bone interior

articular cartilage covers joint surfac

Epiphyseal Line

–found between the diaphysis and the epiphyses, remnant of epiphyseal plate

Why are bones organs

They contain different kinds of tissue

Membranes

CT linings of the internal and external bone surfaces

Periosteum

•doubled layered membrane that lines the external bone surface

–outer fibrous layer - dense irregular connective tissue

–inner osteogenic layer - abuts bone surfaces

»osteoblasts – bone-forming cells

»osteoclasts – bone destroying cells

•richly supplied with nerves and blood vessels secured to the underlying bone by collagen fibers extending from the outer fibrous layer

Outer fibrous layer

Dense irregular connective tissue

Inner Osteogenic Layer

Abuts bone surfaces (osteoblasts and osteoclasts)

Endosteum

•delicate connective tissue membrane

•lines all internal bone surfaces

–trabeculae of spongy bones in marrow cavities

–medullary cavities in compact bone

–canals of compact bone

•contains osteoblasts and osteoclasts.

Structure of short, irregular, and flat bones

-thin pates of periosteum covered compact bone enclosing endosteum covered spongy bone -no diaphysis or epiphyses.

-bone marrow is found between the trabeculae.

-in flat bone the inner layer is spongy bone = diploë.

Where are some hematopoietic tissue found

-found within some cavities of spongy bone in long bones and in diploë of flat bones.

Where hematopoietic tissue is found in newborns

–medullary cavities/all areas of spongy bone contain red marrow.

Where hematopoietic tissue is found in adults

–medullary cavities of long bones contain yellow marrow

•little red marrow present in spongy bone, exceptions are femur and humerus.

–red marrow in cavities of flat bones (sternum), in some irregular bones (hip bone)

Osteon (Haversian system)

structural unit of compact bone

Microscopic structure of compact bone

•very dense, contains thorough system of canals and passageways

•osteon (Haversian System) - structural unit of compact bone

–elongated cylinders running parallel to the long axis of the bone

–hollow tubes of bone matrix arranged concentrically

•lamellae

•orientation of collagen fibers within a lamella

–core of the osteon - Haversian canal (central canal)

–perforating canals (Volkmann's)

•interstitial/circumferential lamellae

-connect nerve and vascular supply of periosteum to those in the central canals and medullarycavity .

Lamellae

Rings of bone matrix with osteocytes in between

Orientation of collagen fibers within lamella

run in a single direction, in adjacent lamella fibers run in opposite directions - withstand tensions.

Core of Osteon (Haversian canal aka central canal)

contains blood vessels and nerve fibers serving cells in osteon.

Perforating Canals (volkmanns)

lie perpendicular to the long axis of bone.

Detailed structure of compact bone

-osteocyte: spider shaped mature bone cells occupy lacunae between lamellae.

-hair-like canals (canaliculi) connect lacunae to each other and to the central canal, effectively connect all osteocytes in the osteon, allow osteocytes to be well nourished.

-interstitial lamellae: incomplete lamellae.

-circumferential lamellae: lamellae beneath periosteum, extend around circumference of the shaft.

Osteocyte

•mature bone cells in lacunae between lamellae

Canaliculu

•hair-like canals between lacunae, continuous with central canal

–critical for osteocyte nourishment

Microscopic structure of spongy bone

-consists of trabeculae a few cell layers thick; contain irregular lamellae and osteocytes interconnected with canaliculi; no osteons.

-trabeculae are arranged along the lines of stress.

Trabeculae in spongy bone are arranged along the lines of stress

–Spongy bone can withstand stresses from many different directions

–Transmit stresses across a joint

–Support and protection for cells of marrow

Compact bone can withstand stresses longitutinally

–Conducts applied stresses from one epiphysis to the other

interstitial lamellae

incomplete lamellae

Circumferential Lamellae

lamellae beneath periosteum, extend around circumference of the shaft.

Osteogenesis aka Ossification

The process of bone formation

Osteogenesis depends on

Developmental Stage

Process of Bone formation in embryo

formation of bony skeleton – ossification

Process of Bone formation in childhood through early adulthood

Bone Growth

Resulting in bone growth and increased size

Process of bone development through middle/late adulthood

Remodeling and repair

Embryonic Skeletons; 6 weeks Osteogenesis

–fibrous CT membranes

–hyaline cartilage plates

Bone formation involves…

The replacement with bone

Intramembranous Ossification

•formation of all flat bones

•bone develops from fibrous membrane

Endochondral ossification

•forms most other bones of skeleton

•bone develops from hyaline cartilage

Intramembranous Ossification

-mesenchymal cells of fibrous membrane differentiate into osteoblasts, secrete osteoid.

-osteoid become mineralized, osteoblasts trapped in lacunae become osteocytes.

-as the osteoid deposits accumulate and mineralization continues, a network of trabeculae formed that encloses local blood vessels - woven bone.

-collagen fibers are arranged irregularly.

-collagen fibers form networks, not lamellae.

-concurrently, a layer of vascular mesenchyme condenses external to the woven bone, periosteum development.

-trabeculae below periosteum thicken, form continuous plates of bone, first woven bone later compact bone.

-trabeculae in center of the bone remain distinct so spongy bone is produced.

-vascular tissue within spongy bone differentiates into red marrow, diploe

Endochondrial ossification

-template is hyaline cartilage.

-begins at the primary ossification center at the center of the hyaline cartilage shaft.

-perichondrium is infiltrated with blood vessels, becomes a vascularized periosteum.

-osteoblasts of newly "converted" periosteum secretes osteoid against hyaline cartilage shaft, encases it in a bone collar.

-hyaline cartilage in center shaft calcifies, bone collar continues formation externally.

-chondrocytes within the shaft enlarge, surrounding cartilage calcifies, nutrients cannot get to center of the shaft, chondrocytes die, the matrix begins to deteriorate - cavity formation.

-forming cavities are invaded by periosteal bud - brings a nutrient artery, vein, lymphatics, nerve fiber, red bone marrow elements, osteoblast/osteoclasts into the cavity.

-entering osteoblasts secrete osteoid around remaining cartilage fragments - bone covered cartilage trabeculae (precursor of spongy bone).

-primary ossification centers enlarge proximally and distally - osteoclasts break down newly formed spongy bone, open up a medullary cavity in the center of the shaft, final step in shaft ossification.

-recall that throughout the fetal period, rapidly growing epiphyses consists only of cartilage.

-shortly before birth, secondary ossification centers appear at the epiphyses.

-cartilage at the center of the secondary ossification centers in the epiphyses calcifies and deteriorates to form a cavity.

-entry of the periosteal bud.

-bone matrix secreted around the remaining cartilage fragments.

-spongy bone is retained and there is no cavity formation.

-cartilage remains only at articular cartilage and at epiphyseal plates.

Long Bones

Lengthen by interstitial growth of epiphyseal plates

Appositional Growth

All bones grow in thickness by…

Zone 1 (outer piece of bone)

Cartilage grows in which zone of the bone

Zone 2 (Inside of bone)

Cartilage is replaced by bone in which zone

Cartilage grows in outside surface and is replaced in inside

Why do bones grow in length

Bone is reabsorbed at epiphyseal line and and added by appositional growth on outside

Why do growing shaft in bone remodeled

Growth in thickness (appositional growth)

–bones widen as they lengthen

–osteoblasts below periosteum produce bone matrix (compact bone)

–accompanied by bone resorption in endosteal surface

In adults

bone deposit and bone resorption is occurring continuously in what individuals

In healthy adults

total bone mass stays constant in which individuals

rate of bone deposit=

the rate of bone resorption.

Osteogenesis

Remodeling and Repair

5-7%

•throughout adulthood – each week recycle _____% of bone mass!!

3-4 years

Replace spongy bone every….

10 years

Replace compact bone every….

Bone deposition

where bone injured or added bone strength required

•Osteocytes

•Osteoblasts at periosteal/endosteal surfaces

–production of osteoid

–calcification

»Ca⁺⁺ removed from plasma

Bone resorption

-conducted by osteoclasts.

-osteoclasts secrete lysosomal enzymes that digest organic matrix, and metabolic acids that solubilize calcium salts.

•Osteoclasts at periosteal/endosteal surfaces

•Osteocytes

–bone digestion – extracellular/phagocytosis

–products released into ISF and blood

»Ca⁺⁺ released to plasma

Osteoid Seam

site of bone deposit is an unmineralized band of bone matrix

Abrupt Transition

Mature

between the osteoid seam and the old mineralized bone there is _____ __________, the calcification front; osteoid must ______ before becoming calcified.