Bone Histology Flashcards
Skeletal System
- Bone
- Cartilages
- Ligaments
- Tendons
Osteology
Study of bone structure and treatment of bone disorders.
Functions of Bone & Skeletal System
- Support ( structural framework by supporting soft tissues and site for tendon attachment)
- Protection ( protect organs)
- Movement (muscles pull on bone)
- Mineral Homeostasis (calcium and phosphorus are storred)
- Blood Cell Reproduction ( in some bones, red bone marrow makes RBC through hempoiesis. Red bone marrow has developing blood cells, fibroblasts, macrophages within matrix of reticular fibers)
- Triglyceride Storage: yellow bone marrow, has adipose cells —> triglycerdies to allow for potenitial energy.
Bone Structure and Cells
Diaphysis: in bone shaft
Epiphysis: distal ends
Metaphysis: region between the diaphysis and epiphysis. In growing bone contains the epiphyseal plate, a thin line of hyaline cartilage that allows the bone to grow in length
Articulating Cartilage: thin layer of hylaine caritlage covering the epiphysis, reduce friction
Periostenium: tough connective tissue, has an outer fiberous dense irregular layer and inner ostegonic cellular layer.
Medullary Cavity: hollow tube within diaphysis has yellow bone marrow, blood vessles
Endostenum: thin mem. lines medullary
Blood Vessles: nutrient artery and vein
Haversian Canal: contain artey vein and nerve
Canaliculi: branch away from Haversian canal to take nutrients to the osteocytes.
Osteocytes: reside in the lacuane within matrix, hard calcified matrix.
Hematopiteic Tissues (red bone marrow)
Tissues where red blood cells are made.
Infants: in the medullary cavities of the diaphysis and all spongey bone areas.
Adults: between trabecular and spongy bones in: sternum, ribs, clavicle etc.
Bone Matrix
Osseous tissues have spread out cells within a vast matrix.
Calcium phosphates (mainly) + calcium hydroxide = hydroxyapatite.
Calcification ( iniated by osteoblasts–> bone builder cells
- As crystals form, they combine with other ions and the mineral salts are deposited into collagen fibers.
Osteoblasts are going to secrete osetiod ( non calcified bone matrix) which is full of collagen. It will then become calcified around the osteoblast.
Bone Linage
Mesenchymal cells (stem cells) –> osteogenic cells (only type that undergo cell divisions. Found along inner periosteum)–>
Osteoblasts ( no cell division, bone builders, secrete matrix using collagen fibers to build) occurs, secrete osteoid (non calcified matrix) and initiate calcification. Becomes stuck in own secretions. As they build around themselves, they become –>
Osteocytes: mature bone cells that do not divide and carry out functions
White blood cell linage
Osteoclasts: large cells created from fusion of monocytes. Found in endostenum, encourage bone reabsorption.
Compact Bone
Found beneath bone periostenum
Makes up the diaphysis
protects
COMPONENTS:
1. Composed of Osetons (Harversian Systems): repeating units.
2. Lamellae: Each osteon has Lamellae around a Haversian Canal. Lamellae are ciricualr plates of extracellular matrix.
3. Haversian Canal: blood vessles, nerves
4. Lacunae: small spaces that contain osteocytes
5. Canaliculi: radiate in directions from osteocytes, provides route for nutritents to reach cells.
Intersteial Lamellae: areas between osteons
Volkmann’s Canal: tranverse canals allow blood vessles and nerves to penetrate
Circumferential Lamellae: arranged around outer/inner shaft.
Spongey Bone
Do not contain osteons
Trabeculae: Lamellae arranged in patterns filled with red, yellow bone marrow.
Covered by Compact Bone ( spongey bone reduced overall weight and trabeculae support red bone marrow)
Cartilage
Cartilage:
1. Surrounded by perichondrium
2. Avascular , no nerves
3. Chondrocytes in Lacunae
4. Flexible Extracellular Matrix ( cell division occurs in a flexible extracellular matrix )
5. Extracellular matrix made via chondorblasts
6. Appositional and Interstitial growth ( Cartilage has a flexible matrix and can grow appositionally and interestially)
Bone
- Surronded via periostenum
- Blood vessles, nerves
- Osteocytes in Lacnuae
- Rigid extracellular matrix ( only support appositional) and does not accomodate cell divsion
- Extracellular matrix made by osteoblasts
- Appositional growth only Grow based on cartilaginous growth, appositional gives bone width while interstitial gives bone length.
Appositional Growth and Interstial Growth
Appositional: Cartilage forming cells in the outer perichondrium secretes new matrix against the existing matrix. Applying matrix to existing matrix. (outside–> inside) Appositional Growth responsible for increasing bone width
Interstitial Growth: Chondrocytes divide and secrete new matrix expanding the cartilage from inside–> outside Responsible for increasing bone length!. Requires a flexible matrix in Cartilage
Bone Formation
Called ossification or osteogenesis
1. Initial Growth of Bones
2. Growth during development
3. Bone remodelling
4. Bone repair
Two Types of Osteogenesis (short answer)
- Intramembranous Ossification
- Endochondral Ossification ( mesechyme to cartilage)
Intramembranous Steps
- Mesenchymal Cells group in clusters and differentiate into osteogenic cells: –>osteoblasts ( ossification center forms)
- Osteoblasts will secrete osteoid: (non calcified bone matrix) which traps osteoblasts. Cause appositional growth by secreting new matrix inside.
- They also initiate calcification traping them–> becoming osteocytes ( mature)
Osteogenic cells in surrounding tissues develop into osteoblasts at edges and continue secreting osteoid. - Trabecular Matrix and Periosteum Forms:
- Clusters of osteoid (spicules) come together around the capillaires to form the trabecular matrix. The boney spicule is the clusters surrounding blood vessel.
- Trabecular fuses forming spongey bone around the blood vessel.
- Osteoblasts on the surface become the periosteum. –> The mesenchymal cells on the outer region begin to condense on outer and develops into periosteum. Innermost layer of periosteum (fibrous) allows for appos. growth “width” and matrix is secreted inside.
Spongey Bone layers:
1) Outer Layer becomes fibrous periosteum
2) Inner Layer becomes osteogenic layer - Osteoblasts will lay compact bone on top of inner trabecular bone. Inside, as the trabeculate condense they add pressure to blood vessels forming red bone marrow.
Repeating units of compact bone–> ostions
Endochondral Ossification Steps
- Blood vessles edge of cartilage model bring osteoblasts onto bony collar:
- ossification begins when the mesenchymal cells in deeper layer of perichodnirum become osteoblasts
- Osteoblasts secrete osteiod agaisnt thehyaline forms bony collar
- As boney collar grows from chondrocytes primary ossification is formed.
- Chondrocytes calfiy cartilage matrix then die and matrix disintegrates - Capillaires pentrate cartilage and despiot bone inside cartilage model.:
- nutrient artey pentrates perichondrium osetogenic–> osteoblast
- osetoblast place boney tissue over cartilage fomring songey bone trabucale.
- Primary oss. center goes out - Cartilage and chondrocytes grow at the end of bone while medullary cavity expands:
- osetoclast break down center trabuclae - Secondary ossfication after birth
- Hyaline caritlge remains at episheal plate and join as artiulating cartilage.
Epiphyseal plate
The site for bone lengthening
- Layer of hyaline caritlage in the metaphysis of growing bone. Divided into two sides: diaphysial and epiphyseal plates
1. Epiphyseal: hyaline cartilage are active and dividing producing hyaline cartilage matrix.
2. Diaphyseal: caritlage that is calcifying dying and being replaced by bone
Growth in bone width
- Periosteal cells–> osteoblasts secrete collage fibers into matrix-> osteocytes, ridges form on sides of periosteal where vessels form.
- Ridges fold together and fuse, periosetnum–> endostenum
- Osteoblasts despot matrix forms lamellae. formation continues inward to vessel and a new Osteon is made
- Osteoblasts deposit new circumferential lamella increase thickness.
Bone Remodelling
- Maintain Calcium Homeostasis: blood Ca 9-11mg
levels: Controlled by hormone Calcitonin (thyroid) and Parathyroid hormone. - PTH: when ca declines, PTCH stimulates osteoclasts to resorb bone and release more Ca in the blood.
- Calcitonin: response to elevated Ca in blood. Calcitonin stimulates Ca deposit into bones.
- Keep bones strength
