bone tissue part 2: support & movement. function of the human skeleton provides support for the...
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Bone Tissue
Part 2: Support & Movement
Function of the Human Skeleton
Provides support for the body Protection to the internal organs Provides & framework for the connection of
skeletal muscles Allows for movement
Contains red bone marrow for blood formation and storage Produces blood cells
Primary storage site for minerals & fats Including calcium!
Bone Tissue
Osseous (Bone) Tissue: Dynamic (ever-changing) living tissue that makes up the skeletal structure.Bone is a type of connective tissue with a
matrix made of hydoxyapatite (a calcium salt).
Two types of bone: Compact BoneSpongy Bone
Bone Tissue
Osteon: The functional unit of compact bone. Contains many types of bone cells.Osteogenic Cells: “Stem Cells” that divide to
provide a constant supply of the other bone cells.
Osteoblasts: “Bone-building” cells that transport calcium from the bloodstream to the bone matrix.
Osteoclasts: “Bone-chewing” cells that reabsorb bone & transport calcium from the bone to the blood.
Structure of Long Bone
Diaphysis: The central shaft of a long bone. Contains the medullary (marrow) cavity – yellow
bone marrow in adults.
Epiphysis: The ends (proximal and distal) of long bone.
Metaphyses: Where the diaphysis and epiphysis means. Contains the epipheseal plate (growth plate) where
cartilage is replaced by bone as the bone grows longer.
Structure of Long Bone
Articular Cartilage: The layer of hyaline cartilage surrounding the epiphysis where bones connect at joints.
Periosteum: The tough covering on the outside of the surface of bone, composed primarily of dense irregular connective tissue.
Endosteum: Thin membrane lining medullary cavity.Contains a single layer of bone-forming cells.
Histology of Compact Bone
Osteons: The type of tissue that makes up compact bones.
Made up of…Central Canal aka Haversian System
Contains concentric lamellae containing lacunae and canaliculi
Perforating Canals aka Volkmann’s Canal Interstitial Lamaellae
Components of Osteons
Central Canal aka Haversian Systems: The functional unit of compact bone. Located in the center of the osteon.Provides a passageway for blood vessels and
nerves through the length of the bone. Surrounded by calcified rings called
concentric lamellae Lacunae: Spaces in the concentric lamellae
containing osteocytes. Canaliculi: Tiny canals between the lamellae.
Components of Osteons
Perforating Canal aka Volkmann’s Canal: Passageways with blood & lymph vessels and nerves running at a right angle to the Haversian canals.Connects blood vessels from Periosteum to
Haversian canals. Interstitial Lamellae: The area between
the osteonsConsists of fragments of old, partially
destroyed osteons
Spongy Bone
Spongy Bone: Consists of a latticework of columns of bones called trabiculae. Named for the “sponge-like” appearance Permeated spaced filled with bone marrow, NOT
osteons Trabeculae develop along lines of stress
Wolf’s Law: Bone mass & density will increase in areas of stress, so bone will be thickest where it is under the greatest stress.
Much lighter than compact bone Found in irregularly shaped bones in places with less
stress or stress from multiple directions Found at the epiphyses of long bones
Bone Marrow
Red Marrow: Found throughout the skeleton in infants and children.Produces all types of blood cellsPrimary found in flat bones in adults & the
ends of long bones Sternum, ribs, skull bones, pelvis
Yellow Marrow: Fills most marrow cavities in adultsFilled with triglycerides (fat) as an energy
reserve
Osseous Tissue Homeostasis
Bone Tissue serves as a reservoir for 99% of calcium & phosphorous in addition to other minerals. Calcium: Important to bone, muscle, & nerve tissue. Phosphate Groups: Important in the formation of
DNA, RNA, ATP, & Phospholipids. Mineralization (Deposition): The process of
depositing calcium and phosphate in bone via osteoblasts.
Mineral Resorption: The process of disolving bone tissue to release minerals into the bloodstream via osteoclasts.
Hypocalcaemia
Hypocalcaemia: Low calcium concentration in the blood. Can result in adverse effects on the nervous
and muscle systems.
Endocrine Regulation of Blood Calcium Level
Parathyroid Hormone (PTH): Raises blood calcium when it drops too low.
Calcitonin: Lowers blood levels of calcium. Produced by the thyroid gland.
Calcitriol: Causes reduced excretion of Ca++ by the kidneys & increased absorption by the GI tract A form of Vitamin D! Manufactured in the skin from a precursor of
cholesterol – stimulated by ultraviolet light Growth Hormone (GH): Affects the epiphyseal
plate
Bone Formation & Development
Ossification: The process by which bones are formed.
TWO Methods of Ossification: Intramembranous OssificationEndochondral Ossification
Intramembranous Ossification
Produces flat bones…. Replaces connective tissue membranes with bone in
the skull, forms the mandible (the lower jaw) and the breastbone
Starts as embryonic connective tissue called mesenchyme
Osteogenic (stem) cells develop into osteoblasts, which secrete bone matrix
Calcification: Osteoblasts deposit osteoid tissue, then calcium phosphate is deposited. Osteoblasts then become osteocytes
Intramembranous Ossification
Bone matrix develops into trabiculae to form spongy bone.
Compact bone tissue then forms around spongy bone as the mesenchyme condenses into periosteum
Spongy bone remains in the center, surrounded by a thin layer of compact bone.
Endochondral Ossification
Develops from a hyaline cartilage modelCartilage model is “invaded” by blood vessels
which start to form a central marrow cavity.Perichondrium: The membrane that forms
around the cartilage model. Perichondrium cells become osteogenic
and begin to produce bone on the otuside of the model, which then grows in length as chondrocytes (cartilage cells) divide.
Endochondral Ossification
Ossification moves inward from the external surface forming a primary ossification center. Cartilage is then “remodeled” into bone by
osteoblasts with mineral deposits. Perichondrium becomes periosteum
Secondary ossifaction proceeds outward from the center of the epiphyses
Hyaline cartilage remains in the growth plates
Cartilage Growth
Cartilage growth occurs in two ways: Interstitial growth involves increasing the internal
cartilage matrix and typically results in an increase in bone length.
Long bones grow in length due to the addition of bone at the growth plates (on the diaphyseal side)
Appositional Growth involves depositing material on the cartilage surface to increase bone thickness.
Due to deposition of bone by osteoblasts at the outer surface while osteoclasts in the endeosteum destroy bone to increase the cavity & diameter of the bone.
Bone stops growing in length by approximately age 25, but may continue to thicken throughout life.
Hormonal & Chemical Factors Influencing Bone Development
Homeostasis Factors: Parathyroid Hormone (PTH)Calcitonin
Bone Growth: Growth Hormone (GH)Thyroxine (Thyroid Hormone)
Sex HormonesEstrogenTestosterone
Hormonal & Chemical Factors Influencing Bone Development Promotion of osteoclast activity
Calcitriol Vitamins:
C K B12 A
Minerals: Calcium Phosphorous Magnesium (Mg) Iron (Fe) Manganese (Mn) Fluorine (F)
Reminder: Cartilage
Types of Cartilage: Hyaline: Found in articular surfaces, growth plates in
long bones Fibrocartilage: Absorbs shock, found in
intervertebral discs Elastic: Found in the framework of the outer ear &
the epiglottis
Chondroblasts: Cells which actively produce cartilage
Chondrocytes: Cells trapped in lacunae of cartilage
Types of Bones
Long Bones: Bones that are longer than they are wide. E.g. humerous, radius, femer, etc.
Short Bones: Closer to equal in length and width. E.g. wrist & ankle bones
Flat Bones: Enclose/protect organs E.g. cranium, breastbone
Irregular Bones: Elaborate shapes that don’t fit the other types E.g. Vertebral bodies, ethmoid and sphenoid bones
Sesamoid Bones: Bone contained in a tendon E.g. patella (kneecap)
Sutures: Small bones located within suture joints.
Bone Processes
Bone Processes: The markings found on the bones.TubercleTuberosityFoveaForamenCondylesFossa
Tubercle
Tubercle: A small, rounded projection. Area where muscle
tendon attaches.
Tuberosity
Tuberosity: A large, rounded projection. Area where tendon
attaches.
Fovea
Fovea: Depression or pit. Example: Fovea
capitis on the head of the femur.
Foramen
Foramen: An opening in a bone. Example: The
foramen magnum in the base of the skull.
Condyles
Condyles: A large, rounded protrusion at articular surfaces that form joins.
Fossa
Fossa: Shallow depressions.
Bone Remodeling
Bone Remodeling: The process of bone rebuilding itself.Used as a means of constant renewal and to
redistribute the bone matrix (such as at areas of increased stress or to heal injuries).
Typically occurs as a balance between resorption by osteoclasts and deposition of osteoblasts.
Types of Fractures
Bone Healing
Stages of Bone Healing/Fracture Healing: Reactive PhaseReparative PhaseRemodeling Phase
Fracture Healing
Reactive Phase: Blood vessels near the fracture constrict to
stop further bleedingExtravascular blood cells (“hematoma”) form a
blood clot within a few hoursThe blood cells within the clot die, while
fibroblasts survive & replicate to create a loose aggregate of cells interspersed with small blood vessels – known as Granulation Tissue
Fracture Healing
Reparative Phase: Days after the fracture…
Fibroblasts within the granulation tissue & the periosteal cells proximal to the fracture replicate into chondroblasts to form hyaline cartilage
the periosteal cells distal to the fracture develop into osteoblasts and form new woven bone.
Both tissues grow in size until they unite to form a fracture callus.
Endochondral ossification occurs: Lamellar bone replaces woven bone and then hyaline catilage.
Eventually, all of the lamellar bone is replaced by trabecular bone, restoring most, if not all, of the bone’s original strength.
Fracture Healing
Remodeling Phase: Trabecular bone is resorbed by osteoclasts,
creating the Hallowship’s Lacuna (the shallow resorption pit) and replaced with compact bone.
The fracture callus is remodeled into a new shape closely duplicating the bone’s original shape and strength.