Bone Tissue

Support Provides attachment for tendons of skeletal muscles Provides attachment for tendons of skeletal muscles

Protection Protects internal organs Protects internal organs Example: Skull (brain), vertebrae (spinal cord), and rib cage ( heart and lungs)

Assistance in movement Contraction of muscles results in pulling of bone due to tendons Contraction of muscles results in pulling of bone due to tendons

Mineral Homeostasis Stores calcium and phosphorous Stores calcium and phosphorous

Blood Cell Production Red bone marrow produces red blood cells, white blood cells and platelets Red bone marrow produces red blood cells, white blood cells and platelets

Triglyceride Storage Yellow bone marrow stores triglycerides Yellow bone marrow stores triglycerides

Newborns Have only red bone marrow Have only red bone marrow

Newborns Red bone marrow changes into yellow bone marrow with increasing age Red bone marrow changes into yellow bone marrow with increasing age

Structure of Bone Diaphysis Diaphysis Epiphysis Epiphysis Metaphyses Metaphyses Articular cartilage Articular cartilage Periosteum Periosteum Medullary cavity Medullary cavity Endosteum Endosteum

Diaphysis Bone’s body or shaft Bone’s body or shaft

Epiphysis The distal and proximal ends of the bone The distal and proximal ends of the bone

Metaphysis The region where the diaphysis joins the epiphysis The region where the diaphysis joins the epiphysis

Metaphysis When the bone is growing the metaphysis consists of an epiphyseal plate. This is a layer of hyaline cartilage that allows the bone to grow in length. When the bone is growing the metaphysis consists of an epiphyseal plate. This is a layer of hyaline cartilage that allows the bone to grow in length.

Metaphysis When the bone stops growing the cartilage is replaced by bone and becomes the epiphyseal line. When the bone stops growing the cartilage is replaced by bone and becomes the epiphyseal line.

Articular Cartilage Hyaline cartilage that covers the epiphyses in order to reduce friction Hyaline cartilage that covers the epiphyses in order to reduce friction

Periosteum Dense irregular tissue that surrounds the bone. Dense irregular tissue that surrounds the bone.

Periosteum Contains osteoblasts responsible for bone growth in thickness. Contains osteoblasts responsible for bone growth in thickness.

Medullary Cavity The space in the diaphysis that contains yellow bone marrow. The space in the diaphysis that contains yellow bone marrow.

Endosteum A thin membrane that lines the medullary cavity A thin membrane that lines the medullary cavity

Bone Histology 25% water 25% water 25% collagen fibers 25% collagen fibers 50% mineral salts 50% mineral salts

Bone Histology Most mineral salts are calcium phosphate and calcium carbonate Most mineral salts are calcium phosphate and calcium carbonate

Bone Histology Continued These minerals crystallize only in the presence of collagen fibers These minerals crystallize only in the presence of collagen fibers

Bone Histology Continued Crystallized inorganic mineral salts responsible for hardness Crystallized inorganic mineral salts responsible for hardness

Bone Cells 1. Osteogenic Cells Only bone cells that undergoes cell division Only bone cells that undergoes cell division Daughter cells becomes osteoblasts Daughter cells becomes osteoblasts

Bone Cells Osteoblasts Osteoblasts Secretes collagen fibers and organic compounds for matrix Secretes collagen fibers and organic compounds for matrix When mature they become osteocytes When mature they become osteocytes

Bone Cells Osteocytes Osteocytes Mature bone cells Mature bone cells Exchange nutrients and waste with blood Exchange nutrients and waste with blood

Bone Cells Osteoclasts Breaks down bone matrix or resorption Breaks down bone matrix or resorption Derived from the fusion of 50 monocytes (wbc) Derived from the fusion of 50 monocytes (wbc)

Compact Bone Tissue Forms the external layer of all bones and most of the diaphysis in long bones Forms the external layer of all bones and most of the diaphysis in long bones

Compact Bone Tissue Provides protection and support Provides protection and support

Compact Bone Tissue Compact bone thickest in areas where stress is applied in few directions Compact bone thickest in areas where stress is applied in few directions

Compact Bone Tissue 1. Osteons – units in bone

Compact Bone Tissue 2. Volkmann’s canals – Tranverse canals in which blood vessels, lymphatic vessels, and nerves reside

Compact Bone Tissue 3. Haversian canals – longitudinal canals

Compact Bone Tissue 4. Concentric lamellae – rings of calcified matrix

Compact Bone Tissue 5. Lacunae – contain osteocytes

Compact Bone Tissue 6. Canaliculi – tiny channels filled with extracellular fluid that contain the fingerlike processes of osteocytes.

Canaliculi  Connect lacunae with one another

Canaliculi  Connect lacuane with Haversian Canals

Canaliculi  Allow osteocytes to communicate with each other via gap junction

Canaliculi  Allow exchange of nutrients and wastes with blood

Compact Bone Tissue 7. Interstitial lamellae – fragments of older osteons

Spongy Bone Tissue Lacks osteons Lacks osteons

Spongy Bone Tissue Contains trabeculae which are an irregular latticework of thin columns of bone Contains trabeculae which are an irregular latticework of thin columns of bone

Spongy Bone Tissue Contains red bone marrow between spaces of trabeculae Contains red bone marrow between spaces of trabeculae

Spongy Bone Tissue Make up most of the bone tissue in short, flat, irregularly shaped bones, and epiphysis of long bones and the narrow rim around the medullary cavity of the diaphysis of long bone Make up most of the bone tissue in short, flat, irregularly shaped bones, and epiphysis of long bones and the narrow rim around the medullary cavity of the diaphysis of long bone

Spongy Bone Tissue Red Bone marrow is found in spongy bone tissue of hip bones, ribs, breastbone, back bones, and ends of long bones Red Bone marrow is found in spongy bone tissue of hip bones, ribs, breastbone, back bones, and ends of long bones

Spongy Bone Tissue Spongy Bone tissue found where stresses are applied from several directions Spongy Bone tissue found where stresses are applied from several directions

Bone Formation 1. Intramembranous ossification 2. Endochondral ossification

Intramembranous Ossification Skull bones and mandible form this way Skull bones and mandible form this way Fetal soft spots harden via this process Fetal soft spots harden via this process

Intramembranous 1. Development of the center of ossification

Development of the center of ossification The site where mesenchymal cells cluster together The site where mesenchymal cells cluster together

Development of the center of ossification The mesenchymal cells become osteogenic cells The mesenchymal cells become osteogenic cells

Development of the center of ossification These osteogenic cells become osteoblasts These osteogenic cells become osteoblasts

Intramembranous 2. Calcification

Calcification Secretion of matrix stops Secretion of matrix stops

Calcification Osteoblasts now called osteocytes and lie within lacunae Osteoblasts now called osteocytes and lie within lacunae

Calcification Calcium and other mineral salt are deposited and the matrix hardens or calcifies Calcium and other mineral salt are deposited and the matrix hardens or calcifies

Intramembranous 3. Formation of trabeculae

Formation of trabeculae Bone matrix develops into trabeculae to form spongy bone Bone matrix develops into trabeculae to form spongy bone

Formation of trabeculae Connective tissue associated with blood vessels in trabeculae become red bone marrow Connective tissue associated with blood vessels in trabeculae become red bone marrow

Intramembranous 4. Development of the periosteum

Development of the periosteum Mesenchyme condenses around the periphery and becomes the periosteum Mesenchyme condenses around the periphery and becomes the periosteum

Development of the periosteum Compact bone replaces spongy bone at the surface Compact bone replaces spongy bone at the surface

Development of the periosteum Spongy bone remains in the center Spongy bone remains in the center

Endochondral Ossification Replacement of cartilage by bone Replacement of cartilage by bone Most bones are formed this way Most bones are formed this way

Endochondral 1. Development of the cartilage model

Development of the cartilage model  Mesenchymal cells cluster together in the shape of the future bone and differentiate into chondroblasts

Development of the cartilage model  Chondroblasts secrete a cartilage matrix, producing a hyaline cartilage model

Development of the cartilage model  A perichondrium develops around the cartilage model

Endochondral 2. Growth of the cartilage model

Growth of the cartilage model  Once chondroblasts are surrounded by matrix called chondrocytes

Growth of the cartilage model  Grows in length because chondrocytes continue to divide and secretion of cartilage matrix

Growth of the cartilage model  Grows in width occurs due to addition of more matrix by new chondroblasts that develop from the perichondrium

Growth of the cartilage model  Cartilage model calcifies

Endochondral 3. Development of the primary ossification center

Development of the primary ossification center  A nutrient artery penetrates the perichondrium and calcified cartilage via a nutrient foramen

Development of the primary ossification center  Osteogenic cells in perichondrium become osteoblasts

Development of the primary ossification center  Osteoblasts secretes a periosteal bone collar made up of compact bone

Development of the primary ossification center  Perichondrium becomes periosteum

Development of the primary ossification center  Capillaries that penetrate the calcified cartilage induce growth of the primary ossification center

Development of the primary ossification center  Osteoblasts deposit bone matrix over calcified cartilage forming spongy bone trabeculae

Development of the primary ossification center  As the ossification center grows length wise it begins to destroy the trabeculae which becomes the medullary cavity

Endochondral 4. Development of the secondary ossification center

Development of the secondary ossification center Epiphyseal artery penetrates epiphyses and a secondary ossification center develops Epiphyseal artery penetrates epiphyses and a secondary ossification center develops

Development of the secondary ossification center Bone formation is similar to that of diaphysis except spongy bone trabeculae is not destroyed Bone formation is similar to that of diaphysis except spongy bone trabeculae is not destroyed

Endochondral 5. Formation of articular cartilage and the epiphyseal plate

Formation of articular cartilage and the epiphyseal plate  Hyaline cartilage that surrounds epiphyses becomes the articular cartilage

Formation of articular cartilage and the epiphyseal plate  There is a layer of cartilage between the epiphyses and the diaphysis called the epiphyseal plate

Bone Growth  Growth in length  Growth in thickness

Growth in Length  Growth in length occurs due to the epiphyseal plate

Growth in Length  The epiphyseal plate is made up of a layer of cartilage with four zones

Four Zones 1. Zone of resting cartilage  Made up of chondrocytes

Zone of resting cartilage  Does not contribute to bone growth

Zone of resting cartilage  Anchors epiphyses to the epiphyseal plate

Four Zones 2. Zone of proliferating cartilage  Chondrocytes larger

Zone of proliferating cartilage  Chondrocytes divide in order to replace dying chondrocytes on the diaphyseal side of the epiphyseal plate

Zone of proliferating cartilage  Responsible for lengthening

Four Zones 3. Zone of hypertrophic cartilage  Chondrocytes larger

Zone of hypertrophic cartilage  Lacunae grows and the matrix between lacunae narrow

Zone of hypertrophic cartilage  Responsible for lengthening

Four Zones 4. Zone of calcified cartilage  Matrix is calcified

Zone of calcified cartilage  Chondrocytes are dead

Zone of calcified cartilage  Osteoclasts dissolve the calcified cartilage

Zone of calcified cartilage  Osteoblasts from diaphysis invade the area and lay down bone matrix

Epiphyseal Line Epiphyseal plate becomes a bony structure called an epiphyseal line between the age of 18 and 25 Epiphyseal plate becomes a bony structure called an epiphyseal line between the age of 18 and 25

Epiphyseal Line Bone replaces all the cartilage and the bone can no longer grow in length Bone replaces all the cartilage and the bone can no longer grow in length

Growth in Thickness Bone can only grow in thickness by appositional growth Bone can only grow in thickness by appositional growth

Growth in Thickness/Step 1 Osteoblasts secrete collagen fibers and organic molecues Osteoblasts secrete collagen fibers and organic molecues

Growth in Thickness/Step 1 Bone ridges form on either side of a periosteal blood vessel Bone ridges form on either side of a periosteal blood vessel

Growth in Thickness/Step 1 A groove forms for the blood vessel A groove forms for the blood vessel

Growth in Thickness/Step 2 The ridges fold and fuse enclosing the blood vessel The ridges fold and fuse enclosing the blood vessel

Growth in Thickness/Step 2 The periosteum is now becomes the endosteum surrounding the blood vessel The periosteum is now becomes the endosteum surrounding the blood vessel

Growth in Thickness/Step 3 Osteoblasts in the endosteum lay down bone matrix forming new concenteric lamellae Osteoblasts in the endosteum lay down bone matrix forming new concenteric lamellae

Growth in Thickness/Step 3 The concenteric lamellae is added toward the center of tunnel The concenteric lamellae is added toward the center of tunnel

Growth in Thickness/Step 4 The periosteum lays down new outer concenteric lamellae The periosteum lays down new outer concenteric lamellae Step 1-4 repeats Step 1-4 repeats

Calcium Homeostasis When blood calcium levels are below normal, parathyroid hormone is released by the parathyroid glands. When blood calcium levels are below normal, parathyroid hormone is released by the parathyroid glands.

Calcium Homeostasis Parathyroid hormone increases bone resorption. In other words it increases the activity of osteoclasts, thereby breaking down bone and releasing more calcium into the blood stream. Parathyroid hormone increases bone resorption. In other words it increases the activity of osteoclasts, thereby breaking down bone and releasing more calcium into the blood stream.

Calcium Homeostasis Parathyroid hormone also act on the kidneys to decrease loss of calcium in urine Parathyroid hormone also act on the kidneys to decrease loss of calcium in urine

Calcium Homeostasis When blood calcium levels are high, calcitonin is released by the thyroid gland in order to increase calcium uptake and stimulate bone formation. When blood calcium levels are high, calcitonin is released by the thyroid gland in order to increase calcium uptake and stimulate bone formation.