Lesson 10

 “Bone is formed from a multitude of tissue and cell types …”  Function of Bone and the Skeletal System  Structure of Bone  Histology of Bone  Blood and Nerve Supply of Bone  Bone Formation  Tortora – Chapter 6 (pg )  Moore – pg

 18% of human body weight  Composed of several different tissues working together …  Bone (osseous) tissue  Cartilage  Dense Connective Tissues  Epithelium  Adipose Tissue  Nervous Tissue

 Support  Structural framework  Supporting soft tissue and providing attachment  Protection  Important organs  Assistance in movement  Attach to most skeletal muscles

 Mineral Homeostasis  Bone tissue stores several minerals ▪ Calcium and phosphorus – create hardness ▪ Protein lends to strength  Contribute to bone strength  Blood Cell Production  Red bone marrow  Hemopoiesis  Triglyceride storage  Yellow bone marrow  Adipose cells – store triglycerides

 Long Bone – greater length than width

Typical Components  1) Diaphysis  Bone Shaft – main portion  2) Epiphysis  Proximal and distal ends of bone  3) Metaphysis  Regions b/w diaphysis and epiphysis  Epiphyseal (growth) plate  Epiphyseal line

Typical Components  4) Articular Cartilage  Thin layer of hyaline cartilage  Articulation joint with another bone  Reduces friction and absorbs shock  5) Medullary Cavity  Hallow, cylindrical space within diaphysis  Contains yellow bone marrow

Typical Components  6)Periosteum  peri- = round  Surrounds external bone  Consists: ▪ Outer fibrous layer ▪ Inner osteogenic layer  Function ▪ Protection and fracture repair ▪ Nourishment and attachment site  Perforating (Sharpey’s) FibersI ▪ Thick bundles of collagen fibers

Typical Components  7) Endosteum  Thin membrane lining of internal bone surfaces  Contains ▪ Single layer of cells ▪ Small amount of Connective tissue

 Bone (osseous) Tissue contains an abundant extracellular matrix surrounding cells  Osteogenesis: when the body is generating bone tissue  Extracellular Matrix contents  25% water, 25% collagen fibers, 50% crystallized mineral salts  Calcification – “dumping calcium on bone  Initiated by “bone-building” blocks/cells - osteoblasts

 Calcification  Calcium Phosphate, Ca3(PO4)2 – most abundant – very easy to remove or deposit unless it is calcified ( then more stable)  The process of hardening the bone is called Calcification:  Hardness happens because of Ca (and other hydroxy-appetite minerals Mg, P, etc)  Flexibility – of bone depends on 25% Collagen = pg 180 Ca3(PO4)2 Other Mineral Salts Hydroxyapatite crystals Other Mineral Salts (ie. Mg, Fl, K, S) Extracellular Matrix (framework)

 Hardness vs. Flexibility  Hardness ▪ Depends on the crystallized inorganic mineral salts in the bone  Flexibility ▪ Depends on the collagen fibers and other organic molecules in bone ▪ Provides tensile strength ▪ Bone growth: results from ▪ Epifigeal – length of bone growth comes from here (at maximal growth between childhood and 18 years of) – but after will ▪ Thickness of bone comes from periosteum and endosteum

4 Types of cells present in Bone Tissue:  1) Osteogenic Cells  2) Osteoblasts  3) Osteocytes  4) Osteoclasts

 1) Osteogenic Cells  Derived from mesenchymal cells  Unspecialized Stem Cells  Only bone cell that undergoes cell division  Location ▪ Inner portion of periosteum ▪ Endosteum ▪ Canals  Develop into osteoblasts

 2) Osteoblasts  -blasts = buds or sprouts; building blocks  Synthesize and secrete collagen fibers and other organic components ▪ Building the extracellular matrix of bone tissue  Initiate calcification  Develop into osteocytes

 3) Osteocytes  -cytes = cells; means that the cell maintains the tissue  Mature and main bone cells  Maintain daily metabolism

 4) Osteoclasts  -clast = to break; means the cell breaks down extracellular matrix  Huge cells derived from many monocytes  Concentrated in the endosteum  Ruffled Border  Resorption ▪ Break down of bone extracellular matrix

 Compact Bone Tissue  Contain few spaces  Strongest form of bone tissue  Location ▪ Beneath the periosteum of all bones  Function ▪ Protection, support, and resistance  Components ▪ Arranged into repeating structural units – osteons ▪ Central canal, lamellae, lacunae, osteocytes, canaliculi

 Spongy Bone Tissue  No Osteons but covered by a layer of compact bone  Location ▪ Interior bone tissue; along epiphysis of long bones ▪ Narrow rim around the medullary cavity  Components ▪ Trabeculae – red bone marrow in the hip bones, ribs, sternum, vertebrae, and ends of long bones

 Compact vs. Spongy Bone Tissue  Spongy bone tissue is light ▪ Reduces overall weight of a bone  Trabeculae of spongy bone tissue ▪ Support and protect the red bone marrow

 Richly supplied with blood  Especially abundant in areas containing red bone marrow Several Arteries  1) Periosteal Arteries  Through perforating canals on diaphysis  Supplies ▪ Periosteum ▪ Outer portion of compact bone

 2) Nutrient Arteries  Passes through nutrient foramen  Able to divide into branches ▪ Proximal and Distal branches  Supplies ▪ Inner portions of compact bone and spongy bone (red bone marrow) ▪ Only up the epiphyseal line

 3) Metaphyseal Arteries  Enter at the metaphysis  Supply red bone marrow and bone tissue within this region  4) Epiphyseal Arteries  Enter at the epiphysis  Supply red bone marrow and bone tissue within this region

 3 Areas of Venous Drainage  Nutrient Veins ▪ One or two; accompany artery  Epiphyseal and Metaphyseal Veins ▪ Numerous: accompany respective arteries  Periosteal Veins ▪ Numerous and small ▪ Accompany respective arteries

 Nerves accompany blood vessels  Periosteum rich in sensory nerves  Responsible in carrying pain sensations  Sensitive to tearing or tension  Explains pain due to bone fractures and bone marrow needle biopsy

 Ossification  ossi- = bone; -fication = making  Process by which bone is formed  Also know as Osteogenesis  4 Areas of Occurrence  Embryo and fetus: initial formation of bones  Infancy, adolescence – adult: growth of bones  Remodeling of bone: replacement of old bone tissue  Fracture of bone (breaks in bone)

 Embryonic skeleton – site of ossification  Ossification occurs during the 6 th week of embryonic development  Two Methods of Bone Formation  Intramembranous ossification ▪ Intra- = within; membran- = membrane  Endochondral ossification ▪ Endo- = within; chondral = cartilage

 Intramembranous ossification  Bone forms directly within mesenchyme arranged in sheet-like layers that resemble membranes  Simper method compared to endochondral  ie. Flat bones of the skull and mandible ▪ Fetal skull (soft spots) – harden after birth

 Intramembranous ossification

 Endochondral ossification  Replacement of cartilage by bone  Common method used for most bones of the body (ie. Long bone)

Endochondral ossification