Essentials of Human Anatomy The Skeletal System 1

Essentials of Human Anatomy The Skeletal System 1 Chapter 5 Dr Fadel Naim Ass. Prof. Faculty of Medicine IUG 1

Bone • Bones are organs • Bones are composed of all tissue types. • Their primary component is osseous connective tissue. • The matrix is sturdy and rigid due to calcification (also called mineralization).

Function of Bones • Support: form the framework that supports the body and cradles soft organs • Protection: provide a protective case for the brain, spinal cord, and vital organs • Movement: provide levers for muscles • Mineral storage: reservoir for minerals, especially calcium and phosphorus • Blood cell formation: hematopoiesis occurs within the marrow cavities of bones • Energy storage (fat in yellow marrow)

Support and Protection • Bones provide structural support and serve as a framework for the entire body. • Bones protect many delicate tissues and organs from injury and trauma.

Movement • Muscles attach to the bones of the skeleton – contract and pull on bone – functions as a series of levers.

Storage of Mineral and Energy Reserves • More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone. – Calcium: needed for • muscle contraction • blood clotting • nerve impulse transmission. – Phosphate: needed for • ATP utilization • structure of nucleic acids (DNA, RNA)

Hematopoiesis Blood Cell Formation • Blood cell production in red bone marrow – located in some spongy bone. • Red bone marrow contains stem cells – form all of the blood cell types.

Bone Classification A. • • Long Bones Short Bones Flat Bones Irregular Bones Sesamoid (Round) Bones

Classification of Bones: By Shape • Long bones – longer than they are wide (e. g. , humerus)

Classification of Bones: By Shape • Short bones – Cube-shaped bones of the wrist and ankle – Bones that form within tendons (e. G. , Patella)

Classification of Bones: By Shape • Flat bones – thin, flattened, and a bit curved (e. g. , sternum, and most skull bones)

Classification of Bones: By Shape • Irregular bones – bones with complicated shapes (e. g. , vertebrae and hip bones)

Classification of Bones • Axial skeleton – bones of the skull, vertebral column, and rib cage • Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip

Bone Structure - External § Cartilage protection for joints

Bone Structure - External §Epiphyses §Expanded ends of long bones §Exterior is compact bone, and the interior is spongy bone Epiphyse §Joint surface is covered with articular (hyaline) cartilage §location of red bone marrow §Epiphyseal line separates the diaphysis from the epiphyses

Bone Structure - External §Diaphysis §Tubular shaft that forms the axis of long bones §Composed of compact bone that surrounds the medullary cavity §Yellow bone marrow (fat) is contained in the medullary cavity Diaphysis

Bone Structure - Internal • Spongy Bonered marrow

Bone Structure - Internal • Compact bone

Compact and Spongy Bone

Bone Structure - Internal • Medullary Cavityyellow marrow

Bone Structure - Internal • Epiphiseal Plate “Growth Plate”

Parts of a Long Bone • epiphysis • distal • proximal • diaphysis • compact bone • spongy bone • articular cartilage • periosteum • endosteum • medullary cavity • trabeculae • marrow • red • yellow

Structure of Short, Irregular, and Flat Bones • Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside • Have no diaphysis or epiphyses • Contain bone marrow between the trabeculae

Bone Membranes • Periosteum – double-layered protective membrane – Outer fibrous layer is dense regular connective tissue – Inner osteogenic layer is composed of osteoblasts and osteoclasts – Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina – Secured to underlying bone by Sharpey’s fibers • Endosteum – delicate membrane covering internal surfaces of bone

Blood and Nerve Supply of Bone • Periosteal arteries – Supply periosteum • Nutrient arteries – Enter through nutrient foramen – Supplies compact bone of diaphysis & red marrow • Metaphyseal & epiphyseal aa – Supply red marrow & bone tissue of epiphyses

Bone Markings: Projections ( Sites of Muscle and Ligament Attachment) • • Tuberosity – rounded projection Crest – narrow, prominent ridge of bone Trochanter – large, blunt, irregular surface Line – narrow ridge of bone

Bone Markings: Projections ( Sites of Muscle and Ligament Attachment) • • Tubercle – small rounded projection Epicondyle – raised area above a condyle Spine – sharp, slender projection Process – any bony prominence

: Bone Markings Projections That Help to Form Joints • Head – bony expansion carried on a narrow neck • Facet – smooth, nearly flat articular surface • Condyle – rounded articular projection • Ramus – armlike bar of bone

Bone Markings: Depressions and Openings • • • Meatus – canal-like passageway Sinus – cavity within a bone Fossa – shallow, basinlike depression Groove – furrow Fissure – narrow, slitlike opening Foramen – round or oval opening through a bone

The Histologic Types: • • • Compact bone ( cortical) Spongy bone ( cancellous) Lamellar bone: regular – mature Woven bone: irregular – immature – fetus - fracture Osteoid Callus: fracture healing

: Compact Bone • Haversian system, system or osteon – the structural unit of compact bone – Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen – Haversian, or central canal – central channel containing blood vessels and nerves – Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

Compact Bone • Osteocytes – mature bone cells • Lacunae – small cavities in bone that contain osteocytes • Canaliculi – hairlike canals that connect lacunae to each other and the central canal

: Compact Bone

Spongy (cancellous) Bone Does not contain osteons. • trabeculae surrounding red marrow spaces •

Cell Types of Bone 4 types of cells in bone tissue • Osteoprogenitor cells: – Undifferentiated cells – Can divide become osteoblasts – Found in inner layer of periosteum and endosteum • Osteoblasts: – Form matrix & collagen fibers but can’t divide • Osteocytes: – Mature cells that no longer secrete matrix • Osteoclasts: – Huge cells from fused monocytes (WBC) – Function in bone resorption at surfaces such as endosteum

Bone Development Osteogenesis and ossification: • The process of bone tissue formation, which leads to: – The formation of the bony skeleton in embryos – Bone growth until early adulthood – Bone thickness, remodeling, and fracture repair

Bone Growth - Ossification • Cartilage template laid down. • Osteoblasts (bone building cells) located in Ossification Centers.

Bone Growth Ossification • Primary Ossification Center in diaphasis. • Secondary Ossification Centers in epiphisis.

Bone Growth - Ossification • Grow toward one another, cartilage remains between them. • As long as cartilage remains undamaged, growth can occur.

Formation of the Bony Skeleton • Begins at week 8 of embryo development • Intramembranous ossification – bone develops from a fibrous membrane • Endochondral ossification – bone forms by replacing hyaline cartilage

Endochondral Ossification • Begins in the second month of development • Uses hyaline cartilage “bones” as models for bone construction • Requires breakdown of hyaline cartilage prior to ossification

Stages of Endochondral Ossification • Formation of bone collar • Cavitation of the hyaline cartilage • Invasion of internal cavities by the periosteal bud, and spongy bone formation • Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses • Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates

Stages of Endochondral Ossification Secondary ossification center Epiphyseal blood vessel Deteriorating cartilage matrix Hyaline cartilage Spongy bone formation Primary ossification center Bone collar Articular cartilage Spongy bone Medullary cavity Epiphyseal plate cartilage Blood vessel of periosteal bud 1 Formation of bone collar around hyaline cartilage model. 2 Cavitation of the hyaline cartilage within the cartilage model. 3 Invasion of internal cavities by the periosteal bud and spongy bone formation. 4 Formation of the medullary cavity as ossification continues; appearance of secondary ossification centers in the epiphyses in preparation for stage 5. 5 Ossification of the epiphyses; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages

Long Bone Growth and Remodeling • Growth in length – cartilage continually grows and is replaced by bone • Remodeling – bone is resorbed and added by appositional growth

Bone Growth in Length • Epiphyseal plate or cartilage growth plate – Cartilage cells are produced by mitosis on epiphyseal side of plate – Cartilage cells are destroyed and replaced by bone on diaphyseal side of plate • Between ages 18 to 25, epiphyseal plates close – Cartilage cells stop dividing and bone replaces the cartilage (epiphyseal line) • Growth in length stops at age 25

Remodeling • Occurs all the time. • Stresses change, bones adapt. • Osteoclasts remove bone, Osteoblasts build bone, Osteocytes maintain bone • Mineral deposits in Spongy Bone form to hold the stress best. • 5 -10% bone / year.

Osteoclast in lacuna;

Control of Remodeling • Two control loops regulate bone remodeling – Hormonal mechanism maintains calcium homeostasis in the blood – Mechanical and gravitational forces acting on the skeleton

Developmental Aspects of Bones • The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms • At birth, most long bones are well ossified (except for their epiphyses) • By age 25, nearly all bones are completely ossified • In old age, bone resorption predominates

Fracture • A disruption in the integrity of a living bone involving injury to: – – Bone marrow Periosteum Adjacent soft tissues

Types of Fractures • green stick • fissured • comminuted • transverse • oblique • spiral • Pathologic • Stress • Occult

Fracture Healing – Bone is the only tissue in the human body other than liver that heals by regeneration instead of by scarring. – For regeneration to occur the bone must be immobilized to allow uninterrupted formation of new bone.

Fracture Healing • Primary healing – Non displaced fractures, fractures with compressive fixation across the fracture site – Osteoblasts traverse the fracture site and lay down lamellar bone without forming immature bone when there is direct contact between cortical bone ends • Secondary healing – No compression across fracture site, motion can occur – Fracture callus forms to stop motion, stage of consolidation and remodeling

Primary Bone Healing

Secondary Bone Healing ¬ ¬ ¬ Fracture hematoma (72 hours) Granulation tissue (3 -14 days) Callus formation (7 -14 days) Ossification (3 weeks- 6 months) Consolidation (3 weeks- 6 months) Remodeling (Up to 1 year)

Rickets • a generalized metabolic bone disorder • characterized by a failure of or delay in calcification of the cartilaginous growth plate in children whose epiphyses have not yet fused. • it is primarily a disease affecting endochondral calcification • manifests clinically and radiographically with widening and deformation of the metaphyseal regions of long bones

THE END