The Skeletal System Learning Objectives 1. Define the skeletal system (composition) 2. Discuss the functions of the skeletal system 3. Discuss bone growth and bone formation 4. Discuss divisions of the skeletal system 5. Discuss bones, their classification, function, types and structure 6. Discuss the different types of joints About the Skeletal System Bony framework of the body It enables us to stand up, move in our environment and do a lot of things like athletics and everyday physical work. It forms body cavities that protects vital body structures Forms joints Act as points of attachment for muscles. Dead as they seem, bones are made of living tissue, the bone tissue It is closely associated with the muscular system Made up of bones, cartilages, ligaments, tendons and other connective tissue that stabilize or connect the bones. BONES There are 206 bones in the adult body Functions of the Skeletal System The skeleton: Supports and stabilizes surrounding tissues like muscles, blood and lymphatic vessels, nerves, fat and skin Support the body weight Protects vital organs of the body like the brain, lungs, heart, spinal cord etc.. Bones work together with muscles to maintain body position and to produce controlled, precise body movements Functions of the Skeletal System It manufactures blood cells. This process of blood cell production is called Hematopoiesis and takes place in the bone marrow. It stores mineral salts especially phosphorus and calcium and fats. Bones contain large amounts of calcium than any other organ When there is a decrease in calcium levels (below normal) in the blood, calcium is released from the bones so that there will be an adequate supply for metabolic needs. When blood calcium levels are increased, the excess calcium is stored in the bone matrix Bone Growth and Bone Formation Infant skeleton is completely formed by three months of pregnancy. But at this stage, the skeleton is mainly cartilage. As pregnancy progresses, ossification (bone formation by the immature cells of the bone tissue) and growth starts to happen Bone ossification occurs when osteoblasts starts invade the cartilage to form bones. Cartilage is the environment in which bone develop The mineral salts (calcium & phosphorus) deposited in the bone matrix are responsible for its amazing strength. Bone Formation (Ossification) Osteoblasts are responsible for formation of bones. Osteoblasts are formed beneath the membrane that covers the bone called the periosteum Bones are completely grown at around the age of 15 for girls and 15 for boys. There after the bones continue to mature until 21 years for both male and female. After maturity the bone continues to undergo the process of remodeling by depositing bone tissue. (Rizzo, 2010) Bone Formation (Ossification) Bone deposition is when calcium phosphate gets deposited on the bones. Bone deposition happens all the time but it slows down as we age. Deposition of bone is dependent on the amount of strain or pressure on the bone. The more strain, the greater the deposition of the bone. E.g. the heel bone )calcaneum is the strongest bone and it is large because it bears the entire body weight during walking. A break in a bone will stimulate injured osteocytes (mature cells) to proliferate/ multiply & secrete large amounts of matrix to form new bone There is another type of one cells called osteoclasts. These cells are responsible for bone reabsorption They remove bone from the inner side during remodeling e.g. when a bone is broken (Rizzo, 2010) Bone Cells Types of Ossification Types of Ossification They are of two types: Intramembranous ossification Layers of the bone are replaced by deposits of inorganic calcium salts forming the bone Endochondral Ossification The process in which cartilage is the environment in which the bone cells develop Both ossifications result in compact and cancellous/ spongy bone Maintaining Bone Calcium levels in the blood and the amount stored in the bones must be at normal set points. These levels are controlled by the endocrine system. There are two hormones responsible for ensuring normal calcium concentrations in the body: Calcitonin – causes calcium to be stored in bones if it is in large amounts in the blood Parathormone- causes calcium to be released into the blood stream when there is low blood calcium levels in the body. Functions of Bones Provide a framework of the body Provide structural support for the entire body Provide a framework for the attachment of muscles and tendons Store minerals and lipids — Calcium storage and store energy reserves as lipids in areas filled with yellow marrow. Produce red and white blood cells in the red marrow which fills the internal cavities of many bones (haemopoiesis). Protect body organs Provide movement — Many bones function as levers that can change the magnitude and direction of the forces generated by muscles Divisions of the Skeleton 1. Axial skeleton Made up of the skull, vertebral column, sternum and ribs. 80 bones in total 2. Appendicular skeleton Made up of the shoulder girdles, upper limbs, pelvic girdle and lower limbs Axial Skeleton Appendicular Skeleton Bone Classification Based on Shape Classified as: 1. Long- have a shaft & two extremities; bear weight 2. Short – bear weight 3. Irregular – e.g. vertebra 4. Flat – thin and usually curved; protect the brain and thoracic organs 5. Sesamoid – Small and round e.g. patella NB: Short, irregular, flat and sesamoid bone do not have shafts or extremities Bone Classification General Structure of a Long Bone It has a diaphysis/ shaft Made up of compact bone with a medullary canal Medullary canal contains fatty yellow bone marrow It has two epiphyses/ extremities Its outer covering is a compact bone with spongy bone inside Epiphyses and diaphysis are separated by epiphyseal cartilages Long Bone Structure cont…… It has a vascular membrane covering called the periosteum Periosteum : covers the entire bone except within joint cavities Allows attachment of tendons and continues with the joint capsule It has two layers: 1. Outer layer – strong and fibrous for protecting the bone under it 2. Inner layer – contains osteoblasts and osteoclasts (these cells are responsible for bone breaking and bone formation); important in repair and remodeling of the bone Blood and Nerve Supply of Bones Blood is supplied by nutrient arteries Nerves enter on the same site as nutrient arteries and branches to cover the entire bone. Cells of a Bone Tissue /Osseous Tissue Four types of bone cells: Osteogenic cells (unspecialized stem cells) They undergo cell division, resulting in the formation of osteoblasts Osteoblasts (bone building cells)- immature cells Secrete osteoid and collagen fibres, initiate calcification & differentiate (become specialized) into osteocytes Osteocytes (mature bone cells within the matrix) –mature cells Responsible for metabolism within the bone; they monitor and maintain bone tissue. Osteoclasts (large multinucleated phagocytic cells) Responsible for bone resorption in order to maintain its normal shape. They do this by secreting hydrochloric acid (HCL) to dissolve mineral salts; while lysosomal enzymes dissolve the organic matrix. Osseous tissue = bone tissue Osseous tissue is made of bone cells and the extracellular matrix. The extracellular matrix is made of 55% crystalised mineral salts (mainly phosphates and calcium salts plus some potassium, magnesium, sulphate & flouride) and 30% collagen fibres, 15% water. Bone Matrix Bone matrix: Intercellular substance of the bone tissue. Synthesized by osteoblasts Consists of collagen fibres and inorganic salts Collagen is very strong and forms part of bone, cartilage, skin and tendons. Collagen also gives bone its flexibility, without it, bone becomes brittle. Extracellular matrix a collection of molecules outside the cells and secreted by cells. Responsible for giving structural and biochemical support to the surrounding cells. Types of Bones Two major types of bones: 1. Compact/ dense 2. Spongy/ cancellous/ trabecular Compact Bone Makes up 80% of the body bone mass Located beneath the periosteum It’s the major part of the diaphysis. Made up of osteons/ harversian system (parallel tube shaped units parallel to the diaphysis- this arrangement gives bone more strength). Each osteon has a concentric lamella (rings of bones) and a harvesian/ central canal Between the lamella are cavities called lacunae which contain tissue fluid with osteocytes suspended in it. This tissue fluid is responsible for bathing, providing nourishment and taking out waste materials from the osteocytes to keep them healthy and alive. The central canal consists of blood vessels, lymphatics and nerves Osteocytes are located in small spaces called lacuna in between the lamellae Spongy/ Cancellous Bone Lighter than compact bone Located in ends of long bones & forms the center of all other bones It is a site for red bone marrow and haemopoiesis Commonly found in the interior of short, sesamoid, flat and irregularly shaped bones. Lamellae are irregular, forming trabeculae (little beams) Trabeculae provide strength to the spongy bone Strategically located along the lines of stress for structural support Gross Anatomy of the long Bone Divisions of the Skeleton 1. Axial skeleton Made up of the skull, vertebral column, sternum and ribs. 2. Appendicular skeleton Made up of the shoulder girdles, upper limbs, pelvic girdle and lower limbs AXIAL SKELETON The Skull Consists of a total of 22 bones (cranial and the facial bones). The cranium Made up of flat and irregular bones Protects delicate tissues of the brain Joints between bones (sutures) are immovable Formed by fusion of 8 bones namely; 1 Frontal 2 Parietal 2 Temporal 1 Occipital 1 Sphenoid 1 Ethmoid The Skull Facial bones The 13 facial bones include: 2 nasal bones 1maxilla 2 lacrimal bones 1mandible 2 zygomatic bones (cheek bones) 2 palatine bones 2 inferior nasal conchae and 1Vomer Features of the Skull It has: 1. Sutures 2. Fontanels spaces between skull bones in an infant or fetus where ossification is not yet complete and sutures not fully formed 3. Paranasal sinuses 4. Foramena 1. Sutures Bones of the skull are held together by seam lines or stitches called sutures. Immovable joints found only between the major skull bones namely: i). Coronal suture Found between the frontal bone and the two parietal bones ii). Sagittal suture ; between the two parietal bones iii). Lambdoidal suture; between the parietal bones and occipital bone iv). Squamosal suture; between the parietal bones and the temporal bones 2. Fontanels During early development, the embryonic skull consists mainly of cartilaginous structures in the shape of bones. This cartilaginous material hardens/ossifies with age to become a bone. At the time of birth there are six remaining unossified membrane filled soft spots found between sutures called fontanels. They close when a baby is about 9-18 months Paranasal sinuses Paranasal means near the nose They are mucus lined air-filled spaces in the bones around the nose leading from air cavities. They are continuous with the nasal lining. Named according to the 4 skull bones to which they are attached being the: Frontal sinuses- above the eyes Ethmoidal sinuses – between the eyes Sphenoidal sinuses - behind the eyes maxillary sinuses- under the eyes Function of Paranasal Sinuses Humidify and warm inspired air Lightens the skull For resonance Shock absorption Regulate intranasal pressure 4. Foramena of the skull Openings through which nerves, blood vessels and lymphatic vessels pass through. The Vertebral Column Also called the spine, constitute about 40 % of the total body weight. A flexible curved structure composed of 26 irregular bones called vertebrae. The vertebrae are separated by intervertebral discs which is a fibrocartilage which acts as shock absorber/ cushion between the vertebrae. The curves of the vertebrae form an S-shape which provides strength and maintain body balance in the upright position. It has hole/ space called the vertebral foramen for passage of the spinal cord Around this foramen/ hole are three extensions called processes which acts as points of attachment for muscles It also has two pedicles which are passage ways for spinal verves to and from the spinal cord. Divisions of the Vertebral Column The vertebral column is divided into 5 distinct regions: 1) the cervical 2) the thoracic 3) the lumbar 4) the sacrum and 5) coccyx. Regions of the Vertebral Column The Cervical Region Consists of the first 7 vertebrae [ C1-C7] they are the smallest vertebrae. The first cervical vertebra (C1) is a ring of bone supporting the head and is called the atlas. The atlas supports the head by articulating with the occipital bone The second cervical vertebra (C2) is called the axis. The axis acts as a pivot to allow the rotational movement of the atlas. Thoracic Region (T1- T12) Larger &stronger than the cervical vertebrae Provide facets/ points of attachments for the ribs. Thoracic Spine (T1- T12) Lumbar region (L1-L5) They are the largest and strongest vertebrae to sustain the weight of the body. They have characteristic triangular shaped vertebral foramena. Sacrum and coccyx The sacrum is a triangular shaped bone formed from fusion of five sacral vertebrae at the age of 16 to 18 years. It articulates superiorly with L5, inferiorly with the coccyx. The sternum Also known as the breastbone, located in the medial line of the anterior thoracic wall. Formed from the fusion of 3 bones; the manubrium , the body and the cartilaginous xiphoid process which ossifies at about 40 years. The diaphragm and the rectus abdominis muscle attach to the xiphoid Ribs Twelve pairs of ribs which make up the thoracic cavity. They posteriorly articulate with the thoracic vertebra. The upper seven articulate/ attach directly to the sternum and are called true ribs. The lower five are called false ribs because they do not articulate directly with the sternum The 2 last ‘false’ ribs (11 & 12) are called floating ribs because they have no cartilage and do not attach anteriorly THE APPENDICULAR SKELETON The Pectoral / Shoulder Girdle Made up of the scapula and the clavicle which along with their muscles form the shoulders which attach the upper limps to the axial skeleton. Anteriorly the clavicle (collar bone) joins the sternum and the scapula laterally. The clavicles are the first bones in the body to undergo ossification. Bones of the upper limbs Include the bones of the arm, fore arm, wrist and hand. Each of the limps consists of 30 bones being; the humerus, the radius, ulna, 8 carpals, 5 metacarpals and 14 phalanges The Humerus Longest bone of the upper extremity, which proximally articulates with the scapula and distally with the radius and ulna. The distal end of the humerus provides projections, the medial and lateral epicondyles for attachment of muscles of the forearm. Radius and the Ulna Two parallel bones forming the bones of the forearm. The radius is located lateral to the ulna and articulates proximally with the humerus and to the ulna at the radial notch. The radius has a radial head, neck and a projection for attachment of the tendons of the brachii muscle. The ulna is longer than the radius and forms the elbow joint with the humerus. Carpals, Metacarpals and Phalanges Bones of the wrist, the palm and the digits make up a total of 27 bones of the hand. Bones of the wrist are called carpals 5 metacarpals make up the palm of the hand Each finger except the thumb has 3 phalanges with the thumb having only two. The phalanges are arranged in rows; proximal, middle and distal rows. Each phalanx has a proximal base, a shaft and a distal head. The pelvic girdle/hip bone The pelvic girdle supports the trunk and provides attachment for the legs. Made up of two hip/ coxal bones united anteriorly at the pubic symphysis pubis and posteriorly to the sacrum. The ring of bone is called the pelvis Each coxal bone is a result of fusion of 3 bones during development, the larger and superior ilium, the posterior ischium and the anterior pubis. Lower limps A total of 60 bones which make up the thigh (femur), leg (fibula and tibia), the foot (tarsals, metatarsals) and the toes (phalanges). Generally stronger than those of the upper limps to sustain the body weight. The femur The longest and strongest bone in the body extensively covered with muscles. It has a head with a central pit called fovea capitis, neck and a long shaft (body). Tibia and fibula Bones of the leg transmitting the weight of the body from the femur to the foot in a standing position. The tibia or shin bone is the largest of the two and is medially located bone of the leg. The fibula AKA calf bone is thinner and lighter than the tibia. It lies lateral to the tibia; does not attach to the femur but articulate with the proximal end of the tibia. Tarsals, Metatarsals and Phalanges These constitute a total of 26 bones of the foot, seven tarsals, five metatarsal bones and 14 phalanges. The tarsals or ankle bones correspond to the carpals of the hand. Metatarsals are numbered I to V from the medial to the lateral one. Each metatarsal has a proximal base, a shaft and a distal head. Metatarsal I is the thickest and shortest, II is the longest. Each digit of the foot has 3 phalanges except the first digit (hallux) which possesses two. Each phalanx has a head, shaft and a base. JOINTS Point of articulation of two or more bones or cartilage and bone. An articulation is a junction between two o more bones despite of the amount of movement allowed by this union/ junction. Some joints allow too much movement while some allow very little to no movement Joints permit growth and movement They can be either movable or immovable and are classified according to their function and structure. Parts of bones which are in contact are always covered by hyaline cartilage 3 Major Joint Classifications There are 3 major groups of joints. These are classified in terms of the degree of movement they allow (function) & the type of material that holds the bones of the joints together (structure). 1. 2. 3. Fibrous joints connect bones with a tough fibrous material Cartilaginous joints Joints formed by a cartilage which acts a shock absorber Synovial joints There is a space between the connecting bones filled with a synovial fluid. Fibrous Joints Bones are joined together by a fibrous tissue with limited or no movement. No synovial cavity. There are three types: a). Sutures b). Syndesmosis immovable joint where bones are connected by connective tissue e.g. tibia & fibula c). Gomphosis A.K.A dental- alveolar joint Binds the teeth to bony sockets in the maxilla and mandible Cartilaginous Joints Bones are held together by cartilage e.g. vertebral bones. Also have no synovial cavity. Limited or no movement at all. Two types: a). Synchondroses- joint formed by hyaline cartilage b). Symphysis – joint by fibrocartilage Synovial Joints Characterised by a space (synovial cavity) filled with synovial fluid between the articulating bones. Examples include, shoulder joint Classified according to: the type of movement they allow or the shape of the articulating surfaces. Types of Synovial Joints 1. Ball and Socket 2. 3. Allows a wide range of movements which include flexion, extension, adduction, abduction, rotation and circumduction. E.g. shoulder and hip joints Hinge Articulating bones form a hinge-like arrangement like a hinge on a door. Movement is restricted to flection and extension e.g. elbow, knee, ankle and between the phalanges Gliding The connecting bones are flat and slightly curved in shape; they glide over one another; movement very restricted The least movable synovial joints e.g. joint between the wrist and carpal bones, tarsal bones of the feet and between spinal vertebral bodies Types of Synovial Joints cont… 4. Condyloid/ Ellipsoidal Condyle is a smooth, rounded projection on a bone. In this joint, the condyle sits in a cups-shaped cavity on the other bone it connects with. E.g. joint between the mandible and the temporal bone; between the metacarpals and phalanges of the hand and between metatarsal and phalanges of the feet Movements include flexion, extension, abduction, adduction and circumduction 5. Saddle The joining bones fit like a man sitting on a saddle. E.g. base of the thumb Movements same as of condyloid joints Synovial Joints Cont….. 6. Pivot Joint Allows the bone and limb to rotate e.g. radio-alnar joint ; atlas and axis joint Synovial Fluid Provides nutrients to the structures within the joint cavity Contains phagocytes to remove microbes and cellular waste materials Lubricate synovial joints Maintains joint stability Cushion joints to prevent friction Main Synovial Joints of the Limbs Shoulder joint Elbow joint Proximal and distal radioulnar joints Wrist joints Hip joint Joints of hands and fingers Knee joint Ankle joint Skeletal Movements Skeletal Movements References Tortora G.J., Grabowski S.R.,(2001). Introduction to the Human Body; The Essentials of Anatomy and Physiology. Von Hoffmann Press, Inc. New York, USA 2. Marieb E.N., Essentials of Anatomy and Physiology. Pearson. 10th edition, USA Rizzo, D.C. (2010). Fundamentals of Anatomy and Physiology, (3rd ed.). Delmar, Cengage Learning. Clifton Park, NY. The end… Questions???????????? ?
