Skeletal System: Functions and Types

• The skeletal system consists of bones, ligaments, and tendons
• The skeletal system provides support and protection for the body
• There are 206 bones in the human body

Functions of the Skeletal System

• Bones offer a solid axis, aiding muscles in generating motion
• Bones such as the skull provide a protective barrier against external forces
• Hematopoiesis refers to the production of red blood cells

Types of Skeletal Systems

• Hydrostatic, exoskeleton, and endoskeleton are the three basic types of skeletal systems in the animal kingdom

Hydrostatic Skeleton

• Earthworms and sea anemones have hydrostatic skeletons
• Circular muscles squeeze the body, longitudinal muscles shorten it

Exoskeleton

• Arthropods, like insects and spiders, possess external skeletons made of chitin, a carbohydrate
• Muscles are attached to the exoskeleton, which is flexible at the joints

Endoskeleton

• Vertebrates have an endoskeleton made of cartilage or bone, which are living connective tissues

Functions of the Endoskeleton

• The endoskeleton provides support and protection for the body
• Locomotion occurs in coordination with muscles
• Blood cells are produced in bone marrow
• Calcium and phosphorus are stored
• Energy stored in yellow marrow

Divisions of the Skeletal System

• The skeletal system is divided into two main parts: axial and appendicular

Axial Skeleton

• The axial skeleton is the central part that protects and supports vital organs

Appendicular Skeleton

• The appendicular skeleton is the skeleton of the extremities
• The axial skeleton consists of 80 bones
• Primary bones of the axial skeleton are the skull, spine, ribs, and sternum (thorax)

Parts of the Axial Skeleton

• The skull protects the brain
• The vertebrae protect the spinal cord and keeps the skeleton upright
• Ribs protect the lungs and heart, provides intercostal muscle to move for breathing

The Skull

• The skull consists of two sets of bones: cranium and facial bones
• Bones of the skull are joined by sutures
• The mandible is the only part of the skull attached by a freely movable joint

The Vertebral Column

• The vertebrae are separated by intervertebral discs
• The spine has a normal curvature
• Each vertebrae is named according to its location

The Bony Thorax

• The bony thorax forms a cage to protect major organs
• The bony thorax consists of the sternum, ribs, and thoracic vertebrae

Appendicular Skeleton

• Appendicular skeleton consists of 126 bones
• Major bones are the shoulder or pectoral girdle, arms, hands, pelvic girdle, legs, and feet

The Pectoral (Shoulder) Girdle

• The pectoral girdle is composed of two bones: the clavicle (collarbone) and the scapula (shoulder blade)
• The bones allow the upper limb to have exceptionally free movement

Bones of the Upper Limb

• The arm is formed by the humerus bone
• The forearm has two bones: ulna and radius
• The hand consists of carpals (wrist), metacarpals (palm), and phalanges (fingers)

Bones of the Pelvic Girdle

• The pelvic girdle consists of hip bones
• Hip bones are composed of three pairs of fused bones: ilium, ischium, and pubic bone
• The total weight of the upper body rests on the pelvis
• The pelvic girdle also protects reproductive organs, the urinary bladder, and part of the large intestine

The Pelvis

• Coxal bone or hip bone compromises the Ilium, Sacrum, Pubic bone and Ischium

Bones of the Lower Limbs

• The thigh has one bone, which is the femur

• The leg has two bones: tibia and fibula

• The foot consists of the Talus (ankle), Metatarsals and the Phalanges (toes)

• Bones are classified according to their shape

Compact Bone

• Bone tissue is classified according to its types, mainly in long bones
• Continuous extracellular matrix with no space
• Contains dense, concentric circles of osseous tissue
• Site of red blood cell formation in children

Spongy Bone

• Bone tissue is classified according to its types, mainly in short bones
• Contains small needle-like pieces of bone and many open spaces
• Site of red blood cell formation in adults and lightens bone

Functions of Bone Tissue

• Supports body tissues
• Protection of underlying organs
• Locomotion through skeletal muscles attached to bones
• Hematopoiesis, or blood cell formation
• All blood cells are formed in the red marrow of certain bones
• Energy storage occurs in the yellow marrow in the shaft of long bones

Classification of Bones: Long Bones

• Long bones are typically longer than they are wide
• Long bones have a shaft with heads at both ends
• Long bones contain mostly compact bone
• Examples include the femur (thigh bone) and humerus (arm bone)
• All the bones of the limbs are long bones (except the wrist and ankle)

Classification of Bones: Short bones

• Short bones are generally cube-shaped
• Short bones contain mostly spongy bone
• Examples: Carpals (wrist), tarsals (ankle)

Classification of Bones: Flat Bones

• Flat bones have thin layers of compact bone around a layer of spongy bone
• Flat bones are usually curved
• Examples: Skull, ribs, sternum (breastbone), scapula (shoulder blade)

Classification of Bones: Irregular Bones

• Irregular bones have irregular shapes
• Irregular bones do not fit into other bone classification categories
• Example: Vertebrae, hip, auditory ossicles

Classification of Bones: Sesamoid (Round) Bones

• Sesamoid bones are small and nodular
• Sesamoid bones are embedded within tendons adjacent to joints
• Example: kneecap (patella)

Parts of a Long Bone

• The diaphysis refers to the shaft of the long bone
• The epiphyses refers to the expanded ends of the long bone
• The epiphyseal plate is the area of hyaline cartilage causing lengthwise growth of a long bone at the junction of the epiphyses and diaphysis

Bone Structure - Gross Anatomy

• The outside covering of the bone is the periosteum
• Thin inner lining of the medullary cavity is the endosteum
• A hollowed central region is referred to as medullary cavity

Canaliculi

• Bone cells are called osteocytes
• Located in pockets called lacunae
• Found in between sheets of matrix called lamellae
• A repeating functional unit called the osteon or Haversian system
• Perforating canals allow for blood vessels in the central canals

Bone maintenance

• Bone is continually remodeled, reabsorption refers to breaking it down by osteoclasts and then reforming by osteoblasts. This slows down by age
• Bone matrix is formed by new bone production
• Osteoclasts help maintain/clean out old bone tissue

Joints

• A joint is a place where two or more bones connect
• A synarthrosis is a joint that allows no movement
• A amphiarthrosis is a joint that allows slight movement
• A diarthrosis is a joint that allows free movement in a variety of directions

Forensic Anthropology

• Most will say that sex from skeleton cannot be exactly know from a skeleton
• Pelvis followed by mandible is probably most reliable feature to analyze

Factors Affecting Bone Development, Growth and Repair

• A deficiency of Vitamin A will retard bone development
• A deficiency of Vitamin C – results in fragile bones
• A deficiency of Vitamin D will cause rickets, and osteomalacia
• Insufficient Growth Hormone will cause dwarfism and Excessive Growth Hormone will cause gigantism, acromegaly
• Insufficient Thyroid Hormone will delay bone growth
• Sex Hormones promote bone formation and stimulate ossification of epiphyseal plates
• Physical Stress stimulates bone growth

Lifespan changes

• Decrease in height at about age 30
• Calcium levels fall and Bones become brittle
• Osteoclasts outnumber osteoblasts
• Spongy bone weakens before compact bone
• Bone loss rapid in menopausal women
• Hip fractures and Vertebral compression fractures are more common

Fractures: Simple Fracture

• Also called closed fracture
• Bone breaks cleanly and does not penetrate the skin
• There is little chance of infection

Fractures: Compound Fracture

• Bone breaks completely and protrudes through the skin
• There is a major chance of bone infection

Fractures: Comminuted Fracture

• Bone breaks into many fragments
• Common in elderly

Fractures: Compression Fracture

• Bone is crushed
• Common in porous bones
• Especially common in vertebrae of osteoporosis patients

Fractures: Depression fracture

• Broken bones are forced inward
• Common in skull fractures

Fractures: Impacted Fracture

• Broken bone ends are forced into each other
• Common in falls

Internal Bone Repair

• Hematoma forms from ruptured blood vessels
• Fibrocartillage callus "splints" broken bone using cartilage and bony matrix
• Osteoblasts migrate to area, forming bone "patch” over break and the fibrocartilage is replaced by bony callus

Skeleton Differences in Male vs Female

• Larger skeleton with thicker bones in Males
• In Female bones maintain many characteristics of Prepubescent skeleton
• In Males puberty changes mostly in muscular attachments

Skeleton Differences: Skull

• Male mastoid process more pronounce
• Superior portion of female orbital (brow ridge) less pronounced
• Female mandible is pointed. While Males is squared

Skeleton Differences: Pelvis

• Female Pelvis wider and more shallow
• Male iliac crests more pointed
• Male pelvis more narrow