The Skeletal System:

IntroductionIntroduction

Joel M. Chavez, PhD Biology (Cand.)

Functions of the skeletal system

• Gives shape

• Supports the body’s weight

• Provides a system of levers & together with

muscles produces movementmuscles produces movement

• Protects soft body parts

Organization of skeletal tissues: On the basis of

function

Exoskeleton

Keratinized exoskeleton (epidermal)

Bony exoskeleton (dermal)

Skeleton

Endoskeleton

Bony endoskeleton

Cartilaginous endoskeleton

Notochord

Organization of skeletal tissue: On the basis of

position

Cranial Skeleton

Splanchnocranium

Chondrocranium

Dermatocranium

Skeleton

Dermatocranium

Postcranial Skeleton

Axial skeleton

Vertebral column

Notochord

Appendicular skeleton

Limbs

Girdle

Histology of the skeletal system

Connective tissue

• Fibrous connective tissue

• Loose connective tissue

• Mesenchyme

• Adipose

Skeletal system

• Cartilage

• Hyaline• Adipose

• Areolar

• Hematopoetic tissue

• Myeloid/lymphoid tissue

• Blood

• Cartilage

• Hyaline

• Elastic

• Fibrous

• Bone

• Hyaline

• Elastic

• Fibrous

• Bone

Histology of the skeletal system

Comparisons Bone Cartilage

Type of cells Osteocytes Chondrocytes

Matrix composition Calcium phosphate Chondroitin sulfate

Type of

vascularization

Vascular Avascular

Degree of structural

organization

Highly organized

into osteons/

Haversian systems

Usually less

organized

Surface covering Periosteum Perichondrium

Bone• Specialized connective tissue

• Osteocytes are either– Osteoblast – bone forming cells

– Osteoclast – bone removing cells

• Composed of calcium phosphate in the form of hydroxyapatite– Invertebrate skeleton is composed of calcium

phosphate (also known as aragonite or calcite)

• Only present in vertebrates• Only present in vertebrates

• Said to have evolved due to the need to deposit calcium, phosphate and other minerals to maintain proper metabolic functioning

• Grows throughout the lifetime of fishes, amphibians and reptiles

• Growth stops in birds and mammals when adult size is reached

Germ Layer Origins of the Skeleton

Neural crest

• Cartilage and bones

EctodermEpimere

• Parts of the brain

Mesoderm

• Cartilage and bones of the lower jaw

• Odontoblasts

• Parts of the brain case

• Vertebral column

Hypomere

• Limbs

• Pharyngeal arches

Classification of Bones

Based on embryonic

development

Endochondral

• Also known as

Based on visual Appearance

Cancellous or

Based on position

• Also known as replacement bones

Intramembranous

Cancellous or spongy

Compact bone

Cortical

Medullary

Introductory Embryology

Origin of the Germinal Layers

Human Development

Human Development

Early Embryonic Development

Early Embryonic Development

Early Embryonic Development

Early Embryonic Development

Germ Layer

Derivatives

Comparative Embryogenesis

Human Development

Human

Development