Skeletal System

Unit 6 Synopsis

The skeletal system is comprised of cartilage, ligaments, and tendons and serves as the structural foundation for the body. The skeletal system also serves as protection, storage, and the site of hematopoiesis.

Affixes and Roots

Brachi

Arm

Chondr-

cartilage

Cost(o)-

Rib

kyph-

bent or hunch

Oste(o)-

Bone

Inter-

between

-clast

break

cervic-

neck

crani(o)-

skull

vertebr-

vertebrae

-gen

creation of

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Primary Break Down of the Skeletal System

The human skeleton can first be divided into two major sections, the axial and appendicular skeleton. The axial skeleton runs along the axis (midline) of the body and is comprised of the skull, vertebral column and ribs. The appendicular skeleton branches off the axial and is comprised of the limbs and girdles.

Axial Skeleton

Appendicular Skeleton

Axial Skeleton Bones - Skull

Cranial Bones

Frontal

Temporal

Occipital

Parietal

Ethmoid

Sphenoid

Facial Bones

Lacrimal

Inferior conchae

Mandible

Maxilla

Nasal

Palatine

Vomer

Zygomatic

Ossicles (Middle Ear Bones)

Malleus

Incus

Stapes

Hyoid

Vertebrae

Cervical (7) - Atlas and Axis

Thoracic (12)

Lumbar

Sacrum

Coccyx

Axial Skeleton Bones - Thorax

Sternum

Ribs

True Ribs - attached to sternum, Ribs 1 - 7

False Ribs - costal cartilage does not directly articulate with the sternum; ribs 8-10

Floating Ribs - no ventral attachments; ribs 11-12

Appendicular Skeleton

Pectoral Girdle

Clavicle

Scapula

Upper Limb

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Pelvic Girdle

Ilium

Ishium

Pubis

Lower Limb

Femur

Patella

Tibia

Fibula

Tarsals

Metatarsals

Phalanges

Bone Classifications

All 206 bones in the body can be separated into 4 shape categories.

Types

Flat Bones

Thin, curved shaped bones
Serve as connection points for muscles
Protection of internal organs
Intramembranous ossification
E.g. Skull (cranial bones), sternum, scapulae, ribs

Short Bones

Cuboidal
Provide stability, support
Allows for some motion
Endochondral ossification
E.g. Carpals, tarsals

The patella is classified as a sesamoid bone (it is the only one ) that is small, round, and embedded in tendons. It serves to protect tendons from compressive forces.

Irregular

Complex
Protect internal organs
Highly specialized
E.g. Vertebrae, facial bones

Long

Cylindrical
Provides leverage, strength, structure
Endochondral ossifcation
E.g. femur, tibia, fibula, ulna, radius, metacarpals/tarsals, phalanges

Long Bone Anatomy

Epiphysis: ends of the long bone that is surrounded by articular cartilage and predominately made of spongy bone

Spongy bone contain buttresses called trabeculae that provide structure and support.

The epiphyseal line is where longitudinal growth will occur. .

Diaphysis: the center section of the bone, made predominately of compact bone.

The osteon is the functional unit of compact bone.

Lamella: the rings of the osteon

Haversian Canal: the center ring in the osteon that allows blood vessels and nerves to run through the bone

Lacunae: Little lakes that house osteocytes

Osteocytes: mature bone cells

Canaliculi: tunnels that connect lacunae and allow for communication between osteocytes

Periosteum: superficial tissue that surrounds the bone

Endosteum: lines the medullary cavity, superficial the marrow

Medullary Cavity: the space in which the bone marrow is found in the shaft of long bones

Bone Marrow

Adults have yellow bone marrow that acts as triglyceride storage.

Children have red bone marrow that acts as the site of hematopoiesis.

Functions of the Skeletal System

Bone Markings

Cells of the Skeletal System

Osteocytes

Mature bone cells ; greatest number of bone cells

Osteoclasts

Break down bone

Osteoblasts

Build up bone

Osteoprogenitor

Bone stem cells

Osteoclasts: break down bone
Osteoblast: build up bone
Osteoprogenitor: bone stem cell

Ossification

Endochondral

* Replaces hyaline cartilage

* In long bones

* Lengthening of long bones at the epiphyseal plate

Intramembranous

* Forms from mesenchyme

* In flat bone

Hormones - Calcium Regulation

PTH: signal to increase blood calcium levels, i.e. activate osteoclast to release calcium from bone

Calcitonin: signal to decrease blood calcium level, i.e. activate osteoblasts to build bone

Hematopoiesis

The formation of blood cells within bones.

Children require a high amount of blood cells to be produced, therefore they will have red bone marrow in comparison to adults that have yellow bone marrow that produce few blood cells.