Functions and structure of skeletal system

Support

Provides structure and stability to the body

Protection

Shields internal organs from injury or damage

Muscle Attachment

Provides surfaces for muscles to attach and facilitate movement

Hematopoiesis

Process of producing red blood cells, white blood cells, and platelets

Red Bone Marrow

Location where hematopoiesis occurs

Triglyceride Storage

Stores fats as a potential energy reserve

Yellow Bone Marrow

Location where triglycerides are stored

Mineral Homeostasis

Maintains critical mineral balances in the body

Calcium Regulation Feedback Loop

Feedback mechanism to maintain stable levels of calcium ions

Calcitonin

Hormone that causes bones to store calcium, lowering blood levels

Parathyroid Hormone (PTH)

Hormone that causes bones to release calcium, raising blood levels

Axial Skeleton

Consists of the skull, vertebral column, and thoracic cage

Appendicular Skeleton

Consists of the body's limbs and the structures they connect to

Long Bones

Bones that are longer than they are wide

Short Bones

Bones that are as long as they are wide

Flat Bones

Thin and wide bones that surround and protect organs

Irregular Bones

Complexly shaped bones that do not fit into other categories

Cranium

Bones that surround and protect the brain

Facial Bones

Bones that form the structure of the face

Cranial Sutures

Fixed joints connecting the bones of the skull

Process

Projection or outgrowth of tissue from a larger body

Condyle

Process that forms an articulation (joint) with another bone

Mastoid Process

Process on the posterior of the temporal bone behind the ear

Styloid Process

Process on the inferior temporal bone, attachment for muscles

Mandibular Condyle

Location where the mandible articulates with the temporal bone

Occipital Condyle

Location where the skull articulates with the vertebrae

External Auditory Meatus

Passage to the ear canal

Zygomatic Arch

Forms the cheekbone

Foramen

Natural hole in a bone for the passage of nerves, arteries, and/or veins

Foramen Magnum

Large hole at the base of the skull where the spinal cord connects to the brain

Carotid Foramen

Passage for the carotid artery (carries blood to the brain)

Jugular Foramen

Passage for the jugular vein (carries blood away from the brain)

Auditory Ossicles

Three small bones in each middle ear: malleus, incus, and stapes

Hyoid Bone

U-shaped bone with no direct attachments, elevates the larynx

Vertebral Column

Central axis of the skeleton, consists of 26 individual bones

Cervical Vertebrae

Vertebrae in the neck region
Atlas (C1)
Holds the head
"Yes" motion
Tilt side to side
Axis (C2)
Rotation around the Dens
"No" motion

Thoracic Vertebrae

Vertebrae in the chest region
Long, thin processes
Extra facet where they articulate (connect) with the ribs

Lumbar Vertebrae

Vertebrae in the lower back region (L1-5)
Large, thick bodies to carry a large amount of weight
Most common area for ruptured intervertebral disks

Sacrum

Is formed by 5 fused sacral vertebrae

Coccyx

Is formed by approximately 4 fused vertebrae, makes up tailbone

Spinal Curvature

Changes in the curvature of the spine throughout life
( - Thoracic → primary curves
) - Cervical → develop over time

Thoracic Cage

Consists of the thoracic vertebrae, ribs, and sternum
Protection of vital organs within the thorax
Prevents collapse of thorax during respiration

True Ribs

Ribs that attach directly to the sternum by cartilage

False Ribs

Ribs that do not attach directly to the sternum through cartilage

Floating Ribs

Ribs that do not attach to the sternum at all

Sternum

Breastbone divided into three parts: manubrium, body, and xiphoid
Allows medical professionals to count ribs

Pectoral Girdle

Attaches the bones of the upper limb to the axial skeleton

Clavicle

S-shaped bone that connects to the scapula and sternum, creates the anterior portion of the pectoral girdle

Scapula

Flat bone that protects organs and serves as an attachment for muscles, creates the posterior of the pectoral girdle

Humerus

Longest and largest bone of the upper limb
Connects proximally with the scapula, and distally with the ulna and radius
Called funny bones

Ulna (pinky side)

Bone in the forearm, longer and medial

Radius (thumb side)

Bone in the forearm, shorter and lateral
Unique disc-shaped head on the proximal end

Carpals

Eight bones in each wrist
each with unique shapes and names

Metacarpals

Five bones of the hand
numbered 1-5 beginning at thumb

Phalanges

Bones of the fingers and toes, except for thumb

Pelvic Girdle

Hip bone made up of the ilium (Largest component, superior,
Iliac crest forms "hip bone"), ischium (Inferior, posterior,
Ischial tuberosity forms "butt bone"), and pubis (Interior, anterior, pubes connect at the pubic symphysis)

Patella

Kneecap, protects the knee joint

Tibia

Shin bone, larger and medial, weight bearing

Fibula

Bone in the lower leg, smaller and lateral, helps stabilize the ankle joint

Tarsals

Seven bones in each ankle, forms the heel and is named calcaneus

Metatarsals

Five bones of the foot

Bone Tissues

Compact bone and spongy bone

Compact Bone

Strongest form of bone tissue, provides protection and support, Arranged into repeating structural units called osteons

Spongy Bone

Bone tissue with an irregular lattice structure, contains red bone marrow, Does not contain osteons, instead it consists of lamellae

Ligaments

Strong connective tissue that attaches bones to other bones

Tendons

Connective tissue that attaches muscles to bones

Intramembranous Ossification

Method of bone formation for flat bones of the skull

Endochondral Ossification

Method of bone formation for long bones

Bone Growth

Increase in bone size and length, grown during infancy, childhood, and adolescence

Epiphyseal Plate

Plate of cartilage where bone grows in length

Bone Resorption

Breaking down or removal of bone tissue by osteoclasts

Bone Deposition

Building of new bone tissue by osteoblasts

Bone Fracture

Any break in a bone according to their severity, shape, or position of fracture line, or the physician who first described them

Hematoma Formation

Formation of a blood clot at the site of a bone fracture

Soft Callus Formation

Formation of a mass of soft cartilage that bridges the broken ends of a bone

Bony Callus Formation

Conversion of cartilage to spongy bone, creating a bony callus

Bone Remodeling

Replacement of old bone tissue with new bone tissue

Exercise and Bone Tissue

Mechanical stress on bones leads to increased strength and thickness

Aging and Bone Tissue

Loss of bone mass and increased brittleness with age

Diaphysis

bone shaft or body, main portion of the bone

Epiphysis

enlarged area on either end of the bone

Metaphysis

Region between each epiphysis and the diaphysis

Articular cartilage

thin layer that covers the part of the epiphysis that forms an articulation with another bone, reduces friction, absorbs shock

Periosteum

layer of dense connective tissue that surrounds bone surface

Medullary (marrow) cavity

hollow space within the diaphysis (contains yellow marrow)

Endosteum

thin membrane that lines the internal bone surface of medullary cavity

Epiphyseal (growth) plate

within the metaphysis, where bone grows in length until age 18-21, when it is replaced by bone, leaving the epiphyseal line

Osteogenic cell

unspecialized stem cells, only bone cells that divide, found in periosteum and endosteum

Osteoblast

bone-building cells, become osteocytes

Osteocyte

mature bone cells, main cell in bone tissue

Osteoclast

bone-breaking cells, created from fusion of white blood cells, found in endosteum

Elongation

occurs at the epiphyseal (growth) plate
Zone of resisting cartilage - anchors epiphyseal plate to the epiphysis
Proliferating cartilage - cells here divide and secrete bone matrix
Hypertrophic cartilage - layer of large maturing cells elongates diaphysis
Calcified cartilage - where osteoclasts dissolve calcified matrix, new bony matrix

appositional growth

Occurs in the periosteum and endosteum
Periosteum - osteogenic cells differentiate into osteoblasts which secrete bone matrix and get trapped, becoming osteo cycles and create new compact bone tissue
Endosteum - osteoclasts destroy bone tissues, lining the medullary cavity, allows cavity to enlarge, increasing bone thickness

Osteon - Central (haversian) canal

Lamellae - calcified rings
Lacunae - small spaces in lamellae
Osteocytes - inside lacunae
Canaliculi - small channels filled with extracellular fluid

[Bone remodeling] Activation

pre-osteoclasts are attracted to the remodeling sites and fuse to form multinucleated osteoclasts

[Bone remodeling] Resorption

osteoclasts dig out a cavity (resorption, pit), releasing calcium

[Bone remodeling] Reversal

osteogenic cells (mesenchymal stem cells) appear along the pit

[Bone remodeling] Formation

mature osteoblast release osteoid, forming new matrix, which is mineralized with calcium and phosphate

[Bone remodeling] Quiescence

resting state, cells remain dormant until the next cycle

Factors that affect bone growth and remodeling

Minerals - bone formation requires a large amount of Calcium and Phosphorus, which can be obtained through dietary intake

Vitamins - vitamin A stimulates osteoblast activity, vitamin C is needed for collagen formation (matrix), vitamin D increases absorption of Calcium from the gastrointestinal tract

Hormones - during childhood, human growth hormones stimulate osteoblasts to promote cell division at the epiphyseal plate, then at puberty, estrogens increase osteoblast activity resulting in "growth spurts" and the changes in bone structures between genders