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Skeletal System is composed of:
bone tissue
cartilage
dense connective tissue
blood
nervous tissue
The skeletal system is __________ and _________
Alive; multifunctional
support and protect softer tissues
movement
blood cell formation
mineral storage
Skeletal system is divided into?
Axial and Appendicular divisions
The adult skeleton has how many number of bones?
206
extra bones include: sutural (wormian) in sutures between major skull bones, small sesamoid bones in tendons (reduce friction), a vertebra
The axial skeleton includes
skull - cranium and facial bones
middle ear bones - move sound to receptors in inner ear
hyoid bone - supports tongue and is muscle attachment site
vertebral column - forms central axis of skeleton
thoracic cage - ribs and sternum, protects organs
TOTAL OF 80 BONES
The appendicular skeleton includes
pectoral girdle - scapula and clavicle, upper limb movement
upper limbs - humerus, radius, ulna, hand
pelvic girdle - hip bones, lower limb movement, forms pelvis
lower limbs - femur, tibia, fibula, patella, foot
TOTAL OF 126 BONES
Bones of the skeletal system vary greatly in these ways
Size and Shape
Bones are similar in these features
Structure, development, function
Long Bones
long and narrow
have expanded ends
short bones
cube-like, length = width
include sesamoid (round) bones, which are embedded in tendons
Flat Bones
plate-like with broad surfaces
Irregular Bones
variety of shapes
most are connected to several other bones
Parts of a Long Bone
epiphysis - expanded end
diaphysis - bone shaft
metaphysis - between diaphysis and epiphysis, widening part
articular cartilage - covers epiphysis
periosteum - encloses bone, dense connective tissue
compact (cortical) bone - wall of diaphysis
spongy (cancellous) bone - makes up epiphysis
trabeculae - branching bony plates, make up spongy bone
medullary cavity - hollow chamber in diaphysis, contains marrow
endosteum - lines spaces, cavity
bone marrow - red or yellow marrow, lines medullary cavity, spongy bone spaces
Osteocytes
mature bone cells
Lacunae
chambers occupied by osteocytes
Canaliculi
tiny passageways through which the cell processes of osteocytes exchange nutrients and wastes
Extracellular Matrix of bone contains
Collagen fibers - gives bone resilience
Inorganic salts - makes bone hard
Compact Bone
consists of cylindrical units = osteons
osteons and layers of matrix (lamellae) cluster around central canal in each osteon
strong and solid
weight-bearing
resists compression
Spongy Bone
consists of branching plates called trabeculae
somewhat flexible
has spaces between trabeculae that reduce the bone’s weight
Major Functions of Bones
provide shape to body - head, face, thorax, limbs
support body structures - bones of lower limbs, pelvis, vertebral column
protect body structures - skull bones protect brain, ears, eyes
aid body movements
contain tissue that produces blood cells
store inorganic salts
Hematopoiesis
blood cell formation
occurs in red bone marrow, includes production of RBC, WBC, platelets
yellow marrow stores fat
red marrow remains in adult skull, ribs, sternum, clavicles, vertebrae, hip bones
Most abundant sale is crystals of
hydroxyapatite (calcium phosphate)'
other salts include: magnesium ions, sodium ions, potassium ions, carbonate ions
Osteoporosis
condition that results from loss of bone mineralization
blood calcium level is regulated by parathyroid hormone and calcitonin
Bones form when bone tissue replaces existing connective tissue in one of two ways:
Intramembranous bones and endochondral bones
Blood calcium level is regulated by?
Parathyroid hormone and calcitonin
Intramembranous Ossification
flat skull bones, clavicles, sternum, and some facial bones
bones form between sheets of primitive connective tissue
Endochondral Ossification
long bones and most of skeleton
bones form from hyaline cartilage models
Osteogenesis Imperfecta
hereditary collagen defect, in which forming bones are brittle, and fetus may have many bone fractures
Process of Intramembranous Ossification
mesenchymal cells in primitive tissue differentiate into osteoblasts
osteoblasts: bone-forming cells that deposit bone matrix around themselves
when osteoblasts are completely surrounded by matrix, they are now osteocytes in lacunae
mesenchyme on outside forms periosteum
Process of Endochondral Ossification
begin as hyaline cartilage models
chondrocytes (cartilage cells) enlarge, lacunae grow
matrix breaks down, chondrocytes die
osteoblasts invade the area, deposit bone matrix
osteoblasts form spongy and then compact bone
once encased by matrix, osteoblasts are now osteocytes
Development of Endochondral Long Bones
Primary Ossification Center: area in center of diaphysis, where bone tissue first replaces cartilage
Secondary Ossification Center: area of the epiphyses, where spongy bone forms later in development
Epiphyseal Plate
band of cartilage that persists between the ossification centers
Growth at the Epiphyseal Plate
Zone of resting cartilage: layer closest to end of epiphysis, resting cells; anchor epiphyseal plate to epiphysis
Zone of proliferating cartilage: rows of young cells, undergoing mitosis
Zone of hypertrophic cartilage: rows of older cells left behind when new cells appear; thicken epiphyseal plate, lengthening the bone, matrix calcifies, cartilage cells die
Osteoclasts
break down calcified matrix
Osteoblasts
invade, replacing cartilage with bone tissue
Bone can thicken by depositing compact bone on outside under ______
periosteum
Bone Remodeling
occurs throughout life
Bone Resorption
removal of bone by osteoclasts
Bone Deposition
formation of bone by osteoblasts
Vitamin D
calcium absorption, deficiency causes rickets, osteomalacia
Vitamin A
osteoblast and osteoclast activity, deficiency retards bone development
Vitamin C
collagen synthesis, deficiency results in slender, fragile bones
Growth Hormone
stimulates cartilage cell division, insufficiency in a child can result in pituitary dwarfism, excess causes gigantism in child and acromegaly in adult
Thyroid Hormone
causes replacement of cartilage with bone in epiphyseal plate, osteoblast activity
Parathyroid Hormone (PTH)
stimulates osteoclasts, bone breakdown
Sex Hormones
promote bone formation, stimulate ossification of epiphyseal plates
Physical Stress
stimulates bone growth
Condyle
rounded process that usually articulates with another bone
Crest
narrow, ridge-like projection
Epicondyle
projection situated above a condyle
Facet
small, nearly flat surface
Fissure
cleft or groove
Fontanel
soft spot in the skill where membranes cover the space between bones
Foramen
opening through a bone that usually serves as a passageway for blood vessels, nerves, or ligaments
Fossa
relatively deep pit or depression
Fovea
tiny pit or depression
Head
enlargement on the end of a bone
Linea
narrow ridge
Meatus
tube-like passageway within a bone
Process
prominent projection on a bone
Ramus
branch or similar extension
Sinus
cavity within a bone
Spine
thorn-like projection
Sulcus
furrow or groove
Suture
interlocking line of union between bones
Trochanter
relatively large process
Tubercle
knob-like process
Tuberosity
knob-like process usually larger than a tubercle
The skull contains how many bones
22
Cranium = 8 bones to enclose and protect the brain
Facial Skeleton = 14 to form the shape of the face
Paranasal Sinuses
air filled cavities found in some cranial and facial bones
reduce weight of skull and increase intensity of voice
Vertebral Column
forms vertical axis of skeleton
consists of many vertebrae separated by cartilaginous intervertebral discs, connected by ligaments
supports head and trunk, permits several types of movements
protects spinal cord in vertebral canal
33 separate bones in infant, 26 in adult
4 Curvatures of Vertebral Column
Cervical (2ndary)
Thoracic (Primary)
Lumbar (2ndary)
Sacral (Primary)
Vertebral Column Consists of
7 cervical
12 thoracic
5 lumbar
5 fused sacral
4 fused coccygeal
Vertebral Body
drum-shaped, anterior portion
Vertebral Pedicles
stalks that project from body, form sides of vertebral foramen
Vertebral Laminae
plates that arise from pedicles, fuse to become spinous process
Spinous Process
posterior projection
Transverse Processes
lateral projections
Vertebral Formane
opening for spinal cord
Superior and Inferior Articular Processes
project upward and downward, to articulate with adjacent vertebrae
Facets
cartilage-covered articulating surfaces of articular processes
7 Cervical Vertebrae
found in neck region, smallest vertebrae
Transverse Foramina
openings for arteries leading to brain; only found on cervical vertebrae
Bifid spinous processes on C2 to C6
Atlas
C1, supports head, articulates with occipital condyles
Axis
C2, atlas pivots around the dens of axis
12 Thoracic Vertebrae
found in chest region, larger than cervical vertebrae, articulate with ribs, long/pointed spinous process/slopes downward
5 Lumbar Vertebrae
found in small of back, large bodies, weight-bearing, thick/short spinous processes/almost horizontal
Sacrum
triangular structure at base of vertebral column
typically 5 fused vertebrae
median sacral crest: fused spinous processes of vertebrae
posterior sacral foramina: openings for blood vessels and nerves
forms sacroiliac joints, which transmit body weight to legs
forms posterior wall of pelvic cavity
sacral promontory: projection at upper margin
sacral canal: formed by vertebral foramina
sacral hiatus: opening at inferior tip of sacrum
Coccyx
tailbone
usually 4 fused vertebrae
fuse between ages 25 and 30
Thoracic Cage
includes ribs, thoracic vertebrae, sternum, and costal cartilages that attach the ribs to the sternum
supports pectoral girdle and upper limbs
protects thoracic and upper abdominal viscera
role in breathing
Ribs
12 pairs of ribs
true ribs = vertebrosternal, 7 pairs, connect directly to the sternum
false ribs = 5 pairs
vertebrochondral ribs = upper 3 pairs, costal cartilages connect to cartilage 7
floating ribs = vertebral, lower 2 pairs, no connection to sternum
Structure of Rib
shaft: main portion, long and slender
head: posterior end, articulates with vertebrae
tubercle: articulates with vertebrae
costal cartilage: hyaline cartilage; connects rib to sternum
Sternum
along midline of anterior thoracic cag
3 parts:
manubrium: upper part
body: middle and largest part
xiphoid process: lower part
articulates with costal cartilages of ribs, and clavicles