Skeletal System

Jaycris C. Agnes
BSED- Biological Science
Skeletal System
Jaycris C. Agnes , 2013

Learning Objectives:
At the end of the discussion the students must be able to:
 Enumerate the major roles of skeletal system
and its parts,
 Explain the process of bone formation,
remodelling, repair and aging; and
 Acclaim the roles of skeletal system to
human survival.

Topic Outline:
I. Function of Skeletal System
A. Bones
B. Cartilages
C. Tendons and Ligaments
D. Joints
II. General Features of Bone
A. Parts of Bone
B. Bone Cells
D. Bone Surface Markings
E. Bone Ossification, Remodelling and Repair
F. Types of Bones

Topic Outline:
III. General Consideration of Bone Anatomy
A. Division of Human Skeleton
IV. Bone and Calcium Homeostasis
V. Articulation
VI. Effects of Aging on the Skeletal System

Functions of the Skeletal System
 Bone
 Mechanical
 Protection — bones can serve to protect
internal organs, such as the skull protecting
the brain or the ribs protecting
the heart and lungs.
 Structure — bones provide a frame to keep
the body supported.

 Movement — bones, skeletal
muscles, tendons, ligaments and joints functi
on together to generate and transfer forces
so that individual body parts or the whole
body can be manipulated in three-
dimensional space. The interaction between
bone and muscle is studied in biomechanics.
 Sound transduction — bones are important
in the mechanical aspect of
overshadowed hearing.

 Synthetic
 Blood production — the marrow, located
within the medullary cavity of long bones and
interstices of cancellous bone, produces
blood cells in a process called
hematopoiesis.

 Metabolic
 Mineral storage — bones act as reserves of
minerals important for the body, most
notably calcium and phosphorus.
 Growth factor storage — mineralized bone
matrix stores important growth factors such
as insulin-like growth factors, transforming
growth factor, bone morphogenetic
proteins and others.

 Fat storage — the yellow bone marrow acts
as a storage reserve of fatty acids.
 Acid-base balance — bone buffers the
blood against excessive pH changes by
absorbing or releasing alkaline salts.
 Detoxification — bone tissues can also
store heavy metals and other foreign
elements, removing them from the blood and
reducing their effects on other tissues. These
can later be gradually released for excretion.

 Endocrine organ — bone
controls phosphate metabolism by
releasing fibroblast growth factor – 23, which
acts on kidneys to reduce phosphate
reabsorption. Bone cells also release a
hormone called osteocalcin, which
contributes to the regulation of blood
sugar (glucose) and fat deposition.
Osteocalcin increases both
the insulin secretion and sensitivity, in
addition to boosting the number of insulin-
producing cells and reducing stores of fat.

 Cartilage
 Cartilage provides a model for bone growth
and formation, provides a smooth cushion
between adjacent bones, and provides firm
and flexible support.

 Tendons and Ligaments
 Tendons attach muscles to bones, and
ligaments attach bones to bones.
 Joints
 Joints allow movement between bones.

Compact Bone
Compact bone makes up the
outer layer of all bones. Although
it looks dense and solid, It is full
of holes for nerves and blood vessels.
Spongy Bone
Spongy bone contains flat
and needlelike structures
that resist stress. Red bone
marrow may fill the open
spaces in some bones.
Central Cavity
Central cavities in long
bones usually contain
yellow bone marrow (fat).
Outer Membrane
An outer membrane
covers most of a long bone.
The inner portion of a membrane
contains cells that build up and
breakdown bone.
General Features of the Bone
 Parts of Bone

 Bone Cells
There are several types of cells constituting the
typical bone:
 Osteocytes
 Mature bone cells
 Osteoblasts
 Bone-forming cells
 Osteoclasts
 Bone-destroying cells
 Break down bone matrix for remodeling and release
of calcium

 Bone Surface Markings
 Bones have characteristic surface markings
 Structural features adapted for specific functions
 There are two major types of surface markings:
 1) Depressions and openings
 Allow the passage of blood vessels and nerves or form
joints
 2) Processes/ Projections
 Projections or outgrowths that form joints or serve as
attachment points for ligaments and tendons

Joint Projections
 1) Condyle: Rounded articular projection
Condyle

Joint Projections
 2) Head: bony
expansion on a
narrow neck
 3) Facet: smooth,
nearly flat articular
surface

Joint Projections
 4) Ramus: Armlike bar of bone

Ligament/Tendon Projections
1) Crest: Narrow ridge
of bone (Line: smaller
than a crest)
2) Epicondyle: Raised
area on or above a
condyle
ULNA

3) Tubercle: Small
rounded projection
4) Tuberosity: large
rounded or
roughened projection
5) Trochanter: very
large, blunt projection
(only on femur)
Proximal Tibia

6) Spine: Sharp, pointed
projection
Thoracic Vertebrae

DEPRESSIONS
 Allow blood vessels or nerves to pass
through.
1) Meatus: (me - A- tus) Canal or tube

Depressions
2) Fossa: shallow basin
3) Fissure: narrow, slit-
like opening

Depressions
4) Sinus: Cavity within a
bone; filled with air
and lined with
mucous membranes
5) Foramen: Round or
oval opening
Foramen Magnum

Depressions
6) Sulcus, Groove or Furrow: a shallow
depression

Bone Markings
Projections
1) Condyle
2) Head
3) Facet
4) Ramus
5) Crest
6) Epicondyle
7) Tubercle
8) Tuberosity
9) Trochanter
10) Spine
Depressions
1) Meatus
2) Foramen
3) Fossa
4) Fissure
5) Sinus
6) Sulcus or Groove or
Furrow

Bone Ossification
 The formation of bone during the fetal stage
of development occurs by two
processes: Intramembranous
Ossification and Endochondral
Ossification.

Intramembranous Ossification
Intramembranous ossification mainly occurs
during formation of the flat bones of
the skull but also the mandible, maxilla, and
clavicles; the bone is formed from
connective tissue such
as mesenchyme tissue rather than from
cartilage.

Intramembranous Ossification
 The steps in intramembranous ossification
are:
1. Development of ossification center.
2. Calcification.
3. Formation of trabeculae.
4. Development of periosteum.

Endochondral Ossification
Endochondral ossification, on the other
hand, occurs in long bones and most of the
rest of the bones in the body; it involves an
initial hyaline cartilage that continues to
grow.

Endochondral Ossification
 The steps in endochondral ossification
are:
1. Development of cartilage model
2. Growth of cartilage model
3. Development of the primary ossification center
4. Development of the secondary ossification
center
5. Formation of articular cartilage and epiphyseal
plate

Bone Growth
 Does drinking milk can make you
taller?

Bone Remodelling
Bone remodelling consists of removal of
existing bone by osteoclasts and deposition
of new bone by osteoblasts.

Bone Repair

 Types of Bones
 Bones can be classified into five types based on
shape:
 Long
 Short
 Flat
 Irregular
 Sesamoid

 Types of Bones
 Long Bones
 Greater length than width and are slightly curved for strength
 Femur, tibia, fibula, humerus, ulna, radius, phalanges
 Short bones
 Cube-shaped and are nearly equal in length and width
 Carpal, tarsal
 Flat bones
 Thin and composed of two nearly parallel plates of compact bone tissue
enclosing a layer of spongy bone tissue
 Cranial, sternum, ribs, scapulae
 Irregular bones
 Complex shapes and cannot be grouped into any of the previous
categories
 Vertebrae, hip bones, some facial bones, calcaneus
 Sesamoid bones
 Protect tendons from excessive wear and tear
 Patellae, foot, hand

General Consideration of Bone Anatomy
 The human skeleton consists of 206 named bones
 Bones of the skeleton are grouped into two principal
divisions:
 Axial skeleton
 Consists of the bones that lie around the longitudinal axis of
the human body
 Skull bones, auditory ossicles (ear bones), hyoid
bone, ribs, sternum (breastbone), and bones of the vertebral
column
 Appendicular skeleton
 Consists of the bones of the upper and lower limbs
(extremities), plus the bones forming the girdles that connect
the limbs to the axial skeleton

Divisions of the Skeletal System

The Axial Skeleton

Skull
 Skull (cranium)
 Consists of 22 bones
 Bones of the skull are grouped into two
categories:
 Cranial bones
 Eight cranial bones form the cranial cavity
 Frontal bone, two parietal bones, two temporal bones, the
occipital bone, the sphenoid bone, ethmoid bone
 Facial bones
 Fourteen facial bones form the face
 Two nasal bones, two maxillae, two zygomatic bones, the
mandible, two lacrimal bones, two palatine bones, two inferior
nasal conchae, vomer

Skull
 The cranial and facial bones protect and support
special sense organs and the brain
 Besides forming the large cranial cavity, the skull
also forms several smaller cavities
 Nasal cavity
 Orbits (eye sockets)
 Paranasal sinuses
 Small cavities which house organs involved in hearing
and equilibrium

Skull
 Immovable joints called sutures fuse most of the
skull bones together
 The skull provides large areas of attachment for
muscles that move various parts of the head
 Skull and facial bones provide attachment for
muscles that produce facial expressions
 The facial bones form the framework of the face
and provide support for the entrances to the
digestive and respiratory systems

Skull (Cranial Bones)
 Frontal Bone
 Forms the forehead
 Parietal Bones
 Form the sides and roof of the cranial cavity
 Temporal Bones
 Form the lateral aspects and floor of the cranium
 Occipital Bone
 Forms the posterior part and most of the base of the cranium
 Sphenoid Bone
 Lies at the middle part of the base of the skull
 Ethmoid Bone
 Located on the midline in the anterior part of the cranial floor medial to
the orbits
 A major superior supporting structure of the nasal cavity
 Contain thin projections called conchae which are lined by mucous
membranes
 Increased surface area in the nasal cavity helps to humidify inhaled air
trapping inhaled particles

Skull (Facial Bones)
 Nasal Bones
 Form the bridge of the nose
 Maxillae
 Form the upper jawbone
 Form most of the hard palate
 Separates the nasal cavity from the oral cavity
 Zygomatic Bones
 commonly called cheekbones, form the prominences of the
cheeks
 Lacrimal Bones
 Form a part of the medial wall of each orbit
 Palatine Bones
 Form the posterior portion of the hard palate
 Inferior Nasal Conchae
 Form a part of the inferior lateral wall of the nasal cavity

Skull (Facial Bones)
 Vomer
 Forms the inferior portion of the nasal septum
 Mandible
 Lower jawbone
 The largest, strongest facial bone
 The only movable skull bone
 Nasal Septum
 Divides the interior of the nasal cavity into right and left sides
 ―Broken nose,‖ in most cases, refers to septal damage rather
than the nasal bones themselves
 Orbits
 Eye socket
 Foramina
 Openings for blood vessels , nerves , or ligaments of the skull

Skull
 Unique Features of the Skull
 Sutures, Paranasal sinuses, Fontanels
 Sutures
 an immovable joint that holds most skull bones together
 Paranasal Sinuses
 Cavities within cranial and facial bones near the nasal cavity
 Secretions produced by the mucous membranes which line the sinuses,
drain into the nasal cavity
 Serve as resonating chambers that intensify and prolong sounds
 Fontanels
 Areas of unossified tissue
 At birth, unossified tissue spaces, commonly called ―soft spots‖ link the
cranial bones
 Eventually, they are replaced with bone to become sutures
 Provide flexibility to the fetal skull, allowing the skull to change shape as
it passes through the birth canal

Auditory Ossicles
 The middle ear has 3 tiny bones: the
Malleus, Incus and Stapes.
 Stapes is the smallest bone in the body
 Helps in hearing.

Auditory Ossicles

Hyoid Bone
 Does not articulate with
any other bone
 Supports the tongue,
providing attachment
sites for some tongue
muscles and for
muscles of the neck and
pharynx
 The hyoid bone also
helps to keep the larynx
(voice box) open at all
times

Vertebral Column
 Also called the spine, backbone, or spinal
column
 Functions to:
 Protect the spinal cord
 Support the head
 Serve as a point of attachment for the ribs, pelvic
girdle, and muscles
 The vertebral column is curved to varying
degrees in different locations
 Curves increase the column strength
 Help maintain balance in the upright position
 Absorb shocks during walking, and help protect the
vertebrae from fracture

Vertebral Column

Vertebral Column
 Composed of a series of bones called
vertebrae (Adult=26)
 7 cervical are in the neck region
 12 thoracic are posterior to the thoracic cavity
 5 lumbar support the lower back
 1 sacrum consists of five fused sacral
vertebrae
 1 coccyx consists of four fused coccygeal
vertebrae

Vertebral Column (Regions)
 Cervical Region
 Cervical vertebrae (C1–C7)
 The atlas (C1) is the first cervical vertebra
 The axis (C2) is the second cervical vertebra
 Thoracic Region
 Thoracic vertebrae (T1–T12)
 Articulate with the ribs
 Lumbar Region
 Lumbar vertebrae (L1–L5)
 Provide for the attachment of the large back muscles
 Sacrum
 The sacrum is a triangular bone formed by the union of five sacral
vertebrae (S1–S5)
 Serves as a strong foundation for the pelvic girdle
 Coccyx
 The coccyx, like the sacrum, is triangular in shape
 It is formed by the fusion of usually four coccygeal vertebrae

Thorax
 Thoracic cage is formed by the:
 Sternum
 Ribs
 Costal cartilages
 Thoracic vertebrae
 Functions to:
 Enclose and protect the organs in the thoracic
and abdominal cavities
 Provide support for the bones of the upper
limbs
 Play a role in breathing

Thorax
 Sternum
 ―Breastbone‖ located in the center of the
thoracic wall
 Consists of the manubrium, body, xiphoid
process
 Ribs
 Twelve pairs of ribs give structural support to
the sides of the thoracic cavity
 Costal cartilages
 Costal cartilages contribute to the elasticity of
the thoracic cage

Thorax

The Appendicular Skeleton

Appendicular Skeleton
 The primary function is movement
 It includes bones of the upper and lower
limbs
 Girdles attach the limbs to the axial skeleton

Skeleton of the Upper Limb
 Each upper limb has 30 bones
 The upper limb consists of the bones of the
arm, forearm, wrist, and hand.

Upper Limb
 1 humerus (arm)
 1 ulna (forearm)
 1 radius (forearm)
 8 carpals (wrist)
 5 metacarpal and 14 phalanges (hand)

Skeleton of the Arm - Humerus
 Longest and largest bone of the free part of
the upper limb
 The proximal ball-shaped end articulates with
the glenoid cavity of the scapula
 The distal end articulates at the elbow with
the radius and ulna

Humerus and Glenohumeral Joint
Figure 8.4

Right humerus in relation to scapula,
ulna, and radius-- Figure 8.5

Right ulna and radius in relation to the
humerus and carpals -- Figure 8.6

Skeleton of the Hand
 The carpus (wrist) consists of 8 small bones
(carpals)
 Two rows of carpal bones (So Long Top Part, Here
Comes The Thumb)
 Proximal row (lateral-medial) - scaphoid, lunate,
triquetrum, pisiform
 Distal row (medial-lateral) - hamate ,
capitate,trapezoid, trapezium
 Scaphoid - most commonly fractured
 Carpal tunnel - space between carpal bones and
flexor retinaculum

Metacarpals and Phalanges
 Five metacarpals - numbered I-V, lateral to
medial
 14 phalanges - two in the thumb (pollex) and
three in each of the other fingers
 Each phalanx has a base, shaft, and head
 Joints - carpometacarpal,
metacarpophalangeal, interphalangeal

Right wrist and hand in relation to ulna
and radius -- Figure 8.8

Pectoral Girdle - Clavicle
 The clavicle is ―S‖ shaped
 The medial end articulates with the
manubrium of the sternum forming the
sternoclavicular joint
 The lateral end articulates with the acromion
forming the acromioclavicular joint

The Pectoral (or Shoulder) Girdle
Figure 8.1

The Clavicle Figure 8.2

Pectoral Girdle - Scapula
 Also called the shoulder blade
 Triangular in shape
 Most notable features include the
spine, acromion, coracoid process and the
glenoid cavity

Scapula
Figure 8.3

Skeleton of the Lower Limb
 Skeleton of the Lower Limb
 Consist of bones of thigh, leg, ankle and foot.
 Each lower limb has 30 bones.

Pelvic (Hip) Girdle
 Each coxal (hip) bone consists of three bones
that fuse together: ilium, pubis, and ischium
 The two coxal bones are joined anteriorly by
the pubic symphysis (fibrocartilage)
 Joined posteriorly by the sacrum forming the
sacroiliac joints (Fig 8.9)

Bony Pelvis Figure 8.9

Right Hip Bone Figure 8.10

Comparing Male and Female Pelves
 Males - bone are larger and heavier
 Pelvic inlet is smaller and heart shaped
 Pubic arch is less the 90°
 Female - wider and shallower
 Pubic arch is greater than 90°
 More space in the true pelvis (Table 8.1)

Table 8.1

Right Lower Limb
Figure 8.12

Skeleton of the Thigh - Femur and Patella
 Femur - longest, heaviest, and strongest bone in the
body
 Proximally, the head articulates with the acetabulum
of the hip bone forming the hip (coxal) joint
 Neck - distal to head, common site of fracture
 Distally, the medial and lateral condyles articulate
with the condyles of the tibia forming the knee joint
 Also articulates with patella

Femur
 Greater and lesser trochanters are projections
where large muscles attach
 Gluteal tuberosity and linea aspera - attachment
sites for the large hip muscles
 Intercondylar fossa - depression between the
condyles
 Medial and lateral epicondyles - muscle site
attachments for the knee muscles

Right Femur Figure 8.13

Patella
 Largest sesamoid bone in the body
 Forms the patellofemoral joint
 Superior surface is the base
 Inferior, narrower surface is the apex
 Thick articular cartilage lines the posterior
surface
 Increases the leverage of the quadriceps
femoris muscle
 Patellofemoral stress syndrome - ―runner’s
knee‖

Patella Figure 8.14

Tibia and Fibula Figure 8.15

Skeleton of the Foot -
Tarsals, Metatarsals, and Phalanges
 Seven tarsal bones - talus (articulates with
tibia and fibula), calcaneus (the heel bone,
the largest and strongest), navicular, cuboid
and three cuneiforms
 Five metatarsals - (I-V) base, shaft, head
 14 phalanges (big toe is the hallux)
 Tarsus = ankle

Right Foot Figure 8.16

Bone and Calcium Homeostasis
 When blood calcium levels are too low,
osteoclast activity increases.
 When blood calcium levels are too high
osteoblast activity decreases.

Bone and Calcium Homeostasis
 Parathyroid hormones (PTH) – stimulates
increased bone breakdown and increased
blood calcium levels by indirectly stimulating
osteoclast activities.
 Calcitonin – decreases osteoclast activity and
thus decreases blood calcium level.

Articulation
An articulation, or
joint, is a place where
two bones come
together.

Kinds of Joint based on movement:
Synarthrosis - non movable joints
e.g.- sutures
Amphiarthrosis - slightly movable joints
e.g.- rib cage
Diarthrosis - freely movable joints
e.g.-joints in the upper & lower limbs

Kinds of Joint based on structural
connection:
Fibrous Joints - consist of two
bones that are united by fibrous tissue and
that are united by fibrous tissue and that
exhibit little or no movement.

 Sutures are fibrous joints between the bones
of skull.
 Syndesmoses are fibrous joints in which the
bones are separated by some distance and
are held together by ligaments. An example
is the fibrous membrane connecting most of
the distal parts of the radius and ulna.
 Gomphoses consist of pegs fitted into
sockets and held in place by ligaments. The
joint between a tooth and its sockets is a
gomphosis.

Cartilaginous Joints - unite two bones
by means of cartilage. Only slight movement
can occur at these joints
 Examples are the cartilage in the
epiphyseal plates of growing long bones
and the cartilages between the ribs and
the sternum.
connection:

connection:
Synovial Joints -
are freely movable
joints that contain
synovial fluid in
cavity surrounding
the ends of
articulating bones.

Types of Joints
Hinge-  A hinge joint allows extension and
retraction of an appendage. (Elbow, Knee)

Ball and Socket-  A ball and socket joint
allows for radial movement in almost any
direction. They are found in the hips and
shoulders. (Hip, Shoulder)

Gliding-  In a gliding or plane joint bones slide
past each other. Mid-carpal and mid-tarsal
joints are gliding joints. (Hands, Feet)

Saddle- This type of joint occurs when the
touching surfaces of two bones have both
concave and convex regions with the shapes
of the two bones complementing one other
and allowing a wide range of movement.
(Thumb)

Types of Movement

Effects of aging on the Skeletal System
 Bone matrix becomes more brittle and
decreases in total amount during aging.
 Joints lose articular cartilage and become
less flexible with age.

End….Jaycris C. Agnes , 2013

Skeletal System

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