The Skeletal System
"Support System"
Types of skeletal systems in the animal Kingdom
1-Hydrostatic skeleton: as in flatworms and annelids, where the fluid found in their ceolom
acts as a skeletal system for support.
2-Exoskeleton: as in Arthropods such as insects, this skeleton is made up mostly from chitin.
It provides protection against damage and enemies, and keeps tissue from during out. It
does not grow as the animal grows so it molt "shed" as the animal grows.
3-Endoskeleton: as in Vertebrates, it is composed of bone and cartilage with joints allow
flexibility. Grows with an animal, so it does not limit space.
Human Skeletal System
Functions:
1-Support: it supports against pull of gravity "legs, pelvis and vertebral column". Mandible
supports the teeth.
2-Protection: the cranium encloses the brain, vertebral column encloses the spinal cord, and
rib cage encloses the heart and the lungs.
3-Movment: Legs and arms.
4-Blood formation: Red bone marrow is the major producer of blood cells.
5-Electrolyte balance: storage calcium and phosphate and releases them according to the
body's need.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
1
6-Detoxification: by removing heavy metals and other foreign elements from blood.
7-Acid-base balance: absorbing and releasing alkaline mineral salts to balance any excessive
pH changes.
Anatomy
Bone structure
The long bone structure:
Long bones are those bones that are longer than wide "Humerus"
Parts of a long bone:
1-Diaphysis "shaft": the shaft of a long bone is composed of compact bone and is surrounding
the marrow cavity.
2-Epiphysis: it is the distal and proximal ends of a long bone. Primarily composed of spongy
bone covered with a shell of compact bone. The ends of epiphysis are covered by articular
cartilage "hyaline".
3-Epiphysial plate "growth plate": it is where the diaphysis joins the epiphysis, consists of
hyaline cartilage that allows the diaphysis to grow in length. As growth stops, this cartilage
is converted to bone, the previous epiphysial plate is known as an epiphysial line.
4-Articular cartilage: it is a hyaline cartilage found at the articulating surface where a joint
forms.
5-Periosteum: DICT that surrounds the surface of the bone tissue, except at the articular
cartilage. The only bone in the body not involved in a joint is the Hyoid bone, therefore, it
will have periosteum over the entire surface. Periosteum serves as an attachment point for
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
2
tendons and ligaments.
The presence of osteoclasts and osteoblasts assists in bone
formation and repair.
6-Endosteum: Fibrous connective tissue linning the marrow cavity containing bone forming
cells.
7-Marrow cavity "Medullary cavity": a space within the diaphysis that is filled with yallow
marrow "adipose".
The bones are of two types:
-The compact bone is the tightly packed bone, protects the spongy bone.
-The spongy bone that found in the epiphysis of long bones and most areas of short, flat and
irregular bones. It contains red marrow, filled with large space to help reduce bone's
weight. It contains bony plates "trabecula" and is covered by compact bone.
Classifications:
1-long bones: are greater in length than in width, include bones of the appendages
"humerus"
2-Short bones: length and width are equal "cube shape" or almost equal "wrist & ankle
bones".
3-falt bones: Thin plate like "ribs, scapula, skull"
4-Irregular bones: Unusually shaped "vertebra, hip bones and some facial bones".
5-Round or sesamoid bones: small bones embedded in tendons at joints "patella"
6-Sutural or Wormain bones: Bones may be present between sutures in the skull.
Axial Skeleton and Markings to learn
You have two divisions: Axial and Appendicular and a total of 206 bones. Axial skeleton lies
at the midline of the body and consists of skull, hyoid bone, vertebral column, and rib cage.
Appendicular skeleton consists of pectoral girdle and upper limbs and pelvic girdle and lower
limbs.
The Axial Skeleton
1-Skull (22 bones) is formed by the cranium and facial bones
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
3
a-Cranium protects the brain, composed of 8 bones fitted tightly together in the adult. In
newborns, some cranial bones are not completely formed and are joined by membranous
region "fontanels", these usually close by 16 months of age. Cranium bones contain
sinuses which are air spaces lined by mucus membrane to reduce weight of skull.
b-Facial bones-14 bones. Most prominent facial bones include mandible, maxillae "upper
jaw", zygomatic "cheekbone", and nasal bone. Mandible- (1) lower jaw is the only
moveable bone of skull which allow to chew food. It also forms the chin.
2.Hyoid bone (what is the function of this bone?) It anchors the tongue and serves as the site
for the attachment of muscles associated with swallowing.
3.Vertebral column
Supports the head and trunk and protects the spinal cord and roots of spinal nerves. Has four
curvatures that provide strength. Also serves as anchor for all other bones of the skeleton. Consists
of 33 vertebrae
-7 cervical vertebrae located in the neck region.
atlas (1st cervical vertebrae)
axis (2nd cervical vertebrae
-12 Thoracic vertebrae (ribs attach to these) -have facets for ribs to attach
-5 Lumbar vertebrae are the largest
-1 Sacrum is formed by 5 fused bones.
-1 coccyx tail bone, is formed by 4 fused bones.
4. The Rib Cage-
The Rib Cage
Composed of the thoracic vertebrae, the ribs and their associated cartilage and the Sternum.
the rib cage protects heart and lungs, yet is flexible to allow breathing.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
4
The sternum "breastbone" lies in the midline of the body, composed of three bones that
fuse during fetal development. Along with the ribs, helps to protect the heart and lungs.
Ribs -12 pairs
All twelve pairs of ribs connect directly to the thoracic vertebrae in back.
7 pairs of ribs connect directly to the sternum "true ribs"
3 pairs of ribs connect via cartilage to the sternum "false ribs"
2 pairs of ribs are totally unattached to the sternum "floating ribs"
Appendicular skeleton
The pectoral "shoulder" girdle and upper limbs re specialized for flexibility. The pelvic "hip"
girdle and lower limbs are specialized for strength.
A - Upper extremities (64 bones)
Pectoral girdle and arm
1-pectoral girdle -attach bones of upper extremity to the axial skeleton (2 bones)
a- Clavicle (collar bone)-most commonly broken bone in the body, connects with the
sternum in the front and scapula in back.
b- Scapula (shoulder bone)- connects with clavicle, but freely movable and held in place by
15 muscles attached to it.
2-Humerus is the longest bone of arm. Its smoothly rounded head fits into the socket of the
scapula.
3-The radius and the ulna make up the lower arm or the forearm. The radius articulates
with the humerus at elbow joint ,
4-Carpals (wrist bones), 8 bones united by ligaments
5-metacarpals (palm) 5 bones
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
5
6-phalanges-14 bones, each finger has 3 bones and each thumb has 2 bones
B-Lower extremities:
Pelvic girdle and leg
1-The Pelvic girdle:
The pelvic girdle consists of two heavy large coxal bones. It bears the weight of the body,
protects the organs within the pelvic cavity, and serves as a place for attachment of the
legs. In female, the pelvic cavity is more shallow, but the outlet is wider than in male.
The pelvis
2-Fumer "thigh bone"
The longest, heaviest, and the strongest bone of the body that extends from the hip to the
knee.
3-Patella-knee bone
4-Tibia and Fibula: the tibia supports the body weight. The fibula non-weight bearing bone,
is a slender bone.
5-Tarsal bones "ankle" 7 bones
6-Mtatarsal bones: 5 bones
7- Phalanges: 14 bones shorter than in fingers.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
6
Articulations "Joints"
Joints are the sites of junction between two or more bones. They permit the bones to move
without damaging each other. Arthrology:
is the study of the anatomy, function,
dysfunction and treatment of joints.
Joints are classified by function or structure
1-Functional classification of joints based on mobility "degree of movement"
a-Synarthrose: those are immovable joints, they are often called fixed joints. They are held
together by connective tissue or they are fused together "ex. Sutures of skull"
b-Amphiarthrose: Partial movements are allowed by these joints "distal end of tibia and
fibula, wrist bones".
c-Diarthrose: freely moveable "majority of joints"
2-Structural classification of joints based on type of connective tissue present at the joint
and the presence or absence of a synovial joint.
a-Fibrous joints: This type of joints are connected by fibrous connective tissue "ligament or
tendon", and does not have a joint cavity. Amount of movement depends on the length of
fibers uniting the bone "distal ends of tibia and fibula, sutures between flat bones of skull
and gomphosis, joints between teeth and socket".
b-Cartilaginous joints; This type of joints are connected by cartilage, and does not have a
joint cavity. May "invertebrate discs" or may not " epiphyseal plate "permit movement
c-Synovial joints-bones connected by fibrous connective tissue and cartilage with a joint
cavity. These allow free movement. They consist of articular cartilage, a joint capsule, a
synovial membrane, and synovial fluid
General structure of a synovial joint:
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
7
Synovial joint
A. the ends of the bones are covered with articular cartilage (hyaline cartilage) and this
helps resist wear and minimizes friction
B. A joint capsule or articular capsule with two distinct layers holds together the bones of a
synovial joint.
C. Ligaments helps reinforce the joint capsule and binds the articular ends of bones
D. The outer layer of the joint capsule is fibrous and completely encloses the other parts of
the joint, but is flexible enough to permit movement.
E.
Inner layer of a joint capsule consists of synovial membrane, which covers all the
surfaces of a joint capsule except where the articular cartilage covers.
F. The synovial membrane surrounds a closed sac called the synovial cavity or joint cavity
that is filled with synovial fluid (viscous fluid which moistens and lubricates the smooth
cartilaginous surfaces within the joint to reduce friction, in the knee you have 0.5 mL or less)
G. Some synovial joints are partially or completely divided into compartments by disks of
fibro cartilage called menisci that make joints more stable.
H. Some synovial joints have fluid filled sacs called bursae that contain synovial fluid and
cushion and aid movement of tendons, reducing friction.
--these are located between the skin and the underlying bony prominences like the patella
or the knee or the olecranon process of the elbow, or between muscle and bone, tendon
and bone, ligament and bone, and within articular capsules
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
8
Ossification "Osteogenesis'
Bone development begins in the embryo by two distinct processes "no histological
differences". The cranial bones of the skull developed by a method called intramembranous
ossification, whereas more other bones "the vertebra, pelvis" form by endochondrial
ossification. The clavicles, mandible and facial bones form by the combination of the two
methods.
1-Intramembranous ossification:
Ossification begins as some mesenchymal cells form a highly vascular sheet or membrane.
Some of its cells "fibroblast" in the inner zone cluster, enlarge and differentiate into
osteogenic cells and osteoblasts. Osteoblasts secret an organic matrix called Osteoid.
Mineralization by adding calcium phosphate salts.
Trabecula is formed and grow thicker
and forming spongy bone, which then will be filled with bone marrow. Some of the
osteoblasts become trapped in lacunae, once trapped they differentiate into osteocytes.
The original membrane becomes periosteum. Osteoblasts and osteoclasts reward the edges
of the formed spongy bone and form a shell of compact bone around the spongy.
2-Endochondrial Ossification:
Most bones of the body are formed in this way, the formation of bones from hyaline
cartilage model. This way is also used to increase the length of long bone and for the healing
of bone fractures.
It begins by a growth of the cartilage model, as it would grow in length by continuous cell
division of the chondocytes, which is accompanied by further secretion of extracellular
matrix. This growth is called interstitial growth. Cartilage model would also grow in
thickness.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
9
Endochondial ossification
a-Primary ossification center
occurs in the middle of diaphysis "shaft"
1-Formation of periosteum, Once vascularized, the perichondrium becomes periosteum.
The peristeum contains a layer of undifferentiated cells, later those cells become
osteoblasts.
2-Formation of bone collar, The osteoblasts secret osteiod against the shaft of the cartilage
model to support the new bone.
3-Calcification of matrix:, Chondocytes in the primary ossification center begin to grow.
They stop secreting collagen and other proteoglycans, and begin secreting alkaline
phosphate, an enzyme essential for mineral deposition. Nutrients can no longer diffuse
when matrix becomes sufficiently calcified, and chondocytes subsequently die, this
creates cavities within the bone.
4-Invasion of peristeal bud: A perioseal bud, which consists of blood vessels, lymph
vessels, nerves, invades the cavity left by the chondocytes, carries hemopoietic cells,
osteoblasts and osteoclasts inside the cavity. The hemopoietic cells will later form the
bone marrow.
5-Formation of trabeculae: Osteoblasts secrete osteoid, which forms the bone trabecula.
Osteoclasts break down spongy bone to form the medullary cavity 'marrow cavity".
b- Secondary ossification center
Occurs in the epiphyseal plate located between the diaphysis "shaft" and the epiphysis
"end" of the bone. It is a replication of the primary ossification, but the marrow cavity is
not formed leaving a spongy bone in the epiphysis. Some of the hyaline cartilage will
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
10
remain to form the articular cartilage. Edges of the spongy bone are remarked to form
compact bone around the spongy bone.
Bone Growth:
1-bone growth in length occurs at the epiphysis plates……..How?
a-cartilage at the epiphysis grows outwards "via mitotic division".
b-cartilage closest to the diaphysis is replaces by bone tissue.
c-this will continue until the end of puberty.
2-bone growth in width occurs as osteoblasts under the peristeum lay down compact
bone. Simultaneously, osteoclasts break down the bone adjust to cavity so that the bone
thickness remain constant.
Factors which affect and control bone formation and growth:
1-Vitamin D
It is needed for the absorption of calcium and phosphors from digestive tract. Its
deficiency will cause a Rickets as in child and osteomalasia as in adult.
2-Growth hormone
Released by the pituitary gland and indirectly stimulates mitosis in cartilage at the
epiphysis plate for bone growth.
3-Thyroxin
Released by thyroid gland, stimulates the replacement of cartilage by bone.
4-Calcitonin
Released by the thyroid gland in response to high level of blood calcium. Stimulates
osteoblasts to build bone and inhibit osteoclasts to break bone.
5-Parathyroid hormone
Released by the parathyroid gland in response to low level of blood calcium. Stimulates
osteoclasts to break bone.
6-Sex hormone "testosterone & estrogen"
During puberty, high levels of these hormones terminate bone growth. Estrogen has
stronger effect, so females tend to terminate growth sooner.
7-weight bearing exercise
Bone thickness where muscle pull on bone.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
11