The Skeletal System. Dr. S. Nishan Silva (MBBS). Under the Skeletal System. Function Classification Histology Formation Gross Anatomy. Function of the Skeletal System. Support- framework that supports body and cradles its soft organs Protection- for delicate organs, heart, lungs, brain
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The Skeletal System
Dr. S. Nishan Silva
Function of the Skeletal System
The bones of the legs, pelvic girdle, and vertebral column support the weight of the erect body.
The mandible (jawbone) supports the teeth.
Other bones support various organs and tissues.
The bones of the skull protect the brain.
Ribs and sternum (breastbone) protect the lungs and heart.
Vertebrae protect the spinal cord
Skeletal muscles use the bones as levers to move the body.
Reservoir for minerals and adipose tissue
99% of the body’s calcium is stored in bone.
85% of the body’s phosphorous is stored in bone.
Adipose tissue is found in the marrow of certain bones
Blood cell formation.
All blood cells are made in the marrow of certain bones
Types of Bones
1.long bones = length is greater than breadth
= consists of shaft (diaphysis) &
two extremities (epiphysis)
diaphysis = filled with yellow marrow
= cylindrical, large space or canal at the center
epiphysis = made up of cancellous tissue
e.g.: femur, humerus, tibia, fibula, radius, ulna, phalanges
Membranes: 1. periosteum
Much longer than they are wide.
All bones of the limbs except for the patella (kneecap),
and the bones of the wrist and ankle.
Consists of a shaft plus 2 expanded ends.
Your finger bones are long bones even though they’re very short
2. short bones = cuboidal in shape
= spongy bone with thin coat of compact bone
= sesamoid bone -- short bone embedded in a
e.g.: carpals (wrist), tarsal (ankle) bones
3. flat bones = broad or elongated flat plates
= for protection & muscle attachments
composition: 2 thin layers of compact tse. enclosing
a thin layer of spongy bone
e.g.: bones of the skull, sternum, ribs, scapula
2. Short Bones
Roughly cube shaped.
Bones of the wrist and the ankle.
Thin, flattened, and usually a bit curved.
Scapulae, sternum, (shoulder blades), ribs and most bones of the skull.
4. Irregular bones = all other bones not assigned to the previous groups
bones of the base of the skull
4. Irregular Bones
Have weird shapes that fit none of the 3 previous classes.
Vertebrae, hip bones, 2 skull bones ( sphenoid and the ethmoid bones).
Other matrix proteins
Bone tissue is a type of connective tissue, so it must consist of cells plus a significant amount of extracellular matrix.
Synthesize and secrete collagen fibers and other organic components of bone matrix.
Initiate the process of calcification.
Found in both the periosteum and the endosteum
The blue arrows indicate the osteoblasts. The yellow arrows indicate the bone matrix they’ve just secreted.
Mature bone cells.
Osteoblasts that have become trapped by the secretion of matrix.
No longer secrete matrix.
Responsible for maintaining the bone tissue.
The osteocyte is “trapped” within the pink matrix
Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell).
Cells that digest bone matrix – this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair.
Concentrated in the endosteum.
Consists of organic and inorganic components.
Organic component consists of several materials that are secreted by the osteoblasts:
Collagen fibers and other organic materials
These (particularly the collagen) provide the bone with resilience and the ability to resist stretching and twisting
Inorganic component of bone matrix
Consists mainly of 2 salts: calcium phosphate and calcium hydroxide.
Bone also contains smaller amounts of magnesium, fluoride, and sodium.
These minerals give bone its characteristic hardness and the ability to resist compression.
Anatomy of a Long Bone
1. compact = solid mass; dense & hard
= forms the outer layer of bone structure
= functional unit --- Haversian system
2. cancellous or spongy = contain spaces filled with bone marrow
= incomplete Haversian system
Shaft plus 2 expanded ends.
Shaft is known as the diaphysis.
Consists of a thick collar of compact bone surrounding a central marrow cavity
In adults, the marrow cavity contains fat - yellow bone marrow
Expanded ends are epiphyses
Thin layer of compact bone covering an interior of spongy bone.
Joint surface of each epiphysis is covered with a type of hyaline cartilage known as articular cartilage. It cushions the bone ends and reduces friction during movement.
The external surface of the entire bone except for the joint surfaces of the epiphyses is covered by a double-layered membrane known as the periosteum
Periosteum is richly supplied with nerve fibers, lymphatic vessels and blood vessels.
These enter the bone of the shaft via a nutrient foramen.
Periosteum is connected to the bone matrix via strong strands of collagen
Internal bone surfaces are covered with a delicate connective tissue membrane known as the endosteum.
Covers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone.
Contains both osteoblasts and osteoclasts.
Picture courtesy Gwen Childs, PhD.
Spider-shaped osteocytes occupy small cavities known as lacunae at the junctions of the lamellae.
Hairlike canals called canaliculi connect the lacunae to each other and to the central canal.
Canaliculi allow the osteocytes to exchange nutrients, wastes, and chemical signals to each other via intercellular connections
A X I A L
ribs & sternum 25_
Upper ExtremitiesLower Extremities
clavicle2hip bone 2
carpals 16tarsals 14
metacarpals 10metatarsals 10
phalanges 28__phalanges 28__
Figure adapted from Rockwood and Green, 5th Ed
soft tissue occupying the medullary cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger haversian canals.
There are 2 main types: red & yellow.
Red bone marrow = blood cell forming tissue = hematopoietic tissue
= skeleton --- head & face
= flattened & irregular
= united by joints (sutures)
cranium -- skull minus mandible
calvarium -- skull after the bones of the face have been removed
cavities: a. Cranial - contains the brain
b. Orbital - contains eyeball
& accessory organs
8 sutured bones in cranium
Facial bones: 13 sutured bones, 1 mandible
attachments for muscles
Sutures are the tight connections between skull bones
In the adult skull , the skull bones are unable to move or separate due to this tight connections
In infant skull this sutures are not well formed and the skull bones are mobile which facilitates the delivery of the baby
In mandibular fossa
intenal acoustic meatus
unpaired (4)paired (4)
1. occipital 1. parietal
2. frontal 2. temporal
b.Facial or visceral cranium
paired (12)unpaired (2)
a. Nasal a. Vomer
b. Lacrimal b. Mandible
d. Zygomatic / malar / cheek bones
f. Inferior nasal concha or turbinate
Forms the forehead
Roof of the orbit
articulates with parietal, sphenoid, lacrimal, nasal, ethmoid, zygomatic and maxilla
Contain 2 air filled cavities. ( frontal sinuses)
Part of the superior and lateral surfaces of the cranium
-articulate with each other – sagittal suture
-articulate with occipital, frontal,
temporal and sphenoid bones
Forms wall of jugular foramen
Associated with ear canal
- zygomatic process
-forms cranial portion of the Tempero Mandibular joint
-inferior to zygo. process – mandibular fossa (mandibular condyle)
- inferior aspect – mastoid process
- inferior and medial to the MP – styloid process
Part of the base of the skull
articulates with parietal, temporal and sphenoid
Surrounds the foramen magnum
Occipital condyles articulate with Atlas – 1st cervical vertebra
The uppermost portion of the human respiratory system, the nose is a hollow air passage that functions in breathing and in the sense of smell. The nasal cavity moistens and warms incoming air, while small hairs and mucus filter out harmful particles and micro-organisms. This illustration depicts the interior of the human nose.
Nasal (2) Maxillae (2) Zygomatic (2)
Mandible (1) Lacrimal (2) Palatine (2)
Inferior nasal conchae (2) Vomer (1)
These are seen in new borns
At birth the junction between skull bones covered with a membrane
This allows the expansion and growth of the brain
Later they become ossified ( bone formation)
= membrane filled spaces found in the skull of
e.g.:1. anterior = largest
3. anterolateral (sphenoidal)
4. posterolateral (mastoid)
= small U-shape; lies in front of the neck
= base of the tongue is attached
= lies between mandible & thyroid cartilage
= small bones of the ear
a. Stapes (stirrup)2
b. Incus (anvil)2
c. Malleus (hammer)2
lower jaw carries teeth
only freely movable bone of the skull
moving articulations with temporal bone
Roof - frontal
lesser wing of sphenoid
Medial wall – maxilla
Floor – maxilla