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Submodule 2.1 2.0

Submodule 2.1 –
Body Organization and Skeletal System
To study Human Anatomy, you have to first know the organization of the human body and
different body systems, where important organs are located. Anatomical orientation is the
foundation for learning anatomy and understanding how to look at various body parts,
whereas the skeletal system provides the framework for the body. Learners who successfully
complete this submodule will be able to:
Locate the body regions and cavities
Describe the systems involved in each region
Identify the major organs (tissues and cells) in each system
Define the anatomical position and planes
Classify different types of bones
Describe the bone structure
Locate the major bones of the skeleton
Reading – Anatomical orientation and terminologies
Anatomists and health care providers use terminology that can be bewildering to the
uninitiated. However, the purpose of this language is not to confuse, but rather to increase
precision and reduce medical errors. For example, is a scar “above the wrist” located on the
forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the
palm-side or back-side? By using precise anatomical terminology, we eliminate ambiguity.
Anatomical terms are made up of roots, prefixes, and suffixes. The root of a term often refers
to an organ, tissue, or condition, whereas the prefix or suffix often describes the root. For
example, in the disorder hypertension, the prefix “hyper-“ means “high” or “over,” and the
root word “tension” refers to pressure, so the word “hypertension” refers to abnormally high
blood pressure.
There are two general approaches to the study of the body’s structures: regional and
systemic. Regional anatomy is the study of the interrelationships of all of the structures in a
specific body region, such as the abdomen. Studying regional anatomy helps us appreciate
the interrelationships of body structures, such as how muscles, nerves, blood vessels, and
other structures work together serve a particular body region. In contrast, systemic anatomy
is the study of the structures that make up a discrete body system – that is, a group of
structures that work together to perform a unique body function. For example, a systemic
anatomical study of the muscular system would consider all of the skeletal muscles of the
Anatomical Position
To further increase precision, anatomists standardize the way in which they view the body.
Just like maps are normally oriented with north at the top, the standard body “map”, is
oriented as the anatomical position - is that of the body standing upright, with the feet at
shoulder width and parallel, toes forward. The upper limbs are held out to each side, and the
palms of the hands face forward as illustrated below. Using this standard position reduces
confusion. It does not matter how the body being described is oriented, the terms are used
as if it is in anatomical position. For example, a scar in the “anterior (front) carpal (wrist)
region” would be present on the palm side of the wrist.
Directional Terms
Certain directional anatomical terms appear throughout this and any other anatomy
textbook (Figure 1.13). These terms are essential for describing the relative locations of
different body structures. For instance, an anatomist might describe one band of tissue as
“inferior to” another or a physician might describe a tumor as “superficial to” a deeper body
structure. Commit these terms to memory to avoid confusion when you are studying or
describing the locations of particular body parts.
o Anterior (or ventral) Describes the front or direction toward the front of the body. The toes
are anterior to the foot.
o Posterior (or dorsal) Describes the back or direction toward the back of the body. The
popliteus is posterior to the patella.
o Superior (or cranial) describes a position above or higher than another part of the body
proper. The orbits are superior to the oris.
o Inferior (or caudal) describes a position below or lower than another part of the body proper;
near or toward the tail (in humans, the coccyx, or lowest part of the spinal column). The pelvis
is inferior to the abdomen.
o Lateral describes the side or direction toward the side of the body. The thumb (pollex) is
lateral to the digits.
o Medial describes the middle or direction toward the middle of the body. The hallux is the
medial toe.
o Proximal describes a position in a limb that is nearer to the point of attachment or the trunk
of the body. The brachium is proximal to the antebrachium.
o Distal describes a position in a limb that is farther from the point of attachment or the trunk
of the body. The crus is distal to the femur.
o Superficial describes a position closer to the surface of the body. The skin is superficial to the
o Deep describes a position farther from the surface of the body. The brain is deep to the skull.
Session 2.1.1 – Organization of Human Body
Before you begin to study the different structures and functions of the human body, it is
helpful to consider its basic architecture; that is, how its smallest parts are assembled into
larger structures. It is convenient to consider the structures of the body in terms of
fundamental levels of organization that increase in complexity: subatomic particles, atoms,
molecules, organelles, cells, tissues, organs, organ systems, organisms and biosphere.
The body is organized from the microscopic atom to the complex human organism.
Tiny atoms form molecules and then in turn form larger molecules. The larger molecules are
eventually organized into cells, the basic unit of life. Similar types of cells form tissues.
Different types of tissues are then arranged into organs like blood vessels, heart, urinary
bladder, and kidneys. Groups of organs then in turn create organ systems. Each organ
system has a function, such as digestion, excretion, or reproduction. We will discuss each of
these organ systems one by one in the following videos. All the organ systems work together
and form the human organism.
So now you can see how our human body is built from the tiny atom to the human being.
The Levels of Organization:
To study the chemical level of organization, scientists consider the simplest building blocks
of matter: subatomic particles, atoms and molecules. All matter in the universe is composed
of one or more unique pure substances called elements, familiar examples of which are
hydrogen, oxygen, carbon, nitrogen, calcium, and iron. The smallest unit of any of these pure
substances (elements) is an atom. Atoms are made up of subatomic particles such as the
proton, electron and neutron. Two or more atoms combine to form a molecule, such as the
water molecules, proteins, and sugars found in living things. Molecules are the chemical
building blocks of all body structures.
A cell is the smallest independently functioning unit of a living organism. Even bacteria,
which are extremely small, independently-living organisms, have a cellular structure. Each
bacterium is a single cell. All living structures of human anatomy contain cells, and almost all
functions of human physiology are performed in cells or are initiated by cells.
A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based
cellular fluid together with a variety of tiny functioning units called organelles. In humans, as
in all organisms, cells perform all functions of life. A tissue is a group of many similar cells
(though sometimes composed of a few related types) that work together to perform a
specific function. An organ is an anatomically distinct structure of the body composed of two
or more tissue types. Each organ performs one or more specific physiological functions. An
organ system is a group of organs that work together to perform major functions or meet
physiological needs of the body.
Session 2.1.2 – Tissues of Human Body
The body contains at least 200 distinct cell types. These cells contain essentially the same
internal structures yet they vary enormously in shape and function. The different types of
cells are not randomly distributed throughout the body; rather they occur in organized
layers, a level of organization referred to as tissue. Although there are many types of cells in
the human body, they are organized into four broad categories of tissues: epithelial,
connective, muscle, and nervous. Each of these categories is characterized by specific
functions that contribute to the overall health and maintenance of the body. A disruption of
the structure is a sign of injury or disease. Such changes can be detected through histology,
the microscopic study of tissue appearance, organization, and function.
Let’s move on to the various types of tissues found in our body. Tissues are composed of
different cells. And these various types of body tissues vary in shape, structure, function and
distribution. Here are the 4 major tissue types in our body, namely, epithelial tissue,
connective tissue, muscular tissue and nervous tissue. Epithelial tissues can be found in our
skin surface as well as lining of GI tract organs
and other hollow organs. They cover exposed surfaces. They line internal passageways &
chambers, such as trachea, blood vessels as well as heart chambers.
Some of these tissues are specialized in glandular secretions such as sweat glands, digestive
juice production along our GI tract. Connective tissues vary widely in appearance and
function. They occur throughout the body but never exposed to the outside environment.
They provide protective structural framework for other tissue types and interconnect parts
of the body. Examples include fat and other soft padding tissues, bones, ligaments and
tendons. Their major functions include filling internal spaces, providing structural support
and storing energy. We need muscle tissues to produce active movement. By processing
active muscular contractions, skeletal muscles offer joint movement; cardiac muscles offer
heart pumping; and
smooth muscles offer intestinal movement, which is called peristalsis. Nervous tissues can
be found in the brain, the spinal cord and nerves. By conducting and receiving electrical
impulses, these tissues perform internal communication
among the whole body.
Four Major Types of Tissues:
Epithelial tissue, also referred to as epithelium, refers to the sheets of cells that cover
exterior surfaces of the body, lines internal cavities and passageways, and forms certain
glands. Connective tissue, as its name implies, binds the cells and organs of the body
together and functions in the protection, support, and integration of all parts of the
body. Muscle tissue is excitable, responding to stimulation and contracting to provide
movement, and occurs as three major types: skeletal (voluntary) muscle, smooth muscle,
and cardiac muscle in the heart. Nervous tissue is also excitable, allowing the propagation
of electrochemical signals in the form of nerve impulses that communicate between
different regions of the body.
Session 2.1.3 – Important body systems Part 1
The next level of organization is the organ, where several types of tissues come together to
form a working unit. Just as knowing the structure and function of cells helps you in your
study of tissues, knowledge of tissues will help you understand how organs function.
In this video, let’s look into the components and structures of the following body systems:
integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, and lymphatic
The first organ system we are going to learn is the integumentary system. It refers to the skin
and its accessory structures, such as hairs, nails and sweat glands. Skin is the largest and
heaviest organ in our body. It makes up about 16% of body weight
and covers an area of 1.5 to 2 m². The skin is composed of multiple layers of cells and tissues,
which are attached to underlying structures by connective tissue.
Skin protects the underlying tissues from injury. As you can see from the diagram shown here,
the skin is composed of 2 main layers, the epidermis and dermis.
The epidermis made of closely packed epithelial cells. Immediately below the epidermis, we
have dermis which composed of different connective tissues. It houses many blood vessels,
hair follicles, sweat glands and receptors as well. With these structures, we can excrete salts
via perspiration, regulate body temperature as well as detect what is happening at the body
surface. Directly below the dermis, we have hypodermis and it serves to connect the skin to
the underlying connective tissues of the bones and muscles. Now we move on to individual
organ systems and see how they work. The skeletal system consists of bones, cartilages,
ligaments, joints and bone marrow. The adult skeleton is composed of 206 bones, but some
of us may have more than this number. Think of those people with extra digit, also known as
Polydactyly. The skeletal system provides support & protection for other tissues AND
framework for skeletal muscle contraction. It also acts as storehouse for minerals such as
calcium and most of our blood cells are made in the bone marrow. Typically we have about
640 skeletal muscles. They can only pull in one direction by contraction. So for this reason,
they always come in pairs. When one muscle in a pair contracts, say to bend the elbow joint,
its counterpart then contracts and pulls in the opposite direction to strengthen the joint out
again. By performing this synchronized muscular contraction, we can do various voluntary
actions ranging from walking, running to playing piano. Moreover, our muscular system also
allows postural maintenance facial expressions as well as heat production so that we can
maintain body temperature. The nervous system is the body’s fast-acting control system. It
consists of the brain, spinal cord, nerves and sensory organs such as eyes and pain receptors
located in the skin. It can be further divided into central nervous system, CNS, and peripheral
nervous system, PNS. CNS is composed of the brain and the spinal cord whereas any neural
tissues outside the CNS belong to PNS. As a whole, the nervous system directs immediate
responses to stimuli, coordinates or moderates activities of other organ systems, provides
and interprets sensory information about external conditions. Like the nervous system, the
endocrine system controls body activities, but it acts much more slowly. The endocrine
glands produce hormones and release them into the blood to travel to relatively distant
target organs.
The major endocrine glands include pituitary gland, thyroid gland, pancreas, adrenal glands,
testes and ovaries. In general, body functions controlled by hormones consist of many and
varied, including growth, reproduction, nutrients use by body cells. Now we move on to
cardiovascular system. The primary organs involved are the heart and
blood vessels. Heart has its own signal conduction system in which itself can generate its own
unidirectional electrical impulse and thus result in contraction of the heart chambers for
pumping blood into the major vessels. So here is the conduction system of the heart.
Specialized conducting components include sinoatrial node, atrioventricular node and
atrioventricular bundle and Purkinje fibers. First, the SA node initiates electrical impulses
which sweeps across the atria to the AV node, and thus the atria contract. It then passes
rapidly through the AV bundle, and its branches and then finally the Purkinje fibers, resulting
in ventricular contraction. Using blood as the transporting fluid, the cardiovascular system
carries oxygen, nutrients, hormones and other dissolved materials to and from the tissue
cells where exchanges are made. The blood also distributes heat and regulates body
temperature. The role of the lymphatic system complements that of the cardiovascular
system. Its organs include lymphatic vessels, lymph nodes and other lymphoid organs such
as the spleen and thymus. The lymphatic vessels return fluid leaked from the blood back to
the bloodstreams so that blood can be kept continuously circulating through the body.
The lymph nodes and other lymphoid organs defends against pathogens.
Session 2.1.4 – Important Body Systems Part 2
Now, let’s look at the remaining four body systems: respiratory, digestive, urinary and
reproductive systems.
The work done by the respiratory system is to keep the body constantly supplied with
oxygen and to remove carbon dioxide. The respiratory system can be further divided into
upper and lower respiratory tract. The major passages and structures of the upper
respiratory tract include the nose, nasal cavity, mouth, throat or pharynx, and voice box or
larynx. The lower respiratory tract consists of airway below the larynx, which is, the
trachea, bronchi and bronchioles and lung. Within the lungs, there are numerous tiny air
sacs called alveoli where gas exchange occurs. Oxygen diffuses from the alveolus into the
pulmonary capillary blood while carbon dioxide diffuses from the pulmonary blood into the
alveolus. Other than gaseous exchange, respiratory system is also important for sound
production so that we can communicate with each other. The digestive system is basically a
very long tube running through the body from mouth to anus. Digestive system consists of
oral cavity, esophagus, stomach, small intestine, large intestine, and accessory organs such
as liver, gallbladder and pancreas. Their role is to process and digest food, absorb and
conserve water, absorb nutrients and eliminate undigested food waste. Urinary system
consists of kidneys, ureters, urinary bladder as well as urethra. The kidney excretes waste
products such as urea from the bloodstream; it also controls water balance by regulating
the volume of urine produced. The kidney also regulates blood ion concentration and pH by
controlling the composition of urine produced. The urinary bladder can temporarily store
urine prior to voluntary elimination. The reproductive system exists primarily to produce
offspring. The testes of the male produce sperms while ovaries of female produce eggs. In
male, sperm cells are produced in seminiferous tubules which are located inside the testes.
These immature sperm cells then passively moved to epididymis for temporary storage and
maturation. Other male reproductive organs include accessory glands like the prostate and
associated duct systems. The female duct system consists of the uterine tubes, uterus and
vagina. Eggs produced in ovary passively passed through the uterine tube and then reach
the uterus. If fertilization occurs, the growing fetus will attach to the uterus by forming the
placenta. Mammary glands are milk-producing glands found in the breasts. After the birth
of a baby, they produce milk in response to hormonal stimulation.
Session 2.1.5 – Location of Organs in Relation to the Body Cavities
The body maintains its internal organization by means of membranes, sheaths, and other
structures that separate compartments. The dorsal (posterior) cavity and the ventral
(anterior) cavity are the largest body compartments. These cavities contain and protect
delicate internal organs, and the ventral cavity allows for significant changes in the size and
shape of the organs as they perform their functions. The lungs, heart, stomach, and
intestines, for example, can expand and contract without distorting other tissues or
disrupting the activity of nearby organs.
Our body maintains its internal organization by having different compartmentalization.
The dorsal and ventral cavities are the largest body compartments. These cavities contain
and protect delicate internal organs. In the dorsal or posterior cavity, we have cranial cavity,
which houses the brain, and the spinal cavity, which encloses the spinal cord. These two
cavities are continuous and uninterrupted so as to protect the delicate nervous system. In
the ventral or anterior cavity, we have the thoracic and the abdominopelvic cavities which
separated by the diaphragm. The thoracic cavity is the more superior subdivision and it is
enclosed by the rib cage. It contains vital organs such as lungs and the heart. The cavity
inferior to the diaphragm is the abdominopelvic cavity, which is the largest body cavity.
It is further subdivided into the superior abdominal cavity which houses the digestive
organs and the inferior pelvic cavity, which houses the organs of reproduction. Have you
noticed that after enjoying buffet dinner, your stomach or belly enlarges quite obviously? It
is because the ventral cavity allows for significant changes in the size and shape of the organs.
However, the dorsal cavity does not allow this to happen.
Subdivisions of the Posterior (Dorsal) and Anterior (Ventral)
The posterior (dorsal) and anterior (ventral) cavities are each subdivided into smaller
cavities. In the posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal
cavity (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord make
up a continuous, uninterrupted structure, the cranial and spinal cavities that house them
are also continuous. The brain and spinal cord are protected by the bones of the skull and
vertebral column and by cerebrospinal fluid, a colorless fluid produced by the brain, which
cushions the brain and spinal cord within the posterior (dorsal) cavity. The anterior (ventral)
cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity.
The thoracic cavity is the more superior subdivision of the anterior cavity, and it is enclosed
by the rib cage. The thoracic cavity contains the lungs and the heart, which is located in the
mediastinum. The diaphragm forms the floor of the thoracic cavity and separates it from
the more inferior abdominopelvic cavity. The abdominopelvic cavity is the largest cavity in
the body. Although no membrane physically divides the abdominopelvic cavity, it can be
useful to distinguish between the abdominal cavity, the division that houses the digestive
organs, and the pelvic cavity, the division that houses the organs of reproduction.
Abdominal Regions and Quadrants:
To promote clear communication, for instance about the location of a patient’s abdominal
pain or a suspicious mass, health care providers typically divide up the cavity into either
nine regions or four quadrants. The more detailed regional approach subdivides the cavity
with one horizontal line immediately inferior to the ribs and one immediately superior to
the pelvis, and two vertical lines drawn as if dropped from the midpoint of each clavicle
(collarbone). There are nine resulting regions. The simpler quadrants approach, which is
more commonly used in medicine, subdivides the cavity with one horizontal and one
vertical line that intersect at the patient’s umbilicus (navel).
Session 2.1.6 – Body Planes and Movements
As mentioned “anatomical position” serves as the basic reference for medical
communication. The body planes and some terminologies of movements will be
introduced in this video.
To communicate in anatomy, we need some point of reference. The basic reference starts
with the anatomical position. In this position the subject stands upright facing forward. The
arms are at the sides with the palms directed forward. The legs spread naturally with the
toes facing forward. The three major anatomical planes are the coronal plane, the sagittal
plane, also called median plane and the transverse plane, also called horizontal or axial
planes. The coronal plane extends vertically along the mid axillary line. It divides the body
into anterior, front, and posterior, back, portions. The sagittal plane also extends vertically
but along the mid sagittal line. It is perpendicular to the coronal plane and divides the body
into right and left portions. The direction towards the midline is called medial. Whereas the
direction away from the midline is called lateral. The transverse plane divides the body or
an organ horizontally into superior, upper and inferior, lower, portions. Other terms that
are used include proximal or cephalad, and distal or caudad. Now that we have learned
some planes, we can carry on to learn some terms about movements. First, we focus on the
arms. Abduction is the movement in the coronal plane away from the midline of the body.
Adduction is the movement towards the midline. To draw circles with the arm is called
circumduction. Similarly in the leg, movement in the coronal plane away from the midline
of the body is called abduction. Movement in the coronal plane towards the midline of the
body is called adduction. Flexion is the movement that decreases a joint angle such as
drawing the forearm towards the shoulder. Extension is the movement that straightens a
joint such as stretching the forearm. Supination and pronation refer to forearm
movements. Supination of the forearm is a movement that turns the palm to face
anteriorly. Pronation is the opposite movement, causing the palm to face posteriorly.
Body Planes:
A section is a two-dimensional surface of a three-dimensional structure that has been cut.
Modern medical imaging devices enable clinicians to obtain “virtual sections” of living
bodies. We call these scans. Body sections and scans can be correctly interpreted, however,
only if the viewer understands the plane along which the section was made. A plane is an
imaginary two-dimensional surface that passes through the body. There are three planes
commonly referred to in anatomy and medicine, as illustrated below.
o The sagittal plane is the plane that divides the body or an organ vertically into right and left
sides. If this vertical plane runs directly down the middle of the body, it is called the
midsagittal or median plane. If it divides the body into unequal right and left sides, it is
called a parasagittal plane or less commonly a longitudinal section.
o The frontal plane is the plane that divides the body or an organ into an anterior (front)
portion and a posterior (rear) portion. The frontal plane is often referred to as a coronal
plane. (“Corona” is Latin for “crown.”)
The transverse plane is the plane that divides the body or organ horizontally into upper
and lower portions. Transverse planes produce images referred to as cross sections.
Session 2.1.7 – The Skeletal System
Bones make good fossils. While the soft tissue of a once living organism will decay and fall
away over time, bone tissue will, under the right conditions, undergo a process of
mineralization, effectively turning the bone to stone. A well-preserved fossil skeleton can
give us a good sense of the size and shape of an organism, just as your skeleton helps to
define your size and shape. Unlike a fossil skeleton, however, your skeleton is a structure of
living tissue that grows, repairs, and renews itself. The bones within it are dynamic and
complex organs that serve a number of important functions, including some necessary to
maintain homeostasis.
The most apparent functions of the skeletal system are the gross functions—those visible by
observation. Simply by looking at a person, you can see how the bones support, facilitate
movement, and protect the human body. Just as the steel beams of a building provide a
scaffold to support its weight, the bones and cartilage of your skeletal system compose the
scaffold that supports the rest of your body. Without the skeletal system, you would be a
limp mass of organs, muscle, and skin.
Bones also facilitate movement by serving as points of attachment for your muscles. While
some bones only serve as a support for the muscles, others also transmit the forces produced
when your muscles contract. From a mechanical point of view, bones act as levers and joints
serve as fulcrums. Unless a muscle spans a joint and contracts, a bone is not going to move.
For information on the interaction of the skeletal and muscular systems, that is, the
musculoskeletal system, seek additional content.
The skeletal system consists of different types of bones located in different body parts. This
video is going to introduce to you the bone classification and markings.
Have you ever wondered how many bones are there in the human skeleton? At birth, there
are about 270 bones, and even more bones formed during childhood. With age, however,
some bones fused and ending up with an average of 206 bones in adults. Bones are classified
into different groups according to their shapes and corresponding functions. The four major
groups are namely: long bones, short bones, flat bones and irregular bones. Long bones
serve as rigid levers that are acted upon by the skeletal muscles to produce body movements.
An example here is the femur. Short bones have limited motion and merely glide across one
another, enabling the ankles and wrists to flex in multiple directions. An example here is the
tarsal bones in the foot. Flat bones enclose and protect soft organs and provide broad
surfaces for muscle attachment. An example here is the sternum in our chest. Irregular bones
include the vertebrae and some skull bones. They are irregular in shape. Externally, most of
the bone is covered with a sheath called the periosteum. Underneath the periosteum is the
hard compact bone. The inner layer is the relatively less dense spongy bone. The bone, even
though stable in shape, is a dynamic tissue. It requires good blood supply through some
nutrient arteries. Inside the spongy bone, the fine structures are arranged according to the
stress lines called trabeculae. The two major bone cells are called osteoblasts which is
responsible for bone building, whereas the osteoclasts are responsible for bone cutting and
resorption. The skeleton is divided into two regions namely the axial and appendicular
skeleton. The axial skeleton forms the central supporting axis of the body and mainly
includes the skull, the vertebral column and the rib cage. The appendicular skeleton includes
the bones of the upper limb and pectoral girdle, and bones of the lower limb and pelvic girdle.
The skull is the most complex part of the skeleton. it is composed of 22 bones. Most of them
are rigidly joined by sutures, joints that appear as seams on the cranial surface. The bones
forming the cranium include the frontal bone, parietal bone, occipital bone, temporal bone,
sphenoid bone and ethmoid bone. Some of the facial bones can be seen such as the nasal
bone, zygomatic bone, maxillary bone and mandible. In this lateral view we can see that the
frontal bone forms the forehead, the parietal bones form most of the cranial roof and part of
its walls, while the occipital bones form the back of the skull. The cranium serves to protect
the brain. Commonly called the backbone, the vertebral column, spine consists of a chain of
33 vertebrae with intervertebral discs of fibrocartilage between most of them. The vertebrae
are divided into five groups – 7 cervical vertebrae in the neck, 12 thoracic vertebrae in the
chest, 5 lumbar vertebrae in the lower back, 5 sacral vertebrae at the base of the spine, and
4 tiny coccygeal vertebrae. This is a lateral view of the vertebral column showing the spinal
curvatures. The thoracic and pelvic curvatures are called primary curvatures because they are
present at birth. Primary curvatures is concave anteriorly and developed during embryonic
growth. The cervical and lumbar curvatures are called secondary curvatures. They are
developed later when the baby lifts its head and starts walking. The thoracic cage consists of
the sternum,ribs and thoracic vertebrae. The sternum, breastbone, is a bony plate anterior
to the heart. It is subdivided into three regions the manubrium, body, and xiphoid process.
There are 12 pairs of ribs. Ribs 1 through 7 are called true ribs; each has its own costal cartilage
connecting it to the sternum. Ribs 8 through 12 are called false ribs because they lack
independent cartilaginous connections to the sternum. The costal cartilages fused to form
the costal margin. Ribs 11 and 12 are also called floating ribs. They are the "trouble-maker"
because when they are fractured in traffic accidents, they may puncture the kidneys and liver
causing severe internal bleeding. Please note that the clavicle and the scapula form the
pectoral girdle and they are part of the appendicular skeleton, not the axial skeleton. A
typical rib has a head that articulates with the body of its corresponding vertebra.
Immediately distal to the head, the rib narrows to a neck and then widens again to form a
rough area called the tubercle. Beyond the tubercle, the rib flattens and widens into a gently
sloping bladelike body, also called shaft. There are 12 thoracic vertebrae T1 – T12,
corresponding to the 12 pairs of ribs attached to them. The most obvious feature of a
vertebra is the body. This is the weight-bearing portion. The pedicle and lamina form the
vertebral arch to surround the vertebral foramen in the centre. This is the passage for the
spinal cord. The transverse process and the spinous process provide points of attachment for
spinal muscles and ligaments. One of the typical features for thoracic vertebrae is that the
body of each thoracic vertebra has small, smooth, slightly concave spots called costal facets
for attachment of the ribs. The rib articulates with the inferior costal facet of the upper
vertebra and the superior costal facet of the vertebra below that. The joints between the ribs
and thoracic vertebrae are called costovertebral joints. There are two costovertebral joints
on each side, namely the costotransverse joint, attaching the tubercule to the transverse
process, and the capitular joint joining the head of the rib to the body of the vertebra.
Bone Classification:
The 206 bones that compose the adult skeleton are divided into five categories based on
their shapes: Long bones, short bones, flat bones, irregular bones, and sesamoid bones.
Their shapes and their functions are related such that each categorical shape of bone has a
distinct function were mentioned in the video above.
Bone Markings:
The surface features of bones vary considerably, depending on the function and location in
the body. There are three general classes of bone markings: (1) articulations, (2) projections,
and (3) holes. As the name implies, an articulation is where two bone surfaces come together
(articulus = “joint”). These surfaces tend to conform to one another, such as one being
rounded and the other cupped, to facilitate the function of the articulation. A projection is
an area of a bone that projects above the surface of the bone. These are the attachment
points for tendons and ligaments. In general, their size and shape is an indication of the
forces exerted through the attachment to the bone. A hole is an opening or groove in the
bone that allows blood vessels and nerves to enter the bone. As with the other markings,
their size and shape reflect the size of the vessels and nerves that penetrate the bone at these
points. The table below describes different bone markings and their examples.
Session 2.1.8 – The bones of the upper and lower limbs
The upper limb includes the shoulder, humerus, elbow, forearm, wrist and hand. This is the
anterior view of the left shoulder. The humerus is the long bone in the upper arm. The scapula
is a triangular plate of flat bone on the back. The head of humerus articulates with the glenoid
fossa of the scapula to form the shoulder joint, also called glenohumeral joint. This is the
lateral view of the left shoulder. We are looking directly at the glenoid fossa from the side of
the body. The spine arises from the dorsal surface. The acromion is the lateral expansion that
corresponds to the summit of the shoulder joint. The coracoid process is a bony projection
that protrudes from the costal surface of the scapula. The head of humerus is characteristic
of a rounded surface that articulates with the glenoid fossa of the scapula. The ill-defined
anatomical neck corresponds to the rim of bone surrounding the base of the humeral head.
The surgical neck corresponds to the common site of traumatic fractures. The lesser tubercle
and the greater tubercle are two bony eminences for the insertions of the rotator cuff
muscles. The intertubular groove, also called bicipital groove is the location of the bicep
tendon. The distal end of the humerus is triangular in profile. The condyle of the humerus is
a collective term corresponding to the trochlea, capitulum, coronoid fossa, radial fossa and
the olecranon fossa. The trochlea and the capitulum are smooth articular surfaces of the
elbow joint. The medial epicondyle and the lateral epicondyle are the bony eminences
bilateral to the humeral condyle. The epicondyles are devoted to the muscles attachment.
The elbow joint consists of a pair of articulations with contributions from the humerus, radius
and ulna. Laterally, the capitulum articulates with the head of the radius. Medially, the
trochlea articulates with the trochlear notch. Flexion and extension of the forearm takes
place at the elbow joint. Supination and pronation of the forearm take place at the superior
and inferior radio-ulnar joints. The superior radio-ulnar joint is an articulation across the head
of radius and the radial notch of ulna. Please note that the radius crosses over the ulna in
pronation. In this specimen, the head, neck and radial tuberosity of the radius are
demonstrated. At the proximal end of the ulna is a deep, C-shaped trochlear notch that
wraps around the trochlea of the humerus. The posterior side of this notch is formed by a
prominent olecranon process. The anterior side is formed by a less prominent coronoid
process. Does it look like a spanner? The hand has a delicate bony framework. There are eight
carpal bones at the wrist, five metacarpal bones I -V at the palm and fourteen phalanges
making up the bones of the thumb and four fingers. Movements of the fingers take place at
the joints which are named according to the corresponding bones. The carpal bones
interarticulate with one another in two rows. The proximal row includes the scaphoid, lunate,
triquetral and pisiform. The distal row includes the trapezium, trapezoid, capitate, and
hamate. One way to remember the order of the carpal bones is to remember the first letter
of the phrase "Sam left the party to take Candy home." The pelvis girdle consists of a
complete ring composed of three bones – two hip bones and the sacrum. Bilaterally, the
sacrum articulates with hip bones via the sacro-iliac joints. Anteriorly, the hip bones
articulate at the cartilaginous pubic symphysis to give continuity of the bony pelvis around
the pelvic brim. The femur is attached to the pelvis at the hip joint. The spherical femoral
head, when fitting into the cup-shaped acetabulum, allows a wide-range of movements at
the hip region. The femur is the longest bone of the human body. The femoral head is an
articular part of the hip joint that connects to the femoral neck. The junction between the
femoral neck and the body is marked by two prominent bony projections known as the
greater trochanter and the lesser trochanter. The long axis of the femoral neck usually makes
an angle of approximately 120º to the long axis of the shaft of the femur. At the distal end of
the femur, there are two very prominent bony parts known as the femoral condyles. The
smooth areas of the medial femoral condyle and lateral femoral condyle contribute to the
articular surfaces of the knee joint. The intercondylar fossa is an integral part of the knee
joint that houses the cruciate ligaments. The patella attaches to the anterior patellar surface.
At the knee joint, the femur articulates with the patella as well as the tibia. The thick strong
tibia on the medial side bears all the weight. The slender fibula on the lateral side helps to
stabilize the ankle. Much of the shaft of the tibia and the shaft of the fibula are devoted to
muscles attachment. The gap between the tibia and the fibula is connected by the
interosseous membrane. At the ankle region, there are two prominent bony eminences
arising from the tibia and fibula known as the medial malleolus and lateral malleolus
respectively. Similar to the hand, the foot is made up of several kinds of bones. Tarsal bones
form the heel and ankle Metatarsal bones form the dorsum of the foot. Phalanges form the
toes. There are seven tarsal bones, namely the three cuneiforms, cuboid, navicular, talus,
and calcaneus.
Humerus, radius and ulna are the long bones of upper limbs. Recall what we mentioned in
video 2.1.7, the structure of a long bone allows for the best visualization of all of the parts of
a bone. A long bone has two parts: the diaphysis and the epiphysis. The diaphysis is the
tubular shaft that runs between the proximal and distal ends of the bone. The hollow region
in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The walls
of the diaphysis are composed of dense and hard compact bone.
The wider section at each end of the bone is called the epiphysis (plural = epiphyses), which
is filled with spongy bone. Red marrow fills the spaces in the spongy bone. Each epiphysis
meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate
(growth plate), a layer of hyaline (transparent) cartilage in a growing bone. When the bone
stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by
osseous tissue and the epiphyseal plate becomes an epiphyseal line.
The medullary cavity has a delicate membranous lining called the endosteum (end- = “inside”;
oste- = “bone”), where bone growth, repair, and remodeling occur. The outer surface of the
bone is covered with a fibrous membrane called the periosteum (peri- = “around” or
“surrounding”). The periosteum contains blood vessels, nerves, and lymphatic vessels that
nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The
periosteum covers the entire outer surface except where the epiphyses meet other bones to
form joints. In this region, the epiphyses are covered with articular cartilage, a thin layer of
cartilage that reduces friction and acts as a shock absorber.