Q #01. Differentiate among the 5 body cavities. Describe what organs are contained in
each body cavity?
Answer:
“A body cavity is any fluid filled space in the body other than those of vessels (arteries,
veins and lymph vessels).”
There are 5 body cavities in the human body. These are:
1. Cranial cavity.
2.
3.
4.
5.
Vertebral cavity.
Thoracic cavity.
Abdominal cavity.
Pelvic cavity.
1…CRAINAL CAVITY:
The cranial cavity is the cavity that is enclosed by the cranium and houses the
brain.
The cranium (skull) is the skeleton of the head. A series of bones form its two parts,
the neurocranium and viscerocranium. The neurocranium is the bony case of the brain
and its membranous coverings, the cranial meninges. It also contains proximal parts of
the cranial nerves and the vasculature of the brain. The neurocranium in adult is formed
by a series of eight bones: four singular bones centered on the midline (frontal,
ethmoidal, sphenoidal, and occipital) and two sets of bones occurring as bilateral pairs
(temporal and parietal). The viscerocranium (facial skeleton) comprises the facial
bones. It forms the anterior part of the cranium and consists of bones surrounding the
mouth (upper and lower jaws), nasal cavity, and most of the orbits (eye sockets or
orbital cavities).
The walls of the cranial cavity vary in thickness in different regions. They are usually
thinner in females than in males and are thinner in children and elderly people. The
bones tend to be thinnest in areas that are well covered with muscles, such as the
squamous part of the temporal bone.
The cranial cavity houses the brain. Brain is divided in to 4 lobes i.e., frontal, parietal,
temporal, and occipital lobes. So the cranial cavity is the site of our consciousness,
ideas, creativity, imagination, responses, decision making, and memory.
This figure shows the bones that form the cranial cavity.
2…VERTEBRAL CAVITY:
The partially closed, membrane-lined sterile anatomical space, a subdivision of
the dorsal body cavity, which houses the inferior portion of the central nervous system,
i.e., the spinal cord; its lining are the three connective tissue layers known as the spinal
meninges, i.e., the dura mater, arachnoid, and pia mater; it is located medially on the
posterior of the trunk and housed within the confines of the vertebrae; it contains the
spinal cord, various spinal blood vessels, adipose tissue, and the roots of the spinal
nerves; it provides a protected space for the spinal cord.
Figure shows the spinal cord that is
present in the vertebra.
3…ABDOMINAL CAVITY:
The closed, membrane-lined sterile anatomical space which houses various
internal organs, particularly those of the digestive system; its lining is a serous
membrane, the peritoneal membrane; it is located medially on the anterior of the
trunk, inferior to the thoracic cavity, superior to pelvic cavity.
The principal viscera of the abdomen are the terminal part of the esophagus and
the stomach, intestines, spleen, pancreas, liver, gallbladder, kidneys, and
suprarenal glands, blood vessels, nerves and lymphatic. Distended urinary
bladder and the gravid uterus are also in the contents of the abdominal cavity.
4…THORACIC CAVITY:
The closed, partially membrane-lined sterile anatomical space, a subdivision of
the ventral body cavity, which houses the lungs, heart, and the organs of the
mediastinum; its linings are the three serous membranes known as the pleural
membranes and the pericardial membrane; it is located medially on the anterior of the
trunk and housed within the confines of the rib cage; it provides a protected space for
those organs.
The thorax is the part of body between the neck and the abdomen. The thoracic
cavity and its walls have the shape of truncated cone, being narrowest superiorly, with
the circumference increasing inferiorly, and reaching the maximum at the junction with
the abdominal portion of the trunk. Diaphragm is a muscular structure that separates the
thoracic cavity from the abdominal cavity.
The majority of the thoracic cavity is occupied by the lungs, which provide for the
exchange of oxygen and carbon dioxide between the air and blood. Most of the
remainder of the thoracic cavity is occupied by the heart and the rest is occupied by the
tracheobronchial tree, and organs of mediastinum.
Figure shows the thoracic cavity and its contents.
5…PELVIC CAVITY:
The pelvic cavity is the inferior most part of the abdominopelvic cavity. The
partially closed, membrane-lined sterile anatomical space which houses some of the
reproductive organs, the urinary bladder, and the distal colon; its lining is a serous
membrane, a portion of the peritoneal membrane; it is located inferiorly within the
abdominopelvic cavity, bounded superiorly by the abdominal cavity, with which it is
continuous, and inferiorly by the walls of the pelvic girdle and its musculature; it
provides a protected space for those organs.
It is continuous with the abdominal cavity at the pelvic inlet but angulated
posterior from it. The pelvic cavity contains the terminal parts of the uterus, the urinary
bladder, rectum, pelvic genital organs, blood vessels, lymphatic, and nerves. In addition
to these distinctly pelvic viscera, it also contains what might be considered an outflow of
abdominal viscera: loops of small intestine (mainly ileum) and, frequently. Large
intestine (appendix and transverse and/or sigmoid colon).
The pelvic cavity is limited inferiorly by the musculofascial pelvic diaphragm,
which is suspended above (but descends centrally to the level of) the pelvic outlet,
forming a bowl-like pelvic floor. The pelvic cavity is bounded posteriorly by the coccyx
and inferiormost sacrum, with the superior part of the sacrum forming a roof over the
posterior half of the cavity.
A very simple figure shows the pelvic cavity and its contents.
Q #02: list the divisions of the spinal cord and specify the numbers of bones contained
in each division. Also, indicate the importance of each division in the total construction
of the body.
Answer:
The vertebral column in an adult typically consists of 33 vertebrae arranged in five
regions:





7 cervical.
12 thoracic.
5 lumbar.
5 sacral.
4 coccygeal.
Figure shows the different segments of vertebral column.
Significant motion occurs only between the 25 superior vertebrae. Of the 9 inferior
vertebrae, the 5 sacral vertebrae are fused in adults to form the sacrum, and after
approximately age 30, the 4 coccygeal vertebrae fuse to form the coccyx. The
lumbosacral angle occurs at the junction of the long axes of the lumbar region of the
vertebral column and the sacrum. The vertebrae gradually become larger as the
vertebral column descends to the sacrum and then become progressively smaller
toward the apex of the coccyx. The change in size is related to the fact that successive
vertebrae bear increasing amounts of the body's weight as the column descends. The
vertebrae reach maximum size immediately superior to the sacrum, which transfers the
weight to the pelvic girdle at the sacroiliac joints.
The vertebral column is flexible because it consists of many relatively small bones,
called vertebrae (singular = vertebra), that are separated by resilient IV discs. The 25
cervical, thoracic, lumbar, and first sacral vertebrae also articulate at synovial
zygapophysial joints, which facilitate and control the vertebral column's flexibility.
Although the movement between two adjacent vertebrae is small, in aggregate the
vertebrae and IV discs uniting them form a remarkably flexible yet rigid column that
protects the spinal cord they surround.
Function of Vertebrae:
Vertebrae vary in size and other characteristics from one region of the vertebral
column to another, and to a lesser degree within each region; however, their basic
structure is the same.
CERVICAL VERTEBRAE
Cervical vertebrae form the skeleton of the neck. The smallest of the 24 movable
vertebrae, the cervical vertebrae are located between the cranium and the thoracic
vertebrae. Their smaller size reflects the fact that they bear less weight than do the
larger inferior vertebrae. Although the cervical IV discs are thinner than those of inferior
regions, they are relatively thick compared to the size of the vertebral bodies they
connect. The relative thickness of the discs, the nearly horizontal orientation of the
articular facets, and the small amount of surrounding body mass give the cervical region
the greatest range and variety of movement of all the vertebral regions.
THORACIC VERTEBRAE
The thoracic vertebrae are in the upper back and provide attachment for the ribs.
Thus the primary characteristic features of thoracic vertebrae are the costal facets for
articulation with ribs.
LUMBAR VERTEBRAE
Because the weight they support increases toward the inferior end of the vertebral
column, lumbar vertebrae have massive bodies, accounting for much of the thickness of
the lower trunk in the median plane.
SACRUM
The sacrum provides strength and stability to the pelvis and transmits the weight of
the body to the pelvic girdle, the bony ring formed by the hip bones and sacrum, to
which the lower limbs are attached.
COCCYX
The coccyx does not participate with the other vertebrae in support of the body
weight when standing; however, when sitting it may flex anteriorly somewhat, indicating
that it is receiving some weight. The coccyx provides attachments for muscles.
Q #03. Define a plane of the body and then identify the 3 types of the planes.
Differentiate among the 3 types of the planes by pointing out significant attributes that
distinguished it from others.
Answer:
Definition:
“An imaginary flat surface that divides the body or a part of the body into two parts; the
standard perspectives for such sections in anatomical imaging are the sagittal, frontal,
and transverse (cross) sections.”
Types of Planes:
1. Sagittal plane.
2. Frontal plane.
3. Transverse plane.
Sagittal Plane:

Sagittal plane is a vertical plane which passes from ventral to dorsal dividing
the body into right and left halves. Sagittal planes also are oriented vertically, but are
at right angles to the coronal planes and divide the body into right and left parts. The
plane that passes through the center of the body dividing it into equal right and left
halves is termed the median sagittal plane. Sagittal plane that divides the body
into unequal right and left regions is known as the parasagittal plane.
Frontal Plane:
Frontal (coronal) planes are vertical planes dividing the body into anterior (front)
and posterior (back) parts. Coronal planes are oriented vertically and divide the body
into anterior and posterior parts.
Transverse Plane:
Transverse, horizontal, or axial planes divide the body into superior and inferior
parts. Dividing the body into superior (upper) and inferior (lower) parts.
Radiologists refer to transverse planes as transaxial, which is commonly
shortened to axial planes.
The figure shows the main planes of the body.
Sagittal
1 It divides the body in to two equal
halves.
2 It is parallel to median plane (the
vertical plane passing longitudinally
through the body divides the body
into right and left halves.).
3 The vertical plane that runs through
the body from front to back or from
back to front.
Frontal or coronal
It divides the body in
to anterior and
posterior parts.
It is right angle to
median plane.
Transverse
It divides the body in
to superior and inferior
parts.
It is right angle to
median plane and
frontal plane.
The vertical plane
that runs through the
center of the body
from side to side.
The horizontal plane
that runs through the
mid section of the
body.
Understanding anatomical directional terms and body planes will make it easier to study
anatomy. It will help us to be able to visualize positional and spacial locations of
structures and navigate directionally from one area to another.
Q #04. Distinguish between X-ray and magnetic resonance imaging (MRI) and
research the differences.
Answer:
X-ray is an electromagnetic wave of high energy and very short wavelength
(between ultraviolet light and gamma rays), which is able to pass through many
materials opaque to light. It is a a photographic or digital image of the internal
composition of something, especially a part of the body, produced by X-rays being
passed through it and being absorbed to different degrees by different materials.
When a radiograph is taken, X-rays reach the film and darken it. The more X-rays reach
an area of the film, the darker that area will be on the radiograph. Therefore, if an object
is very dense, less X-rays will reach the film and consequently the image of the object
will appear white on the radiograph. However, if an object has little density, its image
will appear black on the radiograph because it allows most of the X-ray beam to reach
the film. Only five basic radiographic densities exist. They are in order of increasing
brightness; gas, fat, fluid, bone and metal densities. This is a key concept. Anatomic
structures seen on the radiograph can be identified by their characteristic density. For
example, the lungs are dark, or air density, because they are filled with air. Organs such
as the heart are largely composed of water. Therefore it is no surprise that they appear
lighter than the lungs, because they are fluid density. Bones are brighter structures
because they are composed of calcium.
The basic principles of magnetic resonance imaging (MRI) depend on the fact that
the nuclei of certain elements align with the magnetic force when placed in a strong
magnetic field. At the field strengths currently used in medical imaging, hydrogen nuclei
(protons) in water molecules and lipids are responsible for producing anatomical
images. If a radiofrequency pulse at the resonant frequency of hydrogen is applied, a
proportion of the protons change alignment, flipping through a preset angle, and rotate
in phase with one another. Following this radiofrequency pulse, the protons return
(realign) to their original positions. As the protons realign (relax), they induce a radio
signal which, although very weak, can be detected and localized by antenna coils
placed around the patient.
X-ray
MRI
1 X-Rays uses the electric radiation in order to
capture an image of the internal structure.
MRI uses magnetic radiation to capture the
image.
2 X-rays are primarily used for bones injuries e.g.
broken bones.
MRIs can be used for soft tissues, brain
tumor, spinal cord injury, ligament and
tendons injury etc.
3 X-rat uses the radiation to capture the internal view MRI uses the water in our body and the
of the body.
protons in the water molecules to capture the
image of the body.
4 The time taken for the complete scan is few
seconds
Time taken for the complete scanning
typically runs for about 30 minutes.
5 X-ray emits the radiations so leave the permanent MRI doesn’t emit radiations so it doesn’t have
or hazardous effect on the body e.g. mutations,
any lasting biological hazardous effect on the
birth defects etc.
body.
6 MRI can give images in any plane.
X-ray doesn’t have this ability.
References:





Gray’s anatomy for students. 2nd edition.
Clinically oriented anatomy 6th edition by Keith L. Moore.
Clinical Radiology Made Ridiculously Simple. Series 2003 Edition.
http://www.diffen.com/difference/MRI_vs_X-ray
http://biology.about.com/od/anatomy/a/aa072007a.htm
Thank you 