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CHAPTER 1: AN INTRODUCTION TO THE HUMAN BODY
Learning Outcomes:
1. Differentiate the structure of the body from simplest to most complex, in
terms of the six levels of organization
2. Distinguish the functional characteristics of human life.
3. Label body structures, body regions, and directions in the body
Overview of Anatomy and Physiology
Anatomy is the study of the structure of body parts and their relationships to
one another which includes:
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Gross or macroscopic
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Microscopic
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Developmental
Physiology is the study of the function of the body’s structural machinery.
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Considers the operation of specific organ systems
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Renal – kidney function
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Neurophysiology – workings of the nervous system
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Cardiovascular – operation of the heart and blood vessels
Focuses on the functions of the body, often at the cellular or
molecular level
Gross Anatomy
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Regional – all structures in one part of the body (such as the abdomen
or leg)
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Systemic – gross anatomy of the body studied by system
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Surface – study of internal structures as they relate to the overlying skin
Microscopic Anatomy
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Cytology – study of the cell
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Histology – study of tissues
Developmental Anatomy
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Traces structural changes throughout life
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Embryology – study of developmental changes of the body before birth
Specialized Branches of Anatomy
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Pathological anatomy – study of structural changes caused by disease
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Radiographic anatomy – study of internal structures visualized by X ray
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Molecular biology – study of anatomical structures at a sub-cellular
level
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STRUCTURAL ORGANIZATION OF THE HUMAN BODY
Fig. 1.1 Levels of organization of the body. Source: Tortora and
Derrickson (2013).
1. Chemical Level
It involves interactions between atoms, which are tiny building blocks of
matter. Atoms can combine to form molecules, such as water, sugar,
fats, and proteins. The function of a molecule is related intimately to its
structure.
2. Cellular Level
Cells are the basic structural and functional units of organisms, such as
plants and animals. Molecules can combine to form organelles (or ga˘nelz), which are the small structures that make up cells.
3. Tissue Level
Tissue is made up of similar cells and the materials surrounding them.
The characteristics of the cells and surrounding materials determine the
functions of the tissue. Example: bone and muscle.
4. Organ Level
An organ is an organization of several different kinds of tissues so
arranged that together they can perform a special function. For example,
the stomach is an organization of muscle, connective, epithelial, and
nervous tissues. Muscle and connective tissues form its wall, epithelial
and connective tissues form its lining, and nervous tissue extends
throughout both its wall and its lining.
5. System Level
It is a group of organs that have a common function or set of functions
and are therefore viewed as a unit. For example, the urinary system
consists of the kidneys, ureter, urinary bladder, and urethra.
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6. Organism Level
Organism is any living thing considered as a whole —whether composed
of one cell, such as a bacterium, or of trillions of cells, such as a human.
The human organism is a complex of organ systems, all mutually
dependent on one another.
Body Functions & Life Process
Body Functions
Body functions are the physiological or psychological functions of body
systems. The body's functions are ultimately its cells' functions. Survival is the
body's most important business. Survival depends on the body's maintaining
or restoring homeostasis, a state of relative constancy, of its internal
environment.
Homeostasis is a key word in modern physiology. It comes from two
Greek words - "homeo," meaning the same, and "stasis," meaning standing.
"Standing or staying the same" then is the literal meaning of homeostasis.
Homeostasis is the body’s attempt to maintain a stable internal environment by
achieving some sort of balance. The body is normally able to achieve a
relatively stable internal environment even though the external environment is
constantly changing – from cold to hot, or from dry to wet, and so on. The body
uses various homeostatic mechanisms to monitor and maintain a dynamic
state of equilibrium within the body – that is, a balance in which the internal
environment conditions can react to external environmental conditions by
changing within quite narrow limits.
Fig 1.2
Homeostasis depends on the body's
ceaselessly
carrying
on
many
activities. Its major activities or
functions are responding to changes
in
the
body's
environment,
exchanging materials between the
environment and cells, metabolizing
foods, and integrating all of the body's
diverse activities.
Homeostasis
• Homeostasis is the ability to maintain a
relatively stable internal environment in an
ever-changing outside world
• The internal environment of the body is in a
dynamic state of equilibrium
• Chemical, thermal, and neural factors
interact to maintain homeostasis
Homeostatic Imbalance
• Disturbance of homeostasis or the body’s
normal equilibrium
• Overwhelming of negative feedback
mechanisms allowing destructive positive
feedback mechanisms to take over-possible
disease,death
The body's ability to perform many of
its functions changes gradually over
the years. In general, the body
performs its functions least well at
both ends of life - in infancy and in
old age. During childhood, body
functions gradually become more and more efficient and effective. During late
maturity and old age the opposite is true. They gradually become less and less
efficient and effective. During young adulthood, they normally operate with
maximum efficiency and effectivenes.
Characteristics of Life
All living organisms have certain characteristics in common. Although these
characteristics may differ from organism to organism, they are all important for
the maintenance of life. The following are a brief description of the life process:
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1. Metabolism
Metabolism is a broad term that includes all the chemical reactions that occur
in the body. One phase of metabolism is catabolism in which complex
substances are broken down into simpler building blocks and energy is
released.
2. Responsiveness
Responsiveness or irritability is concerned with detecting changes in the
internal or external environments and reacting to that change. It is the act of
sensing a stimulus and responding to it.
3. Movement
Changes in position as well as motion are parts of movement. On the cellular
level, molecules move from one place to another. Blood moves from one part of
the body to another. The diaphragm moves with every breath. The ability of
muscle fibers to shorten and thus to produce movement is called contractility.
4. Reproduction
It is the formation of new cells or new organisms. Without reproduction,
growth and development are not possible. Without reproduction of the
organism, species become extinct.
5. Growth
Growth refers to an increase in size either through the number of cells or
through an increase in the size of each individual cell. In order for growth to
occur, anabolic processes must occur at a faster rate than catabolic processes.
6. Differentiation
Differentiation is a developmental process by which unspecialized cells
change into specialized cells with distinctive structural and functional
characteristics. Through differentiation, cells develop into tissues and organs.
The life processes described above are not enough to ensure the survival of the
individual. In addition to these processes, life depends on certain physical
factors from the environment. These include water, oxygen, nutrients, heat,
and pressure.
Anatomical Terminology
Before we get into the
following learning units,
which will provide more
detailed
discussion
of
topics on different human
body
systems,
it
is
necessary to learn some
useful
terms
for
describing body structure.
Knowing these terms will
make it much easier for
us to understand the
content of the following
learning
units.
Three
Groups of terms are
introduced here:
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Anatomical Position
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Anatomical Locations
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Directional Terms
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Planes of the Body
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Body Cavities
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Anatomical position is a common visual reference point where in:
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Person stands erect with feet together and eyes forward
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Palms face anteriorly with the thumbs pointed away from the body
Regional terms – names of specific body areas Fig. 1-3
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Axial region – the main axis
of the body
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Appendicular
region – the limbs
Source: Pearson Education 2007
Directional terminology
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Refers to the body
in
anatomical
position
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Standardized terms of directions are
paired terms
Anatomical Locations
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Source: Pearson Education 2007
Cervical: neck
Deltoid: round part of the shoulder
Digital: fingers and toes
Dorsum: back
Femoral: thigh
Frontal: forehead
Gluteal: buttocks
Hallux: big toe
Inguinal: groin
• Pubic: genital region
Lumbar: lower back
• Sacral: lower back
between the hips
Mammary: breast
• Scapular: shoulder
Mental: chin
blade
Nasal: Nose
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Tarsal: ankle
Occipital: base of the skull
• Thoracic: chest
Olecranal: elbow
• Vertebral: spine
Oral: mouth
Orbital: bony eye socket
Otic: ear
Palmar: palm of hand
Patellar: Kneecap
Pedal: Foot
Pelvic: pelvis region
Perineal: area between anus and external genitals
Plantar: sole of foot
Pollex: thumb
Popliteal: behind the knee
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Directional Terms
Directional terms describe the positions of structures relative to other
structures or locations in the body.
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Fig. 1-6
Source: Pearson Education 2007
Fig. 1-7
Source: Pearson Education 2007
Planes of the Body
Coronal Plane (Frontal Plane) - A vertical plane running from side to side;
divides the body or any of its parts into anterior and posterior portions.
Sagittal Plane (Lateral Plane) - A vertical plane running from front to back;
divides the body or any of its parts into right and left sides.
Axial Plane (Transverse Plane) - A horizontal plane; divides the body or any of
its parts into upper and lower parts.
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Median plane - Sagittal plane through the midline of the body; divides the
body or any of its parts into right and left halves.
Oblique Plane- An oblique plane cuts made diagonally. Oblique section
through the trunk
Fig. 1-8
Fig. 1- 9
Source: Pearson Education 2007
Body Cavities
The cavities, or spaces, of the body contain the internal organs, or viscera. The
two main cavities are called the ventral and dorsal cavities. The ventral is the
larger cavity and is subdivided into two parts (thoracic and abdominopelvic
cavities) by the diaphragm, a dome-shaped respiratory muscle.
Fig. 1-10
Source: Pearson Education 2007
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The smaller of the two main cavities is called the dorsal cavity. As its
name implies, it contains organs lying more posterior in the body. The dorsal
cavity, again, can be divided into two portions. The upper portion, or the
cranial cavity, houses the brain, and the lower portion, or vertebral canal
houses the spinal cord.
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Dorsal cavity protects the nervous system, and is divided into two
subdivisions
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Cranial cavity is within the skull and encases the brain
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Vertebral cavity runs within the vertebral column and encases the
spinal cord
Ventral cavity houses the internal organs (viscera), and is divided into two
subdivisions: - Thoracic and Abdominopelvic cavities
Fig. 1-11
Source: Pearson Education 2007
Thoracic cavity
The upper ventral, thoracic, or chest cavity contains the heart, lungs,
trachea, esophagus, large blood vessels, and nerves. The thoracic cavity is
bound laterally by the ribs (covered by costal pleura) and the diaphragm
caudally (covered by diaphragmatic pleura).
Thoracic cavity is subdivided into pleural cavities, the mediastinum, and the
pericardial cavity
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Pleural cavities – each houses a lung
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Mediastinum – contains the pericardial cavity, and surrounds the
remaining thoracic organs
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Pericardial cavity – encloses the heart
Abdominal and pelvic cavity
The lower part of the ventral (abdominopelvic) cavity can be further divided
into two portions: abdominal portion and pelvic portion. The abdominal cavity
contains most of the gastrointestinal tract as well as the kidneys and adrenal
glands. The abdominal cavity is bound cranially by the diaphragm, laterally by
the body wall, and caudally by the pelvic cavity. The pelvic cavity contains most
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of the urogenital system as well as the rectum. The pelvic cavity is bounded
cranially by the abdominal cavity, dorsally by the sacrum, and laterally by the
pelvis.
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The abdominopelvic cavity is separated from the superior thoracic
cavity by the dome-shaped diaphragm
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It is composed of two subdivisions
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Abdominal cavity – contains the stomach, intestines, spleen, liver,
and other organs
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Pelvic cavity – lies within the pelvis and contains the bladder,
reproductive organs, and rectum
Serous cavities – a slit-like space lined by a serous membrane
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Pleura, pericardium, and peritoneum
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Parietal serosa – outer wall of the cavity
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Visceral serosa covers the visceral organs
Fig. 1-12
Source: Pearson Education 2007
Other Body Cavities
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Oral and digestive – mouth and cavities of the digestive organs
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Nasal –located within and posterior to the nose
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Orbital – house the eyes
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Middle ear – contain bones (ossicles) that transmit sound vibrations
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Synovial – joint cavities
MEDICAL IMAGING
1. Radiography- two dimensional image, a single barrage of x-rays
passes through the body, producing an image of interior structure
on x-ray sensitive film.
2. Magnetic Resonance Imaging (MRI)- two –three dimensional
blueprint of cellular chemistry.
3. Diffusion Tension Imaging (DTI)- tracks movements of water
molecules along the length of axons, long processes of nerve cells
that form the white matter in the brain.
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4. Computed Tomography (CT)- x-ray beam traces an arc at
multiple angles around a section of the body. The transverse
section of the body, called a CT scan, is shown on a video monitor.
5. Coronary Computed Tomography Angiography Scan- an iodine
containing contrast medium is injected into a vein and a betablocker is given to decrease heart rate. It results in a threedimensional image of the coronary blood vessels on a monitor.
6. Ultrasound Scanning- High- frequency sound waves produced by
a handheld wand reflect off body tissues and are detected by the
same instrument. Moving or still image shown on monitor also
called sonogram.
7. Endoscopy- visual examination of the inside of the body organs or
cavities using a lighted instrument with lenses called endoscope.
The image is shown on the monitor.
Summary Review: Introduction to the Human Body
Here is what we have learned from Introduction to the Human Body:
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The human body is a single structure but it is made up of billions of
smaller structures of six level of organization: chemical, cellular, tissues,
organs, systems and organisms.
An organ is an organization of several different kinds of tissues so
arranged that together they can perform a special function.
A system is an organization of varying numbers and kinds of organs so
arranged that together they can perform complex functions for the body.
Eleven major systems include the integumentary, skeletal, muscular,
nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive,
urinary, and the reproductive system.
Body functions are the physiological or psychological functions of body
systems. Survival of the body depends on the body's maintaining or
restoring homeostasis, a state of relative constancy, of its internal
environment.
Human life process includes metabolism, responsiveness, movements,
reproduction, growth, and differentiation. All these processes work
together, in fine-tuned balance, for the well-being of the individual and to
maintain life.
Life depends on certain physical factors from the environment, which
include water, oxygen, nutrients, heat, and pressure.
Useful terms for describing body parts and activities include:
o Directional terms
o Terms describing planes of the body
o Terms describing body cavities