The document discusses the levels of structural organization in the human body from smallest to largest: chemicals, cells, tissues, organs, organ systems, and the organism. It provides examples of each level, with chemicals being the smallest building blocks including atoms and molecules, cells being the next level as the basic unit of structure and function, tissues being groups of cells working together, and organs and organ systems being higher levels of organization in the body. Standard anatomical terminology and positions are also introduced to describe body structures.

1. 1
Levels of Structural organization
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,
such as (from smallest to largest): chemicals,
cells, tissues, organs, organ systems,
and an organism.

2. The organization of the
body often is discussed
in terms of the distinct
levels of increasing
complexity, from the
smallest chemical
building blocks to a
unique human organism.
Dr Jyoti Prasad Pattnaik,
MBBS
2

3. 3
Chemical Level
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.
Examples of these elements 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.

4. 4
Cellular Level
A cell is the smallest independently
functioning unit of a living organism. Single celled
organisms, like bacteria, are extremely small,
independently-living organisms with a cellular
structure. Humans are multicellular organisms with
independent cells working in concert together.
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.

5. 5
Higher levels
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.

6. 6
Organ Systems
•Integumentrary
system
•Muscular system
•Cardio-Vascular
system
•Digestive system
•Urinary system
•respiratory system
•Nervous system
•Male Reproductive
system
•Female Reproductive
system
•Endocrine system
•Lymphatic system
There are eleven organ systems in human
body including,

7. Dr Jyoti Prasad Pattnaik,
MBBS
7
Anatomical Nomenclature
Over the centuries, anatomists developed
a standard nomenclature, or method of
naming anatomical structures.
Terms such as "up" or "down" obviously have
no meaning unless the orientation of the body is
clear. When a body is lying on its back, the thorax
and abdomen are at the same level. The upright
sense of up and down is lost.

8. 8
Anatomical Position
In order to standardize nomenclature,
anatomical terms relate to the standard
anatomical position.
When the human body is in the standard
anatomical position it is upright, erect on two legs,
facing frontward, with the arms at the sides with
each rotated so that the palms of the hands turn
forward.

9. 9
Common Anatomical Terms
In the standard anatomical position, superior
means toward the head or the cranial end of the
body.
The term inferior means toward the feet or
the caudal end of the body.
The frontal surface of the body is the anterior
or ventral surface of the body. Accordingly, the
terms "anteriorly" and "ventrally" specify a position
closer to—or toward—the frontal surface of the
body. The back surface of the body is the posterior
or dorsal surface and the terms "posteriorly" and
"dorsally" specify a position closer to—or toward—
the posterior surface of the body.

10. Directional Terms
•Superior
•Inferior
•Medial
•Lateral
•Anterior
•Posterior
•Cranial
•Caudal
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•Proximal
•Distal
•Median
•Right
•Left
•Ventral
•Dorsal
•Prone
•Supine

11. 11
Regions of the body
The principal regions of the human body
include
1. Head
2. Neck
3. Trunk
4. Upper limb
5. Lower Limb

12. Anatomical Planes
Anatomy is often
described in planes,
referring to two-
dimensional sections of
the body. A section is a
two-dimensional surface
of a three- dimensional
structure that has been
cut. A plane is an
imaginary two-
dimensional surface that
passes through the
body.
12

13. 13
Anatomical Planes
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.
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, following Latin corona, which means
"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.

14. Abdomino-pelvic Quadrants
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15. Body Cavities
A body cavity is
any space or
compartment, or
potential space in the
animal body. Cavities
accommodate organs
and other structures;
cavities as potential
spaces contain fluid.
The two largest human
body cavities are the
ventral body cavity, and
the dorsal body cavity.
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16. Body Cavities
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