<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Describe the structure of the human body in terms of six levels of organization
  • List the eleven organ systems of the human body and identify at least one organ and one major function of each

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 ( [link] ).

Levels of structural organization of the human body

This illustration shows biological organization as a pyramid. The chemical level is at the apex of the pyramid where atoms bond to form molecules with three dimensional structures. An example is shown with two white hydrogen atoms bonding to a red oxygen atom to create water. The next level down on the pyramid is the cellular level, as illustrated with a long, tapered, smooth muscle cell. At this level, a variety of molecules combine to form the interior fluid and organelles of a body cell. The next level down is the tissue level. A community of similar cells forms body tissue. The example given here is a section of smooth muscle tissue, which contains many smooth muscle cells closely bound side by side. The next level down is the organ level, as illustrated with the bladder and urethra. The bladder contains smooth muscle while the urethra contains skeletal muscle. These are both examples of muscle tissues. The next level down is the organ system level, as illustrated by the entire urinary system containing the kidney, ureters, bladder and urethra. At this level, two or more organs work closely together to perform the functions of a body system. At the base of the pyramid is the organismal level illustrated with a woman drinking water. At this level, many organ systems work harmoniously together to perform the functions of an independent organism.
The organization of the body often is discussed in terms of six distinct levels of increasing complexity, from the smallest chemical building blocks to a unique human organism.

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.

This book covers eleven distinct organ systems in the human body ( [link] and [link] ). Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system.

Organ systems of the human body

This illustration shows eight silhouettes of a human female, each showing the components of a different organ system. The integumentary system encloses internal body structures and is the site of many sensory receptors. The integumentary system includes the hair, skin, and nails. The skeletal system supports the body and, along with the muscular system, enables movement. The skeletal system includes cartilage, such as that at the tip of the nose, as well as the bones and joints. The muscular system enables movement, along with the skeletal system, but also helps to maintain body temperature. The muscular system includes skeletal muscles, as well as tendons that connect skeletal muscles to bones. The nervous system detects and processes sensory information and activates bodily responses. The nervous system includes the brain, spinal cord, and peripheral nerves, such as those located in the limbs. The endocrine system secretes hormones and regulates bodily processes. The endocrine system includes the pituitary gland in the brain, the thyroid gland in the throat, the pancreas in the abdomen, the adrenal glands on top of the kidneys, and the testes in the scrotum of males as well as the ovaries in the pelvic region of females. The cardiovascular system delivers oxygen and nutrients to the tissues as well as equalizes temperature in the body. The cardiovascular system includes the heart and blood vessels.
Organs that work together are grouped into organ systems.

Organ systems of the human body (continued)

The lymphatic system returns fluid to the blood and defends against pathogens. The lymphatic system includes the thymus in the chest, the spleen in the abdomen, the lymphatic vessels that spread throughout the body, and the lymph nodes distributed along the lymphatic vessels. The respiratory system removes carbon dioxide from the body and delivers oxygen to the blood. The respiratory system includes the nasal passages, the trachea, and the lungs. The digestive system processes food for use by the body and removes wastes from undigested food. The digestive system includes the stomach, the liver, the gall bladder (connected to the liver), the large intestine, and the small intestine. The urinary system controls water balance in the body and removes and excretes waste from the blood. The urinary system includes the kidneys and the urinary bladder. The reproductive system of males and females produce sex hormones and gametes. The male reproductive system is specialized to deliver gametes to the female while the female reproductive system is specialized to support the embryo and fetus until birth and produce milk for the infant after birth. The male reproductive system includes the two testes within the scrotum as well as the epididymis which wraps around each testis. The female reproductive system includes the mammary glands within the breasts and the ovaries and uterus within the pelvic cavity.
Organs that work together are grouped into organ systems.

The organism level is the highest level of organization. An organism    is a living being that has a cellular structure and that can independently perform all physiologic functions necessary for life. In multicellular organisms, including humans, all cells, tissues, organs, and organ systems of the body work together to maintain the life and health of the organism.

Chapter review

Life processes of the human body are maintained at several levels of structural organization. These include the chemical, cellular, tissue, organ, organ system, and the organism level. Higher levels of organization are built from lower levels. Therefore, molecules combine to form cells, cells combine to form tissues, tissues combine to form organs, organs combine to form organ systems, and organ systems combine to form organisms.

Questions & Answers

how many litres of blood does a human body have
George Reply
what is homeostasis
Antwi Reply
it is self regulating ability of the body to adjust to the surroundings
Angela
it is like maintaining an equilibrium type of environment between the inside and outside of the body, so that our body can adjust to the external environmental changes
Angela
this is the negative feedback loop of the body,.... that naturally helps to keep the body in a stable or constant internal environment.
Matthew
this is the activities in the body that keeps the internal environment of the body in equilibrium or to keep it constant.
Ikenze
list four long bones
Mary Reply
the four long bones are: tibia, fibula, femur, and humerus.
Isaac
from Zambia
Mary
femur, radius , ulnar, humerus
Om
humerus, femur, tibia and fibula
Sheryl
Humerus,redius,ulnar,in hand. Femur,tibia,fibula in leg. it is long bone.
Sneha
there is contradiction between radius ulna & tibia fibula because of the variation in the upper and lower limb of the according to growth and development of human body so humerus & femur are longer bones ( ex you can see Michael phaleps upper limb is longer than the lower limb)
Prashant
if anyone having dout so he she can please explain it to me
Prashant
which one want explain something
Dr
sir post which I have send look at it & tell is it correct or not
Prashant
about four long bones is the topic
Prashant
femur, humerus, tibia and fibula
Ikenze
how are you doing
Rekah Reply
hi everyone.
AR
Im new here, I came from the philippines. I study nursing. Im a first year student.
AR
really
Isaac
so what help do you want
Isaac
yeah I came from the philippines..and I have struggle about this subject the anatomy and physiology because I dont any books that I barrowed with. I cant afford buy books.
AR
hii
Meher
I'm from India
Jamy
I struggle with this subject
Jamy
can I ask here a question I hope you can help me because I dont have any references/books that I should see or read it.
AR
AR
Meher
you are from india nice to talk to you jamy.
AR
Alright Always drop your concerns here and they will be addressed. Thanks sister.
Isaac
nice meeting with you
Jamy
I am also from India
shiv
thank you Isaac.
AR
yes Meher?
AR
you are all india
AR
By the way I have question
AR
describe a person in anatomical position?
AR
i come from Ghana
Isaac
are you all nursing students?
AR
no I'm pharmacy student
Jamy
oh nice.
AR
yes
shiv
jamy me too
Meher
yes
shiv
yes
shiv
my name is sweety
Jamy
you have any chat group that we can talk there.
AR
Anatomical position is the description of any region or part of the body in a specific stance. In the anatomical position, the body is upright, directly facing the observer, feet flat and directed forward. The upper limbs are at the body's sides with the palms facing forward. The standard anatomic
Isaac
yes
shiv
jamy is my nick name
Jamy
I am a nursing student
Isaac
thank you Isaac
AR
Final year, level 400
Isaac
ohh what year are you now?
AR
Nice
AR
welcome madam
Isaac
do you have any chat group here
AR
describe the six levels of organization of the body and describe the major characteristics of each level?
AR
ahh its okay jammy
AR
jammy i am from kashmir nd u
Meher
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.
Isaac
hi
Yaminah
am from somalia
Yaminah
5th year in medical student nice to meet ya all
Yaminah
thxs yaminah
Meher
y not.. jamy for what purpose...?
Meher
inbox me i will guide u ...?
Meher
i also dont know...?
Meher
open this app - click 'start learning' - click 'preface' - select the chat that you wanna join into I guess that is it !
Angela
Hello am from Sierra Leone
junisa
I am from Kerala
Angela
I am from india
Om
I am from Tripura
FAKE
tell the easyst way to learn anatomy
Khaliif Reply
try to draw 👌
Rahil
what
shiv
learn subject with drawing anatomy diagrams some with flow chart i dont say it is easiest way bt yes u can rember for longer period
Shakerah
ooh
shiv
hello im new here, im a nursing student
SHUGA Reply
ooh
shiv
welcome
shiv
wlcm
Rahil
dub
Ndowmi
maleria
Ndowmi
Anopheles
shiv
welcome shuga
Om
please am new here. Am a nurse awaiting to be posted .
Ntiamoah
hi I'm new here too
faleke
Feleke Sharon Welcome
FAKE
FAKE DrLUPO thank you
faleke
hello guys
Chuks
hello guys 🤗
Sneha
hello
Chuks
whose in Nigeria
Chuks
🙋🙋
faleke
what is inner breeding
Vijay Reply
you don't have any answer
Vijay
please don't waste my time
Vijay
wait
shiv
inbreeding is mating or breeding with organism that are genetically related
shiv
s
Pankaj
who this SRY
Pankaj
inner breeding is breeding among the same species of organisms
Anna
*inbreeding
Anna
yes same speciesor same genetic organism
shiv
description of the menstruation cycle
Namyalo Reply
explain the menstruation cycle
Namyalo
explain the menstrual cycle
Ugo
menstrual cycle is came due to FSH and LH
shiv
fsh
Ndowmi
This is the periodic release of waste(blood) from the reproductive organ of the females (human) for a period of some days, after which or during then, ovulation takes place, which is the release of eggs from the ovaries for fertilization by the spermatozoa.
Ikenze
Description of menestraul cycle
Amos Reply
what is the anatomy
FAKE Reply
Anatomy is study of structure of organs.
Sneha
thanks
FAKE
The scientific study of the structure of human or animal bodies.
FAKE
I was confused as to which one would be right and I asked
FAKE
My answer and you answer both are right.
Sneha
The scientific study of the human and animal internal and external structure of the body.
Ikenze
i want to improve my study i like this app i interest physiology and anatomy
Su Reply
I also like this app am really interested in learning anatomy and physiology.
Johny
I have this book with my anatomy class it's awesome! also if look at crashcourse anatomy on you tube!
AMY
what the name
isaiah
umesh. rede
Rede
what is heart and long type answer
Lalita Reply
its a organ in the body
ay
describe about hear chambers.. valves.. arteries.. veins.. circulation.. inferior/superior venacava, aorta., tricuspid valve, mitral valve. pulmonary artery/vein, how oxigenation occur,systolic presure diastolic pressure.. stroke volume,cardiac output, ets.. heart located in which place, describe it
Sanjith
if you describe what I cited up, thogh you can write a long type answer about heart
Sanjith
hi
Riyaz
autonomic functions took over
Vanarith Reply
What did they take over?
Eric
what is the average volume of blood in men and why does it varrie from women?
Esther Reply
what is the average volume of blood in men
Esther
5to6liter
Sarita
5to6liter dt
Sarita
umesh. rede
Rede
estimated at 5.5litres
Ikenze
what is the definition of anatomy
Noriah Reply
Search google
killer
^of
chieng
The study of the structure or internal workings of something. "Machiavelli's anatomy 
Eric

Get the best Anatomy & Physiology course in your pocket!





Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask