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Organization of the Human
Body
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Printed: November 1, 2013
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C ONCEPT
Concept 1. Organization of the Human Body
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Organization of the Human
Body
• List the levels of organization in the human body.
• Identify the four types of tissues that make up the body.
Do cells work together?
Cells, like these nerve cells, do not work in isolation. To send orders from your brain to your legs, for example,
signals pass through many nerve cells. These cells work together to perform a similar function. Just as muscle cells
work together, bone cells and many other cells do as well. A group of similar cells that work together is known as a
tissue.
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Organization of Your Body: Cells, Tissues, Organs
Cells are grouped together to carry out specific functions. A group of cells that work together form a tissue. Your
body has four main types of tissues, as do the bodies of other animals. These tissues make up all structures and
contents of your body. An example of each tissue type is pictured below (Figure 1.1).
FIGURE 1.1
Your body has four main types of tissue: nervous tissue, epithelial tissue, connective tissue, and muscle tissue.
They are found throughout your body.
Groups of Tissues Form Organs
A single tissue alone cannot do all the jobs that are needed to keep you alive and healthy. Two or more tissues
working together can do a lot more. An organ is a structure made of two or more tissues that work together. The
heart (Figure 1.2) is made up of the four types of tissues.
Groups of Organs Form Organ Systems
Your heart pumps blood around your body. But how does your heart get blood to and from every cell in your body?
Your heart is connected to blood vessels such as veins and arteries. Organs that work together form an organ system.
Together, your heart, blood, and blood vessels form your cardiovascular system.
What other organ systems can you think of?
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Concept 1. Organization of the Human Body
FIGURE 1.2
The four different tissue types work together in the heart as they do in the other
organs.
Organ Systems Work Together
Your body’s 12 organ systems are shown below (Table 1.1). Your organ systems do not work alone in your body.
They must all be able to work together.
For example, one of the most important functions of organ systems is to provide cells with oxygen and nutrients and
to remove toxic waste products such as carbon dioxide. A number of organ systems, including the cardiovascular
and respiratory systems, all work together to do this.
TABLE 1.1: Major Organ Systems of the Human Body
Organ System
Cardiovascular
Major Tissues and Organs
Heart; blood vessels; blood
Lymphatic
Lymph nodes; lymph vessels
Digestive
Esophagus; stomach; small intestine; large intestine
Pituitary gland, hypothalamus;
adrenal glands; ovaries; testes
Skin, hair, nails
Endocrine
Integumentary
Muscular
Nervous
Reproductive
Cardiac (heart) muscle; skeletal
muscle; smooth muscle; tendons
Brain, spinal cord; nerves
Female: uterus; vagina; fallopian
tubes; ovaries Male: penis; testes;
seminal vesicles
Function
Transports oxygen, hormones, and
nutrients to the body cells. Moves
wastes and carbon dioxide away
from cells.
Defend against infection and disease, moves lymph between tissues
and the blood stream.
Digests foods and absorbs nutrients,
minerals, vitamins, and water.
Produces hormones that communicate between cells.
Provides protection from injury and
water loss, physical defense against
infection by microorganisms, and
temperature control.
Involved in movement and heat production.
Collects, transfers, and processes
information.
Produces gametes (sex cells) and
sex hormones.
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TABLE 1.1: (continued)
Organ System
Respiratory
Major Tissues and Organs
Trachea, larynx, pharynx, lungs
Skeletal
Bones, cartilage; ligaments
Urinary
Kidneys; urinary bladder
Immune
Bone marrow; spleen; white blood
cells
Function
Brings air to sites where gas exchange can occur between the blood
and cells (around body) or blood
and air (lungs).
Supports and protects soft tissues of
body; produces blood cells; stores
minerals.
Removes extra water, salts, and
waste products from blood and
body; controls pH; controls water
and salt balance.
Defends against diseases.
Vocabulary
• cardiovascular system: Organ system made up of the heart, blood, and blood vessels.
• cells: Basic unit of structure and function of a living organism; the basic unit of life.
• connective tissue: Group of cells that are all involved in supporting and binding other tissues of the body; i.e.
tendon, cartilage, bone, and blood.
• epithelial tissue: Layers of tightly packed cells that line the surfaces of the body.
• muscle tissue: Bands of cells that contract and allow movement.
• nervous tissue: Group of nerve cells that sense stimuli and transmit signals; found in brain, spinal cord, and
nerves.
• organ: Structure made of two or more tissues that work together.
• organ system: Organs that work together to serve a common purpose.
• tissue: Group of similar cells working together.
Summary
• The levels of organization in the human body include: cells, tissues, organs, and organ systems.
• There are four tissue types in the body: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.
Practice
1.
2.
3.
4.
What kind of symmetry does the human body plan show? Explain fully what this means.
How does this symmetry extend to our senses?
How much of our body is made of muscle? What does this muscle allow us to do?
How are oxygen and nutrients delivered to the cells of the body?
Review
1. What are the four levels of organization in an organism?
2. List the four types of tissues that make up the human body.
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Concept 1. Organization of the Human Body
References
1. Child: Image copyright igor kisselev, 2012; Tissue images: jessy731 (Flickr). . Child: Used under license
from Shutterstock.com; Tissue images: CC-BY-NC 2.0
2. Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist. . CC-BY 2.5
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