1. Multicellular means made of many cells.
Based on your vocabulary reference sheet, what does the prefix multi- mean?
Multi- means many
Multicellular means
made of many cells. 2

2. Multicellular organisms contain many different forms of specialized cells that work together to meet the needs of the entire organism. Groups of these specialized cells are called tissues. 3

3. These tissues join together inside of animals to form organs
These tissues join together inside of animals to form organs. Every organ is made up of more than one type of tissue.
Caution: The image of a dissected rat you are about to see may be disturbing to some students.
Photo by Allen Lew 4

4. Organs work together to perform complex tasks
Organs work together to perform complex tasks. A group of organs that works together to complete a task is referred to as a body system or an organ system (These are two ways of saying the same thing.) 5

5. To digest and absorb nutrients from food
Organ System:
Digestive System
Primary Function
To digest and absorb nutrients from food
Major Organs
Esophagus
Stomach
Small Intestine
Large Intestine
Nutrients travel from the digestive system directly into the circulatory system.

6. To absorb oxygen and expel carbon dioxide
Organ System:
Respiratory System
Primary Function
To absorb oxygen and expel carbon dioxide
Major Organs
Lungs
Trachea
Bronchi
Diaphragm
Oxygen travels from the respiratory system directly into the circulatory system.

7. Organ System: Circulatory System Primary Function
To distribute oxygen and nutrients throughout the body
Major Organs
Heart
Blood vessels
Major Tissue
Blood
White blood cells are also part of the immune system.

8. To remove waste products from the body
Organ System:
Excretory System
Primary Function
To remove waste products from the body
Major Organs
Kidneys
Bladder
Colon
The colon is also the final section of the digestive system and helps absorb water and salt.

9. Organ System: Skeletal System Primary Function
Provides shape, structure and protection for internal organs
Major Organs
Bones
Major Tissue
Marrow
Ligaments
Marrow inside bones creates new blood cells!

10. Organ System: Muscular System Primary Function
Allows for movement of the skeleton and other tissues in the body
Major Organs
Muscles
Major Tissues
Tendons
Muscles always PULL on bones to make them move.

11. Organ System: Nervous System Primary Function
Transmits signals and stores information
Major Organs
Brain
Spinal cord
Major Tissue
Nerves
All 5 senses are a part of the nervous system!

12. Organ System: Endocrine System Primary Function
Produce hormones to maintain homeostasis
Major Organs
Endocrine Glands
Major Molecule
Hormones
Male and female reproductive organs both produce hormones!

13. Organ System: Immune System Primary Function
Defend the body from germs and parasites
Major Cells
White Blood Cells
Major Molecules
Antibodies
Antibody
White blood cells and antibodies travel through the circulatory system!
White blood cell engulfing anthrax bacteria
(The micrograph was taken by Volker Brinkmann with a Leo 1550 scanning electron microscope.)

14. Removes fluid from around cells and filters it for bacteria
Organ System:
Lymphatic System
Primary Function
Removes fluid from around cells and filters it for bacteria
Major Organs
Lymph nodes
Lymphatic vessels
Spleen
Lymph is the fluid from between body cells that has been absorbed by the lymphatic system.

15. Organ System: Integumentary System Primary Function
Protection from damage and dehydration
Major Organs
Skin
Hair follicles
Skin helps keep the body from overheating by sweating.

16. Produces gamete cells needed for
Organ System:
Reproductive System
Primary Function
Produces gamete cells needed for
sexual reproduction
Major Organs
Testes (male)
Ovaries (female)
The male gamete cell is called a sperm and female gamete cell is called an ovum or egg.

17. Can organs belong to more than one organ system?
Yes! Almost all major organs belong to more than one system.
Heart: Muscular and Circulatory
Lungs: Respiratory and Excretory
Brain: Nervous and Endocrine