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Basic Anatomy - Tissues & Organs

There are many different types of cells in the human body. None of these cells function well on there own, they are part of the larger organism that is called - you.

Tissues
Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.

1. Epithelial Tissue - The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body. Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.
2. Connective Tissue - There are many types of connective tissue in the body. Generally speaking, connective tissue adds support and structure to the body. Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue. In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.
3. Muscle Tissue - Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement. Examples of muscle tissue are contained in the muscles throughout your body.
4. Nerve Tissue - Nerve tissue contains two types of cells: neurons and glial cells. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body.

Organs
Organs are the next level of organization in the body. An organ is a structure that contains at least two different types of tissue functioning together for a common purpose. There are many different organs in the body: the liver, kidneys, heart, even your skin is an organ. In fact, the skin is the largest organ in the human body and provides us with an excellent example for explanation purposes. The skin is composed of three layers: the epidermis, dermis and subcutaneous layer. The epidermis is the outermost layer of skin. It consists of epithelial tissue in which the cells are tightly packed together providing a barrier between the inside of the body and the outside world. Below the epidermis lies a layer of connective tissue called the dermis. In addition to providing support for the skin, the dermis has many other purposes. The dermis contains blood vessels that nourish skin cells. It contains nerve tissue that provides feeling in the skin. And it contains muscle tissue that is responsible for giving you 'goosebumps' when you get cold or frightened. The subcutaneous layer is beneath the dermis and consists mainly of a type of connective tissue called adipose tissue. Adipose tissue is more commonly known as fat and it helps cushion the skin and provide protection from cold temperatures.

A cross-section of skinEpidermisDermisSubcutaneous
layer
Organ Systems
Organ systems are composed of two or more different organs that work together to provide a common function. There are 10 major organ systems in the human body, they are the:

• Skeletal System: Image courtesy of A. McGannMajor Role:
  The main role of the skeletal system is to provide support for the body, to protect delicate internal organs and to provide attachment sites for the organs.Major Organs:
  Bones, cartilage, tendons and ligaments.

• Muscular System:
  Image courtesy of G. HuangMajor Role:
  The main role of the muscular system is to provide movement. Muscles work in pairs to move limbs and provide the organism with mobility. Muscles also control the movement of materials through some organs, such as the stomach and intestine, and the heart and circulatory system. Major Organs:
  Skeletal muscles and smooth muscles throughout the body.

• Circulatory System:
  Image courtesy of G. HuangMajor Role:
  The main role of the circulatory system is to transport nutrients, gases (such as oxygen and CO2), hormones and wastes through the body. Major Organs:
  Heart, blood vessels and blood.

• Nervous System:
  Image courtesy of G. HuangMajor Role:
  The main role of the nervous system is to relay electrical signals through the body. The nervous system directs behaviour and movement and, along with the endocrine system, controls physiological processes such as digestion, circulation, etc. Major Organs:
  Brain, spinal cord and peripheral nerves.

• Respiratory System: Image courtesy of A. McGannMajor Role:
  The main role of the respiratory system is to provide gas exchange between the blood and the environment. Primarily, oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled from the body.Major Organs:
  Nose, trachea and lungs.

• Digestive System: Image courtesy of A. McGannMajor Role:
  The main role of the digestive system is to breakdown and absorb nutrients that are necessary for growth and maintenance.Major Organs:
  Mouth, esophagus, stomach, small and large intestines.

• Excretory System:
  Image courtesy of G. HuangMajor Role:
  The main role of the excretory system is to filter out cellular wastes, toxins and excess water or nutrients from the circulatory system. Major Organs:
  Kidneys, ureters, bladder and urethra.

• Endocrine System:
  Image courtesy of G. HuangMajor Role:
  The main role of the endocrine system is to relay chemical messages through the body. In conjunction with the nervous system, these chemical messages help control physiological processes such as nutrient absorption, growth, etc.Major Organs:
  Many glands exist in the body that secrete endocrine hormones. Among these are the hypothalamus, pituitary, thyroid, pancreas and adrenal glands.

• Reproductive System: Female:
  
  Male:
  Images courtesy of G. HuangMajor Role:
  The main role of the reproductive system is to manufacture cells that allow reproduction. In the male, sperm are created to inseminate egg cells produced in the female.Major Organs:
  Female (top): ovaries, oviducts, uterus, vagina and mammary glands.
  Male (bottom): testes, seminal vesicles and penis.

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