Chakras were first studied in ancient Hindu. Chakra, by definition(Sanskrit), means wheel or vortex and refers to the 7 energy centers of the body. Chakras are not physical but are energy systems.
The wheels of energy, regulate the flow, through our energy system- by way of pumps and valves. The functions are regulated by the way we react to issues and the environment around us. Chakras interact with our physical body, by way of the endocrine system and nervous system.
There are 7 Chakras, that are associated with the one of the 7 endocrine glands and also with the a group of nerves(plexus).
When you are under stress, you will feel that with the associated Chakra and that part of your body. When a person finds a way to eliminate that stress, you then release that negative energy and allow the wheels to spin in a, yet again, positive way.
I have an example....a friend of mine, her husband was diagnosed with Esophageal, Stage 4, Cancer. Her husband, was trained military, his job did not allow for him to discuss his training, nor the frustrations. Unfortunately....this also bled to his personal life and he found himself unable to express feelings, etc....all of this bottled up energy, attacked his weak wheel of energy--the throat chakra! I know this sounds silly to some but it is certainly true.
Here is a photo of the 7 Chakras:

7th Violet: Crown chakra. It is associated with your pineal gland and also known as the cosmic consciousness centre. Also known as your GOD Source. Head, brain and nervous system.
Emotions associated with the Crown are; empathy, selflessness, values and ethics.
6th Indigo, Midnight Blue: Third Eye chakra. Found in the center of the forehead. It is associated with the temples and pituitary gland and carotid plexus.
Third eye relates to spiritualism, clairvoyance, truth, knowledge, intellect, intuitive powers, inner wisdom and open-mindedness.
5th Sky Blue: Throat Chakra. This chakra controls your throat and neck, also arms and hands. The throat chakra is associated with the thyroid gland.
This chakra is responsible for our sense of hearing and related to our creativity and communication.
4th Emerald Green: Heart Chakra. This is associated with our heart and circulatory systems, cardiac plexus, lungs and entire thoracic cavity (chest area), thymus gland.
Heart Chakra is responsible for our sense of touch, perceptions of love, relations, love, happiness, anger, compassion, commitment, etc...
3rd Yellow: Power Center-Solar Plexus. This chakra involves; skin, muscles, solar plexus, large intestines, stomach, liver and eyes, pancreas gland.
Power, control, freedom and mental activity-- are associated with this chakra. Other emotions; trust, fear, guilt, intimidation, self-esteem and self-worth.
2nd Orange: Sensation Center, Spleen Chakra, Sacral. This is the ruler of our sexual organs and reproduction system, also sense of taste and appetite. Gonads (gland).
Associated with the consciousness concerned with sex, food and ability to have children. Sexual Issues, Power, creativity, control, passion, honor, fidelity, greed, money and blame--all associated with the Sacral Chakra.
1st Red: Root Chakra, Security Center. The Perineum--the area between the anus and the sex organs. Lymph system, skeletal system, prostate, bladder, and lower extremities- Adrenal Gland.
Responsible for--- Security, relationship with money, job, home, survival and trust but also...past life issues, instinct, parenting, marriage and family.
I will continue with more of this.....
Let the Wheels of Energy, Spin!!!