The Physical Body
Tantrics consider the human body to be a microcosm, while the entire Universe (or Multiverse) is the macrocosm. In other words, the human body is a representation, or a map, of the whole of reality.
The physical body of a human being corresponds to the material level of the Universe.
Systems of the physical body
Movement and Support
Skeletal system: bones, joints, ligaments
Muscular System: muscles, tendons, fascia
Energy Production and Waste Disposal
Digestive system: teeth, tongue, stomach, intestines, liver and pancreas
Respiratory system: nose, airways, lungs
Cardiovascular system: heart, blood vessels
Urinary system: kidneys, ureters, urinary bladder, urethra
Coordination and Control
Nervous system: brain, spinal cord, nerves
Endocrine system: pineal, pituitary, thyroid, adrenals, etc
Sensory organs: eyes, ears, nose, tongue, skin
The physical body in Tantric sex
The physical body is a core part of Tantric practice. Tantrics invest time and energy in getting to know their own physical bodies. When the physical body is well-maintained, and areas of numbness or tension have been cleared, the Tantric is best prepared for the intense experiences which may arise in Tantric sex.
There are no specific physical practices which make sex "Tantric". During Tantric sex, the physical body may be moving fast or slow, the eyes may be open or closed, the breathing may be synchronised or free-flowing, and Tantric sex can happen in any sexual position.
Many Tantric traditions suggest that men refrain from ejaculating, not just during Tantric sex, but at all times. This is a way to meet the yogic requirement for brahmacharya, or "control of the creative energy". In contrast, ascetic traditions interpret this requirement as a requirement for complete celibacy.
The physical body is viewed as a sacred representation of the Divine. In some Tantric rituals, specific practices are used to "infuse" the Divine into a physical body, as a reminder of this Divininty, and as a form of meditation to create the proper attitude of reverence. As part of a Tantric sex practice, practitioners may worship the Divine in their partner by performing trataka, a relaxed, unblinking gaze, focused on the naked body of their partner. During the trataka, the practitioner actively seeks to see the entire Universe, including the Divine, represented in the body in front of them.
Physical orgasm is an important part of Tantric orgasm, particularly in the early years of practice. However, it is possible to have a Tantric orgasm without the usual physical signs of orgasm. Physical orgasm is a separate physical process from ejaculation, even though in untrained men they usually occur together. Separating physical orgasm from ejaculation is an important part of a man's process of mastering the Tantric orgasm.
Female ejaculation is viewed quite differently from male ejaculation. While male ejaculation involves a loss of brahma (creative energy), the fluids produced by women are not essential for reproduction, and therefore do not contain the same creative energy. Producing female ejaculate is viewed as a siddhi (a superpower), and the fluid is considered sacred.