The weight of the entire body rests on the feet. The heel supports and cushions the shocks of the body. Comprised of many separate parts, the human heel is a marvel of engineering.
The calcaneus is the actual heel bone. This bone forms the base of support for the entire human body and shapes the form of the heel. This bone, in conjunction with the tibia and the fibula, two major bones in the lower leg, forms the basis for the ankle joint.
The Achilles tendon connects the calf muscle to the heel bone. This tendon is one of the thickest tendons in the human body. When the calf muscle shortens, it pulls on the heel bone so that the foot is pushed downwards. This assists in walking, running and movement.
The bursal sac rests between the Achilles tendon and the heel bone. It's a pouch of liquid that prevents the Achilles tendon from rubbing on the bone and creating friction and pain.
The fat pad protects and cushions the heel bone. It is a literal layer of fat between the heel bone and the skin in the heel area. It can be felt starting at the edge of the heel almost to the edge of the arch.
Thickened Layer of Skin
The external layer of the heel is the thickened skin that protects the heel. While the skin is thick at birth, it thickens with pressure and use. In particular, people who go barefoot develop exceptionally thick skin, bordering on callouses.