The heel is the prominence at the posterior end of the

foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

. It is based on the projection of one bone, the

calcaneus In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel; : calcanei or calcanea) or heel bone is a bone of the Tarsus (skeleton), tarsus of the foot which constitutes the heel. In some other ...

or heel bone, behind the articulation of the bones of the lower

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...

Structure

To distribute the compressive forces exerted on the heel during

gait Gait is the pattern of Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on s ...

, and especially the stance phase when the heel contacts the ground, the sole of the foot is covered by a layer of subcutaneous connective tissue up to 2 cm thick (under the heel). This tissue has a system of pressure chambers that both acts as a shock absorber and stabilises the sole. Each of these chambers contains fibrofatty tissue covered by a layer of tough connective tissue made of

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

fibers. These

septa SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

("walls") are firmly attached both to the plantar aponeurosis above and the sole's

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

below. The sole of the foot is one of the most highly vascularized regions of the body surface, and the dense system of blood vessels further stabilize the septa. The

Achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcane ...

is the muscle tendon of the triceps surae, a "three-headed" group of muscles—the soleus and the two heads of the gastrocnemius. The main function of the triceps surae is plantar flexion, i.e. to stretch the foot downward. It is accompanied by a "fourth head", the slight plantaris muscle, the long slender tendon of which is also attached to the heel bone but not visible.

Function

The compressive forces applied to the foot are distributed along five rays, three medial (side of big toe) and two lateral (side of little toe). The lateral rays stretch over the cuboid bone to the heel bone and the medial rays over the three cuneiform bones and the

navicular bone The navicular bone is a small bone found in the feet of most mammals. Human anatomy The navicular bone in humans is one of the tarsus (skeleton), tarsal bones, found in the foot. Its name derives from the human bone's resemblance to a small ...

to the

ankle bone The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body ...

. Because the ankle bone is placed over the heel bone, these rays are adjacent near the toes but overriding near the heel, and together they form the

arches of the foot The arches of the foot, formed by the tarsal and metatarsal bones, strengthened by ligaments and tendons, allow the foot to support the weight of the body in the erect posture with the least weight. They are categorized as longitudinal and t ...

that are optimized to distributed compressive forces across an uneven terrain. In this context the heel thus forms the posterior point of support that together with the balls of the large and little toes bear the brunt of the loads.

Cracked heels

Cracked heels is a common health problem and it may cause

infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

s. It is caused by dryness of the foot skin, and accumulation of dead skin. Over time, it may cause pain and irritations. Various moisturising creams and foot files are available to cure and prevent it.

Other animals

In the long-footed mammals, both the hoofed species ( unguligrade) and the clawed forms which walk on the toes (

digitigrade In terrestrial vertebrates, digitigrade ( ) locomotion is walking or running on the toes (from the Latin ''digitus'', 'finger', and ''gradior'', 'walk'). A digitigrade animal is one that stands or walks with its toes (phalanges) on the ground, and ...

), the heel is well above the ground at the apex of the angular joint known as the hock. In

plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...

species, it rests on the ground. In birds, the heel is the backward-pointing joint which is often mistaken as the "

knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

" (the actual knee of birds is hidden under the plumage).

Notes

References