2 weeks, 1 day ago

This is an interesting question


 
 let's take a look at the difference between the plantar pressure of an elephant and that of a human when standing


 ① person: 
 the average weight of adult male is about 60kg; g = 60 × 10N / kg; the area of each foot is about 25cm ^ 2, and the plantar pressure when standing on both feet is as follows:





 ② elephant: 
 according to the data widely circulated on the Internet, the weight is 5000kg, the area of each foot is 500cm2, and the pressure when standing on four feet is as follows:




It can be seen that the pressure difference between the soles of human and elephant feet is about twice. However, based on the difference between human and elephant soles, elephants can be regarded as a flat cylinder, while human soles are arched, which mainly relies on the heel to bear the load. Therefore, it is difficult to say who is more under the strongest pressure. Therefore, 
, although the weight of elephant is much higher than that of human, the difference between the pressure on the sole of elephant foot and that of human foot is not as large as expected 
. 


 secondly, let's see why the plantar cells can bear the whole body weight without being "crushed and exploded". 


According to the different walking patterns, animals can be divided into plantar, toe and hoofed animals. For plantar behavior, the palms and soles of the feet touch the ground; for toe movements, fingers and toes are used for landing; for hoofs, the fingertips / toes are used for landing. 


 
 the black part is calcaneus 
 
 
 
 according to the structural characteristics of elephant foot, it is between the plantar line and the toe line, which is called half metatarsal line 
. The reason is very simple. The big 
 is actually walking with high heels, which makes it actually walk with its toes, and the soles of the feet seem to be walking, so it is impossible to locate it in one of the above three categories. There is a thick fat pad under the calcaneus and metatarsals of the elephant's foot. During the process of loading, this cushion is responsible for buffering the pressure, reducing the pressure on the plantar nerves and blood vessels, and evenly distributing the animal weight to the whole sole, so that the elephant's foot has a stronger stress structure than expected. 


 
 the structure of the sole of the elephant's feet 
 
 
 
 although we know that the stress on the soles of elephant's feet is balanced, why can't the cells" burst "when such a heavy pressure acts on the bone and skin? 



 the reason is very simple: plant cells have cell walls, and animal cells have similar structures, that is, extracellular matrix (ECM) 
. ECM is secreted by cells and consists of collagen, noncollagen glycoprotein, aminoglycan and proteoglycan, and elastin. ECM plays a physical support role on the cells in the ECM, and orderly connects the cells together to form tissues and organs. As an important structure of load-bearing and buffering, the content of ECM in plantar fat pad is much higher than that in other tissues of the body. There are scattered small and strong connective tissue fiber bundles composed of ECM in the pad, and the arrangement direction is consistent with the main pressure direction. With this structure, the cells in the fat pad naturally do not burst easily. 


 
 
 extracellular matrix and its intracellular cells 
 
 
 
 finally, the plantar skin is covered with a thick layer of keratinized squamous epithelium, that is, the epidermis on the superficial surface of a large number of dense connective tissue forming dermis. 
 the interface between epidermis and dermis contains a large number of dermal papillae, which crisscross with the epidermis. The dermis is a thick reticular layer, which is closely interwoven by collagen fibers, and interspersed with a small amount of elastic fibers. The reticular fibrous connective tissue contains abundant nerves and blood vessels (see figure below). All these characteristics make the skin of elephant's sole have the function of wear resistance and pressure resistance, so it's no surprise to bear body pressure. 


 
 in the transverse section of elephant's paw, the arrow is fibrous connective tissue, and the cavity in it is blood vessel 
 
 
 
 pressure per unit area is not too high, and the force is dispersed. In addition, abundant extracellular matrix support, the force acting on cells is not as terrible as imagined, and the cells in the sole of the foot will not be crushed naturally. 


 
 (Note: all pictures are from the Internet)

References

1、Weissengruber GE, Egger GF, Hutchinson JR, et al. The structure of the cushions in the feet of African elephants (Loxodonta africana). 
J Anat
. 2006;209(6):781-792.

2、Comparative foot  morphology.Wikipedia .

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