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There are 20 feet of blood vessels in each square inch of human skin.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
Adolescents often feel clumsy during puberty because during this time of development, their hands and feet grow faster than their arms and legs do. The body is therefore out of proportion. One out of five adolescents actually experiences growing pains during this period.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
IgA antibodies protect body surfaces exposed to outside foreign substances. IgG antibodies are found in all body fluids. IgM antibodies are the first type of antibody made in response to an infection. IgE antibody levels are often high in people with allergies. IgD antibodies are found in tissues lining the abdomen and chest.
![Urinary catheterization. The procedure involves the insertion of a flexible tube, or catheter, throu](https://biology-forums.com/gallery/47/medium_14755_26_10_12_5_21_07_96742390.jpeg)
![Coronary artery bypass graft (CABG). The grafts are often obtained from the patient’s saphenous vein](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_15_45_100282437.jpeg)