Among the following human anatomical structures, which can be safely harvested from a healthy living donor for a surgical transplant?

The correct option is One functional kidney.

Explanation:
Living organ donation involves removing an organ or a segment of an organ from a living person and transplanting it into a recipient. For a living donation to be medically ethical and safe, the procedure must not endanger the donor's life or cause major permanent health impairment.

Let's evaluate each option:

1. One functional kidney: Humans possess two kidneys, but the human body can function completely normally with just one healthy kidney (due to renal compensation/hypertrophy). Therefore, one functional kidney can be safely harvested from a healthy living donor for surgical transplantation.

2. Whole pancreas: The pancreas produces critical hormones (such as insulin and glucagon) and digestive enzymes. Harvesting the whole pancreas from a living person would cause immediate, severe diabetes and pancreatic insufficiency. While a living donor can occasionally donate a portion (tail/body) of the pancreas, a whole pancreas transplant can only come from a deceased donor.

3. Cornea tissue: Corneas are avascular clear tissues covering the front of the eye. Harvesting a cornea from a living donor would permanently cause blindness or severe vision loss in that eye. Thus, corneas are harvested exclusively posthumously (after death).

4. An intact heart: The heart is a single, vital organ necessary to sustain life. Harvesting an intact heart would result in immediate fatality for the donor. Consequently, heart transplants are performed using organs harvested exclusively from deceased (brain-dead) donors.