Organism death is typically defined as the point at which respiration cannot or is not being maintained. Once respiration stops, oxygen transport is terminated and oxidative metabolic activity (that is, the set of biochemical reactions that store, release, and transfer energy) are limited to the oxygen that remains locally in tissues. The rate at which this is used depends on a number of factors such as redox products, ion concentration, ambient and tissue initial temperature, et cetera. On the cellular level, “death” occurs when the overall rate of catabolic processes in the cell (the collection of processes involved in decomposing proteins, nucleic acids, lipids, and polysaccharides into base amino acids, nucleotides, fatty acids, and monosaccharides) exceed the rate of anabolic processes (processes that construct proteins, nucleic acids, structural lipids, and hormones). Since both catabolic and anabolic processes are occurring simultaneously within the cell at all times, it is difficult to say exactly when cellular “death” occurs, and indeed, a large number of cells are constantly “dying” and being replaced as part of normal metabolic processes.
Curiously, this “death” of a cell doesn’t occur because it runs out of energy or oxygen, but because the hormones that regulate cellular respiratory processes are no longer being maintained. If catabolic processes are allowed to run away (as they will as long as water is available) the cells will literally eat themselves up from the inside out, and then break down, allowing outside bacteria to consume them.
Although all living tissues are subject to this breakdown, cerebral and nervous tissue is particularly subject to this due to axonal degeneration for reasons that aren’t fully understood but appear to involve particularly active proteases (proteins that break down other proteins) that are overstimulated by failure of calcium ion regulation. Hence, why “brain death” tends to occur even when other organs remain viable.
To address the question of the o.p. in practical terms, the skin and blood vessel tissue seems to be the most resilient tissues of the body, and can be stored for several months in a cool, ionic solution before being grafted into another body and resuming normal cellular respiratory processes, although they must be removed from a cadaver within 24 hours of organism death. Blood can obviously be stored for even longer under controlled conditions, although is debatable as to whether you can regard erythrocytes (red blood cells) as technically being alive, lacking as they do nuclear material, most organelles (including energy-regulating mitochondria), and endoplasmic reticulum. Other thoracic and abdominal transplantable organs must be removed more quickly, typically within an hour or less of organism death. So I’d opine that the skin and blood vessels “die” last.
Stranger