Dying & Death

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Questions received:

  1. What are the changes that take place in the human body after death which account for the description rigor mortis?

  2. How is it that muscle cells in a dead frog can react to an electrical stimulus? Also, why does rigor mortis persist in a preserved cadaver - does the preservation chemical retain the properties of the corpse?

  3. I read your description of rigor mortis; is there any situation that you know of in which rigor mortis would not occur after death? Or does it always occur?

  4. How long does it take rigor mortis to set in?

  5. Is rigor mortis a temporary or permanent condition? If temporary, when does it usually end?

  6. What happens to the endocrine, respiratory, nervous, cardiovascular, digestive, and integumentary systems when we die?

  7. My cat has recently died, and when found her lying by the backdoor, her mouth was open a small amount and her eyes were open too . Apart from this she looked as if she had died in her sleep. Please can you advise me whether eyelids do open when animals and humans die. Or did she just slip into death while conscious? I appreciate that you normally have questions regarding humans and not cats, but this is something that I would like to know.

  8. I was just wondering how many minutes or hours it takes a mortician to perform the embalming process?

Responses:

What are the changes that take place in the human body after death which account for the description rigor mortis?

15th July 1998

Rigor mortis is Latin for "stiffness of death". It is used medically to describe the stiffness of skeletal muscles that appears soon after death, usually within the first 4 hours. The face tends to stiffen before the hands and feet, and maximal rigor develops in 12 to 48 hours depending on the environmental temperature and other factors (Krompecher et al, 1983). For a study of the different rates of onset of rigor mortis in different muscles, see Kobayashi et al (1996).

Rigor mortis sets in as muscle cells run out of the energy substance called ATP (adenosine triphosphate). Even when a person is clinically dead, some cells within their tissues continue to survive for a while. After the circulation of blood ceases, surviving muscle cells resort to anaerobic glycolysis but eventually they become unable to make any more ATP. You will probably recall that in healthy muscle cells ATP is involved in unlocking the cross bridges at the end of the power-stroke and energising them ready for the next contraction. Calcium ions also leak into the compromised muscle cells, moving regulatory proteins away from the molecular cross-bridges between the myofilaments. The myofilaments then become locked in position as a result of these changes, and the skeletal muscles no longer ‘give’ or stretch when parts of the body are moved.

Rigor mortis wears off as the tissues begin to decompose - proteolytic enzymes in the lysosomes of the muscle cells escape and begin to dissolve the myofilaments.

References

How is it that muscle cells in a dead frog can react to an electrical stimulus? Also, why does rigor mortis persist in a preserved cadaver - does the preservation chemical retain the properties of the corpse?

30th January 1999

Although the frog you saw in the science laboratory appeared dead, presumably it had been alive up until shortly before you saw it, and many of the muscle cells within it were still 'alive' in the cellular sense. Actually, although we tend to think of the "moment" of death, some cells remain alive for a while after the whole animal has died (that includes humans too). The heart may stop beating, the brain stop functioning, and there may be no signs of life, but deep in the body tissues there are still some cells that remain alive for minutes or hours, even though the blood has stopped circulating. So, in answer to the first part of your question, it is certainly possible for some cells to remain responsive for a while posthumously.

With regard to the second part, the fluid used for embalming contains a chemical, usually formaldehyde in solution, which preserves the structure of the body by stabilising the proteins from which it is partly made. It is a process called fixation. Muscle cells contain bundles of two types of filamentous protein called actin and myosin, which during life work together to produce the muscle contractions. When formaldehyde diffuses through the muscle cells during embalming, it causes chemical cross-linkages in and between the proteins and stops them from degrading - the muscle tissue becomes 'fixed'. This is why embalmed muscle no longer has the springy feel of living muscle, and why if you try to move embalmed limbs passively you find that the movements are very restricted because the muscles are no longer able to ‘give’. Generally, embalming fluids also contain glycerine, which slightly softens the fixed tissues and reduces fluid loss by evaporation, and an antibacterial substance such as phenol to prevent breakdown by micro-organisms.

Our thanks to Dr. T. Clarke, Consultant Histopathologist, Royal Devon & Exeter Hospital N.H.S.Trust, Wonford, Exeter for help with this answer.

I read your description of rigor mortis; is there any situation that you know of in which rigor mortis would not occur after death? Or does it always occur?

18th March 1999

Environmental factors can alter the rate at which rigor mortis develops, but it is not clear whether its appearance can be prevented completely. For example, rapid cooling of the body after death can inhibit rigor mortis, but rigor appears rapidly when the body is thawed. There is a substantial literature about this in relation to the meat processing industry. There have been suggestions that rigor mortis does not appear in people who die from particular diseases, but the evidence is not yet conclusive. Thus, Parekh and Patel (1972) reported that rigor mortis did not develop in children who died of cirrhosis of the liver. However, Schafer (1997) suggested that this observation simply reflects the small muscle mass of babies and children, particularly those confined to bed for long periods, and recommends the development of more accurate means of assessment. So for the time being, the question remains an open one.

References

How long does it take rigor mortis to set in?

28th March 1999

The rate at which rigor mortis it sets in will depend on several factors such as the person's physique, cause of death and the environment, whether warm, cold, dry, or wet. Different sources give different figures, but very broadly and in 'average' circumstances it begins about 3 to 4 hours after death and becomes complete in about 12 hours (Sherwood, 1997).

Reference

Is rigor mortis a temporary or permanent condition? If temporary, when does it usually end?

25th March 1999

Rigor mortis is a temporary condition. It generally appears during the first day after death and then gradually disappears over the next several days as the proteins in the muscles begin to decompose. The timing of these stages will be influenced by a number of factors such as the cause of death, the person's physique, and the surrounding environment, so it is not possible to make precise generalisations.

What happens to the endocrine, respiratory, nervous, cardiovascular, digestive, and integumentary systems when we die?

6th December 1999

The changes that occur at the time of death in the body systems you have listed will depend very much on the manner of death. Think of the body as an interconnected and interdependent web of structures and functions - these are normally kept in harmony by very resilient homeostatic processes. However, if one or several vital parts or functions are lost or damaged, then homeostasis will not be maintained and the individual as a whole will die. Death can be very sudden or more gradual, and result for example from injury, disease, inadequate food or fluid intake, or aging. Very different patterns of change can be detected in the body systems you have selected as people die in these various ways. There is now an added complication: with medical intervention, people can be kept alive even when vital functions have been lost, and this has created new difficulties in defining what we understand by death. Then we must think also about the cellular level of organisation - our bodies are organised from a complex community of living units called cells, a proportion of which die during our lifetime and which in many tissues are continuously replaced. When someone dies, some of the component cells in their tissues remain alive for up to several days afterwards, reminding us that the distinction between life and death is not completely clear-cut.

Reading

For a useful overview, see:

My cat has recently died, and when found her lying by the backdoor, her mouth was open a small amount and her eyes were open too . Apart from this she looked as if she had died in her sleep. Please can you advise me whether eyelids do open when animals and humans die. Or did she just slip into death while conscious? I appreciate that you normally have questions regarding humans and not cats, but this is something that I would like to know.

2nd July 2004

We are sorry to hear that your cat has died. It is indeed possible and common for eyes to open after death, even if they were closed at the time of death. This is due to chemical changes occurring in the muscles within the first few hours, causing them to contract and stiffen. This process is called rigor mortis. Rigor mortis tends to affect the smallest muscles first, and then spread throughout the larger muscles. Typically, rigor is first apparent in the small muscles of the eyelids, then the lower jaw and neck, followed by the limbs. The muscles of the eyelids are called orbicularis oculi and levator palpebrae superioris. In life, orbicularis oculi is used to close the eyelids, while levator palpebrae superioris lifts the upper eyelid to open the eye. When rigor affects the levator muscles first, the eyelids open and the muscles stiffen. Thus, when rigor affects the orbicularis muscles shortly afterwards, the force of contraction they produce is not enough to overcome the stiffness of the levator muscles and the eyes remain open. Rigor mortis continues for a day or two and then the muscles soften as decomposition sets in. So it is possible that your cat passed away in her sleep.

I was just wondering how many minutes or hours it takes a mortician to perform the embalming process?

26th January 2005

The time required for embalming will depend on the reason for carrying out the process, the degree of preservation required, and other factors such as the time and mode of death, the weight of the body, the general overall condition of the body, and the presence or absence of disease. Bodies bequeathed to medical schools for dissection will be studied for many months, and require careful embalming. Bodies are also normally fully-embalmed if the body is to be transported overseas, is going into an above-ground vault; is to be kept unrefrigerated for more than eight hours, or is to be kept for longer than five days.

For full embalming, injection of embalming fluids (for example: combinations of methylated industrial spirit, formalin, phenol, and glycerine) under pressure via the blood vessels may take 2 days, and the process of infiltration of all the tissues with the preservative continues by chemical diffusion for several weeks after the injection. On the other hand, where shorter-term preservation is required, temporary or cosmetic embalming may be carried out to improve the deceased's appearance before a viewing. This process can be carried out in a shorter time, hours rather than days.

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