why people immediately or fastly died when they exposed or swallowed cyanide beacause their respiration inhibited.why it is inhibited here is the explanation .....

1. CYANIDE
POISONING
D A S A R I . S A N D H YA R A N I

2. The term "cyanide" refers to any chemical containing a carbon-nitrogen (CN)
bond.
Many substances contain cyanide, but not all of them are deadly poisons.
Sodium cyanide (NaCN), potassium cyanide (KCN), hydrogen
cyanide (HCN), and cyanogen chloride (CNCl) are lethal, but
thousands of compounds called nitriles contain the cyanide group yet aren't
as toxic. In fact, you can find cyanide in nitriles used as pharmaceuticals,
such as citalopram (celexa) and cimetidine (Tagamet). Nitriles aren't as
dangerous because they don't readily release the CN- ion, which is the group
that acts as a metabolic poison.
HOWCYANIDE POISONS
The cyanide ion, CN-, binds to the iron atom in cytochrome C oxidase in the
mitochondria of cells. It acts as an irreversible enzyme inhibitor, preventing
cytochrome C oxidase from doing its job, which is to transport electrons to
oxygen in the electron transport chain of aerobic cellular respiration.
Without the ability to use oxygen, mitochondria can't produce the energy
carrier adenosine triphosphate (ATP). Tissues that require this form of energy,
such as heart muscle cells and nerve cells, quickly expend all their energy and
start to die. When a large enough number of critical cells die, you die.

4. HOW MUCH CYANIDE IS LETHAL?
How much cyanide is too much depends on the route of exposure, the dose, and duration of
exposure.
 Inhaled cyanide presents a greater risk than ingested cyanide. Skin contact is not as much of a
concern (unless it has been mixed with DMSO), except touching the compound could lead to
accidentally swallowing some of it.
 As a rough estimate, since lethal dose depends on the exact compound and several other factors,
about half a gram of ingested cyanide will kill a 160-lb adult.
 Unconsciousness, followed by death, could occur within several seconds of inhaling a high dose of
cyanide, but lower doses and ingested cyanide may allow a few hours to a couple of days for
treatment. Emergency medical attention is critical.

5. IS THERE A TREATMENT FOR CYANIDE POISONING?
Because it's a relatively common toxin in the environment, the body can detoxify a small
amount of cyanide.
For example, you can eat the seeds of an apple or withstand cyanide from
cigarette smoke without dying.
 When cyanide is used as a poison or a chemical weapon, treatment depends on the dose. A
high dose of inhaled cyanide is lethal too quickly for any treatment to take effect.
 Initial first aid for inhaled cyanide is getting the victim to fresh air. Ingested cyanide or
lower doses of inhaled cyanide may be countered by administering antidotes that detoxify
cyanide or bind to it.
For example, natural vitamin B12, hydroxocobalamin, reacts with cyanide to
form cyanocobalamin, which is excreted in urine.
 Inhalation of amyl nitrite may aid breathing in victims of cyanide and also carbon
monoxide poisoning, although few first aid kits contain these ampules anymore.
 Depending on the conditions, complete recovery may be possible, although paralysis, liver
damage, kidney damage, and hypothyroidism are possible.

6. TOXICITY OF APPLE SEEDS
Apple seeds do contain a small amount of cyanide, which is a lethal poison,
but you are protected from the toxin by the hard seed coating.
If you eat whole apple seeds, they pass through your digestive
system relatively untouched. If you chew the seeds thoroughly, you will be
exposed to the chemicals inside the seeds, but the dose of toxins in an apple
is small enough that your body can easily detoxify it.
HOW MANY APPLE SEEDS DOES IT TAKE TO KILL YOU?
Cyanide is deadly at a dose of about 1 milligram per kilogram of body weight. On average, an
apple seed contains 0.49 mg of cyanogenic compounds. The number of seeds per apple varies,
but an apple with 8 seeds, therefore, contains about 3.92 milligrams of cyanide. A person
weighing 70 kilograms would need to eat 143 seeds to reach the lethal dose or about 18 whole
apples.