Nicotine: Physiological effects
Last modified: Saturday, 20. June 2009 - 1:16 pm
As with the Mental effects of nicotine, the Physiological effects are brought about by its actions on the nervous system, both peripheral and central. Nicotine changes the transmission of nerve impulses by binding to acetylcholine receptors, and induces the release of several chemical messengers, which in turn affect several body systems.
In the cardiovascular system, there is a 10 to 20 beat per minute increase in heart rate, a 5-10 mm increase in blood pressure, and an increase in the strength of heart contractions. Nicotine increases the incidence of cardiac arrhythmia (irregular heartbeat) in susceptible people. It causes constriction of blood vessels in the skin, and causes platelets to adhere together leading to an increased possibility of blood clots.
Nicotine is irritating to the digestive tract. Salivation increases, and the strength of stomach contractions decreases. Nausea and vomiting may occur. Appetite is suppressed, particularly in females for sweet food. Metabolism is increased and brown fat is stimulated, which along with appetite suppression can lead to weight loss.
Nicotine causes local irritation in the respiratory system, as well as decreased motion of the cilia, the tiny hairs that sweep debris and mucus upward, out of the respiratory tract. A recurrent “smoker’s cough” results as the body tries to rid itself of accumulated mucus. Breathing is accelerated by nicotine.
In the endocrine (gland secretion) system, besides increased release of epinephrine and norepinephrine, there is increased release of the growth hormone, cortisol, and the antidiuretic hormone. The increased levels of circulating catecholamines (epinephrine, norepinephrine, and dopamine) play a role in causing cardiovascular diseases by changing the balance of lipoproteins circulating in the blood. They increase the harmful low-density lipoproteins (LDL) and decrease the protective high-density lipoproteins (HDL), increasing the risk of cardiovascular disease.
Ingestion of 60 mg of nicotine can be fatal to an adult. This is an amount that might be ingested with exposure to some insecticide sprays. A smaller amount is toxic to children and pets who accidentally ingest tobacco products. Tobacco pickers and patients on nicotine replacement therapy who continue to smoke have also experienced nicotine toxicity. Symptoms include salivation, dizziness, vomiting, tremors, convulsions, and severely low blood pressure. Death may result in a few minutes due to respiratory failure caused by lung paralysis.
Carbon monoxide and tar
It is important to emphasize that although nicotine causes a wide variety of physical and Mental effects, the majority of health problems from smoking are due to carbon monoxide and tar, much more so than nicotine. CO decreases the ability of the blood to carry oxygen. This leads to an increased production of red blood cells to compensate for the loss of oxygen carrying capacity. Along with nicotine, CO contributes to lipoprotein changes and increased blood-clotting ability, leading to cardiovascular disease. Tar, with its many known carcinogens and other irritants, is largely responsible for various forms of cancer, especially lung cancer.
An attempt to stop using tobacco products, or even decrease their consumption, often results in the user experiencing unpleasant withdrawal symptoms that are due specifically to nicotine. Symptoms may start within hours after cessation of use, peak usually at the second to fourth day and may last for weeks or months.
Withdrawal symptoms include:
• irritability or anger
• difficulty concentrating
• excessive hunger
• loss of energy or fatigue
• decreased heart rate and blood pressure
• stomach or bowel problems
• heart palpitations
• decreased motor performance
• increased muscle tension
• craving for tobacco products
The symptoms are often worse in the evening. Weight gain is common, 4 — 7 lb (2-3 kg) on average.
Among tobacco users with no history of depression, 20% experience depression during withdrawal. The rate jumps to 80% for those with a past history of depression. Women are more prone to depression during withdrawal than men.
Long-term health effects
Smoking causes one third of all cancers and 87% of lung cancer. Because of tobacco use, lung cancer is the number one cancer killer of both men and women. It is also associated with cancer of the mouth, throat, voice box, esophagus, stomach, bladder, kidney, pancreas, uterus, and cervix. Smoking is also possibly linked to leukemia, and cancer of the breast, prostate, and colon. The overall rates of death from cancer are twice as high among smokers as among nonsmokers, with heavy smokers having death rates that are four times greater than nonsmokers. The role of nicotine itself in causing cancer is controversial.
The majority of smoking-related illnesses are cardiovascular and respiratory. Nearly one fifth of heart disease deaths in the United States are related to smoking. It is a major cause of atherosclerosis (narrowing and hardening of the arteries) and high blood pressure and the resulting angina, heart attacks, and strokes due to both hemorrhage and blood clots. It also increases the risk of abdominal aortic aneurysm.
Smoking leads to respiratory problems other than lung cancer. It causes chronic bronchitis, emphysema, and lower resistance to flu and pneumonia. It worsens asthma symptoms in adults and children. As these problems persist, chronic obstructive pulmonary disease (COPD, airway obstruction) develops. Eighty to 85% of deaths due to COPD are from smoking. The role of nicotine in chronic lung diseases such as COPD, emphysema, and asthma is uncertain. However it is known that nicotine can cause an enzyme to be released which is able to destroy parts of the lungs as is seen in emphysema.
Smoking is especially harmful to diabetics who are already at an increased risk of cardiovascular disease, stroke, and kidney disease. The habit also negatively affects joints and interferes with the healing of wounds. Healing of fractures is delayed because smoking impairs the formation of new bone. Smokers are more likely to develop degenerative disorders and injuries of the spine. The risk for peptic ulcers is increased. Smoking also may upset thyroid function.
Heavy smoking is a contributory factor in male impotence due to a decreased amount of blood flowing into the penis. Smoking also increases the risk of infertility in men by decreasing sperm motility and density. A nearly twofold increase in hearing loss, cataracts, and macular degeneration of the eye has been observed in smokers. Smokers have a decreased sense of taste and smell and are prone to periodontal disease, such as receding gums, as well as increased dental cavities.
Women face additional adverse health effects from smoking. About 30% of cancers of the cervix are attributable to both active and passive smoking. Women who smoke have a high risk for osteoporosis and hip fractures following menopause. They are likelier to have early onset of menopause due to nicotine’s anti-estrogen effect. However, the decreased estrogen levels seen in female smokers appear to decrease their risk of endometrial cancer up to 50%. Women smokers have an increased risk of infertility, especially those women who started before age 18 or who smoke one or more packs per day. In 1987, lung cancer surpassed breast cancer as the leading cause of cancer death among women.
Pregnant women who smoke create additional health concerns for their unborn child. Many substances in tobacco smoke, including nicotine, cross the placenta and are found in breast milk. Mothers who smoke heavily have almost a two-fold increase in miscarriage and birth defects and are more likely to deliver low-birth-weight babies. Smoking during pregnancy also causes ectopic pregnancy, premature births, and stillbirths. Infant mortality rates in pregnant smokers are increased 33%.
Sudden infant death syndrome (SIDS) is strongly linked to smoking in pregnant women and new mothers. Children of smoking mothers are more likely to have motor control problems, perception impairments, symptoms of hyperactivity, and conduct disorder in childhood. These children have a higher risk for cancer later in life.
The younger a person begins smoking, the greater the risk of developing serious illnesses. Smoking teens experience adverse health effects, including a general decrease in physical fitness, increased coughing and phlegm, greater susceptibility to respiratory illnesses, and early development of artery disease (a precursor to heart disease). They have a slower rate of lung growth, and by adulthood, possible reduced lung function.
Cigars and pipes
Cigars and pipes have health consequences similar to those of cigarettes, including nicotine dependence, heart disease, and cancer of the lung, mouth, throat, voice box, esophagus, prostate, bladder, and possibly the pancreas. Additionally, pipe smoking causes cancer of the lip. Inhaling cigar or pipe smoke significantly raises the risk of disease.
Smokeless tobacco causes cancer of the mouth, esophagus, and stomach. Users who swallow the tobacco or the saliva increase their risk of esophageal damage and stomach ulcers. Dentists report seeing users with leukoplakia (pre-cancerous lesions) in the mouth, receding gums, dental cavities, chronic mouth sores, with badly discolored teeth, and bad breath. Smokeless tobacco may also contain high levels of sodium, which may contribute to high blood pressure.