11.12: When Smoke Meets Biology — The Cost to Your Cells and Tissues

Smoking interferes with normal oxygen transport, reducing how much oxygen the blood delivers to the body and contributing to widespread health effects besides the obvious damage to the respiratory and cardio vascular systems. 

Master this section and you'll be able to:

• Describe how carbon monoxide and nicotine from smoking affect oxygen transport and cardiovascular function.
• Summarize the short-term and long-term effects of smoking on the respiratory and cardiovascular systems.

Smoking and Carbon Monoxide: How They Affect Oxygen Transport

Smoking influences the body on several levels, from immediate autonomic changes to long-term structural damage of the lungs and blood vessels. Within minutes of inhaling smoke, nicotine alters heart rate, blood pressure, and the narrowing of airways and blood vessels, changing the normal function of the cardiovascular and respiratory systems. Over time, chronic exposure to smoke particles and toxic chemicals inflames and scars lung tissue, stiffens blood vessel walls, and contributes to chronic diseases such as COPD, atherosclerosis, heart attacks, and stroke.

Cigarette smoke contains more than 4,000 chemicals, including hundreds that are toxic and at least 70 that are known carcinogens. Carbon monoxide (CO) is one of these chemicals. CO is produced any time a material burns without enough oxygen for complete combustion. This occurs during smoking because tobacco and paper smolder rather than burn cleanly. Incomplete combustion creates CO along with many other harmful gases.

Once inhaled, CO crosses into the bloodstream and binds tightly to hemoglobin at the same location where oxygen normally attaches. This creates carboxyhemoglobin. CO binds more than 200 times more strongly than oxygen, so hemoglobin will preferentially bind CO even when oxygen levels are normal. As a result, less hemoglobin is available to carry oxygen to body tissues.

Consequences include:

• Reduced oxygen delivery to all organs, including the heart and brain
• Shortness of breath and fatigue, especially during exercise
• Increased workload on the heart as the body attempts to compensate
• Prolonged recovery time after smoking, because carboxyhemoglobin has a half-life of about four hours

The level of carboxyhemoglobin rises with each cigarette. In smokers, typical levels range from about 2 to 15%. Because carboxyhemoglobin breaks down with a half-life of roughly four hours, its concentration decreases relatively quickly once a person stops inhaling smoke.
 

Physiological Effects of Smoking

Smoking has several immediate and long-term effects on the body because nicotine activates the sympathetic, or fight-or-flight, system.

Immediate physiological effects

• The effect of nicotine: nicotine acts on the body within seconds, and its first stop is the brain. Once it arrives, it switches on the sympathetic, or fight-or-flight, system and signals the adrenal 2 glands to release adrenaline. This creates a wave of short-term cardiovascular changes every time a person smokes. Over months and years, this repeated stimulation places chronic stress on the heart, blood vessels, and lungs.

Here is what happens immediately after smoking:

• Nicotine enters the bloodstream and reaches the brain and adrenal glands.
• The sympathetic nervous system becomes activated.
• Adrenaline is released into the blood.
• Heart rate rises as the heart beats faster and more forcefully.
• Blood pressure increases because adrenaline tightens many small arteries.
• Peripheral vasoconstriction reduces blood flow to the skin and extremities, which can cause cold hands and delayed wound healing.

• Effects on gas transport and oxygen delivery: As was discussed above, the carbon monoxide in smoke binds to hemoglobin with much higher affinity than oxygen, forming carboxyhemoglobin and reducing the effective oxygen‑carrying capacity of blood. Additionally, when CO attaches to hemoglobin, it also makes the remaining hemoglobin hold on to oxygen more tightly. This means oxygen is not released easily to the tissues, so the tissues can still become starved for oxygen even if a pulse oximeter shows a normal oxygen saturation.

Long-term Chronic Structural Damage

• Airway and mucociliary changes: The hot, chemical‑laden smoke irritates the airway epithelium, leading to chronic inflammation and edema.
  Mucus production increases, but with narrower airways the lungs are less able to clear it. The buildup of mucus in combination with narrowed airways makes smokers more prone to hypoxia, especially during activity or illness. 
  Cilia are also damaged and eventually lost, so the mucociliary escalator fails; mucus and inhaled particles accumulate, promoting chronic cough, recurrent infections, and further inflammation.

• Cardiovascular pathophysiology: Nicotine and other components of smoke promote endothelial dysfunction, increase oxidative stress, and enhance platelet activation and coagulation, all of which accelerate atherosclerosis. Combined effects (sympathetic activation, higher blood pressure, atherosclerosis, and reduced oxygen delivery) greatly increase the risk of coronary artery disease, myocardial infarction, stroke, and peripheral arterial disease.

• Other chronic adaptations and systemic effects: Persistent hypoxemia can stimulate erythropoietin release, leading to secondary polycythemia, which increases blood viscosity and further strains the heart.
  Chronic inflammation from smoking contributes to systemic endothelial injury and is linked to insulin resistance, decreased bone density, impaired immune function, and increased cancer risk in multiple organs.

Figure \(\PageIndex{1}\): Comparison of Healthy and Smoker’s Lungs. Healthy lungs are pink, elastic, and supported by active cilia that help clear mucus, allowing efficient gas exchange and a normal vital capacity. Smoker’s lungs become dark, rigid, and scarred over time, with damaged alveoli, reduced lung capacity, paralyzed cilia, and much more limited ability to repair themselves.

In conclusion: Smoking does not just damage the lungs; it also starves the tissues of oxygen. Carbon monoxide and other chemicals in smoke reduce how much oxygen the blood can carry, while nicotine and vessel damage reduce blood flow itself. Together, this means that muscles, the heart, the brain, and even the skin may not get enough oxygen, especially during exercise or illness.​

Over time, the tiny alveoli can be destroyed and merge into larger, less efficient spaces, as in emphysema. This reduces the total surface area available for gas exchange, so even if a smoker breathes faster or deeper, the lungs simply cannot move oxygen into the blood or remove carbon dioxide as well as healthy lungs can. As a result, smokers become short of breath more easily and are at higher risk of respiratory failure during infections or surgery.​

Smoking also interferes with healing and immune function. Less oxygen delivery and damaged blood vessels slow the repair of wounds, bone, and other tissues, making surgical complications and infections more likely. At the same time, chronic inflammation and impaired immune cells mean the body is less effective at fighting off pathogens and abnormal (precancerous) cells, further increasing the risk of infections and many types of cancer.​

Myths about Smoking and Cigarettes

Smoking is Just a Choice.

The first time? Yes. After just a few cigarettes? No. Addiction to nicotine can happen quickly. It changes the chemical balance in your brain. Smoking may seem like it’s just a choice or a habit. In fact, most people who use tobacco are addicted. Breaking nicotine addiction is harder for some people than others. Quitting can take several tries. But don’t give up. If you need help to quit, ask your doctor about nicotine replacement, medicines, or coaching.

Filters Make Cigarettes Safer.

Filters do not protect you. They are designed to make smoke particles smaller. That makes nicotine easier to absorb. This increases addiction. Cigarettes have been engineered to speed up nicotine’s path to your brain. Their design feeds addiction. Light or low-tar cigarettes may sound less dangerous. They aren’t. These misleading labels are no longer allowed. No cigarette is safe. Tobacco smoke contains more than 7,000 chemicals. At least 250 are toxic.

An Occasional Cigarette is no Big Deal.

Smoking doesn’t just cause diseases for heavy smokers or longtime smokers. The 2010 Surgeon General’s Report shows how breathing tobacco smoke can cause immediate harm. Tobacco smoke can trigger sudden heart attacks and death, even in nonsmokers. Each cigarette you smoke hurts your lungs, your blood vessels, and cells throughout your body. Smoking a few cigarettes a week can cause a heart attack. Cutting back is not enough to protect you. You have to quit entirely.

It’s Too Late to Quit — The Damage is Already Done.

It’s true that the longer you use tobacco, the more you hurt your body. But at any age, the sooner you quit, the sooner your health can improve. The 2010 Surgeon General’s Report shows how using tobacco causes disease almost everywhere in your body. Within 20 minutes after quitting, your body starts to heal. After 2 to 5 years, your risk for stroke is similar to that of a nonsmoker. In 10 years, your lung cancer risk is cut in half.

Secondhand Smoke May Bother People, But it isn’t Dangerous.

Tens of thousands of nonsmokers die every year from breathing others’ secondhand smoke. Breathing the chemicals in tobacco smoke changes your blood’s chemistry almost immediately. Deadly clots can form and block arteries to your heart or brain. When you smoke at work, home, or at a restaurant, everyone there breathes poisons. If you smoke in your car, rolling down a window does not protect your passengers. It is not healthy to breathe any amount of tobacco smoke.

The Little Bit of Smoke that my Kids Get Doesn’t Hurt Them.

Don’t smoke or let others smoke around your children. They can get bronchitis, pneumonia, and ear infections from smoke. Even if you only smoke by an open window, some of the smoke stays in your house and poisons the air your children breathe. Children with asthma can have a serious, even deadly, asthma attack from breathing secondhand smoke. The best way to protect children is to quit smoking. If you or someone else in your household are not ready to quit, be sure to make your home and car 100% smoke-free.
 

Smoking vs. Vaping

While smoking burns tobacco to create smoke that is inhaled — exposing the lungs to tar, carbon monoxide, and thousands of combustion-related chemicals — vaping does not burn anything. Instead, vaping heats a liquid into an aerosol, containing solvents (like propylene glycol or glycerin) and flavorings, as well as in most cases nicotine.

Vaping is less harmful than smoking because it avoids burning tobacco, which is what produces most of the tar and carcinogens in cigarette smoke. However, “less harmful” does not mean “safe.” Vaping still delivers nicotine, which is addictive, and its aerosols contain chemicals that can irritate airways, trigger inflammation, and potentially harm lung function, especially in young people. So while vaping may be a better alternative for someone trying to quit smoking, it is not considered harmless.

Why can toxic chemicals still form when vaping? When vape liquid is heated, especially at high temperatures:

• Vegetable glycerin and propylene glycol can break down producing formaldehyde, acetaldehyde, and acrolein (all of which are respiratory irritants; formaldehyde is a known carcinogen).

• Flavoring chemicals can degrade into toxic compounds as well.
  Some flavorings contain diacetyl or related chemicals, which have been linked to a special type of bronchiolitis, known as “popcorn lung”, in which the small airways become narrowed or blocked, leading to cough and shortness of breath. It typically occurs as a result of inhaling toxic gases..

• Metal particles (nickel, tin, lead) can shed from the heating coil and be inhaled.

So, while vaping does not involve burning or produce smoke like cigarettes do, heating vape liquid can still create harmful chemicals such as formaldehyde, acrolein, and tiny metal particles, so the aerosol is not harmless.