Dear Doctors: I would like to know why it is that so many medications have side effects. Is it the medications themselves, or is it the additives that are used in making them? Also, why do some people have severe side effects and others don’t have any at all?

Dear Reader: The answer to your question begins with a concept known as homeostasis. As with many medical terms, it has its roots in Greek: The prefix “homeo” means similar, and the suffix “stasis” means stable. The term was coined in 1926 to describe the dynamic feedback loops that allows the many -- and often competing -- physiological processes that contribute to health to remain in balance. Add in the fact they take place simultaneously, dictated by constant changes inside and outside of the body, and you get a sense of the complexity of it all.

Homeostasis starts at the cellular level. It includes functions such as the maintenance of pH levels and ion concentrations in the fluids inside and surrounding the cells; the manufacture of lipids, hormones and proteins; enzyme balance; the production and distribution of energy; and the safe transport and elimination of waste products. That is a pretty long list, and we’ve only scratched the surface.

If the body detects a potentially harmful imbalance, it sends out instructions with the corrections that are needed. The organs and tissues then respond, with the goal of maintaining homeostasis. These finely calibrated feedback loops oversee functions such as regulation of blood pressure, blood sugar control, oxygen transport, digestion, and nutrient production and absorption. They also are crucial to feelings of hunger and thirst and circadian cycles, and they even play a role in mood and emotion.

A departure from homeostasis can result in discomfort, pain or malfunction. When prolonged, it can lead to disease. But the medications that we take, or the treatments that we undergo, can also have an effect on homeostasis. It is those disruptions that can give rise to side effects. For example, a drug known as hydralazine, which relaxes blood vessels, is effective for the management of hypertension. It is believed to work by affecting calcium ion homeostasis. But the drug can also stimulate the sympathetic nervous system, which can lead to side effects such as dizziness or headache.

Another example is non-steroidal anti-inflammatories, or NSAIDs, which ease pain and inflammation. They work by reducing production of an enzyme the body uses to mount an inflammatory response. But NSAIDs also change the behavior of cells in the stomach that help maintain optimal pH levels, which can lead to tissue damage. This side effect of NSAIDs is caused by an unintended disruption of homeostasis.

How a drug affects someone, including the side effects they may experience, depends on a number of factors. These include the person’s size and weight, age, metabolism, kidney and liver function, activity level, genetic makeup and habits such as smoking or drug use. Genetics plays a role, as well. Bottom line: Our response to medications, and the side effects they may cause, are as varied and individual as the people taking them.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I had such bad abdominal pain that my husband took me to the ER. I was told I was passing a kidney stone. It took two days, and it was excruciating. What are kidney stones? Is there anything I can do to keep this from happening again?

Dear Reader: A kidney stone is a bit of solid debris that can form due to a buildup of salts and minerals within the urinary tract. It can range in size from a grain of sand to a small -- or not-so-small -- pebble. It is estimated that 1 in 10 people will pass a kidney stone during their lifetime. Although this can occur at any age, it is most common in people age 30 and older.

As you have discovered (unfortunately!), passing a kidney stone is often very painful. This is because the stone can become stuck on its journey to exit the body. When stones leave the kidney, they pass into the ureter, which is the tube through which urine moves to the bladder. The walls of the ureter are not elastic, and thus cannot yield to a foreign object. When a kidney stone gets stuck, it can cause the ureter to go into spasm, which can cause significant pain.

When a kidney stone is unable to move, the resulting blockage forces urine to back up into the kidney. This leads to mounting pressure that causes widespread pain in the region of the belly, groin and back. Blockages can also lead to infection.

Symptoms include fever, nausea, vomiting, urine that is cloudy or has an unpleasant odor, urinary urgency and blood in the urine. Treatment begins with the use of medications to manage pain, plus hydration to help pass the stones. Larger stones and those that are impacted may require shockwave therapy. This breaks the stone into particles that are small enough to move through the ureter. In very difficult cases, surgical options may be considered.

Anyone who has passed a kidney stone, or knows of someone who has, will be motived to make lifestyle changes to decrease their risks. The first step is to drink plenty of water. This prevents the urine from becoming concentrated, which leads to development of the crystals from which kidney stones are formed. It is also important to pay attention to diet. This is particularly true for someone who has already passed a kidney stone.

Kidney stones fall into several categories. The most common are made up of calcium and oxalate, a natural compound found in vegetables, fruits, nuts and grains. Foods high in oxalate include spinach, walnuts, beets, sweet potatoes, chocolate and tea. It is also important to limit foods high in purines. These contribute to the formation of uric acid, which is associated with the formation of another type of kidney stone. Foods high in purines include red meat, organ meats and shellfish. Alcohol consumption also plays a role in the formation of kidney stones. Your health care provider can help you with the lifestyle changes needed to decrease your risk of kidney stones.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I was in a car accident, and an X-ray showed I had two broken ribs. A second X-ray taken a month later showed I also had a cracked rib. Why didn’t that show up the first time? Why isn’t there more that can be done for a broken rib other than being told to rest? It’s very painful.

Dear Reader: Fractured ribs are one of the most common traumatic injuries. More than 300,000 people visit the emergency room each year with a broken rib, and up to 45,000 wind up spending time in the hospital as a result. The most common causes are a car accident, as happened in your case, or collisions during contact sports. Older adults, whose bones can become frail, are at increased risk of a rib fracture during a fall.

As with any bone in the body, ribs can be bruised, cracked or broken. When this occurs, the muscles and cartilage that hold the rib cage together can also be damaged. The most common site of a rib fracture is the outer curve of the rib, where the bone is weakest. The ribs in the middle of the chest are most likely to be broken. In severe trauma, it is possible for a broken rib to injure the lung. Breaks in the lower ribs can injure the spleen, liver or kidneys, which can be life-threatening.

Diagnosis begins with a physical exam, and can often also include an X-ray. A cracked rib, also known as an incomplete fracture, may not be immediately visible. It is only once the damaged bone has begun to heal, which involves the deposit of specialized cells known as osteoblasts, that the damage to the rib may become visible on an X-ray.

Symptoms of rib injury include localized pain that can be severe. The rib cage glides open a bit with each breath and flexes in response to motion, each of which can also trigger pain or discomfort.

The fracture you are now dealing with shows your rib cage was doing its job. It protected your heart, lungs, liver and other vulnerable tissues from the blunt-force trauma of the car accident. However, the architecture of the rib cage, a light and flexible lattice of bone, muscle and connective tissue, puts limitations on caring for a fracture. Your rib cage needs to be able to expand and contract in order to permit breathing. Unlike a broken arm or leg bone, fractured ribs cannot be stabilized in a cast.

The primary treatments for rib fractures are medications to help manage pain and inflammation and instructions to limit movement. Depending on the severity of someone’s injury and the number of ribs involved, healing can take from six weeks to several months. Once the initial pain has been managed, the challenge becomes limiting motion and activity so that the affected bones are not reinjured.

Recently, researchers have been looking into using an injectable adhesive to stabilize the broken bone. As healing takes place, the adhesive would be absorbed by the body. The approach remains in the research phase and is not yet available.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)