There but this lesson will concentrate on these

There are many ways in which the body gets rid of drugs. In this lesson, we will focus on the kidneys and liver, and the roles that these organs play in drug excretion.


Have you ever been on a detox diet or seen body detoxifying products advertised? Guess what? You have a detoxification system that is way more powerful than anything you can buy – and you got it for free!Your low-priced, hyper-efficient, detoxifying system starts with your kidneys and your liver.

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There are many other systems that also help you detoxify, but this lesson will concentrate on these two. Your body also excretes drugs and other toxic waste products through your saliva, sweat, and lungs and if you have it, through breast milk as well.Sometimes your body excretes drugs intact. Sometimes your body changes the drugs at a molecular level before excreting them.

We call these altered forms metabolites.

Your Kidneys

Renal means ‘pertaining to the kidneys,’ so renal drug excretion describes how your kidneys get rid of drugs and their waste products. One of the primary means by which kidneys remove drugs is through glomerular filtration.A glomerulus is a glob of capillaries in the kidneys. Your kidneys filter all your blood plasma through the capillaries into the surrounding structure, known as Bowman’s capsule. Your kidneys filter about 180L of plasma per day! Most of what is filtered gets reabsorbed, which is why you only urinate around 2L per day. (Otherwise, you’d have to drink a lot more water!)You reabsorb water and most electrolytes, but you can’t reabsorb most polar compounds (compounds in which some atoms are slightly negative while some are slightly positive).

Since most drug metabolites are polar compounds, these molecules will be excreted unless your body has a mechanism to reabsorb them.

Glomerulus and Bowmans capsule
The four humors
The four humors

Sometimes drugs will pass through your liver without being altered at all; sometimes your liver will change the drugs into metabolites.

Either way, the drugs end up in your bile.Your bile then enters your digestive tract at your small intestine, where it is then mixed with the semi-fluid mass of your partially digested dinner and eventually excreted. In other words, drugs filtered out by your kidneys end up in your urine; drugs filtered out by your liver end up in your feces.

Lesson Summary

When was the last time you stopped to appreciate your kidneys and your liver? Let’s all thank our kidneys and our liver for all the hard work they do.Drugs can pass through the body unchanged, or the body can alter them at a molecular level.

These altered forms are called metabolites.Drugs will then be excreted by the body. There are many ways the body can excrete drugs, but two of the most important involve the kidneys and the liver.

Your renal, or kidney, filtration system involves sending your blood through a small glob of capillaries called a glomerulus. The fluid in your blood filters out into the surrounding region, the Bowman’s capsule. Most of that fluid gets reabsorbed, but some substances, such as many drugs, cannot be reabsorbed. These drugs that are filtered out will be passed out of your body via your urine.The pH of your urine also determines how easy it is to excrete certain drugs.

Acidic drugs will be easily excreted in alkaline urine and vice-versa. Doctors will sometimes alter the pH of a patient’s urine to help him or her excrete a drug more quickly.Your hepatic, or liver, filtration system involves bile. Drugs will get caught in your bile and passed to your small intestine, where they will be pass out of your body as feces.


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