Sweat. Where Does it Come From?

The majority of the fluids in our body reside within cells and in the spaces between cells. Broadly, the fluids in our body can be divided into two main compartments:

Intracellular fluid (ICF): This is the fluid that is contained inside our cells. It accounts for about two-thirds (roughly 66%) of the total body water in a typical human.

Extracellular fluid (ECF): This is the fluid that exists outside of our cells. It accounts for about one-third (roughly 33%) of the total body water. The extracellular fluid can be further broken down into:

  • Interstitial fluid: The fluid that lies between cells (in the “interstitial” spaces) and accounts for most of the ECF.
  • Plasma(Circulatory System): The liquid component of blood where the blood cells are suspended.
  • Transcellular fluid: These are small amounts of fluid contained in specific spaces, such as synovial fluid in joints, cerebrospinal fluid in the brain and spinal cord, and intraocular fluid in the eyes.

Sweat consists primarily of water (90% by volume), with 1-3% salt and 0.5-2% urea.

In a typical adult human, total body water might comprise about 60% of the body’s total weight (though this can vary based on factors like age, sex, and body composition). So, around 40% of the body’s weight is from intracellular fluid, and around 20% is from extracellular fluid.

Urea derivatives have a wide range of biological activities, including anticancer, antibacterial, and antiviral. Some urea derivatives, such as N-phenyl-N’-(2-chloroethyl)ureas (CEUs) and benzoylureas (BUs), have shown good anticancer activity. These compounds are tubulin ligands that inhibit the polymerization of tubulin.

Diarylurea is a prominent pharmacophore in anticancer drugs. This activity is due to its near-perfect binding with certain acceptors. The NH moiety acts as a hydrogen bond donor, and the urea oxygen atom acts as an acceptor.

Urea derivatives have also shown anticonvulsant, analgesic, and high-density lipoprotein (HDL) elevating activities.

Sweat originates from both intracellular and extracellular fluids. Here’s how the process works:

1. Initial Formation in Sweat Glands: Sweat is primarily formed in sweat glands, which are distributed across the skin. Initially, sweat glands produce a fluid that is similar to plasma (i.e., the fluid portion of blood without the cells) but without the proteins. This initial sweat is derived from the extracellular fluid, especially the plasma.

2. Modification of Sweat: As the sweat passes through the ducts of the sweat gland, the composition of the sweat is modified. Specifically, cells in the ducts of the sweat glands reabsorb sodium and chloride ions, making the sweat hypotonic relative to plasma. To achieve this reabsorption, cells use energy and move ions against their concentration gradient. In the process, water from inside the cells (intracellular fluid) can also be drawn into the duct due to osmotic forces.

So, while the initial formation of sweat is primarily from the extracellular fluid, the modification of sweat as it passes through the sweat gland ducts can involve intracellular fluid. However, in terms of volume, the majority of the sweat comes from the extracellular compartment.

It’s worth noting that sweating is an essential mechanism for thermoregulation. As sweat evaporates from the surface of the skin, it cools the body down. Additionally, sweat also plays a role in excreting certain waste products. For those that are less active, that is, those that don’t sweat because of inactivity, the kidneys are the primary organs for excretion in the body from the body’s fluid storage.

-Michael J. Loomis & ChatGPT