July 16, 2007

Sweats and Bile

SKIN - Sweating

Perspiration (also called sweating or sometimes transpiration) is the production and evaporation of a fluid, consisting primarily of water as well as a smaller amount of sodium chloride (the main constituent of "table salt"), that is excreted by the sweat glands in the skin of mammals. Sweat also contains the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol).

In humans, sweating is primarily a means of temperature regulation, although it has been proposed that components of male sweat can act as pheromonal cues. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. Hence, in hot weather, or when the individual's muscles heat up due to exertion, more sweat is produced. Sweating is increased by nervousness and nausea and decreased by cold. Animals with few sweat glands, such as dogs, accomplish similar temperature regulation results by panting, which evaporates water from the moist lining of the oral cavity and pharynx. Primates and horses have armpits that sweat similarly to those of humans.

How sweat glands operate
There are two kinds of sweat glands, and they differ greatly in both the composition of the sweat and its purpose:

Eccrine sweat glands are distributed over the entire body surface, but are particularly abundant on the palms of hands, soles of feet, and on the forehead. These produce sweat that is composed chiefly of water with various salts. These glands are used for body temperature regulation.

Apocrine sweat glands produce sweat that contains fatty materials. These glands are mainly present in the armpits and around the genital area and their activity is the main cause of sweat odor, due to the bacteria that break down the organic compounds in the sweat from these glands.

LIVER - Bile

Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. In many species, it is stored in the gallbladder between meals and upon eating is discharged into the duodenum where it excretes waste and aids the process of digestion of lipids

The components of bile include:

Lecithin (a phospholipid)
Bile pigments (bilirubin & biliverdin)
Bile salts (sodium glycocholate & sodium taurocholate)
Bicarbonate ions


Bile is produced by hepatocytes in the liver, draining through the many bile ducts that penetrate the liver. During this process, the epithelial cells add a watery solution that is rich in bicarbonates that dilutes and increases alkalinity of the solution. Bile then flows into the common hepatic duct, which joins with the cystic duct from the gallbladder to form the common bile duct. The common bile duct in turn joins with the pancreatic duct to empty into the duodenum. If the sphincter of Oddi is closed, bile is prevented from draining into the intestine and instead flows into the gall bladder, where it is stored and concentrated to up to five times its original potency between meals. This concentration occurs through the absorption of water and small electrolytes, while retaining all the original organic molecules. Cholesterol is also released with the bile, dissolved in the acids and fats found in the concentrated solution. When food is released by the stomach into the duodenum in the form of chyme, the gallbladder releases the concentrated bile to complete digestion.

The human liver can produce close to one litre of bile per day (depending on body size). 95% of the salts secreted in bile are reabsorbed in the terminal ileum and re-used. Blood from the ileum flows directly to the hepatic portal vein and returns to the liver where the hepatocytes resorb the salts and return them to the bile ducts to be re-used, sometimes two to three times with each meal.

Physiological functions

Bile acts to some extent as a detergent, helping to emulsify fats (increasing surface area to help enzyme action), and thus aids in their absorption in the small intestine. The most important compounds are the salts of taurocholic acid and deoxycholic acid. Bile salts combine with phospholipids to break down fat globules in the process of emulsification by associating its hydrophobic side with lipids and the hydrophilic side with water. Emulsified droplets then are organized into many micelles which increases absorption. Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble vitamins D, E, K and A. Besides its digestive function, bile serves as the route of excretion for the hemoglobin breakdown product (bilirubin) created by the spleen which gives bile its colour; it also neutralises any excess stomach acid before it enters the ileum, the final section of the small intestine. Bile salts are also bacteriocidal to the invading microbes that enter with food.

Bile from slaughtered animals can be mixed with soap. This mixture, applied to textiles a few hours before washing, is a traditional and rather effective method for removing various kinds of tough stains.

Adapted from WikiPedia