1. Sweat Sweat is the watery fluid produced and excreted by the sweat gland. Sweat glands; They are simple tubular glands found in almost every part of the skin( There are two to four million sweat glands distributed all over our bodies). Each gland consists of two parts; 1- A secretory portion which lies deep in the dermis, where the tubule is twisted into a fairly compact tangle. 2- A duct portion passing outwards through the overlying dermis and the epidermis. Sweating control and stimulation; Sweating is controlled from a center in the hypothalamus where thermosensitive neurons are located. Sweat glands are stimulated in response to; 1-high temperature. 2-exercise. 4- hormones. 3-emotional stress (emotionally induced sweating is restricted to palms,soles, armpits and forehead while temperature induced sweating causes sweating throughout the body).

2. Sweat glands There are two types of sweat glands ; 1-TheECCRINE SWEAT GLANDS ; They are located over the entire body surface except for the lips,nipples and part of the external genial, and are innervated by sympathetic nerves. The tiny ducts of the eccrine glands pass through the dermis and epidermis open up and empty directly on to the skin. They are active since birth producing an odorless, clear fluid which is sweat and is mainly a mixture of water and salts. 2- The Apocrine sweat glands ; - They are limited in their distribution to axillary, pubic, and perianal region, and armpits (less than eccrine glands). - They are larger in size compared to the eccrine sweat glands. - They become active with the onset of puberty. - They are associated with hair follicles and open up at the hair follicles. - They produce a thick fluid, which in contact with bacteria on the skin’s surface, produces a characteristic potent "body odor".

3. Sweat glands The apocrine glands differ from the eccrine glands in various ways including: 1- their secretion product, 2- their number, 3- their being limited to certain areas of the body, 4- their having their opening in the hair sheath, 5- their strict linkage of function with the sexual phases of life. 6- their size.

4. Sweat glands Apocrine glandEccrine gland

5. Sweat glands

6. Sweat Composition of sweat ; Eccrine sweat ;is composed mainly of water and 0.2 – 1% solutes,such as ; sodium, potassium lactate, urea, ammonia, serine, ornithine, citrulline, aspartic acid, heavy metals, organic compounds, and proteolytic enzymes.. The primary secretion produced is isotonic which travels through the eccrine duct where NaCl and bicarbonate are actively reabsorbed (only about 25 percent of the sodium can be reabsorbed). Apocrine sweat; consists mainly of sialomucin ( explaining its viscosity ) and large amounts of protein and steroids. Mechanism of sweat secretion;- Eccrine sweat; - When the sweat glands are stimulated the secretory portion of the sweat gland secrets a fluid called the primary secretion which is absorbed by the gland cells from the interstitial fluid and is produced and secreted into the gland lumen by active secretory activity of the epithelial cells lining the coiled portion of the sweat gland. - As the precursor flows through the duct portion it is modified by the reabsorbtion Na + and Cl -.

7. Sweat Factors affecting the composition of sweat ; Composition of human sweat is highly variable, both between individuals and within an individual it is also influenced highly by sweat rate. Low sweat rate (rest, cool temperature); -When the sweat glands are stimulated only slightly the precursor fluid passes through the duct very slowly,thus more Na + and Cl - are absorbed which reduces the osmotic pressure of the fluid leading to water reabsorption concentrating most of the other constituents.Thus at low sweating rates the sweat produced is low in volume and is more concentrated in constituents such as urea, lactic and K + and less concentrated in Na + and Cl -. High sweat rate (work, exercise, hot temperature); When the sweat glands are strongly stimulated large amounts of primary secretion is formed which will flow too rapidly through the sweat duct reducing the chance of Na + and Cl - reabsorption, thus water reabsorption is also reduced leading eventually to the production of a large volume and less concentrated sweat.

9. Function of sweat 1- Thermoregulation which is The principle function of sweat. Sweating allows the body to rid itself of excessive heat production, through the evaporation of water which brings about cooling of the body. 2- Sweat accounts for a large proportion of the water that remains on the skin, forming part of the hydrolipid film which is the indispensable protective covering keeping the skin in good condition and, allowing it to perform its many essential functions. 3- It plays a minor excretory role ( some drugs and toxins are excreted in sweat). Note; Appocrine glands have little physiological importance. Their importance is derived more from the negative effects of their product, from which unpleasant odours arise.

10. Sweating Abnormalities Hyperhidrosis ; It is abnormally increased sweating.. In most cases, the cause of hyperhidrosis is unknown. Some known causes include: Obesity Hormonal changes associated with menopause (hot flushes) Illnesses associated with fever, such as infection or malaria An overactive thyroid gland (hyperthyroidism) Diabetes Certain medications. Treatment options for excessive sweating include; Reducing weight if obese. Medical management to reduce the hot flushes of menopause. Antiperspirant applications sprays, powders and roll-ons. Iontophoresis the activity of sweat glands is temporarily reduced by passing a low- level electric current through the skin. Botox injections to paralyse sweat glands. The effect from a single injection lasts six to nine months. Surgery to the nerves that control sweat glands may be considered in severe cases where all other treatments have been unsuccessful

11. Sweating Abnormalities Hypohidrosis, is a partial loss of sweating, while anhidrosis is a complete lack of sweating. This can occur for a number of reasons, which include: Some skin disorders Burns to skin that damage the sweat glands Underactive thyroid (hypothyroidism) Dehydration

12. Sweat tests Chloride sweat test ; It measures the concentration of chloride that is excreted in sweat, and is used to screen for cystic fibrosis(CF). In cystic fibrosis the CFTR chloride channel is defective, thus preventing chloride to be reabsorbed into sweat duct cells. Consequently, more chloride stays in the duct leading to an elevated concentrations of chloride in sweat of individuals with cystic fibrosis. Method; 1- Sweating is induced both chemically (by pilocarpine) and electrically ( through special electrodes placed at the test site ), 2-The test site is carefully cleaned and dried, then a piece of preweighed filter paper is placed over the test site and covered with parafilm to prevent evaporation. Specialized collection devices may also be used. Sweat is collected for 30 minutes. The filter paper is retrieved and weighed to determine the weight of sweat collected. Several laboratory methods are then used to determine the chloride concentrations. If the concentration of chloride is >60 mEq/L, cystic fibrosis is likely; 40-60 mEq/L is borderline; <40 mEq/L cystic fibrosis is unlikely