Sweat
- It is a clear, salty liquid secreted from the skin by the sweat glands. - sweat glands are small tubular glands situated within and under the skin. - The average person has 2.6 million sweat glands in their skin! Sweat glands are distributed over the entire body -- except for the lips, nipples and external genital organs.
Pore Duct
Types of sweat glands Eccrine - the most numerous type that are found all over the body, particularly on the palms of the hands, soles of the feet forehead and armpits Apocrine - mostly confined to the armpits (axillae) and the anal-genital area. They typically end in hair follicles rather than pores.
Are smaller diameter (50 – 100 μm) Are active from birth Eccrine glands: Are smaller diameter (50 – 100 μm) Are active from birth (Apocrine glands become active only at puberty) Produce a sweat that is free of proteins and fatty acids
The amount of sweat produced depends upon our states of emotion and physical activity. Nerve stimulation Exercise
Function of sweat 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.
Characteristics Sweat has no odor, but reaction with bacteria on the skin can produce an unpleasant smell Maximum volumes of sweat is around 1 liter /hour in a hot climate
Characteristics Composition of the primary secretion is very similar to that of plasma except that it does not contain plasma protein: S.G: 1.002 – 1.005 PH: 4.5 – 7.5 Na+ : 30-70 mg ( less). K+ : 0-5mg (same). Cl- : 30-70 mg (less) . Urea: 4-6 times higher than in plasma. Lactic acid : higher than in plasma specially in athletes. [Glucose] in a very small amount
Factors affecting the composition of sweat Low sweat rate (rest, cool temperature); The primary fluid passes through the duct very slowly. Na+ and Cl- are reabsorbed which reduces the osmotic pressure of the fluid leading to water reabsorption and 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 amount of primary secretion are 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.
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. 3) hormones. 4) emotional stress
Sweating Abnormalities Hyperhidrosis: It is abnormally increased sweating . Some known causes include: Obesity Hyperthyroidism Diabetes Certain medications. .
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
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 transmembrane conductance regulator (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.