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ANATOMY AND PHYSIOLOGY OF

SWEAT GLAND

Dr UJJWALA VERMA1st yr Junior ResidentDept. of Skin and V.D.

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Sweating is perhaps one the most visible physiological events we experience in our daily lives.

It is only humans & apes who sweat.

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TYPES OF SWEAT GLANDS Three structurally & functionally distinguishable

types of sweat glands exist in human skin: the eccrine , apocrine , & apoeccrine glands.

Eccrine glands are merocrine ,in that no breakdown of cellular materials occurs during secretion &the secretion is discharged by the fusion of the membranous walls of the secretory vesicles with the plasma membrane so that only the contents of the vesicles are released.

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In apocrine glands, during secretion a small amount of cytoplasm is “pinched off” along with the secretory vesicles.

Eccrine glands are called atrichial since they develop from the superficial epidermis & remain independent of the hair follicle.

Apoccrine gland are called epitrichial ,because they develop from the external root sheath of the hair follicle & usually remain attached to it.

Eccrine gland produce eccrine sweat which are primarily involved in thermoregulation.

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Apoeccrine gland or mixed glands have some of the morphological & functional features of both eccrine and apocrine glands and are found in adult human axilla &contribute to overall axillary sweating in the adult.

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ECCRINE SWEAT GLANDS Density & distribution: ~Present almost everywhere on the

human skin including glans penis & the foreskin.

~ Absent on the –vermillion border of the lips

-nail bed - ext. ear canal -clitoris,and -labia minora. ~

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~their avg. density varies from 64 glands/cm2 on the back

108 /cm2 ----- forearm 181/cm2 ----- forehead 600-700/cm2 ----- palms and soles~ There are estimated 1.6-4 million sweat gland

on the body surface.~each sweat gland weigh about 30-40 mcgm~aggregate wt in human skin = 100 gm~Sweat gland density also varies with body

size ,& in general, males perspire more profusely than females & prepubertal children.

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Development:~Embryologically , eccrine sweat glands

develop as specialised downgrowths of the epidermis at about the 4th month of intrauterine life of the volar surfaces of the hands & feet & in the 5th gestational month in axillae,and a little later over the other parts of body.

~ by about eighth fetal month they resemble adult sweat glands,

~but are not functional until 2 yr of age.~no new sweat glands are formed after birth.

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Structure:~simple tubular epithelial structures.~Eccrine sweat glands possess-1. Basal coiled portion called fundus or

acinus,situated in the lower third of the dermis or at dermo hypodermal interface;

2. A straight intradermal ductal portion3. A spiral intraepidermal duct

(acrosyringium) that opens directly on to the surface.

The whole length of secretory gland is surrounded by a thin fibrous sheath and an investing basal lamina.

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Secretory coils:--60-80micro m in diameter-2-5 mm in length .-single layered str , made up of three distinct

cell types :large clear cells (secretory) : small dark cell (mucoid) :myoepithelial cells

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Clear cells are the cells pricipally responsible for sweat secretion.

Pyramidal shape Bases resting partly on the basal lamina or

on the myoepithelial cells The cells infrequently reaches the lumen . Instead they face one or more small

intercellular canaliculi that are confluent with the lumen.

The cytoplasm are also rich in glycogen granules & mitochondria.

The basal infoldings of the clear cells show marked Na,K-ATPase activity & the basolateral membrane is believed to be the sodium pump site & the site for active transport of ions during sweat secretion.

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Dark cells occur either as cuboidal cells that rest on the clear cells or as inverted pyramidal cells with their wedge shaped cytoplasmic process extending towards the BM between clear cells

Dark cells occupy almost all the luminal surface of the secretory tubules .

PAS positive glycoprotiens ,the constituents of the human sweat ,are probably secreted by the dark cells.

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Myoepithelial cells are discontinuous row of spindle shaped cells.

These cells are filled with masses of myofilaments

Arranged more or less parallel to the course of the secretory tubules .

Not only provide mechanical support to the secretory coil wall against an Increase in in luminal hydrostatic pressure during sweat secretion .

Also help propel the sweat towards the surface.

Myoepithelial cells respond to cholinergic but not to adrenergic stimuli.

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Peripheral to myoepithelial cells lies a hyaline basement membrane zone containing collagen fibres that separate the glandular epithelium from the richly vascular connective tissue of the periadenexal dermis.

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Intradermal sweat duct: The dermal ductal portion of the eccrine sweat

gland is composed of two layer of cell : - an inner ring of luminal cells , and -an outer ring of basal cells. The cells are small,cuboidal , and are deeply

basophilic. The basal ductal cells are rich in mitochondria &

the entire circumference of the cell membrane shows a strong Na-K-Atpase activity suggesting that the cells play a critical role in ductal sodium reabsorption.

A dense layer of the tonofilament near the luminal membrane (pseudocuticle) gives a certain rigidity to the periluminal region & assures patency.

The proximal (coiled) intradermal duct appears to be functionally more active than the distal (straight)portion.

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Acrosyringium: the intaepidermal sweat duct runs spirally

from the base of the rete ridge to the surface. Consist of the single layer of inner or luminal

cells & two or three rows of outer or basal cells.

Acrosyringeal cells contain desmosomes and occasionally melanocytes & cornify independently of the epidermis.

Prior to keratinisation , acrosyrigeal lumen is lined by an eosinophilic cuticle.

Sweat duct is not an inert conducting channel. It has enzyme systems, a liberal blood supply ,and plays a critical role in the formation of final sweat

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FUNCTION: The principal function of eccrine glands is to

produce sweat during periods of heat stress. Each sweat gland during peak secretory

activity may produce as much as 20nL per min.

One lit. of evaporated sweat removes 585 kilocalories of heat from the body.

During heat stress, a max. sweat rate of 3-4l/hr can attached ,and a rate of 1-1.5 L/hr can be maintained.

The other major function is to moisten the skin of the palms & soles during periods of activity, thus improving their grip.

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Eccrine glands are also lesser organs of excretion and several substances are excreted in sweat

The presence of interleukins & proteolytics enzymes raises the possibilities that eccrine sweat can be potentially pro-inflammatory & is capable of modifying various dermatoses.

Eccrine sweat may also have mitogenic effects on ds such as psoriasis.

Lactate in sweat may regulate desquamation of stratum corneum.

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THE PHYSIOLOGY OF SWEATING

Types of sweating sweat gland activity is controlled by three

principle physiological stimuli: >thermal >emotional >gustatory. Thermoregulatory sweating –believed to

be controlled by thermo-sensitive neurons in the hypothalamus.

It mostly affects the upper trunk & face but may also involve the whole body.

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Emotional stimuli-produces sweating on palms & soles.

sensory stimuli arising from frontal or premotor areas (Brodman area 6)are involved.

Gustatory stimuli-induces sweating on the lips forehead & nose.

controlled by medullary nuclei. Other factors:that may modify the quality

&quantity of sweat in presence of an intact nerve nerve supply include-

-local temperature changes -periglandular vascular activity, -axon & spinal reflexes, -plasma electrolyte concentration -harmones (Androgens)

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The Sympathetic Sudomotor Pathway.

Eccrine sweating is the result of sympathetic activity . The overall chain of sympathetic command

involves -central autonomic network , -preganlionic effector pathways, -post ganglionic sympathetic fibres, -periglandular neurotransmitters,and -glandular receptors. the most imp component of this network is the

nucleus tractus solitarius located in the dorsomedial region of medulla oblongata.

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Mechanism of sweat secretionStimulation of sympathetic neuronal outflow

result in release of periglandular neurutransmitters ,chiefly acetylcholine (Ach).Ach interacts with a special receptor in the secretory cell membrane , triggering a sequence of event leading to sweat secretion.

The formation of sweat within the eccrine sweat gland is a two step process and consist of

1. Elaboration of nearly isotonic , primary or precursor sweat from the interstitial fluid by the secretory coil through active transportation of electrolytes;

2. Modification of the primary sweat through partial reabsorption of NaCl by the sweat duct to produce the ultimate secretory product ,the hypotonic eccrine sweat.

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Effect of aging on eccrine sweat glandular structure & function

• There is either a reduction in absolute number of eccrine sweat glands or

in their functional capacity or both• Microscopically, there is disarray

&shrinkage of secretory cells & the lumen

• Lipofuscin granules within the secretory cells increases both in no. & size with the age

• The sweating response to dry heat is decrease in elderly individuals ,making them prone to heat stress.

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Composition of sweat: Similar in composition to plasma

containing the same electrolytes, although in more dilute conc.

The sweat rate also influences the composition of the final secretory product because ductal modification of primary sweat is often a function of the flow rate.

Eccrine sweat is an odorless, colorless, hypotonic solution with sp. gr. Of 1.005

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Constituents:- Na K Cl urea lactate glucose ammonia amino acid protiens(glycoprotiens& mucopolysaccharides)

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Proteolytic enzymes. -Glandular kallikrein -Kininase -C1 esterase -urokinase - cysteine protienase -& their endogenous

inhibitors Epidermal growth factor

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SWEAT FUNCTION TESTS To test sympathetic axonal integrity local pharmacological sweat test - intradermal inj, or - iontophoretic application of 0.01%

pilocarpine or methacholine QSART(quantitative Sudomotor Axon

Reflux Testing) Galvanic skin resistance test Visualization of individual sweat droplet -Iodine starch method

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Determination of maximal sweat rate: -water vapour analyzer -the filter paper method. -collection of sweat droplet under

mineral oil -anaerobic bag method. Skin biopsy for absence or atrophy of sweat gland

(in ds. As anhidrotic ectodermal dysplasia,scleroderma)

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APOCRINE GLAND

Development Apocrine glands together with hair and

sebaceous glands ,develop from the primary epithelial germs or hair germs during the 4th to 5th month of intrauterine life.

Apocrine gland development is dependent on sex hormones and not their functional activity.

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Distribution: -axillae -areolae (montgomery’s tubercles) -periumbilical, -perineal -cicumoral areas

-prepuce,-mons pubis-labia minora

Modified apocrine glands-ceruminous glands in ext ear canal-the ciliary or Moll’s glands on the

eyelids -mammary glands

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Occasionally ,can be found on the-facescalpabdomen(heterotopic)

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Structure: Larger than eccrine glands. Contains - secretory

- ductal portion.

The coiled secretory portion is situated in the lower dermis or in subcutaneous fat,& a straight excretory duct empties into the infundibulum of the hair follicle slightly above the entrance of the sebaceous duct.

Apocrine ducts ocassionally opens directly on the surface independently of the hair follicles.

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Secretory coil: Simple convulated tubular str. As wide as 2 mm Lumen is lined by single layer of secretory

cells which are either cuboidal or columnar depending upon stage of secretion.

Secretory cells possess an eosinophilic cytoplasm&, except in the apical portion , contains large PAS +ve & Diastase-resistance granules distributed around the nucleus.

Surrounding the secretory cell is a layer of contractile myoepithelial cells.

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Ductal portion:• Apocrine sweat duct is made up of a double

layer of basophilic cuboidal cells & an inner myoepithelial cells.

• Distally,the epithelial of apocrine duct merge into the epithelium of the infundibular portion of the hair follicle.

• The apocrine duct is straight & not spiral.

Apocrine secretion: Human apocrine sweat is a protien

rich ,milky, or viscid ,colourless secretion when it is first formed.

Bacterial decomposition responsible for the characteristic mephitic odor.

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Mechanism of apocrine sweat secretion

Secretion is of apocrine type Merocrine & holocrine type secretion also

occur In classical apocrine type of secretion an

apical cap & a dividing membrane are formed initially. the apical cap is then detached & discharged into the lumen of the gland by a process called “apocapation”.

Although ,apocrine sweat formation is a continuous process ,the secretion is discharged on to the surface only intermitentaly.

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Control of apocrine glandular activity

Apocrine gland respond to emotional stimuli that promote sympathetic discharge.

Denervation or atropine do not abolish apocrine glandular response to emotional stimuli ,suggesting that apocrine glandsare stimulated humorally by circulating catecholamines.

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Humoral influences and apocrine glandular activity

• Gonadectomy of mature individual does not affect apocrine glandular function.

• There is shrinkage of apocrine glands after menopause.

• Apocrine gland possess a marked 5 –alpha reductase activity.

Effects of aging:o With aging ,apocrine glands tends to

accumulate lipofuscin &undergo attenuation .

o That is why there is often a reduced body odor in the aged.

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Function of apocrine glands: Human apocrine glands , especially the

glands in the axillae,are highly specialised functional units and are concerned with human behavioural & sexual interaction.

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APOECCRINE GLANDS

Also called mixed gland. Found in adult human axillae. Represent <10% of all glands in human axilla. Found in all level of the dermis and their size

may be quite variable . Larger than eccrine glands and smaller than

apoccrine glands. Axillary skin of black contains more glands. The apocrine secretory portion is often

irregularly dilated. The apocrine glands has a long duct that

opens directly on to the skin surface.

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Apocrine glands are not present at birth. They develop during puberty from the

eccrine glands or eccrine like precursor glands.

Yeilds copious sweat in response to both methacholine(cholinergic) and epinephrine(adrenergic).

Apoeccrine glands basically eccrine glands that underwent “apoeccrinization’due to local factors.

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