sweat glands anatomy and physiology

7/28/2019 Sweat Glands Anatomy and Physiology

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SESSS


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GLANDS Glands are an aggregation of cells specialized to

secrete or excrete materials .

Glands are divided into two main groups, endocrineand exocrine.

ENDOCRINE GLANDS:- ductless glands, dischargetheir secretions (hormones) directly into the blood.

EXOCRINE GLANDS:-Discharge their secretionsthrough ducts opening on an external or internalsurface of the body.
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TYPE OF GLANDS ACCORDING

TO THEIR SHAPE


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GLANDS OF SKIN Holocrine :- secretory cells are destroyed during the process of

secretion, eg sebaceous glands. Merocrine :-cells are not destroyed during secretion eg sweat

glands.Three subtypes:-

Eccrine- no breakdown of any cellular material.

Apocrine- secretion involves decapitation of apical cytoplasm. Apoeccrine- mixed.


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SWEAT GLANDS

Sweat glands are small tubular structuressituated within and under the skin(in thesubcutaneous tissue).

They discharge a fluid by tiny openings in the

surface of skin called as sweat.

Sweat is a transparent colorless acidic fluid.

It contain some fatty acids and mineralmatter .

Sweat is also called as perspiration.


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ECCRINE SWEAT GLANDS

Distribution-

Whole skin surface except lips, ext. ear canal,labia minora and clitoris.

Total number 2-5 millions.

Number varies with sites- active sweat glandsare present most densely on the sole, foreheadand palm . 620/cm2-soles

120/cm2-thighs &

64/cm2- back

Total weight 100gms


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EMBRYOLOGY

Derived as specialized down-growth of basal layer ofepidermis, at about 3rd month of IU Life on palms andsoles, 5 months elsewhere .

By 12 week anlage of the eccrine sweat gland develops fromthe epidermal ridge as a cord of epithelial cells growingdownward.

By 1415 weeks, the tips of the eccrine sweat gland rudimentshave penetrated deeply into the dermis, and have begun to

form the coils. Morphologically normal at birth but fully functioning unit

about 2 yrs of life.

No new sweat gland develop after birth.


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STRUCTURE OF ECCRINE SWEAT GLAND

Eccrine glands are atrichial simple tubular structure . Each consists of a single tube, the deep part of which is

rolled into an oval or spherical ball, named the body ofthe gland or secretory coil.

The superficial part, or duct, traverses the dermis and

cuticle and opens on the surface of the skin by a funnel-shaped aperture. The uncoiled dimension of the secretory portion of the

gland is approximately3050 m in diameter and 25 mm in length.

The size of the glands varies, large in those regions wherethe amount of perspiration is great, as in the axillae andgroin.


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Secretory coil

Secretory duct

epidermisdermis

Subcutaneous fat


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Basal coil or Secretory coil

Situated in the lower 1/3rd of dermis or border b/wdermis and subcutaneous tissue, surrounded by fatty

tissue. Microscopically the secretoy coil consist of a

pseudostratified epithelium enclosing a lumen.About half of basal coil formed by secretory portion

and another half by coiled ductal portion.


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Secretory portion

contains 3 types of cells Large clear cells (secretory

cells) Small dark cells (mucoid

cells)

Myoepithelial cells

Rest either directly on the

basement membrane or onthe myoepithelial cells. Pyramidal cells, with

abundance of membrane villi,membrane infoldings.

CLEAR CELLS


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CLEAR CELLSWhere two or more clear cells adjoin, intercellular

canaliculi are formed. Canaliculi emerge immediately above the BM or the

myoepithelial cells and open directly into the lumen ofthe gland.

Basolateral plasma membranes are highly folded &

interdigitating with apposed clear cells. Basal infoldings typical of clear cells involved in fluid &

ion transport


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CLEAR CELLS

Nucleus is round and moderately euchromatc. Cytoplasm contains autofluorescent, PAS positive,

diastase liable granules called lipofuscin granules.Also contains glycogen granules, mitochondria, rough

endoplasmic reticulum, and small Golgi complex butfew other organelles.

This is responsible for secretion of water andelectrolytes.


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DARK CELLS

Columnar cells, borders nearly all the apical (luminal)surfaces of the secretory tubules.

Function unknown

Cytoplasm contains basophilic granules which are PASpositive , diastase resistant, a well developed Golgicomplex , numerous vacuoles and vesicles and denseglycoprotein granules.

They secret sialomucin.


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MYOEPITHELIAL CELLS

Spindle-shaped, lie on the BM and adjoin the clearcells.

Contractile with abundant actin filaments Principal function is to provide structural support for

the secretory epithelium.

It propels the eccrine sweat towards the surface.

They respond only to cholinergic stimulation.


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Eccrine sweat duct

Divided into 2 parts-

Intraepidermal duct (acrosyringium)

Intradermal duct Intraepidermal duct is spiral structure, cells are

derived from dermal duct cells.

Dermal duct has an upper straight and lower coiled

part. It has 2 layers of cells but no BM.


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Eccrine units consist of three portions: (1) the acrosyringium or

intraepidermal spiralled duct; (2) the coiled and straight

intradermal duct; and (3) the secretory coiled gland


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Schematic illustration of the ultrastructures of the eccrine duct and

secretory coil and the localization of Na+, K+-ATPase. D, dark cells; C,clear cell;

M, myoepithelial cell; Mc, mitochondria; BM, basement

membrane. The thick lines indicate the localization of Na+, K+-ATPase.


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Sweat Duct

Eccrine sweat duct Consists of mainly two layers ofsmall cuboidal deeply basophilic cells.An outer ring of Basal ductal cells and

inner ring of Luminal ductal cells Proximal (coiled) duct is functionally more active

than the distal (straight) portion. Luminal cytoplasm of the ductal cells forms a

border consisting of a dense layer of tonofilaments

called cuticular border. Cuticle is homogeneous, eosinophilic, PAS positive

and diastase resistant.


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Basal ductal cells have numerous mitochondria and rich inNa-K+-ATPase activity.

Involved in ductal Na+ absorption. Cuticular border of luminal cells provides structural

resilience to the ductal lumen, which may dilate wheneverductal flow of sweat is blocked.

Lumen and duct contain -defensin, an antimicrobial

peptide.


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Histology Sweat glands typically

appear as clusters ofseveral round or ovalprofiles.

tubule consists ofcuboidal epithelium .

Duct Cells, are usuallystained more intenselythan those comprisingthe secretory portion of

the tubule. Secretory portion

appears to be singlelayered with clear anddarkly stained cells.


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STAINING OF ECCRINE GLANDS

Glands and their products can be identified by specialhistochemical, enzymatic & immunohistochemicalmethods.

Demonstration of :-

1. CK7 (cytokeratin 7)2. CK34E12

3. P63

4. CEA- carcinoembryonic antigen.

5. EMA- epithelial membrane antigen.

6. S100-acidic protein binds Ca++ & Zn++ ions, soluble in100% ammonium sulfate at neutral pH, found in cytoplasmand nucleus.


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CK7-secretory+ve& duct-veCK34E12-basal secretory & ductal +ve

P63- basal ductal & scattered secretory +ve CEA- classical luminal expression pattern

EMA- canalicular pattern S100- some secretory cells & stromal nerves


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INNERVATION OF ECCRINE

SWEAT GLANDS

Sympathetic nerve supply which is muscariniccholinergic, unlike other sympathetic fibers.

Glands influence the nerves to secrete appropriate NT,during development.

Also stimulated byand -adrenergic stimulation .

Ratio of maximal secretory rates for human sweatglands is5 : 1 : 1 for cholinergic, -adrenergic and -adrenergic stimulation, respectively.


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AFFERENT PATHWAY FOR THERMAL

STIMULI FROM SKIN

Thermal senses discriminated by 3 types of receptors-cold,warmth and pain receptors, situated in dermis.

Warmth receptors are mainly free nerve endings, calledRuffinis corpuscles.

Warmth sensations transmitted by non-myelinated C-fibers.

Cold receptors known as Krauses end bulb. Cold sensations transmitted by myelinated A nervefibers.


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Sensory nerve fibers arising fromreceptors reach to dorsal root ganglion

cells through related sensory nerves. They terminate in laminae I, II and III of

dorsal horn.

After processing, signals enter in long

ascending fibers that cross to oppositeanterolateral sensory tract (Lateral STT)and runs parallel to pain fibers.

They terminates in both (1)reticularareas of brain stem and (2)ventral-lateral

and ventral-posterior complex ofthalamus .

Few signals also relayed to somato-sensory areas of cortex.


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EFFERENT PATHWAY

Efferent sudomotor pathway consists of the cerebralcortex to Hypothalamus >brainstem and medulla->intermediolateral cell columns of spinal cord-

>preganglionic sympathetic ganglia------------->postganglionic nonmyelinated C fibers-joins themajor peripheral nerves and end around the sweatglands .

Supply to the skin of upper limbs is commonly comesfrom T2 to T8, face & eyelids from T1 to T4,trunk fromT4 toT12 and lower limb T10 to L2 .


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Cerebral cortex-----Hypothalamus----medulla (mostly crossed)----spinal cord


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FUNCTIONS OF SWEAT GLANDS

Thermoregulation- Heat canbe lost through the skin surfaceby radiation, convection,conduction and evaporation.

When skin temp. is greater than

the temp. of surroundings heatcan be lost by radiation,convection ,conduction andevaporation.

But when temp. of surroundingsbecomes greater than skin,

instead of losing heat body gainsheat by both radiation andconduction. Under theseconditions the only means bywhich the body can loose theheat is by evaporation.


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1 gm of water evaporation leads to loss of 0.58 kcal.Heat.

Body loses about 6oo ml-700 ml water per dayinsensibly from the skin and lungs, this causescontinuous heat loss at rate of 16-19 Kcal per hour.

Sweat cools the surface of the skin and reduces bodytemperature.

This cooling is the primary function of sensibleperspiration.


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An increase in local skintemperature of 10 C(50 F) triples the localsweating rate until the

sweat rate plateaus. The effect of core

temperature rise is aboutnine times moreefficient than skin

temperature instimulating sweating.


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Sweat moisten the thick stratum corneum of palms andsoles which improves the pliability, grip and fine tactileskills.

Protection- Merocrine sweat gland secretion providesprotection from environmental hazards by :-1. Diluting harmful chemicals.

2. Discouraging growth of microorganisms by means ofsome immunoglobulins and antimicrobial peptides

present in sweat.


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Excretion- provide a significant excretory route forwater and electrolytes.

Sweat may contain a trace amount of metabolic wastes.

Sweat can be potentially proinflammatory and maymodify various dermatoses, suggested by presence of ILs,

proteolytic enzymes and antibodies in sweat. Lactate and urea in sweat may regulate desquamation.

Active excretion or secretion of drugs such assulfaguanidine, sulfadiazine, amphetamines, iodides,

phenytoin, phenobarbital, carbamazepine, griseofulvin,ketoconazole, f luconazole, ciprofloxacin, diamorphine,cocaine and nicotine may contribute to their efficacy.


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CONTROL OF ECCRINE SWEATING

Alteration of activity occurs in response to

Thermal stimulation

Osmotic changes

Mental and emotional activity

Gustatory factors


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THERMAL SWEATING

Play an important role in keeping the bodytemperature constant.

Occur especially on upper trunk and face with somegeneralized increase.

Heat regulating centre situated in the hypothalamus preoptic area and anterior hypothalamic.Activated by

Change in temperature & osmotic pressure of the bloodperfusing it .

By afferent stimuli from the skin . Deep thermal receptors situated in spinal cord, in or around

visceras and great vessels in abdomen and thorax .


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Signals generated by the temp. receptors of

hypothalamus are extremely powerful.When core temp. of body rises above a certain level

(thermal set point), eccrine sweating is initiated.

Thermal set point is a critical body core temp. of about

37 c (98.4 F), body attempt to bring body temp. backto this set point when body core temp. increases aboveor decreases below this set point.

Hypothalamic thermal set point also influenced by

alterations of blood osmotic pressure.


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Receptors in other parts of body play additional rolein temp. regulation.

Receptors in skin and visceras are more sensitive to

cold rather than warmth. Signals from hypothalamic and other receptors

transmitted to posterior hypothalamic area.

Here, the signals received from all area are combinedand integrated, to control the heat-producing and heatconserving reactions of body.


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MENTAL ( EMOTIONAL ) SWEATING

Consequence of higher cerebral centres (frontalregion) acting on the thermoregulatory centres in theanterior hypothalamus.

Emotions such as fear and anxiety prompt eccrinegland sweating, predominantly of the palms, soles andaxillae.

Emotional sweating on the palms and soles ceasesduring sleep, whereas thermal sweating occurs even

during sleep if the body temperature rises.


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GUSTATORY SWEATING

Physiological gustatory sweating is symmetrical, and itis confined to the forehead & nose and exceptionallythe neck.

Hot spicy foods are the most likely cause. Gustatory sweating is accompanied by flushing of the

face and the upper part of the body, salivation,lacrimation and nasal secretion.

Sensory receptors mediating gustatory sweating areprobably pain fibres.

Substances which stimulate the taste fibres withoutcausing pain do not give rise to gustatory sweating.


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MECHANISM OF SWEAT SECRETION

Eccrine sweat forms in twosteps.

First, the secretory coil secretesisotonic fluid in lumen, rich inNa+ and Cl+.

In the ductal portion, Na+reabsorbed and H+ secreted toproduce hypotonic and acidicfluid.


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Sweat forms in sequential steps:-

(1) Stimulation of the eccrine sweat gland by ACh viaincreased intracellular Ca2+

(2) Ca2+-stimulated loss of cellular K+, Cl-, and H2O,which leads to eccrine gland cell shrinkage;

(3) Volume-activated transcellular plus paracellularfluxes of Na-, CI-, and H2O, which results in net flux

of largely isotonic NaCl solution into the glandularlumen.


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cytosolic Ca2+

Cholinergic stimulation

-Release of ACh

Opening of Ca-sensitive Cl and K channels

Leads to luminal and basolateral secretionof Cl and K, water moves osmotically

Cell shrinkage

Activation of Na/K/2Cl

cotransporter and Na-KATPase

1.Recycling of K+ along basolateral membrane2.Secretion of Cl- into lumen3.Paracellular flux of Na+


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Final product of glandular secretion is therefore thenet movement of Na+, Cl- and H2O into the glandularlumen to form the isotonic NaCl precursor of sweat.

Adrenergic-induced sweating appears to be mediatedby increased intracellular cyclic adenosinemonophosphate.


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MECHANISM OF DUCTAL REABSORPTION

Ductal portion of sweat gland not only reabsorbelectrolytes but also acidify the sweat, which results ina final sweat product that is hypotonic and acidic.

Na+ enters the duct cells through the apical membrane

via amiloride-sensitive epithelial Na+ channels (ENaC)and is transported across the basolateral membrane byNa-K ATPase pumps.

Cl- transport appears to be both transcellular and

paracellular with the cystic fibrosis transmembraneregulator (CFTR) Cl- channels playing an importantrole in transcellular fluxes.


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Na+ enters the apical (luminal) membrane through

epithelial sodium channel (ENaC) and is transported acrossthe basolateral membrane by Na+ K+ ATPase.Cl- transported via CFTR and paracellularly.Sweat acidification by carbonic anhydrase mediated

reaction.


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REGULATION OF SWEAT GLANDS

Sweat glands respond to cholinergic agents, and -adrenergic stimulants, and other periglandularneurotransmitters as VIP and ATP.

Sweat rate in a given area of the skin is determined by

the number of active glands and the average sweat rateper gland.

Aldosterone increases Na+ reabsorption.

Vasopressin may increase water reabsorption in response

to osmotic changes. Other factors as local temp , hormones, circulatory

changes, spinal reflexes and androgens may modifyquantity and quality of sweat.


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EFFECT OF CERTAIN PHYSIOLOGICAL

CONDITIONS ON SWEATING In old age-

1. Spontaneous sweating on the fingertips declines, as a resultof a combination of a reduction in the number of glandsand of the output per gland.

2. Glands tend to display both disarray and shrinkage ofsecretory cells and lumen .

3. Sweating response to dry heat is diminished ,making proneto heat stress in old age.

In pregnancy-1. Eccrine activity may be noticeably increased .

2. This may be responsible for the recognized increasedfrequency of miliaria.


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COMPOSITION OF SWEATVaries from person to person, time to

time & site to site. Constituents

NaCl - 10 to 20 mmol/L at low rates, upto100 mmol/L at high rates

K -5 to 10 mmol/L HCO3 - < 1 mmol/L Urea Lactate- 4 to 40 mmol/L Glucose- 0 to 3 mg/dlAmmonia and Amino acids -0.5 to 8

mmol/l Pr0teins

Ph 4 to 6.8

Specific gravity 1.005


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ALTERATION IN SWEAT COMPOSITION

In hyperaldosteronism, concentration of Na and Cldecreases while K increases.

In Additions Ds, concentration of Na may increase to 70-80 mmol/L .

Increase in sweat electrolytes occurs in Cystic Fibrosis

High sweat glucose found in uncontrolled DM.

Other substances like Antigen and antibodies may befound in sweat.


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IgE level increased in atopic dermatitis.In uremia, the evaporation of sweat with high ureaconcentrations results in the deposition of urea onthe skin, referred to as uremic frost.Abnormal amino acids or their breakdownproducts excreted into sweat results in abnormalbody odor .


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Musty or sweaty or locker room towel odor inPKU.

Malty, caramel-like or maple syrup-like odor inmaple syrup urine disease .

Decayed malt or hops like odor in oasthousesyndrome.

Strong, fishy, fruity or rancid butter-like odor inhypermethioninemia.

Cheesy or sweaty feet odor in isovaleric acidemia.


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APOCRINE SWEAT GLANDS

Develops from upper bulge of hair follicle at 4th monthof intrauterine life.

Initially, solid epithelial cord projects at right angle tolong axis of hair follicle, later, it turns downward.

Survive to become functional only in axillae, genitalarea & areolae just before puberty.


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STRUCTUREApocrine gland also has 3 segments- basal coil,

intraepidermal and dermal duct.

Basal coil situated in subcutaneous fat.

Basal coil forms only by secretory portion.

Have single layer of tall columnar cells, resting on BM.

Duct opens in the pilosebaceous follicle above theentrance of the sebaceous duct or sometimes directlyon surface.

Intraepidermal portion of duct is straight.

Duct consists of double layer of cuboidal cells .


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HISTOLOGY

Diameter of thetubular lumen ofapocrine sweat glandsis much greater thanthat of eccrine sweat

glands, and theepithelium is typicallytaller.

Cells contain largergranules than eccrine

dark cells. Luminal surface has

dome-shaped apicalcap.
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SECRETION

Milky or viscid, colorless & odorless when first secreted.

Subsequent bacterial action is responsible for odorproduction which produces ammonia and short chain

fatty acids( e-3-methy-2-hexenoic acid). Decomposition on the skin surface modified the

secreted substances.

Decomposition results in the typical penetrating rancid(by corynebact. sp.) or sweaty (by micrococcus sp.)body odor.


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Secretion consist of therelease of portion ofcytoplasm.

An apical cap and

dividing tubule areformed initially.

Apical cap is thendetached anddischarged into lumen,it is called decapitation.


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Mode of secretion- pulsatile due to contraction ofmyoepithelial cells.

Secretion is controlled by adrenergic nerve.

Also stimulated by Circulating epinephrine. Modified apocrine glands

In the external ear canal-ceruminous glands.

In the eyelid molls glands.

In the breast mammary glands.


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FUNCTION

No thermoregulatory function.

Because the apocrine glands of humans do not begin

to function until puberty and are odor producing, have5-reductase activity.

May have some sexual function by olfactorycommunication, which may now be vestigial.


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APOECCRINE SWEAT GLANDS

Have features of both apocrine and eccrine.

Develops during puberty from eccrine glands.

Consistently present in the adult axillae, forms


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Larger duct opens nonfollicular skin surface likeeccrine.

Secretory coil- irregularly dilated.

Reponds to cholinergic & also to epinephrine.

Persistent secretion of clear fluid in the presence ofAch.

Sweat rate is variable but higher than eccrine gland

In axillary hyperhidrosis, apoeccrine glands may be50% of axillary glands.


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CHARACTERISTICS OF SWEAT GLANDSECCRINE APOCRINE APOECCRINE

Localization Entire body except lip, labia

minora , and clitoris, externalauditory canal .

Axillae , anogenital area , areolae

(ceruminous glands , moll,sglands of eyelids and mammaryglands are modified apocrineglands).

Axillae.

Morphology Long, thin duct opens to skinsurface secretory coil withnarrow lumen.

Short thick duct opens intoupper part of follicular canalSecretory coil with wide lumen.

Duct comparable to eccrinegland duct secretory coilwith dilated and undilated

tubular segments.

Cell type ofSecretory coil

Large secretory clear cells, darkcells, myoepithelial c ells.

Epithelial and myoepithelial cellsCells contain larger granules theneccrine dark cells.

Eccrine and apocrinemorphologic features.

Maininnervation/transmitter

Sympathetic fibers /acetylcholine.

Sympathetic fibers / mainly byadrenergic (epinephrine andnorepinephrine).

Sympathetic fibers /acetylcholine.

Development Present at birthNo relationship topilosebaceous follicle.

Present at birth but poorlydeveloped, functional at puberty.related to pilosebaceous follicle.

Probably not presentbefore adolescence. Norelationship topilosebaceous follicle.

Function Thermoregulation. Unclear, some role in olfactory

communication.

Thermoregulation,

Role in axillaryhyperhydrosis.


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METHODS OF STUDYING

SWEAT GLAND FUNCTIONTests for distal sympathetic axonal integrity and to

determine receptor function of sweat gland

1. Pharmacological sweat test- Sweat induced byintradermal injection of 0.01% pilocarpine ormethacholine.

2. Quantitative sweat axon reflex test -A small

battery-operated current stimulates the sweat glandsdirectly.

3. Quantitative sudomotor axon reflex test(QSART).


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QUANTITATIVE SUDOM OTOR AXON REFL EX TEST

(QSART)

Test has three parts and measures resting skintemperature, resting sweat output, and stimulated sweatoutput.

Measurements are typically taken on arms, legs or both. A small plastic cup is placed on the skin and thetemperature and amounts of sweat under the skin aremeasured.

To stimulate sweat pilocarpine 0.01% or Ach 10% is

delivered electrically through the skin to a sweat gland. A computer is used to analyze the data to determine howwell the nerves and sweat glands are functioning.


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DETERMINATION OF MAXIMAL SWEAT RATE

Water- vapour analyzer.

Filter paper method.

Collection of sweat droplet under mineral oil.Anaerobic bag method.

Micro-cannulation of the sweat duct or coil.

weighing and analyzing of sweat composition.


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TESTS FOR THERMAL SWEATING

Thermoregulatory sweat test- after change into adisposable bathing suit, apply iodine-starch powder to skin.

Patient then go into a warm and humid large glass room(much like a sauna) for 20 to 30 minutes.

Orange powder turns purple where sweating occurs, tellingwhich parts of the autonomic nervous system are working,and which are not.

Core body temp. must rise at least 1c.


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CHLORIDE SWEAT TEST

Helps diagnose cystic fibrosis (CF), an inheriteddisorder characterized by mutation of gene for CFTR.

Sweat test measures amount of chloride in sweat Child with cystic fibrosis can have 2 to 5 times the

normal amount of chloride in their sweat In a sweat test, the skin is stimulated to produce

enough sweat to be absorbed into a special collectorand then analyzed.

If child has a sweat chloride level of more than 60

mmol/L, its considered abnormal


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VISUALIZATION OF INDIVIDUAL SWEAT DROPLETS

By Iodine-starch test or by sodium alizarinsulfonate (alizarin Red S).

Iodine-starch test Iodinated starch powder is prepared by adding 0.5

to 1g of iodine crystals to 500 g of soluble starch in atightly capped bottle.

Applied to the skin and undergo a dramatic colorchange when moistened by the water (sweat) fromactivated sweat glands.

Iodine-starch reaction also used for sweat imprintpapers.


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A patient with Segmental anhidrosis (Yellow) withcompensatory left-sided hemihyperhidrosis (purple) dueto a Upper thoracic spinal cord injury (sodium alizarinsulfate indicator powder)


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sweat glands anatomy and physiology

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