anatomy and physiology of sweat and sebaceous gland

1. GLANDS OF SKIN
BY-
DR. SHWETA KHUSHALANI
JUNIOR RESIDENT
DEPT OF SKIN & V.D.

2. INTRODUCTION
• Sweat glands
– 2 types
• Eccrine glands cholinergic supply
• Apocrine glands adrenergic supply
• Apoeccrine glands
• Sebaceous gland

3. ECCRINE GLAND
• Thermoregulatory mechanism
• Merocrine gland
• Secretion by exocytosis
• Atrichial
• Distributed entirely over the body, including glans,
foreskin of penis
• Absent –
– vermilion border of lip
– Nail bed
– External ear canal
– Clitoris
– Labia minora

4. • Secretion2-20nL/min/gland
• Density
– Total : 2-5 million
– Back : 64 glands/sq.cm
– Forearm : 108 glands/sq.cm
– Forehead : 181 glands/ sq.cm
– Palms & soles : 600-700 glands /sq.cm
• Weight : 30 – 40 mcg each
• Males > females, prepubertal children
• DEVELOPMENT
4th month IU : Specialised downgrowth of the epidermis on the
volar surface of hands and feet
5th month IU : axillae f/b other parts of body
8th month IU : resemble adult sweat gland
Not functional till 2 years of age

5. STRUCTURE
•Simple tubular epithelial structure
•Basal coiled portion = fundus/acinus
•Situated at dermal-hypodermal
interface
•Eccrine sweat apparatus
•½ to 2/3rd secretory
•Rest ductal
•Secretory part is surrounded by thin
fibrous sheath & basal lamina
•Spiral intraepdermal ductal portion k/a
acrosyringium
•opens on the surface

6. C = clear cell
D = dark cell
IC = intercellular canaliculus
M = myoepithelial cell
BM = basement membrane
• Clear cell ( secretory)
– sweat secretion
– Pyramidal shape
– Cytoplasm : lipofuscin granules,
glycogen granules & mitochondria
– Nucleus : rounded, euchromatic
– Basal infoldings- Na/K ATPase
activity, basolateral membrane sodium
pump site, site for active transport of
ions during sweat secretion.
• Dark cell ( mucoid)
– Inverted pyramidal shape
– Secrete PAS positive glycoprotien
• Myoepithelial cell
– Discontinuous row of spindle shaped
cell
– Support to secretory coil wall
– Help propel sweat to surface
• Basement membrane
– Collagen fibres
– Above vascular connective tissue of
periadnexal dermis

7. ducts
Ductal cells
• Contains desmosomes, occasional melanocytes and cornify
independent of epidermis
Function
Has active enzymme system, liberal blood supply plays
critical role in formation of final sweat

8. Intradermal duct
 cells – deeply basophillic, small
cuboidal.
 single layer outer basal cell
 single layer inner luminal cell
• Basal cell
– rich in mitochondria
– Have Na/K ATPase activity
• Tonofilament near luminal membrane
(pseudocuticle) gives rigidity to
periluminal region, assures luminal
potency
• Activity : Coiled > straight
Acrosyringium
 Runs spirally from base of rete ridges to
surface
 single layer luminal cell
 2-3 cell layer basal cell
 keratohyaline granules in mid epidermis

9. FUNCTIONS
 Thermoregulation
 Improve grip of palms & soles by moistening, during periods
of activity
 Excretion
 Pivotal role in wound healing
 Lactate in sweat gland regulate desquamation of stratm
corneum
 Proinflammatory actions

10. PHYSIOLOGY
GUSTATORY
Controlled by
medullary
nuclei
THERMAL
Thermosensitive
neurons in the
hypothalamus
EMOTIONAL
Palms & soles
? Frontal/
premotor area

11. MECHANISM OF SWEAT
SECRETION
• Stimulation of sympathetic neuronal outflow release Ach, present in
peri-glandular area
• Ach binds to special receptors at secretory part of the gland,
triggering sequence of events
– Elaboration of a nearly isotonic, primary, sweat gland from the interstitial
fluid by the secretory coil through active transportion of electrolytes
– Modification of primary sweat through partial reasbsorption of NaCl by
the sweat duct to produce the ultimate secreory product, the hypotonic
eccrine sweat.
Fectors affecting reabsorption of sweat
aldosterone
size of the glands and ducts
rate of sweating

12. COMPOSITION OF SWEAT
• Eccrine sweat is
– colorless,
– odorless,
– hypotonic solution,
– Specific gravity of 1.005
– Constituents : Na, K, Cl, HCo3, lactate, urea, ammonia, free amino acids,
proteins, glucose, others
• Alteration in the composition of sweat
– Adrenocortical disorders
– Cystic fibrosis
– Increased urea excretion(urhidrosis)
– Increased calcium excretion
– Abnormal aminoacid excretion
• Musty/sweat – phenylketoneuria
• Malty/ maple-syrup like – maple syrup urine disease
• Decayed malt – oasthouse syndrome
• Fishy/fruity/ rancid butter like – hypermethioninemia
• Cheesy/sweaty feet - isovaleric acidemia

13. APOCRINE GLAND
• Epitrichial
• Seen in
– axillae,
– areola,
– periumbilical,
– perineal,
– circumoral area,
– prepuce,
– mons pubis,
– labia minora
• Cerminous glands
• Ciliary or Moll’s Glands Modified Apocrine Sweat Glands
• Mammary glands
Development
4-5th month – primary epithelial germs or
hair germs
Postnatally - dormant untill they develop
their secretory portion & become functional
at around puberty under the influence of
hormonal activity

14. STRUCTURE

15. • Secretory portion
– Simple convoluted tubular structure
– 2mm wide
– Single layer cuboidal/columnar
– Apical portion : PAS positive & diastase
resistant granules, around the nucleus
• Myoepithelial cells
– Surrounding secretory portion
– Surrounded by PAS + hyaline basement
membrane
• Apocrine secretory cells
– Granular/agranular endoplasmic
reticulum
– Golgi complex
– Dense secretory vacuoles

16. • Ductal portion
– Short & straight
– Double layer of basophillic cuboidal cells
– a inner periluminal eisionophilic cuticle
– NO MYOEPITHELIAL LAYER
– Distally epithelium of apocrine gland
merges with epithelium of hair follicle
– Duct secretes into follicular infundibulum
or directly on the surface
• Secretion
– Rich in protein, milky, viscid, colorless
– Bacterial decomposition responsible for
characteristic mephitic odor

17. MECHANISM OF SWEAT
SECRETION
Apical cap with a dividing membrane
formed
Cap is detached & dischraged into the
lumen k/a APOCONATION
Although apocrine sweat secretion is a
continuous process, secretion is
discharged only intermittently due to
myoepithlial cellular contractions

18. CONTROL OF ACTIVITY
• Mainly stimulated humorally by circulating catecholamines
• size of gland : males> females
• Apocrine gland possess a marked 5-alpha-reductase activity
• Glands respond to emotional stimuli that promote sympathetic
discharge
FUNCTION
• No physiological function
• Concerned with human behaviour & sexual interactions
• Express high levels of 15-lipoxygenase-2 (function not
known)

19. Apoeccrine gland
• ECCRINE GLAND GOING APOCRINIZATION
• Found in adult human axillae (<10%)
• Found in all the levels of dermis, variable in size.
• Eccrine < Apoeccrine < Apocrine
• Secretory portion – irregularly dilated
– Few resemble clear cell of eccrine type
– Few resemble cuboidal/columnarcell of apocrine type
• Long duct – opens directly on skin surface
• Develop at puberty from eccrine or eccrine like precursor
glands
• Release copious serous secretion in response to cholinergic as
well as adrenergic stimuli

20. SEBACEOS GLAND

21. DEVELOPMENT
 Arise as buds from outer root sheath of hair follicle at the
junction of future infundibulum & isthmus.
 3rd week – single layer of cell
 4th week – double layer of cell
 10th week – hair germ cell appear f/b growing of hair cell
downwards and a rudiment of sebaceous gland appear on the
posterior surface of hair pegs
 13-15th week – sebaceous gland become distinguishable
 17th week – lumen formed, gland becomes multiacinar, duct
formed
 3rd trimester – becomes functional
 Birth – part of vernix caseosa
 Activity declines by the end of 1 year untill puberty
 Puberty – regains activity under the influence of 5-alpha DHT

22. ANATOMY
• Lobules & acini with a duct converging on the main sebaceous
duct, which opens into pilary canal
• Pilary canal opens on the surface of the skin by widely dilated
follicullar orifice
• Each lobule consists of undifferentated, deeply basophillic ,
flattened germinative cells with a large nuclei.

23. • Electron microscopically
– Germinative cells at the periphery rest
upon the PAS + hayaline basement
membrane
– Connected via desmosomes
– Cells contain tonofilaments, SER,
golgi apparatus, mitochondria
– Lipid droplets arise in SER & golgi
apparatus
• With differentiation
– more fat accumulates
– cells become acidophillic
– Organelles disintegrate before the cell
membrane disorganises & ruptures

24. • Sebaceous duct lined by keratinised squamous epithelium
• One end, cells are continuous with lipid producing cells of the
lobules
• Other end, stratified squamous epithelium of follicular
infundibulum
• Desmodex folliculorum, normal inhabitant

25. DISTRIBUTION
• Scalp, face, EAM, chest, back, anogenital surface
• Except palms and soles
• Larger glands on face & scalp, no. being 400-900/sq. cm
• Extremities <100/sq.cm
• Large glands seen with thin vellus hair, especially on face
• Large glands duct join the canal about 0.5mm below skin
surface
• Modified sebaceous glands open at the surface of skin
– Mebomian glands of eyelid
– Tyson’s gland of prepuce
– Free sebaceous glands on the mucocutaneous surface of female
genitalia
– Montgomery tubercles on aerola of nipples
– Ectopic glands in cervix uteri, tongue, parotid glands
– Margins of lip (Fordyce’s spots)

26. FUNCTION
• Barrier function
• Regulation of percutaneous absorption by preventing the
evaporation of water
• Antifungal action due to products of hydrolysis
• Antibacterial due to certain surface FFA’s
• Protects skin surface lipids on the face by secreting vitamin E
• Vitamin D precursor

27. PHYSIOLOGY OF SEBUM
SECRETION
• Sebacous gland is a holocrine gland.
• Secretion is formed by complete
disintegation of glandular cells.
• Cells differentiate in the center & lipids
acculmulate
• Cells increase in size, cytoplasm becomes
pale & vacuolated
• Nucleus & other organelles are pushed
terminally, become distorted &
disintegrate
• Finally, the cell disintegrate & the mass of
lipid along with cellular debris is
discharged into sebaceous duct as sebum

28. • Rate of secretion depends on
– rate of production of sebaceous cells
– Synthesing capacity of each cell
• Entirely under hormonal control
• Not affected by temperature/ amount of skin surface/ lipid
film/ innervation of glands
• No motor nerve supply
• Sebum production is continuous
• Sebaceous gland form at 7-8 years of age (adrenarche)
• Peak secretion occurs in late teenage
• female < male
• Decreases after 70 years in males, after menopause in females

29. COMPOSITION OF SEBUM
• Sebum from sebaceous gland + material from keratinising
epidermis + secretion from apocrine and eccrine glands
• Composition
– TGA & FFA : 57.5%
– Wax esters : 26%
– Squalene : 12%
– Chlesteryl esters : 3%
– Cholesterol : 1.5%
• On skin surface, sebum undergoes enzymatic degeneration due
to decomposition of bacteria
• Wax esters and squalene reduce from 2-8 years of age, rise to
adult level after 8 years of age

30. ENDOCRINE CONTROL
• ANDROGENS
– Enlargement of sebaceous gland at puberty
– No effect of exogenous hormones
– Most effective androgens
• 17-betahydroxy testosterone
• 5-alpha dihydrotestosterone
• 5-alpha androsterone -3beta-17-beta-diol
– Androgen receptors (present in gland & duct both)
– Sebocyte can synthesise testosterone from adrenal
precursors, also inactivate it to weaker androgen (DHEA)

31. • ESTROGEN
– Decrease the size of gland & sebum production ( only in high
concentration)
– Act at pituitary-gonadal axis, thus reducing endogenous androgen
production
• PROGESTERONE
– No effect
• CORTISONE
– Suppress secretion by suppression of adrenal androgens
• ACTH
– Cause hyperplasia of gland
– Increase sebum production
– Mitosis of sebaceous cells
• Pituitary gland
– Act directly or indirectly through endocrine glands it control
– Important in sebum production
• THYROID GLAND
– Thyroidectomy decrease sebum production & can be reversed by thyroxine
supplements