Skin and its glands

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 4 th month IU : Specialised downgrowth of the epidermis on the volar surface of hands and feet 5 th month IU : axillae f/b other parts of body 8 th 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 2/3 rd 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 4-5 th 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. 3 rd week – single layer of cell 4 th week – double layer of cell 10 th 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 13-15 th week – sebaceous gland become distinguishable 17 th week – lumen formed, gland becomes multiacinar , duct formed 3 rd 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