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Anatomy and physiology of sweat glands

This presentation includes structure and functions of sweat glands i.e. eccrine, apocrine and apoeccrine glands. mechanism of sweat secretion and role of sweat in thermoregulation is included.

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Anatomy and physiology of sweat glands

  2. 2. INTRODUCTION • Sweating is one of the most visible physiological events we experience everyday • On average, 1.6 to 4 million sweat glands on the body • Major function – Regulation of body temperature • Failure can lead to heat exhaustion, heat stroke, hyperthermia and death
  3. 3. TYPES OF SWEAT GLANDS Sweat Glands Eccrine (Atrichial) Independent of Hair Follicle Apocrine (Epitrichial) Attached to Hair Follicle Apoeccrine Develop from eccrine like precursor glands
  4. 4. TYPES OF SECRETION Merocrine • No breakdown of cellular material during secretion Apocrine • A small amount of cytoplasm is pinched off Holocrine • Mature cell disintegrates and become secretory product
  7. 7. DEVELOPMENT OF ECCRINE GLANDS 3rd month • Palms and Soles 5th month • All other parts of the body 8th month • Resemble Adult glands Birth 2 years • Fully functional
  8. 8. DISTRIBUTION OF ECCRINE SWEAT GLANDS Distributed over whole skin surface including glans penis and foreskin Absent on vermilion border of lips, nail bed, external ear canal, clitoris, labia minora
  9. 9. DENSITY OF ECCRINE SWEAT GLANDS Density Part Most Palms and soles, forehead Moderate Dorsum of hand Less Lumbar region, lateral and extensor surfaces of extremities Least Trunk , flexor and medial surfaces of extremities
  10. 10. ECCRINE SWEAT GLAND Number Total – 2 to 5 million Individual surface • Soles – 620/sq.cm • Thighs – 120/sq.cm • Back – 60/sq.cm Weight Total – 100 g Individual gland – 30 to 40 microgram Secretion As much as 10 L in 24 hours Individual gland – 2 to 20 nL/min
  11. 11. MEROCRINE SECRETION No break down of cellular material occurs during secretion Fusion of membranous walls of secretory vesicles with plasma membrane Only the contents of vesicles released Merocrine secretion
  12. 12. STRUCTURE OF ECCRINE SWEAT GLAND Simple tubular epithelial structures Three parts 1. Secretory coil (fundus/acinus) 2. Straight intradermal duct 3. Spiral intraepidermal duct (acrosyringium)
  13. 13. SECRETORY COIL 60 – 80 micron in diameter and 2 – 5 micron in length Surrounded by a thin fibrous sheath and an investing lamina Function – Production of watery isotonic secretion which is further modified by duct Three types of cells 1. Clear cells (Large, Secretory) 2. Dark cells (Small, Mucoid) 3. Myoepithelial cells Electron micrograph of secretory coil Lu – Lumen Cc – Clear cell Dc – Dark cell Icc – Intercellular canaliculi Mc – Myoepithelial cell
  14. 14. LARGE CLEAR CELLS Main secretory cells Rests either on basement membrane or myoepithelial cells Mitochondria and Na+ K+ ATPase activity in basal infoldings Where two or more clear cells abut, intercellular canaliculi is formed Canaliculi open into lumen of the gland
  15. 15. DARK CELLS Cuboidal cells border nearly all apical/luminal surfaces of secretory tubules Resemble mucus secreting cells of other organs Relatively smooth membrane and contains dark cell granules Periodic acid Schiff stain positive glycoproteins Dark cells M – Mucus / Dark cells S – Serous / Clear cells L – Lipid globules
  16. 16. MYOEPITHELIAL CELLS Spindle shaped cells on basement membrane Contractile cell with abundant actin filaments Function – Support the gland, help in propelling sweat towards the surface Peripheral to myoepithelial cells, basement membrane zone CC – Clear cell DC – Dark cell ME – Myoepithelial cell IC – Intercellular canaliculus BM – Basement membrane
  17. 17. DERMAL ECCRINE DUCT Consists of outer ring of peripheral or basal cells and inner ring of luminal or cuticular cells Basal cells – Rich in mitochondria, strong Na+ K+ ATPase activity, plays a major role in ductal reabsorption Layer of tonofilaments (pseudocuticle) give rigidity to periluminal region and assures luminal patency Proximal intradermal duct is functionally more active than distal intradermal duct Cross section of dermal eccrine duct BDC – Basal Ductal cell LDC – Luminal Ductal cell PC – Pseudocuticle L – Lumen
  18. 18. EPIDERMAL ECCRINE DUCT Runs spirally from base of rete ridge to the surface Single layer of inner luminal cells and two to three layers of outer basal cells It has well developed coil structure in palms and soles
  19. 19. PHYSIOLOGY OF SWEATING Types of Human Perspiration Human Perspiration Insensible perspiration Active sweating Thermal Emotional Emotional Sweating Palms and soles Shorter latent period for its onset Immediately attains a rate of secretion that corresponds to intensity of stimulus Subsides quickly after the end of stimulus
  20. 20. CONTROL OF ECCRINE SWEATING Eccrine sweating Thermal Osmotic Mental Gustatory Increase in skin temperature Increase in core temperature Stimulates preoptic hypothalamus Sweating, Vasodilatation & Rapid breathing 10*C increase in local skin temperature – triples local sweating rate Increase in internal temperature – 9 times more efficient than increase in mean skin temperature in stimulating sweat center
  21. 21. SYMPATHETIC SUDOMOTOR PATHWAY Preoptic Hypothalamus Via tegmentum of pons and medullary raphe regions Intermediolateral cell column of spinal cord Emerge via ventral horn pass through white ramus communicans Sympathetic Ganglia Post ganglionic non myelinated C fibers through grey ramus communicans Eccrine Sweat gland
  22. 22. INNERVATION OF ECCRINE SWEAT GLAND Sympathetic and cholinergic Major neurotransmitter is Acetylcholine Respond to cholinergic agents, α and β adrenergic stimulants Other – ATP, catecholamine, vasoactive intestinal peptide, atrial natriuretic peptide, calcitonin gene related peptide and galanin PART ROOT Face and eye lids T1 to T4 Upper limb T2 to T8 Trunk T4 to T12 Lower limb T10 to L2 Ratio of maximal secretory rates Cholinergic α-adrenergic β-adrenergic 5 1 1
  23. 23. Ca2+ Basolateral membrane Cl- K+H2O MECHANISM OF SWEAT SECRETION Ach Lumen
  24. 24. Lumen Basolateral membrane K+ 2Cl- Na+ MECHANISM OF SWEAT SECRETION Cl- Na+/K+/2Cl- antiporter K+ Na+ Na+,K+ ATPase Na+
  25. 25. Lumen Basolateral membrane 1 1 MECHANISM OF DUCTAL REABSORPTION Na+ ENaC K+ Na+ Na+,K+ ATPase Cl- CFTR Cl- H+ + HCO3 -H2O + CO2 Carbonic anhydrase H+ V-ATPase Cl- HCO3 - H+ Na+ NHE1 Cl- H+
  26. 26. MECHANISM OF SWEAT SECRETION Net fluxes – H2O, Cl- and Na+ flow into the lumen (isotonic and neutral pH) Net fluxes – H+ secretion and Na+ and Cl- reabsorption (hypotonic and acidic)
  27. 27. COMPOSITION OF ECCRINE SWEAT Sodium • 10 – 20 mmol/L at low sweat rates and up to 100 mmol/L at high sweat rate Chloride • Concentration is lower than that of sodium Potassium • 5 – 6 mmol Urea • 15 – 25 mg/dl • Derived mostly from serum urea Lactate • 4 – 40 mmol/L (exceeds concentration found in plasma) • Formed from glucose from the blood
  28. 28. ECCRINE SWEAT – MINOR CONSTITUENTS • 20 – 50 times higher than that of plasmaAmmonia • Only in small quantitiesGlucose • Concentration in final sweat in zeroBicarbonate • 0.2 – 1.6 mmol/LPyruvate Proteins including proteases Glandular kallikrein, Kininase, C1 esterase, urokinase, cysteine protease, Epidermal Growth Factor
  29. 29. FUNCTIONS OF ECCRINE SWEAT GLANDS Thermoregulation Improves grip by moistening palms and soles Excretion of drugs Wound healing Desquamation of stratum corneum by lactate Pro inflammatory action Mitogenic effects
  31. 31. DEVELOPMENT OF APOCRINE GLAND Develop from primary epithelial or hair germs during 4th to 5th month of intrauterine life Poorly developed in childhood and begin to enlarge with approach of puberty Do not become functional until puberty Development is associated with sex hormones
  32. 32. STRUCTURE OF APOCRINE GLAND Located in subcutaneous tissue Larger than eccrine gland Size and activity is greater in men than that of women Composed of coiled secretory portion and an excretory duct
  33. 33. SECRETORY COIL OF APOCRINE GLAND Single layer of columnar cells Eosinophilic cytoplasm and large PAS positive and diastase resistant granules distributed around the nucleus (except in apical portion) Surrounded by myoepithelial cells Secretory coil of apocrine sweat gland Me – Myoepithial cells N – Nucleus of secretory cells A – Apical cap of secretory cells
  34. 34. EXCRETORY DUCT OF APOCRINE GLAND Double layer of cuboidal cells Merge distally with the epithelium of the hair follicle Empty the secretion into infundibulum of hair follicle above the sebaceous gland Does not have any reabsorptive function
  35. 35. DISTRIBUTION OF APOCRINE GLANDS Axilla Areola (Montogomery tubercles) Periumbilical Perineal Circumoral MODIFIED APOCRINE GLANDS Ceruminous glands in external ear canal Ciliary or Moll’s glands on eyelids Mammary glands
  36. 36. APOCRINE SECRETION An apical cap and a dividing membrane is formed initially Apical cap is then detached and discharged into the lumen of the gland – APOCOPATION Decapitation secretion – pinching of parts off the cytoplasm Secretion is pulsatile Low secretory output Apocrine secretion
  37. 37. COMPOSITION OF APOCRINE sweat Secretion is milky, protein rich, viscid and colourless Secretion is lipid rich Bacterial decomposition is responsible for characteristic mephitic odour Trans 3 methyl 2 hexanoic acid contributes to the odour Secretion is mixed with sebum
  38. 38. CONTROL OF APOCRINE SECRETION Respond to emotional stimuli Stimulated by epinephrine or norepinephrine given locally or systemically Affected by hormonal factors such as pregnancy and menstruation Undergo atteunation with ageing
  39. 39. FUNCTIONS OF APOCRINE GLANDS Role as odoriferous sexual attractants (Pheromones), territorial markers and warning signals Increases frictional resistance and tactile sensibility Androgen dependent and shows marked 5α- reductase activity High levels of 15 lipoxygenase 2 in secretory cells. Its product function as signaling molecule
  41. 41. APOECCRINE GLAND Eccrine gland that undergone apocrinization due to local factors Not present at birth Develop only during puberty from eccrine glands or eccrine like precursor gland Present in adult human axillae
  42. 42. STRUCTURE OF APOECCRINE GLAND Secretory tubule – thin segment (eccrine like) and thick segment (apocrine like) Segments are functionally connected Some secretory cells resemble clear cells of eccrine gland whereas others resemble cuboidal or columnar cells of apocrine gland Large duct opens directly to skin surface
  43. 43. APOECCRINE SECRETION Functions like eccrine gland yielding copious serous sweat in response to both adrenergic and cholinergic stimuli Significant contribution to overall axillary sweating
  44. 44. EMAIL ID