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.
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. 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. 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
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. APOECCRINE SECRETION
Functions like eccrine gland yielding
copious serous sweat in response to both
adrenergic and cholinergic stimuli
Significant contribution to overall axillary
sweating