1. Anatomy and Physiology of Skin
Dr Ashwini Kalantri

2. Skin
 Largest organ of the body
 Completely covers the body
 Continuous with membranes lining body orifices
 Average thickness: 1-2 mm. (0.5mm eyelids, 6mm
palms and soles)
 pH: 4-5.6
 Renewal of skin takes place in 28-50 days by
shedding of the outer layer.

3. Structure of Skin
Layers
1. Epidermis
2. Dermis

4. Epidermis
 Most superficial layer of the skin composed of
stratified epithelium
 No blood vessels
 Nutrition provided by the capillaries of dermis
 Approx. thickness 0.4-1.5mm, thickest on palms and
soles.

5. Layers of Epidermis
Stratum Corneum {
Stratum Lucidum {
{
Stratum Granulosum
Stratum Mucosum
Stratum Germinativm {

6. Cells in the Epidermis
 Keratinocytes: Major building block of the
epidermis
 Melanocytes: Large cells interspaced among
keratinocytes, produce melanin.
 Langerhans Cells: Antigen presenting cells
 Merkel cells: Represent special nerve endings
within epidermis
 Hair, Sebaceous glands and ducts of sweat glands.

7. Colour of the Skin
 Pigmentation of skin: Melanocytes contain the
pigment melanin which darkens the skin on
exposure to sunlight
 Hemoglobin content in blood: The level of
oxygenation of blood and amount of blood
circulating in the dermis play an important role in
skin colouration.

8. Dermis
 Connective tissue layer made up of dense and stout
collagen fibers, fibroblasts and histocytes. Collagen
fibers have elastic property and are capable of
storing water.
 Layers:
1. Superficial Papillary Layer
2. Reticular Layer

9. Superficial Papillary Layer
 Projects in to the epidermis
 Contains blood vessels, lymphatics and nerve fibers.
 Has some pigment containing cells called
chromatophore.
 Dermal papillae are finger like projections arising
from this layer

10. Reticular Layer
 Made up of reticular and elastic fibers
 These fibers are found around hair bulbs, sweat
glands and sebaceous glands.
 Also contains mast cells, nerve
endings, lymphatics, epidermal appendages and
fibroblasts.
 The hair follicles with hairs, sweat
glands, sebaceous glands and nails.

11. Glands of the Skin
1. Sebaceous Glands
2. Sweat Glands

12. Sebaceous Glands
 Structure: Ovoid or spherical in shape, developed
from hair follicles and covered by connective tissue
capsule
 Secretion: Secrete a oily substance called Sebum.
 Composition: Contains free fatty
acids, sterols, paraffin, waxes, squalene and
triglycerides.
 Functions: FFA has antibacterial and antifungal
properties. Lipids keep skin smooth and
oily, protecting from unnecessary desquamation
and injury.

13. Sweat Glands - Eccrine
 Distributed throughout the body with exterior
opening through sweat pore with watery and clear
discharge.
 Temperature regulation
 Secretion increases with increase in temperature
and emotions under nervous control
 Nerve supply by sympathetic cholinergic fibers.

14. Sweat Glands - Apocrine
 Distributed only in a limited area –
Axilla, pubis, areola and umbilicus.
 Opens in to the hair follicle having thick and milky
secretion.
 Starts functioning with puberty and has no role in
temperature regulation
 Secretions increase under emotional conditions
under hormonal control.
 Supply by sympathetic adrenergic fibers.

15. Functions of Skin

16. Protective
 Protection from bacteria and toxic substances by
secreting lysozyme.
 Protection from mechanical blow
 Protection from UV rays with the help of melanin
pigment.

17. Sensory
 Skin is considered the largest sensory organ
 Many nerve endings forming a specialized
cutaneous receptors.

18. Storage
 Stores fat, water, chloride and sugar.
 Can also store blood with vasodilation of the
cutaneous blood vessels

19. Synthetic
 Vitamin D3 is synthesized in the skin with the
action of UV rays on cholesterol.

20. Temperature Regulation
 Excess heat is lost from the body by
radiation, conduction, convection and evaporation.
 Active role in heat loss by secreting sweat.
 The lipid content of sebum prevents heat loss in
cold temperature.

21. Water and Electrolyte
balance
 Excretion: Waste materials like urea, salts and fatty
substances are also excreted.
 Absorption: skin can absorb fat soluble substances
and some ointments.
 Secretion: Sweat and sebum are secreted by the
sweat and sebaceous glands. Helps in temperature
and water balance. Sebum helps in keeping the skin
smooth and provides protection.