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.
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.
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.
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.
