5. Skin - Epidermis WEB

The Integumentary System
Chapter 5
The Skin
epithelial and connective
tissues working together
the largest organ of the
1.5 - 2 square meters
4 - 5 kg
variable thickness: 0.5 mm
to 4 mm
The Architecture of the Skin
2 main parts:
 Epidermis – keratinized
stratified squamous
 Dermis – areolar & dense
irregular connective tissues
Beneath the dermis:
 Hypodermis (the
subcutaneous layer) –
separates skin from muscle;
contains areolar and adipose
A Bigger Picture
Skin’s Many Functions
regulation of body temperature
protection – a physical barrier & water
sensation – due to sensory nerve endings
excretion – sweat
immunity – epidermis contains phagocytes
synthesis of vitamin D – for calcium absorption
The Epidermis
4 cell types:
filled with protein keratin; waterproof barrier
produce pigment melanin
Langerhans cells
phagocytes (function in immunity); easily damaged
by UV light
Merkel cells
detect touch sensations
Epidermal Cell Layers
Stratum basale
a single layer; mitosis pushes
the other layers to the top;
Merkel cells & melanocytes
Stratum spinosum
8 to 10 layers of closely packed
cells; Langerhans’ cells
Stratum granulosum
3-5 layers of flattened nondividing cells; produce large
amount of keratin; nuclei &
organelles disintegrate
Epidermal Layers Cont.
Stratum lucidum
only in thick skin
3-5 layers of clear, flat dead
cells with keratin
Stratum corneum
25-30 layers of flattened,
dead, keratin-filled cells
continuously shed and
It takes 2-4 weeks for each cell
to move from the stratum
basale to stratum corneum
Epidermal Histology
Stratum Corneum
Stratum Granulosum
Stratum Spinosum
Stratum Basale
Skin Pigments
1. Hemoglobin – red, carries oxygen in red blood
2. Carotene – yellow/orange, converted to
vitamin A, used in the synthesis of vision
3. Melanin – yellow/red or brown/black
Melanin Cont.
The number of melanocytes is similar in all races – but the
amount of melanin produced varies
The UV ↑ production of melanin; melanin protects the
body against UV radiation by absorbing UV
Albinism - inability to produce melanin; genetic
Practice – Be able to complete by Wednesday
A. Epidermis
a. Insulation
B. Hair erector muscle
b. Water proofing
C. Fat cells
c. Protection from sun's rays
D. Sebaceous gland
d. Heat retention
E. Dermis
e. Heat loss
F. Melanin
f. Protection from infection
G. Hair
g. Makes hairs stand on end
H. Sweat gland
h. Secretes oily substance to coat hairs
I. Blood capillaries in the dermis
i. Makes skin tough
J. Keratin
k. Constrict or dilate to control heat loss