244
UNIT 3
Organ Systems
Hair shaft
Duct of eccrine sweat gland
Eccrine sweat gland
Hair root plexus
Nerve
Vein
Artery
Sebaceous gland
Free nerve ending
Meissner corpuscle
Hair papilla
Hair follicle
Hair root
Apocrine sweat gland
Pacinian corpuscle
Arrector pili muscle
Figure 13-1.
Overview of the structure of the skin.
The
skin
is composed of
epithelium
,
connective tissue
,
muscles
,
nerves
,
blood vessels
, and
associated structures
(
glands
,
hair
follicles
,
and
nails
). It can be divided into two basic layers:
epidermis
and
dermis
(Fig. 13-2). The
epidermis
is the super±
cial layer of the skin.
It consists of a strati± ed squamous epithelium (Fig. 13-2). The
dermis
is a layer of connective tissue beneath the epidermis. There is a
transition layer between the skin and underlying muscle called the
hypodermis
(subcutaneous layer), which, strictly speaking, is not
a component of the skin but is closely associated with the skin (Fig. 13-2). This layer contains loose connective tissue, adipose tissue,
nerves, arteries, and veins. The skin contains several sensory structures, which respond to somatosensory stimuli. These include
free
nerve endings
(pain or temperature),
Merkel disks
(continuous touch), and
Meissner corpuscles
(touch).
Pacinian
corpuscles
(vibra-
tion) can be found in the subcutaneous layer (hypodermis). For the function and details of the sensory receptors, see Chapter 7,
“Nervous Tissue,” Figure 7-8A–C. There are several types of glands in the skin, including
sebaceous glands
,
eccrine sweat glands
,
and
apocrine sweat glands
.
Structures of the Skin
I. Layers of the skin
A. Epidermis
1. Stratum corneum
2.
Stratum lucidum
3.
Stratum granulosum
4.
Stratum spinosum
5.
Stratum basale
B. Dermis
1.
Papillary layer
a.
Free nerve endings
b.
Meissner corpuscles
2.
Reticular layer
C. Hypodermis (subcutaneous layer)
1.
Loose connective tissue
2.
Adipose tissue
3.
Pacinian corpuscles
4.
Arteries and veins
5.
Nerves
II. Accessory structures
A. Glands
1.
Sebaceous glands
2.
Eccrine sweat glands
3.
Apocrine sweat glands
B. Hair
1.
Hair shaft
2.
Hair follicles
C. Nail
1.
Nail bed
2.
Nail matrix
3.
Eponychium
4.
Hyponychium
D. Sensory receptors
1.
Meissner corpuscles
2.
Free nerve endings
3.
Pacinian corpuscles
4.
Merkel cells (Merkel cell neurite complexes or Merkel disks)
Layers of the Skin
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