Integument
E
D
H
M
The Epidermis (E) has many layers and is the outermost layer of the integument. The Dermis (D) is below and is the thick layer of connective tissue where many specialized structures are located. There are two parts to the dermis, the upper papillary layer and the reticular layer. The Hypodermis (H) is mainly adipose tissue and rests on the musculature (M). The integument can vary depending on the location on the body.
Epidermis
Stratum Corneum
This layer is also composed of dead cells filled with keratin filaments. This layer provides a waterproofing protective layer to the integument.
Stratum Granulosum
Stratum Lucidum
This layer is formed with dead cells, as you can see they have no nucleus and are composed mainly keratin filaments. The lucid layer is only present in thick skin found on palms and soles of feet. Thin skin does not have this layer.
These cells are undergoing the last stages of keratinization.
Stratum Basale
Stratum Spinosum
This is normally the thickest layer of the integument. it is called the spinous layer because the cells appear "spiny" because of the keratin assembling in these cells.
This basal layer of cells sits on the basement membrane. This area is high in mitotic activity, replacing lost cells as top layers are shed. These cells are called keratinocytes. We also find melanocytes in this layer that are the pigment producing cells of the skin.
Dermal Layer
Dermal Papillae : the uppermost part of the dermis. this is composed of loose connective tissue. it anchors to the basal lamina of the epidermis.
Reticular Layer : this layer is the thickest and is made of dense irregular connective tissue. This is the layer where we find the major accessory structures of the integument like hair follicles, vasculature, pacinian corpuscles, sweat and sebaceous glands.
Specialized Structures
Hair follicles
Medulla
Cortex
Found in the dermal region of the integument, these structures are epidermally derived and will open onto the surface of the skin. Periods of growth (anagen) and rest (catagen & telogen) are characterized by differences in hair follicle structure, especially dermal papillae.
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Many of the
Sebaceous glands
Hair Shaft
Sebaceous glands are associated with hair follicles. These acinus glands secrete a sebum via holocrine secretion. Note its location is always in association with a hair follicle in the dermal region.
Sweat glands
These glands are simple tubular lined with a simple cuboidal epithelium as are most glands. They produce the "sweat" via merocrine secretion.
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These glands also contain myoepithelial cells that will contract to expel the secretions. Note its location in the dermis.
Sensory structures
D
H
P
Pacinian Corpuscle (P) are found deep in the dermis (D) and hypodermis (H) of the integument and respond to pressure touch.
E
M
Meissners corpuscles are found in the papillary layer of the dermis where they receive light (tactile) touch stimuli.