Download Epidermis

Week 13
The
Integumentary
System
SB
The integumentary system consists
of the skin and its derivatives:
hair, nails, and glands
Objective 1: Structures of the Integument
The two primary skin layers are:
Epidermis:
superficial layer made of keratinized stratified
squamous epithelium (subdivided into 4-5 layers)
Dermis:
consists of areolar tissue and dense irregular
connective tissue (subdivided into 2 layers)
Hypodermis:
attaches skin to underlying structures; made of areolar
tissue and variable amounts of adipose
The Epidermis is:
• The superficial layer of
the Integument
• Composed of
keratinized stratified
squamous epithelium
• Majority of cells are
called keratinocytes
• Avascular
The epidermis has either 4 or 5 cell layers
Thin skin has 4
layers; the stratum
lucidum is absent
Thick skin of the
palms and soles of
the feet has 5 layers
Layers of the Epidermis:
Layer
Structure
Stratum corneum
20-30 rows of flat dead
keratinocytes
Stratum lucidum
2-3 rows of dead
keratinocytes, found only in
thick skin
Stratum granulosum
3-5 rows of flat
keratinocytes
Stratum spinosum
8-10 rows of flat
keratinocytes,
Stratum basale
single layer of
keratinocytes; some
melanocytes,
and Merkel cells
Thin vs. Thick Skin
Identify as: Thin skin or Thick skin?
THICK
THIN
The Dermis is:
epidermis
• Deep to the epidermis
• Composed of connective
tissue
Papillary layer
• Consists of a superficial
papillary layer and a deep
reticular layer
• Contains sensory
receptors, nerve fibers,
glands, and hair follicles
dermis
Reticular layer
Layers of the Dermis
Papillary Layer
Areolar C.T.
• Collagen fibers
• Elastic
• Reticular fibers
Reticular Layer
Dense Irregular C.T.
•
Collagen fibers
Skin derivatives found in the dermis:
Sudoriferous (sweat) glands:
Eccrine
Apocrine
Sudoriferous (sweat) glands
Cross section
Low
magnification
High
magnification
Skin derivatives found in the dermis:
Hair Shaft
Arrector pili
muscle
Sebaceous (oil)
gland
Hair Root
Hair Follicle
Hair Bulb
Hair
Papilla
Hair Structures
Hair Bulb
Hair
Root
(embedded)
Hair
Shaft
(visible hair)
Histology – Hair Structures
Hair
Root
Hair
Follicle
Hair
Bulb
Hair
Papilla
Histology – Arrector pili muscle
(smooth
muscle)
Histology – Hair Structures
Hair
follicle
Histology – Hair Structures
Sebaceous (oil) gland
Histology – Hair Structures
Sebaceous (oil)
gland
Hair
shaft
Hair root
Hair
follicle
Arrector
pili
Sebaceous
(oil) gland
Hair
Root
Hair
Follicle
Other important structures found in the
dermis are cutaneous sensory receptors
Sensory receptors can be “encapsulated” or
“unencapsulated” nerve endings
Connective tissue
capsule
Free Nerve Ending
Encapsulated Nerve Ending
Free nerve endings mediate the following sensations:
• Nociceptors detect pain
• Thermoreceptors detect heat and cold
• Proprioceptors detect stretch
• Root hair plexus detect hair movement
Root hair plexus
Free nerve ending
in the epidermis
Encapsulated Receptors
Pacinian corpuscles mediate
deep pressure
Meissner’s corpuscles mediate
light touch
Cutaneous Sensory Receptors
Identify these from models
Meissner's corpuscle
Free nerve ending
Pacinian corpuscle
Hair follicle receptor
(root hair plexus)
Cutaneous Sensory Receptors
Histology
Pacinian corpuscles
Meissner’s corpuscles
Located deep in dermis
Located in dermal papilla
External
See skin models for 3-D structure and structural
clarity
Internal
Consequences of Sensation Loss
Diabetic neuropathy
Nerve damage due to decreased blood flow
•Ulcers and infections - skin damage undetected
•Charcot's Joint (neuropathic arthropathy)
•Loss of motor function
Objective 2
General Sensation
Experiments
Distribution and Discrimination
Experiment A – 2-Point Discrimination
Determine touch receptor density
Experiment B – Mapping Temperature and Touch Receptors
Compare density of cold, heat and touch receptors
Experiment C – Tactile Localization
Localizing the stimulus (receptive field)
Adaptation
Experiment D – Sensory Adaptation
Timing pressure sensation adaptation
Experiment E – Temperature Receptor Adaptation
Compare sensation of hand immersed in hot
water with sensation of hand already immersed