Week 13 The Integumentary System SB The integumentary

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