Week 13 The Integumentary System

The integumentary system consists of: The Skin Its Derivatives Hair Nails Glands

Objective 1 Structures of the Integument

Skin Layers The two primary skin layers are: Plus: 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) Plus: Hypodermis: attaches skin to underlying structures; made of areolar tissue and variable amounts of adipose

The superficial layer of the Integument 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: Mnemonic? Come Let’s Get Some Beer… 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 Number of rows are less in thin skin and more in thick skin

Thin vs. Thick Skin

Identify as: Thin skin or Thick skin?

The Dermis Dermal papillae Dermis

Composed of connective tissue epidermis The Dermis is: Deep to the epidermis Composed of connective tissue Consists of a superficial papillary layer and a deep reticular layer Contains sensory receptors, nerve fibers, glands, and hair follicles Papillary layer dermis Reticular layer

Layers of the Dermis Papillary Layer Areolar C.T. Reticular Layer Collagen fibers Elastic Reticular fibers Reticular Layer Dense Irregular C.T. Collagen fibers

Skin Derivatives Hair shaft Pore Sebaceous (oil) gland Arrector pili muscle Hair root Hair follicle Hair bulb Hair papilla Eccrine (sweat) gland

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 Shaft Hair Root (visible hair) (embedded)

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 follicle Hair root Arrector pili Hair Root Hair Follicle Sebaceous (oil) gland

Cutaneous Sensory Receptors Identify these from models Meissner's corpuscle Free nerve ending Pacinian corpuscle Hair follicle receptor (root hair plexus)

The cutaneous sensory receptors are nerve endings that receive stimuli from the external environment through the skin (Exteroceptors) Spinal cord

Cutaneous Sensory Receptors

Meissner’s corpuscles Located in dermal papilla Histology Pacinian corpuscles Located deep in dermis Meissner’s corpuscles Located in dermal papilla External Internal See skin models for 3-D structure and structural clarity

Note: Although a part of the nervous system, cutaneous receptors can have a direct impact on the integument

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

Consequences of Sensation Loss Leprosy (Hansen’s disease) Lesions and infections from inability to detect tissue and bone injury resulting from nerve damage caused by the bacterium Mycobacterium leprae Appendage loss due to infection Blindness and nasal collapse also result from nerve damage

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) ? cm

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 (adapted)