Histology of Skin and its Appendages.

(Integumentary system)

To

MBBS unit-4

Dr. Laxman Khanal

Asst. Professor, department of Human Anatomy

BPKIHS, Dharan, Nepal

Q. Variation in thickness of epidermis of skin (0.1 to 1mm) is mainly due tovariation in:a. Stratum corneumb. Stratum lucidumc. Stratum granulosumd. Stratum spinousm

Q. ‘Superficial fascia’ described in gross anatomy is equivalent to whichof the following histological layer?a. Stratum basale + stratum spinousmb. Whole of the epidermis of skinc. Dermisd. Hypodermis

Q. Epidermis of the skin is attached to the dermis with the help of:a. Desmosomeb. Hemi desmosomec. Gap junctionsd. Tight junctions

Q. Image shows the case of acne vulgaris.Which glands are involved in this case?a. Eccrine sweat glandb. Apocrine sweat glandc. Holocrine glandd. Glands of Moll

Skin + its appendages= integumentary system

Skin (Cutis): covers the entire outer surface of the body.Structurally, the skin consists of two layers.

These layers have different• Functions• Histological appearance• Embryological origin

Beneath these two layers, layer of loose connective tissue,the hypodermis or subcutis is found which binds the skin to underlyingstructures. It is equivalent to superficial fascia.

Appendages of skin• Hair• Nail• Sebaceous gland• Sweat gland

Epidermis • The epidermis is a keratinized stratified squamous epithelium.

• The main function of the epidermis is to protect the body from harmfulinfluences from the environment and against fluid loss.

• Five different histological layers constitute the epidermis.

1. Stratum basale (Layer of stem cells)

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum

5. Stratum corneum (Keratinized cells)

Cells of the epidermis of the skin will at some time of their life (3-4 week)keratinize and are collectively also called keratinocytes.

Cells of epidermis of skin1. Keratinocytes2. Nonkeratinocytes

Functions of skin

• Barrier

• Drug absorption: eg. Nicotine patch, Steroids

• Immunologic functions

• Homeostasis

• Sensory information

• Endocrine functions

• Excretory function

Thick Skin Thin SkinThickness (mm) 0.1-0.20.5-4.5

Sites

S. Lucidum ×

Epidermal RidgesWell developed poorly developed

Hair follicle

Arrector pili

Sebaceous gland

Sweat gland

Sensory receptors

××

×

More Few

More Few

Stratum Basale (Basal Layer)• It is responsible for the continuous regeneration of

the other layers of the epidermis.• Cells are attached to the basement membrane by

Hemidesmosome.

Stratum spinosum (Prickle cell layer)• Polyhedral cells with prominent nucleoli.• Synthesize the intermediate filament: cytokeratin.• Cytokeratin aggregate and form tonofilaments.• Tonofilaments give resistance to abrasion.• Binding of tonofilaments to desmosome give

spined appearance.

Stratum Granulosum• Transition between metabolically active cell layers

and dead cell layers.• Cells progressively flattened and undergo apoptosis.• Presence of basophilic keratohyaline granules.• Tonofilaments + KHG = Keratin• Presence of lamellar bodies (Odland bodies) makes

it water resistant.

• Keratohyaline granule• Lamellar bodies (Odland bodies)

Stratum lucidum• Only found in thick skin.• Cells are translucent in appearance.

Stratum corneum• 20-25 cell layer thick.• Made up of dead keratinocytes (Corneocytes).• Cells are arranged like ‘brick in the wall’• Epidermal turnover time: 52-75 days

Keratinocyte Melanocyte

Langerhans cellMerkel’s cell

Cells of epidermis of the skin

• Source: Neural Crest Cell• Place: Basal layer• Function: color of skin and hair• More numerous in area exposed to sunlight.

Epidermal melanin Unit:36 keratinocytes associated witheach melanocytes.

Langerhans cells (antigen presenting cells)• Langerhans cells are dendritic cells of the skin.• Derived form mesenchymal cells of bone marrow• Most numerous in stratum spinosum• Have branched shape &central nuclei• Presence of Birbeck’s granules

Merkel’s cell• Found in basal cell layer• Originated from keratinocytes• Function as touch receptors (slowly adapting)

Dermis • Overall thickness of skin depends upon

thickness of dermis.

• Mainly consists of collagen and elastic fibers.

• Responsible for tone and texture of the skin.

• Neurovascular structures and skin appendages are found in dermis.

• It has two layers:

1. Papillary layer – toward epidermis

2. Reticular layer- toward hypodermis

Papillary layer

Reticular layer

• The collagen and elastic fibers arenot randomly oriented but formregular lines of tension in the skincalled Langer’s lines.

• Skin incisions made parallel toLanger’s lines heal with the leastscarring.

Blood circulation of skin

Deep plexus(cutaneous plexus)

superficial plexus(sub-papillary plexus)

Large blood vessels

Glomus bodies

A/C to circulationA. Apical skinB. Non apical skin

Skin appendages

• These are developed as a result of down growth of the epidermis of skin toward dermis and hypodermis.

• It includes

1. Hair follicle: give rise to the hair

2. Sebaceous gland

3. Eccrine sweat gland

4. Apocrine sweat gland

5. Nail

Skin appendages

Hair cycleAnangen phase- fast growing phaseCatangen phase- involution phaseTelogen phase- rest phase

Types of hair1. Laungo hairs2. Vellus hairs3. Terminal hairs

Eponychium

Nail body

Free edge

Lunula

Nail root

HyponychiumEpidermis

Dermis

Nail bed1. Basal layer2. Spinous layer

Nail plate(keratinized)

Nail matrix(site of nail growth)

Sweat gland Sebaceous gland

Open into hair follicleActive only after pubertyOpen into surface of skin

Active throughout life

Sweat gland

which gland ?

Skin appendages

Pilosebaceous unit