General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao INTEGUMENTARY SYSTEM Functions: 1. Body temperature regulation. 2. Reservoir for blood 3. Protection from external environment 4. Cutaneous sensations 5. Excretion and Absorption 6. Vitamin D synthesis Composition: - Skin - Accessory structures:

o Hair o Nails o Various glands

Skin - Largest organ of the body Two principal parts: 1. Epidermis - Superficial portion - With 5 layers 2. Dermis - Inner portion - With 2 regions

Epidermis - A keratinized stratified squamous epithelium - Consists of 4 principal types of cells:

1. Keratinocytes: keratin & lamellar granules - 90% of the epidermal cells - Produced keratin (protein)

Tough fibrous protein that help the skin from heat, microorganisms, underlying tissues of skin and chemicals.

- Lamellar granules Stratum granulosum Functions: Releases a water and proofing

sealant

2. Melanocytes: melanin - 8% of the epiderma cells - Produce pigment – melanin skin color

3. Langerhans cells - Arise from the bone marrow - Migrate to epidermis - Participate in immune responses

General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao

4. Merkel cells - It is the least numerous of epidermal cells - Located at the deepest part of stratum

basale/geminativum. - In contact with tactile disc or merkel disc Function: - Both participate in sensation of touch

Layers of the Epidermis

1. Stratum Corneum - 25 – 30 layers of dead flat keratinocytes. - Contains the dead flat intermediate filaments - Consists of keratohyaline

o Function: Water repellant barrier - Lamellar granules - Lipid from lamellar granules (barrier in between)

- Shed off when you take a bath Continuous Friction - Callous an abnormal thickening of epidermis due

to friction 2. Stratum Lucidum - “lucid” – “clear” - Present in the skin of finger tips, palms, and soles. - 3 – 5 clear layers of flat dead keratinocytes with

intermediate filaments and thickened plasma membrane.

3. Stratum Ganulosum - 3 – 5 layers of flattened keratinocytes - Consists of keratohyaline and lamellar granules

o A distinctive feature of the layer o Darkly staining granules of the

stratum Function: Organized intermediate filaments into thicker bundles. 4. Stratum Spinosum - The superficial of basale - 8 – 10 layers of polyhedral keratinocytes - Fit closely together - Thorn – like spines bundles of intermediate

filaments of the cytoskeleton joins the cell tightly to one another to provide strength and flexibility of the skin.

5. Stratum Basale/Geminativum - Active in cell division - Compose of one layer of simple cuboidal/columnar

keratinocytes. Some considered them as stem cells Continue cell divisions to produce new

keratinocytes - Merker cell - Melanocytes Dermis - Second deeper part of the skin - Composed of connective tissue containing collagen

and elastic fibers o Functions: for extensibility (stretch; obesity)

and flexibility (Return to its original form) - Include cells such as fibroblasts, macrophages, and

some adipocytes - Blood vessels, nerves, glands, and hair follicles are

embedded in dermal tissue

General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao Two regions of Dermis: 1. Papillary region - The superficial portion of the dermis - Consists of areolar connective tissue with tissue

with elastic fibers - Contains dermal papillae

Finger-like projections that indent the epidermis to the dermis.

Contains the following: a. Meissner’s corpuscle - For touch sensation b. Free nerve endings - Contains the dendrites that initiates signals that are

felt such as warm, coolness, pain, tickling and itching.

*Papillary layer – small fine collagen 2. Reticular region - Deeper portion of dermis - Consists of dense irregular connective tissue

containing bundles of collagen and some elastic fibers.

*Reticular layer – more coarsely-textured collagen fibers.

Sensory receptors / free nerve endings of the reticular layer: 1. Nociceptotrs – pain receptor

2. Tactile/Merkel disc - Type one cutaneous mechanoreceptor - For sensation touch

3. Meissner’s corpuscle - Encapsulated - Palmar and planthar - Fingertips

4. Ruffini corpuscles - Type II cutaneous mechanoreceptor 5. Pacinian corpuscle - Located deeper part of the dermis - Encapsulated with multicellular ovoid structures Function: Respond to deeper pressure.

Functions of the connective tissue of the dermis: 1. Tough collagen fibers and resilient elastic fibers

provide mechanical strength for skin. Lines of tension in the dermis called Langer’s lines, affect healing after surgical incision

2. The ground substances of the dermis serve as the substrate for diffusion of nutrients and wastes to and from various other tissue components.

3. Mast cells, lymphocytes and macrophages in the connective tissue carry our surveillance for the immune system.

4. Finally, the dermis together with its associated blood vessels and nerves is capable of active responses to injury, yielding the defensive reaction of inflammation, followed by the healing processes of growth and repair

Subcutaneous layer (Hypodermis) - The hypodermis (hypo – “under” + dermis – “skin”)

or subcutaneous (sub – “below” + cutaneous) layer

General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao

lies below the skin and is made up of loose connective and adipose tissues.

- The hypodermis binds the skin to underlying organs while allowing the skin to move somewhat independently of underlying structures.

- Adipose tissue in the hypodermis provides padding and shock-absorption that helps to protect underlying tissues from damage; it is also important in insulating against loss of body heat.

- Because the subcutaneous layer contains numerous blood vessels but no vital organs, it is a near-ideal place to inject drugs. This is why so many drugs are administered through subcutaneous injection by a hypodermic (hypo-“under”+ dermic – “skin”) needle.

Types of skin 1. Thin skin - Covers all parts of the body except palms, palmar

surfaces of the digits, and soles - Epidermis is thin - Stratum lucidum lacking; stratum spinosum and

stratum Corneum are thin - Has fewer dermal papilla, lacks epidermal ridges - Has hair follicles, arrector pili muscle and oil glands

but fewer sweat glands than thick - Sparser distribution of sensory receptors. 2. Thick skin - Covers palms, palmar surfaces of digits and soles - Thick epidermis - With stratum lucidum and thicker stratum

spinosum and stratum corneum. - More numerous dermal papillae thus has epidermal

ridges - Lack hair follicles, arrector pili muscle, sebaceous

gland. - Has more sweat glands that thin skin - Sensory receptors are more densely clustered. Skin color 1. Melanin - Produced by melanocytes - Yellowish-brown color of the epidermis - Lesser melanin – Light will penetrate easily into the

skin --- prone to cancer. 2. Collagen

- Scatters light from the dermis without altering its color

- Whiteness of white skin - Reflection of collagen 3. Blood - Hemoglobin and RBC - Scatters red light - Responsible for the pinkness in pigmented skin ***The amount of pigment, the thickness of dermis, and the degree of perfusion in dermal capillaries vary. Skin texture - Affect the thickness and smoothness of the

epidermis, by the quality of fibers in the dermis, and by the amount of fluid in dermal connective tissue.

Note: Both edema (accumulation of excess fluid in connective tissue) and dehydration can dramatically alter the appearance of skin Accessory structures of the skin 1. Hairs 2. Glands 3. Nails

Hairs - Composed of columns of dead, keratinized cells

bounded together by extracellular proteins Parts: 1. Shaft – superficial portion 2. Roots – penetrates into the dermis

Concentric layers of shaft and root: a. Medulla - Inner portion - 2 or 3 rows of polyhedral-shaped cells containing

pigment granules and hair spaces. b. Cortex - Middle portion - It forms the major part of the shaft - Contains pigments granules of the hair - White/gray hair – air bubbles c. Cuticle - Outermost layer - Single layer of flat cells that are heavily keratinized

General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao 3. Follicle – tubular invagination lined by stratified

squamous epithelium similar to epidermis; surrounds the root of the hair; made up of: a. External root sheath

- Downward continuation of epidermis - Contains the stratum basale

b. Internal root sheath - It forms the cellular tubular sheath between the

external root and the hair. Hair follicles are associated with: a. Sebaceous glands – secrete oil into the hair follicle

as well as nerve ending and smooth muscle to form the pilosebaceous apparatus.

b. Nerve endings – detects deflection of the hair shaft and also controls piloerection.

c. Smooth muscle – arrector pili ; affect piloerection 4. Bulb – the base of hair follicle; onion-shaped

structure; houses a. Papilla of the hair

- Nipple-shaped indentation - Contains areolar connective tissue - A lot of Blood vessels that nourish the growing hair

follicle b. Matrix

- Germinal layer of the cell w/c rise from stratum basale.

Function: - Responsible for growth of existing hairs - Produce new hairs when old hairs are shed.

5. Arrector pili muscle – smooth muscle cells

- Stimulated by autonomic nerve endings to contract pulling the hair shaft perpendicular to the skin surface during cold or fright.

6. Hair root plexuses

- Dendrites of neurons sensitive to touch - Generate nerve impulses in hair shaft is moved.

Glands

Sebaceous glands - Associated with hair follicles - Holocrine glands

The whole cell is secreted

General Histology and Histotechnique (1st semester; 2012-2013) by K-Dumlao Function: - It coats the surface of the hair and help keep them

from drying and becoming brittle - It prevents excessive evaporation of water from the

skin. - It keeps the skin soft and pliable - It inhibits growth of certain bacteria Sweat glands - 3-4 millions producing their secretion - Exocytosis – release secretion Two types: a. Ecrine - Simple coiled tubular gland - Common sweat gland Function: - Regulates body temperature - Waste removal b. Apocrine - Simple coiled tubular gland - Stimulated during emotional stress and sexual

excitement - Secretion of cold sweat

Nails - Plates of tightly packed, hard, keratinized epidermal

cells. - Cells form a clear, solid covering over the dorsal

surfaces of the distal portions of the digits - Parts:

1. Nail body – visible portion of the nail 2. Free edge – part of that may end pass the distal

ends of digits 3. Nail root – proximal edge of the nail plate that

is buried in the skin. 4. Lunula – whitish crescent shaped covered by

portion of the nail bed. 5. Hyponichium – nail bed; skin of nail bed;

provide support 6. Eponychium/cuticle – a horny epidermal

extension of the tip of the nail folds.