Integumentary system

What is composed of the integumentary system?

Skin

Where is skin thickest?

Heels

Where is skin thinnest?

Eyelids

What is the skin’s functions?

• Protection 

• Temperature regulation 

• Excretion of urea, salt, and sweat

• Production of vitamin D

• Sensory reception 

Epidermis

The most outer layer of the skin, it is keratinized stratified squamous epithelium

Keratinization

Accumulation of protective keratin (skin cells which produce keratin die off as they reach the upper layer, leaving only keratin behind)

Stratum basale 

• Deepest layer of the skin, attaching to the dermis 

• Cells here ACTIVELY divide 

• Contains merkel cells and melanocytes 

What are the 3 layers of skin from deep to superficial?

Hypodermis, dermis, and epidermis

Stratum spinosum 

• Cells here take on a spiny appearance as they extend 

• Contains many intermediate filaments (tonofilaments) to resist tension and contains protein prekeratin for structure 

• Contains Langerhans cells 

Stratum granulosum

• Contains keratinocytes and tonofilaments

• End of the skin cell’s life

What do tonofilaments contain?

• Keratohyaline granules (from keratin)

• Lamellated granules (waterproofing glycolipid)

Stratum lucidum

• Only found in thick skin, such as the palms and soles of the feet

• Around 3 rows of dead keratinocytes to increase strength

• Appears clear

Stratum corneum 

• Thick layer of dead keratinocytes

• Thickened plasma membranes 

• Protects skin from abrasion and penetration  

Keratinocytes 

• 90% of cells 

• Produces keratin (protective fibrous protein)

• Produces antibodies and enzymes

Melanocytes

• Produces melanin for protection, which is then transferred to keratinocytes for protection

Langerhan cells 

• Immune response 

• From red bone marrow 

Markel cells

Connection to sensory nerves with Merkel discs for the sensation of touch

Dermis layer

The second layer of skin, which is the connective tissue and contains the blood vessels and nerves

• Contains flexure lines

Flexure lines 

Permanent creases that can be seen on the exterior of the body due to deep connective tissue 

What are the names of the two layers of the dermis

• Papillary layer (top layer near the epidermis)

• Reticular layer (bottom layer)

What does the outer papillary region contain

• Areolar connective tissue

• Dermal papillae connect to the epidermis

• Meissner corpuscles for the sensation of touch

• Free nerve ending (very sensitive)

Reticular region 

• 80% of the thickness of the dermis layer 

• COntains dense irregular connective tissue 

What does the reticular region contain, excluding the skin tissue?

• Adipose cells

• Hair follicles

• Nerves

• Sebaceous oil gland

• Sudoriferous sweat glands

• Collagen and elastic fibres

Lines of cleavage

Also known as tension lines

• Indicates the predominant direction of underlying collagen fibres 

• Creaveses throughout the body (wrinkles)

Epidermal ridges 

• Contours of the underlying dermal papillae 

• Formation of fingerprints 

• Increase grip through friction 

• Raised bumps 

What is the hypodermis made of?

Areolar and adipose CT

Hypodermis

• Deepest layer of the skin, also known as the superficial fascia 

• Anchor’s skin 

• Helps insulate 

What are the 3 pigments that contribute to skin colour?

Melanin, carotene, and hemoglobin 

Melanin

Created from tyrosine, shades of skin

Ie. freckles 

Carotene

Yellowish pigment

Found in all skin types in the dermis, hypodermis, and stratum corneum 

Hemoglobin

Usually found in lighter skin, causing a red hue to the skin

Nevus

Benign overgrowth of melanocytes

• Commonly known as a mole 

Albinism

Inability to produce melainin

Vitiligo

Loss of melanocytes which leads to patches of whitened skin

What are nails made of?

Hard keratin (think of modified epidermis)

What are the main parts of the nail

• Free edge 

• Body or plate 

• Lunula 

• Root - cell division occurs here with the matrix 

• Eponychium - cuticle 

What is hair made of?

Flexible, dead, keratinized cell

What are parts of the hair?

• Shaft- above the surface 

• Root - Into the dermis, site of division 

• Hair follicle - Surrounds the root for protection 

• Papilla - Blood supply

Sebaceous oil glands, arrector pili muscles, and hair root plexi 

What are the 3 concentric layers of keratinized cells?

Medulla - Central core

Cortex - Surrounds medulla

Cuticle - Outermost layer 

Vellus hairs

Softer body hairs, usually on women and children

Terminal hairs

Coarser body hairs, usually in the pubic, armpit, scalp, and chest hair 

What are some main factors in hair thinning?

• Aging

• Male pattern baldness 

• Weight loss 

• Post-partum 

• Disease 

• Stress 

Merocrine secretion  

These types of cells secrete the product  

• Eccrine sweat glands 

Aprocine secretion

These types of cells pinch off vesicles to release the product

• Mammary glands

Holocrine secretion

These types of cells break down entirely to release the product 

• Sebaceous glands  

What type of glands are sebaceous glands?

Simple alveolar glands that use holocrine secretion

Sebum

Oily substance that collects dirt, softens hair and skin up, and plays an anti-bacterial role

Sweat

Filters blood

• 99% of water and some salts 

• 2% urea with metabolic waste 

Where are sebaceous glands found?

Everywhere except the palms and soles of our feet

Eccrine gland

A type of sweat gland that produces sweat through merocrine secretion

• True sweat

• Temperature control

Ceruminous glands and mammary glands

A type of gland that is a modified version of the apocrine glands 

• Simple coiled tubular 

• Ear wax production

• Collects debris and pathogens 

First-degree burn 

Epidermis is damaged 

Second-degree burn

The upper part of the dermis is damaged

• Blisters 

• Scars 

Third-degree burn

Dermis is fully damaged

• appears white, red, or black 

Basal cell carcinoma

Least malignant and the most common

Squamous cell carcinoma

Keratinocytes of the stratum spinosum (may appear more black)

Melanoma

Cancer of the melanocytes (deep within)

• most dangerous because of the rate of duplication 

Where does the epidermis develop from?

Ectoderm

Where does the dermis/hypodermis develop from?

Mesoderm

Where do the melanocytes develop from?

Neural crest cells in the endoderm

Describe the timeline of skin development in the fetus 

The 4th month is well-formed 

The 5th to 6th month has lanugo (hairs)

7th month, sebaceous glands form to produce vernix caseosa (waxy substance)

Epidermal wound healing

Superficial wounds that only affect the epidermis 

Deep wound healing 

The dermis and/or subcutaneous layer is damaged 

( Macrophages - inflammation - clot - protein fills - scar tissue from fibroblast replaces it )