The Integumentary System:
The main organ of the integumentary system is the SKIN. Its functions include:
There are 3 distinct regions:
- Exterior body cover
- Protection and first line of defense
- Protection from mechanical (physical) damage
- Protection from chemical damage
- Protection from thermal (heat) damage
- Protection from microbial invasion
- Insulation and cushioning
- Excretes wastes (sweat, urea, salts, water) in sweat or perspiration
- Produces antibodies and immune cells for immunity
- Synthesizes vitamin D in a form the body can use
- Contains the sensory organs
- Maintains thermoregulation of body temperature
There are 3 distinct regions:
- Epidermis (superficial)
- Dermis (underlying)
- Hypodermis (subcutaneous) (adipocyte tissue and blood supply underneath)
Epithelial Cells:
Epithelial tissue makes up the skin of the integumentary system.
The Epidermis:
- Superficial layer
- Keratinized stratified squamous epithelium
- 4 cell types:
- Keratinocytes (keratin cells): produce tough keratin protein for strength and durability
- Melanocytes: produce the pigment melanin and protect against UV radiation and add color to the skin
- Basal cells: very active mitosis to replace dead cells
- 4-5 layers:
- Stratum basale (basal layer)
- Bottom or deepest epidermal layer
- Single row of cells
- Constantly undergo mitosis or cell division
- Produce millions of new cells each day
- Contain melanocytes, which are the pigment-producing cells (25%)
- Contain basal cells, which are always dividing (75%)
- Receive nourishment from the dermis via diffusion
- Stratum spinosum (spiny layer or warm layer)
- Lies just above the basal layer
- Cells look spiky
- Cell division occurs here but not as much
- Receive nourishment from the dermis via diffusion
- Stratum granulosum (granular layer)
- Lots of granules are found here and they contain glycolipids, which waterproof the skin, as well as keratin subunits for building keratin
- Stratum lucidum (clear or translucent layer)
- Thin transluscent layer of flat, dead, keratinocytes
- ONLY present in THICK skin, like on the palms of the hands and soles of the feet
- Stratum corneum (horny layer)
- Outermost epidermal layer (most superficial)
- Approximately 20-30 cell layers thick
- Consists of only dead cells with flattened remnants containing keratin
- The cells in this layer are always shedding and being replaced by cell division of the deeper basal cells in the basal layer
- Stratum basale (basal layer)
The Dermis:
The dermis is a thick layer underlying the epidermis. It is dense, fibrous, and consists of a papillary layer and a reticular layer. Throughout the dermis, elastic and collagen fibers may be found. They make the dermis tough and durable and flexible. This aids in keeping the skin hydrated as well, elastic and stretchy. Defense cells, including phagocytes, and fibroblasts and adipose cells are also located here.
Papillary Layer:
Papillary Layer:
- Contains dermal papillae, uneven projections that produce the unique loops and ridges that make our fingerprints and footprints
- Capillaries are found here, and they nourish the upper epidermis and play a role in regulating body temperature
- They allow heat to radiate up to the surface of the skin
- Pain receptors are found here
- Touch receptors (Meissner's corpuscles) are found here
- Free nerve endings are found here, and they are responsible for feelings of "itchiness" or "tickling" or "pins and needles"
- Underlies the papillary layer
- Deepest layer of skin
- Blood vessels found here, which enable the dermis to play a key role in regulating body temperature
- Sweat glands (eccrine and apocrine) are found here
- Oil glands are found here (sebaceous)
- Pressure receptors (Pacinian corpuscles) are found here
Dermal Receptors:
There is a rich nerve supply in the dermis, which is very sensitive and receptive to stimuli. Many nerve endings have receptor organs that respond to stimuli, including
- pain
- pressure (light, heavy, extended)
- temperature extremes (hot, cold)
- itching
- tickling
- pins and needles
Meissner's (Tactile) Corpuscle:
- Responds to touch
- Responds to light pressure or light touch
- Usually found in hairless areas
Pacinian (Lamellar) Corpuscle:
- Responds to deep pressure
- Responds to extended pressure
Merkel Cell (Tactile Disc):
- Mechanoreceptors
- Detect light touch
- Highly abundant in fingertips
- A rare type of cancer may rarely affect these cells (Merkel cell carcinoma)
- Aggressive skin cancer
- Hard to treat
- Mechanoreceptor
- Slow to adapt
- Sensitive to skin stretch
- Lots of them are found around the fingernails
- Respond to sustained pressure
Root Hair Plexus:
- Specialized nerve fiber endings associated with the hair follicle
- Mechanoreceptor
- Associated with touch
Free Nerve Endings:
- Cutaneous nociceptors
- Detect pain
- Associated with itching
- Associated with tickling
- Associated with feeling of pins and needles
Hair Follicles and Hair and Glands:
- Sebaceous Gland: oil gland found almost all over the skin, other than the palms and soles, whose duct empties into a hair follicle and occasionally directly onto the skin and keep the hair lubricated
- Sebum: product of the sebaceous gland, consisting of oil substances and fragmented cells for skin lubrication
- Blackheads: buildup of dried sebum + bacteria in the hair follicle
- Whiteheads: buildup of dried sebum in the hair follicle
- Acne: active infection of the sebaceous glands
- Sebum: product of the sebaceous gland, consisting of oil substances and fragmented cells for skin lubrication
- Sudoriferous Gland: sweat gland that opens to a pore
- Exocrine glands
- Eccrine gland: produces clear perspiration made of water, salts and urea
- Aprocrine gland: found mainly in the axillary, genital and alveolar areas and produces a lipid-rich, milky, protein-based substance containing water, salts and urea, which provide nutrients for bacteria on the skin, and is commonly referred to as sweat
- Exocrine glands
- Hair: found all over the body except for the palms and soles, external genitals, nipples and lips
- enclosed in a hair follicle
- part enclosed inside the follicle is the root
- part projecting from the skin is the shaft
- formed via mitosis of germinal epithelial cells at the base of the follicle in the hair bulb
- growth is due to pushing of daughter cells away from growing region, where they become keratinized (dead)
- consists of a central region (medulla)
- surrounded by a cortex
- protected by a cuticle
- associated with a tiny muscle called an arrector pili muscle that connects the hair follicle to the dermis and contracts during cold or fright, creating "goose bumps" or "chills" and aids in warming the surface of the body
The Hypodermis/Subcutaneous Tissue:
The subcutaneous tissue, or hypodermis, lies under the skin and consists of adipocytes (fat cells) for insulation, and larger blood and lymph vessels. In fact, this is the vessels where IV catheters are inserted and some blood is drawn.
Nails:
- Nail: transparent, colorless, hard material made of keratin
- Lunule: the crescent-shaped region at the bottom of the nail matrix
- Free edge (visible attached portion)
- Root (part embedded in the skin)
- Nail bed (part the nail sticks to and overlies)
- Nail folds (skin folds that overlap the nail)
- Cuticle (thick proximal nail fold)
- Nail matrix (germinal cells are here, the thickest proximal part of the nail bed, responsible for nail growth)