Lecture 11: Integument Flashcards
Integument layers
-Epidermis (epithelium)
-Dermis; papillary + reticular (connective tissue)
-Hypodermis
Periderm
Unilaminar embryonic integument. Specialized to interact with amniotic fluid and protect the epidermis developing basal to it.
Papillary dermis
More cellular, loose CT. Smaller dermis layer closer to the epidermis
Reticular dermis
More fibrous, dense irregular CT. Significantly larger than papillary dermis.
Dermal papillae
Small bumps that extend from the dermis and invaginate the epidermis. Interrupted by interpapillary pegs (rete). Increases mechanical strength of layers.
Capillary plexus
Comprised of deep (lower) and shallow (upper) sections within the dermis. Blood supply for epidermis. Shunting blood to/from the shallow plexus helps in temperature regulation.
Functions of the integument
-Structure
-Immune barrier/surveillance
-Fluid retention
-Vitamin D production
Keratinocytes
Primary epidermis cell. Produces keratins. SCs located in stratum basale. Connected by desmosomes.
Epidermis layers
Basal to apical:
-Stratum basale
-Stratum spinosum
-Stratum granulosum (LM visible in thick skin only)
-Stratum lucidum (LM visible in thick skin only)
-Stratum corneum
Stratum basale
Basal layer of epidermis. Contains keratinocyte stem cells and melanocytes.
Stratum spinosum
Contains daughter cells from basal stem cells through asymmetric vertical division.
Stratum granulosum
Contains cells with visible keratohyalin granules
Stratum lucidum
0-2 cells thick, contains dying cells that still retain their cytoplasm.
Stratum corneum
Composed of keratin sheets bound by lipids and keratohyalin; originally contained in lamellar bodies of cells. Fillagrin precursor becomes a glue for keratin sheets that cells release as they die. Forms an H2O barrier.
Minor epidermis cell types
- Melanocytes
- Langerhans cells
- Merkel cells
Melanocytes
Produce melanin and export to surrounding keratinocytes via cytocrine secretion of melanosomes. Primarily responsible for skin color and respond to UV radiation.
Langerhans cells
Resident dendritic APCs of the integument.
Merkel cells
Serve some role in interfacing with the nervous system and in mechanosensation.
Nervous elements of the dermis
-Meissner’s corpuscles
-Pacinian corpuscles
-Free nerve endings
-Ruffini endings
-Krause corpuscles
Meissner’s corpuscles
Located in papillary dermis. Sense touch.
Pacinian corpuscles
Located in deep dermis/hypodermis. Sense pressure.
Hypodermis
Deep, adipose tissue-rich layer of integument.
Free nerve endings
Located in dermis and epidermis. Can associate with hair follicles sensing hair deflections. Also sense pain and temperature.
Ruffini endings
Located in dermis. Sense sustained pressure.
Krause corpuscles
Located in dermis. Sense light touch and low frequency vibrations.
Eccrine sweat glands
Coiled tubular serous glands that traverse the epidermis. Ducts are stratified cuboidal.
Apocrine sweat glands
Large tubular serous glands. Found only in a few places, e.g. axilla. Typically secrete into hair follicles.
Hair follicle structure
Invagination of the epidermis. Center hair shaft supported by inner and outer root sheaths (IRS, ORS)
Inner root sheath
IRS is dominant to the follicle base and surrounds newly formed hair.
Inner root sheath layers
- Cuticle
- Huxley’s layer
- Henle’s layer
Outer root sheath
Dominant to the follicle apex, continuous with the epidermis.
Hair bulb
Base of hair follicle from which hair shaft grows. Includes dermal papilla of hair and hair matrix
Dermal papilla of hair
Connective tissue which organizes follicle development.
Hair matrix
Epithelial region within follicle base which grows the hair shaft.
Glassy membrane
Thick basement membrane continuous with epidermal basement; separates the follicle epithelium from CT parts. Facilitates the relative motion of hair as it grows.
Radial layers of the hair shaft
Deep to outer:
1. Medulla
2. Cortex
3. Cuticle
Hair growth phases and duration (in scalp)
- Anagen (2-3 years)
- Catagen (2-3 weeks)
- Telogen (2-3 months)
Anagen
IRS elongates and pushes the hair bulb deeper into the dermis/hypodermis
Catagen
Apoptotic regression of follicular epithelium, pulling the hair bulb back to the epidermis which forces the hair shaft out.
Telogen
Resting phase throughout which the hair shaft is shed. Dermal papilla of hair and bulge region must be in close contact to re-enter anagen.
Bulge region of hair
Small bulge in hair follicle where stem cells are found. Associates with arrector pili muscle.
Arrector pili muscle
Attaches to follicle at the bulge; innervated by sympathetic nerve fibers to raise hair shaft erect.
Types of burns
1st degree: epidermis
2nd degree: epidermis + superficial dermis
3rd degree: epidermis + deep dermis (nerve endings destroyed)
4th degree: epidermis, dermis, underlying bones/muscles/tendons (nerve endings destroyed)
Raynaud’s phenomenon
AKA Renault’s disease. Loss of blood flow/sensation to the extremities. Defect in arteriovenous anastamosis control.
Stratum corneum brick and mortar model
S. granulosum cells fill with lamellar bodies/granules with lipids, as well as other structural lattice proteins and keratin filaments bundled by filaggrin. Upon apoptosis, vesicles (mortar) are released to fill spaces between dead keratinocytes (bricks).
Stratum corneum protein-lipid barrier molecular components
Outer lipid barrier with involucrin structural proteins. Inner tonofilaments bound by filaggrin, loricrin, and small Pro-rich proteins.
Epidermal protective functions
Barrier to water, macromolecules/ions/toxins (except small moderately lipophilic substances), radiation (melanin), pathogens (antimicrobial peptides)
Tanning process
- Photo-oxidation of melanin
- Redistribution of melanin granules to upper layers
- Increased # of melanin granules in skin -> color
Keratinocyte vitamin D production
UV light cleaves 7-dehydrocholestrol into pre-vitamin D3 in epidermis; later transported from dermis by blood to liver then kidney and converted into active vitamin D.
Vitamin D effects
Stimulates Ca absorption by GI, Ca reabsorption by kidney, bone resorption by Ocls
Integument body temperature regulation mechanisms
- Activation of eccrine sweat glands
- Vasodilation of cutaneous blood vessels
- Arteriovenous anastamosis
Arteriovenous anastamosis mechanism
Closure of AVA directs more blood toward the upper horizontal plexus, closer to the skin. Results in increased heat lost through radiation.
