The Integumentary System Flashcards
Components of the Integumentary System
Skin (Cutaneous Membrane - Epidermis & Dermis) & Accessory Structures (Hair, nails, exocrine glands)
Functions of the Integumentary System
- physical and immunological protection
- thermoregulation (capillary beds, fat insulation, sweat glands, etc.)
- sensation
- metabolic functions
Four Tissue Types
- Epithelium
- Connective Tissue
- Muscle
- Nerve
Epithelium
type of tissue, covers surface, forms boundaries
Connective Tissue
supports epithelium, provides strength and resiliency
Muscle
type of tissue, controls diameter of blood vessels, adjusts position of hairs
Nerve
type of tissue, controls smooth muscles, generates sensation, stimulates glands
Features of the Skin
- largest organ system of body
- covers area of ~2 sq. m
- constitutes ~15% body weight
- ranges in thickness from 0.5mm (axilla or inner thigh) to 4.0mm (heel, toe pad) - average 1-2mm
Structure of Skin
Outer: Epidermis –> Dermis (epi- and dermis = cutaneous membrane) –> hypodermis: Inner
Cutaneous Membrane
epidermis + dermis of skin, interlock - strengthens connection between them
Keratinocytes
skin cells, filled with fibrous protein called keratin
Stratum Germinativum
aka stratum basal
- composed of large basal cells (stem cells that divide to give rise to new keratinocytes)
- firmly attached to basal lamina
Stratum Spinosum
- “spiny layer”
- composed of keratinocytes
- keratinocytes contain bundles of tonofilaments (intermediate filaments - attach to desmosomes)
- desmosomes attach keratinocytes together
- keratinocytes still capable of division (not fully differentiated)
Stratum Granulosum
- “granular layer”
- develop large numbers of keratin filaments
- synthesize keratohyalin granules (keratohyalin forms matrix around filaments)
- secrete lipids that fill spaces between cells (forms water-repellant sealant)
- keratinocytes die –> move up into cornified layer
Stratum Lucidum
- “clear layer”
- found only in thick skin of finger tips, palms and soles of feet
- large amounts of keratin and thickened plasma membranes
Stratum Corneum
- corn = hard or hoof-like
- multiple layers of dead cells
- cells continuously shed and replaced
- water repellant barrier
- protects against abrasion and microbe invasion
Thick vs. Thin Skin
Thin Skin:
- stratum corneum much thinner
- other layers less clear
- papillae less well developed
- has all the same components (except stratum lucidum) but everything is just thinner
Melanocytes
- constitute ~8% of epithelial cells
- produce melanin pigment
- cells contain long, slender processes (insert between keratinocytes)
- transfer melanin granules to keratinocytes
- skin cells are pigmented but do not produce pigment themselves
Langerhans Cell
- arise in bone marrow and migrate to epidermis
- phagocytic cells
- function in immune response (modify antigens so that other cells can identify them as foreign - just specialized macrophages)
Merkel Cell
- least numerous cell type
- located in basal layer
- function in touch sensation
Skin Colour
Due to combination of:
- dermal blood supply
- variable quantities of three pigments (produced by melanocytes) = melanin (brown/black), pheomelanin = red/yellow, carotene (yellow/orange)
Melanin
brown/black
Pheomelanin
red/yellow
Carotene
yellow/orange
Pale Skin
- pink colour due to hemoglobin in dermal blood vessels
- dilation of blood vessels during inflammation increases red colour (ie. blushing)
- lowered oxygenation of blood = hemoglobin darkens & skin appears blue - cyanosis
Cyanosis
in pale skin:
- lowered oxygenation of blood –> hemoglobin darkens –> skin appears blue
Dark Skin
- due to increased amount of pigment
- number of melanocytes remains constant
- rate of melanin synthesis & transfer (from melanocytes –> keratinocytes) increases
Function of Melanin
- absorbs UV and prevents UV-induced DNA damage
- pigment accumulates around cell nucleus
- melanocytes increase rate of synthesis in response to UV exposure = tanning (making more melanin and moving it faster)
Tanning
in response to UV exposure, melanocytes increase rate of synthesis of melanin and move it out faster
UV-Induced Skin Damage
Epidermis:
- chromosomal damage (melanin is not enough to filter out UV rays so DNA damage occurs)
- causes skin cancer
Dermis:
- damage to fibroblasts
- alters composition of extracellular matrix (cannot produce fibres as well, skin is weaker)
- premature wrinkling
Dermis
connective tissue layer beneath epidermis
Two components:
1. Superficial papillary layer
2. Deep reticular layer
Papillary Layer
Superficial layer of dermis
- thin
- consists of areolar CT
- papillae increase area of contact with epidermis
- contain nerve endings (reticular layer is too thick): touch, temperature, pain, tickle/itch
Reticular Layer
deep layer of dermis
- thick
- consists of dense irregular CT = strength in any direction
- many elastic fibres
- provides extensibility & elasticity to skin
Lines of Cleavage
- collagen fibre bundles in dermis align differently in different regions of skin
- align along lines of tension
- clinically significant (parallel cut will close with minimal scarring, perpendicular cut will remain open (everytime muscle contracts it will pull cut open)
Subcutaneous Layer
aka hypodermis or superficial fascia
- “packing material” between muscle & skin
- stabilizes position of skin relative to underlying tissues
- loose connective tissue that stores fat
- distribution of subcutaneous fat differs between sexes - influences body shape
Accessory Structures
hair, nails, exocrine glands
Hair
- ~5 million hairs on body (only 2% on head)
- covers all body surfaces except palmar surfaces of hands and fingers and plantar surfaces of feet and toes
- head = UV protection, thermal insulation
- eyes and nose = air filter
- general body = touch sensation
Sebaceous Gland
part of hair follicle, secretes sebum (an oily lipid)
Arrector Pili Muscle
part of hair follicle, makes hair stand up
Hair bulb
part of hair follicle, anchors the hair
Hair papilla
part of hair follicle - capillary bed
- provides nutrients for cells
Hair Growth Cycle
Active Phase (2-5 years, continued growth, approx. 0.33mm/day) –> regression –> resting phase (loosening of attachment in follicle) –> reactivation (loss of club hair) –> active phase
Hair Growth (Scalp Hair)
- grows ~2-6 years
- rests ~3 months
- ~85% in growth phase at any given time
- as you age, follicles go into resting phase and never re-enter the growth phase –> hair thinning/loss
Hair Thinning/Loss
as you age, follicles go into resting phase and never re-enter the growth phase
Hair Types
- Vellus hairs
- Intermediate hairs
- Terminal hairs
Vellus hairs
fine “peach fuzz” hair found over most of the body
Intermediate hairs
hairs of the upper and lower limbs, change in response to sex hormones (create coarser hair)
Terminal hairs
heavy and more pigmented - scalp, eyebrow, & eyelash hair
Nails
- protect exposed tips of the digits
- limit distortion when digits subjected to mechanical stress
Lunula
“little moon”, white part of nail
- appears lighter because it has more collagen fibres - cannot see capillary beds as well
Eponychium
part of nail - cuticle
- attaches skin of finger to nail
Glands of the Skin
Two types: EXOCRINE
- Sebaceous glands
- Sweat glands
Sebaceous Glands
exocrine, secrete oily lipid (sebum)
- coats hair shafts and skin surface
- holocrine secretion (entire cell is the secretion)
- secretes directly onto skin
Sweat Glands
exocrine, secrete water and electrolytes
- simple, coiled tubular glands
- Two Types: 1) Merocrine (eccrine) - secrete normal sweat, 2) Apocrine - secrete odiferous sweat, USING MEROCRINE SECRETION
BOTH TYPES STILL USE MEROCRINE SECRETION (normal exocytosis)
Acne
- inflammation of sebaceous glands and follicles
- usually occurs at onset of puberty - glands increase in size, sebum secretion increases in response to sex hormones
- inflammation results from: blockage of ducts or bacterial infection of glands
- treated by antibiotics (kill bacteria causing infection)
Merocrine Sweat Glands
- most common, distributed over majority of body
- secrete water and electrolytes
- regulate body temperature
Apocrine Sweat Glands
- name is a misnomer - secrete by MEROCRINE secretion
- less numerous than eccrine glands
- distribution: axilla, groin, areolae of breast, bearded region of face in males
- secrete water, electrolytes, lipids, proteins (acted on by bacteria to produce odors)
- stimulated during emotional stress and sexual excitement
Modified Sweat Glands
Ceruminous glands and Mammary glands
Ceruminous Glands
- located in external auditory canal of ear
- modified merocrine sweat glands
- secrete waxy cerumen (ear wax)
Mammary Glands
- modified apocrine sweat glands
- regulated by interaction of sexual and pituitary hormones
- supply nutrition for newborn
