Skin Flashcards
What are the five main functions of the skin?
(1) Protection (2) Thermoregulation (3) Sensation (4) Metabolism (vitamin D, adipose) (5) Sexual attraction
Describe the 3 main divisions of skin.
(1) Epidermis (surface epithelium) - self-regenerating stratified squamous, produces keratin layer for protection (2) Dermis - dense collagenous connective tissue w/ hair follicles, sweat glands, blood/lymphatic vessels, sensory receptors/nerves, & connective tissue cells (3) Hypodermis - Rich in white adipose cells and contains large blood vessels that supply smaller vessels of dermis
What kinds of cells to all layers of the epidermis contain?
Keratinocytes - proliferating, differentiating, & differentiated
Name and describe the four layers of epidermis (deep to superficial).
(1) Stratum Basale - Keratinocytes begin in this deepest layer (stratum basale) = row of columnar cells resting on basal lamina, separate dermis & epidermis, mitosis exclusively here, (2) Stratum Spinosum - short projections attach via desmosomes to adjacent cells, aka “prickly layer” due to characteristic spines, cells produce cytokeratin (intermediate filament precursor to keratin) (3) Stratum Granulosum - keratinocytes become squamous cells w/ granules of keratohyaline, precursor to extracellular keratin, lipid-rich lamellar bodies(4) Stratum Corneum - most superficial, acellular, most functionally important, flat, keratinized scales, shed and replaced continuously, final kertin product (= cytokeratin & keratohyaline)
What layers do mucous membranes lack? Why?
Stratum granulosum & stratum corneum; Instead of protection by keratin, kept moist by glandular secretions
Name and describe the cell types in epidermis.
(1) Melanocytes - intervals among basal keratinocytes, produce melanin pigment (syntehsized from tyrosine and transferred as melanin granules to surrounding epithelial cells), (2) Langerhans - typically located in stratum spinosum & equivalent of macrophages in skin tissue, (3) Merkel cells - attached to keratinocytes by desmosomes, found in highly sensitive areas (e.g., fingertips - touch receptors)
Name and describe the 2 layers of dermis.
(1) Papillary - most superficial, loose connective tissue immediately beneath epidermal basement membrane, contains blood vessels, nerves, and sensory receptors (e.g., Meissner’s corpuscles for light touch) (2) Reticular - dense, irregular collagenous connective tissue
What layer of the dermis contains blood vessels, nerves, and sensory receptors?
Papillary layer
What is the hypodermis? Where is it thickest versus absent? What does it contain?
Fatty layer beneath the dermis; Thickest = abdominal wall, Absent = eyelid, scrotum, penis, & dorsal side of hand; Fibroblasts (synthesize collagen & elastin), Pacinian corpuscles (for deep touch)
Name the epidermal derivatives.
Hair follicles, sebaceous glands, eccrine sweat glands, apocrine sweat glands, mammary glands
What encases hair follicles? What do they contain?
Invagination of epidermis into dermis = external root sheat; Specially organized keratin in long tubular structures, generous blood & nerve supplies;
Describe the 3 states of hair follicles.
(1) Anagen - growing follicles synthesize hair, long & most numerous in scap (2) Catagen - resorbing follicles in short phase of regression that signals end of active hair growth (3) Telogen - Resting follicles contain fully formed hair
Name and describe the 3 types of sweat glands.
(1) Sebaceous: pear-shaped alveolar glands, secrete sebum (oil substance) to moisturize and waterproof hair, usually attached to hair follicles near arrector pili muscle (= hair “stand up”), extensive capillary plexus (2) Eccrine: thoughout most of skin, long tubules extending from epidermis deep into dermis/hypodermis, secretory portion = tightly wound, looks like collection of cross-sectioned tubuled, encased by myoepithelial cells (contain actin filaments, recieve input from nerve fibers –> contract & expulse sweat from gland (3) Apocrine: much larger size & thicker secretion than eccrine, straight, narrow ducts run parallel to hair follicles and frequently open in pilosebaceous canal, occur in axilla, areola of nipple, labia majora, & circumanal region
What organs do not have eccrine sweat glands?
Glans penis, inner surface of foreskin, clitoris, & labia minora
What is the basic structure of mammary glands? Where is milk collected? In which sex are mammary glands found? When are they fully developed?
Inner cuboidal epithelium & outer layer of myoepithelial cells, alveoli make up tubuloalveolar glands, or lobes, which connect via lactiferous ducts to base of nipple; ducts –> Lactiferous sinuses (spindle-shaped enlargements); Both sexes; in females, after partuition;
What are the important structural changes that occur in mammary glands over the course of a female’s lifetime?
(1) Nonpregnant, sexually mature - glandular tissue = ducts w/ small terminal alveoli embedded in abundant connective tissue stroma that contains many adipose cells (2) During pregnancy - hormonal stimulation –> proliferation of intralobar ducts & terminal alveoli, epithelial cells become enlarged & vacuolated as milk fat production increases (3) After parturition - gland enters active secretory phase & produces watery milk containing membrane-bound lipid droplets as well as milk proteins, lactose, & cellular debris (4) Suckling - release of prolactin (from anterior pituitary) –> maintains milk production & oxytocin (from posterior pituitary) –> contraction of myoepithelial cells & ejection of milk
Name and describe the 3 different types of exocrine secretion, including which glands utilize each.
(1) Merocrine (eccrine) secretion - exocytosis = mode of both eccrine & apocrine glands (2) Apocrine secretion - portion of plasma membrane containing secretion buds off from cell = mode of mammary glands & mucous-producing cells NOT apocrine sweat glands (3) Holocrine secretion - entire cell disintegrates in order to release its secretion = Sebaceous glands
Name the 4 layers of the epidermis and the state of kerating associated with each.
Stratum basale, Stratum spinosum - cytokeratin, Stratum granulosum - keratohyaline, Stratum corneum - keratin
What are the important differences between sebaceous glands, eccrine sweat glands, and apocrine sweat glands?
Sebaceous - sebum to protect hair, Eccrine - thin, watery sweat all over skin, Apocrine - much larger, produce thicker sweat in select areas; Sebaceous undergoes holocrine secretion, both sweat glands undergo eccrine secretion
What is the structure of mammary gland? What key differences do you expect to see between active and inactive mammary tissue?
Acini make up lobes, which empty into lactiferous sinuses via lactiferous ducts; Inactive tissue - will not be producing much milk, lumina will be empty and epithelial cells will be smaller & have fewer visible lipid droplets; Active tissue - abundant lipid droplets, visible milk, & taller cells
What are rete ridges? What purpose do they serve?
Downgrowths of epidermis into dermal layer; Generate strong bond between epidermis and dermis and help skin resist shearing forces
What are key histological features for distinguishing epidermal layers?
Stratum basale - dark staining DNA = mitosis, cuboidal; Stratum spinosum - tonofilaments (keratin filaments) in cytoplasm, heavy staining nucleoli due to keratin production, & prickly spines connecting cells; Stratum granulosum - more flattened and stain noticeably darker (keratohyaline) than deeper layers; Stratum corenum - anucleated, filled w/ keratin filaments, most flattened appearance, displaying sheets of keratin
What layer of epidermis has cells that produce lipid-rich lamellar bodies? What purpose do these lamellar bodies serve?
Stratum Granulosum; Secreted to form lipid layer to prevent water loss
What mediates the “prickle” intercellular connections/interactions in stratum spinosum?
Desmosomes, prickles due to fact that they do not retract during fixation
