Skin

Question 1

What are the five main functions of the skin?

Answer 1

(1) Protection (2) Thermoregulation (3) Sensation (4) Metabolism (vitamin D, adipose) (5) Sexual attraction

Question 2

Describe the 3 main divisions of skin.

Answer 2

(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

Question 3

What kinds of cells to all layers of the epidermis contain?

Answer 3

Keratinocytes - proliferating, differentiating, & differentiated

Question 4

Name and describe the four layers of epidermis (deep to superficial).

Answer 4

(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)

Question 5

What layers do mucous membranes lack? Why?

Answer 5

Stratum granulosum & stratum corneum; Instead of protection by keratin, kept moist by glandular secretions

Question 6

Name and describe the cell types in epidermis.

Answer 6

(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)

Question 7

Name and describe the 2 layers of dermis.

Answer 7

(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

Question 8

What layer of the dermis contains blood vessels, nerves, and sensory receptors?

Answer 8

Papillary layer

Question 9

What is the hypodermis? Where is it thickest versus absent? What does it contain?

Answer 9

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)

Question 10

Name the epidermal derivatives.

Answer 10

Hair follicles, sebaceous glands, eccrine sweat glands, apocrine sweat glands, mammary glands

Question 11

What encases hair follicles? What do they contain?

Answer 11

Invagination of epidermis into dermis = external root sheat; Specially organized keratin in long tubular structures, generous blood & nerve supplies;

Question 12

Describe the 3 states of hair follicles.

Answer 12

(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

Question 13

Name and describe the 3 types of sweat glands.

Answer 13

(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

Question 14

What organs do not have eccrine sweat glands?

Answer 14

Glans penis, inner surface of foreskin, clitoris, & labia minora

Question 15

What is the basic structure of mammary glands? Where is milk collected? In which sex are mammary glands found? When are they fully developed?

Answer 15

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;

Question 16

What are the important structural changes that occur in mammary glands over the course of a female’s lifetime?

Answer 16

(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

Question 17

Name and describe the 3 different types of exocrine secretion, including which glands utilize each.

Answer 17

(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

Question 18

Name the 4 layers of the epidermis and the state of kerating associated with each.

Answer 18

Stratum basale, Stratum spinosum - cytokeratin, Stratum granulosum - keratohyaline, Stratum corneum - keratin

Question 19

What are the important differences between sebaceous glands, eccrine sweat glands, and apocrine sweat glands?

Answer 19

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

Question 20

What is the structure of mammary gland? What key differences do you expect to see between active and inactive mammary tissue?

Answer 20

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

Question 21

What are rete ridges? What purpose do they serve?

Answer 21

Downgrowths of epidermis into dermal layer; Generate strong bond between epidermis and dermis and help skin resist shearing forces

Question 22

What are key histological features for distinguishing epidermal layers?

Answer 22

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

Question 23

What layer of epidermis has cells that produce lipid-rich lamellar bodies? What purpose do these lamellar bodies serve?

Answer 23

Stratum Granulosum; Secreted to form lipid layer to prevent water loss

Question 24

What mediates the “prickle” intercellular connections/interactions in stratum spinosum?

Answer 24

Desmosomes, prickles due to fact that they do not retract during fixation

Question 25

What are keratin filaments? Where are they found? To what do they connect?

Answer 25

Form of intermediate filament; found in stratum spinosum; Connect to desmosomes at plasma membrane

Question 26

What is the primary difference between thick and thin skin?

Answer 26

Thickness of lipid layer that coats plasma membrane of stratum corneum cells

Question 27

Where do melanocytes localize? Between which keratinocytes in the epidermis do they extend processes? What function do melanocytes serve? How is melanin produced and transported?

Answer 27

Stratum basale; Stratum basale & stratum spinosum; Produce pigment melanin that protects against ultraviolet radiation; Produced in membrane-bound organelles called melanosomes that derive from Golgi, Melanosomes transported to ends of of melanocyte processes & neighboring keratinocytes phagocytose melanosomes

Question 28

What are Pacinian corpuscles? How do they appear under microscope?

Answer 28

Sensory receptors in skin that sensitive to mechanical and vibratory pressure; Large onion-like structures in dermis and hypodermis, central core = myelinated nerve ending, outer layers = flattenned cells, collagen fibers, & lymph-like fluid

Question 29

What are Meissner’s corpuscles? How do they appear under microscope?

Answer 29

Touch receptors in skin that are enriched in fingers and toes; Localized in dermis between epidermal ridges, unmyelinated nerve endings surrounded by Schwann cells

Question 30

What do hairs play an important role in? What is the significance of hair follicle versus hair bulb?

Answer 30

Regulating body temperature; Hair follice - where hair production & growth occur, Hair bulb - Contains stem cells that will differentiate into various types of cells that make up hair

Question 31

What are the layers of epithelial cells that comprise hair follicles? Describe each layer’s key characteristics.

Answer 31

(1) Medulla - does not always extend the entire length of hair, (2) Cortex - will become keratinized and constitute the bulk of shaft, (3) Cuticle - will fill with keratin & eventually lose their nuclei;

Question 32

Contrast outer versus inner root sheath.

Answer 32

Outer root sheath - Continuous with epidermis, Inner root sheath - only extend up to where sebaceous gland enters the hair follicle

Question 33

What is the dermal papilla of a hair follicle? What is the matrix of a hair follice?

Answer 33

An invagination of underlying dermis into the hair follice; Epithelial cells surrounding the dermal papilla that give rise to cells of hair shaft and root sheath

Question 34

How do sebaceous glands stain in H & E? How do they connect with the hair follicle?

Answer 34

Pale; Short duct called pilosebaceous cancals