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HSF > HSF 1 - Unit 3 Histology > Flashcards

HSF 1 - Unit 3 Histology Flashcards

Skin

1
Q

what is the largest organ of the body and what percent of the body mass does it make up?

A

skin; 15-20%

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2
Q

what are the 4 main functions of the skin and how does it do these things?

A

1) protection: from UV, mechanical, chemical, and thermal insult
2) sensation: largest sense organ of the body, contains receptors for touch, pressure, pain, and temperature
3) thermoregulation: insulation via hair and SQ fat; heat loss facilitated by sweat glands and dermal capillary network
4) metabolic functions: energy stored in SQ fat (1’ as TGs); vitamin D synthesized in the skin via uv. maintains homeostasis; excretory function (sweating); immune defense

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3
Q

what are the 3 layers of the skin?

A

epidermis, dermis, hypodermis (subcutis)

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4
Q

what kind of epithelium is found in the epidermis?

A

keratinized, stratified squamous epithelium

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5
Q

what are keratinocytes?

A

the cells of the epidermis

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6
Q

how thick is the epidermis?

A

1-5mm, dubbed thin and thick skin respectively

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7
Q

where is thick skin found?

A

volar (soles) and palmar (palms) surfaces; lacks hair

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8
Q

what kind of skin covers most of the body?

A

thin, which has a thin keratinized epidermis

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9
Q

what is the blood supply to the epidermis?

A

absent, blood vessels do not penetrate the basement membrane

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10
Q

how do nutrients get to the epidermis?

A

by blood vessels in underlying dermis

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11
Q

what is the structure of the dermis?

A

dense, irregular, collagenous CT (type I collagen), interspersed with elastic fibers

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12
Q

how does the skin age?

A

progressive damage to the elastic fibers of the dermis which results in loss of skin’s tone

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13
Q

what is the blood supply to the dermis?

A

highly vascular and also contains many sensory receptors

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14
Q

what are the layers of the dermis?

A

papillary (superficial)

reticular (deep)

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15
Q

what are the characteristics of the papillary layer of the dermis?

A

it is relatively thin and interdigitated through corrugations with the epidermis to increase surface area for attachment so we can prevent mechanical abrasions and shearing

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16
Q

what are dermal ridges?

A

also called dermal papillae, dermal projections into the epidermis

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17
Q

what are fingerprints?

A

large dermal ridges in thick skin; also called dermatoglyphs and are unique to each individual

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18
Q

what are epidermal ridges?

A

also called rete ridges, epidermal projections into the dermis

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19
Q

how does the reticular layer compare to the papillary layer?

A

thicker and less cells

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20
Q

what special things does the reticular layer have?

A

contains hair follicles, sweat and sebaceous glands

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21
Q

what is the reticular layer connected to?

A

the hypodermis (subcutis)

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22
Q

what are Langer’s lines?

A

thick collagen bundles and elastin fibers in the reticular layer form tension lines, skin incisions parallel to these lines will heal with less scarring

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23
Q

what is the structure of the hypodermis?

A

loose, irregular CT and adipose, which is the subcutis/superficial fascia/panniculus adiposus

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24
Q

what are the different vascular plexi of the skin?

A

superficial subpapillary plexus, deep cutaneous plexus, and deeper subcutaneous plexus

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25
Q

where is the subpapillary plexus?

A

at the junction of the papillary and reticular layers

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26
Q

where is the cutaneous plexus?

A

at the junction of the reticular layer and hypodermis

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27
Q

where is the subcutaneous plexus?

A

deep within the hypodermis

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28
Q

which plexus is the largest?

A

the subcutaneous

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29
Q

what are the special features of the subcutaneous plexus?

A

used in thermoregulation in the fingertips and ears, and is associated with AV shunts containing glomus bodies so we can bypass capillary bed, re-route blood from arterial to venous circulation

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30
Q

what are glomus bodies?

A

thickened regions of smooth mm in the wall of arterioles, surrounded by connective tissue capsule

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31
Q

how does the growth and death/falling off of skin cells happen and how long does this process take?

A

takes around 25-50 days for the cells to travel from the deep germinal layer, mature, and be sloughed from the superficial epidermis

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32
Q

what is psoriasis?

A

keratinocyte maturation only takes about a week, so there is an absence of a granular layer and abnormal keratinohyaline and tonofibrils

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33
Q

what are the layers of the epidermis?

A 
stratum basale
stratum spinosum
stratum granulosum
stratum lucidum (thick only)
stratum corneum
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34
Q

what are characteristics of the base layer of the epidermis?

A

it is a mitotic layer of cuboidal germinal cells that are bound to the basement membrane by hemidesmosomes, and they attach to the underlying dermis via anchoring filaments and microfibrils

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35
Q

what are characteristics of the stratum spinosum?

A
  • cells are spiny (because of numerous cytoplasmic processes and lateral folding of cell membrane) and polyhedral with prominent intercellular bridges (desmosomes); thickest layer in thin skin
  • produces cytokeratin, forms tonofilaments which aggregate into larger tonofibrils, and anchor onto desmosomes
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36
Q

what are characteristics of the stratum granulosum?

A
  • it is the granular cell layer and characterized by cells containing basophilic, keratinohyaline granules
  • keratinization of cells represents interaction between keratinohyaline granules and tonofibrils
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37
Q

what are keratinohyaline granules?

A

non-membrane bound electron dense granules

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38
Q

what are characteristics of the stratum lucidum?

A

only present in thick skin, homogenous, compact layer enucleate cells between stratum granulosum and stratum corneum

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39
Q

what happens when cells are keratinized?

A

there is a rupture of keratinohyaline granules that is initiated by release of lysosomal enzymes and a polymerization of their contents which forms a matrix for tonofibrils of cytokeratin

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40
Q

what is cytokeratin?

A

amorphous mass of mature keratin

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41
Q

what happens when lysosomal enzymes are released?

A

death of the cell

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42
Q

as keratinocytes mature, what happens?

A

they die and lose their nuclei

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43
Q

what are keratinosomes and where are they found?

A

membrane-bound, lamellar structures that contain glycolipids, provide waterproofing coat for skin cells; they are found in the granular layer

44
Q

what happens to cells of the granular layer as they mature?

A

they form a waterproof layer of keratinized cells, with a glycolipid coating on the surface of the epidermis

45
Q

what are characteristics of the stratum corneum?

A
  • it is the most superficial layer, and the thickest layer in thick skin
  • contains flattened, enucleate, dead cell remnants, called squames
  • composed primarily of soft keratin that acts as a hydrophobic barrier, prevents desiccation
  • the cells are continuously exfoliated (desquamation)
46
Q

what are the common types of skin tumors, where are they each derived from and how aggressive are they?

A

squamous cell carcinoma, basal cell carcinoma, melanoma
all aggressive
first 2 derived from epithelial cells, melanoma derived from melanocytes

47
Q

what is first intention healing?

A
  • from a clean/surgical approximated incision
  • incision immediately fills with blood and clots, and this clot is infiltrated by neutrophils within 3-24 hours, this is considered the acute phase
  • epithelial cells of stratum basale begin mitosis and epithelial closure (reapproximation) happens within 24-48 hours
  • day 3-7 the neutrophils begin to be replaced by macrophages (transition from acute to subacute phase)
  • day 5 the incision is filled with granulation tissue
  • week 2 there is continued fibroplasia and collagen accumulation to make mature granulation tissue and you get a progressive decrease in inflammation, but the presence of inflammatory cells and their products results in itching while healing
  • month 2 you get a CT scar, without inflammation that is covered by intact epithelium
48
Q

what are the 3 processes of the acute-subacute phase of healing?

A

neurovascularization, fibroplasia (fibroblasts elaborate collagen), re-epithelization (epithelial profileration) these together result in the formation of granulation tissue

49
Q

what are the differences between first and second intention healing?

A

2nd: larger scab, inflammation more intense because there are more necrotic debris, exudate, and fibrin to remove, and you have larger amounts of granulation tissue because of a larger defect, also involves wound contraction

50
Q

what is a keloid?

A

excess fibroplasia that results in raised, thickened CT scar

51
Q

what is second intention healing?

A

=occurs with more extensive loss of tissue, where the wound edges do not approximate so you get an infarct, abscess, or ulcer

  • following the initial clot formation, the epithelial cells of stratum basale migrate from edges of wound at round 0.5 mm per day, taking about 3 weeks to fill a 1 cm wide cut
  • in haired skin, migration of cells from external root sheath of hair follicles augments re-epithelization
  • simultaneous proliferation and maturation of keratinocytes behind migrating front slowly restores multilayered, stratified epidermis
  • takes about 25 days for cells to mature from stratum basale to stratum corneum through keratinization which results in the desquamation and lifting of the scab from the periphery after 3 weeks
  • wound contraction due to myofibroblasts
  • in full thickness abrasion or 3rd degree burns, re-epithelialization is limited by the size of the wound, and grafting is generally necessary
52
Q

what are the different degrees of burns and how do they vary?

A

1st: involves only epidermis
2nd: involves epidermis and dermis
3rd: involves epidermis, dermis, and hypodermis

53
Q

what are melanocytes?

A

come from neural crest, are neuroectoderml dendritic cells that are present in the epidermis, usually restricted to stratum basale but cytoplasmic processes that may extend into the spinosum

54
Q

what do melanocytes do?

A

-produce melanin, which is skin pigment, this is released from melanosomes and taken up by surrounding epidermal cells

55
Q

eumelanin

A

dark brown, black pigment, present in dark haired individuls

56
Q

pheomelanin

A

red to yellow pigment, presents in individuals with red or blonde hair

57
Q

what is special about the number of melanocytes an individual has?

A

we all have the same, but variable rates of melanin production and degradation by lysosomal enzymes, resulting in different skin tones

58
Q

what is vitiligo?

A

autoimmune disease that destruction of melanocytes and depigmentation

59
Q

what does melanocyte stimulating hormone do?

A

melanin synthesis, it is under the control of this pituitary hormone

60
Q

what is the precursor of melanin?

A

tyrosine, gets oxidized to DOPA by tyrosinase located in premelanosomes, followed by conversion of DOPA to melanin in melanosomes

61
Q

what causes albinism?

A

lack tyrosinase, so DOPA and melanin are not formed, premelanosomes get formed but do not mature

62
Q

why does our skin make melanin?

A

the DNA is subject to damage by UV, and melanin can act as a shield to protect the nucleus and inhibit mutagenesis. UV can also stimulate melanin synthesis, resulting in a tan. Melanin is also necessary for normal neural development

63
Q

what are Langerhans cells? where are they?

A

fixed tissue macrophage, phagocytic and contain distinctive Birbeck granules that are visible on EM. found in stratum spinosum and involved in contact allergic dermatitis, contain abundant cytoplasmic extensions.

64
Q

where is coarse hair found and what is it called?

A

scalp, axilla, and pubis and known as terminal hair

65
Q

what does the hair shaft consist of? what is it covered by? what is it produced by?

A

outer cortex and inner medulla; covered by a thin cuticle of overlapping keratin plates that prevents matting; produced by hair follicles, cylindrical downgrowths of epithelium surrounded by collagen sheaths

66
Q

where does hair growth occur?

A

within a deep terminal expansion of the follicle called the hair bulb (=hair root)

67
Q

what is the hair bulb lined with? what is found at its base?

A

actively dividing epithelial cells homologous to stratum basale; a vascular core (dermal papilla), finger-like invagination of dermis containing blood vessels

68
Q

what happens to the epithelium lining the hair bulb as they mature?

A

they fill with hard keratin filaments arranged in parallel bundles

69
Q

how does the hair have color?

A

melanocytes adjacent to the hair follicle produce melanin and this becomes incorporated into the cortex

70
Q

how is the developing hair protected?

A

surrounded by an internal and external root sheath that line the hair follicle

71
Q

what is the glassy membrane?

A

a modified basement membrane, separates hair bulb from surrounding dermis

72
Q

what is the purpose of hair?

A

aids in protection and thermoregulation, is absent in thick skin of palms and soles

73
Q

what are arrector pili?

A

bundles of smooth muscle cells that attach to the hair follicle sheath and insert on the epidermal ridges, contraction of them raises hair and results in “goose bumps” = piloerection

74
Q

what causes piloerection?

A

sympathetic stimulation due to cold, fear, or aggression

75
Q

how does hair grow?

A

not continuously, 4 phases of growth

76
Q

what are the 4 phases of hair growth?

A

growth phase: anagen
involuting phase (loss of blood supply): catagen
inactive resting phase: telogen
shedding of old hair shaft: exogen

77
Q

what happens to hair at puberty?

A

fine hair in children and women (vellus) is replaced by coarser, terminal hairs

78
Q

what is androgenic alopecia?

A
  • most common form of hair loss, affecting 30-40% of adults, genetic and androgen dependent
  • affected individuals have high levels of 5-alpha-reductase, the enzyme that converts testosterone to dihydroxytestosterone which leads to follicular atrophy
79
Q

what does the nail consist of?

A

flattened nail plate: rests on stratified squamous epithelium of nail bed (=hyponichium)
nail root: proximal end of the nail that extends into the dermis, attaches to periosteum of distal phalanx

80
Q

how does nail growth occur?

A

by proliferation and differentiation of epithelium at nail root in germinative zone of the nail matrix

81
Q

where is the nail matrix?

A

underlies the white crescent at the base of the nail, lunula, covered by superficial cuticle, or eponychium

82
Q

what happens as epithelial cells at the nail mature?

A

they fill with keratin and die, forming the nail plate, which consists of densely packed, parallel, hard keratin filaments embedded in amorphous matrix

83
Q

what are sebaceous glands?

A
  • alveolar, holocrine glands, consisting of branched acini
  • entire cell secreted
  • one or more glands associated with each hair follicle, develop as outgrowths of external root sheath
84
Q

what do sebaceous glands secrete? what is this secretion used for?

A

oily sebum via pilosebaceous canal, high in lipid content and cell debris; used for waterproofing, moisturizing skin and hair

85
Q

what is seborrhea?

A

excessive secretion of sebum

86
Q

what is a pilosebaceous unit?

A

a hair follicle and its associated arrector pili muscle and sebaceous gland

87
Q

what is a sweat gland? what are the types?

A

simple, coiled, tubular glands, surrounded by myoepithelial cells that assist in secretion; merocrine/eccrine and apocrine are the 2 types

88
Q

what is a merocrine gland?

A

also called eccrine sweat glands, secrete only the product and distributed over most of the body surface, other than lips and the genitalia; unbranched, coiled, tubular glands with 1-2 layers of cuboidal to columnar epithelium with excretory ducts

89
Q

how do merocrine glands excrete their product?

A

sweat onto surface of skin via sweat pore on the epidermal ridge; sweat contains a hypotonic solution of salts, ammonia, urea, uric acid that are important for thermoregluation and evaporative cooling

90
Q

what is thermoregulatory sweating?

A

cholinergic (parasympathetic), first starts in axillae, forehead, scalp- last on hands and feet

91
Q

what is emotional sweating?

A

adrenergic (sympathetic), begins on palms and soles

92
Q

sweat glands are innervated by _______, but _______ Nn, so…

A

sympathetic, cholinergic, don’t use adrenaline

93
Q

what are apocrine glands?

A

secrete product along with some cytoplasm; coiled, tubular glands with large dilated lumina; located in axillae, groin; develop at puberty; secretory, cuboidal epithelium, 2-3 cell layers thick, surround the large glandular lumen

94
Q

what do apocrine glands secrete?

A
  • thick, viscid secretions into hair follicle that contains proteins, carbohydrates, ammonia, lipids, and organic products that are odorless when secreted by bacterial breakdown gives it an acrid odor
  • serves as a sexual attractant, pheromone that is used in scent marking, territoriality
  • secretion is adrenergic
95
Q

what are ceruminous glands?

A

modified apocrine glads in the external auditory meatus (ear canal) that secrete cerumen (ear wax)

96
Q

what are mammary glands?

A
  • develop along paired epidermal ridges- mammary ridges or milk lines- extend from axillae to groin
  • in humans only the first pair of glands along the milk line develops
  • highly modified apocrine sweat glands; identical in male and female until puberty
  • females’ develop under influence of pituitary and ovarian hormones; following pregnancy, produce milk to feed young
  • at menopause, atrophy and involute
97
Q

what are mammary glands composed of (tissue type) when inactive?

A

-mainly of dense, irregular, collagenous connective tissue, interspersed with adipose tissue and occasional smooth muscle

98
Q

what are secretory lobules?

A

organized groups of tubulo-acinar glands that are drained by terminal ducts; drain into larger lactiferous ducts; which empty into lactiferous sinus in region of nipple

99
Q

what is the areola?

A

pigmented region of epidermis surrounding the nipple, made of stratified squamous epithelium with deep dermal ridges; contains numerous areolar glands, including merocrine sweat and sebaceous glands

100
Q

what happens during lactation?

A
  • mammary glands enlarge due to hypertrophy of secretory cells and accumulation of secretory product
  • first few days after birth secrete colostrum (an alkaline, yellowish secretion, with high protein and salt content, low lipid and carbohydrate; contains large amounts of antibodies, important in transfer of passive immunity to offspring)
  • milk production is both merocrine and apocrine- protein secretion is primarily merocrine; lipid fraction is primarily apocrine
101
Q

what are meissner’s corpuscles?

A
  • mechanoreceptors/touch receptors in the dermal ridges of the papillary layer that are especially prominent in the hands, feet, lips, and genitalia
  • cylindrical structures that are about 150 micrometers long
  • afferent nerve fibers associated with minimally modified Schwann cells
102
Q

what are pacinian corpuscles?

A
  • mechanoreceptors located in dermis and hypodermis
  • large, ovoid structures (over 1mm)
  • prominent in fingertips and around joints- detect mechanical and vibratory pressure
  • consist of afferent nerve fibers surrounded by highly modified Schwann cells- form concentric lamellae separated by fluid-filled spaces
103
Q

what are ruffini corpuscles?

A

small dermal mechanoreceptors, especially common in soles of feet

104
Q

what are free nerve endings?

A
  • most numerous, present in epidermis and papillary dermis-surround most hair follicles
  • lack CT capsule and associated Schwann cells and serve multiple sensory modalities- heat, cold, touch, pain, movement
105
Q

what are merkel cells?

A

epidermal cells derived from the neural crest, look like melanocytes located in stratum basale, contain dense core granules, pressure sensitive mechanoreceptors associated with free afferent nerve endings

HSF (23 decks)

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