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%
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
3
Q
what are the 3 layers of the skin?
A
epidermis, dermis, hypodermis (subcutis)
4
Q
what kind of epithelium is found in the epidermis?
A
keratinized, stratified squamous epithelium
5
Q
what are keratinocytes?
A
the cells of the epidermis
6
Q
how thick is the epidermis?
A
1-5mm, dubbed thin and thick skin respectively
7
Q
where is thick skin found?
A
volar (soles) and palmar (palms) surfaces; lacks hair
8
Q
what kind of skin covers most of the body?
A
thin, which has a thin keratinized epidermis
9
Q
what is the blood supply to the epidermis?
A
absent, blood vessels do not penetrate the basement membrane
10
Q
how do nutrients get to the epidermis?
A
by blood vessels in underlying dermis
11
Q
what is the structure of the dermis?
A
dense, irregular, collagenous CT (type I collagen), interspersed with elastic fibers
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
13
Q
what is the blood supply to the dermis?
A
highly vascular and also contains many sensory receptors
14
Q
what are the layers of the dermis?
A
papillary (superficial)
reticular (deep)
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
16
Q
what are dermal ridges?
A
also called dermal papillae, dermal projections into the epidermis
17
Q
what are fingerprints?
A
large dermal ridges in thick skin; also called dermatoglyphs and are unique to each individual
18
Q
what are epidermal ridges?
A
also called rete ridges, epidermal projections into the dermis
19
Q
how does the reticular layer compare to the papillary layer?
A
thicker and less cells
20
Q
what special things does the reticular layer have?
A
contains hair follicles, sweat and sebaceous glands
21
Q
what is the reticular layer connected to?
A
the hypodermis (subcutis)
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
23
Q
what is the structure of the hypodermis?
A
loose, irregular CT and adipose, which is the subcutis/superficial fascia/panniculus adiposus
24
Q
what are the different vascular plexi of the skin?
A
superficial subpapillary plexus, deep cutaneous plexus, and deeper subcutaneous plexus
25
where is the subpapillary plexus?
at the junction of the papillary and reticular layers
26
where is the cutaneous plexus?
at the junction of the reticular layer and hypodermis
27
where is the subcutaneous plexus?
deep within the hypodermis
28
which plexus is the largest?
the subcutaneous
29
what are the special features of the subcutaneous plexus?
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
30
what are glomus bodies?
thickened regions of smooth mm in the wall of arterioles, surrounded by connective tissue capsule
31
how does the growth and death/falling off of skin cells happen and how long does this process take?
takes around 25-50 days for the cells to travel from the deep germinal layer, mature, and be sloughed from the superficial epidermis
32
what is psoriasis?
keratinocyte maturation only takes about a week, so there is an absence of a granular layer and abnormal keratinohyaline and tonofibrils
33
what are the layers of the epidermis?
```
stratum basale
stratum spinosum
stratum granulosum
stratum lucidum (thick only)
stratum corneum
```
34
what are characteristics of the base layer of the epidermis?
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
35
what are characteristics of the stratum spinosum?
- 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
36
what are characteristics of the stratum granulosum?
- it is the granular cell layer and characterized by cells containing basophilic, keratinohyaline granules
- keratinization of cells represents interaction between keratinohyaline granules and tonofibrils
37
what are keratinohyaline granules?
non-membrane bound electron dense granules
38
what are characteristics of the stratum lucidum?
only present in thick skin, homogenous, compact layer enucleate cells between stratum granulosum and stratum corneum
39
what happens when cells are keratinized?
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
40
what is cytokeratin?
amorphous mass of mature keratin
41
what happens when lysosomal enzymes are released?
death of the cell
42
as keratinocytes mature, what happens?
they die and lose their nuclei
43
what are keratinosomes and where are they found?
membrane-bound, lamellar structures that contain glycolipids, provide waterproofing coat for skin cells; they are found in the granular layer
44
what happens to cells of the granular layer as they mature?
they form a waterproof layer of keratinized cells, with a glycolipid coating on the surface of the epidermis
45
what are characteristics of the stratum corneum?
- 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
what are the common types of skin tumors, where are they each derived from and how aggressive are they?
squamous cell carcinoma, basal cell carcinoma, melanoma
all aggressive
first 2 derived from epithelial cells, melanoma derived from melanocytes
47
what is first intention healing?
- 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
what are the 3 processes of the acute-subacute phase of healing?
neurovascularization, fibroplasia (fibroblasts elaborate collagen), re-epithelization (epithelial profileration) these together result in the formation of granulation tissue
49
what are the differences between first and second intention healing?
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
what is a keloid?
excess fibroplasia that results in raised, thickened CT scar
51
what is second intention healing?
=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
what are the different degrees of burns and how do they vary?
1st: involves only epidermis
2nd: involves epidermis and dermis
3rd: involves epidermis, dermis, and hypodermis
53
what are melanocytes?
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
what do melanocytes do?
-produce melanin, which is skin pigment, this is released from melanosomes and taken up by surrounding epidermal cells
55
eumelanin
dark brown, black pigment, present in dark haired individuls
56
pheomelanin
red to yellow pigment, presents in individuals with red or blonde hair
57
what is special about the number of melanocytes an individual has?
we all have the same, but variable rates of melanin production and degradation by lysosomal enzymes, resulting in different skin tones
58
what is vitiligo?
autoimmune disease that destruction of melanocytes and depigmentation
59
what does melanocyte stimulating hormone do?
melanin synthesis, it is under the control of this pituitary hormone
60
what is the precursor of melanin?
tyrosine, gets oxidized to DOPA by tyrosinase located in premelanosomes, followed by conversion of DOPA to melanin in melanosomes
61
what causes albinism?
lack tyrosinase, so DOPA and melanin are not formed, premelanosomes get formed but do not mature
62
why does our skin make melanin?
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
what are Langerhans cells? where are they?
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
where is coarse hair found and what is it called?
scalp, axilla, and pubis and known as terminal hair
65
what does the hair shaft consist of? what is it covered by? what is it produced by?
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
where does hair growth occur?
within a deep terminal expansion of the follicle called the hair bulb (=hair root)
67
what is the hair bulb lined with? what is found at its base?
actively dividing epithelial cells homologous to stratum basale; a vascular core (dermal papilla), finger-like invagination of dermis containing blood vessels
68
what happens to the epithelium lining the hair bulb as they mature?
they fill with hard keratin filaments arranged in parallel bundles
69
how does the hair have color?
melanocytes adjacent to the hair follicle produce melanin and this becomes incorporated into the cortex
70
how is the developing hair protected?
surrounded by an internal and external root sheath that line the hair follicle
71
what is the glassy membrane?
a modified basement membrane, separates hair bulb from surrounding dermis
72
what is the purpose of hair?
aids in protection and thermoregulation, is absent in thick skin of palms and soles
73
what are arrector pili?
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
what causes piloerection?
sympathetic stimulation due to cold, fear, or aggression
75
how does hair grow?
not continuously, 4 phases of growth
76
what are the 4 phases of hair growth?
growth phase: anagen
involuting phase (loss of blood supply): catagen
inactive resting phase: telogen
shedding of old hair shaft: exogen
77
what happens to hair at puberty?
fine hair in children and women (vellus) is replaced by coarser, terminal hairs
78
what is androgenic alopecia?
- 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
what does the nail consist of?
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
how does nail growth occur?
by proliferation and differentiation of epithelium at nail root in germinative zone of the nail matrix
81
where is the nail matrix?
underlies the white crescent at the base of the nail, lunula, covered by superficial cuticle, or eponychium
82
what happens as epithelial cells at the nail mature?
they fill with keratin and die, forming the nail plate, which consists of densely packed, parallel, hard keratin filaments embedded in amorphous matrix
83
what are sebaceous glands?
- 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
what do sebaceous glands secrete? what is this secretion used for?
oily sebum via pilosebaceous canal, high in lipid content and cell debris; used for waterproofing, moisturizing skin and hair
85
what is seborrhea?
excessive secretion of sebum
86
what is a pilosebaceous unit?
a hair follicle and its associated arrector pili muscle and sebaceous gland
87
what is a sweat gland? what are the types?
simple, coiled, tubular glands, surrounded by myoepithelial cells that assist in secretion; merocrine/eccrine and apocrine are the 2 types
88
what is a merocrine gland?
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
how do merocrine glands excrete their product?
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
what is thermoregulatory sweating?
cholinergic (parasympathetic), first starts in axillae, forehead, scalp- last on hands and feet
91
what is emotional sweating?
adrenergic (sympathetic), begins on palms and soles
92
sweat glands are innervated by _______, but _______ Nn, so...
sympathetic, cholinergic, don't use adrenaline
93
what are apocrine glands?
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
what do apocrine glands secrete?
- 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
what are ceruminous glands?
modified apocrine glads in the external auditory meatus (ear canal) that secrete cerumen (ear wax)
96
what are mammary glands?
- 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
what are mammary glands composed of (tissue type) when inactive?
-mainly of dense, irregular, collagenous connective tissue, interspersed with adipose tissue and occasional smooth muscle
98
what are secretory lobules?
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
what is the areola?
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
what happens during lactation?
- 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
what are meissner's corpuscles?
- 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
what are pacinian corpuscles?
- 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
what are ruffini corpuscles?
small dermal mechanoreceptors, especially common in soles of feet
104
what are free nerve endings?
- 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
what are merkel cells?
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
