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Histology > Lecture 25 > Flashcards

Lecture 25 Flashcards

1
Q

Skin covers ____ % of body mass

A

15-20%

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2
Q

3 Main layers of skin

A

Epidermis, dermis, hypodermis

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3
Q

Epidermis

A

Stratified Squamous Keratinized Epithelium

• 4-5 layers

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4
Q

Dermis

A
  • Papillary Layer (Loose CT)
  • Reticular Layer (Dense Irregular CT)

Blood vessels, receptors, ducts, glands found here

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5
Q

Hypodermis

A
  • Mostly adipose tissue (Loose CT)

Glands present here

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6
Q

What is b/w epidermis and dermis?

A

Basement membrane separates the epidermis from dermis

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7
Q

Vasculature of the skin

A
  • Subcutaneous Plexus in Hypodermis
  • Cutaneous Plexus in reticular layer of dermis
  • Subpapillary Plexus in papillary layer of dermis
  • Epidermis is avascular, but nutrients and oxygen come off of subpapillary plexus and go to epidermis through diffusion
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8
Q

7 main functions of the skin and additional functions

A

7 main functions:
• Protection (from mechanical stress, or anything that could hurt you)
• Water/Temperature homeostasis
• Sensation (via PNS receptors)
• Vitamin D synthesis (needed for bone and CT tissue, dependent on UV exposure) (Vit D is signalling molecule)
• Excretion (waste products like excess water, urea, ammonia, etc. Occurs via eccrine sweat glands that release sweat.)
• Immunity
• Hormone production

Additional Functions:
• Insulation (skin has lipids)
• Scent signaling (can communicate behaviour and emotions to other beings)

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9
Q

Pacinian corpuscle

A

Looks like onion with unmyelinated nerve fiber in centre and is surrounded by Schwann cells around it; it is sensory PNS
receptor

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10
Q

Sebaceous glands

A

Associated with hair follicles and makes sebum that reaches skin surface to act as skin’s natural moisturizer

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11
Q

Thick skin (epidermis, hair follicles, arrector pili muscle, sensory receptors, glands, location)

A

5 layers with thick stratum corneum and thick stratum granulosum. No hair follicles, no arrector pili muscles. More sensory receptors compared to thin skin (Has papillae that contain more sensory organs). No sebaceous glands, but many eccrine sweat glands. Located at palms of hands and soles of feet.

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12
Q

Thin skin (epidermis, hair follicles, arrector pili muscle, sensory receptors, glands, location)

A

4 layers without a stratum lucidum, and has a single layer OR absent stratum granulosum. Has thin layer of dead skin cells on top. Hair follicles in most layers except lips, labia minora and glans penis. Arrector pili muscle is present and associated with hair follicles. Sparse sensory receptors compared to thick skin. Has many sebaceous glands, but fewer eccrine sweat glands. Located everywhere else, aside from thick skin locations.

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13
Q

The 5 layers of epidermis from superficial to deep

A

Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basale

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14
Q

Stratum corneum

A

Keratinized layer made up of lots of dead cells; sheets of keratin and lots of dead skin cells. Is anuclear, and can be called acellular layer of epidermis

Desquamation occurs here, which is when dead skin cells shed off

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15
Q

Stratum Lucidum

A

Has blue color to it, specifically present in thick skin but not in thin skin.

Is where a water-permeable layer exists and the cells start to die and migrate upwards.
Water barrier is first established here b/c of presence of lipid-filled organelles known as lamellar bodies

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16
Q

Stratum granulosum

A

Is thick in thick skin, but 1 cell or absent in
thin skin

Has secretory granules known as keratohyalin granules, stains dark b/c of secretory granules. Lots of cross linking of keratin filaments in stratum granulosum that
eventually causes cells to die and migrate up

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17
Q

Stratum spinosum

A

Ranges from 10 cell layers to more, and is made of keratinocytes (cells that make keratin). Also has Langerhans cells

18
Q

Stratum basale

A

Has cells high in mitotic activity, they are constantly dividing

Has lots of pigmented cells and basal cells that are high in mitotic activity, there are also sensory cells

19
Q

Epidermal Ridge

A

Numerous epidermal bridges form fingerprint

20
Q

Interpapillary peg

A

Extension of epidermis that buries itself into the dermis is called the interpapillary peg, which is a finger like projection that goes
deep into the dermis and the purpose is to increase SA for attachment of epidermis to the dermis

21
Q

Dermal papillae

A

Between interpapillary peg is dermal papillae

Is extension of papillary layer of dermis that contains sensory receptors like meissner’s corpuscle

22
Q

Meissner’s corpuscle

A

Sensory receptor in dermal papillae that discriminates b/w fine touch

23
Q

Prickle cells

A

Keratinocytes (located in stratum spinosum) are also called prickle cells. There is a zipper appearance due to desmosomes located between adjacent keratinocytes, giving the prickly appearance.

The desmosomes are intercellular connections b/w plasma membrane of keratinocytes.

Keratin intermediate filaments (tonofilaments) insert themselves into the desmosomes

24
Q

Hemidesmosomes of stratum basale

A

Allow the basal cells of stratum basale to be anchored to basal lamina. A lot of integrin molecules organize themselves into
hemidesmosomes. There are also keratin intermediate filaments (tonofilaments) that insert themselves into hemidesmosomes

25
Q

Stratum Corneum and Stratum Lucidum content

A
  • Cornified cell envelope forms due to protein deposition inside the plasma membrane
  • Water barrier formed by release of lipids from lamellar bodies (Prevents water loss)
  • Keratinocytes undergo apoptosis
26
Q

Stratum Granulosum content

A
  • Keratohyalin granules (Proteins: filaggrin, involucrin, loricrin)
  • Lipid-rich lamellar bodies
  • Desmosomes
27
Q

Stratum Spinosum content

A
  • Differentiated cells from Stratum Basale
  • Accumulation of Keratin fibers (1 and 10)
  • Desmosomes
28
Q

Stratum Basale content

A
  • Mitotically-dividing cells that mature and migrate upwards
  • Keratins 5 and 14
  • Contains desmosomes and hemidesmosomes
29
Q

Keratohyalin granules

A

Are a network of proteins that help aggregate keratin filaments to form a cornified cell envelope in stratum corneum
and lucidum

Keratin filaments aggregate with the help of keratohyalin granules (Filaggrin, Loricrin, Involucrin) to form a cornified cell envelope (Inner surface of Plasma membrane)

30
Q

Lamellar body

A

Golgi produces lipids packaged into vesicles called lamellar body

Lamellar bodies are vesicles that package lipids and eventually help release the lipids that then coat the flattened cells to form a water barrier

Exocytosis of lamellar bodies and eventually its secretion of lipids form a water permeable barrier (Outer surface of Plasma membrane)

31
Q

Going from deep to superficial skin layers, keratinocytes will…

A

Keratinocytes will become flattened, then

anucleated, and then undergo apoptosis

32
Q

Melanocytes

A

Melanocytes makes melanin. Melanin made by melanocytes and melanin is packaged into melanosome. Stratum basale is filled with melanocytes, but not all the cells in stratum basale are melanocytes.

Melanocytes also donate pigment to
neighbouring keratinocytes. To identify melanocyte, find a white halo in its cellular shape.

The number of melanocytes is equal in all people, but what differs is the type of melanin produced and rate of melanosome breakdown

Melanosomes are vesicles that contain melanin and melanosomes are within a melanocyte. The melanosomes are donated to neighbouring cells to donate the pigment

33
Q

To identify a melanoma

A
  • A – Asymmetry
  • B – Border (Irregular?)
  • C – Colour variations
  • D – Diameter (> 6 mm?)
  • E - Evolving
34
Q

Langerhans cells: the basics

A

AKA dendritic cells, are for immunity, located in stratum spinosum

35
Q

Merkel cells: the basics

A

Are sensory cells in stratum basale

36
Q

Melanin production steps

A

Tyrosine to 3,4-hydroxyphenylalanin (DOPA) to Melanin

37
Q

Pigment donation process

A
  1. Melanin accumulates in premelanosomes after synthesis from DOPA
  2. Melanosomes migrate upward to the tip of melanocyte processes and invaginate into neigbouring keratinocytes’ cell membrane. Kinesin molecules help melanosomes migrate and move and accumulate at the tips of cytoplasmic processes
  3. Keratinocytes phagocytose tips of these processes containing melanin-filled melanosomes (Pigment donation)
  4. Melanosomes are released into the cytoplasm of keratinocytes and accumulate at the UV side of nucleus. Melanosomes protect UV side of nucleus of keratinocytes
38
Q

Langerhans Cells

A
  • Are antigen-presenting cells involved in immunity; captures antigen from foreign microorganisms
  • Monocyte-derived; Langerhans are macrophages of the skin
  • Localized in Stratum spinosum
  • Has desmosomes between cells
  • Goal: To migrate to Lymphoid organs
  • Rod-shaped Birbeck granules are within Langerhans cells. Birbeck granules make proteins called leptins, which have a sugary aspect that attracts antigens of foreign particles
  • Found in other squamous epithelia as well (Oral cavity, Vagina, etc.)
39
Q

Langerhans cells - antigen-presenting process

A
  1. In epidermis, immature dendritic cells (DC) or Langerhans cells sense their environment for any foreign microorganisms
  2. Captures antigen via birbeck granules and cell loses adhesiveness to epidermis
  3. Dendritic cells migrate and mature. It travels through afferent lymphatic vessel.
  4. Presentation of antigen to lymphoid organs, such as lymphocytes (T-cells) at the Lymph node. T cell activation, B cell activation and downstream immune responses occur
40
Q

Merkel Cells

A
  • Involved as sensory receptor, so it sends signals; Merkel cells are coupled with axon terminals (of unmyelinated nerve fiber) and together it is referred to as a mechanoreceptor; They are sensitive mechanoreceptors at the Stratum Basale
  • Appear as modified keratinocytes
  • Lobed nucleus
  • Can form a complex with an unmyelinated nerve fiber; Associated with terminal bulbs of unmyelinated nerve fibers; The nerve fibers first start as myelinated, then become unmyelinated
  • Neurosecretory granules present in the cytoplasm. The granules contain neurotransmitters, which is released and taken up by axon terminals of nerve fibers
  • Localized in sites of high tactile sensitivity (E.g. fingertips, lips, oral mucosa)

Histology (25 decks)

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