Histology of the Dermis: Integumentary System and Wound healing

Question 1

What is the integumentary system and what does it consist of?

Answer 1

largest organ of the human body (15-20% body mass) and consists of
- Skin
- Skin derivatives: hair follicles and hair, nails and glands

Question 2

what are the functions of the integument system?

Answer 2

• Provides protection: Physical barrier and Immunologic barrier
• Participates in homeostasis: regulates temperature by conserving or dissipating heat and regulates water loss to prevent dehydration
• Perceives sensory stimuli: sensory receptors are abundant in skin
• Performs endocrine and exocrine functions: synthesizes Vitamin D, secretes hormones, cytokines and growth factors and secretes sweat and sebum

Question 3

what are the 3 basic layers of the skin?

Answer 3

epidermis
dermis
hypodermis

Question 4

what is the portion of the skin that contributes to finger prints?

Answer 4

dermal papillae

Question 5

what are the two types that skin are classified into and what are the components?

Answer 5

• thin epidermis: skin on most of the body (eyelids are thinnest), contains hair follicles and sebaceous glands
• thick epidermis: soles of feet and palms of hands; no hair follicles or sebaceous glands; epidermis can have an extra layer and has significantly more keratin

Question 6

what layer of the skin can reflect the overall health of an individual?

Answer 6

epidermis

Question 7

what is the epidermis?

Answer 7

stratified squamous epithelium with varying degrees of keratinization that is tough (keratin proteins, desmosomes) and flexible (elastic fibers)

Question 8

how often does the epidermis renew?

Answer 8

has continuous growth, fully renews in 45 days and maintains thickness due to desquamation

Question 9

what are the distinct layers of the epidermis from deep to superficial?

Answer 9

• stratum basale
• stratum spinosum
• stratum granulosum
• stratum lucidum (only in thick)
• stratum corneum

Question 10

How do keratinocytes migrate in the epidermis

Answer 10

cells in the stratum basale constantly produce new keratinocytes that ascend to the stratum corneum and rapidly increase keratin synthesis and lose nuclei/cytoplasmic organelles along the way

Question 11

What are key structural features of the epidermis related to nutrition and cell junctions?

Answer 11

• avascular: lacks blood vessels; nutrients come from dermal vessels
• contain desmosomes and hemidesmosomes

Question 12

What are desmosomes?

Answer 12

cell-to-cell adhesion structures that anchor keratinocytes together and connect intracellular cytoskeletons via intermediate filaments and transmembrane proteins like desmogleins and desmocollins

Question 13

What proteins form desmosomes in the epidermis?

Answer 13

• Dsg1: in superficial layers
• Dsg3: in deeper layers (near stratum basale)

Question 14

What is the role of desmosomes in skin integrity?

Answer 14

Desmosomes maintain epidermal structure by tightly linking cells and loss of desmosomal proteins (e.g., in autoimmune diseases) leads to blistering due to layer separation

Question 15

What is pemphigus foliaceus?

Answer 15

A milder autoimmune blistering disease where antibodies target Dsg1, causing superficial epidermal separation and shallow blisters filled with fluid

Question 16

What is pemphigus vulgaris?

Answer 16

A more severe autoimmune disease where antibodies target Dsg3 (and sometimes Dsg1), leading to deeper epidermal separation near the basal layer and lesions often affect the mouth and genitals as well

Question 17

What are hemidesmosomes?

Answer 17

Hemidesmosomes are anchoring junctions that attach the basal layer of epidermal cells to the basement membrane and connect the cytoskeleton (keratin filaments) to the basement membrane using bullous pemphigoid antigen proteins (BPAG1 & BPAG2)

Question 18

What is bullous pemphigoid?

Answer 18

an autoimmune blistering disease where antibodies target BPAGs in hemidesmosomes that causes separation between the epidermis and dermis, leading to large, tense subepidermal blisters

Question 19

What is the stratum basale and what are the cells that are present?

Answer 19

deepest layer of the epidermis, adjacent to the dermis, made of a single row of cuboidal cells sitting on the basement membrane (same in thin and thick skin) that contains mitotically active stem cells that produce keratinocytes and contain melanocytes and merkel cells

Question 20

what are melanocytes and what are their role?

Answer 20

cells that synthesize melanin which protect keratinocytes from UV radiation and lend melanin granules to keratinocytes that surround the nucleus and protects its DNA

Question 21

what is Albinism?

Answer 21

congenital disorder of decreased tyrosinase activity that produces skin hypopigmentation
* Normal number of melanocytes, defect in melanin production

Question 22

What is vitiligo and what causes it?

Answer 22

a skin disorder characterized by patches of depigmentation caused by the loss of melanocytes (pigment-producing cells), triggered by oxidative stress, which damages melanocyte stem cells and activates immune responses.
**T cells may target and destroy melanocytes, but the exact mechanism remains unclear

Question 23

What causes moles and are they dangerous?

Answer 23

benign clusters of melanocytes that proliferate in the skin that can be dark or flesh-colored, flat or slightly raised and most are harmless, but monitoring for changes is important to detect possible melanoma

Question 24

What are the ABCDE signs of melanoma?

Answer 24

• Asymmetry: One half doesn’t match the other
• Border: Irregular or blurred edges
• Color: Multiple or uneven colors
• Diameter: Larger than 6 mm
• Evolving: Changing in size, shape, or color

Question 25

What is a Merkel disk and what does it detect?

Answer 25

a sensory receptor in the stratum basale, made of a Merkel cell and an afferent nerve ending - Detects skin indentation, helping to sense shape and texture and are highly concentrated in fingertips for fine touch discrimination

Question 26

What are free nerve endings and what do they sense?

Answer 26

unmyelinated sensory axon terminals found throughout the skin, including around hair follicles that respond to: - Pain - Temperature - Light touch or harmful stimuli - Hair movement

Question 27

What is the stratum spinosum and why is it called the "prickle cell layer"?

Answer 27

- largest layer of the epidermis, located just above the stratum basale and as cells move up, they flatten and align parallel to the skin surface - called the "prickle cell layer" because during tissue processing, cells shrink and expose desmosomal connections, which appear spiny under a microscope

Question 28

What do keratinocytes do in the stratum spinosum?

Answer 28

produce more tonofilaments, which form tonofibrils and also make membrane-coating granules (rich in lipids) that help make the skin waterproof

Question 29

What are the components of the Stratum Granulosum and what occurs in this layer?

Answer 29

contain granules that give it a dark (basophilic) stain: - Membrane Coating Granules (MCGs): released into intercellular space to form a water barrier. - Keratohyalin granules: contain filaggrin, which helps keratin fibers stick together (tonofibril aggregation). *Cells begin losing organelles, starting the transition into the upper layers.

Question 30

What is the Stratum Lucidum and its role?

Answer 30

- a layer found only in thick skin made of flat, dead keratinocytes that look shiny and transparent and its cells lack nuclei and organelles - Acts as part of the water barrier inside the cell, filaggrin binds tonofilaments to form a dense internal layer and outside the cell, lipids from membrane-coating granules (MCGs) form a waterproof layer

Question 31

What is the Stratum Corneum and its function?

Answer 31

- the outermost layer of the epidermis made of dead, flattened keratinocytes with no nuclei or organelles, packed with tonofibrils and surrounded by a compound cell envelope (lipids outside, proteins inside) for waterproofing - its main function is in desquamation (shedding skin): outer skin is acidic → activates proteases that break down desmosomes

Question 32

what is the dermis and what does it contain?

Answer 32

- a highly vascularized, supportive middle layer of connective tissue divided into a reticular and papillary layer - contains ducts of sweat glands, hair follicles, lymphatics, collagen, elastic and sensory fibers

Question 33

what is the papillary layer of the dermis and what is its function?

Answer 33

loose, areolar connective tissue that contains dermal papillae that house many blood vessels and sensory receptors (afferents and meissner's corpuscles) - provides nutrients - regulates temperature

Question 34

What are Meissner’s Corpuscles and what do they detect?

Answer 34

ovular, encapsulated modified free nerve endings wiith axons that wind between Schwann cells in the dermis - detect light touch and dynamic pressure and motion over the skin

Question 35

what is the reticular layer of the dermis and what does it contain?

Answer 35

dense, irregular connective tissue with thick collagen bundles that provide tensile strength and collagen fibers contribute to skin tension lines important for surgery and contains accessory structures such as - sebaceous glands - secretory portions of sweat glands - bases of hair follicles, which may also extend into the hypodermis

Question 36

what is the hypodermis and what does it contain?

Answer 36

layer of loose connective tissue and adipose that links skin to underlying muscle for insulation and energy storage and contains: - pacinian corpuscles - hair follicles - sweat glands

Question 37

What are Pacinian corpuscles and how do they work?

Answer 37

large, layered sensory structures that detect vibration and deep pressure (like holding an electric toothbrush) - contain a nerve ending surrounded by many layers (like an onion). - layers shift (due to pressure) and trigger the nerve to send a signal

Question 38

what are sweat glands and what is their main role?

Answer 38

Coiled, tubular structures that extend from the hypodermis to the epidermis to release sweat to the surface of the skin to cool skin via evaporation and also has antimicrobial properties

Question 39

what are the two types of sweat glands and where are they found?

Answer 39

- Eccrine: most common, found everywhere except lips and external genitalia and concentrated on soles of the feet, palms of the hands, and forehead - Apocrine: only in axillary and anogenital region to produce a protein-rich substance that contains pheromones that is responsible for body odor, become functional at puberty, respond to sex hormones and emotional stimuli

Question 40

What activates eccrine sweat glands, and what is their function?

Answer 40

when body temperature rises due to heat or exercise signals from the hypothalamus regulate body temperature by producing sweat and help with excretion of waste products

Question 41

What are the two main parts of eccrine sweat glands seen in histology?

Answer 41

- Secretory Portion (in dermis/hypodermis): coiled tubes that produce sweat - Ductal Portion: carries sweat from the secretory part to the skin surface

Question 42

What is sweat composed of?

Answer 42

- Water and NaCl (salt): some NaCl is reabsorbed - IgA, enzymes, antimicrobial peptides: provide skin defense - Urea, uric acid, ammonia: waste removal

Question 43

what defect occurs in cystic fibrosis patients?

Answer 43

defective CFTR channel leads to salty sweat due to failed NaCl reabsorption

Question 44

What cell types are found in the secretory portion of eccrine glands and what do they do?

Answer 44

- Clear cells: secrete water and electrolytes - Dark cells: produce antimicrobial glycoproteins - Myoepithelial cells: contractile cells that push sweat into ducts; look like small, pointy cells near the basement membrane.

Question 45

What are the features of the ductal portion of eccrine sweat glands?

Answer 45

made of stratified cuboidal epithelium, darker staining that extends from the secretory coils to the surface and passes through the dermis, epidermis, and exits at the skin surface (sweat pore). *Often appears highly coiled under the microscope.

Question 46

What are the main functions of hair and the associated structures?

Answer 46

- Protection: Blocks irritants (e.g., dust in nose/ears) - Heat retention: Traps warm air when hair stands - Sensation: Nerve endings detect hair movement - Stem cells: In follicles, help heal damaged skin - Sebaceous glands: Secrete sebum to protect/moisturize hair - Arrector pili muscle: Raises hair to retain heat and squeeze sebum out

Question 47

What are the three main parts of a hair follicle and what do they contain?

Answer 47

1. Hair bulb: - Hair papilla: Vascular dermal nodule - Hair matrix: Stem cells + melanocytes for growth and color - Free nerve endings: Detect bending. 2. Hair root: - Between bulb and shaft; anchored by arrector pili muscle - Contains follicular bulge with reserve stem cells 3. Hair shaft: - Visible part above skin; highly keratinized.

Question 48

What is the structure and function of the sebaceous gland?

Answer 48

contains a - secretory portion: solid mass of lipid-filled cells (appear bubbly) with an outer rim made of basal cells that continuously produce new secretory cells and secretes via holocrine secretion (cells rupture to release contents) - Duct portion: empties into hair follicle

Question 49

What does the arrector pili muscle do?

Answer 49

Connects the hair follicle to the papillary dermis where smooth muscle is innervated by sympathetic fibers and when it contracts, it: - Raises the hair (goosebumps) - Squeezes sebum from the sebaceous gland into the follicle

Question 50

What are the main parts of the nail and their roles?

Answer 50

- Nail plate: Hard keratinized surface made of cross-linked keratinocytes - Nail bed: Modified epidermis under the nail plate - Nail matrix: Growth zone; adds new cells at nail root and starts keratinization - Eponychium: Proximal edge (forms part of the cuticle) - Hyponychium: Area beneath the nail tip, attaches nail to fingertip

Question 51

what are the 4 general phases of wound healing?

Answer 51

- Hemostasis: stop bleeding - Inflammation: fight infection - Proliferation: fill in wound with new cells and blood vessels - Remodeling: form scar, finish process

Question 52

What happens during the hemostasis phase of wound healing?

Answer 52

1. Vasospasm: Blood vessels constrict to reduce blood loss 2. Platelet plug forms: Platelets stick to the wound via lamina propria receptors and Von Willebrand factor 3. Coagulation cascade activated: Fibrin mesh forms to trap platelets → creates a blood clot, cytokines attract neutrophils and macrophages and clot seals the wound and guides immune cells

Question 53

What happens during the inflammation phase of wound healing?

Answer 53

1. Vasodilation: Blood vessels widen → allows white blood cells to reach wound (causes redness & warmth) 2. Neutrophils infiltrate: arrive within minutes and kill bacteria by phagocytosis 3. Macrophages arrive: clear dead cells and debris, release signals to activate endothelial cells, keratinocytes, and fibroblasts and trigger angiogenesis (new blood vessels)

Question 54

What happens during the remodeling phase of wound healing?

Answer 54

1. Collagen in granulation tissue is reorganized and cross-linked for strength 2. Some fibroblasts become myofibroblasts that contract to pull wound edges together 3. The scab falls off as skin cells shed *This phase can last up to a year as tissue strengthens and matures