Here is your complete, exam-ready study guide for PHAR1612 - Skin Anatomy & Physiology (Section B: SAQ & LAQ):
🏆 PHAR1612 SKIN ANATOMY & PHYSIOLOGY
MASTER STUDY GUIDE — Section B (SAQ & LAQ)
Prof. Edition | All Learning Objectives Covered
SECTION A: ANATOMY OF THE SKIN
LO1 - Describe the Anatomy of the Skin (Cutaneous & Subcutaneous)
The 3 Main Layers at a Glance
| Layer | Also Called | Key Contents | Function |
|---|
| Epidermis | Cutaneous (outer) | Keratinocytes, Melanocytes, Langerhans cells, Merkel cells | Barrier, protection, UV absorption |
| Dermis | Cutaneous (inner) | Blood vessels, nerves, collagen, elastin, glands, hair follicles | Nourishment, sensation, elasticity |
| Hypodermis | Subcutaneous / Subcutis | Adipose (fat) tissue, large blood vessels | Insulation, energy storage, cushioning |
The 5 Layers of the Epidermis (Stratum by Stratum)
| Stratum (Layer) | Key Features | Cells Found |
|---|
| Stratum Basale (deepest) | Single layer of columnar cells, active division | Stem cells, Melanocytes, Merkel cells |
| Stratum Spinosum | Polygonal cells, most keratin production, desmosomes | Keratinocytes, Langerhans cells |
| Stratum Granulosum | Keratohyalin granules, nucleus degrades, membrane-coating granules | Keratinocytes (flattening) |
| Stratum Lucidum | Only in thick skin (palms/soles), clear/translucent | Dead keratinocytes |
| Stratum Corneum (outermost) | Dead, flattened corneocytes, hardened keratin, skin barrier | Corneocytes (dead) |
MEMORY TRICK - "Come, Lets Get Some Beer"
- Corneum → Lucidum → Granulosum → Spinosum → Basale
(from outside to inside)
The 5 Cell Types of the Epidermis
| Cell Type | Location | Key Function | Bold Keyword |
|---|
| Keratinocyte | All strata | Structural cell, produces keratin | Squamous shape, biggest population |
| Stem Cell | Stratum basale | Divides to make new cells | Mitotic, self-renewing |
| Langerhans Cell | Stratum spinosum | Antigen presenting, immune defense | Dendritic, bone marrow origin |
| Melanocyte | Stratum basale | Produces melanin, UV protection | Melanosome, dendrites |
| Merkel Cell | Stratum basale | Sense of touch | Mechanoreceptor |
MEMORY TRICK - "King Suleiman Loves Making Medicines"
Keratinocyte → Stem Cell → Langerhans → Melanocyte → Merkel
Dermis Contents Summary Table
| Component | Details | Key Fact |
|---|
| Blood vessels | Nourish epidermis and dermis | Absorbed substances enter here |
| Nerves | Pain, cold/hot, pressure, touch | Sensory function |
| Hair + arrector pili muscle | Protection from cold, touch | Arrector pili causes goosebumps |
| Collagen & Elastin | Structural fibers | Elasticity and contour |
| Sweat gland (Eccrine) | Produces sweat | Cools body via evaporation |
| Sebaceous gland | Produces sebum | Attached to hair follicle, moistens skin |
| Apocrine gland | Armpit & genital area | Active at puberty, causes body odor |
LO2 - Hair, Nail & Glands Associated with the Skin
HAIR - Structure
| Component | Description |
|---|
| Hair follicle | Epidermal penetration into dermis where hair originates |
| Hair shaft | Exposed portion above skin surface |
| Hair root | Below skin, anchored in follicle |
| Hair bulb | Deep in dermis; contains hair matrix (mitotically active cells) |
| Hair papilla | Connective tissue inside hair bulb; contains blood capillaries & nerve endings |
| Medulla | Central core of hair |
| Cortex | Surrounds medulla; compressed, keratinized cells |
| Cuticle | Outermost layer; very hard, keratinized cells |
3 Types of Hair
| Type | Features | Location |
|---|
| Lanugo | Very fine and long; seen in fetus at 20 weeks | Shed before birth; visible in premature babies |
| Vellus | Short, fine, light-colored | Most of the body |
| Terminal | Thick, coarse, long, darker | Scalp, armpit, pubic, eyebrow, beard |
MEMORY TRICK - "Little Villains Terrorize" = Lanugo → Vellus → Terminal
Hair is ABSENT from:
"Pass, Go, VIP" = Palm, Glans penis, Vulval introitus, sole (Plantar)
NAIL - Structure Table
| Structure | Definition |
|---|
| Nail plate | The hard visible part of nail |
| Nail bed | Under nail plate; pink due to blood vessels; contains nerve endings |
| Nail matrix | Where nail plate is made; matrix cells produce nail plate |
| Lunula | White half-moon at nail base; visible part of matrix |
| Cuticle | Dead, colorless tissue; prevents foreign microorganism invasion |
| Eponychium | Living skin at base of nail plate covering nail matrix |
| Perionychium | Living skin bordering root and sides of nail plate |
| Hyponychium | Thickened skin under nail at the free edge |
Nail growth rate: 0.1 mm/24 hours for fingernails (toenails are slower)
MEMORY TRICK for nail anatomy - "E-P-H" = Edge-to-Proximal-Hypo:
- Hyponychium = under free Hanging edge
- Eponychium = near End (base) living skin
- Perionychium = Perimeter/sides
GLANDS Summary Table
| Gland | Type | Secretion | Location | Key Function |
|---|
| Sebaceous | Saclike | Sebum (oily) | Opens into hair follicle | Lubricate skin & hair, prevent drying |
| Meibomian | Large sebaceous | Lipids | Eyelids | Forms superficial tear film layer |
| Eccrine (Sudoriferous) | Sweat | Sweat (watery) | All over body | Cool body via evaporation |
| Apocrine | Modified sweat | Organic secretion | Armpit, genital | Body odor (bacteria break down secretion) |
| Ceruminous | Modified eccrine | Earwax (cerumen) | Ear canal | Protect ear canal |
| Mammary | Modified eccrine | Milk | Breast | Lactation |
SECTION B: PHYSIOLOGY OF THE SKIN
LO3 - Keratinocyte Maturation Process
Timeline Table
| Stage | Location | Duration | Key Events |
|---|
| Division | Stratum basale | Every 200-400 hours | Stem cells divide |
| Shape change | Stratum spinosum | - | Columnar → Polygonal; most keratin produced; tonofilaments → desmosomes |
| Granule formation | Stratum granulosum | - | Nucleus & organelles degrade (enzymes); keratohyalin produced; membrane-coating granules form skin barrier |
| Horny layer | Stratum corneum | 14 days from basale | Dead, flattened corneocytes; hardened keratin (disulphide bonds); absorbs 3x its weight in water |
| Shedding | Surface | 14 more days | Corneocytes shed daily |
Total keratinocyte maturation = 28 days minimum
- Age 60+: can take 3-4 months
- Psoriasis: turnover is SIGNIFICANTLY SHORTENED
Key Terms to Know:
- Desmosome = distributes mechanical stress evenly in epidermis
- Keratohyalin = granule in stratum granulosum
- Membrane-coating granule = cement between corneocytes = skin barrier
- TEWL = Trans-Epidermal Water Loss (prevented by skin barrier)
- Corneocyte = dead, flattened keratinocyte in stratum corneum
MEMORY TRICK - "Big Strong Gorillas Can Shed"
Basale → Spinosum → Granulosum → Corneum → Shed
(Cells go from Basale, grow Spinosum, make Granules, become Corneum, then Shed)
LO4 - Hair Growth Phases
| Phase | Meaning | Duration | Key Facts |
|---|
| Anagen | Growing phase | 3-7 years (scalp); 4 months (eyebrow) | 80-90% of scalp hairs in this phase; 50-100 follicles switch to catagen/day |
| Catagen | Resting/transitional phase | 3-4 weeks | Hair protein synthesis stops; follicle retreats toward surface; dermal papillae retract; 10-20% of scalp hairs |
| Telogen | Shedding phase | - | Short club hair present; 50-100 hairs shed/day; only 1% of scalp hairs in this phase |
MEMORY TRICK - "ACT it out!"
Anagen (Active/growing) → Catagen (Cease/rest) → Telogen (Terminate/shed)
LO5 - Melanocyte Function
| Feature | Detail |
|---|
| Location | Stratum basale |
| Dendrites | Extend into stratum spinosum and even granulosum |
| Organelle | Melanosome = where melanin is packed |
| Transfer | Melanosome absorbed by keratinocytes; color reflected from cytoplasm |
| Color determination | More melanin production = darker skin (number of melanocytes is SAME across all races) |
| UV protection | Melanin granules form a UV-absorbing blanket in horny layer |
| UV stimulation | UV causes photo-oxidation of melanin + stimulates more melanin production |
| Albinism | Lack of melanocyte → pale appearance |
LO6 - Thermoregulation
| Mechanism | How It Works | Effect |
|---|
| Vasodilation | Blood vessels widen near skin | Increase heat loss |
| Vasoconstriction | Blood vessels narrow | Decrease heat loss |
| Arteriovenous anastomoses | Direct shunts between arteries and veins | Decrease heat loss |
| Sweating (evaporation) | Sweat evaporates from skin surface | Cools body temperature |
Sweat Composition Table
| Component | Concentration |
|---|
| Na+ and Cl- | 30-70 mEq/L (equal amounts) |
| K+ | 5 mEq/L |
| Lactate | 4-40 mEq/L |
| Other | Urea, ammonia, amino acids |
| pH | 4 - 6.8 (acidic) |
- Minimum insensible perspiration/day: 0.5 L
- Maximum insensible perspiration/day: 10 L
- Men sweat more than women
- Body core temperature maintained at ~37°C
MEMORY TRICK for sweat contents - "Na Cl K La"
= Natrium Chloride + K (potassium) + Lactate (plus urea/ammonia)
SECTION C: BIOCHEMISTRY OF THE SKIN
LO7 - The FOUR Important Biomolecules
MEMORY TRICK - "KMCG" = Keratin, Melanin, Collagen, Glycosaminoglycan
OR: "Kings Make Cool Glycoproteins"
Biomolecule Master Table
| Biomolecule | Produced By | Location | Key Properties |
|---|
| Keratin | Keratinocytes | Stratum corneum, hair, nails | High MW polypeptide; epidermal keratin (less cystine, more glycine) vs hair keratin; different keratins at each epidermal level |
| Melanin | Melanocytes | Epidermis | Pigment from tyrosine; Eumelanin (brown-black) vs Pheomelanin (yellow-red); most have both |
| Collagen | Fibroblasts | Dermis | 70-80% of dermis; main AA: glycine, proline, hydroxyproline (unique to collagen); 14 types |
| Glycosaminoglycans (GAG) | Fibroblasts | Dermis | Ground substance; provides viscosity & hydration; main GAG = chondroitin sulphate; form proteoglycans with protein core |
Collagen Types Summary
| Collagen Type | Location |
|---|
| Type I | Reticular dermis |
| Type III | Papillary dermis |
| Type IV & VII | Basement membrane |
| Type VIII | Endothelial cells |
Melanin Forms
| Type | Color |
|---|
| Eumelanin | Brown-black (black hair) |
| Pheomelanin | Yellow or red (blonde hair) |
| Both | Red hair |
| Loss of melanin | Grey hair |
MEMORY TRICK for Melanin:
"Eumelanin = Ebony (dark/black)"
"Pheomelanin = Phoenix (fire/red)"
LO8 - Skin Surface Secretions, Subcutaneous Fat & Hormones
| Topic | Key Details |
|---|
| Skin Surface Secretion | Mainly lipid-based products; mix with sweat to form acid mantle (pH 5.5); acid mantle suppresses microbial proliferation |
| Subcutaneous Fat | Triglyceride (TG) synthesized from β-glycerophosphate + acyl CoA; broken down by lipase → free fatty acids (FFA) + glycerol |
| Function of FFA | Energy source + glycerol production |
MEMORY TRICK for TG synthesis:
"Beta + Acyl = Triglyceride" → Lipase breaks it down to FFA + Glycerol
SECTION D: IMMUNOLOGY OF THE SKIN
LO9 - Immunological Components of the Skin
Three-Level Immune System
| System | Components | Key Function |
|---|
| Structural Barrier | Epidermal barrier (corneocytes), Acid mantle (pH 5.5), Sebum (lipids), Desmosomes | Physical/chemical block against pathogens |
| Cellular Barrier | Langerhans cells, T cells, Mast cells, Keratinocytes, Dermal dendritic cells, Dermal macrophages | Immune cell-based defense |
| Functional Systems | Skin-associated lymphoid tissue (SALT), Lymph vessels/nodes, Cytokines, Anti-microbial proteins, Complement system, Adhesion molecules | Amplification and coordination of immune response |
Cellular Components Table
| Cell | Origin | Type of Immunity | Function |
|---|
| Langerhans cells | Bone marrow | Innate (antigen-presenting) | Outermost sentinel; dendritic; presents antigens |
| T helper cells | Thymus | Adaptive | Amplify immune response; form memory cells |
| Cytotoxic T cells | Thymus | Adaptive | Kill infected/abnormal cells |
| Mast cells | Bone marrow | Innate | Release histamine and vasoactive molecules |
| Keratinocytes | Epidermis | Innate | Secrete pro-inflammatory cytokines; express MHC Class II |
| Dermal dendritic cells | Bone marrow | Innate | Antigen presenting cells |
| Dermal macrophages | Bone marrow | Innate | Antigen presenting cells |
MEMORY TRICK - "LTKMD" = "Langerhans Takes Killer Mast Duties"
Langerhans → T cells → Keratinocytes → Mast cells → Dermal cells
LO10 - Hypersensitivity Reactions Involving the Skin
Master Comparison Table
| Type | Name | Antibody/Cell | Mechanism | Timing | Skin Example |
|---|
| Type I | Immediate / Anaphylactic | IgE bound to mast cells | Antigen crosslinks IgE → mast cell degranulation → histamine, prostaglandins, leukotrienes | Within minutes | Urticaria (hives), Anaphylaxis, Allergic reaction |
| Type II | Antibody-dependent Cytotoxicity | IgG or IgM | Antibody binds antigen on skin cells → NK cell kills target cell OR complement activation → lysis | Hours | Pemphigus vulgaris, Vasculitis (ANCA) |
| Type III | Immune Complex Disease | IgG (antigen-antibody complex) | Complex adheres to blood vessel walls → complement activation → platelet aggregation → neutrophil lysosomal enzymes → tissue damage | Hours | Dermatomyositis, Arthus reaction |
| Type IV | Delayed / Cell-mediated | T helper cells (no antibody) | Second/third contact with antigen → T helper activation → immune amplification → cell recruitment | 48-72 hours | Allergic contact dermatitis, Leprosy, Tuberculosis |
MEMORY TRICK - "I Am Immune, Delayed"
I = Type I (Immediate, IgE)
A = Type II (Antibody cytotoxicity, IgG/IgM)
Im = Type III (Immune complex)
D = Type IV (Delayed, T cells)
Type I vs Type IV - Quick Distinguisher
| Feature | Type I | Type IV |
|---|
| Speed | Minutes | 48-72 hours |
| Mediator | IgE + Mast cells | T helper cells |
| Example | Allergy, urticaria | Contact dermatitis |
SECTION E: SUPER MEMORY TRICKS SUMMARY PAGE
| Topic | Memory Trick |
|---|
| Epidermal layers (outside→in) | "Come, Lets Get Some Beer" - Corneum, Lucidum, Granulosum, Spinosum, Basale |
| Epidermal cells | "King Suleiman Loves Making Medicines" - Keratinocyte, Stem, Langerhans, Melanocyte, Merkel |
| Hair types | "Little Villains Terrorize" - Lanugo, Vellus, Terminal |
| Hair absent from | "Pass Go VIP" - Palm, Glans, Vulval introitus, (Plantar) sole |
| Hair growth phases | "ACT it out!" - Anagen, Catagen, Telogen |
| Keratinocyte maturation | "Big Strong Gorillas Can Shed" - Basale→Spinosum→Granulosum→Corneum→Shed |
| 4 Biomolecules | "Kings Make Cool Glycoproteins" - Keratin, Melanin, Collagen, GAG |
| Melanin types | Eumelanin = Ebony (dark) / Pheomelanin = Phoenix (fire/red) |
| Sweat contents | "Na Cl K La" - Sodium chloride, Potassium, Lactate |
| Collagen main AA | "Glycine Pronto Hydroxy" - Glycine, Proline, Hydroxyproline (hydroxyproline is UNIQUE to collagen) |
| Hypersensitivity types | "I Am Immune, Delayed" - Type I (Immediate), II (Antibody), III (Immune complex), IV (Delayed) |
| Skin immune layers | "SCF" = Structural → Cellular → Functional |
SECTION F: LIKELY EXAM QUESTIONS & HOW TO ANSWER THEM
SAQ (Short Answer Questions) - Quick Answer Templates
Q: Name the layers of the epidermis from innermost to outermost.
Stratum basale → Stratum spinosum → Stratum granulosum → Stratum lucidum (thick skin only) → Stratum corneum. Use: "Big Strong Gorillas Can Stand."
Q: What is the role of desmosomes in the epidermis?
Desmosomes are formed from tonofilaments (aggregated keratin) in the stratum spinosum. They distribute mechanical stress evenly across the epidermis, providing structural integrity.
Q: How long does keratinocyte maturation take? What affects it?
Minimum 28 days: 14 days from basale to corneum, then 14 days for shedding. Slows with age (3-4 months at age 60). In psoriasis, turnover is significantly shortened.
Q: What is the function of the acid mantle?
The acid mantle is formed by lipid-based skin surface secretions mixing with sweat, giving a pH of 5.5. Its function is to suppress microbial proliferation on the skin surface.
Q: Differentiate Type I from Type IV hypersensitivity.
Type I: immediate, IgE-mediated, mast cell degranulation, results in urticaria/anaphylaxis. Type IV: delayed (48-72 h), T helper cell-mediated, no antibody, results in allergic contact dermatitis.
LAQ (Long Answer Questions) - Full Framework
Q: Describe the keratinocyte maturation process.
Answer structure:
- Definition (differentiation from basale to corneum)
- Timeline (28 days; basale replication 200-400h)
- Stratum basale - division
- Stratum spinosum - shape change, keratin/tonofilaments/desmosomes
- Stratum granulosum - nucleus degradation, keratohyalin, membrane-coating granules, skin barrier, TEWL
- Stratum corneum - dead corneocytes, disulphide bonds, 3x water absorption
- Clinical relevance - age effect, psoriasis
Q: Describe the immunological components of the skin.
Answer structure:
- Structural barrier - epidermal barrier, acid mantle, sebum, desmosomes
- Cellular barrier - Langerhans (innate, dendritic, bone marrow), T cells (adaptive, memory), Mast cells (histamine), Keratinocytes (cytokines, MHC II), Dermal dendritic + macrophages
- Functional systems - SALT, lymph vessels, cytokines, AMP, interleukins, IFN-γ, complement, adhesion molecules
Q: Compare and contrast the four types of hypersensitivity reactions affecting the skin.
Answer using the Master Comparison Table above - cover antibody type, mechanism, timing, and skin example for each type.
SECTION G: HIGH-YIELD BOLD KEYWORDS MASTER LIST
| Topic | Must-Know Keywords |
|---|
| Epidermis | Stratum basale, spinosum, granulosum, lucidum, corneum, corneocyte, desmosome, tonofilament, TEWL |
| Cells | Keratinocyte, Langerhans, Melanocyte, Merkel, Stem cell |
| Hair | Anagen, Catagen, Telogen, hair matrix, hair papilla, hair bulb, medulla, cortex, cuticle |
| Nail | Nail matrix, lunula, eponychium, perionychium, hyponychium, nail plate, bed epithelium |
| Glands | Sebum, sebaceous, eccrine, apocrine, meibomian, ceruminous |
| Keratinocyte maturation | Keratohyalin, membrane-coating granule, skin barrier, disulphide bond, psoriasis |
| Biochemistry | Keratin, Melanin, Collagen, GAG, eumelanin, pheomelanin, hydroxyproline, chondroitin sulphate, proteoglycan |
| Melanin | Melanosome, tyrosine, UV-absorbing blanket, photo-oxidation, albino |
| Thermoregulation | Vasodilation, vasoconstriction, arteriovenous anastomosis, insensible perspiration, acid pH (4-6.8) |
| Immunology | Langerhans, MHC Class II, SALT, complement, cytokines, AMP, IFN-γ, adhesion molecules |
| Hypersensitivity | IgE, IgG, IgM, mast cell degranulation, histamine, T helper, NK cell, complement, 48-72 hours, urticaria, pemphigus vulgaris, contact dermatitis |
Pro Exam Tip: For any LAQ, always follow this structure:
- Define the topic (1-2 sentences)
- List/classify (use numbers or table if allowed)
- Explain mechanism (the "how")
- Give clinical significance (psoriasis for keratinocyte, albinism for melanocyte, anaphylaxis for Type I, etc.)
- Conclude with one bold fact (e.g., "Hydroxyproline is UNIQUE to collagen and used as a marker")
Good luck in your exams! Your skin is your asset - so is this knowledge. 💪
