The Skin

Question 1

WHAT DOES THE INTEGUMENTARY SYSTEM CONSIST OF?

Answer 1

The skin and its accessory structures (hair, nails. glands and sensory receptors)

Question 2

THE INTEGUMENTARY SYSTEM

•Comprises the skin and its accessory structures

–hair, nails, glands and sensory receptors

•Covers the _ surface of the body

–Adult human skin has:

• a surface area of between 1.8 and 2.0 m2
• a _ of between 0.5 and 4.5 mm
• a mass of between 4.5 and 5 kg
• an extensive vasculature
• an abundance of secretory glands (sweat, sebaceous)
• an abundance of _ receptors (touch, pain, thermal)

Answer 2

External

Thickness

Sensory

Question 3

INTEGUMENTARY SYSTEM; STRUCTURE

Question 4

TWO MAJOR SKIN TYPES

Question 5

THE EPIDERMIS- A KERATINISED, STRATIFIED SQUAMOUS EPITHELIUM

Composed of layers or strata of _ that differ in form and function

• Stratum basale - single layer of columnar keratinocytes resting on a basement membrane: site of production of new keratinocytes.
• Stratum spinosum – multiple rows of closely packed, many sided keratinocytes tightly linked by desmosomes
• Stratum granulosum – multiple rows of flattened keratinocytes containing darkly staining keratohyalin granules and lipid-rich lamellar bodies – on release these form an hydrophobic, impermeable barrier
• Stratum lucidium – multiple rows of clear, flat, dead, keratin-rich keratinocytes; present only in _ skin.
• Stratum corneum - multiple rows of dead, flat, enucleate keratinocytes that comprise mostly cross-linked keratin fibres (squame cells)

Answer 5

Keratinocytes

Thick

Question 6

WHAT IS THE STRATUM SPINOSUM?

Answer 6

Multiple rows of closely packed, many sided keratinocytes tightly linked by desmosomes

Question 7

WHAT IS THE STRATUM GRANULOSUM?

Answer 7

Multiple rows of flattened keratinocytes containing darkly staining keratohyalin granules and lipid-rich lamellar bodies – on release these form a hydrophobic, impermeable barrier

Question 8

WHAT IS THE STRATUM CORNEUM?

Answer 8

Multiple rows of dead, flat, enucleate keratinocytes that comprise mostly cross-linked keratin fibres (squame cells); the stratum corneum allows you to get wet without absorbing lots of water

Question 9

WHAT IS THE STRATUM BASALE?

Answer 9

Single layer of columnar keratinocytes resting on a basement membrane: site of production of new keratinocytes

Question 10

WHAT IS THE STRATUM LUCIDIUM?

Answer 10

Multiple rows of clear, flat, dead, keratin-rich keratinocytes; present only in thick skin

Question 11

WHAT IS THE EPIDERMIS COMPOSED OF?

Answer 11

Layers of strata of keratinocytes that differ in form and function

Question 12

STRUCTURE OF THE EPIDERMIS

Question 13

KERATINS

•Family of _ filament-forming proteins

–54 proteins in two families: type I (acidic) & type II (neutral or basic)

•Comprise 25-30 % of total protein in the epidermis

–80 - 85 % of total protein in the stratum corneum

•Form branching, rope-like bundles in the cell _.

–associate with junctional (anchoring) complexes at the cell periphery

• Desmosomes (cell-cell) and hemidesmosomes (cell-matrix)
• Maintain the structural integrity of the epidermis
• Allow the epidermis to resist and dissipate mechanical forces

Answer 13

Cytoskeleton

Cytoplasm

Question 14

WHAT ARE KERATINS AND WHAT DO THEY DO?

Answer 14

Family of cytoskeleton filament-forming proteins that maintain the structural integrity of the epidermis

Question 15

JUNCTIONAL COMPLEXES ANCHOR KERATINOCYTES TO EACH OTHER AND TO THE BASEMENT MEMBRANE

Answer 15

Question 16

PRESENCE AND DISTRIBUTION OF OTHER CELL TYPES IN THE EPIDERMIS

Langerhans cells- they move within the epidermis, they are also _-presenting cells. They will present antigens to T-cells.

Merkel cell- Sensory- synaptic connections to _ endings.

Melanocyte cell- makes _.

Answer 16

Antigen

Nerve

Melanin

Question 17

WHAT DO LANGERHANS CELLS DO?

Answer 17

They move within epidermis and are antigen-presenting cells (they will present antigens to T-cells)

Question 18

TRANSFER OF MELANOSOMES FROM MELANOCYTES TO KERATINOCYTES IN THE EPIDERMIS

Question 19

MELANOSOMES TRANSFERRED TO KERATINOCYTES MIGRATE TO THE PERI-NUCLEAR REGION AND FORM A PROTECTIVE ‘CAP’

Question 20

WHAT DETERMINES SOMEONE’S SKIN COLOUR?

Answer 20

Determined by the absolute and relative amounts of eumelanin and pheomelanin synthesised (the number of melanocytes in the skin is similar in all individuals).

Question 21

STRUCTURE OF THE DERMIS

Question 22

WHAT ARE THE TWO REGIONS OF THE DERMIS?

Answer 22

• Papillary (20% of total dermis thickness)
• Reticular (80% of total dermis thickness)

Question 23

ACCESSORY SKIN STRUCTURES: HAIR

•Grow from hair _ located in the dermis

–follicles develop from downward projections of the _.

•Composed of columns of dead, keratinized epithelial cells

–originate from a germinal matrix or stratum _ located in the hair bulb.

Answer 23

Follicles

Epidermis

Basale

Question 24

WHERE DOES HAIR GROW FROM?

Answer 24

Hair follicles located in the dermis (hair follicles develop from the downwards projections of the epidermis).

Question 25

WHAT IS HORRIPILATION?

Answer 25

Goosebumps

Question 26

THE GROWTH OF HAIR IS CONTINUOUS. TRUE OR FALSE?

Answer 26

FALSE It isn't continuous

Question 27

WHAT ARE THE FOUR STAGES OF THE HAIR GROWTH CYCLE?

Answer 27

1. *Anagen*/Growth phase 2. *Catagen*/Transition phase 3. *Telogen*/Resting phase 4. *Exogen*/Shedding phase

Question 28

**_THE HAIR GROWTH CYCLE_** THE GROWTH OF HAIR IS NOT CONTINUOUS 1. *Anagen* or growth phase: –85-90% of all body hair –Duration determines _ of hair * scalp: 2-8 years; eyebrows: 4-7 months * *Catagen* or transition phase –Hair follicle shrinks and detaches from \_. * scalp: 2-3 weeks; eyebrows: 3-4 weeks * *Telogen* or resting phase –10-15% of all body hair * scalp: ~ 3 months; eyebrows: ~ 9 months * *Exogen* or shedding phase –extension of the resting phase •normal scalp 50-100 hairs shed per day

Answer 28

Length Papilla

Question 29

WHAT DETERMINES THE LENGTH OF YOUR HAIR?

Answer 29

The duration of the *Anagen*/growth phase in your hair

Question 30

**_ACCESSORY SKIN STRUCTURES: GLANDS_** •Specialised, secretory structures formed by _ cells –two categories: endocrine (ductless) and exocrine (with ducts) All the glandular structures in the skin are \_. •exocrine glands can be categorised further according to: –their structure (simple or compound) –their mode of _ (merocrine, apocrine or holocrine)

Answer 30

Epithelial Exocrine Secretion

Question 31

WHAT ARE THE TWO CATEGORIES OF GLANDS?

Answer 31

Endocrine (ductless) Exocrine (with ducts)

Question 32

ALL THE GLANDULAR STRUCTURES IN THE SKIN ARE ENDOCRINE. TRUE OR FALSE?

Answer 32

FALSE They are exocrine

Question 33

WHAT TWO THINGS CAN YOU USE TO CATEGORISE EXOCRINE GLANDS?

Answer 33

Their structure (simple or compound) Their mode of secretion (*merocrine*, *apocrine* or *holocrine*)

Question 34

WHAT ARE THE TWO MAIN TYPES OF GLAND IN THE SKIN?

Answer 34

Sebaceous Sudoriferous (eccrine and apocrine)

Question 35

**_SEBACEOUS GLANDS_** •Produce lipid-rich sebum: - triglycerides ~ 40% - wax esters ~ 26% - squalene ~ 12% - free fatty acids ~ 16% - cholesterol ~ 4% •Holocrine secretion - directly into hair _ or onto _ surface •Active at birth - activity increases at \_ •Absent from plantar and palmar surfaces

Answer 35

Follicles Skin Puberty

Question 36

**_SUDORIFEROUS (APOCRINE AND ECCRINE) SWEAT GLANDS_** ## Footnote **Apocrine** (25% of total): * Limited distribution (axilla, groin, bearded regions of face) * Duct opens into the hair follicle * Secretory mechanism is merocrine * Similar to eccrine but more viscous due to presence of _ and proteins * Activity linked to emotional state (secretion may contain pheromones) * Active from \_ **Eccrine** (75% of total): * Widely distributed esp. forehead, plantar and palmar surfaces * Duct opens at the _ surface * Secretory mechanism is merocrine * Hypotonic and slightly \_ contains H2O, Na+, Cl-, K+, urea, lactate * ~ 600 ml/day at rest * Active from shortly after \_

Answer 36

Lipids Puberty Epidermal Acidic Birth

Question 37

WHEN DO ECCRINE SWEAT GLANDS BECOME ACTIVE?

Answer 37

Shortly after birth

Question 38

WHERE DO APOCRINE GLANDS OPEN UP INTO?

Answer 38

Into the hair follicle

Question 39

WHAT ARE THE THREE TYPES OF SKIN (CUTANEOUS) SENSORY RECEPTORS?

Answer 39

Mechanoreceptors Thermoreceptors Nociceptors

Question 40

**_MECHANORECEPTORS IN THE HUMAN HAND_**

Question 41

**_FUNCTION: THERMOREGULATION_**

Question 42

**_BARRIER FUNCTION OF THE SKIN_**

Question 43

**_PRODUCTION OF VITAMIN D3_**

Question 44

**_STRATUM CORNEUM: A PERMEABILITY BARRIER THAT MINIMISES TRANS-EPIDERMAL WATER LOSS (TEWL)_**

Question 45

**_FACTS ABOUT THE SKIN_** * Thickness = ~1 mm, on average * Epidermis is only 1/10th of the total membrane (~0.1 mm) * Stratum corneum represents 1/10th of the \_. (~0.01 mm) * 60% of an adult’s weight is \_. * Total surface area of skin in a typical adult = ~2 m2 = 20,000 cm2 * Concentration of water inside the body = ~50 Molar!!!! * Concentration of water outside the body is usually very small * However, we only lose 200-300 mL across the skin per day due to the stratum \_.

Answer 45

Epidermis Water Corneum

Question 46

WHAT IS A COMMENSAL RELATIONSHIP?

Answer 46

One of the partners benefits but the other suffers no harm

Question 47

WHAT IS A MUTUALISTIC RELATIONSHIP?

Answer 47

Where both partners benefit

Question 48

WHAT IS A PATHOGENIC RELATIONSHIP?

Answer 48

Causing or capable of causing disease

Question 49

**_THE HUMAN EPIDERMIS IS COLONISED BY A WIDE VARIETY OF MICRO-ORGANISMS (MICROBIOTA OR MICROBIOME)_**

Question 50

PATHOGENIC STRAINS CAN EMERGE FROM COMMENSAL POPULATIONS OF BACTERIA. TRUE OR FALSE?

Answer 50

TRUE

Question 51

**_THE ANTIMICROBIAL BARRIER FUNCTION OF THE SKIN IS MULTIFACTORIAL AND NOT LIMITED TO THE STRATUM CORNEUM_** ## Footnote * Intact skin presents a physical barrier to invasion * Acidity of the skin surface and stratum corneum (pH 4.5 - 5.5) –secretion of sebum and _ sweat –enzymatic breakdown of _ to produce free fatty acids –extrusion of H+ in exchange for Na+ by cells in the stratum granulosum –release of acidic _ by-products by microorganisms •Production of a wide range antimicrobial peptides (AMPS) –potent, broad spectrum –rapidly produced in response to invading _ (0 - 4 hrs) **Form a major part of the innate immune response!!!**

Answer 51

Eccrine Phospholipids Metabolic Pathogens

Question 52

WHAT IS THE pH OF THE SKIN SURFACE AND STRATUM CORNEUM?

Answer 52

4.5-5.5

Question 53

WHY IS THE SKIN SURFACE AND STRATUM CORNEUM ACIDIC?

Answer 53

–Secretion of sebum and eccrine sweat –Enzymatic breakdown of phospholipids to produce free fatty acids –Extrusion of H+ in exchange for Na+ by cells in the stratum granulosum –Release of acidic metabolic by-products by microorganisms

Question 54

**_ANTIMICROBIAL BARRIER FUNCTION OF THE SKIN: PRODUCTION OF AMPs IN RESPONSE TO INVADING PATHOGENS_**

Question 55

**_EPIDERMAL KERATINOCYTES AND LANGERHAN'S CELLS CO-OPERATE IN THE MOBILISATION AND TARGETING OF CELLS OF THE ADAPTIVE IMMUNE SYSTEM_** ## Footnote •Release of intercellular chemical messengers –cytokines •e.g., Interkeukins: IL-1, IL-6, Tumour Necrosis Factor (TNF)-a –chemokines (CC- and CXC-chemokine ligands) * e.g., CCL20, CXCLs 8 (also known as IL-8), 9 and 10 * Dynamic adjustment of tight junctions –allows Langerhan’s cells to sample antigens in the stratum corneum

Question 56

**_BARRIER FUNCTION OF THE SKIN: RAPID ACTIVATION OF INNATE IMMUNITYLEADS TO DELAYED ACTIVATION OF ADAPTIVE IMMUNITY_** Innate section shows within hours Adaptive shows within days

Question 57

**_IN HEALTH, EPIDERMAL HOMEOSTASIS MAINTAINS THE BARRIER FUNCTION OF THE SKIN_** Loss of cells from the stratum corneum is precisely matched by the proliferation, upward migration and differentiation of cells from the stratum \_. In the human epidermis stem cells are located in specialised ‘niches’ within the inter-follicular epidermis and bulge region of the hair \_.

Answer 57

Basale Follicle

Question 58

WHERE IN THE HUMAN EPIDERMIS ARE STEM CELLS LOCATED?

Answer 58

They are located in specialised ‘niches’ within the inter-follicular epidermis and bulge region of the hair follicle

Question 59

**_KINECTICS OF TURNOVER IN THE HUMAN EPIDERMIS_** ## Footnote * In healthy skin, homeostasis maintains a functional barrier. * However, in atopic dermatitis, or eczema, the balance is disrupted. * Desquamation accelerates and barrier is weakened. * More facile penetration of irritating chemicals now possible. * Exacerbates the disruption.