msts

Question 1

functions of skin

Answer 1

Protection from pressure, temp, chemicals, uv, bacteria (forms physical barrier against water loss)

Thermoregulation

Cutaneous sensation

Excretion - metabolic waste products excreted via sweat

Absorption of lipid-soluble products

Vitamin D synthesis

Question 2

what are the 3 skin layers

Answer 2

epidermis
dermis
hypodermis/subcutaneous layer

Question 3

what is epidermis and its function

Answer 3

• uppermost layer of skin
• responsible for the look and health of skin
• acts as a protective barrier against moisture loss & penetration of harmful particulate matter + micro-organisms

Question 4

what cells does the epidermis contain?

Answer 4

1. keratinocytes
2. langerhans cells
3. melanocytes
4. merkel cells/ tactile cells

Question 5

use of keratinocytes

Answer 5

• approx 90% of epidermal cells
• produces keratin (tough and fibrous protein, protect skin)
• produces lamellar granules (release a water-repellent substance that helps waterproof the skin)

Question 6

use of langerhans cells

Answer 6

• responsible for skin immunology
• recognise foreign microbes, engulfs and destroys
• present their antigens to immune system for further action

Question 7

use of melanocytes

Answer 7

• produce melanin granules (responsible for skin colour)
• melanin absorbs UV radiation to protect skin from damage

Question 8

use of merkel/tactile cells

Answer 8

• found at the border btwn epidermis and dermal layer
• each Merkel cell is associated with a Merkel disc (sensory nerve ending)
• together acts as a slowly-adapting touch receptor

Question 9

layers of epidermis

Answer 9

1. stratum corneum (top)
2. stratum lucidum
3. stratum ganulosum
4. stratum spinosum
5. stratum basale (bottom)

Question 10

describe the keratinisation process

Answer 10

typically takes abt 28 days, speed indirectly proportional to age

1. new stem cells, keratinocytes & melanocytes are produced in the stratum basale, pushing older cells towards surface
2. cells at stratum spinosum are alive and joined together by desmosomal connections
3. at the stratum granulosum, keratinocytes are mature and flattened. keratin and glycolipids are produced
4. cells at stratum corneum are dead, flattened and engorged with keratin. They undergo desquamation and flake away (skin shedding)

Question 11

‘Brick and Mortar’ structure for stratum corneum

Answer 11

brick = staggered and layered lattice of keratinocytes
mortar = intercellular lipid bilayer matrix (liquid)
bricks are connected by corneodesmosomes

Question 12

dermis use

Answer 12

• tough, viscoelastic tissue matrix
• responsible for elasticity and strength of skin
• supplies epidermis w nutrients
• impt role in thermoregulation

Question 13

what is dermis made of

Answer 13

• connective tissues: collagen and elastin fibers (fibroblasts) ✨⭐️
• most nerve endings, blood vessels, immune and lymphatic systems of skin
• hair follicles and sweat glands

Question 14

fibroblasts

Answer 14

collagen fibers
- 70% of dermis
- impart toughness and strength & resistance to stretching forces

elastin fibers
- 2% of dermis
- loosely arranged in all directions
- provide elasticity

Question 15

what happens when skin age? (use fibroblasts)

Answer 15

when skin ages, the amt of collagen and elastin fibers reduce.

collagen fibers will lose some of their strength —> skin becomes more susceptible to damage

elastin fibers lose their elasticity —> produces sagging skin

Question 16

function of arrector pili muscle

Answer 16

• it is associated to each hair on the skin surface
• in cold temps/fear/emotion, arrector pili muscle contracts —> erects the hair producing ‘goose pimples’

Question 17

types of sweat glands

Answer 17

1. eccrine (on skin surface)
2. apocrine (at hair follicle)

Question 18

eccrine glands

Answer 18

• more abundant
• produce a clear, slightly salty fluid
• composed of water, inorganic (nacl, k+) and organic compounds (lactic/citric acid)
• odorless
• cools the body and prevent overheating (thermoregulation)

Question 19

apocrine sweat glands

Answer 19

• less abundant
• produce a milky fluid containing fatty acids
• composed of water, proteins. carbohydrates, ammonium salts & organic fatty acid
• fatty organic compounds break down by bacteria to produce characteristic odour
• no thermoregulation

Question 20

hypodermis uses

Answer 20

• functions as protective cushion and insulator

Question 21

how is melanin produced

Answer 21

melanocytes produce the enzyme tyrosinase (biological catalyst) —> converts tyrosine to melanin (oxidation + polymerisation rxn)

enzymatic activity increases upon exposure to UV —> melanin production increase upon exposure to sunlight

Question 22

Does the number of melanocytes determine skin colour?

Answer 22

No. People have same number of melanocytes but the amount of pigment/melanin produced by each melanocyte differs

Question 23

2 types of melanin produced

Answer 23

1. pheomelanin = pink to red colour
2. eumelanin = yellow to brown/black

Question 24

functions of hair

Answer 24

1. serve primarily as a covering and protection
2. hair on head protects scalp from direct heat from sun/damages/other harsh external environment
3. acts as thermoregulator
4. used for decorative manner for physical appearance

Question 25

how does hair act as a thermoregulator?

Answer 25

Cold - hair will erect to trap air —> provide insulation and keep body warm Hot - hairs lie flat —> heat can escape - hair will facilitate the evaporation of perspiration—> cools body

Question 26

structure of hair

Answer 26

1. hair bulb (swelling at base in dermis) 2. hair root (remainder of hair within follicle) 3. hair shaft (above skin surface/hair we see)

Question 27

what is dermal papilla and its function

Answer 27

- a bud of *vascular connective tissue* where hair bulb grows around - provides hair w its sole source of nutrition

Question 28

what is hair matrix

Answer 28

- region of *mitotically active* cells - hair’s growth center - immediately above papilla

Question 29

hair shaft formation

Answer 29

1. hair grows from *stem cells* (generated by sebaceous glands sitting beside follicle) 2. stem cells are *keratinized* (cytoplasm of stem cells are replaced by keratin) 3. keratinized cells contain no cytoplasm or nucleus, tough and insoluble 4. as more keratinized cells are generated, they are pushed into *follicle canal* 5. when entire canal is packed, a column of keratinized cells emerge from follicle and form hair shaft

Question 30

structure of hair shaft

Answer 30

1. medulla (innermost) 2. cortex 3. cuticle (outermost)

Question 31

what is cuticle and its function

Answer 31

- *transparent* layer made of overlapping scale-like cells (each individual scale is attached to cortex) (penetration of water/dye occurs *between scales*, not through) - *hard* —> protects the more delicate cortex and medulla from fraying and falling apart - does not contribute much to hair strength - responsible for shine of hair

Question 32

cortex function

Answer 32

- formed from cortical cells - gives hair its *strength, flexibility, elasticity & colour*

Question 33

kinds of cortical cells

Answer 33

1. orthocortical cells - larger diameter - more matrix btwn microfibrils - *more sulfur content* 2. paracortical cells - smaller dia - smooth rounded borders - *low sulfur content* 3. mesocortical cells - btwn the 2

Question 34

what do cortical cells do

Answer 34

- decides the hair curl - lesser size diff btwn the 2 diff cortical cells = less curl (vice versa)

Question 35

medulla

Answer 35

- essentially one of empty space - runs the length of hair in continuous/discontinuous form - does not contain cysteine - increases thermal insulation of fiber - found on thick hairs, not thin

Question 36

composition of hair

Answer 36

cysteine-rich keratin proteins keratin = insoluble, complex protein glutamic acid = major amino acid found in hair keratin

Question 37

types of bonds in hair keratin

Answer 37

1. peptide bonds 2. hydrogen bond 3. salt linkages 4. disulphide bonds

Question 38

peptide bonds

Answer 38

keratin —> amino acids joined tgt by peptide/amide bonds (condensation/dehydration rxn) to form long chain polypeptides long chains are coiled & linked tgt to form a helix structure (backbone of hair keratin)

Question 39

hydrogen bond

Answer 39

located btwn coils of alpha helix (along the backbone of keratin protein structure) H-O/N/F easily disrupted by water/heat weak bonds, but bcs there are many hydrogen bonds, it gives 35% of hair’s total strength & 50% of elasticity bonds break & reform every time hair wets and dries

Question 40

what happens when hair is wet

Answer 40

- water is inserted into strands via hydrogen bonding - water breaks down bonds btwn protein strands temporarily & reforms

Question 41

why does hair curl in high humidity conditions

Answer 41

high humidity in air = high water content in air more H bonds forms btwn keratin protein strands in hair & hair will fold back on itself at a greater rate

Question 42

salt linkages

Answer 42

- formed by electrostatic attraction btwn cation of amino acid & anion of another amino acid - formed by electron transfer from side chain of basic amino grp to side chain of acidic amino acid - dependent on pH of environment + pKa of side chains - easily broken by strong acidic or alkaline solutions

Question 43

disulfide bonds

Answer 43

- formed when 2 S atoms from neighbouring protein strands containing cysteine are joined - covalent bond = strong = not easily broken by water/heat - wet strength of hair fibers is determined by conc of disulfide bonds - strength of dry hair fibers is dependent largely on Van der Waals forces and ionic interactions

Question 44

permanent-waving of hair

Answer 44

- create chemical and physical changes in hair disulfide bonds 1. disulfide bonds in keratin are opened w a reducing agent (thioglycolate) 2. hair is put in curlers & put under strain to separate thiol grps that were once paired 3. hair is treated w oxidising agent —> converts thiol back to disulfide (thiol grps find new partners, keeps hair in a new configuration)