MTM WK4 - DERMIS/EPIDERMIS

Question 1

LAYERS OF SKIN

Answer 1

• epidermis (apendages are nails, hair, sweat glands)
• dermis (angulations (bends) in bottom of epidermis stick to dermis to anchor it (Dermal-epidermal junction)
  (papillary layer on top then reticular)
• hypodermis (has adipose tissue & larger vessels which supply & drain dermal blood vasculature)

Question 2

JOBS OF SKIN (3 jobs)

Answer 2

• thermoregulation (sweat)
• protect against external threats (mechanical, water loss, biological, UV light)
• resist bacteria/fungal invasion as have langerhan cells (antigen-presenting) to do immune response

Question 3

INNERVATION OF SKIN (efferent & afferent)

Answer 3

EFFERENT NERVE SUPPLY - non-myelinated fibres from sympathetic part of autonomic nervous system
AFFERENT NERVE SUPPLY - transmits impulses from sensory nerve endings to CNS (free nerve endings needed for pain sensation & detecting temp)

Question 4

BLISTER

Answer 4

friction leads to epidermis & dermis separating so fluid accumulates & blister forms

Question 5

KERATINOCYTES

Answer 5

• synthesise keratin (used to strengthen epidermis)
• start in basal layer then move up to form prickle cell layer & do terminal differentiation & lose nucleus & die to form dead, protective, waterproofing keratin layer (become corneocytes as we get to top & die)

Question 6

LAYERS OF EPIDERMIS (superficial to deep)

Answer 6

1. STRATUM CORNEUM (dead keratinocytes/corneocytes)(horny layer)
2. STRATUM LUCIDUM (only exists in thick skin layers)
3. GRANULAR LAYER (stratum granulosum)(keratohyalin granules (strength) & enzymes which degrade bi-layer)
4. PRICKLE CELL LAYER (stratum spinosum)(has langerhans cells)
5. STRATUM BASALE (has melanocytes) (has merkel cells) (cells here change)

Question 7

PRICKLE CELL LAYER (spinosum) keratin doings

Answer 7

keratin (from keratinocytes) accumulates within each spinous cell (keratin passed between adjacent cells upwards (as spinous cells full) at desmosome junctions)

Question 8

HOW MELANOCYTES WORK

Answer 8

produce melanin & have dendrites throughout layer which are phagocytosed to spew out melanin

Question 9

MERKEL CELLS

Answer 9

mechanoreceptors for touch sensation in dermal/epidermal junction (basal layer)

Question 10

PSORIASIS

Answer 10

• abnormal growth & differentiation of keratinocytes

- appears as excessive scaling of skin

Question 11

ALLERGIC CONTACT DERMATITIS

Answer 11

due to epidermal Langerhans cells & T-lymphocytes

Question 12

MALIGNANT MELANOMA

Answer 12

• malignant tumour of melanocytes

- if tumour cells above basal membrane it is good but otherwise is worrying

Question 13

VITILIGO

Answer 13

autoimmune disease on melanocytes

Question 14

PILOSEBACEOUS UNIT

Answer 14

• has hair sheath (outskirt) & hair shaft & sebaceous gland (secretes oils of skin into hair shaft) & arrector pilli muscle to keep up hair

Question 15

ECCRINE SWEAT GLANDS

Answer 15

release sweat directly into skin surface (is mostly water w some nutrients)

Question 16

APOCRINE SWEAT GLANDS

Answer 16

release sweat into hair follicles (apocrine secretion which is digested by microbes to form body odour)

Question 17

VASCULATION OF SKIN

Answer 17

smaller blood vessels (e.g. capillary) in epidermis lniked to larger blood vessels in dermis by interconnecting vessels

Question 18

FIRST DEGREE BURN

Answer 18

epidermal damage only (red but no blister)

Question 19

SECOND DEGREE BURN

Answer 19

• SUPERIOR PARTIAL THICKNESS (all the way through epidermis & touches top of dermis (papillary layer))(red blistered)
• DEEP PARTIAL THICKNESS (into upper dermis (reticular layer))(yellow/white)

Question 20

THIRD DEGREE BURN

Answer 20

all the way through dermis (white/brown but painless as all way through dermis)

Question 21

REVERSE TRANSCRIPTASE

Answer 21

converts RNA to DNA

Question 22

WHY RNA LESS STABLE THAN DNA

Answer 22

RNA has -OH group at carbon 1 but DNA only has H (de-oxy) & the RNA can be attacked by water due to having that -OH)

Question 23

DNA REPLICATION style

Answer 23

semi conservative (each daughter has one old & one new strand)

Question 24

DNA polarity

Answer 24

enzymes bind from 5-prime to 3-prime (uni-directional)

Question 25

dNTP's

Answer 25

building blocks for DN synthesis (if adenine = dATP, cytosine = dCTP)

Question 26

DNA SYNTHESIS

Answer 26

- 5-prime to 3-prime - complementary base binds to first base & DNA polymerase binds next complementary dNTP but loses 2 phosphates doing it

Question 27

REPLICATION FORK

Answer 27

DNA polymerase bonds from 3-prime to 5-prime in the 5-prime strand (leading) BUT in lagging strand, there would be a gap behind where DNA polymerase starts so DNA polymerase enzymes bind in multiple sites to form okazaki fragments (joined by DNA ligase)

Question 28

HOW DNA POLYMERASE PROOF READS

Answer 28

DNA polymerase adds a base (dNTP), moves back to check it & removes it if it is wrong then moves on

Question 29

DNA TRANSLATION

Answer 29

ribosome comes in on mRNA & has 2 binding sites (P-site & A-site). First brings tRNA molecule (held in P-site) complementary to first codon & then tRNA complementary to next codon (tRNA in A-site)

Question 30

TRANSCRIPTOME

Answer 30

complete set of RNA transcripts (varies from cell to cell)

Question 31

TELOMERES

Answer 31

- PROS - allow replication all the way to tip of chromosome - CONS - long tracts of repeats can be unstable which leads to deletions immediately below telomeres - side of chromosome & there are repeat sequences here to protect chromosome)

Question 32

CENTROMERES

Answer 32

used for segregation during cell division

Question 33

MINI SATELLITES

Answer 33

no purpose but can cause mispairing in cell division to give duplication/deletion between homologous chromosomes

Question 34

CHROMATIN

Answer 34

used in DNA packaging (DNA wraps around chromatin & chromatin fibres packed into nucleosome) - HETEROCHROMATIN (inaccessible as in nucleus) - EUCHROMATIN (accessible and can be activated or inactivated for transcription)

Question 35

MITOSIS

Answer 35

1. P - chromosomes condense & spindle fibres are formed 2. M - nuclear membrane broken down, spindle fibres to equator, tension on kinetochores at centromere facing opp. directions 3. A - kinetochore microtubules disappear & chromosomes go to opp. poles 4. T - nuclear membrane reforms around chromosomes & RNA synthesis begins 5. C - cytoplasm divides to 2 daughter cells

Question 36

INDEPENDENT ASSORTMENT

Answer 36

mix of maternal & paternal chromosomes = genetic variation

Question 37

CROSSING OVER

Answer 37

- homologous pair of paternal chromosomes duplicate & cross over (recombine) to give mix of chromosomes (genetic variation) - cross over at chiasmata

Question 38

CHIASMATA

Answer 38

hold chromosomes together & is when DNA exchanged between homologous chromosomes

Question 39

EGG

Answer 39

each month, one egg ovulated & meiosis 1 forms polar body (useless) & another cell that is cytoplasm which divides in meiosis 2 to form zygote (whole cytoplasm) & 2nd polar body

Question 40

MEIOSIS USES

Answer 40

used for reduction division (23 not 46) and to get re-assortment of genes (independent segregation & crossing over)

Question 41

MEIOSIS STEPS

Answer 41

1. MEIOTIC METAPHASE 1 (each of 2 copies of chromosome has kinetochore joined to it so goes to centre) 2. MEIOTIC ANAPHASE 1 - arms of sister chromatids unglued & leads to mix of maternal & paternal & go to side 3. MEIOTIC META/ANA 2 - diploid to haploid