Week 4 Flashcards

1
Q

What are the functions of skin

A

Physical protection -acts as a barrier
Thermoregulation
Sensation - lots of sensory receptors in skin
Metabolic functions- fat, adipose tissue, Vit D production
Indicator of general health
Shock absorption
Maintenance of fluid balance

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2
Q

What are the three main layers of skin

A

Epidermis
Dermis
Hypodermis/ subcutis

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3
Q

What is the epidermis

A

Keratinised stratified squamous epithelium
Mostly filled with keratinocytes
Four/five discrete layers
Cuboidal cells at the basal layer (stratum basale)
Squamous layer at top

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4
Q

What is the stratum basale/basal layer

A

Cuboidal cells
Most deep layer
Sat on the basement membrane
Mitosis occurs to replenish above layers
Melanocytes present

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5
Q

What is the stratum spinosum/ prickle layer

A

8-10 cell layers- biggest layer in epidermis
Connected by desmosomes
Gives prickly appearance on dehydration
Produces cytokeratin- intermediate filament of cytoskeleton

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6
Q

What is the stratum granulosum/ granular layer

A

3-5 cell layers
Become squamous cells
Granules contain keratohyalin- one of steps in keratin maturation
Stains deeply with H&E

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7
Q

Keratin maturation

A

Keratin is produced as intermediate filaments- cytokeratin, which matures into packed extracellular keratin
The epidermis is constantly being replenished every 25-30 days in normal skin

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8
Q

Process of keratin maturation in layers

A

Stratum corneum- keratin
Stratum granulosum- keratohyaline granules
Stratum spinosum- cytokeratin- tonofibrils
Stratum basale- mitosis, some cytokeratin

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9
Q

What is the stratum lucidum

A

Layer between the stratum granulosum and corneum
Only present in thick skin

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10
Q

What is the stratum corneum/cornified layer

A

Mature keratin= cytokeratin & keratohyaline
Dead/dying keratinocytes cells ‘squames’
No cytoplasm/nucleus/organelles

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11
Q

what aremelanocytes

A

Produce melanin
Found in basal layer
Can’t see with H&E
UV protection
Pigment

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12
Q

What are Merkel cells

A

In stratum basale
Associated with free nerve endings
Sensory- light touch

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13
Q

What are Langherhan’s cells

A

Found in all layers and dermis
Immune cell, like a macrophage
Specialised immune cell
Antigen presenting cell
Involved in immune and allergic reactions

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14
Q

What is the papillary layer

A

In dermis
Above the reticular dermis
The dermal papillae (elevations) increase surface area, diffusion nutrients

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15
Q

What is the reticular layer

A

Dense irregular collagenous tissue- more collagen
Elastin present throughout dermis
This elastic reduces age

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16
Q

Neurovascular supply in the dermis

A

Complex of vessels present
Subpapillary and cutaneous plexus with shunting vessels between
Important in thermoregulation
Controlled by ANS

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17
Q

Types of skin mechanoreceptors

A

Meissner corpuscle - papillary layer
Pacinian corpuscle - dermis & hypodermis
Ruffini’s corpuscles
Merkels disks
Free nerve endings

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18
Q

What are free nerve endings for

A

Pain, nociception (feeling pain)

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19
Q

Merkel disks

A

Perception of shape , texture

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20
Q

Meissners corpuscle

A

Motion detection
Grip control

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21
Q

Ruffini ending

A

Skin stretch
Tangential force

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22
Q

Pacinian corpuscle

A

Perception of distant events through vibrations

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23
Q

What are the unencapsulated mechanoreceptors

A

Merkel
Free nerve endings

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24
Q

What are encapsulated mechanoreceptors

A

Pacinian
Ruffinis
Meissners

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25
Q

What type of skin are hairs found

A

Thin skin

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26
Q

What is hair made of

A

Keratin, densely packed

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27
Q

What are sabaceous glands

A

Secrete oily sebum on upper part of hair follicle

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28
Q

Sweat glands

A

Found in the superficial hypodermis
Watery fluid
Secrete sweat through exocytosis- termed merocrine secretion

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29
Q

Sebaceous glands

A

Attached to hair follicles
Secrete sebum
Cells fill with secretory vesicles then dissociates- termed Holocrine secretion

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30
Q

What are the two types of sweat glands

A

Eccrine
Apocrine
Both are merocrine secretion

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31
Q

Eccrine sweat glands

A

Directly on skin
Function in heat loss (ANS)
Less viscous
Found everywhere

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32
Q

Apocrine sweat glands

A

Open into hair follicle
Regulated by hormones
More viscous
Limited to axilla/ genitals and areola
Secrete through merocrine secretion

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33
Q

burns classification

A

Superficial epidermal
Partial thickness- superficial dermal
Partial thickness- deep dermal
Full thickness- burn extends through all layers of skin to subcutaneous tissue

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34
Q

What is an autograft

A

Layer of own skin used

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35
Q

What is a allograft

A

Donor skin cadaver

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36
Q

What does central dogma mean

A

A theory stating that genetic info flows only in one direction from DNA to RNA to protein

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37
Q

Structure DNA

A

Double stranded
High molecular weight

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38
Q

Structure RNA

A

Single stranded
Heterogeneous in size, smaller, vary in size

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39
Q

What does a nucleotide consist of

A

Phosphate group
Pentose sugar
Base

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40
Q

Sugar used in RNA

A

B-D-ribose

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41
Q

Sugar used in DNA

A

B-D-2-deoxyribose

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42
Q

What bonds join nucleotides

A

Phosphodiester bonds between phosphate group and sugar

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43
Q

Comparison of RNA and DNA

A

RNA has a OH group at ribose C2 DNA doesn’t
RNA uses uracil where DNA used thymine

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44
Q

Why is RNA unstable

A

Because the lone pair of electrons on OH group on C2 can react with phosphate

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45
Q

What are purines

A

Adenine and guanine

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46
Q

Pyrimidines

A

Cytosine and thymine

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47
Q

How is DNA wound up

A

Double helix with antiparallel strands
Helices interact via hydrogen bonding between complimentary bases G&C and A&T
DNA strands have 5’ and 3’ ends
The base sequence of one strand determines the sequence of the others

48
Q

What does 5’ and 3’ mean

A

The number of carbon atoms in a deoxyribose sugar molecule to which phosphate group bonds

49
Q

Is C&G or A&T stronger

A

Guanine-cytosine base pair

50
Q

What is a chromosome

A

A single molecule of DNA

51
Q

What is a gene

A

Sequence of nucleotides that codes for a protein

52
Q

What are mitotic chromosomes formed from

A

Tightly packed chromatin

53
Q

Where is DNA found

A

In the nucleus and in mitochondria

54
Q

How is DNA packaged into chromatin

A

By histones and other chromosomal proteins

55
Q

How can DNA sequence differences be used

A

To paint chromosomes
Specific probes of different colours reveal each chromosome pair

56
Q

What are exons

A

Coding DNA

57
Q

What are introns

A

Non coding DNA
Removed from primary RNA by splicing machinery

58
Q

Human genome contains repeated sequences

A

Often occur in blocks of tandem repeats
Called ‘satellite DNA’ - highly repetitive DNA consisting of short sequence so repeated a large number of times

59
Q

Types of satellite DNA

A

Mini satellite - highly polymorphic up to 1000 copies in one block also found at telomeres

Micro satellite- small arrays of simple sequence repeats
Usually in intergenic/ intronic (non coding) DNA

60
Q

Telomeres

A

Allow replication to tip of chromosomes
Long tracts of repeats can be unstable= deletions immediately below telomeres

61
Q

Centromeres

A

Essential for segregation during cell division
Proteins involved in cell division bind to centromeric sequences

62
Q

Mini satellite

A

No known purpose
Can cause mispairing during cell division to give
Large scale duplication/deletion between homologous chromosomes
Translocation of DNA between non-homologous chromosomes

63
Q

What is the fundamental unit of chromatin

A

The nucleosome- this is DNA wound a histone core

64
Q

How are decondensed chromosomes structurally organised in non-dividing cells

A

Attachment to nuclear skeleton
Has a functional role e.g. clustering of ribosomal genes in the nucleolus

65
Q

What is nucleolus

A

Large structure within the nucleus where ribosomal RNA is transcribed and ribosomal subunits are assembled

66
Q

What is euchromatin

A

Transcriptionally active form of chromatin
Prevalent in gene rich areas less compact allowing access for proteins involved in transcription

67
Q

What is heterochromatin

A

Highly condensed region of an interphase chromosome generally gene poor and transcriptionally inactive
Can exist in active (decondensed) or inactive (condensed) forms
Or can always be inactive and condensed
Found at telomeres and centromeres

68
Q

When does chromatin structure change

A

During the cell cycle
Also modified during gene regulation (allowing access to regulatory proteins and RNA polymerase)

69
Q

DNA replication is

A

Semi conservative

70
Q

What end are nucleotides added

A

at the 3’ end dNTPs (deoxyribonucleotide triphosphate) required

71
Q

Where is DNA replication initiated

A

At replication origins
The double helix opened with aid of initiator proteins, single stranded DNA templates ready for DNA synthesis

72
Q

DNA polymerase

A

Mediates DNA replication
Proceeds in a 5’ to 3’ direction
Adds 1000 bases/ second to the chain
Requires dNTPs
Must have template and RNA primer
Has ‘proof reading’ activity

73
Q

What is a mutation

A

Is a permanent change in the sequence of DNA

74
Q

Why does DNA polymerase have a high fidelity

A

Stability of base pairing
Proof reading by DNA polymerase

75
Q

How do DNA repair mechanisms work

A

Minimise introduction of mutations
DNA mismatch repair proteins bind
Removal of newly synthesised DNA strand
Repair of gap by DNA polymerase and ligase

76
Q

What is depurination

A

Lose a base

77
Q

What is deamination

A

Cytosine becomes uracil

78
Q

During which phase of cell cycle does DNA replication occur

A

S

79
Q

Phases of mitosis

A

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

80
Q

What is the purpose of mitosis

A

Cell division
Organismal growth
Genetically identical products

81
Q

Prophase

A

Chromosomes condense
Centrosomes move apart

82
Q

Prometaphase

A

Nuclear membrane breaks down
Spindle microtubules attach to the kinetochores and move actively

83
Q

Metaphase

A

Chromosomes align at the equator of the spindle
Kinetochores from paired sister chromatids attach to opposite poles of spindle

84
Q

Anaphase

A

Sister chromatids synchronously separate. Fast
Kinetochore microtubules shorten
Spindle poles move apart

85
Q

Telophase

A

Chromosomes arrive at poles
Nuclear envelope reassembles giving 2 new nuclei
Nucleoli reappear- RNA synthesis begins
Initiation of plasma membrane cleavage

86
Q

Cytokinesis

A

Contractile ring is formed and mediates division of the cell in two

87
Q

Function of meiosis

A

Reduction division (23 chromosomes per gamete)
Re assortment of genes: independent segregation of chromosomes, crossing over

88
Q

Mechanism of meiosis

A

Each homologue replicates to give two chromatids
Homologous pair
Exchange of material between non-sister chromatids
Chiasmata (visible cytologically) are the physical manifestations of crossing over

89
Q

What generates genetic variation

A

Independent assortment of maternal and paternal homologues at meiosis I
Re-assortment of genes by crossing over

90
Q

What are chiasmata

A

Hold chromosomes together first phase of meiosis
Typical bivalent has at least one chiasma
Larger chromosomes show more

91
Q

Meiosis metaphase I

A

Kinetochore microtubules of sister chromatids point in same direction
Kinetochores of sister chromatids function as a unit

92
Q

Meiotic anaphase 1

A

Arms of sister chromatids become unglued

93
Q

Meiotic metaphase II

A

Kinetochores point in opposite directions (as in mitosis)

94
Q

Meiotic anaphase II

A

Cohesions in centromere degraded; sister chromatids separate

95
Q

Difference between mitosis and meiosis

A

Mitosis designed to generate identical daughter cells
Meiosis designed to make haploid gametes and generate genetic diversity

96
Q

Genome

A

Complete set of DNA
DNA sequence

97
Q

Transcriptome

A

Complete set of RNA transcripts

98
Q

Proteome

A

Complete set of proteins produced

99
Q

Transcription

A

RNA synthesis needs a DNA template (RNA polymerase as enzyme)
Nucleoside Triphosphates
RNA is synthesised in a 5’ to 3’ direction
Only one strand is copied
RNA polymerase adds 50 bases per second

100
Q

The ‘primary’ RNA transcript binds proteins involved in RNA processing ‘spliceosome’

A

Splicing requires RNA-protein complexes called snRNP
Some genes have alternative splicing leading the production of different mRNA and proteins from same gene

101
Q

What is tRNA

A

An adaptor molecule
3 ‘hairpin’ stem-loop structures
Stabilised by base pairing
Distinct functional regions
Specific aminoacyl-tRNA synthetases
Contains an anti codon

102
Q

Polyribosome/polysome

A

More than one ribosome attaches to a single mRNA

103
Q

How many possible reading frames does DNA sequence have

A

3
Defining start of coding region is important

104
Q

The genetic code

A

Code is read in groups of 3 bases
Read in a 5’ to 3’ direction
3 possible reading frames
Each amino acid is coded for by a codon
Some amino acids have more than one codon some only have one
3 codons do not encode amino acids (UAA, UGA and UAG are stop codons)
Code is universal

105
Q

Mutations can affect protein sequence

A

Deletion or insertion of one or more nucleotides
Substitution or point mutations- alteration of a single base position
Consequences depend on nature and position of mutation- biggest impact if in coding or regulatory region of gene

106
Q

What is the name of the fascia that connects skin to body

A

Superficial fascia is found directly under the skin and superficial adipose layers

107
Q

Epidermis definition

A

Keratinised stratified squamous epithelial cells. Located superficially to the dermis
Avascular

108
Q

Dermis definition

A

Deep to the epidermis and made of connective tissue
Contains blood vessels and nerves
Split into papillary and reticular dermis

109
Q

Hypodermis definition

A

Loose connective tissue which connects skin to underlying tissues

110
Q

Burns definition

A

Damage from heat, chemicals, electricity or radiation
A scald is normally caused by water or steam

111
Q

Skin appendages definition

A

Specialised structures associated with the skin such as hair, nails, glands

112
Q

What is dermatitis

A

A medical condition in which skin becomes red, swollen and sore sometimes with small blisters
Resulting from direct irritation of skin by an external agent or an allergic reaction

113
Q

Eccrine sweat gland definition

A

A type of simple sweat gland that’s found in almost all regions of skin, these glands produce watery substance, sweat directly on skin surface
Help to maintain homeostasis, primarily by stabilising body temperature, cools skin

114
Q

Apocrine sweat gland definition

A

Open into the hair follicle leading to surface of skin
Develop in areas with many hair follicles such as scalp, armpits and groin
Tubular secretory glands
Secrete a more viscous, odorous product

115
Q

Sebaceous glands definition

A

Secrete sebum, which is an oily substance that helps skin/hair to be water-proof. Mostly associated with hair follicles
Not found in palms and soles and are found in higher concentrations in face and scalp