Histology

Question 1

How many skin diseases are known?

Answer 1

> 2000

Question 2

What proportion of GP consultations have to do with skin complaints?

Answer 2

~ 20%

Question 3

What does skin comprise

Answer 3

Epidermis
Dermo-epidermal junction
Dermis
Sub-cutis (mostly fat)

Question 4

Where does the epidermis arise?

Answer 4

Ectoderm forms a single-layered periderm
Number of layers increase
Periderm cells cast off

Question 5

Where does the dermis come from?

Answer 5

Formed from mesoderm below ectoderm

Question 6

Where do melanocytes come from?

Answer 6

Neural crest

Question 7

Name the layers of skin present at 4 weeks of foetal development.

Answer 7

Periderm
Basal layer
Dermis

Question 8

Name the layers of skin present at 16 weeks of foetal development.

Answer 8

Keratin layer
Granular layer
Prickle cell layer
Basal layer (with melanocytes)
Dermis

Question 9

What is the growth pattern of skin?

Answer 9

Along Blaschko’s lines. Does not follow vessels, lymphatics or nerves

Question 10

Name 4 skin appendages

Answer 10

Nails
Hair
Glands e.g. sebaceous
Mucosae e.g. buccal

Question 11

Describe the epidermis/

Answer 11

4 defined layers +
Melanocytes
Langerhans cells
Merkel cells

Question 12

Control of epidermal turnover is mediated by:

Answer 12

Growth factors
Cell death
Hormones

Question 13

Name 2 conditions wherein there is loss of control of epidermal turnover

Answer 13

Skin cancer

Psoriasis

Question 14

How long does it take the average keratinocyte to migrate from the basement membrane to shedding

Answer 14

28 days

Question 15

Describe the basal layer (4 features)

Answer 15

One cell thick
Small cuboidal cells
Lots of INTERMEDIATE keratin filaments
High metabolically active

Question 16

Describe the prickle cell layer (3 features)

Answer 16

Larger polyhedral cells
Lots of desmosomes
Intermediate filaments connect to desmosomes

Question 17

Describe the granular layer (6 features)

Answer 17

2-3 layers of flatter cells
Large keratinohyallin granules with filaggrin and involucrin proteins
Odland bodies present
High lipid content
Origin of cornified envelope
Cell nuclei lost

Question 18

Describe the keratin layer (3 features)

Answer 18

Made of corneocytes; is the insoluble cornified envelope
Tight waterproof barrier
Lamellar granules release lipid

Question 19

Describe melanocytes

Answer 19

Migrant cells from the neural crest to basal layer
During first 3 months of foetal development
Produce melanin
Form protective cap over nucleus

Question 20

Describe melanosomes

Answer 20

Organelles of melanocytes
Convert tyrosine to melanin pigment
Transferred between adjacent keratinocytes via dendrites

Question 21

What colour pigment does Eumelanin yield?

Answer 21

Brown or black

Question 22

What colour pigment does Phaeomelanin yield?

Answer 22

Red, yellow

Question 23

Define vitiligo

Answer 23

Autoimmune disease with loss of melanocytes

Question 24

Define albinism

Answer 24

Genetic partial loss of pigment production in the skin

Question 25

Describe Nelson's Syndrome

Answer 25

Disorder wherein melanin stimulating hormone is produced in excess by the pituitary May indicate pituitary malignancy

Question 26

Describe 4 features of Langerhans cells

Answer 26

Have a mesenchymal origin (bone marrow) Found in the prickle cell level, dermis and lymph nodes Involved in skin immune system Characteristically contain Birbeck granules (tennis rackets)

Question 27

Describe Merkel cells (2 features)

Answer 27

Found in the basal layer | Myelinated mechanoreceptors

Question 28

Describe pilosebaceous units

Answer 28

Specialised keratins + adjacent sebaceous glands Comprises an epidermal component + dermal papilla Hair pigment comes from melanocytes above dermal papilla

Question 29

Name the phases of hair growth

Answer 29

``` Anagen = growing Catagen = involuting Telogen = resting ```

Question 30

What phase of hair growth is the papilla still attached to the hair?

Answer 30

Anagen

Question 31

Decribe alopecia areata

Answer 31

Autoimmune hair loss

Question 32

Describe nails

Answer 32

Specialised keratins | Those on fingers grow faster than on toes

Question 33

What are the 3 parts of the nail plate? | same as matrix subdivisions

Answer 33

Dorsal (outermost) Intermediate Ventral (closest to nailbed)

Question 34

What is the dermo-epidermal junction?

Answer 34

- interface between epidermis and dermis | - role in support, growth, adhesion, barrier and filter between epithelium and mesenchymal cells

Question 35

What are the parts of the DEJ?

Answer 35

``` Lamina lucida (top part) Lamina densa (bottom) ```

Question 36

Name an inherited disease of the DEJ

Answer 36

Epidermolysis bullosa | - simplex or dystrophic

Question 37

Name acquired diseases of the DEJ

Answer 37

Pemphigus Pemphigoid Dermatitis herpetiformis

Question 38

Describe Epidermolysis Bullosa simplex

Answer 38

Baby has fragile skin | Even holding them causes skin to tear

Question 39

Describe Epidermolysis Bullosa dystrophica

Answer 39

Skin over-heals | Toes and fingers may end up sticking together

Question 40

Name the components of the dermis

Answer 40

``` Collagen (Type I and III) Elastin Ground substance Blood vessels, lymphatics, nerves Fibroblasts, macrophages, mast cells, langerhans cells ```

Question 41

What do fibroblasts in the dermis produce?

Answer 41

Collagen | Elastic fibres

Question 42

Describe the blood supply through the skin

Answer 42

Arteriole --> precapillary sphincters --> arterial capillaries --> venous capillaries --> post-capillary venules --> collecting venules

Question 43

What is a haemangioma?

Answer 43

Overgrowth of local blood vessels | May lead to port wine stains

Question 44

Lymphatic dysfunction may lead to:

Answer 44

Lymphoedema | - leads to cellulitis, vasculitis and other infections

Question 45

Name the nerves in the skin

Answer 45

``` Somatic: Free nerve endings Pascinian corpuscles Meissners corpuscles Autonomic: to blood vessels and glands Control sweating ```

Question 46

What is neurofibromatosis?

Answer 46

Benign skin tumours | Cutaneous nerves are abnormally thickened

Question 47

Name the 3 types of skin glands

Answer 47

Sebaceous Apocrine Eccrine

Question 48

Describe sebaceous glands

Answer 48

Wide distribution but especially on face and chest Hormone-sensitive (androgens) Produces sebum Open into hair follicles

Question 49

Describe acne

Answer 49

Increased sebum production Blocked ducts Increased bacterial activity

Question 50

Describe apocrine sweat glands

Answer 50

Part of pilosebaceous unit Found in axillae and perineum Androgen dependent Scent

Question 51

Describe eccrine sweat glands

Answer 51

Opens directly onto skin surface Widespread, esp palms, soles, axillae Sympathetic cholinergic nerve supply Cool the body by evaporation

Question 52

Name 6 functions of the skin

Answer 52

``` Barrier function Metabolism & detoxification Thermoregulation Immune defence Communication Sensory functions ```

Question 53

How does skin act as a barrier?

Answer 53

Physically: mechanical trauma, UVR Chemical: allergens, toxins Pathogens: bacteria, viruses, fungi

Question 54

Describe the skin's metabolic activity

Answer 54

Vitamin D metabolism | Thyroid hormone metabolism

Question 55

What are the steps of vitamin D metabolism?

Answer 55

Presence of 290-320nm UV light Leads to formation of D3 Stored in the liver

Question 56

How is thyroid hormon formed?

Answer 56

Conversion of T4 to T3 80% of this happens in skin 20% in thyroid gland

Question 57

How does skin affect social interactions and communication?

Answer 57

Visual Odour Socio-sexual

Question 58

What is the papillary dermis?

Answer 58

Layer nearest to the epidermis | Thin

Question 59

What is the reticular dermis?

Answer 59

Thicker Type I collagen Contains appendage structures

Question 60

What does the epidermal basement membrane comprise?

Answer 60

Laminin | Collagen IV