Week 1 - B - Skin structure/function 3&4 - Basement membrane/corpuscles/skin glands, vit D/thyroxine metabolism, summary

Question 1

The dermal-epidermal junction is the area of tissue that joins the dermal and the epidermal layers of the skin. Also known as the epidermal basement membrane zone What are the key roles of the dermo-epidermal junction?

Answer 1

Key role in epithelial-mesechymal interactions * Support, anchorage, adhesion, growth and differentiation of basal cells * Semi-permeable membrane acing as a barrier and a filter

Question 2

What are the three parts of the epidermal basement membrane? What connects the basal cells of the epidermis to the basememant membrane?

Answer 2

Lamina lucida Lamina densea Sub-lamina densa zone The epidermal cells of the basement membrane are connected to the dermo-epidermal junction by hemidesmosomes

Question 3

What is an example of a condition where antibodies are formed that cause the separation of the epidermal and dermal skin layers due to blister (bullae) formation?

Answer 3

This would be bullous pemphigoid Anti-hemidesmosome antibodies form causing the separation of the skin layers and large bullae formation

Question 4

What are the main cells and fibres found in the dermis?

Answer 4

Cells - mainly fibroblasts, macrophages, mast cells, lymphocytes, langerhans cells Fibres - mainly collagen and elastin

Question 5

Is the blood vessel supply to the skin less than its metabolic need? Describe the flow of blood through the skin?

Answer 5

No. The blood supply to the skin is greater than its metabolic needs Arteries –> precapillary sphincters –> arterioles –> capillaries –> post-capillary venules –> collecting venules –> veins

Question 6

What are the important cells involved in immune surveillance in the skin?

Answer 6

This would be circulating lymphocytes and langerhans cells (Langerhans cells are found in prickle cell layer, dermis and lymph nodes)

Question 7

Nerve supply to the skin includes somatic sensory nerves (both free nerve endings and special nerve rceptors) As well as an autonomic nerve supply (nervous innervation to blood vessels, nerves and glands) What are the special nerve receptors in the skin? * Which sense pressure? * Which senses vibration? What do the free nerve endings provide sense for?

Answer 7

Pacinian corpuscles - sense pressure Meissner’s corpuscles -sense vibration Free nerve endings provide sensation for temperature and pain

Question 8

What are the three types of skin glands? Which involve the hair follicle?

Answer 8

Sebaceous skin glands Apocrine skin glands Eccrine skin glands The sebaceous gland is adjacent to the hair follicle The apocrine gland is attached to the hair follicle

Question 9

What do the sebaceous glands secrete? What is the function of the secretions?

Answer 9

Sebaceous glands secrete an oily secretion known as sebum into the pilary canal The function of the secretions is to control moisture loss and to provide protection from fungal infections

Question 10

What area of the body is high in sebaceous glands? Which area does not contain any sebaceous glands?

Answer 10

The whole body especially the head,neck and chest are high in sebaceous glands (not palms/soles of feet)

Question 11

Which gland develops as part of the pilosebaceous unit? What does it produce and what is it dependent on? Where is it found and what does it cause?

Answer 11

This would be the apocrine sweat glands They produce an oily fluid that is androgen dependent and causes an odour after bacterial decomposition Found in the axilla and perineum

Question 12

What do the eccrine sweat glands produce and where are they found? What is the function?

Answer 12

These are essentially found in the whole body with the highest density in the palms and the soles of the feet The function is to aid the body in cooling by evaporation Also to moisten palms/soles to aid grip

Question 13

What is the significance of the melanin cap on the basal cells?

Answer 13

The malanin caps absorb ultraviolet rays to protect the DNA in the basal cells nuclei

Question 14

What is the other name for all 4 layers in the epidermis? What causes a hair follicle to stand on end?

Answer 14

Keratin layer - stratum corneum (due to keratinocytes become corneocytes here) Granular layer - stratum granulosum (keratinocytes lose their nuclei and the cytoplasm has a granular appearance) Prickle cell layer - stratum spinosum Basal layer - stratum basale Contraction of the arrector pili muscle causes the hair to stand on end

Question 15

Skin is metabolically active What is the highly metabolically active layer? Skin is involved in the metabolism of which vitamin and which hormone?

Answer 15

The basal layer is the highly metabolically active layer of the skin Skin is involved in the metabolism of vitamin D and thyroxine

Question 16

Lets discuss the vitamin D metabolism What is the precursor to vitamin D3 that is produced in the skin and what causes this to be converted to vitamin D3? What is vitamin D3 biological name?

Answer 16

The skin produces 7-dehydrocholesterol Upon exposure to the ultraviolet rays in the sunlight, the keratinocytes in the skin metabolise this to cholecalciferol (vitamin D3)

Question 17

Once vitamin D3 has been synthesised in the skin or obtained from the diet, what is it converted to and where is it stored? What type of vitamin d is obtained from the diet?

Answer 17

Once cholecalciferol (vit D3) has been synthesised in the skin (from 7-dehydrocholesterol), it is converted to 25-hydroxy cholecalciferol (25 OH vit D3) in the liver where it is stored Viamin D2 and vitamin D3 can be obtained from the diet

Question 18

What is 25 hydroxy vitamin D converted, by what and where?

Answer 18

25 hydroxy vitamin D3 is converted to 1,25 dihydroxy vitamin D3 (calcitriol) in the kidney by 1-alpha hydroxylase

Question 19

What are the different function of calcitriol (1,25 dihyroxy vitamin D3) in the body?

Answer 19

Promotes the absorption of dietary calcium in the small bowel Promotes the mineralisation of bone releasing calcium and phosphorus Increases renal tubular reabsorption of calcium

Question 20

80% of thyroid hormone metabolism (Thyroxine T4 to Triiodothyronine T3) takes place in peripheral (to the thyroid) tissues including the skin Where does the other 20% take place?

Answer 20

The other 20% of this conversion occurs in the thyroid gland

Question 21

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Answer 21

A - melanocyte B - dermis C - epidermis D - sebaceous gland - produces sebum to moisturize the skin

Question 22

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Answer 22

A - Keratin layer- stratified squamous epithelium B - Granular layer - 2or3 layers thick C - Prickle cell layer - large polyhedral cells D - Basal layer - one cell thick simple cuboidal epithelium E - dermo-epidermal junction (lamina lucida, lamina densa, sub-lamina densa)

Question 23

Where are apocrine glands found? Which area of the body is highest in eccrine glands?

Answer 23

A - scalp B - axilla or perineum (two of the few areas to contain apocrine glands (blue) C - soles of feet or palms (no sebaceous glands here) (highest density of eccrine glands in these areas)

Question 24

Where are sebaceous glands found? Where in highest density?

Answer 24

Sebaceous glands are found in the whole body (except the palms and soles off feet) Especially present in the head, face/neck, scalp and chest

Question 25

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Answer 25

A - bullous pemphigoid - can see the separation of the dermo-epidermal junction due to large bullae B - normal C - sacroptes scabie D - psoriassi -can see the thickened keratin layer and blood vessels trying to reach the surface

Question 26

What metabolises vitamin D in the skin and from what to what? Where is energy stored in the skin?

Answer 26

Keratinocytes metabolise vitamin D in the skin from 7-dehydrocholesterol to cholecaciferol (vitamin D3) in response to UVB rays Subcutaneous fat is where energy is stored in the skin

Question 27

What cells are responsible for epidermal proliferation?

Answer 27

The basal cell layer

Question 28

Which structure contributes to the tensile strength of skin?

Answer 28

Collagen

Question 29

Where are langerhan cells formed? Where are they found in the skin? What is their function?

Answer 29

Langerhans cells are foemed in the bone marrow Int he skin they are found in the prickle cell layer of the epidermis, the dermis and the lymph nodes Immunologically active cells - They are dendritic cells (antigen presenting cells) and present antigen to the lymph nodes

Question 30

Where do keratinocytes begin to become enucleated?

Answer 30

This takes place in the granular layer of the epidermis