Lecture 18

Question 1

What is the skin also referred to as?

Answer 1

the integumentary system

Question 2

What is the skin?

Answer 2

Largest organ in the body

- 12-15% body weight and 1.6-1.8m2 of surface area

Question 3

What are the main functions of the skin?

Answer 3

Protection
- against impact, chemicals, infection…
(e.g.) burns: issue is a result of damage since the body is prone to toxins and infections
Temperature maintenance
- regulates heat gain and loss
Synthesis and storage of nutrient:
- vitamin D3 synthesis
Sensory reception
- the skin contains receptors that relay information to the nervous system
Excretion and secretion
- excretes salt, water; secrete mile (mammary glands)
Visual part of body:
- implications on social life and psychological health (pale = anaemia)

Question 4

What forms the integumentary system?

Answer 4

Skin+accessory structures

Question 5

What are the three layers of the skin?

Answer 5

Epidermis: has various layers
Dermis: where you have various tissues and sweat glands, hair cells nails etc
Hypodermis:

Question 6

What are the accessory structures of the skin?

Answer 6

Glands (2 sweat of glands, sebaceous gland), hair and nails

Question 7

What are the two types of skin?

Answer 7

Thick skin
 - palm of hands and feet, fingertips
 - no hair
 - 5 layers (called stratum)
Thin skin
 - rest of the body
 - 4 layers

Question 8

What does stratified mean?

Answer 8

has layers

Question 9

What is squamous cells?

Answer 9

Contain dead cells to be removed and has active mitotic cells

Question 10

What are keratinized cells?

Answer 10

keratinocytes produce keratin in epidermis

Question 11

Skin is one of the few systems that can generate. What are other examples?

Answer 11

Liver, skeletal muscles

(more friction causes faster regeneration)

Question 12

How long does self-regeneration last?

Answer 12

2-4 weeks

Question 13

How often does self-regeneration occur?

Answer 13

life-time

Question 14

Where are keratinocytes born and where do they go?

Answer 14

Keratinocytes are born in the lower layer and migrate upward during their life

Question 15

What are the three cell types of Stratum Basale?

Answer 15

Keratinocytes, melanocytes, tactile cells

Question 16

What are keratinocytes?

Answer 16

Majority are mitotic
Basal lamina separates keratinocytes from extracellular matrix (ECM)
When keratinocytes are in contact with ECM, it divides

Question 17

What are melanocytes?

Answer 17

Provide skin color with beta-caroten
Combinations of pigments form sin color
 - eumelanin: brown insoluble pigment
 - phenomelanin; red soluble pigment
(e.g.) 
Fair skin
 - pigments in granules in superficial layer of epidermis
Dark skin
 - pigments accumulate in cell layers of epidermis
Tactile cells (or Merkel)
 - connected to sensory nerves and participate to the sense of touch
 - can be target of cancer

Question 18

What is the stratum spinosum?

Answer 18

Thickest layer of epidermis, contains keratinocytes and up to 800 dendritic (Langerhans) cells
per mm2

Question 19

What is the stratum spinosum composed of?

Answer 19

Keratinocytes (layer keratin content)
- still mitotic (especially the deeper ones
- more flattened shape
- provide elasticity to skin
- detached from basement membrane, and migrate upward
Subset of dendritic type cells
- Langerhans
- mediating immune response to infective agent

Question 20

What is the Stratum granulosum?

Answer 20

Last layer of epidermis to have cells containing nuclei

Question 21

What does the stratum granulosum contain?

Answer 21

Contains 3-5 layers of flat keratinocytes
Keratinocytes
- post-mitotic
- make large amount of keratin and a glycolipid
- - glycolipids
—– lipid layer
—– water resistance
—– prevent water loss and absorption from body
—– high content of granules
—– prevent diffusion beyond layer (beyond layer - dead cells only)
Keratin forms filaments that are durable

Question 22

What is the stratum lucidum?

Answer 22

Exists only in thick skin
Translucent
 - keratinocytes
 - - densely packed
 - - contain no nuclei or organelles

Question 23

What is the Stratum corneum?

Answer 23

Most superficial layer of the skin

• 15-30 layers of dead, keratinized cells
• high lipid content - permeability barrier
• cells at the surface flake off
• • rate depends on level of friction

Question 24

Which is thicker, the dermis or the epidermis?

Answer 24

the dermis

Question 25

Is the dermis as regular as the epidermis?

Answer 25

No; stratified but layers are not easily identifiable

Question 26

What are the two layers of the dermis?

Answer 26

Papillary layer
- made of connective tissue
- interdigits with epidermis (and reticular layer)
Reticular layer
- irregular, dense connective tissue rich in collagen
- protects organs

Question 27

What are accessory organs?

Answer 27

glands, hair, nails

Question 28

What does the dermis contain other than accessory organs?

Answer 28

Blood vessels, sensory nerves, muscles

Question 29

What is the hypodermis also called?

Answer 29

Subcutaneous layer

Question 30

What does the hypodermis consist of?

Answer 30

Connective tissue with adipocytes

Question 31

What are the functions of the hypodermis?

Answer 31

Important in newborns
- protective layer against heat loss
In adults, subcutaneous fat is restricted to specific area of the body

Question 32

What are the different cutaneous glands?

Answer 32

Mammary glands
Ceruminous glands
 - in external ear - earwax production
Sebaceous glands
 - sebum production (protection against infection)
 - active in teenagers
 - responsive to levels of hormones
Sweat glands
 - made of duct and globular structures
Apocrine glands
 - secrete product into hair follicles or armpits
 - duct connects to shaft of hair cells
 - in abundance of hair (armpits, beard etc)
Merocrine glands:
 - 2-5 million
 - secrete perspiration (99% water)
 - 500ml per day in normal conditions
 - 1L per hour under exercise
 - duct comes directly to epidermis
 - distributed throughout 
 - thermoregulation

Question 33

How is skin a barrier?

Answer 33

Inside-out barrier (against water loss)
Outside-in barrier (infections
Physical
- toughness of keratin prevents entry of infectious agents (exceptions: cuts, burns, vectors)
- e.g. mosquitoes - malaria
- elasticity
Biochemical
- sebum contains bactericidal substances and sweat brings the pH 4-6 (unfavorable to bacteria growth)
* soap: pH 5
- contributes in maintaining antibacterial activity
Immunological
- Langerhans cells in epidermis (Stratum spinosum) trigger immunological response if infection
- - affect lymph nodes
Maintains integrity

Question 34

How does skin produce vitamin D3?

Answer 34

7-dehydrocholesterol

• leads to pre-vitamin D3
• (isomerisation) leads to Vitamin D3

Question 35

Where does vitamin D3 production take place?

Answer 35

Takes place in Stratum basale and spinosum
Isomerism requires UV rays to occur
Vitamin D3 enters the blood to the liver to the kidney for hydroxylation

Question 36

What is Vitamin D3 also called?

Answer 36

cholecalciferol

Question 37

What does cholecalciferol turn into after hydroxylation?

Answer 37

Calcidiol - 25(OH) D3

then Calcitriol - 1alpha25(OH)2D3

Question 38

What happens when Calcitriol binds to VDR (vitamin D3 receptor)?

Answer 38

Control of gene expression

Question 39

What does calcitriol act as?

Answer 39

Factor of gene regulator

Question 40

How does sun screen with a high index factor work?

Answer 40

Prevents vitamin D3 production
Deleterious effect on production of calcium phosphate
Weak bones

Question 41

What can too much UV lead to?

Answer 41

Skin cancer

Question 42

What can too little UV lead to?

Answer 42

brittle bones