Lecture 18 Flashcards
What is the skin also referred to as?
the integumentary system
What is the skin?
Largest organ in the body
- 12-15% body weight and 1.6-1.8m2 of surface area
What are the main functions of the skin?
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)
What forms the integumentary system?
Skin+accessory structures
What are the three layers of the skin?
Epidermis: has various layers
Dermis: where you have various tissues and sweat glands, hair cells nails etc
Hypodermis:
What are the accessory structures of the skin?
Glands (2 sweat of glands, sebaceous gland), hair and nails
What are the two types of skin?
Thick skin - palm of hands and feet, fingertips - no hair - 5 layers (called stratum) Thin skin - rest of the body - 4 layers
What does stratified mean?
has layers
What is squamous cells?
Contain dead cells to be removed and has active mitotic cells
What are keratinized cells?
keratinocytes produce keratin in epidermis
Skin is one of the few systems that can generate. What are other examples?
Liver, skeletal muscles
(more friction causes faster regeneration)
How long does self-regeneration last?
2-4 weeks
How often does self-regeneration occur?
life-time
Where are keratinocytes born and where do they go?
Keratinocytes are born in the lower layer and migrate upward during their life
What are the three cell types of Stratum Basale?
Keratinocytes, melanocytes, tactile cells
What are keratinocytes?
Majority are mitotic
Basal lamina separates keratinocytes from extracellular matrix (ECM)
When keratinocytes are in contact with ECM, it divides
What are melanocytes?
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
What is the stratum spinosum?
Thickest layer of epidermis, contains keratinocytes and up to 800 dendritic (Langerhans) cells
per mm2
What is the stratum spinosum composed of?
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
What is the Stratum granulosum?
Last layer of epidermis to have cells containing nuclei
What does the stratum granulosum contain?
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
What is the stratum lucidum?
Exists only in thick skin Translucent - keratinocytes - - densely packed - - contain no nuclei or organelles
What is the Stratum corneum?
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
Which is thicker, the dermis or the epidermis?
the dermis
Is the dermis as regular as the epidermis?
No; stratified but layers are not easily identifiable
What are the two layers of the dermis?
Papillary layer
- made of connective tissue
- interdigits with epidermis (and reticular layer)
Reticular layer
- irregular, dense connective tissue rich in collagen
- protects organs
What are accessory organs?
glands, hair, nails
What does the dermis contain other than accessory organs?
Blood vessels, sensory nerves, muscles
What is the hypodermis also called?
Subcutaneous layer
What does the hypodermis consist of?
Connective tissue with adipocytes
What are the functions of the hypodermis?
Important in newborns
- protective layer against heat loss
In adults, subcutaneous fat is restricted to specific area of the body
What are the different cutaneous glands?
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
How is skin a barrier?
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
How does skin produce vitamin D3?
7-dehydrocholesterol
- leads to pre-vitamin D3
- (isomerisation) leads to Vitamin D3
Where does vitamin D3 production take place?
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
What is Vitamin D3 also called?
cholecalciferol
What does cholecalciferol turn into after hydroxylation?
Calcidiol - 25(OH) D3
then Calcitriol - 1alpha25(OH)2D3
What happens when Calcitriol binds to VDR (vitamin D3 receptor)?
Control of gene expression
What does calcitriol act as?
Factor of gene regulator
How does sun screen with a high index factor work?
Prevents vitamin D3 production
Deleterious effect on production of calcium phosphate
Weak bones
What can too much UV lead to?
Skin cancer
What can too little UV lead to?
brittle bones
