Lecture 23A - Topical Infections Flashcards
How do you calculate the area of your skin?
0.007184 x weight (kg)^0.425 x height (cm)0.725
What is the outer layer of the skin?
the waterproof cornified out layer of keratin proteins and lipids, made by epidermis
What is the outermost section of the skin called?
the epidermis
What does the epidermis include?
the waterproof layer and cells from which the surface coat of skin is derived
What is the dermis?
a supporting layer with blood and lymphatic vessels, sensory nerve ending, hair roots depending on the type of skin and sweat glands
Where can sweat gland secrete into?
a sub-surface enclosed space (apocrine) or directly onto the skin surface (eccrine)
What is the hypodermis?
a fatty layer which insulates the body from heat loss and fluid loss and protects muscle and organ tissue beneath
What are eccrine sweat glands?
secrete directly onto skin surface
thermoregulation, salt excretion, antibacterials
What are apocrine sweat glands?
bud fatty secretions in vesicles off into enclosed areas like hair follicles
Where are apocrine sweat glands especially found?
in axilla and pubic areas - pheromones
Where are hair follicles housed?
A specialised mini organ called the psilosebaceous unit which lies in the dermis
What does the psilosebaceous unit contain?
a muscle which can be used to pull the lower end of the hair shaft towards a verticle position and make your hair stand on end
What does the psilosebaceous unit secrete?
sebum
What is sebum?
an oily, waxy liquid of low pH
What does sebum do?
can be antibacterial, helps lubricate the skin, waterproof it in cold wet conditions and with different lipid composition helps slow the rate of evaporation of sweat in hot conditions which helps flid retention
How is sebum antibacterial?
it contains antibacterial proteins but can also be antibacterial because of its pH
What can blockage of the psilosebaceous unit cause?
acne amongst a variety of other conditions
How often does skin renew itself?
every 4 weeks
What are the components of the epidermis?
dead anuclear squammes layer
granual layer with keratin vacuoles
spindle layer with early differentiation
germinal layer
What is the cornified envelope?
in the dead layer
physical barrier and immune modulation
What are keratin filaments?
provide structural integrity in the granular layer
SRC signaling
What are desmosomes and adherens junctions?
provide intercellular adhesion and differentiation in the spinel layer
What are integrins?
ECM adhesion
stem cell maintenance in germinal layer
What other cells are in the spindle layer?
langerhans antigen presenting cells
which are tissue specific macrophages
Where does generation of skin begin?
in the lowest level, the germinal layer
What happens in the germinal layer?
keratinocytes divide and begin their transition through the 3 layers above them to the outer surface of the skin
What happens as keratinocytes migrate upwards?
they differentiate and mature
What helps to drive migration of keratiocytes?
a small potential difference of tens of millivolts across the epidermis
What do cells in the spindle secrete?
proteins to aid adherence between cells so that a uniform sheet of cells is created
What do cells in the granular layer produce?
keratin filaments, which give mechanical strength to the maturing skin layer
What other cells are found in the germinal layer?
melanocytes
What happens to the cells in the sqammes layer?
they have lost their nucleus and are dead
What creates the tough waterproof barrier?
the tight bonding between cells in the sheet and abudance of keratin fibres and lipid
What mediates the sense of touch?
innervation of glabrous (non-hairy) skin by fast conducting, low threshold mechano-receptors (LTMRs)
What is glabrous skin?
most sensitive for and to touch
hands, feet, genitalia, lips, cheeks
very specialised ski areas
What is glabrous skin innervated by?
A-beta LTMRs including Abeta SA1-LMTRs terminating in merkel cells
What responds to light pressure?
meissner corpuscles
What responds to deeper pressure?
pacinian corpuscles
What can sustained light pressure be detected by?
merkel cells
What is skin on the back like?
less densely innervated and it is more difficult to discriminate between two closely positioned pressure points
What can skin sense?
vibration and pressure
What does skin respond do?
temperature, touch, pain, itch
Where are low threshold mechanoreceptors found?
close to the skin surface, have narrower receptive fields
What does innervation of hair shafts on hairy skin in rodents allow?
enables them to be used a sense organs
What is innervation of hairy skin?
less dense and therefore less sensitive to touch, conveys affective sensations
What is hairy skin in rodents innervated by?
distinct combinations of LTMRs
Where are touch domes of merkel cells found in rodents?
above the level of the sebaceous glands of guard hair follicles
What are guard hairs innervated by?
A-beta RA-LTMR lanceolate endings
What are awl/auchene hairs innervated by?
three tyes of lanceolate ending LTMRs
Aβ RA-LTMRs, Aδ-LTMRs, and C-LTM
What are zigzag hairs innervated by?
Aδ-LTMRs and C-LTMRs
What do circumferential endings encircle?
the longitudinal lanceolate endings of all three types of hair follicles
Where is glabrous skin found?
on the palms and soles of the feet
What is glabrous skin rich in?
sensory nerve endings
Where is hair skin found?
major part of the body surface, but quite varied
back, scalp, eyebrows
Where is thick/flexible skin found?
knees, elbows, soles of the feet
Why is the thickness of skin important?
some drugs are applied as ointments or dermal patches where the drug is absorbed by the skin
What is the microenvironment?
different skin regions vary greatly in their appearance and in the amounts of moisture and oiliness they typically carry
temperature and pH vary also
Functions of the skin?
a physical barrier to noxious agents and entry of pathogens
immunological barrier to ingress of pathogenic organisms
assist retention of heat and regulation of temp
retains moisture and maintains osmotic balance i the body
sensory organ
excretion, salt balance, secretion of antibacterial peptides and pheromones
vit D production
protection from UV
What can widespread burns remove?
the skins role in osmoregulation
What is a life threatening complication of burns?
fluid loss which can be followed by circulatory collapse
