Flashcards in Chapter 2 Deck (20):
What are the three skin layers and together what do they function to do?
Epidermis, dermis, and hypodermis
They protect the body, regulate temperature, sensation, excretion, immunity, a blood reservoir, and vitamin D synthesis
What does the epidermis do, and what do melanocytes do?
Epidermis prevents water loss through evaporation, acts as a re lector organ, and provides a protective barrier
Melanocytes are cells in the epidermis that produce pigment and synthesize vitamin D
What does the dermis do?
It's a layer of connective tissue that supports the epidermis--a.network of cells, fibres, and blood vessels that provides structural support and nourishment for the epidermis--acts as a blood reserve
What does the hypodermis do?
It's a loose connective tissue that contains a pad of fat that contours the body and serves as an energy reserve--fibres link the hypodermis to the dermis and epidermis
What is the only appendage of the friction skin, and how do they differ there?-
The only skin appendage of friction skin is the eccrine sweat gland--friction skin has the highest concentration at 2500-3000/sq inch--
Eccrine sweat glands regulate temperature by secreting sweat and excreting metabolic waste
--appendages of smooth skin are hair, nails, sebaceous glands
What are the four types of epidermal cells, and what are their functions?
Keratinocytes: these are the cells that undergo differentiation and are sloughed off---they're the primary cells of the epidermis, accounting for 90-95% of epidermal cells--keratin is a durable protein that provides structural support to the cell, reinforcing them so they don't break--there are 20 varieties of keratin--keratinocytes of friction skin are only cells to have keratin K9-- there is more mechanical stress on the ridges vs the furrows--the ridges compress when touch surface requiring more durability and the furrows have more pliable keratin and act as a hinge
Communication of keratinocytes with the other cells is necessary:
Melanocytes--produce pigments and vitamin d
Langerhans cells--an extension of body's immune system
Merkel cells--extension of nervous system--participate in sensation of touch
The layers of the epidermis are named based upon appearance of the keratinocytes. As they are pushed towards the surface they undergo differentiation, and the cells fill with keratin. Which layer is the blueprint layer?
Stratum Basale--a single layer of keratinocytes--the basal cells are connected to the basement membrane by hemidesmosomes--desmosomes connect basal cells to each other---there's a supra-basal layer between the Basale and spinosum layers in the primary ridges
---basal cells undergo cell mitosis where cell replicates it's DNA--copy of cell sits on top, and gets pushed upward as new columnar cells are generated---the hemidesmosomes of basal cells and interlocking fibres throughout the basement membrane zone prevent the basal cells from migrating---as the cells progress upward in concert, the desmosomes are continually reinforced until they are broken down when cells reach outer portion of stratum corneum
---basal cells of secondary ridges have long projections into dermis for anchoring--basal cells of primary ridges produce more cells due to tissue demand, and increased abrasion to ridges--when primary ridge cell divides the cell spends some time in the supra-basal layer where it divides a couple more times
--layer above Basale--desmosomes are reinforced--keratin production increased--cells appear spiny--pockets of lipids appear but are not active
--layer above spinosum--further structural and chemical modification occurs to cells
--layer above granulosum--cells are keratinized and have completed their programmed cell death
Top layer of epidermis--arrangement of keratinocytes is described as brick and mortar mode--the keratin-filled cells are surrounded by the lipids--as cells are pushed toward surface desmosomes degrade and cells shed
How do cells in epidermis communicate?
--rate at which basal cells divide must coincide with cells sloughing at surface
--cells communicate via gap junctions which are connections between cells, and cell surface receptors
--through a feedback mechanism the basal layer knows when to stop production
--molecules released at granulosum layer called chalones signal basal cells to halt production when cell concentration too high
How is the outer morphology of friction ridge skin a direct reflection of its function?
The ridges and sweat pores allow the hands and feet to grasp surfaces firmly, and the crease allow the skin to flex--ridges, creases, as scars are durable morphological features
Talk about dermis.
--dermis supports epidermis and binds it to hypodermis
--2 layers: papillary layer (outer layer) that secures dermis to basement membrane--forms the dermal papillae which are peg like projections of the papillary dermis between the primary and secondary ridges...these increase surface area of attachment
--other layer is the reticular layer---connected to hypodermis by a network of fibres
--dermis layers house arterial blood vessels, and a vast network of sensory and autonomic nerve branches
Eccrine sweat glands of the palms and soles are larger, more active, and denser than anywhere else. What is the breakdown of sweat?
Remains are inorganic and organic solids like urea, amino acids, sodium chloride
--adipose tissue (fat) that serves as energy store, cushions the skin, contours the body, and allows for mobility of skin over underlying structures--primary cells are adipocytes
Talk about homeostatis of skin, and physical attachments specifically the three levels of attachment.
The --homeostatis is the concept of keeping things the same despite constant input and output of materials and energy--achieved in the skin through physical attachments and regulation of cell production in the stratum Basale via cell communication
--the primary and secondary ridges support ridges and furrows--the sweat glands of the primary ridges are firmly rooted in dermis or lower
--fibres generated by dermis and Basale layer are interwoven to create the fibrous sheet, or basement membrane that locks the epidermis to the dermis
--cell-to-cell attachments between keratinocytes by desmosomes and focal tight junctions
So, list why friction ridge skin persists.
--physical attachments throughout the skin
--three dimensional morphology of ridges is maintained by increased cell production in supra basal layer of primary ridges and enhanced anchorage of the basal cells in the secondary ridges
--cell communication ensures basal cell proliferation is stimulated and inhibited in a coordinated matter
--desmosomes bind basal cells together as they move upward in concert
What effects does aging have on the friction ridge skin?
1. Surface ridges tend to flatten due to atrophy of epidermis and remodelling of the dermal papillae--the number of dermal papillae increases with age---does not affect ridges on surface---stratum corneum thickness is maintained for life, however basal keratinocytes slow down rate of production which leads to a thinning of the living layers of epidermis (Basale, spinosum, granulosum)
2. Dermis loses elasticity and causes skin to become flaccid and wrinkle--fibre networks in dermis degrade and are compacted resulting in less stretchable, wrinkly skin