integument 1,2,3 Flashcards
integument
- skin and
- structures derived from it:
- hair
- nails
- glands
- hooves
- horns
functions of skin
- Environmental Barrier; prevents water loss
- Physical Protection; areas of wear & tear highly cornified
- Temperature Regulation
- sensory reception
- secretion
- social functions
- locomotion
- protection from UV
- immune responses
- protection from parasites and microbes
- calcium homeostasis
- capture of prey
calcium homeostasis
- vitamin D produced by skin in response to sunlight
- converted to calcitriol
- negative consequence of head-to-toe SPF 30+
skin consists of 2 layers
- Epidermis: ectoderm
- Dermis: mesoderm
Hypodermis
- not formally “skin”
- loose connective tissue layer
- attaches skin to underlying
fascia, muscle & bone
hypodermis contains
adipocytes
appendages such as hair, horns and hooves are
keratinized
epidermis epithelium
- stratified squamous epithelium keratinised
- avascular
- Four – five layers:
- stratum basale (B)
- stratum spinosum (S)
- stratum granulosum (G)
- stratum lucidum (L)
- stratum corneum (C)
where does epidermis get its nutrients and O2 from
O2 & nutrients from
vascularised dermis
what would skin with non-keratinized stratified squamous epithelium be
mucous membrane
Stratum basale/germinativum
- cuboidal or columnar cells
- mitotic
- separated from dermis by basal lamina
- desmosomes & hemidesmosomes
Stratum spinosum
- thickest layer
- especially in hairless areas
- large polyhedral cells becoming flatter
- cell separation increased making desmosomes highly visible
- cells appear prickly
- ‘prickle cell layer’
Stratum granulosum
- thinner layer
- flattened cells
- most superficial cells lost nuclei
- cells contain keratohyalin
- precursor to keratin
Stratum corneum
- dead cells
- nuclei & organelles lost
- cells filled with keratin
- surface cells sloughed
- layer thickest in areas subject to greatest wear & tear
Stratum lucidum
- clear, translucent layer
- some non-hairy areas
- eleidin replaces keratohyalin
- a derivative of keratin
- cells dead & lack organelles
- areas where epidermis v. thick
- footpads
- planum nasale
- teat
- reduces friction & shear forces between granulosum & corneum
- may be water repellent
4 cell types of epidermis
- Keratinocytes
- Melanocytes
- Langerhans Cells
- Merkel Cells
- Keratinocytes
- most numerous epidermal cell
- progressive keratinisation
Melanocytes
- stratum germinativum
- also in root sheath of hair & ducts of glands
- contain melanin, bound in melanosomes
- eumelanin: brown-black
- phaemelanin: yellow-red
- transfer melanosomes to keratinocytes
- melanocytes vary in number & distribution: species, season, exposure to sunlight, neoplasia (melanoma)
Although melanocytes produce the melanin,
they transfer it to
keratinocytes
Melanin is produced via oxidation of the amino acid _____
tyrosine
Mutation in tyrosinase responsible for most common form
of _____
albinism
albinism
- Melanin is produced via oxidation of the amino acid tyrosine
- Mutation in tyrosinase responsible for most common form of albinism
- autosomal recessive
- Skin, hair & eyes have little, or no, melanin
- eyes appear red due to blood vessels
leucism
- Failure in differentiation, or migration, of neural crest cells
- affects all pigment cells, including melanocytes
- exception: cells of retina
- eyes often appear blue
langerhan cells derived from
bone marrow
what is first line of defence in epidermis
langerhans cells
Langerhans Cells where are they found
all layers except stratum corneum, but most common in the upper layer of stratum spinosum
langerhans cells are antigen presenting cells and so
- immune function
- phagocytose antigens & then present to T lymphocytes
merkel cells
- Merkel Cells
- common origin with
Schwann cells - lobed, irregular nuclei
- stratum germinativum
- planum rostrale/nasale
- external root sheath of
sinus/tactile hairs - mechanoreceptors for touch
what cells are mechanoreceptors for touch
merkel cells
dermis
- connective tissue layer
- few cells
- amorphous ground substance
- collagen, reticular & elastin fibres
2 layers of dermis
papillary layer
* underlying the epidermis
* loose connective tissue
* thinner
reticular layer
* continuous with hypodermis
* dense connective tissue
* thicker
cells in dermis
- cells include fibroblasts & migratory connective tissue cells
- macrophages, mast cells/histiocytes, plasma cells
in dermis what provides strength
- collagen & reticular fibres provide strength
- elastin fibres vary with age and location
dermis contains
- cells include fibroblasts & migratory connective
tissue cells - macrophages, mast cells/histiocytes, plasma cells
- collagen & reticular fibres provide strength
- elastin fibres vary with age and location
- blood & lymph vessels
- nerves
- sebaceous glands, sweat glands, hair follicles
- smooth & skeletal muscle
- continuous with hypodermis
in thick skin, junction between the dermis and epidermis consists of:
- epidermal pegs
- dermal papillae
hypodermis aka
subcutis
hence, subcutaneous injections (s.c.), hypodermic
needles etc
hypodermis connective tissue
loose connective tissue
what does hypodermis do
anchors skin to underlying structures
adipose tissue in hypodermis
- variable amounts of adipose tissue
- panniculus adiposus
- especially thick in pigs & marine mammals (“blubber”)
smooth muscle in hypodermis
- variable amounts of smooth muscle
does hypodermis contain striated muscle
- may contain striated muscle
- voluntary movement of skin
- cattle & horses twitching in response to flies
what is hair
- Flexible fibre
- Composed of keratinised (i.e. dead) epithelial cells
hair is formed within a
hair follicle
hair follicle
- epithelial invagination
- extends to reticular layer of dermis or hypodermis
cells that from the hair constitute the
hair bulb
hair bulb contains _____ that from an epithelium over the ____
matrix cells
papilla
papilla of hair bulb contains
blood capillaries
within the follicle the root of the hair surrounded by
- inner root sheath
- outer root sheath
The free part of a hair is the
shaft
The portion of hair within the follicle is the
root
3 zones of hair in transverse section
- medulla
- cortex
- cuticle
medulla of hair
- produced by the matrix
- cuboidal cells
cortex of hair
- produced by the matrix
- densely packed squamous keratinised cells
- contain melanin
- from melanocytes in matrix
cuticle of hair
- produced by the matrix
- single layer of overlapping squamous cells
- shape & size of cuticle is species specific
surrounding the cuticle of hair is an
inner root sheath
inner root sheath produced by the
matrix
inner root sheath 3 layers
- root sheath cuticle: similar to hair cuticle, cells interdigitate with hair cuticle
- Huxley’s layer: 1-3 layers cuboidal epithelium, deeply staining
- Henle’s layer, single layer of flattened cells
surrounding the inner root sheath is the
outer root sheath
outer root sheath produced by
the matrix
outer root sheath
- number of layers of cells
- resembles stratum spinosum
Separating the outer root sheath & the dermis
is the
glassy membrane
Fibres & cells of dermis form a
dermal root sheath
Associated with some hair follicles are
sebaceous & apocrine sweat glands
Arrector pili muscle
- smooth muscle
- attached to dermal root sheath & inserts into the reticular layer of the dermis
- erects hair: insulation, display
sinus (tactile) hairs
- Hairs that are modified for sensory function
- Follicle extends deep into hypodermis
- Inner & outer dermal root sheaths surround a blood-filled sinus
- pressure on hair transmitted to blood sinus
- multiplies signal
- transmits to nerve endings in sinus wal
skin appendages: most are _____ structures of epidermal origin
keratinized
tori
- pads
- contact surfaces of extremities
tori consists of what 3 layers
- epidermis; extensive stratum corneum
- dermis; high papillary layer
- subcutaneous cushion (pulvinus); adipose tissue, glands
scales are formed by
highly keratinized stratum corneum over a fold of skin