Skin, Hair, and Nails Flashcards
Label the skin
What are the four layers of the epidermis? (top to bottom)
- Horny cell layer
- Granular cell layer
- Spinous layer
- Basal layer
Describe each of the four layers of the epidermis:
- Horny cell layer
- Granular cell layer
- Spinous layer
- Basal layer
- Horny cell layer
- Cells have lost all organelles, no metabolic activity - dead cells (sacs filled w/ keratin)
- Granular cell layer
- Cells flatten, organelles begin degenerating, protein granules
- Spinous layer
- Cells start making keratin
- Stuck together with desmosome adhesions between spinous cells
- Basal layer
- Dividing cells
- Stem cell layer (1-cell thick)
Epidermis is a ________, _______ epithelium with _____ main layers
Epidermis is a multilayered, stratified epithelium with 4 main layers
Epidermis is derived from:
Ectoderm
Epidermis starts as:
While it develops it is covered by a ______
Epidermis starts as: the single-cell layer of ectoderm → gives rise to epidermis
While it develops it is covered by a temporary protective coat: Periderm
How is the periderm formed?
Periderm is temporary protective coat that covers the developing epidermis.
Ectoderm gives rise to a new layer of squamous epithelium - the periderm
layer under is the basal layer
Label the skin at 4, 7, 11 weeks and at birth
Periderm is maintained until _____ at which point the _____ has developed and the periderm is ______
Periderm is maintained until mid-pregnancy at which point the horny/cornified layer has developed and the periderm is sloughed off
What are two functions of the periderm
- Protective barrier from amniotic fluid
- Prevents adhesion of adjacent epithelia
Loss of periderm is associated with severe congenital malformations
The periderm is shed at ~____ week. If not shed, called a ______ baby
The periderm is shed at ~21 week. If not shed, called a colloidon baby
- usually associated with a skin disorder
What is vernix caseosa?
- means “cheese varnish”
- Shed periderm cells and fatty secretions from sebaceous glands produce the vernix caseoso covering newborns
- Protects developing fetal skin from amniotic fluid in utero
- different theories on function post-natally (some believe should be left to absorb rather than bathed off)
Shed periderm cells and fatty secretions from sebaceous glands produce the ____________ covering newborns
Shed periderm cells and fatty secretions from sebaceous glands produce the vernix caseoso covering newborns
Function of the vernix caseosa?
- Protects developing fetal skin from amniotic fluid in utero
Epidermal ridges form through _________
Epidermal ridges form through proliferation of basal cells
Epidermal ridges form through proliferation of basal cells
- Downward growth of epidermal ridges forms ________
Epidermal ridges form through proliferation of basal cells
- Downward growth of epidermal ridges forms dermal papillae
- interdigitations that links dermis and epidermis
- What forms in the dermal papillae?
Capillary loops and sensory nerve endings
- _________ form through proliferation of basal cells
- ________ forms dermal papillae
- Epidermal ridges form through the proliferation of basal cells
-
Downward growth of epidermal ridges forms dermal papillae
- interdigitations that links dermis and epidermis
Dermis on the back is formed by _______
Dermis elsewhere on the torso and limbs is formed by _______
Head dermis is from ________
Dermis on the back is formed by Dermatome (from somites spitting into dermamyotome and sclerotome; dermamyotome differentiates into dermatome and myotome)
Dermis elsewhere on the torso and limbs is formed by somatic lateral plate mesoderm
Head dermis is from Neural crest cells
What is Ichthyosis? Cause?
- Family of skin disorders categorized by dry, cracked, scaly skin
- Caused by genetic defect that impairs skin barrier function
- Epidermal cells hyperproliferate and/or become overly adherent and don’t shed properly - causing scalty appearance
What are ectodermal appendages? (5)
Growths off developing skin that have epidermal contributions
- Hair
- Sweat glands
- Nails
- Mammary Glands
- teeth
Ectodermal appendages follow the same pattern of development initially:
- formation of ______
- Formation of _____
- _______
Ectodermal appendages follow the same pattern of development initially:
- formation of placode (ectodermal placode)
- localized thickening of ectoderm → bulge into underlying mesenchyme
- Formation of ectodermal bud
- _extension into mesenchyme (_mesoderm in body; neural crest in head)
-
Morphogenesis
- Shaping
How does the ectodermal placode grow?
Grows via cell migration - not proliferation
What is the ectodermal placode?
- local thickening of ectodermal epithelium
- Stratified
- Results from cell migration
The _______ generates hair and extends through epidermis into dermis
The hair follicle generates hair and extends through epidermis into dermis
Label the hair follicle and surrounding structures
The dermal papilla originates from _____
The dermal papilla originates from mesenchyme (origin from mesoderm or neural crest cells in head)
Blood vessels and nerves enter the hair follicle through the _______
Blood vessels and nerves enter the hair follicle through the dermal papilla
What is the germinal matrix?
Stem cells in the hair follicle
Divide and add cells (keratinocytes which mature → dead cells) to the root → lengthens
What are the four stages of hair follicle development?
- Placode
- Hair germ
- Hair peg
- Mature follicle
The ________ doesn’t contribute cells to the hair. It induces formation of the germinal matrix and maintains it
The dermal papilla doesn’t contribute cells to the hair. It induces formation of the germinal matrix and maintains it
Role of the Dermal papilla in hair follicle development?
The dermal papilla doesn’t contribute cells to the hair. It induces formation of the germinal matrix and maintains it
In both the placode stage and the hair germ stage (of hair follicle development), what is present?
Dermal condensate → becomes the dermal papilla
What is the hair peg stage of hair follicle development?
Mesenchymal cells are condensed into an invagination of hair peg → papilla
Papilla sits directly under stem cells and acts as a signalling centre to maintain stem cells
Label the stages of hair follicle development
Melanocytes sit just above the ______ in the hair follicle. They arise from _______, invade the follicle and _______
Melanocytes sit just above the dermal papilla, by the germ matrix in the hair follicle. They arise from neural crest, invade the follicle and contribute pigment to the hair
What is notable about hair follicle arrangement?
- There is a regular arrangement of follicles all facing same direction
- Signaling mechanisms regulate location and direction
- PLANAR CELL POLARITY
What is lanugo?
First hairs that start forming at week 12 - very soft
Function of lanugo?
- lanugo: first, soft hairs forming at week 12
- Helps trap the vernix caseosa (cheesy layer - protect skin in utero)
How does hair change after birth?
Lanugo (first hairs) are replaced mostly by Vellus hair (stronger, finer, less pigmented (all over body))
Lanugo on head is replaced by darker, thicker terminal hair
What happens to hair at puberty?
Hair in select regions switches from vellus to terminal
How are new hair follicles added post-natally?
They aren’t. We are born with ~5 million hair follicles and no new ones are added
What are the four phases of the hair cycle?
- Growth
- Regression
- Rest
- Renewal
The _____ muscles are around the base of the hair follicle and cause the hair to stand erect (goosebumps)
The Arrector pili muscles are around the base of the hair follicle and cause the hair to stand erect (goosebumps)
Arrector pili muscles are ________ derived from the _______
Arrector pili muscles are smooth muscle derived from the mesenchyme (mesodermal derived)
Sebaceous glands are ______ derivatives that protrude off the ______
Sebaceous glands are ectodermal derivatives that protrude off the hair follicle
Sebaceous glands produce _____ through a ______ mechanism
Sebaceous glands produce oily secretion through a holocrine mechanism
- build up substance within the cell then whole cell is shed and breaks down to release oily secretion
Sebaceous glands produce _____ through a ______ mechanism
Sebaceous glands produce oily secretion through a holocrine mechanism (do not have a lumen)
- build up substance within the cell then whole cell is shed and breaks down to release oily secretion
Sebaceous glands form _______.
Central cells of the gland continually ______ to produce ______ to protect the skin from friction and dehydration
Sebaceous glands form as extension of hair follicle.
Central cells of the gland continually breakdown to produce oily secretion (sebum) to protect the skin from friction and dehydration
Eccrine sweat glands develop from _______
Eccrine sweat glands develop from separate ectoderm placode (not associated with hair follicle)
Eccrine sweat glands:
- extensions of ______
- ________ to make lumen
- ectodermal cells develop into _______
- Surrounding mesenchymal cells become _______
Eccrine sweat glands:
- extensions of epidermal cells into dermis
- central cells degenerate to make lumen
- ectodermal cells develop into secretory cells
- Surrounding mesenchymal cells become smooth muscle
Eccrine sweat glands:
- extensions of epidermal cells into dermis
- central cells degenerate to make ______
- ________ develop into secretory cells
- Surrounding _________ become smooth muscle
Eccrine sweat glands:
- extensions of epidermal cells into dermis
- central cells degenerate to make lumen
- ectodermal cells develop into secretory cells
- Surrounding mesenchymal cells become smooth muscle
- How do mammary glands develop?
- Two lines of ectodermal thickening appear on the ventral side of the body
- In humans, the ridges disappear and just one site on each side gives rise to primary mammary gland
Mammary gland development: 1
- Two lines of ________ appear on the ________ side of the body
- In humans, the ridges disappear and just one site on each side gives rise to ________
Mammary gland development:
- Two lines of ectodermal thickening appear on the ventral side of the body
- In humans, the ridges disappear and just one site on each side gives rise to primary mammary gland
Mammary gland development 2
- _____ branches into _______ which becomes the ________
- ______ prenatally in response to placental hormones
- After birth:
- _______ around surface opening (_______) proliferates to form areola and nipple
- _____ will form the smooth muscle around nipple and ducts
Mammary gland development 2
- Primary bud branches into secondary buds which becomes the lactiferous ducts
- Canalize prenatally in response to placental hormones
- form lumen
- After birth:
- Connective tissue around surface opening (mammary pit) proliferates to form areola and nipple
- Mesenchyme will form the smooth muscle around nipple and ducts
Mammary gland:
_________ makes support cells
_________ makes lining and functional (secretory cells)
Mammary gland:
mesodermal-derived mesenchyme makes support cells
endoderm makes lining and functional (secretory cells)
Breasts of neonates contain _____ but not ______
Breasts of neonates contain ducts but not alveoli (secretory sacs)
What part of the breast forms at puberty in females?
The alveoli (secretory sacs)
- primary source of milk
- Allow milk to be held and secreted
What is witches’ milk?
Neonatal ductal cells do have some ability to make milk, which may happen in response to maternal hormones (lasts <1 week)
Crown of the tooth is covered in _____ while root is covered in ______-
______ forms the middle layer
_____ forms the inner part of the tooth
Crown of the tooth is covered in enamel while root is covered in softer cementum
dentin forms the middle layer
pulp forms the inner part of the tooth
Label the tooth anatomy
______ is >90% inorganic, very hard but also brittle
enamel is >90% inorganic, very hard but also brittle
_______ is avascular/acellular and cannot be renewed
enamel is avascular/acellular and cannot be renewed
______ is 45% inorganic, softer but less brittle than enamel
Dentin is 45% inorganic, softer but less brittle than enamel
______ line outer wall of pulp chamber and add dentin throughout life so pulp chamber shrinks
Odontoblasts line outer wall of pulp chamber and add dentin throughout life so pulp chamber shrinks
What cells make dentin?
Odontoblasts
What are the four stages of tooth development?
- Placode
- Bud
- Cap
- Bell
What is the enamel knot and where is it found?
Enamel knot is a cluster of ectodermal cells sitting just above the dental papilla
During which stage does the enamel knot arise?
Arises during the cap stage and is an important signaling center for tooth development. In molars, secondary enamel knots develop - one for each cusp
Function of enamel knot?
Important signaling centre for tooth development
- one for each cusp
In tooth development, the placode grows into mesenchyme which is derived from ______
In tooth development, the placode grows into mesenchyme which is derived from Neural crest cells (head and neck)
What is the dental papilla?
Invagination of mesenchymeinto placode
What stages of tooth formation are shown in the image?
What stages of tooth formation are shown in the image?
Label
What is the enamel reticulum?
Connective tissue network that forms during tooth development
Label the bell stage
What two cell types differentiate in the bell stage and where does this differentiation start?
- Ameloblasts
- Odontoblasts
Differentiation starts at cusps and spreads down both sides
What induces odontoblast differentiation?
What induces ameloblast differentiation?
- Odontoblasts:
- Signals from enamel knot induce odontoblast differentiation from ectoderm
- Ameloblasts:
- Basal membrane breaks down, so two cell layers are intact
- Odontoblasts induce ameloblast differentiation from neural crest
- Odontoblasts:
- Signals from _______ induce odontoblast differentiation from ______
- Ameloblasts:
- ______ breaks down, so two cell layers are intact
- ______ induce ameloblast differentiation from ______
- Odontoblasts:
- Signals from enamel knot induce odontoblast differentiation from ectoderm
- Ameloblasts:
- Basal membrane breaks down, so two cell layers are intact
- Odontoblasts induce ameloblast differentiation from neural crest
Odontoblasts secrete ______ creating _____
Odontoblasts secrete pre-dentin creating separation between cell layers
Odontoblasts leave behind ______ which also secretes components of pre-dentin
Odontoblasts leave behind processes (in pre-dentin) which also secretes components of pre-dentin
Ameloblasts secrete ______
Ameloblasts secrete pre-enamel
Label the developing tooth
label the developing tooth
Function of OEE (outer enamel epithelium)
OEE supports enamel development and tooth eruption but is subsequently lost
What is important about the fold of inner enamel epithelium and outer enamel epithelium (IEE/OEE)
The fold of inner enamel epithelium and outer enamel epithelium (IEE/OEE) will expand to establish the root of the tooth
What is the dental lamina and what is its function?
Dental lamina:
- Ectodermal extension
- Temporarily connecting developing tooth to surface ectoderm
- eventually degenerates
Bud for permanent tooth develops as extension off ______
Bud for permanent tooth develops as extension off dental lamina
Why might the following dental abnormalities arise?
- demonstrate the importance of patterning
- signalling mechanisms that control where teeth form (Morphogen signaling)
