27. Skin Devo Flashcards
The epidermis forms from the
Surface Ectoderm.
epidermal
derivatives such as hair follicles, sweat and sebaceous glands and nails develop from
the ectoderm.
The dermis of the skin is derived from.
Mesenchyme
On the ventrolateral aspect of the body the dermal forming mesenchyme originates
from ________, while in the back of the trunk, it forms from the _________
somatic mesoderm
dermatomes.
In the head and neck, it dermis forming mesenchyme originates from the
neural crest and head mesoderm.
How is the epidermis formed?
Week 3-4 Surface ectoderm (SE) is a single layer of cuboid epithelial cells
Week 4*-8 now a bilayer; outer Periderm and inner Basal layer
Week 11 Intermediate layer now present between periderm and basal layer
Week 11-21 All definitive layers of the skin form. Epidermal ridges extend into the forming dermis
Week 21 Periderm and stratum corneum coexist;periderm disappears before birth
caseosa consists of sloughed periderm cells and sebum, a waxy secretion of sebaceous glands. It protects the fetal skin from damage by constant exposure to amniotic fluid and its contents, e.g. urea and other metabolic products. It also facilitates childbirth because of its lubricating nature.
The vernix
Sebacceous vs Eccrine
Origin
Sebaceous: Buds from epithelial root
sheath of hair follicle
Eccrine: Epidermial placode that becomes a bud which
extends into the dermis
Sebacceous vs Eccrine
Structure
Sebacceous: Buds branch
Eccrine: Buds elongate and coil
Sebacceous vs Eccrine
Duct
Sebacceus: short
Eccrine: long
Sebacceous vs Eccrine
Secreation
Sebacceous: Oily
Eccrine: water
Sebacceous vs Eccrine
Time of Function
Sebacceous:Fetal period
Eccrine: Shortly after birth
Why do eccrine sweat glands open onto the surface of the skin
develop as an epidermial placode –>bud that extends into the dermis, so the duct empties onto the surface of the
skin.
Why do apocrine sweat open into hair follicles ?
develop as buds from the hair follicles in the axilla, pubic and perineal regions. ducts open into the upper portion of the hair follicle proximal to the opening of the ducts of sebaceous glands.
Origin of Hair
Starts as epithelial thickening or placode that proliferates
–> formation of a bud or hair peg, extends into the dermis.
Distal end of bud expands to form hair bulb.
Extension of dermis into base of bulb from dermalpapilla.
Hair follicle =
hair bulb + epithelium connecting it
to surface
When does hair start forming?
early in fetal period
Devo of nails
Nail fields Become surrounded by epidermal folds laterally & proximally–> A flat nail plate grows distally from the proximal fold. Nails reach digit tips at
32 (UL) & 36 (LL) weeks
thickened areas of epidermis on the dorsal surface of the digit tips.
Nail fields
When do nails form?
week 10 for fingernail and 14 weeks for toenails
first hair appearing at week 12 and present in abundance by 7-20 weeks. It is fine, soft and lightly pigmented and helps hold the vernix caseosa onto the skin.
Lanugo
During the ______ lanugo hair is replaced by more mature hair. During_______ courser hairs replace the normal hair in the pubic region.
perinatal period
puberty
By examining the fingernails of a newborn, how could you determine if this infant was born prematurely?
In premature infants the nails (nail plates) have not reached the tips of the digits.
Devo of nail pigment: melanocytes
week 6-7 neural crest derived melanoblasts appear in the forming dermis–> migrate to the junction between the dermis and epidermis +differentiate into melanocytes –> go to stratum basale.
contain pigment (melanin) granules that are transferred to cells in the base of the epidermis just before birth.
Melanocytes
migrate into hair follicles where they differentiate into melanocytes.
Melanoblasts
What is the precursor of the arrector pili muscles?
dermal mesenchyme adjacent to the forming hair follicle.
What would you suspect if you delivered a baby with gray hair?
Albinism, a autosomal recessive trait. lack pigment in the skin, hairs and retina. The melanocytes of affected individuals are unable to make melanin because they lack the enzyme tyrosinase.
EnZ dysfunx in albinism
enzyme tyrosinase so they can’t melanin
a group of skin disorders resulting from excess keratinization. The skin is dry and scaly.
Ichthyosis
Infants born with this form of ichthyosis have skin
composed of large plate like scales of epidermis. The cornified layer is unable to be shed properly which leads to skin permeability problems.
Lamellar ichthyosis
Cause of lamellar ichthyosis
This condition is the result of a defect in the gene for transglutaminase 1.
a form of ichthyosis. The infant is covered by a thick, taut
membrane of keratin that gives the impression that the infant is wrapped in parchment. Eventually the membrane cracks and sloughs in sheet-like fashion over a period of weeks. The exposed skin may be normal in appearance.
Collodin Infant/Baby –
This is the most severe type of ichthyosis. Massive
armor-like plaques cover the newborn skin. Cracks appear after birth. Cannot open their eyes or mouth and have trouble breathing. Most die w/in couple of weeks
Harlequin Ichthyosis –
absence or loss of scalp hair caused by failure of hair
follicles to develop or production of poor-quality hair.
Congenital Alopecia –
a tumor of endothelial cells. Also called birth or strawberry marks often found on the face, scalp or neck. They are rubbery, reddish-purple and raised.
Hemangioma
These are flat leasion of dilated capillaries in the
superficial dermis. They are also called a port-wine stain or nevus flammeus or birthmarks. They persist through life and grow proportionally with the child.
Capillary Malformation –
Cause of Capillary Malformation
increased levels of VEGF and VEGF-R2.
Oculular albinism has what type of inheritance
Xlinked recessive
characteriaed by absent pigmentation in the skin, hair and iris. The defining characteristic is presence of vision
problems that are due to abnormal retinal development and optic nerve abnormalities.
Oculocutaneous Albinism –
Oculocutaneous Albinism cause:
The condition is due to a genetic
defect in production of tyrosine.
primary defects in two or more tissues derived from epidermis or oral ectoderm. This includes hair, eccrine glands, teeth and nails.
Congenital Ectodermal Dysplasia
Congenital Ectodermal Dysplasia inheritance
The condition is most commonly transmitted by X-linked recessive inheritance.
