27. Skin Devo

Question 1

The epidermis forms from the

Answer 1

Surface Ectoderm.

Question 2

epidermal

derivatives such as hair follicles, sweat and sebaceous glands and nails develop from

Answer 2

the ectoderm.

Question 3

The dermis of the skin is derived from.

Answer 3

Mesenchyme

Question 4

On the ventrolateral aspect of the body the dermal forming mesenchyme originates
from ________, while in the back of the trunk, it forms from the _________

Answer 4

somatic mesoderm

dermatomes.

Question 5

In the head and neck, it dermis forming mesenchyme originates from the

Answer 5

neural crest and head mesoderm.

Question 6

How is the epidermis formed?

Answer 6

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

Question 7

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.

Answer 7

The vernix

Question 8

Sebacceous vs Eccrine

Origin

Answer 8

Sebaceous: Buds from epithelial root
sheath of hair follicle
Eccrine: Epidermial placode that becomes a bud which
extends into the dermis

Question 9

Sebacceous vs Eccrine

Structure

Answer 9

Sebacceous: Buds branch
Eccrine: Buds elongate and coil

Question 10

Sebacceous vs Eccrine

Duct

Answer 10

Sebacceus: short
Eccrine: long

Question 11

Sebacceous vs Eccrine

Secreation

Answer 11

Sebacceous: Oily
Eccrine: water

Question 12

Sebacceous vs Eccrine

Time of Function

Answer 12

Sebacceous:Fetal period
Eccrine: Shortly after birth

Question 13

Why do eccrine sweat glands open onto the surface of the skin

Answer 13

develop as an epidermial placode –>bud that extends into the dermis, so the duct empties onto the surface of the
skin.

Question 14

Why do apocrine sweat open into hair follicles ?

Answer 14

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.

Question 15

Origin of Hair

Answer 15

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.

Question 16

Hair follicle =

Answer 16

hair bulb + epithelium connecting it

to surface

Question 17

When does hair start forming?

Answer 17

early in fetal period

Question 18

Devo of nails

Answer 18

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

Question 19

thickened areas of epidermis on the dorsal surface of the digit tips.

Answer 19

Nail fields

Question 20

When do nails form?

Answer 20

week 10 for fingernail and 14 weeks for toenails

Question 21

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.

Answer 21

Lanugo

Question 22

During the ______ lanugo hair is replaced by more mature hair. During_______ courser hairs replace the normal hair in the pubic region.

Answer 22

perinatal period

puberty

Question 23

By examining the fingernails of a newborn, how could you determine if this infant was born prematurely?

Answer 23

In premature infants the nails (nail plates) have not reached the tips of the digits.

Question 24

Devo of nail pigment: melanocytes

Answer 24

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.

Question 25

contain pigment (melanin) granules that are 
transferred to cells in the base of the epidermis just before birth.

Answer 25

Melanocytes

Question 26

migrate into hair follicles where they differentiate into melanocytes.

Answer 26

Melanoblasts

Question 27

What is the precursor of the arrector pili muscles?

Answer 27

dermal mesenchyme adjacent to the forming hair follicle.

Question 28

What would you suspect if you delivered a baby with gray hair?

Answer 28

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.

Question 29

EnZ dysfunx in albinism

Answer 29

enzyme tyrosinase so they can’t melanin

Question 30

a group of skin disorders resulting from excess keratinization. The skin is dry and scaly.

Answer 30

Ichthyosis

Question 31

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.

Answer 31

Lamellar ichthyosis

Question 32

Cause of lamellar ichthyosis

Answer 32

This condition is the result of a defect in the gene for transglutaminase 1.

Question 33

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.

Answer 33

Collodin Infant/Baby –

Question 34

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

Answer 34

Harlequin Ichthyosis –

Question 35

absence or loss of scalp hair caused by failure of hair

follicles to develop or production of poor-quality hair.

Answer 35

Congenital Alopecia –

Question 36

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.

Answer 36

Hemangioma

Question 37

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.

Answer 37

Capillary Malformation –

Question 38

Cause of Capillary Malformation

Answer 38

increased levels of VEGF and VEGF-R2.

Question 39

Oculular albinism has what type of inheritance

Answer 39

Xlinked recessive

Question 40

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.

Answer 40

Oculocutaneous Albinism –

Question 41

Oculocutaneous Albinism cause:

Answer 41

The condition is due to a genetic

defect in production of tyrosine.

Question 42

primary defects in two or more tissues derived from epidermis or oral ectoderm. This includes hair, eccrine glands, teeth and nails.

Answer 42

Congenital Ectodermal Dysplasia

Question 43

Congenital Ectodermal Dysplasia inheritance

Answer 43

The condition is most commonly transmitted by X-linked recessive inheritance.