Skin: Development

Question 1

In what week of development does the periderm form?

Answer 1

4th week
(after neurulation when the neural tube is formed)

Question 2

Layer beneath the periderm

Answer 2

Basal layer

Question 3

This layer forms the stratum germinativum and the intermediate layer

Answer 3

Basal layer

Question 4

Post-neurulation in the 4th week, the surface epithelium proliferates and forms this, which is a new outer layer of simple squamous epithelium

Answer 4

Periderm

Question 5

The periderm consists of this morphological cell type

Answer 5

Simple squamous epithelium

Question 6

This constitutes the layer of stem cells (stratum basale) that will continue to replenish the epidermis throughout life

Answer 6

Stratum germinativum

Question 7

The cells of this layer contain the keratin proteins, which is characteristic of differentiated epidermis (therefore these cells are called keratinocytes)

Answer 7

Intermediate layer

Question 8

The periderm is sloughed off by this week of development

Answer 8

21st week

Question 9

This layer is replaced by the 3 definitive layers of the outer epidermis: the inner stratum spinosum, the middle stratum granulosum, and the outer stratum corneum

Answer 9

Intermediate layer

Question 10

Peridermal cells are eventually desquamated and form part of this, a greasy substance of peridermal cells and sebum from the sebaceous glands that protects the embryo’s skin

Answer 10

Vernix caseosa

Question 11

The vernix caseosa is a greasy substance composed of these 2 things, which protects the embryo’s skin

Answer 11

Peridermal cells and sebum

Question 12

Proliferation of cells in this layer also produces epidermal ridges, which extend into the developing dermis

Answer 12

Stratum germinativum

Question 13

The pattern of these that develops on the surface of the palms of the hands and the soles of the feet is determined genetically and constitutes the basis for examining fingerprints (dermatoglyphics) in criminal investigation and medical genetics

Answer 13

Epidermal ridges

Question 14

Epidermal ridges appear in embryos at this week

Answer 14

10 weeks

Question 15

Epidermal ridges appear in embryos at 10 weeks and are permanently established by this week

Answer 15

17th week

Question 16

These are derived from neural crest cells that migrate into the stratum basale of the epidermis

Answer 16

Melanoblasts

Question 17

Melanoblasts are derived from these which migrate into the stratum basale of the epidermis

Answer 17

Neural crest cells

Question 18

Melanoblasts are derived from neural crest cells that migrate into this location

Answer 18

Stratum basale

Question 19

These differentiate into melanocytes by mid-pregnancy, when pigment granules called melanosomes are observed

Answer 19

Melanoblasts

Question 20

When do melanoblasts differentiate into melanocytes?

Answer 20

By mid-pregnancy
This is when melanosomes are also observed

Question 21

Merkel cells arise from this type of cell

Answer 21

Epidermal cells

Question 22

These cells function as slow-adapting mechanoreceptors in the skin, but cytochemical evidence suggests that they may also function as neuroendocrine cells at some stage

Answer 22

Merkel cells

Question 23

When separated, do ectoderm and underlying mesenchyme differentiate?

Answer 23

No
Recombinations show that the dermis (mesoderm) determines the nature of the ectodermal differentiation

Question 24

Recombinations show that this determines the nature of the ectodermal differentiation

Answer 24

The dermis (mesoderm)

Question 25

Tissue with a triple embryonic origin that underlies the epidermis and contains blood vessels, hair follicles, nerve endings, sensory receptors

Answer 25

Dermis

Question 26

The dermis is derived from these three different sources

Answer 26

Lateral plate mesoderm (limbs and body wall) Neural crest cells (head and neck) Paraxial mesoderm (back)

Question 27

Dermis derived from lateral plate mesoderm applies to these regions of the body

Answer 27

Limbs and body wall

Question 28

Dermis derived from neural crest cells applies to these regions of the body

Answer 28

Head and neck

Question 29

Dermis derived from paraxial mesoderm applies to these regions of the body

Answer 29

Back

Question 30

The dermis is loose connective tissue made of these cells

Answer 30

Mesoderm cells (aka mesenchymal cells or mesenchyme)

Question 31

The mesenchymal cells in the dermis secrete a watery-type ECM rich in these two components

Answer 31

Glycogen and Hyaluronic acid

Question 32

These cells secrete a watery-type ECM rich in glycogen and hyaluronic acid

Answer 32

Mesenchymal cells of the dermis

Question 33

These cells differentiate into fibroblasts, which secrete increasing amounts of collagen and elastic fibers into the ECM

Answer 33

Mesenchymal cells

Question 34

The mesenchymal cells differentiate into fibroblasts, which secrete increasing amounts of these two components into the ECM

Answer 34

Collagen and elastic fibers

Question 35

Where are the tactile sensory receptors (such as Meissner corpuscles) found in the skin?

Answer 35

In the projections of the dermis into the epidermis, called dermal papillae

Question 36

Principle types of fibers in the dermis

Answer 36

Type I and III collagen and elastic fibers

Question 37

This initially covers the entire nail plate, but it eventually degenerates, except for a thin persisting rim along the proximal end of the nail

Answer 37

Eponychium

Question 38

The thickened epidermis underly the distal most part of the nail

Answer 38

Hyponychium

Question 39

This marks the border between dorsal and ventral skin under the distal part of the nail

Answer 39

Hyponychium

Question 40

In humans, mutation in a novel WNT ligand, R-SPONDIN-4, or the FRIZZLED 6 RECEPTOR, causes this

Answer 40

Nail defects, including anonychia (absence of nails)

Question 41

In humans, mutation in this causes nail defects, including anonychia (absence of nails)

Answer 41

A novel WNT ligand, R-SPONDIN-4 or FRIZZLED 6 RECEPTOR

Question 42

These glands form as diverticula of hair follicle shafts, budding from the root sheath about 4 weeks after the hair germ elongation begins to elongate

Answer 42

Sebaceous glands

Question 43

Glands that initially form over most of the body but are lost in later months except in certain areas, such as the axillae, mons pubis, prepuce, scrotum, and labia minora Begin to secrete at puberty

Answer 43

Apocrine sweat glands

Question 44

In the development of eccrine sweat glands, the central cells degenerate to form the gland lumen, and the peripheral cells differentiate into an inner layer of secretory cells and an outer layer of this type of cell, which are innervated by sympathetic fibers and contract to expel sweat from the gland

Answer 44

Myoepithelial cells

Question 45

During the development of ectodermal placodes, mammary glands, hair follicles, and tooth buds are also differentiating as derivatives of this

Answer 45

Epidermal invaginations

Question 46

These first appear in the 4th week as thickened lines of epidermis that extend from the thorax to the medial thigh

Answer 46

Mammary ridges

Question 47

Secondary mammary buds form during the 3rd month and become canalized to form these during the last 3 months of fetal life

Answer 47

Lactiferous ducts

Question 48

When do secondary mammary buds form?

Answer 48

During the 3rd month

Question 49

When in development do secondary mammary buds become canalized to form lactiferous ducts?

Answer 49

During the last 3 months of fetal life

Question 50

A group of skin disorders that results from an excess of keratin formation The skin is characterized by dryness and scaling, which may involve the entire body surface

Answer 50

Ichthyosis

Question 51

Ichthyosis is a group of skin disorders that results from an excess of this The skin is characterized by dryness and scaling, which may involve the entire body surface

Answer 51

Keratin formation

Question 52

Disorder resulting from a rare keratinizing disorder that is inherited as an autosomal recessive trait and caused by a mutation in the ABCA12 gene

Answer 52

Harlequin ichthyosis

Question 53

What is the inheritance pattern of Harlequin ichthyosis?

Answer 53

Autosomal recessive

Question 54

What mutation causes Harlequin ichthyosis?

Answer 54

Mutation in the ABCA12 gene

Question 55

What is the prognosis of neonates with Harlequin ichthyosis?

Answer 55

Poor Most require intensive care, 70% die early

Question 56

The periderm is normally shed completely by this week of development

Answer 56

21st week

Question 57

Condition where the periderm persists until birth, forming a "cocoon" around the newborn Is either removed by the physician or shed spontaneously during the first weeks of life

Answer 57

Collodion babies

Question 58

In collodion babies, this persists until birth rather than being normally shed completely by the 21st week of development

Answer 58

Periderm