Flashcards in Module 2B Deck (251)
Dual Origins of the Skin
Epidermis(superficial layer) –develops from surface ectoderm
Dermis(deep layer) –develops from the underlying mesenchyme
Initially, the embryo is covered by a single layer of ectodermal cells. In the beginning of the second month, this epithelium divides, and a layer of flattened cells,__, is laid down on the surface.
the periderm, or epitrichium
With further proliferation of cells in the basal layer during the second month, a third, ___ is formed
Finally, at the end of the fourth month, the epidermis acquires its definitive arrangement, and four layers can be distinguished, namely:
BASAL LAYER, OR GERMINATIVE LAYER - is responsible for production of new cells. This layer later forms ridges and hollows, which are reflected on the surface of the skin in the fingerprint.
SPINOUS LAYER - consists of large polyhedral cells containing fine tonofibrils.
GRANULAR LAYER - contains small keratohyalin granules in its cells.
HORNY LAYER - forming the tough scalelike surface of the epidermis, is made up of closely packed dead cells containing keratin.
True or False
Cells of the periderm are usually cast off during the second part of intrauterine life and can be found in the amniotic fluid
During the first 3 months of development, the epidermis
is invaded by cells arising from the neural crest. These cells synthesize melanin pigment in __
Dermis is derived from mesenchyme that has three sources:
1. Lateral plate mesoderm - supplying cells for dermis in the limbs and body wall
2. Paraxial mesoderm - supplying cells for dermis in the back
3. Neural crest cells - supplying cells for dermis in the face and neck
During the third and fourth months, the corium forms many irregular papillary structures called __ which contain a capillary and sensory nerve organ
- a deeper layer of the dermis which contains a large amount of fatty tissue
- a whitish paste formed by secretion from sebaceous glands and degenerated epidermal cells and hairs
- it protects the skin against the macerating action of amniotic fluid
Hairs begin development as solid epidermal proliferations from the germinative layer that penetrates the underlying dermis. At their terminal ends, ___ invaginate.
- are rapidly filled with mesoderm in which vessels and nerve endings develop
cells in the center of the hair buds become spindle-shaped and keratinized, forming the hair shaft, while peripheral cells become cuboidal, giving rise to the __
epithelial hair sheath
The ___ is formed by the surrounding mesenchyme. A small smooth muscle (arrector pili), also derived from mesenchyme, is usually attached to the dermal root sheath.
dermal root sheath
Continuous proliferation of epithelial cells at the base of the
shaft pushes the hair upward, and by the end of the third month, the first hairs appear on the surface in the region of the __.
eyebrow and upper lip
The first hair that appears, __, is shed at about the time of birth and is later replaced by coarser hairs arising from new hair follicles.
Cells from small bud at epithelial wall of hair follicle form the __
Cells from the central region of the gland degenerate, forming a fat-like substance __ secreted into the hair
follicle, and from there, it reaches the skin.
Two types of Sweat Glands
1. Eccrine - Buds from germinative layer of the epidermis
2. Apocrine - From same epidermal buds that produce hair follicles
Sweat glands and mammary glands develop from __
Mammary glands are modified sweat glands and first appear as bilateral bands of thickened epidermis called __
mammary lines or mammary ridges
Development of Nails
- Ectodermal thickening in the dorsum of digits
- Nail fields, surrounded by nail folds
- Largest organ
- Integument, cutaneous covering
Functions of the Skin
- Sexual signaling
the skin is composed of:
epidermis - an epithelial layer of ectodermal origin
dermis - a layer of mesodermal connective tissue
At the irregular junction between the dermis and epidermis, projections called __ interdigitate with invaginating epidermal ridges to strengthen adhesion of the two layers.
Beneath the dermis lies the ___ a loose connective tissue layer usually containing pads of adipocytes.
subcutaneous tissue or hypodermis
- consists mainly of a stratified squamous keratinized
epithelium composed of cells called keratinocytes.
- forms the major distinction between thick skin and thin skin
- Germinal basal layer mitosis
There are also three much less abundant epidermal cell
antigen-presenting Langerhans cells
tactile epithelial cells called Merkel cells