Lecture 19

Question 1

List the epithelial layers of thick skin in the correct order (from deepest to most shallow)

Answer 1

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum lucidum

Stratum corneum

Question 2

What epidermal layer do the following characteristics describe?

polyhedral-shaped cells (prickle cells) that feature tonofibrils that form intercellular bridges

Keratins 1 an 10 (high molecular weight keratins)

Keratohyalin granules develop here

Membrane-coating granules first appear (lamellar bodies)

Answer 2

Stratum spinosum

Question 3

What epidermal layer do the following characteristics describe?

represented by only a few cells in thin skin but it is generally considered a multilayered layer of skin

Keratins 2e and 9

Flattened nucleated keratinocytes

Keratohyalin aggregates: fillagrin induces cross-linkage of keratin filaments by disulfide bonds

Membrane coating granules (acyglucosylceramide –> intercellular spaces)
tonofilaments

Answer 3

Stratum Granulosum

Question 4

What epidermal layer do the following characteristics describe?

composed of a single layer of columnar to high cuboidal keratinocytes that are held together by desmosomes

Held to the basal lamina by hemidesmosomes

Have high mitotic activity

Keratins 5 an 14 (low molecular weight keratins)

Answer 4

Stratum basale

Question 5

What epidermal layer do the following characteristics describe?

absent in thin skin and consists of flat keratinocytes lacking nuclei and organelles

Contains eleiden

Answer 5

Stratum lucidum

Question 6

What epidermal layer do the following characteristics describe?

thicker in thick skin and it’s cytoplasm is replaced by keratin

Multilayered

Enucleated, flattened, dead kearatinocytes

Cytoplasm contains keratin cross-linked filaggrin which becomes a cornified cell envelope

Answer 6

Stratum corneum

Question 7

Discriminate between the two layers of the dermis and list characteristics of each layer .

Answer 7

Papillary layer (closest to epidermis): separated from the epidermis by the basal lamina and is composed of loose CT
Network of fine elastic fibers and abundant capillaries

Reticular layer: composed of dense irregular CT and includes fibrocytes, macrophages, and adipocytes

Question 8

Describe the characteristics of the hypodermis (what its composed of, tissue classification, layers)

Answer 8

Loose CT that underlies the dermis and corresponds to the superficial fascia of gross anatomy

Technically not part of the skin

May contains fat cells that can form a thick layer called the panniculus adiposus

Question 9

Compare thick skin to thin skin.

Answer 9

Thick skin displays all 5 epidermal layers and only occurs on palms of the hands and soles of the feet (hairless)
Epidermis between 0.4 mm and 0.6 mm

Thin skin is lacking stratum lucidum and it’s epidermal layers are less distinct
Thinnest skin is on the eyelids, thickest is on the back (75 to 150 micro mm thick)
Thicker on extensor surfaces than on flexor surfaces

Question 10

Explain how ridges are created in the skin to form the basis for fingerprinting.

Answer 10

Primary dermal ridges are formed during the 3rd and 4th months of fetal life, when interpapillary pegs form via a downgrowth of the epidermis into the dermis

Secondary dermal ridges occur in double rows and are composed of thin collagenous, reticular, and elastic fibers

Question 11

Describe the process of keratinization.

Answer 11

The keratinocytes (skincells)areproduced in the Basale layer, thenare pushed up to the Spinosum where theyarelinked by filaments before reaching the Granulosum.

At this point, the cells secrete lipids and lose their organelles whichare replaced with keratin

Question 12

Describe Langerhans cells (derived from, what they contain, where are they found)

Answer 12

Langerhans Cells: aka dendritic cells that act as antigen-presenting cells

From monocytes, and migrate from the epidermis to the lymph nodes

Contain birbeck granules

Found primarily in stratum spinosum

Question 13

Describe Merkle cells (function, location, contents)

Answer 13

Merkle Cells: mechanoreceptors that are usually found in the stratum germinativum and may act as neuroendocrine cells

Contains catecholamine-like granules (their equivalent of neurotransmitters)

Question 14

Describe Melanocytes (derived from, function, attachments in the epidermis, explain skin tone differences among humans)

Answer 14

Melanocytes: cells derived from melanoblasts that inject melanin granules into keratinocytes

Do not form desmosome attachments in the epidermis

All humans have a very similar number of melanocytes, however skin tone is determined by the number of melanin granules that are actually injected into keratinocytes

Question 15

Explain the embryonic origins of the epidermis and dermis.

Answer 15

Epidermis starts as a single layer of ectodermal cells that divides during the 6th week to form the periderm

Dermis is derived from the mesoderm

Question 16

Describe sebacous glands (type of secretion, ducts, secretion produce, when they form, location)

Answer 16

Sebacous glands are Holocrine glands with branched acinar glands that feature short ducts

They continuously produce sebum, which is released into the hair follicle

Their growth is stimulated at puberty by sex hormones

Found everywhere EXCEPT the palms and soles

Question 17

Name and describe the 2 types of sudoriferous glands (describe their ducts)

Answer 17

Merocrine glands: coiled, simple tubular secretory portions and cholinergic endings

Duct system consists of stratified cuboidal epithelium except in the epidermis

Apocrine glands: their excretory duct opens into the hair follicle and it’s secretions are thicker and more viscous than merocrine secretions

Found in the labia majora, areola, axillary and anal regions

Receive Adrenergic innervation and they are inactive until puberty

Question 18

What do ceruminous glands and Glands of Moll have in common?

Answer 18

they are both classified as “special apocrine glands”

Question 19

Describe the histological structure of the following hair follicle structures:
hair bulb and both external and internal root sheaths.

Answer 19

Hair bulb: the expanded lower part of the hair follicle that features the Matrix and vascularized dermal papilla

External root sheath: down growth of the epidermis

Internal root sheath: generated by the bulb matrix
Layers:
Henle’s layer (outermost)

Huxley’s layer

Cuticle, which interlocks with the cuticle of the hair shaft

Question 20

name characteristics that all hair follicles have in common

Answer 20

Hair follicles develop from the epidermis as elastic, keratinized threads

Each hair follicle features sebaceous glands and arrector pili muscles