Integument I and II

Question 1

Epidermis

Answer 1

composed of the keratinized stratified squamous epithelium that grows continuously and desquamates from the surface. Epidermis is derived from ectoderm

Question 2

Epidermal derivatives

Answer 2

hair follicles and hair, sebaceous glands, eccrine and apocrine sweat glands, and mammary glands.

Question 3

Dermis (or cutis)

Answer 3

composed of connective tissue that provides support for the skin and hosts epidermal appendages, blood vessels, and nerves. Dermis is derived from mesoderm.

Question 4

Hypodermis (or subcutis)

Answer 4

contains a variable amount of adipose tissue. It is equivalent to the subcutaneous fascia described in gross anatomy. Its main function is insulation.

Question 5

Thick skin

Answer 5

found on the palms of hands and soles of feet. The skin here is hairless and has a much thicker epidermis.

very thick stratum corneum of the epidermis and lacks the pilosebaceous apparatus

Question 6

Thin Skin

Answer 6

found elsewhere in the body. It has much thinner epidermis and has hair follicles associated with it.

Question 7

Epidermis

Answer 7

most superficial layer of the skin and is composed of keratinized stratified squamous epithelium.

Question 8

keratinocytes

Answer 8

Principal cells of the epidermis. undergo maturation process as they move up within the epidermis. As the cells reach the apical layers they undergo apoptosis, or programmed cell death and eventually are sloughed off the surface. Within the keratinized stratified squamous epithelium it is possible to identify four distinct layers. Fifth layer can be identified in thick skin

Question 9

Stratum basale

Answer 9

the deepest layer represented by a single layer of cuboidal or columnar cells resting on the basement membrane, which separates epidermis from the dermis. The layer contains mitotically active cells that give rise to new keratinocytes that progress towards the apical layers of the epidermis.

Question 10

Hemidesmosomes

Answer 10

link the keratinocytes of the stratum basale to the basal lamina.

Question 11

Autoimmune reactions to hemidesmosomes or basement membrane components

Answer 11

result in a blistering disease, bullous pemphigoid. These blisters are thick-walled and do not rupture easily

Question 12

stratum spinosum

Answer 12

typically several cells thick. Keratinocytes here are larger than in the stratum basale and connected to each other by numerous desmosomes, which look like “spines” in the fixed tissue in a light microscope (hence the name, “spinosum”). Cells in this layer are more or less spherical in shape.

Question 13

Autoimmune reactions to desmosomes

Answer 13

result in another blistering disease, pemphigus vulgaris. Blisters formed in patients with this condition are painful and rupture easily.

Question 14

Stratum granulosum

Answer 14

contain keratohyalin granules that stain intensely. Cells in this layer are flattened and squamous in appearance.

Question 15

Stratum lucidum

Answer 15

usually visible only in the thick skin. It is a highly refractile layer that contains cells that have gone through apoptosis and their nucleus and organelles became disrupted. This layer stains very lightly with H&E.

Question 16

Stratum corneum

Answer 16

contains most differentiated cells in the epidermis. These cells have lost their nucleus and cytoplasmic organelles and became filled entirely with keratin filaments. The spaces between cells are filled with lipid, which makes this layer impermeable to water (see II.b.i.2.b). This layer stains rather dark with H&E

Question 17

2 Roles of keratinocytes

Answer 17

production of keratin and formation of epidermal water barrier. Keratinocytes are also responsible for the production of vitamin D3

Question 18

Keratinocyte structure

Answer 18

The cytoplasm of keratinocytes contains numerous free ribosomes and intermediate (keratin) filaments. Keratinocytes are bound to each other by desmosomes. Two unique types of structures are found within keratinocytes: keratohyalin granules and lamellar bodies.

Question 19

Keratohyalin granules

Answer 19

start appearing in the upper layers of the epidermis (stratum granulosum). They contain two main proteins associated with intermediate filaments: filaggrin and trichohyalin.

Question 20

2 proteins associated with intermediate filaments

Answer 20

filaggrin and trichohyalin

Question 21

Keratinization

Answer 21

As the granules are released into the cytoplasm of keratinocytes they promote the aggregation of keratin filaments into fibrils

Keratohyalin granules are aggregates of protein and are not surrounded by a membrane, i.e. they are not secretory granules.

Question 22

Lamellar (or Odland) bodies

Answer 22

membrane-bound vesicles that contain a mixture of lipids, which play a key role in making the epidermis a water-impermeable layer. The lamellar bodies are secreted by exocytosis into the intercellular spaces. Lipids from these granules coat the keratinocytes and form an extracellular hydrophobic barrier which extends between the cells. Disruption of the epidermal water barrier (e.g. in severe burns) can lead to life-threatening loss of body fluid.

Question 23

Exposure to sun (ultraviolet light) causes rapid production of _____ by ______ in the stratum ____ and stratum _____ of the epidermis.

Answer 23

Exposure to sun (ultraviolet light) causes rapid production of vitamin D3 (cholecalciferol) by keratinocytes in the stratum basale and stratum spinosum of the epidermis. Vitamin D3 enhances the intestinal absorption of calcium and phosphate, and its deficiency can lead to osteomalacia in adults and rickets in children.

Question 24

Tumors derived from keratinocytes

Answer 24

a. Squamous cell carcinoma is a malignant tumor that is derived from the keratinocytes of the stratum spinosum.
b. Basal cell carcinoma is the most common type of skin cancer and is derived from the keratinocytes within the stratum basale.

Question 25

Melanocytes

Answer 25

derived from the neural crest cells and are mostly found within the stratum basale. They form a unique functional association with keratinocytes.
1. The main function of melanocytes is the production and distribution of melanin, which protects the organism against the damaging effects of the ultraviolet irradiation.

Question 26

Melanocyte Cell Structure

Answer 26

rounded cell body and numerous long processes that extend between the keratinocytes into the stratum spinosum. Melanocytes are not bound to other cells by desmosomes. Because of the processes melanocytes are called dendritic cells (do not confuse with the dendritic antigen-presenting cells of the immune system!). Melanocytes contain melanosomes, which are granules containing melanin. Melanosomes are mostly found near the ends of the cellular processes of melanocytes. The tips of the processes are phagocytized by the neighboring keratinocytes, which incorporate melanin granules into their cytoplasm.

Question 27

Skin color is determined by:

Answer 27

…the rate of degradation of melanin and not by the number of melanocytes.

Question 28

malignant tumor of melanocytes

Answer 28

malignant melanoma. Small melanomas are easily excised, but the larger tumors quickly penetrate into the dermis and metastasize via lymphatic vessels

Question 29

Langerhans’ cells

Answer 29

monocyte-derived dendritic-antigen-presenting cells of the epidermis. They generate the skin immune response when pathogens enter the skin. After accumulating antigens within the epidermis, they migrate (via lymphatic vessels originating in the dermis) to lymph nodes where they present these antigens to lymphocytes. They have an indented nucleus with racquet shaped endosomes called Birbeck granules. NOT BOUND by desmosomes

Question 30

Merkel’s cells

Answer 30

epidermal cells responsible for cutaneous sensation.

1. The main function is mechanoreception. They make synaptic contacts with sensory nerve fibers. most abundant in the areas of acute sensory perception, e.g. fingertips.
2. bound to adjacent keratinocytes by desmosomes. They are located in the stratum basale and form synaptic contacts with afferent nerve fibers. Their cytoplasm contains numerous dense-core granules that are released into the synaptic cleft and act as neurotransmitter to excite the afferent myelinated nerve fibers.

Question 31

Merkel’s cell carcinoma

Answer 31

arises from uncontrolled growth of Merkel cells. It is a rare skin cancer that proves fatal in roughly 1/3 of patients and should receive immediate treatment.

Question 32

Dermis

Answer 32

composed of connective tissue and receives extensive vascular and nerve supply. the same cells that are found in the connective tissue proper.

Question 33

Junction between the epidermis and dermis.

Answer 33

Attachment of the epidermis to the dermis is enhanced by the increased surface between the two tissues. For this purpose the epidermis forms numerous ridges called the rete ridges and the dermis forms numerous projections called the dermal papillae. organized into two layers, the more superficial papillary layer and the deeper reticular layer

Question 34

reticular layer

Answer 34

deep to the papillary layer. It is considerably thicker and less cellular than the papillary layer. It is composed of very dense irregular connective tissue characterized by numerous thick, irregular bundles of collagen type I.

Question 35

Vasculature

Answer 35

Skin receives extensive blood supply as it is extremely important for thermoregulation. The two most important components of the skin blood supply are the vascular plexuses and capillary loops

Question 36

Capillary loops

Answer 36

extend into the dermal papillae and bring blood towards the surface of the skin. The pink skin color results from the blood present in these capillary loops

Question 37

Superficial vascular plexus

Answer 37

blood vessels is found at the junction between papillary and reticular layers of the dermis. Capillary loops are supplied by this plexus.

Question 38

deep vascular plexus

Answer 38

located at the cutaneous/subcutaneous junction.

Question 39

Hypodermis

Answer 39

has variable thickness throughout the body and is composed mostly of adipose tissue, loose connective tissue, smooth muscle, and sometimes striated muscle. This layer serves as a major energy storage site and provides insulation.

Question 40

Epidermal skin appendages

Answer 40

include the pilosebaceous apparatus, eccrine and apocrine sweat glands.

Question 41

Pilosebaceous apparatus

Answer 41

hair follicles and their product, hair and sebaceous glands.
i. Each hair follicle represents an invagination of the epidermis, in which hair is formed. The hair follicle is responsible for production and growth of the hair.

Question 42

Hair

Answer 42

composed of keratinized cells that develop from hair follicles. The part of the hair located within the follicle is called the root; the part that projects above the surface of the epidermis is called the shaft. The hair is composed of several layers:

1. The innermost layer of the hair is the medulla, which contains large vacuolated cells.
2. Surrounding the medulla is the cortex, which contains live cells accumulating keratin.
3. The outermost layer of the hair is formed of dead squamous cells and is called the cuticle.

Question 43

Arrector pili muscle

Answer 43

connects the deeper part of the follicle to the superficial dermis. It is composed of smooth muscle. Contraction of these muscles causes the erection of hairs and produces “goose bumps” on the human skin. In furred mammals, elevation of the hair is important in thermoregulation. Innervation of this smooth muscle is by the sympathetic nervous system.

Question 44

Sebaceous glands

Answer 44

secrete sebum that coats the hair and skin surface. Sebaceous glands develop as outgrowths of the follicular wall. The sebum is produced via holocrine secretion, i.e. as the cell becomes filled with the lipids it produces, it goes through apoptosis and the cell contents are released into the hair follicle. New cells are produced by mitoses of basal cells adjacent to the basal lamina. As the cells mature they move up towards the lumen of the follicle.

1. The proliferating immature cells are located adjacent to the basal lamina. As more cells are produced, some of the cells are “pushed” out of this layer and begin to mature.
2. Maturing cells enlarge, have abundant SER and accumulate lipid droplets.
3. Mature cells are large, terminally differentiated cells, which are filled with large lipid droplets. These cells undergo apoptosis: the nuclei become pyknotic and these cells break apart as they are released into the hair follicle.

Question 45

Eccrine sweat glands

Answer 45

distributed over the entire body except the lips and parts of the genitalia. Their main function is thermoregulation via the production of sweat. Eccrine sweat glands are simple coiled tubular glands that are not associated with the hair follicle. Each gland is a blind-ended tube that consists of a secretory portion and a duct. The duct is lined with stratified cuboidal epithelium. The secretory portion is lined with a stratified epithelium that contains three main cell types: clear cells, dark cells, and myoepithelial cells.

i. Clear cells produce the watery component of the sweat.
ii. Dark cells are characterized by abundant RER and glycoprotein granules. They secrete the proteinaceous component of the sweat via merocrine secretion.
iii. Myoepithelial cells produce contractions that help discharge sweat into the duct

Question 46

Apocrine sweat glands

Answer 46

large-lumen tubular glands associated with hair follicles. Structurally apocrine sweat glands are very similar to eccrine sweat glands in having a coiled tubular secretory portion and duct lined with stratified epithelium. Apocrine glands are different in having more dilated secretory segments, due to the fact that they store the secretion within the lumen. Their ducts open into the hair follicles. The secretory part contains a single type of secretory cell. Apocrine glands secrete a protein-rich secretion containing pheromones via merocrine secretion. The human apocrine glands have more restricted distribution as they are only found near the lips, in the axilla, in the areola of the breast, and in the perineal regions. Apocrine sweat glands are small and inactive until puberty, when they increase in size in response to steroid hormones.

Question 47

Mammary glands are modified ____ glands

Answer 47

apocrine sweat glands

Regulation. Mammary glands develop under the influence of sex hormones. Like apocrine sweat glands, the mammary glands are small and inactive until puberty, when in females they enlarge in response to steroid hormones. The actual secretion is initiated by prolactin, secreted by the adenohypophysis. The ejection of milk from the breast is stimulated by oxytocin, released from neurohypophysis and is due to the action of myoepithelial cells located between secretory cells and the basal lamina

Question 48

Structure of Mammary Gland

Answer 48

composed of 15 to 20 irregular lobules.

i. Each lobule is a branched tubuloalveolar gland embedded into loose connective tissue. Spaces between lobules are filled with dense irregular connective tissue.
ii. Near the nipple the ducts of tubuloalveolar glands dilate to form lactiferous sinuses, lined with stratified cuboidal epithelium.
iii. The terminal parts of the ducts are called lactiferous ducts and open within the mammary papilla, or nipple. The lactiferous ducts are lined with stratified squamous epithelium.

Question 49

Inactive Mammary Gland

Answer 49

The tubuloalveolar glands do not contain secretory end-pieces and contain large amounts of connective tissue.

Question 50

During pregnancy the mammary glands undergo

Answer 50

dramatic proliferation and development as they start actively secreting milk and become active or lactating mammary glands. Under the influence of progesterone the compound tubuloalveolar glands quickly develop secretory end-pieces that proliferate at a significant rate. At the same time the connective tissue regresses to allow for the glandular growth. Both merocrine and apocrine secretion are involved in the production of milk

Question 51

Mammary merocrine secretion

Answer 51

The proteinaceous component of milk is synthesized in the RER, packed within the Golgi apparatus and secreted via merocrine secretion

Question 52

Apocrine mammary secretion

Answer 52

The fatty (lipid) component of milk is formed within the cytoplasm. The larger droplets coalesce and migrate towards the apical portion of the cell, where they project into the lumen of the acinus. The droplets are then invested into the envelope formed by the plasma membrane and released from the cell via apocrine secretion.