TBL 1 - Embryonic and Fetal Development & Skin

Question 1

During what weeks are embryos highly susceptible to teratogens and what occurs during this time?

Answer 1

Weeks 3-8 and organogenesis

Question 2

Describe the morula and how it splits

Answer 2

16 cell stage. In lumen of uterine, fluid penetrates the walls forming the blastocyst where the inner cell mass (embryoblast, forms embryo) is pluripotent and forms the embryo and the outer cell mass (trophoblast) forms the surrounding structures (i.e. embryonic portion of developing placenta)

Question 3

Which layer implants into the uterine wall and at what week does this occur?

Answer 3

Trophoblast at end of week 1

Question 4

What makes the bilaminar disc and when does this form?

Answer 4

Epiblast - amniotic cavity, cushion
Hypoblast - yolk sac, nutrition prior to formation of umbilical circulation
Week 2

Question 5

When does the bilaminar disc become a trilaminar disc? Describe the process

Answer 5

Week 3. The caudal side of the epiblast forms a depression called the primitive streak. Gastrulation occurs where the epiblast cells by the streak invaginated into the space between the epiblast and hypoblast. This forms the 3 layers, endoderm (where hypoblast was), mesoderm, and ectoderm (where epiblast was)

Question 6

What happens if epiblast cells remain at the primitive streak which disappears at end of week 3

Answer 6

Epiblast cells are pluripotent and can form teratomas which are tumors that contain tissues from all the germ layers

Question 7

From what layer does the notochord form?

Answer 7

Mesoderm

Question 8

Where does the 12-16 cell stage zygote reside

Answer 8

Junction of uterine tube with the uterus

Question 9

Why do inner mass cells have clinical potential?

Answer 9

They are pluripotent and can differentiate into many different cell types.

Question 10

What forms the maternal portion of the placenta?

Answer 10

The uterine epithelium and underlying connective tissue

Question 11

Describe the vitelline artery and vein in the yolk sac wall of a 5 week embryo

Answer 11

Blood from the embryo is taken by the vitelline artery to the capillaries in the yolk sac wall and then the vein brings the blood back to the embryo

Question 12

Describe what happens as the umbilical vessels “replace” the yolk sac.

Answer 12

By week 10, the amniotic cavity becomes larger causing the yolk sac to be compressed against the connecting stalk containing the umbilical vessels. At this point, the yolk sac begins to progressively obliterate.

Question 13

The ectoderm becomes these tissues:

Answer 13

Spinal cord and tissues that contact outside environment like the epidermis of skin

Question 14

The endoderm becomes these tissues:

Answer 14

Forms epithelia lining derivatives of the gut tube

Question 15

Describe the paraxial and intermediate mesoderm

Answer 15

They come from mesenchymal cells that create bilateral longitudinal columns which are these two mesodermic layers

Question 16

The intermediate mesoderm becomes

Answer 16

The urinary system and gonads

Question 17

The paraxial mesoderm forms

Answer 17

They form block-like somites adjacent to the neural tube that form the vertebral column (spine).

Question 18

What does the lateral plate mesoderm (the mesoderm on the sides that is thin)?

Answer 18

Forms the parietal and visceral layers

Question 19

The parietal mesoderm layer forms

Answer 19

dermis of skin, bones, muscles of body wall and extremities

Question 20

The visceral mesoderm layer forms

Answer 20

Connective tissue and smooth muscle of gut tube derivatives

Question 21

Embryonic period is from weeks _ to _ and fetal period is from weeks _ to _

Answer 21

1-8 and 9-birth

Question 22

What is in the superficial fascia?

Answer 22

Fatty tissue and the anchors of hair follicles and sweat glands. The white fat consists of adipocytes with large fat droplets. The dense microcirculation of white fat ensures that fat is fuel along with insulation and padding.

Question 23

Describe the epidermis

Answer 23

Contiguous cells in multiple layers covered in a layer of keratin.

Question 24

Describe the dermis adjacent to the epidermis

Answer 24

Loose connective tissue and a variety of cells dispersed in clear interstitial fluid, collagen fibers, and small blood vessels

Question 25

Describe the derma-epithelial junction on the epidermal side

Answer 25

Single layer of epithelial cells forming the basal layer. Mitosis in this layer generates the stratified keratinized epithelium

Question 26

Describe the cells superficial to the basal layer of the epidermis

Answer 26

There are called keratinocytes and they accumulate keratin as they move towards the surface of the skin. They lose their nucleus as they fill up forming the corneum (keratin layer). The superficial cells are eventually shed

Question 27

How are diseases such as psoriasis related to turnover times of basal cells to keratin-filled cells in the epidermis

Answer 27

Turnover time from basal to keratin filled is usually 20-75 days but is only about 8 days in psoriasis. This leads to the buildup of plaques on the apical surface.

Question 28

Describe desmosomes

Answer 28

Intracellular junctions between keratinocytes and they resist mechanical abrasion of the epidermis

Question 29

Describe the basement membrane and its three functions

Answer 29

Epidermis lies on this like all epithelia do.

• It supports and cushions the epithelia
• Acts as a semipermeable barrier
• Controls epithelial cell differentiation for growth and tissue repair

Question 30

Describe what hemi-desmosomes do at the dermo-epithelial junction

Answer 30

Hemi-desmosomes connect the basal surface of the stratified epithelium to the basement membrane and counteract disruptive forces at the junction.

Question 31

Compare carcinomas and adenocarcinomas.

Answer 31

Carcinomas - cancers of the surface epithelia
Adenocarcinomas - cancers of the glandular epithelium
Tumor cells need to breech the basement membrane in order to become malignant

Question 32

How do desmosomes and hemi-desmosomes counteract mechanical forces that could cause blistering disorders?

Answer 32

Disrupted adhesion of the epidermis is a main cause of blistering disorders

Question 33

Is basal cell carcinoma or squamous cell carcinoma more likely to breech the basement membrane? Which tumor is more prevalent?

Answer 33

Basal cell is more prevalent and grows slower but squamous cell is more likely to breech basement membrane

Question 34

Where are Langerhans cells dispersed and what do they do

Answer 34

Between basal cells and keratinocytes. They engulf pathogens and activate immune responses

Question 35

What produces melanin pigment and describe how it works?

Answer 35

Melanocytes produce melanosomes that produce melanin. The rate of melanosome production determines skin/hair color.

Question 36

How does tanning of the skin occur and why isn’t it a permanent change?

Answer 36

Eumelanin (brown to black) is produced to protect the cell centers from damage from UV radiation. This isn’t permanent because the melanosomes are often packaged in secondary lysosomes in the target cells so they are degraded with time. Also keratinocytes are shed and thus, the increase eumelanin is lost with it

Question 37

Describe how basal cells form the hair papillae.

Answer 37

Proliferating basal cells form hair buds that penetrate into the dermis and the terminal ends invaginate forming the hair papillae

Question 38

What forms the hair shaft?

Answer 38

Basal-cell derived keratinocytes of the papillae. The hair shafts move progressively upward.

Question 39

Describe sebaceous glands and their secretory product, sebum.

Answer 39

The glands arise from the epithelial wall of the follicle. The sebum is lipid-rich decomposed glandular cells

Question 40

Describe what arrestor pili muscles attach to and what they do.

Answer 40

They attach to the follicular wall near the sebaceous glands and involuntary contraction of the smooth muscles compresses the glands and causes sebum excretion

Question 41

How is thick and thin skin differentiated and what the difference is.

Answer 41

The relative thickness of the keratin layer distinguishes thin from thick. Thick skin lacks hair follicles and shafts like on the palms of hand and soles of feet

Question 42

Describe sweat glands in general

Answer 42

Long invaginations into the dermis and superficial fascia. The terminal ends of the invagination form secretory units called acini. The acini are connected to the surface of the skin via tortuous ducts. The ducts often have cuboidal epithelium

Question 43

How do eccrine sweat glands help maintain body temperature?

Answer 43

Evaporative heat loss. Secrete sweat in response to thermal and emotional stimuli

Question 44

Where are odoriferous sweat glands and why do their excretions have a musky odor?

Answer 44

Found in axillae, scrotum, prepuce, labia minora, nipples, and perianal regions. Bacterial decomposition causes the musky odor in their yellow, viscous, oily secretion

Question 45

Describe the function of collagen and elastin in the dermis and what produces it.

Answer 45

Collagen (Type I usually) creates tensile strength and elastin helps skin recoil after stretching or dissension. Collagen and elastin are produced by fibroblasts

Question 46

Describe the difference between the superficial and deep dermis.

Answer 46

Superficial - contains lymphocytes and plasma cells and macrophages, and mast cells for immune response
Deep - Type I collagen more densely packed, fewer cells, less interstitial fluid

Question 47

What type of collagen do basement membranes contain and what function is important?

Answer 47

Type IV collagen in fine, fibrous meshworks for selective filtration

Question 48

Describe brown fat.

Answer 48

Adipocytes with many small lipid droplets with lots of mitochondria. Serves to provide heat. More in newborns (2% weight) than adults.

Question 49

What does the microcirculation consist of in the skin and where is it?

Answer 49

It is the arterioles, capillaries, and venues and resides in the dermis to nourish both the dermis and epidermis.

Question 50

What does the superficial plexus supply and what feeds it?

Answer 50

Superficial dermis and adjacent, avascular epidermis. Subcutaneous arteries feed it.

Question 51

What does the deep plexus supply and what feeds it?

Answer 51

Deep dermis and superficial fascia. Subcutaneous arteries feed it.

Question 52

What are arteriovenous shunts?

Answer 52

They are direct anastomoses between arterioles and venues and are in the deep plexus, notably in the dermis of fingers, toes, and lips

Question 53

Why are dermal arteriovenous shunts open in response to cold ambient temperatures, and closed in response to hot ambient temperatures?

Answer 53

When open, they divert blood from the superficial plexus to the deep plexus to reduce heat loss. When closed, they prevent this.

Question 54

How do bluish, reddish, and yellowish skin colorizations provide clues for diagnosing certain clinical conditions?

Answer 54

Bluish - not enough blood through lungs
Reddish - skin injury, exposure to heat, infection, inflammation, allergic reactions cause capillary beds to engorge and thus, appear red
Yellowish - Too much blurb from liver disorder

Question 55

What do tight junctions that span the intercellular clefts of capillary endothelium do?

Answer 55

Prevent indiscriminate exchange between the blood and interstitial fluid. Important for diffusion of nutrients into the interstitial fluid and diffusion of waste into blood

Question 56

Where are mast cells and what do they do after laceration of skin? What is this process?

Answer 56

They are in the dermis and they release histamine when activated that opens capillary tight junctions allowing plasma proteins and monocytes to leak into the interstitial fluid and surround the site of injury. Inflammation.

Question 57

What causes the edema and what cell differentiation happens in it?

Answer 57

The mast cell activation and leakage causes edema in the dermis. In this fluid, the monocytes become macrophages to engulf the pathogens

Question 58

How does the inflammation/immune response resolve?

Answer 58

histamine is down-regulated after 10-15 min and fibroblasts restore the injured tissue. Angiogenesis restores microcirculation

Question 59

How do basal cells and the basement membrane contribute to remodeling of the epidermis after skin lacerations?

Answer 59

Basal cells replicate, change shape, and migrate to cover the wound. Many growth factors are secreted. The basement membrane is very important for rapid repair

Question 60

What three sensory structures exist in skin and where does each reside? Also, what stimuli activates each type?

Answer 60

Free nerve endings in the epidermis respond to touch
Meissner’s corpuscle in the superficial dermis respond quickly to light touch
Pacinian corpuscle in the superficial fascia, response to deep pressure or vibration
Meissner’s and Pacinian are often in the thick skin