TBL 1

Question 0

Where does the zygote reside after 3 days?

Answer 0

3 days after fertilization, the 12-16 cell zygote resides at the junction of the uterine tube with the uterus.

Question 1

What is unique about embryos up to the eight-cell stage?

Answer 1

The eight embryonic stem cells can differentiate into all cell types in the embryo and placenta i.e., the cells are totipotent.

Question 2

What happens to the zygote once it enters the lumen of the uterus?

Answer 2

Fluid penetrates between cells of the zygote to form the blastocyst with an inner cell mass and an outer cell mass.

Question 3

What is formed from the inner cell mass of the blastocyst?

Answer 3

The inner cell mass becomes the embryoblast with pluripotent cells that can differentiate into all cells of the embryo but not the placenta.

Question 4

Why do cells from the inner cell mass of the blastocyst have clinical potential?

Answer 4

These cells are pluripotent and can form virtually any cell or tissue type, they have the potential for curing diseases.

Question 5

What becomes of the outer cell mass of the blastocyst?

Answer 5

The outer cell mass becomes the trophoblast that penetrates the uterine epithelium to initiate blastocyst implantation by the end of the first week.

Question 6

What forms the embryonic portion of the placenta? The maternal part?

Answer 6

The trophoblast forms the embryonic portion of the placenta. The uterine epithelium and underlying connective tissue form the maternal part of the placenta.

Question 7

What does the embryoblast differentiate into? When does this happen?

Answer 7

Early in the second week, the embryoblast differentiates into the epiblast and hypoblast, which surround the amniotic cavity and line the yolk sac respectively.

Question 8

What is the function of amniotic fluid? What is the function of the yolk sac?

Answer 8

Amniotic fluid progressively fills the amniotic cavity to provide a protective cushion.

The yolk sac contains nutritive substances, which are essential prior to development of the umbilical cord.

Question 9

What are lacunae? Where do they form, and what enters them?

Answer 9

Lucunae are are tiny spaces that develop in the trophoblast. Maternal blood from branches of the uterine artery enters the lacunae during the 2nd week.

Question 10

What is amniotic fluid derived from?

Answer 10

Amniotic fluid is derived from maternal blood.

Question 11

What maintains continuity of the blastocyst with the trophoblast?

Answer 11

The connecting stalk (primitive umbilical cord)

Question 12

What does the epiblast and hypoblast form, and where is the primitive streak located?

Answer 12

At the end of the second week, the epiblast and hypoblast form the bilaminar germ disc.

The primitive streak, a linear groove in the surface of the epiblast facing the amniotic cavity, is located in the caudal region of the developing embryo and the opposite end is the cranial region.

Question 13

What happens during the process of gastrulation?

Answer 13

At the onset of the 3rd week during a process called gastrulation, epiblast cells proliferate and some of the cells pass through the primitive streak form mesodermal cells in between the hypoblast and epiblast.

Question 14

How do the endoderm and ectoderm form?

Answer 14

Some of the migrating epiblast cells form endodermal cells that displace cells of the yolk sac hypoblast.
The remaining epiblast cells form the ectoderm cells.

Question 15

What vessels circulate blood in the 5 week embryo?

Answer 15

Blood from the embryo goes from the vitelline artery to the capillaries in the yolk sac wall, where nutritive substances in the lumen of the sac. The vitelline vein delivers it back to the embryo.

Question 16

What happens to the yolk sac by the 10th week?

Answer 16

Enlargement of the amniotic cavity compresses the yolk sac against the connecting stalk, which contains the umbilical vessels.
The umbilical vessels sustain continued growth of the embryo as progressive obliteration of the yolk sac occurs.

Question 17

What is the trilaminar disc made up of? What does its appearance coincide with?

Answer 17

The epiblast solely generates the ectoderm, mesoderm, and endoderm, which compose the trilaminar disc.

Appearance of the trilaminar disc coincides with disappearance of the primitive streak.

Question 18

How is the primitive streak related to the formation of teratomas and why do the tumors contain a mixture of tissue types?

Answer 18

Sometimes, remnants of the primitive streak persist in the sacrococcygeal region. These clusters of pluripotent cells proliferate and form tumors, known as sacrococcygeal teratomas, which commonly contain tissues derived from all three germ layers.

Question 19

What tissues does the ectoderm form?

Answer 19

The ectoderm from s the spinal cord and tissues that contact the external environment e.g., epidermis of the skin.

Question 20

What tissues does the endoderm initially form?

Answer 20

The endoderm initially forms the lining of the yolk sac and observe endoderm subsequently form epithelia such as those lining the derivatives of the gut tube.

Question 21

What are mesenchymal cells and what layer are they derived from.

Answer 21

Mesenchymal cells are stem cells derived from the mesoderm.

Question 22

What tissues do the intermediate mesoderm form?

Answer 22

The intermediate mesoderm forms the urinary system and gonads.

Question 23

What do the mesenchymal cells create?

Answer 23

The mesenchymal cells create bilateral longitudinal columns composed initially of paraxial mesoderm and intermediate mesoderm.

Question 24

What arises from the paraxial mesoderm? What does this structure form?

Answer 24

The paraxial mesoderm forms block-like somites adjacent to the neural tube. The somites form the vertebral column that encloses the neural tube-derived spinal cord.

Question 25

What is the lateral plate mesoderm? What does it split into?

Answer 25

The lateral plate mesoderm is the mesoderm that is further from the midline and remains thin. The plate splits into parietal and visceral layers.

Question 26

What tissues does the parietal layer form?

Answer 26

The parietal layer forms the dermis of the skin, and the bones and muscles of the body wall and extremities.

Question 27

What tissues does the visceral layer form?

Answer 27

The visceral layer of the lateral plate mesoderm forms connective tissue and smooth muscle of the gut tube derivatives.

Question 28

When is the mebryo most susceptible to teratogens?

Answer 28

The critical embryonic period (weeks 3-8) is when the embryo is most susceptible.

Question 29

When does the fetal period begin and what happens?

Answer 29

Maturation of developing tissues and organs proceeds during the fetal period that begins at the 9th week and ends at birth, which typically occurs 38 weeks after fertilization.

Question 30

What does the superficial fascia consist of?

Answer 30

The subcutaneous superficial fascia consists mainly of fatty tissue and locate hair follicles and sweat glands anchored within it.

Question 31

What is the epidermis composed of?

Answer 31

The epidermis is composed of contiguous cells arranged in multiple layers, which are covered by a layer of keratin.

Question 32

What is the basal layer?

Answer 32

The single layer of epithelial cells at the dermo-epidermal junction forms the basal layer of the epidermis. Mitosis of the basal cells generates the stratified keratinized epithelium.

Question 33

What are keratinocytes and where are they located?

Answer 33

Epithelial cells superficial to the basal layer are called keratinocytes because their cytoplasm accumulates the protein keratin as the cells move progressively toward the apical surface of the skin.

Question 34

What are the functions of the basement membranes?

Answer 34

1. Supports and cushions epithelia 2. Is a semipermeable sieve or selective filtration barrier 3. Controls epithelial cell differentiation in growth and tissue repair

Question 35

Compare locations and functions of melanocytes and Langerhans cells.

Answer 35

In the epidermis, melanocytes and Langerhans cells are dispersed between the basal cells and keratinocytes, respectively. Melanocytes produce melanin pigment in cytoplasmic organelles called melanosomes. Langerhans cells engulf invading pathogens and assist in activating immune responses for selective destruction of the pathogens.

Question 36

What is the keratin layer made up of, and how are these cells shed?

Answer 36

Near the apical surface, keratinocytes are completely filled with keratin and lose their nuclei thereby creating the keratin layer (aka corneum). The most superficial anucleate cells are shed via desquamation i.e., proliferation of the basal cells continuously pushes successive generations of keratinocytes toward the apical surface.

Question 37

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

Answer 37

The normal time for tunrover of keratinocytes from stratum basale to uppermost stratum corneum varies from 20-75 days. Turnover and transit times may be even more rapid in some diseases, such as psoriasis, in which transit time is about 8 days.

Question 38

What are keratinocytes connected by?

Answer 38

Keratinocytes are connected by intercellular junctions called desmosomes.

Question 39

What is the function of desmosomes?

Answer 39

Desmosomes are sites of "spot-weld" intercellular continuity that resist mechanical abrasion of the epidermis.

Question 40

What links the basal surface of the stratified epithelium to the basement membrane?

Answer 40

Hemi-desmosomes counteract disruptive forces at the dermo-epidermal junction.

Question 41

What is the difference between carcinomas and adenocarcinomas?

Answer 41

Malignant neoplasms of surface epithelium are carcinomas. Those originating from glandular epithelium are adenocarcinomas. Tumor cells must breech the basement membrane to become malignant cells.

Question 42

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

Answer 42

Blistering disorders of the skin result from disrupted epidermal adhesion and attachment. Antibodies attack the body's own desmosomes and hemi-desmosomes.

Question 43

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

Answer 43

Basal cell carcinoma accounts for more than 90% of all skin cancers. It grows slowly and seldom spreads to other parts of the body. Squamous cell carcinoma is associated with long-term exposure to sun and has a greater likelihood of metastasis.

Question 44

What determines skin and hair color?

Answer 44

Rate of melanosome production determines skin and hair color. Melanosomes are deposited in the cytoplasm of keratinocytes.

Question 45

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

Answer 45

Melanosomes rearrange themselves within cells in response to external cues such as UV rays. Tanning of the skin caused by UV exposure represents increased eumelanin content of the epidermis.

Question 46

How are hair buds formed?

Answer 46

Proliferating basal cells form hair buds that penetrate into the dermis, where invagination of their terminal ends creates the hair papillae.

Question 47

How are hair shafts formed?

Answer 47

Basal cell-derived keratinocytes of the papillae form hair shafts that move progressively upward in the follicles.

Question 48

What are sebaceous glands formed from, and what do they secrete?

Answer 48

Short glandular buds arise from the epithelial wall of the follicle, and the cells of the buds form sebaceous glands. Sebum, the secretory product of the sebaceous glands, consists of lipid-rich decomposed glandular cells.

Question 49

Where do arrector pili muscles attach, and what is their function?

Answer 49

Arrector pili muscles attach to the follicular wall, near the sebaceous glands. Involuntary contraction of the smooth muscle arrector pili compresses the gland to expedite sebum secretion into the follicle.

Question 50

Where is thick skin present? What does it lack?

Answer 50

Thick skin lacks hair follicles and shafts. | It is present on the soles of the feet and palms of the hand.

Question 51

What are sweat glands formed from?

Answer 51

Long invaginations of the epidermis into the dermis and superficial fascia form sweat glands.

Question 52

What forms at the terminal ends of sweat glands?

Answer 52

In the dermis and superficial fascia, terminal ends of the invaginations form secretory units (acini), which are connected to the apical surface of the skin by tortuous ducts derived from the remaining portions of the invaginations.

Question 53

What is the difference between eccrine and apocrine sweat glands?

Answer 53

Eccrine sweat glands occur throughout the body and maintain body temperature by evaporative heat loss. Apocrine (odoriferous) sweat glands are found in the axillae, scrotum, prepuce, labia minora, nipples and perianal regions. Their yellow, viscous, oily secretion has an acrid or musky odr in response to bacterial decomposition.

Question 54

What does the dermis adjacent to the epidermis consist of?

Answer 54

The superficial dermis consists of loose connective tissue containing many small blood vessels.

Question 55

The connective tissue of the dermis is made up of what? What does this do for the dermis?

Answer 55

Collagen fibers reside in the connective tissue, and their cable-like structure provides tensile strength to the dermis Distensible elastic fibers also reside in the dermis, thus enabling the skin to passively recoil after stretching or distension..

Question 56

How are the constituents of the dermis made?

Answer 56

Fibroblasts produce the collagen and elastic fibers and macromolecules normally present in the dermis. Multiple types of collagen are created by variations in amino acid compositions, and Type I collagen forms the thick fibers of the dermis.

Question 57

What kinds of cells are present in the superficial dermis?

Answer 57

Lymphocytes and plasma cells that contribute to immune reactions are present in the superficial dermis. Also, macrophages and mast cells that are active during acute inflammatory responses.

Question 58

What is the difference between superficial and deep dermis?

Answer 58

Type I collagen fibers are more densely packed in the deep dermis, positioned between the superficial dermis and superficial fascia. The deep dermis is characterized by fewer cells and less interstitial fluid than the loose connective tissue of the superficial dermis.

Question 59

What type of collagen is present in basement membranes and what are they essential for?

Answer 59

Type IV collagen is organized into fine fibrous meshworks that are essential for selective filtration functions of the basement membrane.

Question 60

What does white fat of the superficial fascia consist of? What is it used for?

Answer 60

White fat consists of adipocytes with large fat droplets filling their cytoplasm. White fat is used for 1. Ready source of metabolic fuel 2. Insulation and padding for underlying tissues

Question 61

What does brown fat consist of? What is its function?

Answer 61

Adipocytes of brown fat are filled with many small lipid droplets interspersed by large numbers of mitochondria. Its main function is heat generation, or nonshivering thermogenesis.

Question 62

Where does microcirculation of the skin reside?

Answer 62

In the dermis. It nourishes both the dermis and epidermis.

Question 63

What do the superficial and deep plexuses of microcirculation supply?

Answer 63

The superficial plexus supplies the superficial dermis and adjacent, avascular epidermis. The deep plexus supplies the deep dermis and superficial fascia.

Question 64

What feeds the deep and superficial plexuses?

Answer 64

Subcutaneous arteries.

Question 65

What is unique about the deep plexus, especially in the dermis of fingers, toes, and lips?

Answer 65

Arteriovenous shunts, direct anastamoses between arterioles and venules, are present in the deep plexus.

Question 66

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

Answer 66

The arteriovenous shunts are under autonomic vasomotor control and divert blood from the superficial to the deep plexus to reduce heat loss during cold temperatures.

Question 67

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

Answer 67

Blue skin -- the blood is not carrying enough oxygen from the lungs (cyanotic) Red skin -- Skin injury, exposure to excess heat, infection, inflammation, or allergic reactions may cause superficial capillary beds to become engorged Yellow skin -- bilirubin builds up in the blood in certain liver disorders (jaundice)

Question 68

What are capillaries formed by?

Answer 68

Capillaries are formed by endothelium, a single layer of squamous epithelial cells residing on a basement membrane.

Question 69

How is indiscriminate exchange between blood and interstitial fluid prevented? Why is this exchange important?

Answer 69

Tight junctions span the intercellular clefts of capillary endothelium. This exchange is essential for diffusion of nutrients from the blood into the interstitial fluid and diffusion of metabolic wastes from the interstitial fluid into the blood.

Question 70

What happens after a laceration to the skin?

Answer 70

Activated mast cells release histamine that temporarily opens the capillary tight junctions so that plasma proteins and monocytes can leak into the interstitial fluid surrounding the site of injury.

Question 71

Why is there edema after a skin laceration?

Answer 71

The increase in interstitial fluid volume in the dermis caused by plasma proteins and monocytes leads to localized swelling of the skin.

Question 72

What is the role of monocytes in edematous fluid?

Answer 72

After emigration from circulation across the capillary wall, a monocyte becomes a macrophage, which engulfs invading pathogens.

Question 73

What happens to engulfed pathogens inside of macrophages?

Answer 73

Lysosomal enzymes cleave antigens into small peptide fragments, and some of the fragments are ferried to the macrophage cell membrane for selective recognition by dermal lymphocytes.

Question 74

What happens 10-15 minutes after a skin laceration?

Answer 74

Histamine levels are down-regulated, and fibroblasts restore the injured dermis. Angiogenesis restores the damaged microcirculation.

Question 75

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

Answer 75

Basal cells contribute because the capacity of epithelial cells to undergo mitosis and regenerate is clinically important. The basement membrane is critical for rapid recovery, if it is destroyed, healing is relatively slow.

Question 76

Where are Meissner's corpuscles and Pacinian corpuscles found?

Answer 76

Meissner's corpuscles are in the superficial dermis, while the Pacinian corpuscles are in the superficial fascia. They are typically present in thick skin of fingertips, palms of hands, and soles of feet.

Question 77

What are the respective stimuli that activate the three types of sensory nerve terminals?

Answer 77

Pacinian corpuscles respond to pressure, vibration, and gross tactile stimuli.