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ACE (M) > TBL 1 > Flashcards

TBL 1 Flashcards

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0
Q

Where does the zygote reside after 3 days?

A

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

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1
Q

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

A

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

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

What becomes of the outer cell mass of the blastocyst?

A

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

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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

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

A

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.

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9
Q

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

A

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.

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10
Q

What is amniotic fluid derived from?

A

Amniotic fluid is derived from maternal blood.

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11
Q

What maintains continuity of the blastocyst with the trophoblast?

A

The connecting stalk (primitive umbilical cord)

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12
Q

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

A

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.

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13
Q

What happens during the process of gastrulation?

A

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.

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14
Q

How do the endoderm and ectoderm form?

A

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.

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15
Q

What vessels circulate blood in the 5 week embryo?

A

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.

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16
Q

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

A

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.

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17
Q

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

A

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.

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18
Q

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

A

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.

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19
Q

What tissues does the ectoderm form?

A

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

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20
Q

What tissues does the endoderm initially form?

A

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.

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21
Q

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

A

Mesenchymal cells are stem cells derived from the mesoderm.

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22
Q

What tissues do the intermediate mesoderm form?

A

The intermediate mesoderm forms the urinary system and gonads.

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23
Q

What do the mesenchymal cells create?

A

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

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24
Q

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

A

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.

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25
Q

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

A

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

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26
Q

What tissues does the parietal layer form?

A

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

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27
Q

What tissues does the visceral layer form?

A

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

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28
Q

When is the mebryo most susceptible to teratogens?

A

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

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29
Q

When does the fetal period begin and what happens?

A

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.

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30
Q

What does the superficial fascia consist of?

A

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

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31
Q

What is the epidermis composed of?

A

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

32
Q

What is the basal layer?

A

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.

33
Q

What are keratinocytes and where are they located?

A

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.

34
Q

What are the functions of the basement membranes?

A
  1. Supports and cushions epithelia
  2. Is a semipermeable sieve or selective filtration barrier
  3. Controls epithelial cell differentiation in growth and tissue repair
35
Q

Compare locations and functions of melanocytes and Langerhans cells.

A

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.

36
Q

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

A

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.

37
Q

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

A

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.

38
Q

What are keratinocytes connected by?

A

Keratinocytes are connected by intercellular junctions called desmosomes.

39
Q

What is the function of desmosomes?

A

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

40
Q

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

A

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

41
Q

What is the difference between carcinomas and adenocarcinomas?

A

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.

42
Q

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

A

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

43
Q

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

A

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.

44
Q

What determines skin and hair color?

A

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

45
Q

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

A

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.

46
Q

How are hair buds formed?

A

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

47
Q

How are hair shafts formed?

A

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

48
Q

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

A

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.

49
Q

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

A

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.

50
Q

Where is thick skin present? What does it lack?

A

Thick skin lacks hair follicles and shafts.

It is present on the soles of the feet and palms of the hand.

51
Q

What are sweat glands formed from?

A

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

52
Q

What forms at the terminal ends of sweat glands?

A

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.

53
Q

What is the difference between eccrine and apocrine sweat glands?

A

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.

54
Q

What does the dermis adjacent to the epidermis consist of?

A

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

55
Q

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

A

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..

56
Q

How are the constituents of the dermis made?

A

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.

57
Q

What kinds of cells are present in the superficial dermis?

A

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.

58
Q

What is the difference between superficial and deep dermis?

A

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.

59
Q

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

A

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

60
Q

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

A

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
61
Q

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

A

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.

62
Q

Where does microcirculation of the skin reside?

A

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

63
Q

What do the superficial and deep plexuses of microcirculation supply?

A

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

The deep plexus supplies the deep dermis and superficial fascia.

64
Q

What feeds the deep and superficial plexuses?

A

Subcutaneous arteries.

65
Q

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

A

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

66
Q

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

A

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.

67
Q

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

A

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)

68
Q

What are capillaries formed by?

A

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

69
Q

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

A

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.

70
Q

What happens after a laceration to the skin?

A

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.

71
Q

Why is there edema after a skin laceration?

A

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

72
Q

What is the role of monocytes in edematous fluid?

A

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

73
Q

What happens to engulfed pathogens inside of macrophages?

A

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.

74
Q

What happens 10-15 minutes after a skin laceration?

A

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

75
Q

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

A

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.

76
Q

Where are Meissner’s corpuscles and Pacinian corpuscles found?

A

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.

77
Q

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

A

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

ACE (M) (2 decks)

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