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Histology > Embryology 2 > Flashcards

Embryology 2 Flashcards

1
Q

What process occurs after implantation and placentation?

A
  • bilaminar and trilaminar disphormation
  • gastrulation
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2
Q

What are the three primary germ layers?

A
  • ectoderm
  • mesoderm
  • endoderm
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3
Q

Why are the ectoderm, mesoderm, and endoderm called the “primary cell layers”?

A

all origins of all organs can be tracked back to these layers

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4
Q

What is the function of the ectoderm/mesoderm/endoderm?

A

form specific parts or the organism

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5
Q

What does the ectoderm form?

A
  • epidermis of the skin,
  • epithelium of the oral cavity,
  • epithelium of the nasal cavities,
  • nervous system
  • sense organs.
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6
Q

What does the mesoderm form?

A
  • muscle,
  • connective tissue,
  • notochord
  • bone,
  • circulatory system components (eg. RBC),
  • urinary system components (eg. kidney tubule),
  • genital system components,
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7
Q

What does the endoderm form?

A
  • mucosal epithelium
  • glands of the respiratory system (eg. lung cell)
  • glands of the digestive system (eg. stomach cell)
  • pharynx (eg. thyroid cell)
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8
Q

What is gastrulation?

A

the morphogenic process that gives rise to three germ
layers: ectoderm, mesoderm, and endoderm.

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9
Q

What process gives rise to the three primary germ cell layers?

A

gastrulation

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10
Q

What are germ cells?

A

male: sperm
female: egg

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11
Q

What are the names of the three cells in order (from fertilization to tissue)?

A

zygote –> blastula –> gastrula

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12
Q

State the order of cell differentiation.

A

stem cell –> committed cells –> specialized cells

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13
Q

What is cell differentiation? When does it occur?

A
  • result of cells expressing some genes and supressing others within a common genome
  • cells differ because they produce different proteins/peptides
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14
Q

Why do cells differ?

A

because they produce different proteins/peptides

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15
Q

State examples of proteins/peptides involved in cell differentiation.

A
  • structural components (cytoskeleton/extracellular components)
  • enzymes (controlling cell metabolism)
  • secretory products (hormones/digestive enzymes/etc.)
  • channels & pumps (passage of mollecules across membranes)
  • receptors (communication, etc)
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16
Q

What does gastrulation begin with? What cell?

A

blastocyst

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17
Q

Explain the process of gastrulation. How does it occur?

A
  • proliferation of inner cell mass cells –> thickened embryonic disc (blastocyst surface)
  • degeneration of trophoblast layer (overlaying the inner cell mass)
  • formation of the hypoblast: inner cell mass cells migrate forming a new cell layer
    inside the trophoblast layer
    (hypoblast will form a yolk sac)
    (remaining inner cell mass=epiblast)
  • primitive streak formation (epiblast surface) (differential cell growth
    generates a pair of ridges separated by a depression)
  • coelom forms (deep to the primitive streak, b/w the hypoblast and epiblast)
  • mesoderm filling of coelom
  • mesoderm undergoes cavitation (gives rise to body cavities)
  • proliferation of epiblast cells (along primitive streak margins)
  • migration of epiblast cells (streak –> coelom) forming endoderm & mesoderm layers.
    (embryonic endoderm= cells joining the hypoblast layer)
    (mesoderm=majority of migrating cells that enter the primary mesenchyme)
  • migartion of the primary mesenchyme
    (laterally and cranially)
    (not along the midline region
    directly cranial to the primitive
    streak where notochord will form).
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18
Q

What does the primitive streak define? What does it indicate?

A
  • defines the embryo’s longitudinal axis
  • indicates the start of germ layer formation
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19
Q

What 2 new layers are formed as the trophoblast degenerates?

A

epiblast:
- on top,
- takes most of the remaining inner cell mass cells.

hypoblast:
- inner cell mass layer
- cells detatch

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20
Q

What is the name of the structure after the formation of the two layers? What are the two layers?

A

bilaminar disk:
- epiblast
- hypoblast

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21
Q

What is the location called which used to be the “embryoblast”/”inner cell mass”?

A

epiblast

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22
Q

What is the process of gastrulation initiated by?

A

the formation of the primitive streak

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23
Q

What happens as more cells are produced?

A

cells are pushed towards the primitive streak (center), then they must migrate due to the ‘push effect’ of the epiblastic cell division.

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24
Q

State the location of the ectoderm, mesoderm, prospective endoderm, and endoblast layers.

A
  • ectoderm: on top
  • mesoderm: in the center of the disk, and in the middle
  • prospecive endoderm: center, going towards the bottom layer
  • endoblast: bottom layer
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25
Q

What does the formation of the primitive streak allow us to do?

A

determine the location:
- where the head and tail will go,
- which is the right and left side,
- which is the top and ventral surface

26
Q

How can we determine where the head will develop?

A

the frontal part doesn’t have the primitve streak!
(no line in the center)

27
Q

What does most of the mesoderm volume transform into?

A

mesenchyme!!
(embryonic connective tissue giving rise to adult connective tissue)

28
Q

What is the function of the ectoderm? Where is it located?

A

ectoderm:
- forms outermost layer of the embryo
- forms the outermost layer of the adult organism/fetus (epidermis), nervous system,

29
Q

What is the function of the mesoderm? Where is it located?

A

mesoderm:
- major embryo contributor
- cells used to build bones, cartilage, c.t. components, skeletal system, lymphatic system, circulatory system, reproductive system, urinary system, epidermis

mesenchyme (–> adult connective tissue) is a product of mesoderm

30
Q

What does the fact that the ectoderm develops into the nervous system reflect?

A

reflects the evolutionary process:
- external sensory apparatus sensing chemicals, nutrition, light

31
Q

What is the function of the endoderm?

A
  • epithelia of the respiratory system, gastrointestinal tract
  • glands (eg. pancreas, liver)
32
Q

What is the notochord? Where is it located? What does it occupy?

A

What?
- rod-shaped aggregate of cells

Location:
- between ectoderm
and endoderm
- anterior to the primitive streak

Occupation?
- midline coelomic space (not invaded by migrating primary
mesenchyme)

33
Q

What are the principal functions of the notochord?

A
  • formation of the head process,
  • development of the nervous system,
  • formation of somites
34
Q

What is associated with the caudal and cranial part of the embryo? (oversimplified)

A

caudal: primitive streak
cranial: notochord

35
Q

What does the notochord mark?

A

the future location of:
- the vertebral column
- cranium base

36
Q

What is the ultimate fate of the notochord? Become which part of the intervertebral disks?

A

become nucleus pulposus of
intervertebral discs

37
Q

What does the notochord develop from? Where does this happen?

A
  • develops from the primitive node,
  • located at the cranial end of the primitive streak
38
Q

What are somites?

A

blocks of the mesoderm, adjacent to the notochord.

39
Q

What is neurulation?

A
  • notochord-induced transformation of ectoderm into
    nervous tissue
40
Q

When does neurulation begin?

A

third week

41
Q

What is the location of neurulation?

A

begins: region of the future brain
progresses: caudally into the region of the future spinal chord

42
Q

State what happens to cells during neurulation.

A
  • ectodermal cells surrounding the notochord become tall columnar (neuroectoderm);
  • form a thickened area designated the neural plate.
  • other ectodermal epithelium is flattened.
43
Q

What is formed during neurulation? How is it formed?

A
  • neural groove
  • edges of the neural plate
    become raised on each side of a midline depression.
44
Q

What is formed from the neural groove? How is it formed? What does it seperate?

A
  • formed as the neural groove undergoes midline
    merger     of its dorsal edges.
  • the tube separates from non-neural ectoderm
45
Q

How does non-neural ectoderm unite to the tube?

A

dorsally

46
Q

Where does tube formation begin? Where does it continue?

A

begins: central nervous
system (cranial cervical region)
continues: cranially and caudally

47
Q

What does the neural tube become?

A

the central nervous system!
- brain
- spinal cord

48
Q

How is the neural crest formed?

A
  • cells detach bilaterally as the neural groove closes;
    (where the neural groove is joined to non-neural ectoderm)
  • cells proliferate
  • cells assume a position dorsolateral to the neural tube
49
Q

Why are neural cells special?

A

form a remarkable range of structures:
- pigment cells of the skin (dorsal migration)
- neurons and glial cells of the PNS (peripheral nervous system)
- adrenal medulla cells

50
Q

What does the neural crest form in the head? What does this become?

A
  • neural crest forms the mesenchyme (ectomesenchyme)
  • becomes meninges, bones, fascia, and teeth.
51
Q

What do mesoderm blocks induce? Where are they located?

A

mesoderm blocks:
- located lateral to the notochord,
- induced somite development.

52
Q

How many somites does an individual have?

A
  • pair of somites for every vertebra,
  • half dozen somite pairs in
    the head.
  • somites # in an embryo is indicative of age,
  • individual somites develop chronologically, in craniocaudal order.
53
Q

How do individual somites develop?

A
  • chronologically,
  • craniocaudal order.
54
Q

How many regions does each somite differentiate into? What are they?

A

3:
- sclerotome (ventromedial)
- dermatome (lateral)
- myotome (intermediate)

55
Q

What does the sclerotome region of the somite give rise to? Where is this region located?

A
  • ventromedial region

gives rise to:
- vertebrae,
- ribs,
- endochondral bones (base of skull)

56
Q

What does the dermatome region of the somite give rise to? Where is this region located?

A
  • lateral region

gives rise to:
- skin dermis

57
Q

What does the myotome region of the somite give rise to? Where is this region located?

A
  • intermediate region

gives rise to:
- skeletal muscles

58
Q

What is the structure of the early embryo? What must it develop into?

A

early embryo = flat,

vertebrate body
plan = cylindrical

59
Q

What does the trasition from a flat to cylindrical embyo involve?

A

1) lateral body folds
2) head process formation
3) tail fold formation

60
Q

Explain the formation of lateral body folds.

A
  • embryo grows (dorsal elevation),
  • lateral body folds adduct and join together ventrally,
    —> tubular embryo separated from extra-embryonic tissue (fetal membranes).
61
Q

Explain the formation of the head process. Which end of the embryo?

A
  • dorsal and forward growth of embryo (cranial end)
  • projects above the region originally in front of the embryo.
  • cylindrical head process elongates by additional growth from its base
62
Q

Explain the formation fo the tail fold. Which end of the embryo?

A
  • embryo (caudal end)
  • cylindrical tail fold is formed
  • similar to head process formation
  • dorsal and backward growth of embryo
  • cylindrical tail process elongates by additional growth from its base

Histology (20 decks)

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