Gastrulation

Question 1

thick layer of glycoproteins surrounding the oocyte that supports the oocyte in development

Answer 1

zona pellucida

Question 2

Describe the different types of granulosa cells (responsible for follicle development):

Answer 2

• cumulus oophorus: anchor oocyte to follicle wall
• mural granulose cells: line the wall of the follicle
• corona radiata: firmly anchored to the zona pellucida

Question 3

Describe the process of fertilization:

Answer 3

(sperm contact the plasma membrane of the oocyte)

1. acrosome reaction: sperm head releases enzymes allowing for its passage through corona radiate and zona pellucide

(a single sperm enters the oocyte)

2. zona reaction: changes in the zona pellucide renders it impermeable to other sperm
3. fusion of egg and sperm cell membranes
4. sperm head and tail enter the secondary oocyte
5. formation of male and female pronuclei: nucleus of the oocyte is now the female pronucleus; sperm head enlarges, forming the male pronucleus while the sperm tail diffuses
6. pronuclei fuse forming the zygote (n=46)
7. metabolic activation/initiation of cleavage, chromosomes of the zygote are arranged on a cleavage spindle

Question 4

Describe the process of cleavage and when it occurs:

Answer 4

• begins ~30 hours after fertilization
• repeated mitotic divisions of the zygote
• cells in this stage are named, blastomeres
• at 9-cell stage, undergo compaction
• at 12-32 cells, the developing human is named morula (means mullberry)

*cell growth is limited because of the zona pellucida, thus the cells start compacting and become smaller in size*

Question 5

Describe blastogenesis and when this occurs:

Answer 5

• morula enters the uterus ~day 4
• blastocystic cavity appears ~day 5 (create from fluid called uterine milk)
• developing human is now termed blastocyst: embryo and its membranes (trophoblast and embryoblast)
• after ~2 days, the zona pellucida degenerates and that blastocyst “hatches”

(zona pellucida degrades from enzymes released by blastocyst, forming the late blastocyst which is ready to implant in the uterine wall)

Question 6

Diagram of fertilization:

(good study tool)

Answer 6

Question 7

• many zygotes, morulae, and blastocysts are lost early on in development, at a rate of ~45%
• causes: inadequate production of progesterone/estrogen from corpus luteum; chromosomal abnormalities, including abnormal segregation, duplication, deletions, dispermy (69 chromosomes), etc.
• may require dilation and curettage (D&C)

Answer 7

spontaneous abortion

Question 8

Describe implantation and trophoblast differentiation, and when they occur:

Answer 8

• late blastocyst attaches to endometrium in the uterus, with the embryoblast (inner cell mass) being adjacent to the uterine wall, occurs ~6-8 days
• trophoblast (inner layer of cells within blastocyst) differentiates into cytotrophoblast and syncytiotrophoblast
• syncytiotrophoblast invades the endometrium via enzymatic digestion
• blastocyst “burrows” into the endometrium and becomes superficially implanted

Question 9

Describe the embryoblast, trophoblast, cytotrophoblast, and syncytiotrophoblast:

Answer 9

• embryoblast: inner mass of cells that gives rise to the human body
• trophoblast: inner lining of cells that plays a role in inplantation and placenta formation; gives rise to cytotrophoblast and syncytiotrophoblast
• cytotrophoblast: remains as boundary of the inner lining of blastocyst
• syncytiotrophoblast: lack cell membranes, produces syncytium which is a single cell or cytoplasmic mass containing several nuclei, plays a role in blastocyst implantation

Question 10

Describe the process of bilaminar embryonic disc formation and when it occurs:

Answer 10

• embryoblast differentiates during implantation ~7 days, into the epiblast and hypoblast
• hypoblast creates the exocoelomic membrane ~9-10 days (these cells are an inner layer to the cytotrophoblast), which eventually gives rise to the chorion
• epiblast remains as a mass of cells; an amniotic cavity forms and cells separate from epiblast, forming the amnion (encloses the embryo and houses amniotic fluid)

Question 11

Describe the process of primary umbilical formation:

Answer 11

• primary umbilical vesicle = hypoblast + lining of the exocoelomic membrane
• gives rise to the extraembryonic mesoderm, a layer of tissue that surrounds amnion and umbilical vesicle, will develop spaces that join and fuse to create the extraembryonic coelom

*primary umbilical vesicle is equivalent to the yolk sac present in other animals*

Question 12

Describe the process of the formation of the secondary umbilical vesicle:

Answer 12

• extraembryonic coelom forces primary umbilical vesicle to decrease in size
• majority of the primary umbilical vesicle pinches off and is eventually lost
• secondary umbilical vesicle forms from hypoblast cells (these cells migrate inside of the primary umbilical vesicle, site of origin of primordial germ cells)

Question 13

At the same time as the formation of secondary umbilical vesicle, the chorionic sac is formed, describe this process:

Answer 13

• extraembryonic coelom separates the extraembryonic mesoderm into: extraembryonic somatic mesoderm (lines trophoblast and amnion) and the extraembryonic splanchnic mesoderm (surrounds umbilical vesicle)
• the chorionic sac is thus formed, which is the extraembryonic somatic mesoderm + trophoblast; the chorion is the fetal component of the placenta

Question 14

• when the implantation of the blastocyst occurs outside of the uterine cavity
• 2% of all pregnancies
• typically occur in the oviduct (95-98%)
• sx: abdominal pain, amenorrhea, vaginal bleeding, profuse bleeding and rupture of the oviduct wall

Answer 14

ectopic pregnancy

Question 15

• process by which cells from the epiblast migrate to form the primary germ layers
• establishes basic body plan: a tube within a tube
• begins during week 3 of development, w/ formation of the primitive streak (thin depression on the surface of the epiblast)
• once all germ layers are present, the trilaminar embryonic disc is established
• defines all body axes: cranial-caudal, dorsal-ventral, medial-lateral, left-right

Answer 15

gastrulation

Question 16

• germ cell tumor (benign or malignant) derived from pluripotent primitive streak cells
• persistent remnants of primitive streak, incidence of ~1:35,00 live births, largely female (80%)
• may be derived from any/all germ layers
• surgically excised

Answer 16

sacrococcygeal teratoma

Question 17

• rod of cells that defines longitudinal axis of the embryo
• cells migrate cranially from the primitive node and pit, forming this structure
• extends to prechordal plate, site of future mouth
• gives rise to the notochord

Answer 17

notochordal process

Question 18

Descibe the process of formation of notochordal process and when this occurs

Answer 18

1. formation begins w/ cranial extension from primitive node
2. forms a hollow tube, the notochordal process
3. grows cranially between ectoderm and endoderm until it reaches the prechordal plate
4. hollows out, forming a canal
5. by day 20, the formation of notochordal process is complete

Question 19

• solid mesodermal rod derived from the primitive node
• extends from the oropharyngeal membrane to the primitive node
• functions as the primary inductor (signaling center) in the early embryo
• induces the formation of the neural plate from the embryonic ectoderm and provides signaling for development of axial musculoskeleton
• will degenerate as the vertebral bodies form and give rise to the nucleus pulposus (intervertebral discs)

Answer 19

notochord

Question 20

Describe the process of notochord formation:

Answer 20

1. floor of the notochordal process fuses w/ the underlying embryonic endoderm
2. fused layers will degenerate, allowing contact between the notochordal canal into the umbilical vesicle
3. floor of the notochordal canal disappears and the notochordal process forms the notochordal plate (flattened, grooved plate of cells in contact laterally w/ the embryonic endoderm)
4. cranially, notochordal plate cells proliferate and undergo infolding, forming the notochord
5. notochord pinches off from the endoderm and the umbilical vesicle
6. separates the germ layers (endoderm and mesoderm)

Question 21

• notochord formation occurs in cranial regions anterior to the primitive streak
• in caudal regions, the primitive streak swells to produce the _____ ________ (or the tail bud) which is a group of median, mesodermal cells
• gives rise to the most caudal structures of the body (cells will extend caudally forming a transient tail)
• tail bud contributes cells to the caudal end of the neural tube and neural crest cells, caudal somites

Answer 21

caudal eminence

Question 22

• primary germ layer
• epidermis of the skin and epidermal derivatives
• central and peripheral nervous systems
• neural crest cells, eyes, and internal ears

Answer 22

ectoderm

*epithelia comes from all germ layers*

Question 23

• primary germ layer
• all skeletal muscle
• visceral smooth muscular coats, serosal linings of all body cavities, urogenital ducts and organs
• most of the cardiovascular system, blood cells, lining of vasculature
• cartilage, bones, tendons, ligaments, dermis, and stroma of internal organs in the trunk

Answer 23

mesoderm

*epithelia comes from all germ layers*

Question 24

• primary germ layer
• epithelial linings of the respiratory and digestive tracts
• glands opening into the GI tract
• glandular cells of accessory GI organs (liver and pancreas)

Answer 24

endoderm

*epithelia comes from all germ layers*

Question 25

What does the pneumonic "you CLEAN the Surface with SOAP" refer to?

Answer 25

(the derivatives of the surface ectoderm from the ectoderm) - Canal (anal) - Lens - Epidermis - Adenohypophysis - Nipple (mammilary gland) - Sweat gland - Olfactory epithelium - Auditory organs - Parotid gland

Question 26

What does the pneumonic "a Tube of NEASPOREN" refer to?

Answer 26

(think of a tube of Neosporin ointment, refers to the neural tube derivatives of the ectoderm) - Neural tube - Astrocytes - Spinal cord - Pineal gland - Oligodendrocytes - Retina - Ependymal cells - Neurohypophysis

Question 27

What does the pneumonic "SPAMS MOTEL with Crest toothpaste" refer to?

Answer 27

(refers to the derivatives of the neural crest from the ectoderm) - Schwann cells - Peripheral nervous system - Adrenal medulla - Myenteric plexus - Spiral membrane - Melanocytes - Odontoblasts - Thyroid C-cells - Endocardial cushion - Laryngeal cartilage

Question 28

What does the pneumonic "a CLEAR TV with Malcolm in the Middle" refer to?

Answer 28

(abnormalities in the mesoderm if it does not form properly) - Cardiac - Limb - Esophageal - Anal - Renal - Tracheal - Vertebral

Question 29

What structures do the following populations of mesodermal masses contribute to? - paraxial mesoderm: - intermediate mesoderm: - axial mesoderm: - somatic layer of lateral plate mesoderm: - splanchnic layer of lateral plate mesoderm:

Answer 29

- paraxial mesoderm: forms somites - intermediate mesoderm: kidneys/gonads - axial mesoderm: musculature - somatic layer of lateral plate mesoderm: contributes to the body wall - splanchnic layer of lateral plate mesoderm: forms the lining of body cavities

Question 30

Caudal dysplasia results from defects in which developmental process?

Answer 30

gastrulation

Question 31

All three primary germ layers develop from the same cellular layer in the bilaminar embryonic disc as which extraembryonic membrane?

Answer 31

amnion (both amnion and primary germ layers are derived from migrating epiblast cells)

Question 32

What are the three extraembryonic membranes?

Answer 32

secondary umbilical vesicle, amnion, chorion