Early embryology self study guide week 2

Question 1

During weeks 4 and 5 of development _____ germ cells located in the wall of the yolk sac migrate to the ____ ____.

Answer 1

1. primordial
2. gonadal ridge

Question 2

Gametogenesis is the production of converting _____ germ cells into human gamets (oocytes and spermatozoa) and involves the process of _____ which reduces the number of chromosomes (n=23), resdistributes chromosomal material to ensure genetic variablity, and exchanges a small amount of maternal and paternal DNA through _____ _____.

Answer 2

1. primordial germ cells
2. meiosis
3. homologous recombination (crossover)

Question 3

Male gametes are produced through a process called _____.

Answer 3

spermatogenesis

Question 4

Describe the process of spermatogenesis.

Answer 4

Primordial germ cells (diploid, 46 chromosomes) from the wall of the yolk sac arrive in the primitive testis during week 4 of embryonic development and remain dormant until pubertyl Type A spermatogonia undergo mitosis to make more Type A spermatogonia and also Type B spermatogonia. Type B spermatogonia enter meiosis I to form primary spermatocytes (diploid) which then complete meiosis I to form 2 secondary spermatocytes (haploid) which then go on to complete meiosis II to form 4 spermatids.

Question 5

Through a process called _____ spermatids undergo changes resulting in sperm.

Answer 5

spermiogenesis

Question 6

What is capacitation? (relates to sperm)

Answer 6

a process ejaculated sperm must go through to become capable of fertilization of an oocyte. occurs in the female reproductive tract

Question 7

Female gametes are derived from ____ ____ in the ovaries. All ___ _____ (diploid) are formed by the 5th month of fetal ife and remain dormant in ____ (cell cycle stage) of meiosis I until puberty. During an ovarian cycle, the ____ ___ will complete meiosis I to form a ____ ___ (haploid) and remains arrested in ____ (cell cycle stage) of meisosis II until/if fertilization occurs. At fertilization, the ____ ____ completes meiosis II to form a ____ ____.

Answer 7

1. primary oocytes
2. primary oocytes
3. prophase
4. primary oocyte
5. secondary oocyte
6. metaphase
7. secondary oocyte
8. mature oocyte

Question 8

At ovulation, the oocyte is surrounded by what 2 layers?

Answer 8

1. zona pellucida
2. outer corona radiata

Question 9

What 3 layers must a spermatozoa penetrate to fertilize an oocyte? (list in order)

Answer 9

1. corona radiata
2. zona pellucida
3. plasma membrane of oocyte

Question 10

What 3 processes occur after a spermatocyte has entered an oocyte?

Answer 10

1. oocyte completes meiosis II and forms the female pronucleus
2. zona pellucida becomes impenetrable to other spermatozoa
3. head of the sperm separates for the tail, swells, and forms the male pronucleus

(pronuclei are nuclei of sperm and oocyte fusion of their genetic material-membranes dissolve)

Question 11

What are 3 results of fertilization?

Answer 11

1. restoration of diploid number of chromosomes
2. determination of chromosomal sex
3. initiation of cleavage

Question 12

Fertilization normall occurs in the ____ of the uterine tube.

Answer 12

ampulla

Question 13

True or false: Fertilization is followed by cell divisions occuring in the uterine tube in preparation for implantation in the uterine body.

Answer 13

True.

Question 14

What is the name for the series of mitotic divisions the fertilized ovum must undergo? What are the names of the cells produced as a result?

Answer 14

1. cleavage
2. blastomeres

Question 15

When the dividing mass of cells (blastomeres) reach the 16-cell stage it is called a ____. The ____ enters the uterus on the 3rd of 4th day after fertilizaiton and a cavity within the developing zygote begins to appear. At this point, the morula is referred to as a ____ which has a ____ cavity and inner and outer cell layers. The inner cell mass will develop into the ____ and the outer cell mass will develop into the _____.

Answer 15

1. morula (aka zygote)
2. morula
3. blastocyst
4. blastocyst cavity
5. embryo
6. trophoblast

Question 16

The outer cell layer of the zygote, called the ____, has what functions?

Answer 16

develops into the placenta and membranes that nourish and protect the developing organism

Question 17

If all goes well beforehand, implantation is completed during week ____.

Answer 17

2

Question 18

What 2 layers does the trophoblast develop into during implantation and what are their functions?

Answer 18

cytotrophoblast: has distinct cell boundaries and undergoes mitotic division to form the synctiotorphoblast
synctiotrophoblast: (cell boundaries are blurred so whole thing looks like a blob with nuclei) grows into the endometrium to make a connection with endometrial (maternal) blood vessels and glands producing the hormone human chorionic gonadotropin (hCG)

Question 19

True or false: week 2 is focused on the development of a 2 layered embryo and is called the “Week of 2s”.

Answer 19

True.

Question 20

What occurs during the week of 2s?

Answer 20

• trophoblast differentiates into cytotrophoblast and synctiotrophoblast
• embryoblast forms epiblast and hypoblast
• extraembryonic mesoderm splits into somatpleure and splanchnopleure
• 2 cavities form: amniotic sac and yolk sac

Question 21

What is ectopic pregnancy? Where can the blastocyst potentially implant? H

Answer 21

1. implantation of the blastocyts outside of the uterine cavity
2. sites for ectopic pregnancy include the uterin tube, abdominal cavity, peritoneal covering of intestines

Question 22

gastrulation

Answer 22

development of the 3 basic embyronic layers: ectoderm, endoderm, and mesoderm

Question 23

Gastrulation begins with formation of the ___ ___ on the dorsal surface of the epiblast. It is visible as a narrow groove with slighlty bulging regions on either side.

Answer 23

primitive streak

Question 24

Cells of the epiblast migrate toward the primitive streak and slip beneath it through a process known as _____ to form the inner-placed embryonic ____. Some cells lie btwn the epiblast and the ____ (same as previous blank) to form ____ (middle layer). The remaining cells form the _____ (outer layer).

Answer 24

1. invagination
2. endoderm
3. endoderm
4. mesoderm
5. ectoderm

Question 25

The ____ extends from the primitive node to the oropharyngeal membrane and plays and inductive role in organ formation. Formation of the ____ (same as previous) occurs during ____ (embryonic cell layer) formation.

Answer 25

1. notocord
2. notocord
3. mesoderm

Question 26

In the adult, the notocord perists in the intervertebral discs as ___ ___. What is its fxn?

Answer 26

1. nucleus pulposus
2. gel like substance of intervertebral discs that is composed primarily of water and loose network of collagen. allows vertebral discs to withstand compression and torsion

Question 27

True or false: Gastrulation results in defining 3 important orientations: cranial-sacral axis, right-left orientation, dorsal-ventral orientation.

Answer 27

True.

Question 28

True or false: The embryonic disc begins as a flat rounded structure. It will continue to grow and elongate in a cephalocaudal direction. This results in a folding of the cranial and caudal ends creating head and tail folds. The heart which originates in the most cranial position will swing down to the position of the future thorax. Thus gastrulation, or formation of the germ layers, continues in caudal segments while cranial structures are differentiating, causing the embryo to develop cephalocaudally.

Answer 28

True.

Question 29

True or false: Lateral folding of the embryo completes the formation of the adult form by extending laterally first and then ventrally closing off body cavities.

Answer 29

True.

Question 30

During lateral folding, the yolk sac persists for a while and is later pinched off. A body cavity is formed around the tube of endoderm which forms the ____. The cavity is lined with cells from the ____ mesoderm and persists as the parietal layer of serous membranes. Cells from the ___ mesoderm develop into smooth and cardiac muscle cells.

Answer 30

1. gut
2. somatic
3. splanchic

Question 31

True or false: during lateral folding, two important precursor structures are formed: the neural plate (from ectoderm) and somites (from mesoderm).

Answer 31

True.

Question 32

Neuralation: The notocord induces the overlying ectoderm around the center of the embryo to thicken and form the ___ ____. The central ends (of previous blank) make up the _____. The (previous blank) forms a groove which deepens. The lateral edges of the group migrate toward each other to form the primitive spinal cord. During this time, ___ ____ __ form at the edges of the neuroectoderm. These cells migrate through the embryo to form adult structures.

Answer 32

1. neural plate
2. neuroectoderm
3. neural crest cells

Question 33

True or false: An important concept in nervous system development is the mitosis of cells and migration to their adult location. Any interruption in this 2 step process can produce a developmental effect.

Answer 33

True.

Question 34

Where are neural crest cells originally located? What do they go on to form in the body?

Answer 34

1. neural tube. undero mitosis and exit neuroepithelium to migrate to their adult locations in the body
2. In the nervous system neural crest cells make important contributions to:
   * Schwann cells, PNS myelinated cells, dorsal root ganglia, some cranial nerve ganglia and numerous autonomic ganglia, gut intrinsic innervation-myenteric plexus and submucosal plexus, the adrenal medulla, part of the meninges surrounding CNS.
3. In the head and neck neural crest cells contribute to:
   * part of head mesenchyme, forming parts of facial bones, muscles, and ligaments, odontoblasts and the dentin producing cells of teeth.
4. In skin neural crest cells contribute to making the pigment-producing cells, melanocytes.

Question 35

What is DiGeorge syndrome? What are sx? What is it caused by?

Answer 35

1. deletion in chromosome 22
2. subtle craniofacial anomalies, cardiovascular anomalies, sometimes thymic and parathyroid aplasia
3. results from abnormal migration and differentiation of head and neck neural crest cells

Question 36

What are neural tube defects? Etiologies of neural tube defects? Severity?

Answer 36

1. congenital birth defects typically caused by failure of neural tube closure and/or induction of bony neural arches of spinal cord
2. mutlifactorial etiology: some genetic and some environmental
3. range in severity from spina bifida occulta (mildest form of spina bifida) to fatal anencephaly (missing large part of brain and spinal cord)

Question 37

What are the 3 layers of mesoderm?

Answer 37

1. paraxial mesoderm
2. intermediate mesoderm
3. lateral plate mesoderm

Question 38

What is the paraxial mesoderm composed of and what do its components develop into?

Answer 38

paraxial mesoderm cells are close to the midline and are organized into segments called somites. there are occipital, cervical, thoracic, lumbar, sacral, and coccygeal pairs of somites.

sclerotome somites surround the spinal cord to form the vertebral column and form tendons/cartilage/bone

dermomytome is composed of mytome and dermatome. mytome provides the segmental muscle component and the dermatome forms the dermis of the back.

Question 39

What does the intermediate mesoderm differentiate into?

Answer 39

urogenital structures

Question 40

What does the lateral plate mesoderm differentiate into?

Answer 40

parietal and visceral laters line the intraembryonic cavity and surround organs

Question 41

List examples of adult structures formed from the 3 primary germ layers.

Answer 41

• Ectoderm (outer layer)- organs and structures that maintain contact with the outside world: nervous system, sensory epithelium of ear, nose, and eye, skin, hair, nails, pituitary, mammary, sweat glands and enamel of the teeth.
• Mesoderm (middle layer) - connective tissues, tendons, cartilage, bone, muscle, some urogenital structures, blood cells, adrenal cortex
• Endoderm Layer (inner layer) - gastrointestinal tract; epithelial lining of the respiratory tract; parenchyma of the thyroid, parathyroids, liver, and pancreas, stroma of the tonsils and thymus, the epithelial lining of the urinary bladder, urethra and lining of the tympanic cavity and auditory tube

see image on pg 20 of notes