Embryology

Question 1

Gametogenesis

Spermatogenesis

Type A vs Type B spermatogonia

Spermiogenesis

Capacitation

Answer 1

• Production of converting primordial cells into human gametes (oocytes and spermatonoa) through meiosis (redistribute chorosome material and exchange DNA for maternal/paternal homologous recombination)
• Primordial germ cells arrive in primitive testis from yolk sac in week 4 and are dormant until puberty
• Type A do mitosis to make Type A and Type B
• Type B enter mitosis to form primary spermtocytes (46 c), then complete Meiosis I to form 2 secondary spermatocytes (23 c) and complete Meiosis II to form 4 spermatids (23 c).
• Spermatids undergo changes resulting in sperm
• Ejaculated sperm can’t fertilize until they undergo capacitation in female reproductive tract

Question 2

Oogenesis

Oocytes come from what?

Ovarian cycle

Which membranes must be penetrated by sperm?

What happens once spermatocyte enters oocyte?

Answer 2

• Oocytes comes from primary oocytes in ovaries, remain dormant in Meiosis I (46 c) until puberty
• Primary oocyte completes meiosis I to become secondary oocyte (23 c), enters meiosis II and remains arrested in metaphase until fertiliation occurs
• Sperm first penetrate corona radiata, then zona pellucida, then oocyte cell membrane
• Oocyte finishes 2nd meiotic division forming female pronucleus, zona pellucida becomes impenetrable to other sperm, head of sperm separates from tail, swells, and forms male pronucleus

Question 3

What are the results of fertilization? (3)

Where does fertilization occur normally?

Steps post-fertilization

What is morula called when enters the uterus?

What do inner and outer layers become?

Answer 3

1. Restoration of diploid # of chromosomes (46)
2. determination of chromosomal sex
3. Initiation of cleavage
   - Ampulla of the uterine tube
   - Cleavage increases cells (blastomeres) into a 16-cell ball shape called morula
   - blastocyst (blastocyst cavity w/ inner and outer layers)
   - Inner becomes embryo, outer becomes trophoblast (placenta)

Question 4

Implantation

Trophoblast develops into 2 layers…

Preganncy testing works by…

What happens in week 2?

Answer 4

• tropohoblast implants in uterine cavity on superior wall in anterior or posterior position
  1. Cytotrophoblast has distinct cell boundaries and undergoes mitotic division to form syncytiotrophoblast
  2. Syncytiotrophoblast (blurred cell boundaries) connect with endometrial blood vessels and glands producing hCG
• Detecting hCG in maternal blood (day 8) or urine (day 10)
• Week of 2’s: 2 layer trophoblast, 2 layers embryo (epiblast [becomes all 3 tissue layers] vs hypoblast [yolk sac]), extraembryonic mesoderm splits in 2 (somatopleure [ectoderm] vs splanchnopleure [endoderm]), 2 cavities form (Amniotic and yolk sac)

Question 5

Ectopic pregnancy

Sites for ectopic pregnancy

When does embryo usually die

Answer 5

• Implantation of blastocyst outside the uterine cavity
• Uterine tube, abdominal cavity, peritoneal covering intestinal tract
• 2nd month of gestation

Question 6

Gastrulation

What is formed first?

What contains each germ layer?

When does notochord form?

What are the 3 orientations that result from gastrulation?

Explain head and tail folding

Lateral folding

Splanchic mesoderm cells develop into…

Answer 6

Development of 3 basic embryonic layers (Ectoderm/mesoderm/endoderm)

• primitive streak on dorsal serface of epiblast
• Trilaminar disc
• During mesoderm formation
• Cranial/sacral axis, right/left, dorsal/ventral
• Embryonic disc is flat and rounded, grows and elongates in cephalocaudal direction, resulting in folding of cranial and caudal ends (i.e. heart starts cranial and swings down to future position)
• Extends laterally then ventrally to close off body cavities, eventually yolk sac will pinch off a swell.
• Smooth and cardiac muscle cells

Question 7

Below is the process of neurulation:

Which germ layer does the neural plate and somites form from?

How does neural plate thicken and form?

What are the central cells of the neural plate?

How does primitive spinal cord form?

What forms at edges of neuroectoderm? Where are they located?

How could developmental defects occur?

What do neural crest cells form in NS/Head&neck/skin?

Answer 7

• Ectoderm, mesoderm
• Notochord induces overlying ectoderm
• neuroectoderm
• lateral edges of neuroectoderm migrate toward each other
• neural crest cells, located on dorsal midline of neural tube
• Anything that interrupts the 2-step process of cell mitosis and migration during nervous system development
• NS: Schwann cells, PNS myelinated cells, many ganglia, gut intrinsic innervation-myenteric plexus & submucosal plexus, adrenal medulla, meninges
• Head/Neck: Head mesenchyme forming facial bones/muscles/ligaments, odontoblasts, dentin producing cells in teeth
• Skin: Melanocytes (pigment producing cells)

Question 8

Neural Crest Cell Defects

What is DiGeorge Syndrome (mutation, symtpoms, reason)?

Neural Tube defects (etiology)

Answer 8

• Deletion in C22, subtle craniofacial abnormalities, cardiovascular anomalies, thymic/parathyroid aplasia. Results from abnormal migration & differentiation of head/neck neural crest cells
• Genetic and environmental basis, caused by failure of neural tube closure and/or induction of bony neural arches of spinal cord. Range in severity from asymptomatic spina bidifa to fatal anencephaly

Question 9

Somites (from mesoderm)

Mesoderm is divided into 3 layers… Explain each

Define somites

Sclerotome

Dermomyotome (Myotome & dermatome)

Answer 9

1. Paraxial mesoderm: cells are close to midline, organized into segments

Somites are the segments, develop cephalocaudal

Sclerotome- surround spinal cord to form vertebral column and also tendons/cartilage/bone

Dermyotome made of myotome (segmental muscle component) and dermatome (dermis of back)

2. Intermediate mesoderm- differentiate into urogenital structures
3. Lateral plate mesoderm- parietal and visceral layers line intraembryonic cavity & surround organs

Question 10

What structures are derived from…

ectoderm

mesoderm

endoderm?

Answer 10

Ecto- anything that contacts outside world: NS, sensory epithelium of ear/nose/eye, skin, hair, nails, pituitary/mammary/sweat glands, teeth enamel

Meso- connective tissues, tendons, cartilage, bone, some urogenital, blood cells, adrenal cortex

Endo- GI track, epithelial of respiratory tract; parenchyma of thyroid, parathyroids/liver/pancreas, stroma of tonsils/thymus, epithelial of urinary bladder, urethra, lining of tympanic cavity/auditory tube