Exam #1 Flashcards
When do primordial sperm cells (spermatogonia) become 1˚ spermatocytes, i.e. when does spermatogenesis begin? Were are they located?
At puberty; seminiferous tubules of the testes.
When do oogonia proliferate and transform into 1˚ oocytes, i.e when does oogenesis begin?
Early in fetal life (in contrast to spermatogenesis in males, which begins at puberty).
Describe the state of oogonia in females up to the point of puberty.
Oogenesis BEGINS during the fetal period, but is not completed until after puberty. All primary oocytes have completed PROPHASE I (of meiosis), but are arrested in this phase (prophase I) UNTIL PUBERTY.
p.16
What will be the karyotype of affected spermatids if abnormal gametogenesis occurs during Meiosis I (2)?
- ) Two spermatids with 24, XY.
2. ) And TWO spermatids with 22, 0.
Oogenesis is not complete until when?
FERTILIZATION
Gametogenesis results in ______(#) of (haploid or diploid) cell.
Results in FOUR HAPLOID cells.
At ______, spermatogonia are signaled to begin maturation. What is this process called?
At puberty, spermatogonia begin SPERMATOGENESIS.
Monosomic nondisjunction often results in _______.
Termination of the embryo.
What must be shed from the blastocyst before implantation can occur?
Zona Pellucida
What metamorphosis do the spermatids undergo during spermiogenesis? (3)
- ) Nucleus condenses
- ) Acrosome forms
- ) Most of cytoplasm is shed
How long does spermiogenesis require, and how long does it persists in males?
Requires ≈ 2 months; normally continues throughout the reproductive life of a male. p.15
Where are the new sperm stored?
The epididymis.
When and how do oogonia become primary oocytes?
During early fetal life, oogonia proliferate by MITOSIS and enlarge to form primary oocytes.
Oocytes remain in _____ until puberty.
Prophase
By birth, all 1˚ oocytes have completed the ______ of ______.
prophase of the first meiotic division.
Shortly before ovulation, a 1˚ oocyte ______. How does this stage differ from the corresponding stage in spermatogenesis?
Completes the first meiotic division.
The division of cytoplasm is unequal, and the 2˚ oocyte receives almost all of the cytoplasm, whereas the FIRST POLAR BODY RECEIVES VERY LITTLE, causing it to degenerate after a short time.
At ovulation, the nucleus of the 2˚ oocyte _______, but only progresses to _______.
the 2nd meiotic division, but only progresses to METAPHASE.
What completes the second meiotic division of the 2˚ oocyte?
Fertilization.
Nondisjunction occurs during _____ when _______.
At what time is it likely that the cause of this chromosomal event occurred?
- Gametogenesis when homologous chromosomes fail to separate.
- Meiosis I of oogenesis.
Development of an ovarian follicle is characterized by (4 things):
Growth and differentiation of a primary oocyte.
• Proliferation of follicular cells.
• Formation of the zona pellucida.
• Development of a connective tissue capsule
surrounding the follicle – the theca folliculi.
What triggers ovulation?
LH surge in maternal circulation; ovulation follows within 24 hours of this surge.
Before fertilization, the secondary oocyte is where?
The uterine tube.
Each chromosome in male and female pronuclei is made up of only _______.
One chromatid.
What pre-embryonic group of cells are destined to become the placenta?
Trophoblast
What pre-embryonic group of cells form the primordium of the embryo?
Embryoblast
How many days post-fertilization does a blastocyst form?
Where is it located?
≈ 4 days
In the uterine cavity
What lets the blastocyst rapidly grow in size?
Degeneration of the zona pellucida
What prevents the blastocyst from sticking to the walls of the uterus prior to implantation?
The zona pellucida
During implantation, which layer of cells begins to invade the endometrium?
Syncytiotrophoblast
The zona pellucida is shed by day ______.
≈ 5-6
Implantation begin at week ______, and ends by week ______.
Begins week 1, ends by week 2. Lecture says will be fully implanted by DAY 10
Which cells produce the hCG that is detected for pregnancy tests?
Syncytiotrophoblasts
The endometrium is in the _____ phase of menstruation at the time of implantation.
Secretory
What structure turns into the primary yolk sac (aka 1˚ umbilical vessel)? What turns it into the primary yolk sac?
Blastocele; endoderm proliferating and closing it off.
In between which cell layers does the amniotic cavity form?
Which cells form the amnion?
- Embryoblast/Ectoderm and trophoblast.
- Amniogenic cells from the EPIBLAST organize and enclose the blastocele. The thin membrane they form is called the amnion.
After which day does fetal and maternal circulation become united? Which event causes this?
≈ Day 12; when adjacent STB networks fuse.
What are the contents of the mature umbilical cord? (5)
- Two umbilical arteries
- One umbilical vein (L umbilical vein)
- Wharton’s Jelly
- Remains of allantoic diverticulum
- Remains of vitellointestinal duct (remnant of yolk sac)
- p.71 Clinical
Give the timeline (in weeks) that each stage of the chorionic villus appears. What happens at each stage?
Primary villus: Week 2
-CTB surrounded by STB invades trabeculae.
Secondary villus: Early week 3
-Extraembryonic somatopleuric mesoderm (deep to CTB) invades each villus.
Tertiary villus: End of week 3
-Blood vessels develop in the mesoderm of the 2˚ villi.
p.65 Clinical
What are the four embryonic components of the diaphragm and what do they become?
- ) Septum Transversum – Central tendon
- ) Pleuroperitoneal membranes – Posterolateral/Dorsolateral aspect of diaphragm .
- ) Dorsal mesentery of the esophagus – Crura of diaphragm.
- ) Lateral body walls, i.e. migrating myoblasts – Muscle of diaphragm.
What defect causes CDH?
Pleuroperitoneal membrane failure to form or fuse with the other three parts of the diaphragm (large opening in the posterolateral aspect of diaphragm that intestines come out through).
Concerning neural tube closure, where does closure begin? Which closes first: Rostal or caudal neuropore?
Closure begins at the midline –Rostral closes before caudal.
By week _____, the intraembryonic coelem becomes 3 cavities, what are they?
Week 8: Pericardial, pleural, and peritoneal.
The ____ is the maternal contribution to the placenta.
Decidua basalis.
Which somites go on to form the diaphragm? Innervation?
Cervical somites 3-5 (Phrenic nerve)
What causes the apparent descent of the diaphragm during development?
Rapid dorsal growth.
What must happen to sperm before fertilization, describe? What are the steps to fertilization (6)? Briefly state what happens at each stage.
Sperm must undergo CAPACITATION – glycoprotein and plasma membrane coat in the acrosomal region is removed.
- ) Penetration of the corona radiata (ONLY capacitated sperm).
- ) Penetration of zona pellucida (Acrosomal rxn of sperm, then zona reaction makes it impermeable).
- ) Fusion of sperm and oocyte cell membrane (head and tail enter, plasma membrane and mitochondrial sheath left behind
- ) Completion of 2nd meiotic division (oocyte), and formation of female pronucleus (second polar body produced).
- ) Formation of male pronucleus (gametes change from ‘n’ to ‘2n’ –two chromatids each).
- ) Zygote formation: 2n zygote from ootid (female pronuclei).
a. ) 24, XX + 23, XY = ? (what condition, examples?)
- Where/when is this likely to occur?
b. ) 23, XX + 22, XY = ?
a. ) Trisomy (most likely from the mother during meiosis II of oogenesis…if mother >38y/o, chances of occuring in Meiosis I increase). T21 = Down, T18 = Edwards, T13 = Patau.
b. ) Monosomy ≈ Death of fetus.
Describe Klinefelter Syndrome
(XXY): The primary feature issterility.Often symptoms may be subtle and many people do not realize they are affected. Sometimes symptoms are more prominent and may include weaker muscles, greater height, poorcoordination, less body hair, smallergenitals,breast growth, and less interest in sex. Often it is only atpubertythat these symptoms are noticed.
Describe Turner Syndrome
Turner Syndrome (XO): A condition in which afemaleis partly or completely missing anX chromosome. Often, a short andwebbed neck,low-set ears, low hairline at the back of the neck,short stature, andswollenhands and feet are seen at birth. Typically they arewithout menstrual periods, do not developbreasts, and areunable to have children.Heart defects,diabetes, andlow thyroid hormoneoccur more frequently.
What secretes early pregnancy factor and when?
Trophoblast ≈ 24-48 hrs after fertilization (applicable for first ten days).
What lets the blastocyst rapidly increase in size?
Degeneration of the z.pellucida
What early embryonic structure (immediately after implantation) becomes the placenta and connecting stalk?
Decidua basalis
_________ produces human chorionic gonadotropin (hCG), which enters the maternal blood and can be used as a pregnancy test possibly by the end of the second week (if enough is produced).
Syncytiotrophoblast
By day ten, what might indicate ectopic pregnancies or syndromes?
Abnormal levels of hCG may indicate ectopic pregnancies or syndromes (e.g. trisomy 21).
Oocytes begin to stop being viable at _______.
about age 50 with menopause.
The usual site of fertilization is in the ______, the longest and widest part of the _______.
ampulla
uterine tube
_______ degenerate adjacent to the penetrating syncytiotrophoblast, being engulfed and providing the syncytiotrophoblast with embryonic nutrition.
Decidual cells
What separates the embryo from the uterine cavity after implantation?
Decidua capsularis
Where is the most common ectopic pregnancy? What normally prevents the blastocyst from implanting in undesirable locations?
Uterine tube (95%) – called "tubal pregnancy." Z.pellucida.
What is placenta previa?
When blastocyst implants near/overlying the internal os and then the developed placenta is attached to the LOWER UTERINE SEGMENT, thereby BLOCKING THE CERVICAL CANAL.
p.83 BWAB
What forms the chorion/chorion sac?
- A mixture of extraembryonic mesoderm (engulfs yolk sac and ectoderm) and trophoblast (essentially a three-layered trophoblast).
- It then hollows out to create a space between the chorion (outer) and amion (inner). p.41 Netter
Where do the chorionic villi first arise? What becomes of them?
- All over the chorion, but disappear on the decidua capsularis side, becoming the smooth chorion (chorion levae).
- They persist in the decidua basalis (leafy chorion – chorion frondosum) and become the fetal portion of placenta.
Describe the role and fate of extraembryonic mesoderm the the extraembryonic coelem.
Extraembryonic mesoderm increases and isolated EEC spaces appear within it. These spaces fuse to form a large, isolated cavity called the EEC.
Forms cavity, and connecting stalk (future placenta and umbilical cord).
What becomes of the decidua basalis during chorionic villi formation and what role does it play? How does it become trabeculae?
It is eroded by STBs and becomes thickened. Lacunae appear in it as it continues to be eroded. Lacunae increase in size and become separated by portions of STB called trabeculae.
How do villi form from the lacunae?
STBs erode the blood vessels of the EM, allowing blood to enter the lacunae. The lacunae then communicate with each other AROUND THE TRABEULAE and form INTERVILLOUS SPACES.
How do villi form?
CTBs invade the trabeculae in its center (surrounded by STBs, which do the eroding). The finger-like projections of STB and CTB are called 1˚ villi.
Describe the three phases of villi formation and the timeframe.
- ) WEEK 2: The initial finger-like projections of STB and CTB are called 1˚ villi.
- ) EARLY WEEK 3: EEM invades the 1˚, become 2˚ villi.
- ) LATE WEEK 3: Blood vessels develop in the mesoderm of the 2˚ villi; now they are 3˚ villi.
p. 65 Clinical
How are anchoring villi formed? What affect does this have on the intervillous spaces?
CTBs pass through the STBs within the villi and form a continuous layer, thus completely encasing the villi (called the CTBlastic shell – CTBS). The CTBS anchors all villi to the outside decidua; with one end at the chorion (fetal side) and one end with the decidua (maternal side).
New villi invade the chorionic side, converting the intervillous spaces into a “bag of vascular sponges”.
What becomes of the intervillous spaces/bag of vascular sponges?
Oxygenated maternal blood (from maternal vein) through 80-100 SPIRAL VESSELS – though vessels do not enter, the blood just pours in.
How does the placenta develop after the anchoring villi?
After formation of anchoring villi, septae grow inward from the uterine endometrium into the intervillous spaces and divide the placenta into lobes called cotyledons, each of which containing 2-3 anchoring villi.
- ) What are the layers of the early placenta – outer to inner? (4).
- ) What are the layers after the 20th week (full term)? What happens to the layers?
- ) Syncytiotrophoblast, cytotrophoblast, connective tissue of the villus, and endothelium of the fetal capillaries.
- ) STB (thinned; form syncytial knots), connective tissue, endothelial cells of fetal capillaries. CTBs DISAPPEAR!
- STBs contact endothelium of fetal capillaries in areas of placenta that have become very thin, thus forming a VASCULOSYNCYTIAL MEMBRANE (lets most things pass through, e.g. DRUGS).
Describe the exchange at the placenta. Through which vessels does the fetus get its blood?
Maternal vessels open into the intervillous spaces and fill them with blood. Fetal UMBILICAL ARTERIES AND VEINS from the umbilical cord run up into the villi and exchange there.
Gets it blood from the UMBILICAL VEIN (O2 rich). p.67 Clinical.
Describe the appearance of the maternal and fetal surfaces of the placenta.
Maternal surface: Lobulated, cobblestone appearance.
Fetal: Smooth and shining.
What does the placental barrier do?
Separates fetal from maternal blood –NO MIXING.
What are the three main functions of the placenta?
Metabolism (e.g. synthesis of glycogen), transport of gasses and nutrients, and endocrine secretion (e.g. hCG).
What are the contents of the mature umbilical cord? (5)
- Two umbilical arteries
- One umbilical vein (L umbilical vein)
- Wharton’s Jelly
- Remains of allantoic diverticulum
- Remains of vitellointestinal duct (remnant of yolk sac)
What increases the incidence of fraternal twinning?
Incidence increases with maternal age.
What is a fraternal twin?
Dizygotic: They result from the fertilization of two different secondary oocytes by two different sperms. The resultant two zygotes form two blastocysts—each of which implants separately into the uterine endometrium. These twins are not genetically alike. They do not look alike and can be of different sex. In such twins, the placenta, chorionic, and amniotic sacs are separate and independent. Since these twins have totally different genetic constitutions, they have no more resemblances than any other two brothers and sisters (siblings).
What is one thing identical twins (monozygotic) do not share during development?
Umbilical cord (there are two; though one placenta).
What type of monozygotic twinning will occur if cleavage occurs on the following days:
- ) Days 1-3 (Morula)
- ) Days 4-8 (Blastocyst)
- ) Days 8-13 (Implanted blastocyst)
- ) Days 13-15 (Formed embryonic disc)
- ) Dichorionic/Diamniotic
- ) Monochorionic/Diamniotic
- ) Monochorionic/Monoamniotic
- ) Conjoined Twins
At what age (in weeks) does a fetus become viable?
22 weeks
At which week is the external sex of a fetus determinable?
12 weeks
At what age in weeks is it possible, but unlikely, for a fetus to survive and why?
24 weeks, though they begin secreting surfactant at this age, the respiratory system is still underdeveloped.
At which weeks is the quickening felt (fetus moving)?
17-20 weeks
When does fetal lung development occur?
26-29 wks
When does CNS control breathing and temperature?
26-29
When is the pupillary light reflex developed?
Week 30
When has the nervous system developed and the chance of survival great?
30 weeks
Describe the locations of hematopoiesis in terms of weeks
Yolk sac until week 6, then liver, then spleen at wk 12, and BONE MARROW AT 28 WEEKS
At how many weeks are the circumference of the head and abdomen approximately equal?
36 weeks
How many weeks after fertilization is a baby expected to be delivered? LMNP?
38 weeks after fertilization
40 weeks since LMNP
What is the primary source of energy for fetal metabolism?
Glucose
- What is the most common viral infection of fetus? When is it normally fatal?
- What if it is asymptomatic?
- What condition does it typically cause?
- Cytomegalovirus: Usually fatal in first trimester (3 months).
- Can lead to hearing/vision/neurologic conditions.
- Microcephaly (p.312 BWAB)
Name the benign tumor occurring early in development. What is its origin?
Sacrococcygeal Teratoma: Primitive streak in origin.
80% female
During which weeks is the heart most sensitive?
3-7
What does the amniotic cavity eventually replace?
Chorionic sac and uterine cavity.
The amniotic sac and the umbilical vesicle are analogous to two balloons pressed together (at the site of the embryonic disc) and suspended by a cord (the connecting stalk) from the inside of a larger balloon (the chorionic sac).
p.33 BWAB
What is a major contributor to amniotic fluid after the first trimester?
Fetal urine
Why are there false knots in umbilical cord?
Vein is longer than arteries Lecture 2 (placenta), #37
What does the umbilical cord derive from?
Connecting stalk (EE mesoderm that the EE coelem does not develop in).
What moves the umbilical cord from the caudal end to the umbilicus?
Formation of tails folds
What does the 1˚ mesoderm of the umbilical cord become, what does it do?
Wharton’s Jelly; it protects the umbilical vessels.
What is detected with ultrasonography?
- Placental and fetal size
- multiple births,
- abnormalities of placental shape
- abnormal presentations can also be determined. Some developmental defects can also be detected prenatally by ultrasonography.
What is alpha fetoprotein assay good for detecting and why (2)?
- Open neural tube defects (e.g. spina bifida, myeloschisis) i.e. anything not covered with skin because the protein escapes fetal circulation and goes into the amniotic fluid. It is produced in fetal liver and umbilical vessel.
- Can also enter amniotic fluid from open ventral wall defects, e.g. gastroschisis and omphalocele.
What is chorionic villus sampling? When can it be done?
To detect chromosomal errors, inborn errors of metabolism, and X-linked disorders.
As early as 7 weeks.
What are the contents of the primitive umbilical ring (3)?
1.) Connecting stalk with umbilical vessels
2.) Yolk sac (vitellointestinal duct)
3.) Allantois (the fetal membrane lying below the chorion in many vertebrates, formed as an outgrowth of the embryo’s gut. In eutherian mammals it forms part of the placenta.)
(#32, placenta)
When does the physiological umbilical hernia reduce?
Vitellointestinal duct reduces by 12th week.
What does the allantois become?
Degenerates into the median umbilical ligament.
What is a congenital umbilical hernia?
Protrusion into weak umbilical opening that is covered by all layers of abdominal wall.
How is amniotic fluid turnover achieved?
Swallowing
What creates the fibrous pericardium? what is sealed?
Ventral fusing of pleuropericardial membranes to esophagus.
Pleural cavities are sealed superiorly.
By week _____, the intraembryonic coelem becomes what THREE cavities?
Week 8: Pleural, pericardial, peritoneal.
What accounts for the positioning and innervation of the diaphragm?
Cervical somites 3-5 (phrenic nerve)
-This is where it starts! This is why innervation comes from so high.
What growth spurs the development of the pleuroperitoneal and pleuropericardial membranes?
Growth of the lung buds in between
What substances do not cross the placenta? (5)
Cholesterol, triglycerides, protein hormones (INSULIN), IgD, IgE, IgM, Bacteria, MANY MEDICATIONS.
STEROID HORMONES DO CROSS
What hormone does the placenta secrete in the last trimester?
Relaxin; softens the cervix
What is preeclampsia, what causes it, and what vessels are affected?
When the STBs don’t or don’t fully infiltrate the uterine spiral arteries and create low pressure circulation. This will raise the BP of the mother.
What are indications for diagnostic amnio? When?
WEEKS 15-18 Advanced maternal age (>38), previous trisomy, chrom. abnormality in either parent, carriers of x-linked recessive (e.g. Hb), family history of NTD, carriers of inborn error of metabolism.
When can you do chorionic villus sampling? What is the major advantage?
As early as 7 weeks (maybe 10-12 weeks) – EARLIER THAN AMNIO, but slightly riskier (1% risk of miscarriage)
Describe the chorionic sac – what is it?
The amniotic sac and the umbilical vesicle are analogous to two balloons pressed together (at the site of the embryonic disc) and suspended by a cord (the connecting stalk) from the inside of a larger balloon (the chorionic sac).
p.33 BWAB
What forms the chorion (2)?
Extraembryonic somatic mesoderm and the two layers of trophoblasts.
p.33 BWAB
