Embryology and Development 1 Flashcards
Another name for sex cells and the organs that produce them
gametes, gonads
Describe process of egg release during menstrual cycle
~14 days after menstruation begins
- 1 ovary matures a female gamete cell (SECONDARY OOCYTE) and releases it (ovulation)
- swept into UTERINE (fallopian) tube
- enters enlarged site called AMPULLA where fertilization occurs
What is a female gamete cell called? Why is it called that?
Secondary oocyte
- secondary because the gamete has not undergone its second meiotic division
Describe sperm journey to egg
- propelled by flagella through vagina until the uterus, where contractions help push. Contractions stimulated by semen and hormones released during intercourse. Sperm continues until it meet the egg at the ampulla.
How many sperm actually make it to the egg? why is that?
1-200/20 million
crazy!
can’t make it because some sperm have bad motility (can’t swim) or female reproductive system pH kills them
window for fertilization
egg only viable for 24 hours, sperm viable up to 6 days
window = 6 days before, 1 day after
3 Prenatal Development periods (from conception to birth)
GERMINAL period: first 2 weeks of development
EMBRYONIC period: week 3-8; organ systems develop (we can call it an embryo here!)
FETAL period: week 9-birth; organ systems grow and mature
terminology for timing of developmental events (how do we know how far along someone is)
- Clinical/medical events: date since last menstrual period (clinical age of unborn child)
- Embryologists: post ovulatory age (aprx. 14 days less than clinical age)
Why is the clinical age of the unborn child about ___ days more than the post ovulatory age?
clinical events timed from start of menstrual period whereas post-ovulatory age is timed from the start of fertilization (day 14 of menstrual cycle)
describe structure of the oocyte
- nucleus
- first polar body (only 1 because hasn’t undergone 2nd division)
layers of protection - ZONA PELLUCIDA (thin layer against membrane)
- CORONA RADIATA (loosely packed follicular cells left over from when cell was in the ovary)
How do sperm pass into the oocyte?
- weave through corona radiata
- acrosome (head) of sperm binds onto ZP3 GLYCOPROTEIN (“sperm receptors”) on zona pellucida, casuing ACROSOMAL REACTION
- leads to digestion of zona pellucida via enzymes from acrosome
need many sperm to break down zona pellucida, but only one will make it through
Why are centaurs and human goats impossible in nature?
well you see…
ZP3 glycoproteins on the zona pellucida are species specific, so non-human sperm can’t pass into the egg (oocyte)
Explain steps of fertilization
- Many sperm penetrate corona radiata
- Acrosome (head of sperm) binds to ZP3 receptor in zona pellucida causing ACROSOMAL REACTION. Leads to digestion of zona pellucida
- ONE sperm gets into plasma and binds to INTEGRIN alpha6beta1, causing depolarization (FAST BLOCK TO POLYSPERMY). The successful sperm enters oocyte
- Female nucleus undergoes 2nd meiotic division (forms ovum and 2nd polar body)
- Female pronucleus and male pronucleus form (male and female genetic code)
- Fusion of haploid pronuclei produces single nucleus - a ZYGOTE (diploid)
Term for when sperm shocks and kills all other sperm when it reaches the plasma membrane. How does this happen?
FAST BLOCK TO POLYSPERMY
(say no no to more sperm)
Sperm binds to integrin alpha6beta1 in oocyte plasma and quickly depolarizes cell, killing other sperm around it.
What stops multiple sperm from fertilizing the oocyte? 2 methods
Fast block to polyspermy
- depolarization
Slow block to polyspermy
- intracellular release of Ca2+
- Ca out, water also moves out
- fluid out, so oocyte shrinks, zona pellucida denatures
- ZP3 becomes inactive!
What do you call the successive cellular divisions of the zygote?
cleavage
Stages and characteristics of cleavage (cell division of zygote)
cells duplicate faster, get smaller and move closer to uterus along uterine tube as cleavage progresses
- Day 1: 2 cells
- Day 5: when 12+ cells made, cluster called the MORULA
- Day 6: HATCHING - where morula will break free and surround z.p., creating a BLASTOCYST. At this point, cells are in the uterus.
describe structure of the blastocyst
- TROPHOBLAST (outer layer of cells) forms placenta and structures outside the embryo
- BLASTOCELE: fluid filled cavity inside
- INNER CELL MASS (what actually becomes the embryo)
How does the zygote get nutrients while moving towards the uterine cavity?
- originally surviving on nutrients within its own cytosol and UTERINE MILK (glycogen rich secretions from uterine lining)
Define totipotent and pluripotent
TOTIPOTENT: meaning one cell can divide and differentiate into EVERY single cell type in the body
PLURIPOTENT: can only differentiate so far
explain stages of implantation and formation of placenta
Day 7: Implantation
blastocyst implants onto uterine endometrium, inner cell mass closest to the lining. These cells become the EMBRYO PROPER
Day 8-12: trophoblast differentiation
- SYNCYTIOTROPHOBLASTS: farther from embryo proper, invade uterine wall to connect to maternal blood supply (blood sucked to embryo). Multinucleated.
- CYTOTROPHOBLATS: closer, provide separation between embryo proper and maternal blood supply
- Trophoblast cells also release HUMAN CHORIONIC GONADOTROPHIN into blood: keeps uterine endometrium thick, used to detect pregnancies
Day 14-20: lacunae formation
- CONNECTING STALK to developing embryo
- cytotrophoblasts form finger-like projections
- syncytiotrophoblasts digest walls of arteriols and form LACUNA/LACUNAE (pools of blood)
1 month: formation of cytotrophoblast cords
- surround syncytiotrophoblasts and lacunae (separate embryonic from maternal blood)
what is the uterine endometrium?
wall of uterus closest to uterine cavity
- layer of uterus that changes with each monthly menstrual cycle
what is HUMAN CHORIONIC GONADOTROPHIN
horomone released by trophoblast cells into maternal blood to keep uterine endometrium thick. Pregnancy tests detect it.
define implantation
burrowing of blastocyst into uterine wall
syncitiotrophoblast
after implantation, this multinucleated cell invades endometrium to access maternal blood
cytotrophoblast
after implantation, this cell remains close to embryonic tissue
Lacunae
pools of blood formed by syncitiotrophoblast surrounding maternal blood vessels an digesting their walls
describe structure and function of mature placenta
- cytotrophoblast chords form CHORIONIC VILI (contain fetal arterioles and venules)
- this is surrounded by one big lacuna that connects to maternal arterioles
tip imagine this like you’re sticking your fist into a bucket of water (mom’s blood) and soaking it in through your skin*
- CHORION: mature barrier made of remaining syncytiotrophoblasts + basement membrane (cytotrophoblasts gone)
Describe direction of blood flow through umbilical cord
UMBILICAL VEINS carry O2 rich blood back to heart
UMBILICAL ARTERIES carry C02 away from heart
what is the chorion? name layers (and surrounding blood supplies) from maternal to embryotic side
- mature barrier between maternal and embryonic blood supplies
lacuna
syncytiotrophoblast
basement membrane
fetal capillary
cytotrophoblast not apart of Chorion. they gone ! disappeared!
At what location does fertilization occur?
At the AMPULLA in the uterine tube
When does implementation occur?
~7 days after fertilization
describe the process of hatching
Day 6 of development
- morula will break free and surround zona pellucida, creating the BLASTOCYST. At this point, cells are in the uterus.
