Mar 11th Flashcards
How are spermatozoa transported to the epididymis?
Non-motile, infertile spermatozoa are passively transported to the epididymis for spermiation.
How long does sperm transport to the epididymis take?
4-12 days
What happens to sperm upon ejaculation?
Spermatozoa pass through the ductus deferens and mix with secretions from accessory glands.
What do the seminal vesicles contribute to seminal fluid?
Fructose (energy source) & prostaglandins (aid sperm motility).
What does the prostate gland contribute to seminal fluid?
Citric acid, acid phosphatase, zinc, & magnesium ions (help sperm function).
Sperm Transport in the Female
- Sperm deposited in upper vagina (rapid elevation of pH)
- Passage through cervix (fast & slow phases)
- Passage through uterus/uterine horns
- Entry into oviducts
- Passage up oviducts by flagellar movement & contractions of
oviducts
Where is seminal fluid deposited during copulation?
In the upper vagina.
How does seminal fluid protect spermatozoa in the upper vagina?
It buffers vaginal acidity, raising pH from 4.3 to 7.2 in 10 seconds.
How long does the buffering effect last?
A few minutes, enough time for sperm to reach the cervix.
What is the optimal pH for sperm motility?
6.0 - 6.5
What are the two functions of the cervix in sperm transport?
(1) Major barrier to sperm and (2) Sperm reservoir.
How does the cervix act as a barrier to sperm?
- Cervical mucus is viscous & gelatinous, making it hostile to sperm.
- Cervical rings & folds physically inhibit sperm travel.
How does the cervix act as a sperm reservoir?
- Cervical folds & crypts trap sperm.
- Cervical mucus helps sperm survive & reach the oviduct.
sulfomucin
- viscous
- prevents sperm motility
sialomucin
- watery
- facilitates sperm motility
type of mucus in follicular, ovulation and luteal phase
follicular: thick mucus (makes passage difficult)
ovulation: watery mucus (allows passage)
luteal phase: thick mucus (hinders passage)
what is rapid transport in the cervix
- spermatozoa penetrate sialomucin
- Quickly transported through cervical canal (aided by muscular contractions of the female tract)
- Reach the uterus
slow transport in the cervix
- Spermatozoa swim through cervical mucus (2-3
mm/hr) - Sequential release of stored sperm
- Slow release ensures continued availability of
spermatozoa to enter oviduct for fertilization
- Can last up to 3-4 days after ejaculation
What guides spermatozoa toward the oviducts?
A chemoattractant secreted by the COC and ovary.
How does the uterus support sperm movement?
Contractile activity of the myometrium (uterine smooth muscle).
What happens when spermatozoa enter the utero-tubal junction?
Capacitation begins.
Capacitation
the alteration of glycoprotein surface of spermatozoa under influence of female
tissue secretions within the reproductive tract à enables zona pellucida penetration
epididymal vs ejaculated vs capacitated
epididymal - surface contains proteins and carbs
ejaculated - surface proteins coated with seminal plasma proteins
capacitated - surface proteins removed, exposing molecules that bind zona pellucida of oocyte
Sperm Storage in the Isthmus
- sperm enter oviduct
- calcium reduced in sperm
- De novo protein production by OEC
- progesterone increase at ovulation
What is sperm hyperactivation?
A change in motility where sperm exhibit stronger, whip-like tail movements, increasing their ability to reach and penetrate the oocyte.
steps of fertilization
- arrival of the sperm
- acrosome reaction
- penetration of the zona pellucida
- membrane fusion
- fusion of the nuclei
What happens when the dominant follicle ruptures?
It releases the cumulus-oocyte complex (COC) into the peritoneal cavity.
What structure captures the COC after ovulation?
The fimbria of the infundibulum.
How is the COC transported once inside the oviduct?
The ciliated epithelium of the oviduct guides it towards the ampulla.
What happens when sperm reach the cumulus-oocyte complex (COC) in the ampulla?
They remove the cumulus cells surrounding the oocyte.
What enzyme on the surface of capacitated sperm helps degrade the cumulus cells?
Hyaluronidase, a hydrolytic enzyme.
Besides enzymes, what mechanism helps sperm degrade the cumulus cloud?
Sperm motility, which physically disrupts the cumulus cells.
What enables capacitated sperm to bind to the zona pellucida (ZP)?
ZP proteins, which allow species-specific binding.
How does the ZP prevent multiple sperm from fertilizing the ovum?
ZP proteins block additional sperm entry after fertilization
What event does ZP binding trigger in sperm?
The acrosome reaction.
Acrosomal Reaction
- Sperm makes contact with egg
- Acrosome reacts with zona pellucida
- Acrosome reacts with perivitelline space
- Plasma membrane of sperm and egg fuse
- Sperm nucleus enters egg
- cortical granules fuse with egg plasma membrane, which renders the vitelline layer impenetrable to sperm
What happens after sperm penetrates the zona pellucida and reaches the perivitelline space?
Cortical granules migrate to the periphery of the oocyte.
What part of the sperm fuses with the oocyte plasma membrane?
The equatorial segment of the sperm.
What immediate change occurs after sperm-oocyte membrane fusion?
Membrane depolarization, and the fertilizing sperm is engulfed by the oocyte.
What is released into the perivitelline space after sperm fusion?
Cortical granules, which help prevent polyspermy.
What happens to the sperm nucleus after fusion?
The sperm nuclear membrane disappears, and the nucleus decondenses.
What is the fast block to polyspermy?
Membrane depolarization due to Na+ ion influx, creating an electrical barrier to sperm entry.
What triggers fast block prevention of polyspermy?
Rapid depolarization of the vitelline membrane through NaK+ pumps.
What is the slow block to polyspermy?
Cortical granule reaction, which releases enzymes that prevent additional sperm from binding.
What enzymes are released during the cortical granule reaction?
- Peroxidases: Harden glycoproteins to form an impenetrable layer.
- Glycosaminoglycans: Attract water into the perivitelline space → 3. Fertilization envelope.
Proteases: Destroy sperm-binding sites on ZP proteins.
What is the function of calcium oscillations after fertilization?
Calcium oscillations trigger DNA synthesis and resume the cell cycle.
What enzyme is activated by calcium waves to support membrane biosynthesis?
NAD+ Kinase
How do calcium waves restore meiotic cell division?
- Degradation of cyclin → Inactivates MAP kinase
- Meiotic cell cycle resumes
What key cellular processes are stimulated by calcium oscillations?
- Protein synthesis
- DNA replication
- Cytoplasmic maturation
What event triggers the completion of meiosis in the oocyte?
Calcium (Ca²⁺) wave
What two key processes occur during oocyte activation?
- Extrusion of the 2nd polar body
- Formation of the maternal pronucleus
Zygote Formation steps
- Completion of meiosis results in a female pronucleus.
- Sperm nucleus decondenses to form male pronucleus.
- Sperm centriole forms microtubules that integrate
with ovum microtubules, drawing the pronuclei closer. - Fusion of the two pronuclei:
a) Cellular membranes break
b) Chromatin from both intermix before condensing into chromosomes
c) Embryonic development begins
AI
Artificial insemination (AI)
* Also called intra-uterine insemination (IUI)
* Sperm is washed & then injected into uterus
Classic IVF
- In-vitro Maturation: oocyte maturation (FSH, LH, E2)
- In-vitro Fertilization: incubate with sperm (18h)
- In-vitro Cell Culture: incubate until hatched blastocyst
Intracytoplasmic Sperm Injection (ICSI)
- Treatment for severe male factor sterility
- Sperm quality (motility and morphology) assessed
- Sperm injected into secondary oocyte cytoplasm
What structure moves the embryo toward the uterus after fertilization?
Ciliated epithelium of the oviduct
What is the end goal of early embryo transport?
Implantation of the embryo via burrowing into the uterine endometrium
what kind of cleavage do mammals have
- rotational
- asynchronous
What are the initial divisions of the zygote called?
Early embryonic cleavage
What type of cell division occurs during early embryonic cleavage?
Rapid mitotic divisions with no growth phases
What are the identical daughter cells formed during cleavage called?
Blastomeres
How does the size of blastomeres change with each division?
Blastomeres become smaller with each division
Until what stage are blastomeres totipotent?
Up to the 8-cell stage
At what stage does compaction occur?
8-cell stage
What structure forms after compaction?
16-cell morula
What happens to the blastomeres during compaction?
They tightly adhere, forming a compact structure where cells lose individual identity
What mediates compaction?
Calcium-activated cell adhesion molecules
What cell adhesion protein is present during early embryonic development?
E-cadherin
What molecule associates with E-cadherin during compaction?
Epithin
Blastocyst Structure - inner cell mass
- Embryoblast
- Gap junctions form
- Becomes the embryo proper
Blastocyst Structure - outer cell mass
- Trophoblast
- Tight junctions form
- Becomes fetal placental contribution
- Forms other extraembryonic membranes
When does blastocyst hatching occur?
Prior to implantation
How does the embryo break through the zona pellucida?
Proteases secreted by the blastocyst
What is one cause of infertility related to blastocyst hatching?
Inability to hatch
What are the two key steps of implantation?
Apposition & Adherence, and Penetration
How does the embryo adhere to the uterine endometrium?
Via cell adhesion molecules, LIF involvement, L-selectin, and trophinin
What is the role of the syncytiotrophoblast in implantation?
It is an invasive, multinucleated trophoblast that secretes digestive enzymes and establishes contact with maternal blood vessels.
What is the decidual reaction?
The uterine tissue responds to trophoblast invasion by forming an immunological barrier called the decidua, which becomes the maternal portion of the placenta.
What are the two layers of the bilaminar disc?
Epiblast (maternal portion) and Hypoblast (embryonic portion).
What happens to the hypoblast by week 3?
It undergoes changes to form the three embryonic germ layers during gastrulation.
What are the three germ layers formed during gastrulation?
Ectoderm, Mesoderm, and Endoderm.
What is organogenesis?
A highly complex and conserved developmental process forming internal organs and systems.
What structures arise from the ectoderm?
Integumentary system (epidermis) and nervous system.
What structures arise from the mesoderm?
Circulatory system, integumentary system (dermis), musculoskeletal system, urogenital system.
What structures arise from the endoderm?
Digestive system, glandular tissues, and respiratory system.
What is the function of the chorion?
Forms the fetal portion of the placenta and provides fetal oxygen and nourishment.
What is the function of the amnion?
Encloses the embryo, is filled with amniotic fluid, and provides physical protection from impact.
What is the function of the yolk sac?
Initial site of blood cell production (hematopoiesis), synthesizes proteins, and contains primordial germ cells (PGCs).
What is the function of the allantois?
Functions in independent waste storage and respiration (non-mammals).
germinal period
0-2 weeks
fertilization until implantation
- zygote until embryonic disc
embryonic period
3-8 weeks
gastrulation until the 8th week of pregnancy
- neurulation
- organogenesis
fetal period
9weeks - birth
from 9th week of pregnancy until parturition
- age of viability 22 to 28 weeks
Which hormones are synthesized by both maternal and fetal contributions of the placenta?
hCG, Estriol (E3), Progesterone (P4), PTHrP, and CRH.
What is the function of estriol (E3) during pregnancy?
Regulates uterine myometrium, promotes oxytocin receptors, and develops breast ducts.
What role does progesterone (P4) play in pregnancy?
Suppresses uterine contractions, forms cervical plug, and stimulates milk gland development.
What is the function of PTHrP during pregnancy?
Mobilizes maternal bone calcium for fetal development.
How does CRH (corticotropin-releasing hormone) contribute to fetal development?
Aids in fetal lung maturation.
What is labor?
A sequence of powerful myometrial contractions needed to expel the fetus.
Which two key mediators regulate uterine contractions during labor?
Oxytocin and Prostaglandins.
Where is oxytocin produced and released?
Produced in the hypothalamus, released by the posterior pituitary, and also produced in the uterus.
What are prostaglandins, and where are they produced?
Cyclic fatty acids with paracrine functions, produced by uterine glands.
Which two types of prostaglandins are involved in labor?
PGF₂⍺ and PGE₂.
Role of Fetal Hypothalamus in Parturition
Releases corticotropin-releasing hormone (CRH), initiating the hormonal cascade for labor.
Role of Fetal Anterior Pituitary in Parturition
Releases adrenocorticotropic hormone (ACTH), which stimulates the fetal adrenal gland.
Role of Fetal Adrenal Gland in Parturition
Produces dehydroepiandrosterone sulfate (DHEAS) and cortisol, which contribute to labor initiation.
Three Key Pathways Activated in Parturition
- Positive Feedback
- Uterine Sensitivity
- Maternal Hypothalamic-Pituitary-Oxytocin Pathway
Positive Feedback Loop in Parturition
- Fetal hypothalamus releases CRH (corticotropin-releasing hormone).
- CRH stimulates the fetal anterior pituitary to release ACTH (adrenocorticotropic hormone).
- ACTH stimulates the fetal adrenal gland to produce cortisol.
- Cortisol stimulates the placenta to release more CRH, reinforcing the cycle.
Role of CRH Accumulation in Parturition
- Most important determinant of primate parturition.
- Stimulates fetal lung maturation and surfactant production.
Role of Fetal Adrenal Gland in Uterine Sensitivity
Produces dehydroepiandrosterone sulfate (DHEAS), which is converted into estriol (E3) in the placenta.
Placental Role in Uterine Sensitivity
- Converts DHEAS into estriol (E3).
- Produces prostaglandins and oxytocin.
- Stimulates changes in the maternal myometrium:
- Increases oxytocin receptors.
- Increases prostaglandin receptors.
- Increases gap junctions for coordinated contractions.
How Uterine Sensitivity Affects Labor
- Oxytocin and prostaglandin F2⍺ stimulate Ca²⁺ channels in the plasma membrane, leading to muscle contraction.
- Gap junctions help coordinate and synchronize uterine contractions.
Hypothalamic-Pituitary-Oxytocin Pathway During Labor
- Maternal hypothalamus produces oxytocin.
- Oxytocin is released from the posterior pituitary.
- Oxytocin binds to myometrium.
- Stimulates Ca²⁺ opening → muscle contraction.
- Cervical stretch triggers a positive feedback loop.
Role of Oxytocin After Labor
- Maintains myometrial muscle tone.
- Reduces hemorrhaging from uterine arteries.
- Promotes uterine involution (shrinking from ~1 kg to 60 g in 6 weeks).
