Placental Development Flashcards
Describe sperm capacitation
Physiological changes necessary to penetrate the egg
Removal of some epididymis and seminal glycoproteins
Increase in membrane permeability to Ca2+
Ca2+ influx maximizes cAMP, increases sperm motility
What process involves the removal of epididymal and seminal glycoproteins, increase in membrane permeability to Ca2+, and Ca2+ influx that maximizes cAMP and increases sperm motility?
Sperm capacitation
What must precede fertilization?
Sperm maturation (epididymis) Sperm capacitation (female reproductive tract)
What are the three main events in fertilization?
Sperm binding to ZP3
Acrosome reactin
Sperm-egg fusion
Describe sperm binding ZP3
Outer membrane of sperm binds to ZP3 receptor
This allows for the acrosome reaction
What is the acrosome reaction?
Release of enzymes (neuramidase and acrosin) from acrosomal space of sperm to break down zona pellucida
Describe sperm-egg fusion
After first sperm fertilizes egg, proteases released from cortical granules present in the egg remove oligosaccharides from ZP3 and partially cleave ZP2
This is also called cortical reaction
Prevents polyspermy
Describe polyspermy
Egg fertilized by more than one sperm
Results in nonviable zygotes
What proteins are required for sperm to fuse with eggs?
Immunoglobulin superfamily protein Izumo (sperm)
CD9 (egg)
What happens when there is a mutation in Izumo?
Inability for sperm to fuse to egg and undergo acrosome reaction
Describe the fast component of the cortical reaction
Change in resting potential of oocyte plasma membrane prevents further binding of sperm
What component of the cortical reaction is characterized by a change in the resting potential of the oocyte plasma membrane that prevents further binding of sperm?
Fast component
Describe the slow component of the cortical reaction
Release of cortical granules containing enzymes (into PVS) that destroy sperm receptors
What component of the cortical reaction if characterized by release of cortical granules containing enzymes that destroy sperm receptors?
Slow component
Describe the development of the blastocyst
Zygote undergoes cleavage
Develops into morula, once it has attained 8-cell number
Differentiates blastocyst, with outer trophoblast, inner mass, and surrounding blastocyst cavity
Blastocyst hatches from its zona pellucida at 6 to 7 days
Describe implantation of blastocyst
Hatch from zona pellucida
Apposition: adhesion to endometrium
Trophoblastic and endometrial cells express adhesions molecules (integrins)
Implantation mediated by penetrating trophoblastic cells
Invade part of myometrium (interstitial invasion)
Reduction in number of desmosomes facilitates embryo penetration
Describe optimal state of endometrial maturation for implantation
Vascular and edematous endometrial stroma, secretory endometrial glands, apical microprocesses, pinopodes on the apical domains of luminal endometrial lining cells
Cells enlarge, become pale–staining and store lipids & glycogen under the influence of progesterone
What are pinopodes?
Apical epithelial cellular protrusions of the endometrium
what are the apical epithelial cellular protrusions of the endometrium?
Pinopodes
Describe interstitial invasion
Invasion of endometrium and inner third of myometrium
Determined by action of secretory proteolytic enzymes released by syncytiotrophoblast
Proteases erode the branches of the spiral uterine arteries to form spaces or lacunae of maternal blood within syncytiotrophoblast
Describe endovascular invasion
Initiates primitive uteroplacental circulation and represents the starting point of future intervillous space
When is uteroplacental circulation established?
When trophoblastic cells are in direct contact with maternal blood
The syncytiotrophoblast begins secretion of __ into maternal lacunae. It controls the secretion of estrogens and progesterone by corpus luteum
Human chorionic gonadotropin (hCG)
What does human chorionic gonadotropin (hCG) do?
Secreted by syncytiotrophoblast into maternal lacunae
Controls secretion of estrogens and progesterone by corpus luteum
Describe the role of the decidual cells during implantation
Decidua provides immune-protective environment for the development of the embryo
Production of immunosuppressive substances (mainly prostatglandins) to inhibit activation of natural killer cells at implantation site
Infilitrating leukocytes in endometrial stroma that secrete interleukin-2 to prevent maternal tissue rejection of implanting embryo
Syncytiotrophoblastic cells do not express major histocompatibility complex class II and cannot present antigens to maternal CD4+ T cells
What forms primary villi?
At the end of the second week, cytotrophoblastic cells proliferate and extend into syncytiotrophoblast mass
At the end of the second week, cytotrophoblastic cells proliferate and extend into syncytiotrophoblast mass, forming ___
Primary villi
Describe secondary villi
Early in third week, extraembryonic mesoderm extends into primary vili, forming secondary villi
In cross section, secondary villus is formed by a core of extraembryonic mesoderm surrounded by a middle cytotrophoblast layer and an outer layer of syncytiotrophoblast
What is formed by a core of extraembryonic mesoderm surrounded by a middle cytotrophoblast layer and an outer layer of syncytiotrophoblast?
Secondary villi
Describe tertiary villi
Cells of extraembryonic mesoderm differentiate into capillary blood cells, forming tertiary villi
Presence of capillaries in tertiary villi distinguish them from secondary villi
What is formed when cells of extraembryonic mesoderm differentiate into capillary and blood cells?
Teritary villi
Describe the placenta
Temporary organ with embryonic (chorion frondosum) and maternal (decidua basalis) components
What is the embryonic contribution to the placenta?
Chorion frondosum
What is the maternal contribution to the placenta?
Decidua basalis
What are the functions of the placenta?
Protect the fetus Provide for nutrition, respiration, excretion, and hormone protection during development Exchange of gases Transfer of maternal immunoglobulins Rh (D antigen) isoimmunization Steroid hormone production
Describe the transfer of the maternal immunoglobulins across the placenta
Maternal antibodies, mainly IgG, are taken up by syncytiotrophoblast and then transported to fetal capillaries for passive immunity
Larger IgM does not cross placental barrier
What immunoglobulin can cross the placental barrier?
IgG
Describe Rh (D antigen) isoimmunization
Maternal antibodies against D antigen causes hemolytic disease (erythroblastosis fetalis)
Fetus is Rh-postitive, but mother lacks D antigen (Rh-negative)
Isoimmunization refers to maternal exposure and sensitization to fetal Rh+ red blood cells, mainly during delivery
In subsequent pregnancy, antibodies to D antigen (IgG) cross placenta and cause hemolysis of fetal red blood cells
Describe decidua basalis
Portion underlying implantation site and forms maternal part of placenta
what is the portion that underlies the implantation site and forms the maternal part of the placenta?
Decidua basalis
Describe decidua capsularis
Portion overlying implanted embryo and separating it from uterine cavity
What is the portion that overlies implanted embryo and separates it from uterine cavity?
Decidua capsularis
Describe decidua parietalis
Remainder of endometrium
What portion is the remainder of the endometrium?
Decidua parietalis
Describe the villus structure
Chorionic villus is the basic structure involved in maternal-fetal exchanges
Each villus has a core of mesenchymal connective tissue and fetal blood vessels (arterioles and capillaries)
Describe placental abruption
Premature separation of normally implanted placenta
Hemorrhage into decidua basalis leads to premature placental separation and bleeding
Impairs oxygenation of fetus
What is the premature separation of the normally implanted placenta caused by hemorrhage into decidua basalis and impairs oxygenation of fetus?
Placental abruption
What is placenta previa?
Implantation of placenta over cervical os
What is implantation of placenta over cervical os?
Placenta previa
what is placenta accreta?
Abnormal trophoblastic invasion
What is abnormal trophoblastic invasion?
Placenta accreta
What is placenta increta?
Abnormal trophoblastic invasion into myometrium
What is abnormal trophoblastic invasion into myometrium?
Placenta increta
What is placenta percerta?
Abnormal trophoblastic invasion through serosa and into surrounding tissues
What is abnormal trophoblastic invasion through serosa and into surrounding tissues?
Placenta percerta
What is uterine atony?
Contractions of uterine muscles are not strong enough and postpartum bleeding occurs
What happens when contractions of uterine muscles are not strong enough and postpartum bleeding occurs?
Uterine atony
What are the predisposing factors of uterine atony?
Abnormal labor
Substantial enlargement of the uterus
Uterine fibroids (leiomyomas)
What decreases the possibility of uterine atony?
Intravenous infusion of oxytocin, which stimulates uterine contractions
Describe placental calcification
Sign of placental aging
Pattern of calcification (precipitation of calcium hydroxyapatite) is similar to that seen in other aging tissues
Probably a response to cell death and diminished blood circulation in localized regions of placenta
One significant risk factor: smoking
Describe lithopedion
Fetal death with ectopic pregnancy
Fetus is too large to be reabsorbed by the body and calcifies
What is the term for a fetus that died in utero, was too large to be reabsorbed by the body, and calcified?
Lithopedion
What is gestational trophoblastic disease?
Group of neoplasms, both benign and malignant, that arises from fetal tissue invading maternal host
Tumors are composed of trophoblastic tissue
Malignant GTD diagnosed on basis of elevated tumor markers, primarily beta-hCG
GTDs are highly responsive to chemotherapy
Describe complete hydatidiform mole
No fetus
Diploid, but all chromosomes paternal (fertilization of egg which has lost its chromosomes by 2 sperm, or 1 sperm replicates itself)
Describe parital hydatidiform mole
Fertilization of a haploid ovum and duplication of paternal haploid chromosomes or from dispermy
Describe malignant GTDs
15-20% of complete moles develop malignant sequelae
Invasive moles: invasion into myometrium of edematous chorionic villi covered with layers of proliferative trophoblastic cells, beta-hCG moderately elevated
Choriorcarcinoma: admixture of malignant cytotrophoblast and syncytiotrophoblast, no villi
Compare karyotype of complete vs partial mole
Complete: 46XX, paternal origin; 46XY, paternal origin
Partial: triploidy, tetraploidy
Describe presence of fetal tissue in complete vs partial mole
Complete: absent
Partial: present (maternal chromosomes present)
Describe hydropic villi. Compare complete vs partial mole
Genomic imprinting is the epigenetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner
Complete: extensive (grapelike clusters are diagnostic characteristic (poor or absent blood vessels))
Partial: limited and focal
Describe trophoblastic hyperplasia in complete vs partial mole
Complete: extensive with significant atypia
Parital: focal with mild atypia
