L18 Fertilization (cont.) and Pregnancy

polysphermy

when more than one sperm penetrate the egg at the same time. this results in extra mitotic spindles formed and faulty segregation of chromosomes during cell division

Embryogenesis

week 0-2; process by which a fertilized egg transforms into a multi-cellular embryo

Embryonic Phase 

week 3-8

-formation of basic body plan

-development of all major organ systems

fetal phase 

week 9-40

-growth and further development of body tissues and organs

zygote 

lives off the cytoplasm of the original egg cell. that cytoplasm of the egg subdivides into smaller and smaller blastomeres

morula

cells draw together, maximizing contact and form a compact ball. this enters the uterus because the corpus luteum secretes progesterone, causing the sphincter muscle barrier to be released from the fallopian tube

ectopic pregnancy

occurs when a fertilized egg implants and grows outside the uterus, most commonly in a fallopian tube. they are not viable and must be terminated via medication or surgery to prevent rupturing the fallopian tube 

embryogenesis: step 1

cleavage (cell division without cell growth) and morula (solid ball of cells)

embryogenesis: stage 2

compaction (cells of the morula come closer and closer together) and differentiation (cells begin to separate into 2 cells types: trophoblasts and embryoblasts)

embryogenesis: stage 3

blastulation: formation of a hollow ball with two cell types and fluid filled space, and the loss of the zona pellucid 

blastocyst: formation of a trophoblast, inner cell mass, and blastocoel

trophoblasts

the outer layer of cells in a blastocyst. it helps to implant the embryo into the uterus and later forms part of the placenta. It secretes hCG (the hormone detected in pregnancy tests)

embryoblasts

group of cells inside the blastocyst, this becomes the actual embryo. and later these will go on to form three germ layers: ectoderm, mesoderm, and endoderm) and then all the tissues / organs in the body

blastocyst

hollow ball of cells and has 3 parts (trophoblasts, blastocoel, and embryoblast). it forms after the morula stage

primary decidualization reaction

digestion of maternal tissue to release metabolic substrates which are taken up by the growing conceptus

It's like the uterus switching from “monthly cleanup mode” (menstruation) to “baby bed prep mode” — softening the tissue, adding nutrients, and preparing for a long-term guest.

haemotrophic nutrition

nutrition from the maternal blood supply

Human Chorionic Gonadotropin (hCG)

trophoblast produces hCG to signal it’s presence to the mother, it mimics LH, and maintains the corpus luteum so it will keep producing estradiol and progesterone

corpus lute um 

-helps maintain early pregnancy,

-produces increasing amounts of progesterone,

-synthesizes estrogen,

- if the placenta can’t take over hormone production, it can result in miscarriage 

-important for production 6-7wks of pregnancy

human hemochorial placenta 

type of placenta in which the maternal blood is in direct contact with the fetal (chorionic) tissue.

-each blood vessel is separated from the surface by a thin trophoblastic layer

fetal lobule

terminal villi project into maternal blood space;

In the placenta, particularly on the fetal side, the structure is organized into units or lobes:

functional unit of the placenta where exchange between maternal blood and fetal blood occurs.

hemochorial placenta:

characterized by direct contact between maternal blood and fetal trophoblast cells, facilitating efficient nutrient and gas exchange, and is associated with a highly invasive trophoblast

fetoplacental unit

refers to the collaborative system between the fetus, the placenta, and the mother that produces estrogens, especially during pregnancy.

estrogen causes changes in the uterus, cervix, vagina, and breasts and affects metabolism