Embryonic and Fetal Development Flashcards
Where does fertilization usually occur, and what happens when a sperm cell penetrates the egg’s plasma membrane?
Fertilization usually occurs in a single oviduct (fallopian tube), and when a sperm cell penetrates the egg’s plasma membrane, it triggers the completion of meiosis II in the egg.
What is the result of the fusion of sperm and egg nuclei?
The fusion of sperm nucleus (n=23) and egg nucleus (n=23) forms a zygote (2n=46).
Describe the cleavage process of a zygote.
The zygote undergoes its first mitotic division within 30 hours of fertilization as it travels down the oviduct, progressing from 2 cells to 4 cells, and then to 8 cells, while remaining relatively the same size.
What is a blastocyst
A blastocyst is a sphere formed from the morula (16 cells) filling with uterine fluid. The inner blastocyst cells form the embryo, and the outer cells (trophoblast) become the chorion, which eventually forms the placenta.
When does blastocyst implantation occur?
Blastocyst implantation occurs when the developing embryo, moving as a blastocyst through the uterus, makes contact with the uterine wall and remains attached to it until birth.
What are the three primary germ layers formed during gastrulation, and what does the developing embryo become after implantation?
The three primary germ layers formed during gastrulation are, ectoderm, mesoderm, and endoderm. The developing embryo is considered an embryo after implantation is complete (around 2 weeks after fertilization).
Describe the function of ectoderm, endoderm, and mesoderm during neuralation and organ formation.
Ectoderm: forms the nervous system and epidermis
Endoderm: forms the lining of the digestive and respiratory systems, and endocrine glands
Mesoderm: forms the skeleton, muscles, and reproductive structures.
What is the role of human chorionic gonadotropic hormone (hCG) during pregnancy?
hCG is secreted by the outer cells (chorion) of the blastocyst to maintain the corpus luteum, increasing until maximum concentration is reached near the end of the first trimester and then decreasing for the remainder of the pregnancy. This maintains progesterone and estrogen levels to preserve the endometrium.
How do progesterone and estrogen production change throughout pregnancy?
Progesterone production increases throughout pregnancy until it levels off near the end. Estrogen levels increase slowly throughout pregnancy, with a more rapid increase as the end of pregnancy approaches.
Describe the function of the amnion, chorion, and allantois as supportive structures during pregnancy.
Amnion: forms fluid-filled sac (amniotic sac) providing insulation and protection
Chorion: chorionic villi invade endometrium, allowing nutrient/waste transfer between maternal and fetal blood, eventually becoming the placenta
Allantois: initial nutrient source in first 5 weeks, forms umbilical cord.
What are the main events during the first trimester of fetal development?
Formation of germ layers, growth to 7mm, considered fetus after 8th week, heart and brain formation, limb buds development, placenta and umbilical cord development, and sucking reflex.
What are the key developments during the second trimester of fetal development?
Reflexes, identifiable sex, skin changes, mother feels fetal movement, organ maturation, and fetus is able to hiccup.
What are the main events during the third trimester of fetal development?
Rapid growth, organ maturation, taste bud development, fat layer formation, skin changes, brain growth, kidney maturation, and preparation for birth.
What is parturition, and what are the main steps involved in the process?
Parturition is birth, involving uterine contractions, cervix thinning and dilation, labor initiation, amniotic membrane rupture, and baby moving through the birth canal.
What are the roles of relaxin, oxytocin, and prostaglandins during birth?
Relaxin: loosens pelvic ligaments and dilates cervix
Oxytocin: initiates/strengthens contractions
Prostaglandins: trigger more contractions.
