Menstrual Flashcards
When ovulation occurs, cilia at the ends of the fallopian tube create a current that draws the egg into the oviduct. If fertilization is to occur, it usually occurs within 24 hours of ovulation in the upper parts of the fallopian tube. Millions of sperm enter the female reproductive tract, but only one will fertilize the egg. Sperm usually survive up to 48-72 hours in the female body. As soon as one sperm penetrates, the egg completes meiosis to form a haploid nucleus. The sperm which is also haploid, deposits it’s genetic material into the egg to form a diploid zygote (fertilized egg). Immediately the electrical and chemical properties of the egg cell membrane change, preventing any more sperm from entering. Cilia and weak contractions move the egg towards the uterus.
Fertilization
After fertilization the zygote continues down the oviduct towards the uterus. The zygote divides as it approaches but does not increase in size. This is called cleavage. As soon as the zygote begins cleavage it is called an embryo. White it is undergoing cleavage the mass of identical cells that is produced is called the morula. The division continues until it forms a rounded/hollow ball of cells, called a blastocyst (blastula I’d the general term, blastocyst for mammals). As cell divisions continue, a group of cells in one part of the blastocyst form the inner cell mass which will eventually form the baby and amnion. The hollow fluid filled cavity inside the blastocyst is called the blastocoel. The later of cells around the blastocoel is called the trophoblast. The cells of the trophoblast will form the chorion which will become th placenta. At the end of the first week the blastocyst becomes buried in the tissue of the endometrium. Here it will further develop to form the fetus and the developing membranes. The trophoblast also secretes HCG/human chorionic gonadotropin. This will keep the corpus luteum from disintegrating. For three weeks corpus luteum will continue to secrete progesterone which maintains the endometrium.
Implantation
During the second week the cells of an embryo start to form 3 layers. This is called gastrulation. These are the ectoderm, endoderm, and mesoderm. The embryo is referred to as a gastrula at this point.
Gastrulation and Differentiation
Forms skin, nervous tissue, sense organs
Ectoderm
Forms kidneys, skeleton, muscles, blood vessels and gonads
Mesoderm
Forms the lungs and the lining of the digestive tract
Endoderm
Mesoderm forms a rod called the notochord. Just above this the ectoderm forms the nervous system. Cells above the notochord fold in two regions until they fuse to form a hollow nerve cord. The notochord will eventually form the spine and the neural tube will form the spinal cord. When a neural tube forms it is called a neurula.
Neurulation/Neural development
