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Human/Mammalian Fertilization. Human fertilization, or conception , is the biological process in which the human egg and sperm meet and fuse. It occurs mostly in the fallopian tube.
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Human/Mammalian Fertilization • Human fertilization, or conception, is the biological process in which the human egg and sperm meet and fuse. • It occurs mostly in the fallopian tube.
After entering the female reproductive system, the sperms swim towards the oocyte (or egg) through flagellation. • The oocyte has several “defenses” to make sure that only one sperm reaches the nucleus.
Two simultaneous processes occur when the sperm and egg meet.
Cortical Reaction – occurs in the egg cell • It is an exocytosis of the cortical granules.
Polyspermy • It is the condition wherein two or more sperms fertilize an egg. • Fast block to polyspermy – once the sperm binds to the vitelline layer, the plasma membrane depolarizes, disallowing entry of other sperm. • Slow block to polyspermy – after the plasma membrane depolarizes, the vitelline layer hardens into the fertilization membrane which ultimately disallows the entry of sperm.
Once the cell membranes fuse, the nucleus of both sperm and egg prepare to fuse. • At this point, the nuclei of the egg cell and sperm cell are now called the pronuclei. • Each pronuclei has 23 chromosomes.
After the sperm and egg pronuclei fuse, it then proceeds to its first mitotic division resulting in the zygote. • The zygote is still traveling down the Fallopian tube. • After the first mitotic division, the process is now known as cleavage. This refers to the divisions that forms the blastula.
After the cleavage forms over 100 cells, the zygote is now called a blastocyst. This occurs at the fifth day after conception. • After cleavage is completed, the blastocyst is now the blastula.
Once the blastocyst has formed, it attaches to the endometrium or the uterus lining. The blastocyst contains the inner cell mass, and the trophoblast.
The inner cell mass forms into the ectoderm, mesoderm and endoderm layers of the embryo. • The trophoblast eventually forms the placenta which will supply the nutrients for the embryo in the future. • The trophoblast is the part that connects the blastocyst to the endometrium.
First Trimester • At the moment of conception to about 12 weeks later is the first trimester. • Organogenesis is the process wherein the inner cell mass becomes the endoderm, ectoderm, and mesoderm then becomes the innner organs.
First Trimester • Human chorionic gonadotropin (HCG) - is the hormone made by the embryo that maintains the production of progesterone. Progesterone thickens the lining of the uterus to ensure safety for the fetus and to provide nutrients to the placenta.
Second Trimester • This is the 4th month to the 6th month of pregnancy. • The zygote is past its embryonic stage and is now called a fetus. • The placenta is now developed and regulates nutrients in and out of the fetus. • Umbilical cord - connects the fetus to the placenta.
Third Trimester • The pregnancy period or the gestation is nearing its end.
Labor/Parturition • Stage 1: Contractions • 8 hour duration women’s first birth • 4 hour duration for second birth and so on. • Stage 2: Delivery • The part of labor when the head of the baby is through the pelvis up to the time when the baby is fully outside. • The umbilical cord can be safely cut then. • Stage 3: Placenta • The female reproductive system will remove the placenta within 30 minutes of childbirth.
Post-Childbirth • Lactation – secretion of milk from the mammary glands. Also known as breastfeeding. • The hormones prolactin and oxytocin are produced. Prolactin stimulates milk production. Oxytocin stimulates milk ejection.
Pregnancy Complications • Placental Abruption • It is a condition wherein the placenta separates from the endometrium. • It is occurs most commonly after 20 weeks of gestation.
Ectopic Pregnancy • A condition where the embryo develops anywhere but the uterus. • A symptom may be hematosalpinx(fallopian tube bleeding).
Mammalian Adaptations in Pregnancy • Attachment of infant to the mother.
