SECOND TERM E-LEARNING NOTE
SUBJECT: BASIC SCIENCE
CLASS: JSS 1
WEEK THREE DATE: …………..
TOPIC: HUMAN REPRODUCTION I
Meaning of menstruation
Menstruation, also known as a period or monthly, is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The first period usually begins between twelve and fifteen years of age, a point in time known as menarche. However, periods may occasionally start as young as eight years old and still be considered normal. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days). Bleeding usually lasts around 2 to 7 days. Menstruation stops occurring after menopause, which usually occurs between 45 and 55 years of age. Periods also stop during pregnancy and typically do not resume during the initial months of breastfeeding. A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not occurred in 90 days. Other problems with the menstrual cycle include painful periods and abnormal bleeding such as bleeding between periods or heavy bleeding. The menstrual cycle occurs due to the rise and fall of hormones. This cycle results in the thickening of the lining of the uterus, and the growth of an egg, (which is required for pregnancy). The egg is released from an ovary around day fourteen in the cycle; the thickened lining of the uterus provides nutrients to an embryo after implantation. If pregnancy does not occur, the lining is released in what is known as menstruation.
Menstrual hygiene and cleanliness
Ovulation is the release of egg from the ovaries. In humans, this event occurs when the de Graaf's follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized by sperm. In addition, the uterine lining (endometrium) is thickened to be able to receive a fertilized egg.
Signs of Ovulation
Another option is a saliva test, which takes a peek at levels of estrogen in your saliva as ovulation nears. When you're ovulating, a look at your saliva under the test's eyepiece will reveal a microscopic pattern that resembles the leaves of a fern plant or frost on a windowpane. There are also devices that detect the numerous salts (chloride, sodium, potassium) in a woman's sweat, which change during different times of the month. Called the chloride ion surge, this shift happens even before the estrogen and the LH surge, so these tests give a woman a four-day warning of when she may be ovulating, versus the 12-to-24-hour one that the standard pee-on-a-stick OPKs provide.
No OPK can guarantee that you will get pregnant or that you're actually ovulating; they can only indicate when ovulation may be occurring. So no matter which device or method you choose, patience and persistence are key.
Fertilization and conception
After ovulation, the egg is swept into the fallopian tube and drifts along, brushed by waves of hairlike cilia toward the womb. The sperm will typically meet the egg in the lower quadrant of a fallopian tube and start to swarm around the egg. The ovum is covered by a protective field known as the zona pellucida, and in order for fertilization to take place, sperm cells must find a keyhole (or receptor) to unlock the zona pellucida, gain entrance, and burrow their way to the oocyte, the genetic core of the ovum. Only one sperm will connect with the oocyte, precipitating genetic combination – signaling that fertilization has just taken place. . At the moment of fertilisation, your baby's genetic make-up is complete, including its sex. Since the mother can provide only X chromosomes (she is XX), if a Y sperm fertilises the egg, your baby will be a boy (XY); if an X sperm fertilises the egg, your baby will be a girl (XX). With fertilization, the ovum becomes the zygote or embryo and now passes through complex phases of cell division and differentiation. You have just conceived! It’s often thought that fertilization and conception are synonymous with pregnancy. However, at this stage, the zygote is free-floating in the womb. In the “free floating” phase prior to implantation, cell differentiation takes place. Here, some cells will become the fetus and other cells, in a surrounding halo or constellation, will become the trophoblast, comprising the placenta, umbilical cord, and amniotic sac. For pregnancy to be successfully achieved, however, the embryo must implant in the endometrium (hence the importance of a thick, vascular-rich uterine lining). The start of pregnancy from the first day of your last menstrual period is called the "menstrual age.
READING ASSIGNMENT: Nigerian Basic Science Project Book Two page; 65-66
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