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-A secondary oocyte can be fertilized for about 24 hours after ovulation
-Sperm remain viable for up to 48 hours within the female reproductive tract
-This gives a three day window for intercourse to result in fertilization: two days before to one day after ovulation
-Fertilization usually takes place in the outer one-third of the uterine tube, but can take place in the abdominal cavity
-Sperm swim up the female reproductive tract, aided by muscular contractions of the uterus stimulated by prostaglandins in the semen
-The oocyte may also secrete a chemical that attracts sperm
-Sperm undergo a functional change in the female tract called ---:
-During this process the membrane around the acrosome becomes fragile, and its enzymes are released
-It requires the combined action of many sperm to allow one sperm to penetrate the oocyte
-When the first sperm enters the egg, the cell depolarizes causing the release of calcium ions inside the cell
-This stimulates the release of granules that cause changes in the zona pellucida to prevent entry of other sperm
-Secondary oocyte completes division, and nuclei of ovum and sperm unite to form a ---
-Dizygotic or fraternal twin occur when two separate eggs are ovulated. May be of different sexes.
-Monozygotic or identical twins occur when a single egg is fertilized but dividing cells break into groups and develop into two individuals. Genetically identical (clones)
--- undergoes rapid mitotic cell division, but these do not increase the size of the zygote -- called cleavage divisions
Cleavage produces a solid sphere of cells, still surrounded by zona pellucida -- now called a ---
at 4.5-5 days cells have developed into a hollow ball of cells ---
- At this stage it enters the uterus
--- has an outer layer of cells called the trophoblast, an inner cell mass, and a fluid filled cavity called the bastocele
The --- and part of the inner cell mass will form the membranes of the fetal portion of the placenta, at the rest of the inner mass forms the embryo
-The blastocyst remains free in the uterus a short time, during which the zona pellucida disintegrates
-Blastocyst nourished by glycogen from glands of the endometrium
-At about 6 days after ovulation blastocyst implants - orient cell mass toward endometrium, and secretes enzymes which allow it to penetrate (digest) the endometrial wall. This nourishes the blastocyst for about a week after implantation
-Implantation can also occur in uterine tube, cervix, or the abdominal cavity
-Implantation anywhere outside the uterus is called an --- pregnancy
-It is possible for fetus to grow in the abdominal cavity, but growth inside the uterine tube causes the tube to rupture, resulting in severe bleeding
-As early as 8-12 days after fertilization, the blastocyst begins to secrete human chorionic gonadotropin or ---
-hCG keeps the corpus luteum active until the placenta can produce estrogens and progesterone
-The presence of hCG is the basis for pregnancy tests
Inner cell mass forms --- ---:
The yolk sac and Amniotic cavity
-In humans the yolk sac produces blood cells and future sex cells
-The amniotic cavity becomes the cavity in which the embryo floats. Fluid is produced from fetal urine, and secretions from the skin, respiratory tract, and amniotic membranes
Primary Germ Layers
--- --- ---:
-In between the yolk sac and the amniotic cavity is the embryonic disc, which gives rise to the primary germ layers:
-Divided into three trimesters
-During first trimester individual starts out as a zygote, then morula, blastocyst, after implantation is called an embryo.
-Embryonic phase of development lasts from fertilization until the 8th week of gestation, when it becomes a fetus
-By day 35 the heart is beating, and eye and limb buds are present
-By month four, the rudiments of all organ systems are formed and functioning, and from then on, fetal development is primarily a matter of growth
-By the end of the third month the --- is functioning
-The chorion develops into the fetal part of the placenta
-The chorionic villi connect the fetal circulation to the placenta
-Composed of both fetal and maternal tissues
Functions of the placenta
--- --- --- ---:
1 Transfer gasses
2 Transport nutrients
3 Excretion of wastes
4 Hormone production -- temporary endocrine organ -- estrogen and progesterone
5 formation of a barrier -- incomplete, nonselective -- alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross
-The first movement of fetus felt by the mother, usually occurring during the fourth or fifth month of pregnancy
-By month seven the fetus is quite active
-During the last month the fetus becomes less active (usually due to space considerations)
-At the end of pregnancy both the mother and the uterus become "irritable"
-The uterus undergoes braxton-hicks contractions: intermittent, painless contractions which can come 10 to 20 minutes apart
-Become more frequent as gestation progresses, and can be mistaken for onset of labor
-Cervix begins to thin and dilate
-Stage one- the period from the onset of true labor contractions until the cervix is completely dilated at 10 cm
-The uterine contractions cause the cervix to dilate, and the amniotic sac may rupture
-usually lasts 6-24 hours depending on the number of previous deliveries
-Period from maximal cervical dilation until the birth of the baby
-Lasts minutes to an hour
-Contractions become more intense and frequent
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