Chapter 28 Flashcards
Gestational Period
Time from last menstrual period until birth
Embryo
Fertilization through week 8
Fetus
Week 9 through birth
Capacitated
Priming, motility must be enhanced, membranes must become fragile to release hydrolytic enzymes. Fluids in Female reproductive tract prepare for sperm
5 Steps leading to a sperm entering an egg
- ) Approach - weave passed granulosa cells of corona radiata.
- ) Acrosomal Reaction - Binding of sperm to sperm-binding receptors on zona pellucida causes the Ca2+ levels to rise.
- ) Binding - sperms membrane binds to oocyte’s sperm-binding receptors.
- ) Fusion - The sperm and oocyte plasma membranes fuse, allowing sperm contents to enter oocyte.
- ) Block of Polyspermy- Calcium is released, triggers cortical reaction, zona pellucida hardens and sperm receptors are clipped off.
Steps leading to true fertilization
- ) After the sperm penetrates the secondary oocyte, The oocyte Completes meiosis II, forming the ovum and second polar body.
- )Sperm and ovum nuclei swell, forming pronuclei.
- ) Pronuclei approach each other and mitotic spindle Forms between them.
- ) Chromosomes of the pronuclei intermix. Fertilization is
accomplished. Then, the DNA replicates in preparation for the first cleavage division.
What is cleavage?
Miotic divisions of zygote while zygote moves toward uterus, first cleavage at 36 hours (2 daughter cells).
Cleavage of cells
36 hours - 2 daughter cells
72 hours - Morula (16 cells)
4-5 days - Blastocyst (100 cells)
6-7 days - Implanting Blastocyst
Events of Implantation
- 6-7 days after ovulation
- Trophoblast cells adhere to site with proper receptors and chemical signals and proliferate into cytotrophoblasts (inner layer) and syncytiotrophoblast (outer layer)
- Inflammatory-like response occurs in endometrium
- Blastocyst begins conversion to gastrula
- Inner cell mass develops into embryonic disc
Cytotrophoblast
Inner layers of cells
Syncytiotrophoblast
Cells in outer layers that start to invade and digest endometrium
Blastocyst at implantation
burrows into lining surrounded by pool of leaked blood; endometrial cells cover and seal off implanted blastocyst
What secretes hCG and what does it do?
Human Chorionic Gonadotropin, secreted by trophoblasts. Prompts corpus luteum to continue secretion of progesterone and estrogen which promotes placental development, HCG levels rise until end of 2nd month.
Placenta
It is a temporary organ from embryonic and maternal tissues.
Maternal portion = Decidua Basalis
Fetal portion = Chorionic villi
Fully formed and functional by end of third month
Roles of Amnion
Epiblast cells form transparent sac filled with amniotic fluid
- Provides buoyant environment that protects embryo
- Helps maintain constant homeostatic temp
- Allows freedom of movement, prevents parts from fusing
- Amniotic fluid comes from maternal blood and later fetal urine.
Roles of Yolk sac
Forms part of digestive tube and earliest source blood cells and vessels
What’s the allantois?
Small outpocket of yolk sac, base for umbilical cord and part of urinary bladder
Chorion
Helps form placenta
Encloses embryonic body
Neurlation
17 days - Flat 3-layered embryo has completed gastrulation, notochord, and neural plate are present
20 days - Neural folds from folding of the neural plate which deepens, 3 mesodermal layers form on each side
22 days - neural folds have closed forming tube, embryonic body is beginning to undercut.
4 weeks - Embryo undercutting complete (sclerotome, myotome, dermtome)
3 vascular shunts in fetus
Ductus Venosus - Bypasses liver (umbilical vein - ductus venosus - IVC)
Foramen ovale - opening in interatrial septum; bypasses pulmonary circulation
Ductus arteriosus - bypasses pulmonary circulation (pulmonary trunk ductus arteriosus aorta)
8 weeks
Limbs present, digits webbed, cardiovascular system fully functional, head nearly as large as body
9-12 weeks
Sex readily detect, Retina of eye is present, Liver prominent and bile being secreted, blood cells formation begins in bone marrow
13-16 weeks
Cerebellum becomes prominent, blinking of eyes, face looks human and body growth beginning to outpace head.
17-20 weeks
Limbs reach near final proportions, quickening occurs, lanugo covers skin
21-30 weeks
Myelination of spinal cord begins, eyes are open, skin is wrinkled and red, body is lean and well proportioned.
30-40 weeks
Skin whitish pink, fat laid down in subcutaneous layer.
Anatomical Changes of mother
Reproductive organs engorged with blood
Uterus expands, occupying most of abdominal cavity
Lordosis - curvature of spine
Relaxin causes pelvic ligaments and pubic symphysis to relax to ease birth passage
Weight gain
Initiation of Labor
Fetal secretion of cortisol stimulates placenta to secrete more estrogen, causes production of oxytocin by myometrium which causes formation of gap junctions between uterine smooth muscle cells. Antagonizes calming effects of progesterone leading to Braxton Hicks contractions in uterus.
Dilations Stage
6-12 hours
cervix effaces (softens) and dilates to 10 cm
Amnion ruptures, releasing amniotic fluid
Expulsion stage
Full dilation to delivery, strong contraction every 2-3 min. urge to push increases, crowning, baby’s head extends as it is delivered
Placental Stage
Strong contractions, detachment of placenta and delivery.
What stimulates the first breath
CO2 stimulates respiratory control and takes a tremendous effort, tiny airways, lungs collapsed, surfactant helps reduce surface tension.
Benefits of breast feeding
Fats and iron better absorbed, amino acids more easily metabolized. Immune system building, natural laxative encourages colonization of large intestine.
