Exam 4 Pregnancy and Human Development
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tawnberger on April 25, 2011
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63 terms
Terms | Definitions |
|---|---|
 Pregnancy | Events that occur from fertilization until the infant is born |
| Conceptus | The developing offspring |
| Gestation period | From that last menstrual period until birth |
| Preembryo | Conceptus from fertilization until it is 2 weeks old |
| Embryo | Conceptus during the third through the 8th week |
| Fetus | Conceptus from the 9th week through birth |
| Accomplishing Fertilization | -The oocyte is viable for 12 to 24 hours after ovulation -Sperm is viable 24 to 72 hours |
| For fertilization to occur... | coitus must occur no more than: -3 days before ovulation -24 hours after ovulation |
| Fertilization | When a sperm fuses with an egg to form a zygote |
| Acrosomal Reaction and Sperm Penetration | An ovulated oocyte is encapsulated by: -the corona radiata and zona pellucida -extracellular matrix Sperm binds to the zona pellucida and undergoes the acrosomal reaction -enzymes are released near the oocyte -hundreds of acrosomes release their enzymes to digest the zona pellucida |
| Acrosomal Reaction and Sperm Penetration | Once a sperm makes contact with the oocyte's membrane: -Beta protein finds and binds to receptors on the oocyte membrane -Alpha protein causes it to insert into the membrane |
| Blocks to Polyspermy | Only one sperm is allowed to penetrate the oocyte |
| 2 mechanisms ensure monospermy | -*Fast block to polyspermy: membrane depolarization prevents sperm from fusing with the oocyte membrane -*Slow block to polyspermy: zonal inhibiting proteins (ZIPs): +destroy sperm receptors +cause sperm already bound to receptors to detach |
| Completion of Meiosis II and fertilization | Upon entry of sperm, the secondary oocyte: -completes meiosis II -casts out the second polar body The ovum nucleus swells, and the 2 nuclei approach each other |
| Pronuclei | When fully swollen, the 2 nuclei are called ____ |
| *Fertilization | when the pronuclei come together |
| Preembryonic Development: Blastomeres | The first cleavage produces 2 daughter cells |
| Morula | The 16 or more cell stage (72 hours old) |
| Preembryonic Development | By the 4th or 5th day, the preembryo consists of 100 or so cells (blastocyst) |
| *Blastocyst | A fluid-filled hollow sphere composed of: -a single layer of trophoblasts -an inner cell mass Trophoblasts take part in placenta formation The inner cell mass becomes the emryonic disc |
| Implantation | -Begins 6 to 7 days after ovulation when the trophoblasts adhere to a properly prepared endometrium -The trophoblasts then proliferate and form 2 distinct layers |
| Implanted blastocyst | The _____ is covered over by endometrial cells |
| 14th day after ovulation | Implanation is completed by the ___________ |
| Implantation: trophoblasts | -Viability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblasts |
| Progesteron and Estrogen | hCG prompts the corpus luteum to continue to secrete _____ and _____ |
| Chorion | Developed from trophoblasts after implantation, continues this hormonal stimulus |
| Between the 2nd and 3rd month, the placenta: | -assumes the role of progesterone and estrogen production -is providing nutrients and removing wastes |
| Placentation: The chorion develops fingerlike villi, which: | -Become vascularized -Extend to the embryo as umbilical arteries and veins -Lie immersed in maternal blood |
| The Placenta | -The placenta is fully formed and functional by the end of the 3rd month |
| Germ Layers | -The blastocyst develops into a gastrula with 3 primary germ layers: ectoderm(outside), endoderm(inside), and mesoderm(middle) -Before becoming 3-layered, the inner cell mass subdivides into the upper epiblast and lower hypoblast -These layers form 2 of the four embryonic membranes |
| Embryonic Membranes- *Amnion: | Epiblast cells form a transparent membrane filled with amniotic fluid |
| *Amnion | -Provides a buoyant environment that protects the embryo -Helps maintain a constant homeostatic temperature -Amniotic fluid comes from maternal blood, and later, fetal urine |
| Yolk Sac | Hypoblast cells that form a sac of the ventral surface of the embryo -Forms part of the digestive tube -Produces earlies blood cells and vessels -Is the source of primordial germ cells |
| Allantois | A small outpocketing at the caudal end of the yolk sac -Structural base for the umbilical cord -Becomes part of the urinary bladder |
| Chorion | Helps form the placenta -Encloses the embryonic body and all other membranes |
| *Gastrulation | During the 3rd week, the 2-layered embryonic disc becomes a 3-layered embryo |
| Primary Germ Layers | 1. Ectoderm 2. Endoderm 3. Mesoderm |
| Primitive streak | Raised dorsal groove that establishes the longitudinal axis of the embryo |
| *Gastrulation | As cells begin to migrate: -The first cells that enter the groove form the endoderm -The cells that follow push laterally between the cells forming the mesoderm -The cells that remain on the embryo's dorsal surface form the ectoderm |
| Notochord | Rod of mesodermal cells that serves as axial support (where the spine is) |
| Primary Germ Layers serve as: | primitive tissues from which all body organs will derive |
| Ectoderm | Forms structures of the nervous system and skin epidermis |
| Endoderm | Forms epithelial linings of the digestive, respiratory, and urogenital systems |
| Mesoderm | Forms all other tissues |
| Endoderm and Ectoderm are: | Securely joined and are considered epithelia |
| Organogenesis | -Gastrulation sets the stage for organogenesis, the formation of body organs -By the 8th week all organ systems are recognizable |
| Specialization of Ectoderm: Neurulation | The first event of organogenesis gives rise to the brain and spinal cord |
| Specialization of Ectoderm | -Ectoderm over the notochord thickens, forming the neural plate -The neural plate folds inward as a neural groove with prominent neural folds |
| Specialization of Ectoderm | -By the 22nd day, neural folds fuse into a neural tube, which pinches off into the body -The anterior end becomes the brain; the rest becomes the spinal cord -Associated neural crest cells give rise to cranial, spinal, and sympathetic ganglia |
| Effects of Pregnancy: Anatomical Changes | -Breast enlarge and their areolae darken -The uterus expands, occupying most of the abdominal cavity |
| Chadwick's Sign | The vagina develops a purplish hue |
| Effects of Pregnancy: Anatomical Changes | -Breasts enlarge and their areolae darken -The uterus explands, occupying most of the abdominal cavity -Typical weight gain is about 29lbs -Relaxin causes pelvic ligaments and the pubic symphysis to relax |
| Lordosis | Common due to the change of the body's center of gravity (causes spine to bend due to weight in the front) |
| Parturition: Initiation of Labor | *-As birth nears, oxytocin and prostaglandins cause uterine contractions |
| Emotion and physical stress: | -Activate the hypothalamus -*Sets up positive feedback mechanism, releasing more oxytocin |
| Stages of Labor: Dilation Stage | -From the onset of labor until the cervix is fully dialated (10cm) -Initial contractions are 15-30 minutes apart and 10-30 seconds in duration -The cervix effaces(thins out) and dilates -The amnion ruptures, releasing amniotic fluid (breaking of the water) -Engagement occurs as the infant's head enters the true pelvis |
| Stages of Labor: Expulsion Stage | -From full dilation to delivery of the infant -Strong contractions occur every 2-3 minutes and last about 1 minute -The urge to push increases in labor without local anesthesia -Crowning occurs when the largest dimension of the head is distending the vulva |
| Stages of labor: Explusion Stage delivery of placenta | -The delivery of the placenta is accomplished within 30 minutes of birth -All placenta fragments must be removed to prevent postpartum bleeding |
| Afterbirth | The placenta and its attached fetal membranes |
| Lactation | -*The production of milk by the mammary glands -Estrogens, progesterone, and lactogen stimulate the hypothalamus to release *prolactin-releasing hormone (PRH) -The anterior pituitary responds by releasing prolactin |
| Lactation: Colostrum | Colostrum -Solution rich in vitamin A, protein, minerals, and IgA antibodies -Is released the first 2-3 days -Is followed by true milk production |
| Lactation and Milk Let-down Reflex | After birth, milk production is stimulated by the sucking infant |
| Advantages of breast milk for the infant | -Fats and iron are better absorbed -Its amino acids are metabolized more efficiently than those of cow's milk -Beneficial chemicals are present - IgA, other immunoglobulins, complement, lysozyme, interferon, and lactoperoxidase -Interleukins and prostaglandins are present, which prevent overzealous inflammatory responses -Its natural laxatives help cleanse the bowels of meconium |
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