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29 Dev/Inheritance
Development and Inheritance
| Question | Answer |
|---|---|
| Fertilization | normally occurs in uterine tubes; sperm undergoes caparitation |
| Caparitation | series of functional changes that prepare its plasma membrane to fuse with oocyte; must penetrate the corona radiata and zona pellucida; acrosomal enzymes and stong movements help with penetration |
| Events following fertilization | prevent polyspermy; fast block and slow block |
| Polyspermy | fertilization by more than one sperm |
| Fast block | oocyte cell membrane depolarizes; positively charged sperm repelled |
| Slow block | depolarization > intracellular release of Ca2+ > exocytosis of secretory vesicles > hardens entire zona pellucida |
| Dizygotic | fraternal twins are produced by the release of 2 secondary oocytes and fertilization by separate sperm |
| Monozygotic | identical twins develop from a single fertilized ovum |
| First week of development | zygote cleavage (first 24 hours, 2 cells); morula (day 4); blastocyst (day 4/5); implantation (day 6); burrows into endometrium (day 7) |
| Morula | solid sphere of cells surrounded by zona pellucida; appears around day 4 |
| Blastocyst formation | morula moves through uterine tube towards the uterus; after 32-cell stage fluid collects and forms the blastocyst cavity (blastocoel) |
| 2 cell populations of blastocyst | Embryoblast (inncer cell mass, develops into embryo) and trophoblast (outer layer, forms wall and develops into outer chorionic sac surrounding fetus) |
| Decidua | modified portion of endometrium after implantation |
| Second week of development | development of trophoblast, bilaminar embryonic disc, amnion, yolk sac, sinusoids and extraembryonic coelom, and chorion |
| Trophoblast | day 8; develops into 2 layers that becomes part of chorion (syncytiotrophoblast and cytotrophoblast); secretes human chorionic gonadotropin (hCG) |
| Syncytiotrophoblast | secretes enzymes that enable the blastocyst to penetrate the uterine lining |
| Cytotrophoblast | differentiates into the other forms of trophoblastic tissue |
| Human chorionic gonadotropin (hCG) | maintains corpus luteum so it continues to secrete estrogens and progesterone that maintain the uterine lining |
| Bilaminar embryonic disc | day 8; embryoblast develops into 2 layers (hypoblast and epiblast) |
| Hypoblast | primitive endoderm |
| Epiblast | primitive ectoderm; within the epiblast a small cavity appears and enlarges to form the amniotic cavity |
| Amnion | eventually surrounds entire embryo; amniotic fluid derived from maternal blood and fetal urine |
| Amniotic fluid function | shock absorber for the fetus; regulates fetal body temperature; helps prevent the fetus from drying out; prevents adhesions between the skin of the fetus and surrounding tissue |
| Yolk sac | day 8; cells at the edge of hypoblast migrate and form the exocoelomic membrane; former blastocyst cavity |
| Yolk sac functions | supplies early nutrients; source of blood cells; contains primordial germ cells that migrate to gonads to form gametes; forms part of the gut; functions as a shock absorber; prevents desiccation |
| Sinusoids | endometrial capillaries dilate to form maternal sinusoids |
| Extraembryonic coelom | day 12; a single, large cavity develops fused by cavities in the extraembryonic mesoderm |
| Chorion | formed by the extraembryonic mesoderm and 2 layers of trophoblast; becomes principal embryonic part of placenta; protects embryo from immune responses of mother; produces hCG |
| Third week of development | day 15; bilaminar embryonic disc transforms into trilaminar embryonic disc to form the 3 primary germ layers |
| Primary germ layers | ectoderm, mesoderm, and endoderm |
| Ectoderm | forms skin and nervous system |
| Mesoderm | forms muscle, bones, connective tissue, and peritoneum |
| Endoderm | forms epithelial lining of GI tract, respiratory tract, and several other organs |
| Primitive streak | establishes head (primitive node) and tail ends; spinal cord formation |
| Gastrulation | brick work for physical structures of the embryo |
| Notochordal process | day 16 |
| Notochord | days 22-24; induces tissue to become vertebral bodies |
| Oropharyngeal membrane | later breaks down to connect mouth to pharynx and GI tract |
| Cloacal membrane | will degenerate to form opening of anus, urinary and reproductive tracts |
| Allantois | when the cloacal membrane appears, the wall of the yolk sac forms this; extends into a connecting stalk; functions in early formation of blood, blood vessels, and urinary bladder |
| Neurulation | notochord induces formation of neural plate > edges elevate to form neural fold > fuse to form neural tube |
| Neural tube cells | develop into brain and spinal cord |
| Neural crest cells | give rise to all sensory neurons and postganglionic neurons of the PNS, the adrenal medullae, melanocytes, arachnoid mater, and pia mater of the brain and spinal cord; most of the head |
| Neural tube (head end) | develops into 3 primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain) |
| Somites | longitudinal columns of paraxial mesoderm; each somite has 3 regions (myotome, dermatome, and sclerotome) |
| Myotome | develops into skeletal muscles of neck, trunk, and limbs |
| Dermatome | develops into connective tissue |
| Sclerotome | develops into vertebra and ribs |
| Intraembryonic coelom | lateral plate of mesoderm forms splanchnic mesoderm and somatic mesoderm |
| Splanchnic mesoderm | heart, blood vessels, smooth muscle, and connective tissues of respiratory and digestive systems |
| Somatic mesoderm | bones, ligaments, and dermis of the skin |
| Angiogenesis | formation of blood vessels; pluripotent stem cells form blood cells; by the end of 3rd week a heart forms and begins to beat |
| Chorionic villi | projections into the endometrium; blood vessels connect them to the embryonic heart through a body stalk which later becomes the umbilical cord |
| Placentation | 12th week; fetal and maternal parts; allows oxygen and nutrients to diffuse from maternal to fetal blood; exchanges carbon dioxide and wastes to maternal blood; not a complete barrier |
| Umbilical cord | 2 umbilical arteries carry deoxygenated fetal blood to placenta and 1 umbilical vein carries oxygenated blood away from the placenta |
| Fourth week of development | organogenesis, embryo triples in size; 3D cylinder (embryonic folding); head fold brings heart and mouth into position; tail fold brings anus to position; lateral fold for primitive gut; limbs appear |
| Primitive gut | GI tract; foregut (superior), midgut (middle), and hindgut (inferior) |
| Pharyngeal arches | give rise to specific structures in the head and neck |
| Fifth week of development | brain develops rapidly, head growth is considerable |
| Sixth week of development | limbs show substantial development; heart now 4-chambered |
| Eighth week of development | digits of hands are short; tail shortens and disappears; eyes open; auricles visible; external genitals begin to differentiate |
| Otic placode | future internal ear |
| Lens placode | future ear |
| Teratogen | any agent or influence that causes developmental defects in an embryo |
| Cigarette smoking | causes of low infant birth rate, cardiac abnormalities, and anencephaly |
| Irradiation | x-rays may cause microcephaly, mental retardation, and skeletal malformations |
| Fetal ultrasonography | determine fetal age; confirm pregnancy; evaluate fetal viability and growth; determine fetal position |
| Amniocentesis | test presence of certain genetic disorders (ex: Down); week 14-18 |
| Chorionic villi testing | identify the same defects as amnio; week 8 |
| Noninvasive prenatal tests | mother's blood is analyzed for the presence of maternal alpha-fetoprotein (AFP); week 12-15; a high level of AFP after week 16 indicates fetus has a neural tube defect (ex: spina bifida) |
| Estrogens and progesterone | secreted by corpus luteum during the first 3-4 months of pregnancy; 3rd month placenta produces high levels; maintains lining of uterus and prepares mammary glands to secrete milk |
| Human chorionic gonadotropin (hCG) | secreted by chorion; maintains corpus luteum to continue production of progesterone and estrogens |
| Relaxin | produced by corpus luteum and placenta; increases flexibility of pubic symphysis; helps dilate cervix during labor |
| Human chorionic somatomammotropin (hCS) or human placental lactogen (hPL) | produced by chorion; helps prepare mammary glands for lactation; regulates certain aspects of fetal and maternal metabolism |
| Corticotropin releasing hormone (CRH) | produced by placenta; in nonpregnant women secreted by hypothalamus; possibly part of labor clock; increases secretion of cortisol, needed for maturation of fetal lungs and production of surfactant |
| Maternal changes during pregnancy | uterus nearly fills entire abdominal cavity; weight gain due to fetus; increased storage of proteins, triglycerides, and minerals; marked breast enlargement; lower back pain due to lordosis (hypercurvature of lower lumbar) |
| More maternal changes during pregnancy | cardiovascular system (increased maternal blood flow to placenta and increased metabolism), respiratory (increased TV), digestive (increased appetite), and urinary (incontinence and increased renal filtering) |
| Labor (parturition) role of hormones | levels of estrogen must rise to overcome inhibiting effect of progesterone; estrogen increases number of oxytocin receptors on uterine muscle fibers; oxytocin stimulates contractions; relaxin increases flexibility of pubic symphysis and dilates cervix |
| Labor | contractions force fetal head into cervix; stimulated stretch receptors cause release of more oxytocin; more stretching; cycle broken when stretching stops as baby exits |
| Stages of true labor | dilation, expulsion, and placental |
| Adjustments after birth | foramen ovale closes (fossa ovalis), ductus arteriosus constricts (ligamentum arteriosum), umbilical arteries become medial umbilical ligaments; umbilical vein becomes ligamentum teres of the liver |
| Physiology of lactation | prolactin (anterior pituitary) promotes milk synthesis and secretion, inhibited during pregnancy by progesterone; stimulus maintaining prolactin is suckling |
| Oxytocin | causes milk ejection reflex |
| Colostrum | cloudy fluid before true milk on 4th day; contains important antibodies |
| Allele | alternative forms of a gene that code for the same trait and are at the same location on the homologous chromosomes |
| Mutation | permanent heritable change in allele that produces a different variant |
| Genotype | allele combinations |
| Phenotype | gene expression |
| Nondisjunction | error in cell division resulting in abnormal number of chromosomes |
| Aneuploid | chromosomes added or missing |
| Monosomic | cell missing 1 chromosome |
| Trisomic | cell has additional chromosome |
| Simple dominant recessive | dominant allele expressed when present; recessive allele expressed only in the absence of dominant gene (ex: PKU) |
| Incomplete dominance | neither allele dominant over the other; heterozygote has intermediate phenotype (ex: sickle cell anemia) |
| Multiple-allele inheritance | some genes may have more than two alternative forms (ex: blood type) |
| Polygenic inheritance | inherited traits controlled by more than one gene |
| Complex inheritance | inheritance based on combined effects of many genes and environmental factors |
| Folic acid | neural tube deficits are more common if the mother lacks adequate folic acid in the diet |
| Karyotype | shows 46 chromosomes |
| Autosomes | 22 pairs |
| Sex chromosomes | 23rd pair |
| Sex-linked inheritance | many of the genes are on the X and not the Y (ex: color blindness and hemophilia) |
| X-chromosome inactivation | females have a double set of all genes on the X chromosome; X-chromosome genes reduced to a single set in each female's body; barr body in the nublei of the cells = inactivated X chromosome |
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sibuxiang
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