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29 Dev/Inheritance

Development and Inheritance

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
Created by: sibuxiang



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