Development Flashcards
Fertilization -
The fusion of a haploid sperm cell nuculus and a secondary oocyte, forming a single nuculus which restores the diploid number, fertilization usually occurs in the uterine tube. Zygote - the name for the fertilized ovum tha combines the egg and sperm DNA, the first cell of the new organism. The oocyte is moved through the uterine tube by peristaltic contractions and the cilia in the ducts. The sperm are swimming against the current. Capacitation - the tails of the sperm beat faster and the acrosome starts to breakdown, this occurs hours after the sperm reach the oocyte, the exact mechanism is unknown. Acrosomal reaction - there are receptor molecules on the oocyte in the zona pellucidia that bind to sperm resulting in the breakdown of the head of the sperm and release of enzymes that will breal through the zona pellucida. Polyspermy - too much genstic material would fuse resulting in a nonviable cell. Blockage of polyspermy : Oocyte membrane block - when sperm fuse with the plasma membrane, the plasma membrane forms exocytic vesicles containing the receptors for sperm. Cortical reaction - calcium starts to leave the cell via exocytosis which hardens the zona pellucida making it difficult for other sperm to enter. Dizygotic ( aka fraternal ) twins - 2 oocytes released and each oocyte is fertilized by a diffrent sperm. Monozygotic (aka identical ) twins - developing cells from a single sperm that fertilizes a single ovum divide into 2 embryos sometimes proir to the 8th day of development, they each have nearly identical genetic material. Conjoined twins - if the seperation occurs after the 8th day, sometimes some body structures are shared.
Formation of the Morula (“little mulberry”) -
- 1st division is completed aout 36 hours after fertilization, 2 blastomers (cells). 2. 2nd division is completes about 48 hours after fertilization, 4 blastomers form. 3. 3rd and 4th are completed by 72 hours after fertilization to form the morula ( - 16 cells but still same size as the zygote - 100 um).
Development of the Blastocyst -
blastocyst - a nearly hollow ball of the cells that develops 4 -5 days after fertilization, 3 parts : trophoblast, inner cell mass, and blastocyst cavity. Trophoblast - thin layer that will implantinto the uterine lining (endometrium). Embryoblast - (aka inner cell mass) that becomes the embro. Blastocyst cavity - the fluid filled cavity.
Implantation -
The blastocyt reaches the uterus at about 4 -5 days after fertilization and floats around in the uterine cavity for 2 days until its implantation starts in the uterus (-day 6 - 7 after ovulation). Trophoblast becomes : 1. syncytiotrophblast - made up of cells that secrete enzymes which allow the embryo to use the nutrients of the endometrium and allow it to burrow into the lining.
2. cytotrophoblast - layer of defined cells in between the syncytiotrophoblast and the inner cell mass. Implantation usually takes about a week so implantation is completed by about day 14 after ovulation. hCG - human chorionic gonadotropin, produced by the trophoblast, it stimulates the corpus luteum to produce estrogen and progrsterone which leads to the development of the placenta. Gestation - the period of time between the start of the last menses and birth, usually 40 weeks. Embryonic period - the 1st 8 weeks of development. Fetal period - at the start of the 9th week and beyond.
Primary germ layer -
Gastrulation - the differentiation and rearrangement of the inner cell mass into 3 germ layers: ectoderm, mesoderm, and endoderm. Ectoderm - forms closest to the amniotic cavity and develops into the epidermis of the skin, nervous system, special senses, salivary glands, anal canal and oral and nasal cavities. Mesoderm - forms in the middle and develops into muscle (cardiac,skeletal,and smooth), bone, dermis and blood. Endoderm - forms within the body and develops intp epithelia of the GI and respiratory tracts (except oral and nasal cavity and anal canal), urinary bladder,gallbladder and liver.
Embryonic membranes -
These membranes protect and nourish the developing embryo. They include the yolk sac, amnion, chorion and allantois. Yolk sac - (yellow in the art) the site of blood cell formation, some cells differentiate into spermatogonia and oogonia, later the yolk combines with endoderm to form parts of the GI tract. Amnion - a thin membrane (aka “bag of water” )- contains the amniotic fluid and functions to absorb shock, later it contains urine and sloughed cells from the fetus. Amniocentesis - removal of fluid to check for genetic disorders. Chorion - the outermist membrane that encloses all of the other membranes, becomes the fetal portion of the placenta, initially it has villi known as the chorionic villi. CVS = chorionic villus sampiling to detect genetic disorders. Allantois - an outpouching of the yolk sac that becomes the umbilical cord and later becomes the urinary bladder.
Placenta and umbilical cord -
Together the placenta and the umbilical cord forms the connection between the mother and fetus. Umbilical cord - made up of 2 umbilical arteries and 1 umbilical vein. Placenta - pancake shaped, 8” diameter x 1” thick, functions in the transfer of nutrients and wastes between mother and fetus. Completely formed by week 9.
Heredity -
Inheritance - heredity, the transfer of genes from parents to offspring. Gene - a sequence of DNA that codes for a protein when transcribed and translated. Alleles - diffrent molecular forms of the gene, i.e. different DNA sequences. Genome- the sum total of the DNA of an organism. Autosomes - the 22 pair of homologous chromosomes that do not carry gender specific genes. Mutation - a change in the DNA that is passed on as a permanent change, could create a new allele. Dominant allele - makes the presence of the other allele. only one is needed to see the trait. Recessive allele - not expressed if only a single copy is present.
Phenylketonuria (PKU) -
Phenylketonuria - lack of phenylalanine hydroxylase (enzyme) - When the allele “p” is present, enzyme is not present (recessive trait) . When the allele “P” is present, the enzyme is present (dominant trait). Diploid cells represent the combination of 2 alleles that might be the same or different. Heterozygous - the alleles present are different “P,p”. Homozygous - the alleles present are the same “P,P, or “p,p”. Genotype - which alleles are present. Phenotype - which proteins are made, the traits expresses, the outward appearance. 1/4 would have PKU (25%) 3/4 would produce the phenylalanine hydroxylase (75%). 3 possible genotypes: PP,Pp,pp… 2 possible phenotypes: lack of enzyme, production of enzyme. Pp are said to be carriers of the trait. In reality most patterns of inheritance are not simple dominant - recessive relationships. Usually another gene product will play a role or multiple genes control the trait.
Incomplete dominance -
not an either / or situation, neither allele is dominated over the other. Examples: sickle cell anemia - heterozygotes produce both normal hemoglobin and abnormal (sickle) hemoglobin.
Codominance -
multiple allele inheritance, more than 2 possible alleles. Example: ABO blood groups - A and B are codominated and O (absence or A or B) is recessive. Different possible genotypes: Iai, IaIa, IBi,Ib Ib, IA IB , ii. A,B AB, and O.
Sex - linked inheritance -
22 autosomal chromosomes, 23rd pair are the sex chromosomes. XX = female XY = male Examples : red -green color blindness - this gene is carried on th X chromosome s mostly males are affected if mom is a carrier. In order for a female to be affected the dad would have to be color blind and mom would have to also be color blind or a carrier and pass on the color blindness gene. Hemophilia - inability to clot blood, also sex- linked and mostly males are affected for same reasons as above.
