Embryology Lecture 1-Intro to Embryology: Gametogenesis and Week 1 Flashcards
___% - ___% of zygotes never implant by week ___
30%-50% of zygotes never implant by week 2
___% of recognized pregnancies result in miscarriage during the first ___ weeks
15% of recognized pregnancies result in miscarriage during the first 12 weeks
___% of miscarried conceptuses have _________ abnormalities
60% of miscarried conceptuses have chromosomal abnormalities
___% of neonatal deaths are attributed to congenital malformations
20% of neonatal deaths are attributed to congenital malformations
___%-___% of live births have at least one birth defect
1.5-3.5% of lie virths have at least one birth defect
___%-___% more birth defects are discovered by end of 1st year of life
3%-7% more birth defects are discovered by end of 1st year of life
Birth defects are attributed to: 10% ________ 10% ________ 80%________
Birth defects are attributed to: 10% Environment (smoking or alcohol use during pregnancy 10% Genetics 80% Gene-Environment interaction
Development Timing: Zygote
weeks 1-2
Development Timing: Embryo/Embryonic Period
week 3 to week 8, rapid organ development, brain and heart are growing really rapidly
Development Timing: Fetus/Fetal Period
week 9 to week 38 (first two weeks are from first day or last period)
Terminology for Postnatal Human vs. for Embryo:
Superior vs. _____
Anterior vs. _____
Posterior vs. _____
Inferior vs. _____
Terminology for Postnatal Human vs. for Embryo:
Superior vs. Cranial
Anterior vs. Ventral
Posterior vs. Dorsal
Inferior vs. Caudal
Define Gametogenesis
a biological process by which diploid primordial germ cells ( spermatogonium and primary oocyte) undergo cell division and differentiation (meiosis) to reduce the number of chromosomes and form mature haploid gametes.
Characteristics of Trisonomy 21
Class III skeletal phenotypes, fissured tongue, concave facial profile, high rates of malocclusion, dental anomalies including hypdontia, brusixm, low carries, high periodontal disease
Threadlike structure in the nucleus of cell, made of protein and DNA, inherited from parents
Chromosome
Each chromosome contains a number of _____
Each chromosome contains a number of genes.
Humans have ___ pairs of chromosomes. ___ autosomes and ___ sex chromosomes
Humans have 23 pairs of chromosomes. 22 autosomes (paired chromosomes, non-sex chromosomes) and 1 sex chromosome.
For sexual reproduction, a critical step in meiosis is to reduce the chromosome to a “haploid” (23 chromosomes). Why is this?
Because if you join extra information (chromosomes) it results in chromosomal abnormalities.
_______ restores the “diploid” number
Fertilization restores the “diploid” number
Define “Mitosis”
Cell division that results in two daughter cells having the same number (diploid) and kind of chromosomes as the parent nucleus
Define “Meiosis”
Cell division that results in four daughter cells each with half (haploid) the number of chromosomes of the parent cell
Name and describe this phase of Mitosis
Prophase- Homologous chromosomes pair up. Each consists of two sister chromatids.
Describe Oogenesis in sequence.
- ) In the ovaries, primary oocytes and support cells (follicle cells) form. Follicular cells encircle the primary oocyte.
- )Later during development, a glycoprotein called the zona pellucida forms covering the oocyte.
- ) Primary oocytes begin first meiotic division before birth. First meiosis is not complete until puberty. Follicular cells ensure arrest in prophase by hormonal secretion.
- ) At puberty maturation continues. Primary oocyte increases in size, follicular cells mature.
- ) Before ovulation the primary oocyte completes first meiosis giving rise to the secondary or mature oocyte.
- ) A polar body is also formed which recieves little cytoplasm and goes on to degenerate.
- ) At ovulation the secondary oocyte begins second meiosis progressing to metaphase before again halting.
- ) Second meiosis is only completed upon fertilization.
Describe Spermatogenesis in sequence.
- ) Primary germ cells transformation to mature sperm.
- ) At puberty primary spermatocytes undergo meiosis, forming two cells in first meiosis (haploid). Forming four cells in second meiosis.
- ) Spermatids then transform gradually into mature sperm by differentiation (spermiogenesis).
Define/describe spermiogenesis.
Several morphological changes occur:
- ) elongation
- ) loss of cytoplasm
- ) tail formation
- ) Acrosome develops (contains enzymes important for fertilization).
Name and describe this phase of Mitosis
Anaphase- The centromeres are split, and the new daughter chromosomes are pulled toward the poles.
Sperm also have support cells know as ____ ____.
Sperm also have support cells known as Sertoli Cells.
The first week of develoopment is characterized by:
- ) fertilization
- ) rapid cell division
- ) compaction
- ) initial differentiation
- ) implantation
Begining at puberty, the female undergos regular cycles (ovarian cycles) controlled by the _________.
Begining at puberty the female undergos regular cycles (ovarian cycles) controlled by the brain/hypothalamus.
Name and describe this phase of Mitosis
Prometaphase- The nuclear membrane breaks apart, the chromosomes inside form protein structures called kinetochores, kinetochore microtubules emerge from the centrosomes at the poles and attach to the kinetochores. Microtubules move the chromosomes toward the centre of the cell.
4 important hormones that control the ovarian cycle:
- ) GnRH- Gonadotropin-Releasing Hormone
- ) FSH- Follicle Stimulating Hormone
- ) LH- Luteinizing Hormone
- ) P4 or E- Progesterone or Estrogen
GnRH
GnRH- gonadotropin releasing hormone
stimulates secretion of FSH and LH
FSH
Follicle Stimulating Hormone
acts to drive follicular cell growth
LH
Luteinizing hormone
acts to stimulate oocyte maturation
stimulates P4 production by the follicle cells causing later rupture and ovulation
E-Estrogen
Estrogen
secreted by follicular cells cause a thickening of the uterine wall
Describe ovulation in sequence.
- ) Shortly before ovulation the fimbriae of the uterine tube (fallopian tube) begin to sweep over the surface of the ovary
- ) LH surge causes oocyte to complete meiosis I and enter meiosis II
- ) Further hormonal changes cause a rupture and release of the oocyte.
- ) Support cells form the corona radiata and corpus luteum. The corpus luteum secretes estrogen and progesterone causing thickening of the uterine wall.
- ) The shed oocyte enters the uterine tube and is carried by peristaltic contractions toward the uterus.
Name and describe this phase of Mitosis
Metaphase- The chromosomes align in the equator of the cell before being separated into each of the two daughter cells.
Describe fertilization.
Sperm move from the vagina to cervix to the uterine tube by their own propulsion taking anywhere from 30 minutes to six days.
Male and female gametes meet in the dilated end of the uterine tube ampulla.
Sperm must undergo capacitation and acrosomal reaction in order to fertilize the oocyte.
Define Capacitation
Glycoprotein coat and seminal plasma proteins are removed from the sperm by the mucosal surface of the uterine tube. Only capacitated sperm can penetrate the corona radiate.
Acrosomal Reaction
Occurs after binding to the zona pellucida allowing for the release of enzymes necessary to penetrate the zona pellucida
Name and describe this phase of Mitosis
Anaphase- Chromosomes pull apart
Phases of Fertilization
- ) Penetration of corona radiate- many sperm can participate in this stage if capacitated
- ) Penetration of zona pellucida- only one sperm passes through the zona
- ) Zona reaction making the oocyte membrane impenetrable
- ) Fusion of oocyte and sperm
- ) Completion of the oocyte second meiosis
- ) Approximation of the male and female pronucleus, DNA synthesis, and mitotic division (restoration of diploidy)
- ) The zygote has now entered the two cell stage
Describe Cleavage
The zygote undergoes a series of mitotic divisions. Cells become smaller with every division due to compaction within the now hardened zona pellucida membrane.
The 16 cell stage is termed “morula”
Name and describe this phase of Mitosis
Cytokinesis- the cytoplasm divides into two daughter cells. The duplicated chromatids are separated into the cytoplasm of the separated daughter cells.
Name and describe this phase of Meiosis
Prophase I of Meisosis I- homologous chromosomes pair up, chiasmata forms, and crossing over of fragments occurs. 2n=4
Describe Morula
The 16 cell stage of cleavage.
Inner cell mass is distinct and will go on to become the tissues of the embryo proper.
Outer cells will provide the support structures.
Describe Blastocyst Formation
Upon entering the uterine cavity, fluid penetrates the zona pellucida forming a cavity known as the blastocele or blastocyst cavity.
The developing embryo is termed a blastocyst.
The zona pellucida will disintergrate to allow for implantation.
Embryoblast
inner cells of blastocyst
Trophoblast
Outer cells of blastocyst
Describe Implantation
If fertilization has occurred, trophoblast cells will approximate the uterine wall around 6 days after fertilization, then begin to penetrate the uterine wall.
If fertilization has not occurred, the endometrium is shed along with the oocyte.
Name and describe this phase of Meiosis
Metaphase I- homologue pairs line up at the metaphase plate to begin to pull apart
Name and describe this phase of Meiosis
Anaphase I of Meiosis I- homologues spearate to opposite ends of the cell.
Name and describe this phase of Meiosis
Telophase I of Meiosis I- newly formed cells are haploid (n=2). Each chromosome has two non-identical sister chromatids.
Name and describe this phase of Meiosis
Telophase II of Meiosis II- At the completion of division there are four daughter cells that are different from one another. Cells contains 23 single chromosomes.
Describe Blastocyst Formation
•Upon entering the uterine cavity fluid penetrates the zona pellucida forming a cavity known as the blastocele or blastocyst cavity.
•
- The developing embryo is now termed a blastocyst.
- Inner cells = embryoblast
- Outer cells = trophoblast
- Now the zona pellucida will disintegrate to allow for implantation.
What are the inner cells of the blastocyst called?
embryoblast
What are the outer cells of the blastocyst called?
trophoblast
Describe Implantation
- If fertilization has occurred
- Trophoblast cells will approximate the uterine wall around 6 days after fertilization
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•These cells begin will then begin to penetrate the uterine wall
•
- If fertilization does not occur
- the endometrium is shed along with the oocyte
