Preparation for Pregnancy Flashcards
Gametogenesis
The process in which cells undergo meiosis to form gametes
- Oogenesis in females
- Spermatogenesis is males
4 Phases of Gametogensis
(1) the extraembryonic origin of the germ cells and their migration into the gonads
(2) An increase in the number of germ cells by mitosis
(3) A reduction in chromosomal number by meiosis
(4) Structural and functional maturation of the eggs and spermatozoa
Primordial germ cells
Cells are responsible for differentiating into eggs and sperm
* Earliest recognizable precursors of gametes
When does oogenesis begin? spermatogenesis?
Females = before birth Males = at puberty
Describe what happens during the first phase of the Gametogenesis
Primordial germ cells arise outside the gonads and migrate into the gonads during early embryonic development
Describe the migratory path of PGC’s
They exit from the yolk sac into the hindgut epithelium and then migrate through the dorsal mesentery until they reach the primordia of the gonads (initially at the level of L1)
Obstetric age vs. scientific age
Obstetric:
- begins at the beginning of the last menstrual cycle
- 40 weeks = 280 days
Scientific:
- Begins when the sperm actually penetrates the egg
-38 weeks = 266 days
When must fertilization take place to create a viable pregnancy?
Within 24 hours of ovulation otherwise the egg degenerates
4 Actions during development
- Growth
- apoptosis
- differentiation
- organization
What happens during growth?
(1) Hypertrophy
- increased cell size
(2) cell proliferation
- increase cell number
(3) accretion
- Increase extracellular matrix
What is apoptosis?
Programmed cell death
Describe the process of differentiation
The process by which a cell changes from a multipotent state of fundamental specificity
What happens during organization phase of development?
The fate of cells is sometimes based on their 3-D organization
What is morphogenesis?
The origin and development of landforms and other structures
* For example as shape changes so does function
When do the embryonic and fetal periods begin and end?
Embryonic Period:
- From fertilization through the end of the eighth week
Fetal Period:
- From the ninth week to birth (approximately 38 weeks after fertilization or 40 weeks after the last period)
How is a nine month pregnancy typically split?
Into three trimesters
At how many weeks (scientific age) does a fully formed fetus occur? how long is it?
About eight weeks and it is approximately 3 cm long
At how many weeks (obstetric age) is there a 50% survival rate?
24 wks
What is CR?
Crown rump length
*from the top of the skull to the gluteus maximus
Given CR length how can gestational age be approximated?
Age in weeks =CR length + 6.5
Two major parts of the uterus
- Body
- cervix
Describe the uterine tubes
- Approximately 10 cm long and 1 cm in diameter.
- extend laterally from the horns of the uterus and into the peritoneal cavity at its distal end
Where does fertilization occur?
In the ampulla of the uterine tube
What is a morula?
A solid ball of cells resulting from division of a fertilized ovum and from which a blastula is formed
How many cells are allowed to penetrate the egg?
Only one
- once the zona pellucida is penetrated it becomes impervious to other sperm
Fertilization creates a _______ cell called a _______.
Totipotent
Zygote
Define totipotent
Capable of giving rise to any cell type or a complete embryo
Of the 23 pairs of chromosomes how many are autosomes and how many are allosomes?
22 pairs of autosomes and 1 pair of sex chromosomes (allosomes)
Mitosis vs. meiosis
Mitosis is the process whereby one cell divides giving rise to two daughter cells each with 46 chromosomes
Meiosis is the cell division that takes place in the germ cells to generate male and female gametes. This process requires to 2 cell divisions to reduce the number of chromosomes from 46 to the haploid number of 23
How many sperm form from one primary spermatocyte?
4
How many mature oocytes result from maturation of a primary oocyte?
1
Three importances of meiosis
(1) Provides consistency of the chromosome number from generation to generation by making diploid cells haploid
(2) allows random assortment of maternal and paternal chromosomes between gametes
(3) relocates segments of maternal and paternal chromosomes by crossing over of chromosome segments which “shuffles” the genes and produces recombination
Describe to sperm features that are required for fertilization
1) The head has an acrosomal full of enzymes to help penetrate the ovum
2) Mitochondria in the spermatozoa provide energy that allows them to swim upstream in the uterus and against contraction of the uterine tube
What do the spermatozoa contribute to the ovum?
DNA
- this includes the mitochondrial DNA
Where does final maturation of the spermatozoa occur?
Epididymis
Where are sperm deposited?
In the posterior fornix of the cervix
Describe it which glands and hormones control the ovarian cycle
The hypothalamus produces gonadotropin releasing hormone (GnRH) which acts on the anterior lobe of the pituitary gland. This in turn secretes follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These two gonadotropins stimulate and control cyclic changes in the ovary
What does FSH do?
It is the gonadotropin that stimulates the development of ovarian follicles and the production of estrogen by the follicular cells
What does LH do?
It serves as the “trigger” for ovulation (release of the secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone
What effect does LH have on the endometrium during pregnancy?
Implantation causes the pituitary gland to continue to release LH which signals to the corpus luteum to continue to secrete progesterone and estrogen for the upkeep of the uterine wall
What happens to the uterine wall if implantation does not take place?
LH is not released so the corpus luteum does not continue to release estrogen and progesterone and the uterine wall is shed
When does implantation typically occur and where?
In the posterior wall of the uterus on day six
What must occur for the trophoblast (Outer cell mass of the blastocyst) to implant?
The zona pellucida must degenerate
What is the menstrual cycle?
The time during which that oocyte matures, is ovulated, and enters the uterine tube
Name of the five phases of the ovarian cycle
1) Menstrual phase
2) proliferative phase
3) ovulation
4) secretory (luteal) phase
5) ishemic phase
Describe the menstrual phase
The first phase of the menstrual cycle during which the lining of the uterus is shed
Describe the proliferative phase
The second phase of the menstrual cycle in which the endometrium regenerates and thickens
Describe ovulation
The third phase of the menstral cycle in which an ovum is released from the ovary
Describe the secretory or luteal phase
The fourth phase of the menstrual cycle in which the corpus luteum secretes progesterone which prepares the endometrium for implantation
Describe the Ishemic Phase
The last phase of the menstrual cycle in which the lining of the uterus disintegrates and prepares to be shed
How many days is the average menstrual cycle?
28 fays
How long is the menstrual phase and on what days does it begin and end?
1-4
4 days long
How long is the Proliferative phase and on what days does it begin and end?
5-13
9 days long
How long is the ovulation phase and on what days does it begin and end?
13-16
4 days long
How long is the Luteal phase and on what days does it begin and end?
16-28
13 days long
How long is the Ischemic phase and on what days does it begin and end?
27-28
2 days long
The endometrium is a ______ of the ovarian cycle. Why?
“Mirror”
It responds in a consistent manner to the fluctuating concentrations of Gonadotropic and ovarian hormones
How can a woman tell if she is ovulating?
Basal body temperature increases 0.5°C
At approximately what day does the blastocyst implant in the endometrium?
In the sixth day of the luteal phase which is day 20 of the 28th day cycle
What roles do FSH and LH play in males?
FSH affects the Sertoli cells which stimulate the process of spermatogenesis to occur.
LH triggers the Leydig cells of the testes to produce and secrete testosterone, which is essentially needed for sperm production
Describe human development all the way from fertilization up to birth
1) Zygote which is a single pluripotent cell until 8 cells
2) Morula which is a solid ball of 16 cells
3) Blastocyst which is when the zygote divides to 32 cells
4) Embryo which is the third week through the eighth week
5) fetus which is the ninth week until birth
When is a morula considered a blastocyst?
When a cavity appears in the morula
What are the three parts to the morula and what will they become?
1) Intercell mass which will become the embryo
2) Blastocyst cavity Will become the blastocoel
3) Outer Cell mass which will become the trophoblast and will contribute to the placenta
At the end of week one what do we have?
Two layers to the embryo: - epiblast - hypoblast Two layers of the trophoblast - cytotrophoblast - syncytioyrophoblast Two cavities - amniotic cavity - blastocyst cavity (aka the primary yolk sac)
Describe the syncytioyrophoblast
The outer layer of the trophoblast that invades the endometrial epithelium and underlying tissue
* It also secretes hCG to maintain the corpus luteum
By the end of the first week the blastocysts is superficially implanted in the endometrium with the help of the _____ and the _____.
Syncytiotrophoblast
Hypoblast
What percent of pregnancies end in spontaneous abortion?
50%
