Fertilization and prenatal development Flashcards
define Fertilization
fusion of gametes to initiate the
development of a new individual organism
parts of a spermatozoa
head, neck, mid piece, tail
where are sperm produced
seminiferous tubules in the testes
Sperm maturation
1., 2. caput epididymis 0%
3. corpus epididymis 14%
4. corpus epididymis 97%
5.,6. cauda epididymis 99%
complete in approx. 60 days
Ovum nucleus at fertilization is at what divisional phase
At the time of fertilization, most mammal ovum do not yet have a haploid number of chromosomes. Only after fertilization do the final divisions complete.
Exceptions: dogs and foxes.
define Capacitation
Capacitation is required to render spermatozoa competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation.
Their motility changes, they become hyperactive.
define Acrosome reaction
The spermatozoa fusing to the egg cell usually causes little problem, whereas penetrating through the egg’s hard shell or extracellular matrix can be more difficult.
Therefore, sperm cells go through the acrosome reaction to facilitate penetration.
the acrosome fuses with the plasma membrane of the sperm’s head, exposing the contents of the acrosome.
The contents include surface antigens necessary for binding to the egg’s cell membrane, and numerous enzymes which are responsible for breaking through the egg’s tough coating and allowing fertilization to occur.
what enzymes are involved in the acrosomem reaction
acrosin & hyaluronidase
The steps of Fertilization
What is the SRY gene?
Sex-determining region Y protein found on the Y chromosome that is responsible for the initiation of male sex determination in therian mammals.
Those without it develop into females.
Prerequisites for embryo implantation (4)
- Development inside ZP –7p
- Hatching 7-10p
- Maternal recognition of pregnancy
- Placentation
Early stages of a developing zygote?
zygote
morula
blastocyst
gastrula
what is the elongation stage of embryo development
Embryonic elongation is therefore a late phase of the embryonic development. It consists of the extension of the embryo along its longitudinal axis and a reduction of its transverse diameter. This involves a dramatic modification of the shape of the hypodermal cells.
Rapid growth from 2mm to 1 m in some species (30-40mm/h).
Maternal recognition of pregnancy is necessary to
prevent luteolysis and keep high progesterone concentration
What does the embryo produce in cows and the ewe, in order to prevent luteolysis?
Cow and ewe – embryo produces proteins that prevent luteolysis
What does the embryo produce in sows, in order to prevent luteolysis?
embryo produces estradiol that gives a signal about
pregnancy to female and stimulates myometric
contractions to support even distribution of embryos in uterus
What does the embryo produce in mares in order to prevent luteolysis?
presence of embryo prevents luteolysis
Necessary migration of embryo from one uterine horn to another 12-14x/day in between 12-14 days of pregnancy.
- Embryo has round shape and needs to pass the signal to endometrium cells.
Development of placenta
mesoderm and endoderm form in blastocele.
the endoderm grows smaller, will form the yolk sack.
Trophoblast + primitive endo- and
mesoderm form chorion and amnion.
Chorion attaches to the uterine surface.
Amnion is filled with fluid and protects
embryo.
Allantois functions as liquid waste reservoir.
The expanding allantois forms the allantochorion when united with the chorion.
Explain placental Implantation
attachment of the placenta to the uterine endometrium
Chorion – fetal side. The chorion forms finger-like projections calle dchorionic villi. Uterine endometrium is the maternal side.
- Attachment occurs only in certain zones
- Platcenta produces hormones for pregnancy and birth
Placental classification is based on
placental shape and contact points
species with diffuse placenta
sow, mare
cotyledonary placenta in what animal
cow
can contain even 120+ cotyledons
are called caruncles from the maternal side but caruncle + cotyledon together are placentomes.
species with discoid placenta
rodents, primates
species with zonary placenta
cat, dog
Placental Classification Based on Layers Between
Fetal and Maternal Blood
(max 6-min 3 layers)
Prefix = mother side + suffix = fetal side
- Epitheliochorial
- Synepitheliochorial (cow,sheep)
- Endotheliochorial
- Hemochorial
Transport through placenta
- Water, gases, electrolytes – diffusion along osmolar gradient
- Glucose -simplified transport
- Proteins – too large
- Peptides, amino acids – active transport
- Immunoglobulins – only in hemo- and
endoteliochorial placenta - Low molecular mass hormones
(steroids, thyroid hormones, epinephrine, norepinephrin), vitamins, minerals pass placenta - Lipids and triglycerides are decomposed in the placenta, where
Teratogens
agents that can disturb the development of an embryo or fetus by passing through teh palcental barrier.
- Toxins (alcohol, tin, phosphor, mercury)
- Drugs (opiates, barbiturates, antibiotics)
- Microorganisms (viruses, bacteria)
the placenta secretes hormones that:
preserve pregnancy, (progesterone)
stimulate fetal growth, (lactogens)
stimulate growth of mammary gland, (lactogens)
help during calving (estrogens)
progesterone functions
suppression of contractility in uterine smooth
muscle, inhibits release of GnRH from hypothalamus, prepares the mammary gland
Sow needs progesterone from CL when?
during whole pregnancy
for ewe placental progesterone is enough starting from
day 50 of gestation
for mare placental progesterone is enough starting from
day 70 of gestation
for cow placental progesterone is enough starting from
month 6-8 of gestation
Mare loses the CL on what day of gestation?
150-180 day of pregnancy
function of relaxin
softens connective tissue,
enables uterus to enlarge and accomodate the growing fetus,
widens the pelvis, concentration increases
before birth.
Mare - placenta produces relaxin
Cow, sow - CL produces relaxin
function of estrogen during pregnancy
increases the blood circulation in uterus, prepares the mammary gland
function of placental lactogens
prepares the mammary gland
function of eCG
Mare placenta produces equine chorionic gonadotropin – eCG which helps maintain primary CL and form additional CL; if administered to other
species initiates follicular growth (similar to FSH).
function of hCG
Human chorionic gonadotropin (hCG) is secreted from d. 8-10, is the basis of pregnancy tests, supports the maintaining of CL and progesterone
production, if administered to animals induces ovulation.
it can be called a fetus from what point
a fetus is developing organism whose organs are
formed depending on species 28-50 d after
fertilization, bovine fetus 45d.
