Reproduction 3 - fertilization, pregenancy, lactation Flashcards
What is Fertilization?
Fusion of the male and female gametes to form a zygote
After fertilization: duration of hours pregnancy or gestation
- First two months: embryo
- After 8 weeks (two months): fetus
- About nine months (40 weeks) of gestation • parturition or birth
Site of Fertilization
• Female oviduct
Timing for fertilization is limited how?
- Sperm viable for 5 days
* Oocyte viable for 12-24
Sperm initially incapable of fertilization
Why?
• Requires capacitation
Sperm Movement in the Uterine Tube, only ~100 make it there, why?
- Damage due to acidic pH of the female tract
* Some loss due to leakage from cervix
How long do sperm survive in female tract?
5 days
Why is polyspermy not favored?
Because only one sperm cell carrying n # of chromosomes is allowed in the egg to maintain the diploid zygote.
How is polyspermy prevented?
To prevent polyspermy:
- Change in membrane potential
- Release of contents from cortical granules
- Enzymes enter and harden zona pellucida
- Enzymes inactivate sperm binding receptor
Events of fertilization
1) sperm heads bind to receptor of zona pellucida = acrosome rxn
2) sperm move through zona pellucida
3) one sperm binds to egg plasma membrane
4) 3 simultaneous events:
- Egg blocks polyspermy (secretory vesicles and enzymes enter zona pellucida).
- Meiosis II = zygote = embryogenesis
- egg enzyme activated - embryogenesis
What happens to the oocyte during fertilization?
• oocyte —> ovum (meiosis II)
– Sperm plasma membrane degrades
– Chromosomes from sperm and ovum migrate to centre
– DNA replicated —> zygote
Early Embryonic Development and Implantation
Mitotic divisions —> morula
• Cell cleavage
(4 cells stage, no increase in overall size)
——>
• Morula contains 16-32 Totipotent cells cell
(3-4 days post fertilization)
—-> Moves to uterus
Division of totipotent morula cells results in
identical twins
Fertilization of two oocytes (released during the same cycle) results in
non-identical (fraternal) twins
3-4 days after fertilization, the morula loses its
Zona pellucida
What does the morula become?
Blastocyst
Blastocyst
Lost zona pellucida = lost totipotency
– Outer cell layer = trophoblast = becomes fetal placenta
– Inner cell mass = becomes embryo
– Fluid-filled cavity = blastocoele
The trophoblast, inner cell mass, and fluid filled cavity of the blastocyst becomes
Trophoblast becomes placenta
Inner cell mass becomes embryo
Fluid filled cavity becomes blastoceole
Early Embryonic Development and Implantation
Zygote —> early cleavage (4 cell)
—> morula (totipotent) —-> blastocyst (totipotency lost)
Why does the blastocyst lose its totipotency ?
Because the inner cell mass has all the info required to make embryo
embryo is in the first
2 months of growth
When does implantation occur and what phase does it occur in menstrual cycle?
- 6-7 days after fertilization.
- within the Luteal phase of the menstrual cycle = lots of progesterone
During implantation what hormone is very high and what does it cause?
lots of progesterone = decreases constracility and keeps env calm = prevents miscarriage or early abortion of implanted embryo.
Implantation
The blastocyst implants via sticky trophoblast cells (become placenta) 6-7 days after fertilization
( ~day 21 of ovulation cycle)
- disidual response
- Syncytiotrophoblast
- cytotrophoblast
What are Syncytiotrophoblast and cytotrophoblast during implantation
Syncytiotrophoblast: fused trophoblast cell layer, outlayer of trophoblast
cytotrophoblast: inner layer of trophoblast, its the interior of the Syncytiotrophoblast.
Late Embryonic and Fetal Development
3 weeks:
- endometrium secretes glycogen rich fluid for growth & implantation of blastocyst.
5 weeks:
- heart beat begins
- early placenta development
- amnion and chorion
8 weeks:
- amnion and chorion
- embryo —-> fetus
- placenta fully developed
By 5 weeks,
placenta functioning, heart beating
Chorion
Trophoblast cell layer closest to amniotic cavity. As fetus grows, surrounds fetus inside.
Amnion
Forms amniotic sac that Contains amniotic fluid, protect fetus
Placental development form what kind of cells
The endothelial cells in the chorionic villus and the endothelial cells
What do the The endothelial cells in the chorionic villus and the endothelial cells create?
creates a barrier between mother blood and fetus blood (cell barrier)
Is there ever mixing of blood between mother and fetus ?
NO NEVER
Placenta function as:
- exchange tissue: Respiratory gases, nutrients and waste products
- Temporary endocrine gland
- blood barrier
Chorionic villus
Projections Implanting into the endometrial tissue, surrounded by blood filled space.
Umbilical cord contains
Umbilical vein (blood in) and umbilical artery (blood out)
Why is the barrier created by the placenta to speerate the bloods important?
Filter/Immunological protection: protect form mother antibodies or lymphocyte, so mothers bodies doesn’t reject fetus.
Major Hormones in pregnancy
- human chorionic gonadotropin (HCG) (glycoproteins)
- human placenta lactogen (HPL) (protein)
- estrogen
- progesterone (steroid)
Where is HCG released from?
Trophoblast cells that make up the corionic tissue
HCG is released when
released as blastocysts being implanted.
HCG acts as a detector for ______? How?
pregnancy
HCG peak secretion found around 60-80 days (~2months) after the last menstrual cycle and then drops sharply and remains low for the remainder of pregnancy.
What is the indicator for pregnancy?
A sharp drop in HCG after 2 months of pregnancy indicates pregnancy
HCG peak secretion found around
60-80 days (~2months) after the last menstrual cycle and then drops sharply and remains low for the remainder of pregnancy.
Early in pregnancy, what levels are E and P?
They are low,
Do the low levels of E and P go back up during early pregnancy? How?
Slowly rise as the placenta develops and begins to act as n endocrine gland, secreting a lot of E and P. This continues until birth (placenta expelled)
Human chorionic gonadotropin ( hCG)
Function:
(glycoprotein)
- Maintains corpus luteum functions in early pregnancy
Human chorionic
somatomammotropin (hCS)
or human placental lactogen
(hPL)
Function:
(protein)
– GH-like and anti-insulin like actions in the mother (prevents sugar uptake by muscle cells/adipose cells of liver, hyperglycaemia)
- helps the fetus to avail more glucose
Is the hyperglycaemia caused by HPL good for the fetus
Yes cuz more sugar in blood available to help with baby growth
Progesterone
function:
(steroid)
- decreases uterine contractions
- inhibits LH and FSH
- growth of mammary glands and alveolar glands
- secretes sperm unfriendly mucus
Estrogen
Function:
- growth of uterus (myometrium)
- growth of mammary glands
- inhibits LH and FSH
How is the secretion of E and P stimulates and where is it from?
Placenta (HCG) —-> corpus luteum
= (E and P)
Effects of Estrogen on the uterus
- nor’easter contractile activity
- increase responsiveness to OXY
Effects of Estrogen on the ant pit
- PRL sec
- grow breast tissue
Effects of Estrogen on the breast
- grow duct tissues
- fat deposition
- suppression of lactation
Effects of progesterone on the uterus
- Suppress contrails activity
(counter to E and OXY) - maintains secretory phase conditions
Effects of progesterone on the breast
- brow glandular tissue
- suppression of lactation
• The highly developed breast tissue where milk lactation is suppressed is caused by the
high levels of both estrogen and progesterone that are secreted by the placenta.
Which hormones increases contractile activity and which suppresses it ?
E = increases contractile activity
P = decreases contractile activity
In the placenta can cholesterol be turned to androgens (E) ?
Why or why not?
No because there are no enzymes there to convert C —> P —> A —> E
How is E produced if placenta cannot produced it?
C and P inside the mothers blood are transferred to the placenta where:
C ——> P
Then P moves to the fetus where:
P—-> A
Then A move back to the placenta where:
A —> E (E then moves back to the mother)
Control of Parturition
OXY secretion from posterior pituitary (strengthen uterine contractions) = pressure of fetus against cervix ((+)feedback to produce more OXY) = partition / birth
Myometrial contractions are increased by:
- E
- Prostaglandins
- OXY
- stretch
Myometrial contractions are inhibited by:
- Progesterone
- Relaxin
Cervical ripening is increased by:
- prostaglandins
- relaxin
Cervical ripening is inhibited by:
-progesterone
Source of Relaxin in human:
Corpus luteum, placenta
Cervical ripening:
At end of pregnancy, cervix goes through enzymatic action = collagen fibres get loosened and area gets more relaxed = fetus can push itself upwards and out.
Relaxin:
It has vasodilatory effects = increases blood flow to uterus and towards fetus.
Helps manage the renal capacity for mother to accommodate the increase in blood volume.
When is relaxin important?
important effects during the middle to end of pregnancy.
Partition
1) cervix ripens
2) beginning of partition, cervix dilates = labour (uterine contractions)
3) baby leave head first
4) expulsion of placenta (after birth)
The Mammary gland
- Birth to puberty
• Rudimentary ducts, few if any alveoli
The Mammary gland
- At puberty
- Ducts grow and branch out (E)
- Some alveolar growth (P)
- Deposition of fat and alveolar tissue
The Mammary gland
During Pregnancy and lactation:
Full development (E, P, PRL, hPL and growth factors needed)
• Prolactin: lactogenesis (initiation of milk synthesis - low E + P) • hPL, growth factors • Oxytocin (milk ejection = lactation)
Breasts filled with lobular structures called
alveoli which are connected to several ducts that end up to the outside of the breast tissue, through the nipple area.
Alveolar structure of a mammary gland
- myoepithelial cells
- alveolar cells
Alveolar cells
secretory epithelial cells, site where milk protein is synthesized and is released into the lumen within the alveolus
- Have brush border enzymes
Stored milk protein within the
alveolus can be let out through the small ducts.
myoepithelial cells located
outside the alveolus
Myoepithelial cells
Contract in response to OXY that increased by E.
Suckling stimulates the tactile receptors of nipple which is then carried to
hypothalamus = oxytocin produced further = Post. Pit to be released into the blood stream = taken to myoepithelial cells. Increased recpetors = contraction of myoepithelial cells.
once epithelial cells contract under oxytocin =
contract milk secreting epitheialel cells of the alveolar cells = milk proteins made and released out the lumen = let out the ducts of nipples = excreted
Suckling Reflex
Receptor in nipples —> hypothalamus—>
1) Ant. Pit. = increase PRL = milk secretion by alveoli
2) increase activity of neurosecretory cells
—-> Post. Pit. = OXY = contraction of myepthial cells = milk ejection
Suckling causes stimulation where?
Hypo —> both Ant. Pit (PRL) and Post. Pit. (OXY)
