REB 16. Pregnancy Flashcards
What is the common site of fertilization?
Ampulla
- the upper 1/3rd of the oviduct
What are the ends of the fallopian tubes called?
Fimbria - because they are fimbriated ends
When must fertilization occur by (in regards to the ovum)? How is this different to how long the sperm may survive in female reproductive tract?
- must occur within 24 hours after the ovulation
- sperm can survive about 48 hours, but may live up to 5 days in female reproductive tract
When released from the ovary, the oocyte is surrounded by 2 layers:
[1] Corona Radiata (outer)
- layer of follicular cells
[2] Zona Pellucida (inner)
- matrix of glycoproteins
When does human fertilization begin?
when sperm breaks through corona radiata to bind to SUGAR GROUP on zona pellucida
What are the 3 parts of the sperm?
[1] Head
[2] Midpiece
[3] Tail
What is special about the head of the sperm?
it contains enzymes to break through the Corona Radiata and Zona Pellucida
Explain how the sperm breaks through the outer layers of the ovum/oocyte to fertilize it.
[1] sperm breaks through Corona Radiata via the enzymes of its head
[2] sperm binds to ZP3 receptors on Zona Pellucida
[3] binding of sperm leads to triggering the acrosome reaction in which hydrolytic enzymes in the acrosome are released onto Zona Pellucida
[4] acrosomal enzymes digest Zona Pellucida creating a path for the sperm
[5] sperm and oocyte fuse
[6] sperm nucleus enters the ovum cytoplasm
[7] the sperm stimulates release of Ca2+ stored in cortical granules of ovum
[8] Ca2+ inactivates ZP3 receptors leading to the blockage of polyspermy
What happens 1 hour after fertilization?
the sperm and egg nuclei fuse
What happens 3 to 4 days after fertilization?
zygote remains within ampulla (of oviduct) and undergoes mitotic cell divisions
- morula is created!
After fertilization, there is a rising level of progesterone from the corpus luteum which stimulates…?
release of glycogen from the endometrium
- used as energy by the early embryo
- after 3 to 4 days, the morula is allowed to enter the uterus because enough nutrients were allowed to accumulate
What happens 6 to 7 days after ovulation/fertilization under the influence of progesterone?
- uterine lining being prepared for implantation
- uterus is in its secretory, progestational phase
- stores up glycogen + becomes righly vascularized (builds up wall)
The endometrium is suitable for implantation after how long?
1 week after ovulation
- at this stage, morula has descended into uterus and differentiated into blastocyst
What are the layers of the blastocyst? What are the functions of each layer?
[1] Inner Cell Mass
- becomes the embryo
[2] Trophoblast
- becomes the placenta
- makes fuel + raw materials available for embryo
During implantation, what happens to trophoblastic cells?
[1] release enzymes permitting trophoblastic cells to penetrate endometrium
[2] cells degenerate - becoming fetal portion of placenta
At the area of implantation, what changes does the endometrial tissue undergo?
- it enhances its ability to support the embryo
- now called the decidua
What is the relationship between the decidua and the blastocyst?
- the blastocyst burrows into the decidua
- a layer of endometrial cells covers over the surface of the hole
- the trophoblastic layer continues to digest surrounding decidual (endometrial) cells providing energy for the embryo
On what day is the embryo embedded in the decidua?
day 12
On day 12 after fertilization, the trophoblastic layer is 2 cell layers thick and is called…?
Chorion
What does the Chorion do? (general overview)
- it releases enzymes and expands and forms a network of cavities within decidua
- maternal blood leaks from capillaries to fill the cavities
- chorionic tissue extend into the pools of maternal blood
- developing embryo sends capillaries into these chorionic projections to form placental villi
- maternal + fetal blood do not mingle (but we know this sometimes may not be the case)
The placenta is made up of 2 tissues which are:
[1] Trophoblastic Tissue (Tissue from Blastocyst)
[2] Decidual Tissue (Endometrial Tissue)
What type of organ does the placenta temporarily become during pregnancy?
a temporary endocrine organ
Why is the placenta unique among endocrine tissues?
[1] composed of tissues of 2 organisms (mom + baby)
[2] transient tissue
[3] secretion of its hormones is not subject to extrinsic control
- depends on the stage of pregnancy
What are the 4 main hormones that the placenta secretes?
[1] Estrogens
[2] Progesterone
[3] Human Chorionic Gonadotropin (hCG)
[4] Human Placental Lactogen (hPL)
What is the source of secretion for hCG?
chorion, then the placenta
What are the functions of hCG?
[1] stimulates + maintains corpus luteum so it does not degenerate
- progesterone is produced leading to thicmening of endometrial lining + produces energy
[2] in male fetus, stimulates precursor of Leydig cells so that testosterone may be secreted
- masculinizes the reproductive tract
How is hCG excreted from the body and why is this important?
- excreted in urine
- pregnancy tests detect hCG in urine as early as the 1st month
What is the source of secretion for hPL?
initially trophoblast, then later the placenta
What are the functions of hPL?
[1] lactogenic (breast feeding) + growth hormone like actions
[2] promotes cell specialization in mammary gland
- BUT is less potent than PRL is stimulating milk production
- BUT is less potent than GH in stimulating growth
[3] ensure adequate fuel supplies for fetus
- effects on carbs, protein and fat metabolism are simialr to those of GH
- conserves carbs, builds protein and uses fat
What is the MAIN function of hPL? [1]
ensure adequate fuel supplies for fetus
- effects on carbs, protein and fat metabolism are simialr to those of GH
- conserves carbs, builds protein and uses fat
When is there a peak of hCG? When is there a peak in hPL?
hCG: maximal at week 10
hPL: maximal at around week 35
What are the sources of progesterone?
initially corpus luteum, but then the placenta
same as estrogen
What are the functions of progesterone?
[1] essential for maintaining uterus + early embryo
[2] inhibits myometrial contractions (prevents miscarriage!)
[3] promotes formation of a mucus plug in cervical canal to prevent vaginal contaminants from reaching uterus
[4] suppresses maternal immunological responses to fetal antigens
[5] precursor for steroid production by fetal adrenal glands
[6] stimulates development of milk glands in breasts in preparation for lactation
[7] role in onset of parturition
What are the sources of progesterone?
initially corpus luteum, but then the placenta
same as progesterone
What are the functions of estrogen?
[1] increase size of uterus
[2] increase uterine blood flow
[3] critical in timing of implantation
[4] induce formation of uterine receptors
[5] enhance fetal organ development
[6] promote development of the ducts within mammary glands
When is hCG the highest? Why does it drop?
- hCG is the highest at the beginning of pregnancy
- then there is a sharp drop in hCG
- hCG is kind of like the precursor for estrogen + progesterone
- as hCG decreases, both estrogen and progesterone increase
What are the 3 stages of labour?
[1] Cervical Dilation
- longest stage
- 10 cm
- last from several hours to 24 hours
[2] Delivery of Baby
- usually lasts 30 to 90 minutes
[3] Delivery of Placenta
- second series of uterine contractions
- separates placenta from myometrium + expels it
- shortest stage
What is the longest stage of labour?
Cervical Dilation
What is the name for when the uterus shrinks after delivery?
Involution
What are the 2 main triggers that lead to the onset of labour?
[1] Hormones
- progesterone, estrogen, prostaglandins, oxytocin + relaxin
[2] Mechanical Factors
- distension of uterine muscle + softening of cervix
How does progesterone lead to the onset of parturition (labour)?
- typically inhibits uterine contraction
- prevents premature delivery
- rise in placental progesterone-binding protein or a decline in the number of receptos alters its effective concentration
How does estrogen lead to the onset of parturition (labour)?
- soaring levels of estrogen
- promotes the synthesis of connexons within uterine smooth muscle cells
- contract as coordinated unit
- increase concentration of myometrial receptors for oxytocin
- promotes production of local prostaglandins
(contributes to cervical ripening - dilation of cervix - and increase the uterine responsiveness to oxytocin)
How does oxytocin lead to the onset of parturition (labour)?
- circulating levels of oxytocin remains constant prior to onset of labour
- BUT the uterine responsiveness to oxytocin is 100x greater in women at term
- labour is initated when myometrial responsiveness to oxytocin reaches CRITICAL THRESHOLD
- side note: used to clinically induce labour
How does relaxin lead to the onset of parturition (labour)?
- relaxin is large polypeptide produced by corpus luteum + decidua
- softens the cervix, permitting passage of fetus
- increases oxytocin receptors!
How is labour maintained through a positive feedback loop?
- the cervical stretch stimulates release of oxytocin
- additional oxytocin stimulates release of oxytocin from the posterior pituitary
- this leads to more stretch and more oxytocin being released
- oxytocin stimulates prostaglanding production by decidua
- porstaglandin softenst the cervix allowing for head of baby to move through
this is the Ferguson Reflex!!
What is the NAME of the positive feedback loop that maintains labour?
Ferguson Reflex
