Pregnancy Flashcards
An increase in the Na+ permeability of the oocyte membrane is a feature of which of the following?
capacitation
fast block to polyspermy
slow block to polyspermy
polyspermy
acrosomal reaction
fast block to polyspermy
The structure which grows into the endometrium by digesting endometrial cells during blastocyst implantation in known as a?
morula
zygote
syncytiotrophoblast
suncityohwotablast
embryoblast
syncytiotrophoblast
Approximately what proportion of ejaculated spermatozoa make it as far as the ampullae of the follopian tubes?
0.1%
10%
0.001%
0.01%
0.0001%
0.001%
(3000/300 million x 100)
How many days following ovulation does implantation begin?
3 - 4 days
14 - 15 days
1 - 2 days
4 -5 days
6 - 8 days
6-8 days
The exocytosis of neurotransmitter from an axon terminal during synaptic transmission is remarkably similar to which of the following?
binding of the spermatozoa to the zona pellucida
slow block to polyspermy
acrosomal reaction
fast block to polyspermy
Frankie Sinatra
slow block to polyspermy
Which of the following is NOT involved in the preparation for parturition?
An increase in the circulating concentration of oxytocin.
An increase in the expression of oxytocin receptors on the smooth muscle cells on the uterus
An increased flexibility of the joint between the pelvic bones.
An increase in electrical coupling between adjacent smooth muscles cells in the myometrium
An increase in the formation of cross bridges between the collagen fibres in the walls of the cervix
An increase in the formation of cross bridges between the collagen fibres in the walls of the cervix
The movement of spermatozoa from the vagina to the ampullae of the fallopian tubes is greatly enhanced around the time of ovulation by?
Human chorionic gonadotropin
Oestrogen
Progesterone
Oestrogen
During fertilsation penetration of the corona radiata is enabled by which of the following processes?
Cooperative action of spermatozoa.
Enzymes associated with plasma membrane.
The acrosomal reaction.
Cooperative action of spermatozoa.
Enzymes associated with plasma membrane.
The acrosome reaction is triggered by which of the following?
binding of the spermatozoa to the oocyte membrane
binding of the spermatozoa to the corona radiata
fertilisation
binding of the spermatozoa to the zona pellucida
emission
binding of the spermatozoa to the zona pellucida
fertilisation usually takes place in the _________ of the fallopian tubes and so the _____ million or so spermatozoa secreted into the vagina during ejaculation have a long way to travel
ampullae
300
the physiological process that facilitate the transport of spermatozoa to the ampullae of the Fallopian tube
Motility of Spermatozoa
Thinning of Cervical Mucus
Uterine Contractions
Motility of Spermatozoa: the motility of spermatozoa is greatly enhanced at pH of __ and in the presence of ______ and _______ from _______ _____. This movement is enabled by the _______ of their tails which results in them ______ along the walls of the female reproductive tract towards the ampullae.
6.0
fructose
prostaglandins
seminal fluid
thrashing
slithering
Thinning of Cervical Mucus: Cervical mucus presents a fairly _______ _______ for spermatozoa. However the high levels of ______ present at ovulation cause a _______ in the thickness of this mucus which makes it easier for the spermatozoa to move through the _______ ______ at this phase of the cycle.
formidable barrier
oestrogen
decrease
cervical canal
Uterine Contractions: The _______ ________ of the uterus during the female _____ are believed to enhance the transfer of semen into the uterus. In addition, _______ in semen are thought to stimulate ________ of both the uterus and fallopian tubes and further potentiate the transport of spermatozoa.
rhythmic contractions
orgasm
prostaglandins
contractions
some spermatozoa reach the ampullae within __ to __ minutes following ejaculation (although the majority take _____ ____to complete the trip)
5 to 10
several hours
only _____ to _____ of the ejaculated spermatozoa make it as far as the ampullae of the fallopian tubes.
2000 to 3000
In the - hours following ejaculation the plasma membrane surrounding the spermatozoa’s acrosome undergoes a number of changes including the reorganisation of membrane proteins and a dramatic increase in the permeability of the membrane to ____. The increase in ____ causes an increase in _____ _______. These changes in the spermatozoa are known as __________ and are a prerequisite to successful fertilisation.
6-8
Ca2+
Ca2+
sperm motility
capacitation
The stages of fertilisation
A. Penetration of the corona radiata
B. Binding to the zona pellucida
C. Acrosome reaction
D. Binding to Oocyte Membrane
A. Penetration of the corona radiata:
spermatozoa act cooperatively to break down ___? why?
The mechanism responsible is believed to be mediated by?
The follicular cells, the first barrier to fertilisation, are broken down by spermatozoa to expose the underlying zona pellucida.
enzymes associated with the plasma membrane covering the head of the spermatozoa.
B. Binding to the zona pellucida:
Spermatozoa binding to the zona pellucida is __________ and acts to reduce the possibility of ______ fertilisation. The interaction between the two appears to involve binding mediated by ? which are derived by?
species-specific
cross-species
binding mediated by cell-surface glycoproteins and the species-specificity is believed to be derived from the nature of these glycoproteins.
C. Acrosome reaction:
The process by which the acrosome breaks down and releases a complex mixture of enzymes (including _______ and ______) through pores in the plasma membrane. This process is believed to be triggered by? and allows?
hyaluronidase and acrosin
glycoproteins in the zona pellucida and allows the released enzymes to break down the zona pellucida.
D. Binding to the Oocyte Membrane:
With the ________ of the zona pellucida the still motile spermatozoa contact the ______ _______ of the oocyte. The plasma membranes of the two gametes fuse and the _____ of the spermatozoon is incorporated into the oocyte ________. Within an _____ the two nuclei fuse giving rise to a fertilised ovum (now known as a _____).
breakdown
plasma membrane
nucleus
cytoplasm
hour
zygote
What is polyspermy?
fertilisation of an oocyte by more than one spermatozoon
How is polyspermy prevented?
Fast block - Within a few seconds of a spermatozoon binding to the oocyte, Na+ channels in the oocyte membrane open allowing Na+ ions to flow down their concentration gradient into the oocyte and thus depolarise the membrane from a resting value of -70 mv to around +10 mV. This rapid depolarisation of the oocyte temporarily prevents any further spermatozoa from binding to it.
Slow block - Within a few seconds of the fusion of the spermatozoon and oocyte membranes there is a marked increase in the permeability of the oocyte membrane to Ca2+. As a result Ca2+ flows into the cell and triggers a large number of granules lying just underneath the plasma membrane (known as cortical granules) to fuse with the membrane and exocytose their contents. The enzymes released from the cortical granules hydrolyse the glycoproteins of the zona pellucida and within 30 seconds turn it into an impenetrable barrier and producing a long term block to polyspermy.
The time course of movement of a zygote along the length of the Fallopian tube.
- 3-4 days post fertilisation, zygote remains in ampulla and undergoes mitotic divisions -> solid ball of cells (morula)
- Morula transported to uterus, continues division, whilst living freely within uterine cavity for 3-4 days
- endometrium is still developing in days following ovulation and not ready for implantation
- whilst in uterus, morula is nourished by secretions of the endometrial glands and discards the zona pellucida
- results in blastocyst - consists of hollow sphere of flattened cells (trophoblast) surrounding fluid-filled cavity with a dense accumulation of cells on one side (embryoblast)
Processes involved in implantation
- 6-8 days following ovulation, the blastocyst becomes attached to the posterior wall of the fundus or body of the uterus -> buried in the endometrium
- enabled by trophoblast in 2 ways:
1. they secrete substances which stimulate thickening of the underlying endometrium
2. syncytiotrophoblast is formed which grows into the endometrium by digesting endometrial cells - after another 6-8 days, proliferation of endometrium -> blastocyst embedded in endometrium -> completion of implantation
Implantation coincides with the end of the secretory phase so corresponds with the time when the functional layer of the endometrium would normally be shed. What happens to prevent shedding?
The trophoblast begins to secrete human chorionic gonadotropin (hCG) which is a hormone that stimulates the corpus luteum to continue to secrete oestrogen and progesterone. Because it is the decline in progesterone levels that stimulate the menstrual phase of the uterine cycle, menstruation is prevented and thus the endometrium containing the blastocyst is retained. In physiological terms pregnancy is considered to begin with implantation.
The difference between a tubal pregnancy and an abdominal pregnancy.
In a small proportion of cases the blastocyst implants somewhere other than the uterus.
- obstruction in fallopian tube blocks movement of morula into uterus -> implantation in fallopian tubes (tubal pregnancy) - can be fatal if not detected
- blastocyst flows out of the distal end of the fallopian tube and can implant in one of a number of well-vascularised abdominopelvic organs (abdominal pregnancy) - usually requires termination however pregnancy can sometimes proceed and delivered by caesarean section
Define parturition
the birth of the baby as well as the subsequent delivery of the placenta
stages of parturition
- cervix and contractions during pregnancy
- last month of pregnancy
- onset of labour
- during labour
- placenta after birth
- most of pregnancy the cervix is constricted and inflexible due to dense network of interlinked collagen fibres in the extracellular matrix of its walls - contractions of uterus are weak and infrequent to to stabilise the environment for the developing foetus
- last month, contractions become stronger/more frequent, foetus moves lower - head is down (95% cases) in close apposition to cervix
- onset of labor (baby transported through the birth canal) - amniotic sac ruptures & contractions increase
- during labour, contractions increase, head acts as wedge that dilates the cervix allowing passageway - can take 8->24 hours during 1st preg
- umbilical cord and placenta continue to nourish but shortly after birth the blood vessels linking the placenta to the uterus constrict, placenta detaches and delivered through the birth canal
Why are contractions weak and infrequent during first 7 months of pregnancy?
the smooth muscle cells of the myometrium are not electrically coupled (and therefore unable to produce coordinated contractions of the uterus) and relaxed under the influence of progesterone.
Towards the end of pregnancy however the inhibitory influence of _________ begins to decline whilst _________ levels continue to increase.
progesterone
oestrogen
Control of Parturition:
Oestrogen stimulates the expression of ______ in the smooth muscle cells of the uterus which is required for the formation of ______ that enables?
connexin
connexons
the formation of electrical-coupling between adjacent cells. With electrically coupled cells contractions action potentials spread quickly through the myometrium so produce more synchronised and therefore stronger contractions.
Control of Parturition:
Oestrogen causes a marked increase in the expression of ______ receptors on the smooth muscle cells on the uterus which?
oxytocin
is a peptide hormone produced by the posterior pituitary gland and is a potent stimulator of uterine contractions which binds to receptors on the smooth muscle cells of the myometrium which stimulates further contraction of the uterus. This results in the baby’s head exerting more pressure on the cervix and in a classic positive feedback mechanism increasing the amount of oxytocin being secreted.
Control of Parturition:
Oestrogen stimulates the production of ______ that?
enzymes
break down the cross bridges between the collagen fibres in the walls of the cervix and thus increases its flexibility.
Control of Parturition:
________ is a peptide hormone produced by the placenta also stimulates enzymes that?
Relaxin
help break down the extracellular matrix of the cervix, stimulates the growth of the cervix, vagina and increases the flexibility of the joint between the pelvic bones.
The resultant stretching of the cervix is detected by _______ __________ and this information is relayed to the _______ _____ ______ which responds by secreting ______ into the circulation.
sensory neurones
posterior pituitary gland
oxytocin
The mammary glands consists of around 20 ____ that radiate from the nipple. Each ___ is separated from its neighbour by ______ or _____ tissue and is made up of large numbers of ______ ______ that are the functional units of lactation. During lactation milk flows out of each lobule through ________ _____.
lobes
lobe
connective
adipose
epithelial glands
lactiferous ducts
Before puberty the epithelial glands of the breast consist of _______ ________ ______ structures.
fairly simple tubular
How the structure of mammary glands changes during pregnancy and the hormones responsible for these changes
before puberty, fairly simple tubular structures -> during puberty, extensively branched (due to oestrogen) -> once ovarian cycle is established and during luteal phase, growth of alveoli (due to progesterone) (synthesise breast milk) - change in size and weight during menstrual cycle
- extensive growth during pregnancy, the tubular ducts and alveoli undergo hypertrophy (due to oestrogen, progesterone, human placental lactogen (hPL) and prolactin) -> by mid 2nd trimester, breasts have increased and capable of milk production
Despite development of breasts during pregnancy, here is no significant secretion of milk until after the baby is born. This appears to be because although _______ and _______ help stimulate the development of the glandular tissue they also _____ milk production. When the _____ is delivered during parturition the circulating levels of oestrogen and progesterone _____ and this acts as the trigger for _______.
oestrogen
progesterone
inhibit
placenta
decline
lactation
Difference between milk let-down and milk production
suckling -> mechanoreceptors stimulation -> anterior pituitary gland -> prolactin -> secretory cell -> milk production
suckling -> mechanoreceptors stimulation -> posterior pituitary gland -> oxytocin -> myoepithelial cell -> milk let-down
milk let-down
The transfer of the milk from the alveoli into the ducts is mediated by the contraction of myoepithelial cells associated with the alveoli that contract and squeeze the milk into the adjacent ducts. The movement of fluid is known as the milk let-down (or milk ejection) and is mediated by the reflex release of oxytocin in response to suckling of the infant.
milk production
milk production is almost entirely dependent upon circulating prolactin levels and this is regulated by a neuroendocrine reflex similar to that responsible for milk let-down. Suckling of the infant (detected by mechanoreceptors in the nipple) stimulates an increase in prolactin release from the anterior pituitary gland and maintains circulating prolactin levels and thereby sustains milk production. Milk production therefore decreases following weaning because suckling ceases.
For the first few days following parturition the fluid produced by the mammary glands is relatively low in fats and carbohydrates but rich in protein, mineral, some vitamins and immunoglobulins. This fluid is called _____ and the _______ provide the new born with some protection against infection. Over the next couple of weeks the fat and carbohydrate levels of the fluid gradually increase as it develops into mature milk.
colostrum
immunoglobulins
