Group 2 - Sperm to Establishment of Preg - COMPLETE*** Flashcards
What is Spermatogenesis?
a process where spermatozoa are formed
Spermatogenesis: How long generally does it take?
- Where does it take place?
5-9 weeks
in the seminiferous tubules
Spermatogenesis: State the names of the spermatozoa starting with the earliest one 7
A spermatogonia
Intermediate spermatogonia
B spermatogonia
primary spermatocytes
secondary spermatocytes
spermatids
spermatozoa
Spermatogenesis: State the 3 general stages and explain what happens in each
proliferation - A spermatogonia undergo mitotic divisions to produce B spermatogonia
meiosis - this produces haploid spermatids and crossing over ensures their genetic heterogeneity
differentiation - this forms a cell capable of fertilisation
Spermatogenesis: Where in the seminiferous tubules does it start?
- what happens first?
- What is maintained?
- What are the cells connected by and what does this enable them to do?
at the most lateral edge
A spermatogonia undergo mitosis
a pool of stem cells
intercellular bridges enabling them to divide in unison towards the lumen
Spermatogenesis: Why do some spermatogonia not have intercellular bridges?
to replenish the pool of germ cells so continuous sperm production can occur
Spermatogenesis: What do Primary spermatocytes undergo to give secondary spermatocytes?
- What about secondary spermatocytes to give spermatids?
meiosis 1
meiosis 2
Spermatogenesis: State the 4 phases of differentiation
Golgi phase
cap phase
acrosomal phase
maturation phase
Spermatogenesis: What happens in the Golgi phase? 6
vesicles inside Golgi apparatus fuse to form proacrosomal granules
these granules fuse to form an acromic vesicle
the acrostic vesicle contains an acrostic granule
centrioles move the the base of the nucleus
the proximal centriole anchors the tail to the nucleus
the distal centriole forms the central flagellum
Spermatogenesis: What happens in the Cap shape? 3
the acrostic vesicle forms a cap structure over the top of the nucleus
the Golgi apparatus migrate and disappear
the primitive flagellum forms
Spermatogenesis: What happens in the Acrosomal phase?
the acrosome spreads and the nucleus elongates
manchette tubules are formed
the neck and annulus are formed
Spermatogenesis: What happens during the Maturation phase?
the manchette form the post nuclear cap
the mitochondria form in a spiral assembly in the middle piece
Spermatogenesis:
- What is contained within there acrosome?
- What 4 sections is the tail composed of?
hydrolytic enzymes for penetrating the zona pellucida
capitum
middle piece
principle piece
terminal piece
Spermatogenesis: What is ‘one cycle of the seminiferous epithelium’?
- How long is it?
progression through a complete series of stages at one location along a seminiferous tubule
it varies between species
Spermatogenesis: How many different sections are there on the seminiferous epithelium?
- Do the intercellular bridges extend between sections?
8
no
Spermatogenesis: How many cycles does it take for spermiation to occur?
4.5 cycles
Spermatogenesis: How long does it take primary spermatocytes to become secondary spermatocytes?
- How long does it take secondary spermatocytes to become spermatids?
21 days
1.7 days
Spermatogenesis: What is a Spermatogenic wave?
the differences at any given instant in time along the seminiferous tubule
Spermatogenesis: What is spermatogenesis dependent on? 3
GnRH secretion from the hypothalamus
FSH and LH secretion from the anterior pituitary
Testosterone and Oestradiol secretion from the gonad
Spermatogenesis: What does LH do when released from the anterior pituitary?
it binds to receipts on Leydig cells
this stimulates Leydig cells to secrete testosterone
Spermatogenesis: What does FSH do when released? 4
it binds to receptors on Sertoli cells
this enables them to function
this stimulates Sertoli cells to convert testosterone to oestradiol
and they secrete inhibin
Spermatogenesis: After Leydig cells secrete testosterone, what happens to the testosterone?
some of the testosterone is converted in oestradiol by Sertoli cells under the influence of FSH
oestradiol has a negative feedback effect on the hypothalamus
some of the testosterone diffused into the seminiferous cords
it is converted into dihydrotestosterone
dihydrotestosterone has a negative feedback effect on the hypothalamus
Spermatogenesis: Which part of the Sperm contain the mitochondria needed to generate ATP for the flagellum to propel the sperm?
the middle piece
Spermatogenesis: Once the spermatids have differentiated into Spermatozoa, what happens?
- When in the head of the epididymis, explain whether or not they can fertilise an oocyte
spermatozoa are released into the seminiferous tubule lumen
they enter rete tubules
they travel through efferent ducts into the head of the epididymis
no they cannot as they are not fully mature or motile
Spermatogenesis: how long does it take for sperm to progress through the head, body and tail of the epididymis to become fully mature?
- What is happening to the sperm as they move further down the tubule? 2
2 weeks
they become more mature and motile
the cytoplasmic droplet is moving down the sperm
Spermatogenesis:
- Is the time taken to travel through the head and body variable?
- what about to go through the tail and why?
no it is fixed
yes because the tail has limited storage capacity
What is the function of seminal plasma? 6
it provides a transport medium for sperm
it contains fructose which provides nutritional support for sperm
it has a buffering capacity to protect sperm against the acidic conditions in the vagina
it contains antioxidants to get rid of free radicals formed by sperm during ATP production
it contains proteins which bind to the sperms head
prostaglandins produced from the prostate gland causes the muscles in the female tract to contract and helps sperm progress
Semen: Where is semen deposited in the cow?
- How much is deposited?
- how long is copulation?
in the cranial aspect of the vagina
1ml
1-3 seconds
Semen: Where is semen deposited in sheep?
- How much is deposited?
- how long is copulation?
in the vagina
8ml
1-2 seconds
Semen: Where is semen deposited in the sow?
- How much is deposited?
- how long is copulation?
in the cervix and leaks into uterus
250ml
5-20 minutes
Semen: Where is semen deposited in Camelids?
- How much is deposited?
- how long is copulation?
in the vagina and leaks into cervix and uterus
8ml
5-20 minutes
Semen: Where is semen deposited in the Horse?
- How much is deposited?
- how long is copulation?
in the cranial vagina and leaks into the cervix and vagina
100ml
60 seconds
Semen: Where is semen deposited in the dog?
- How much is deposited?
- how long is copulation?
in the vagina
3ml
5-45 minutes
Post Copulation: For species where sperm are not deposited in the cervix, the sperm need to cross the cervix to enter the uterus.
- Which species form a vaginal plug?
- What is it made from?
- What is its purpose? 2
rodents
coagulated semen
to prevent further mating
to prevent retrograde transport of sperm
Post Copulation: Why must fertilisation happen quickly after copulation?
because the sperm will be recognised as foreign by the immune system and destroyed
Post Copulation: when are sperm activated?
- Describe how they move 3
- what assists the transport of sperm?
after ejaculation
they swim in a straight line
their head rotates
their flagellum moves in a wave motion
contractions of the female tract
Post Copulation: State some tail abnormalities in sperm that would result in abnormal movement and lead to lower fertility 4
coiled tail
folded tail
detached head
double mid piece
Post Copulation: Cervix
- Via which pathway do sperm cross the cervix?
- Describe the journey of sperm across the cervix 2
- What is the purpose of the barrier this mucus presents? 2
the privilege pathway
the cervix secretes sulphomucin which is a highly viscous mucus secretion which the sperm cannot swim through
the cervix also secretes sialomucin which is a low viscosity mucus secretion which the sperm can swim through
to slow down the sperm to ensure there is a sperm reservoir
to remove any non-motile sperm
Post Copulation: Describe sperm transport through the uterus
- why is this the case? 3
it is rapid
due to elevated tone and motility of the muscular layers of the female tract
this is stimulated by oestradiol and oxytocin at oestrus
it is also stimulated by prostaglandins in the seminal fluid
Post Copulation: At the tip of the uterine horn, the sperm must cross which junction?
- Describe the lumen for the uterine tube
- What does passage through this tube require from sperm?
the uterine-tubal junction
narrow lumen
it requires vigorous sperm motility
Post Copulation: Uterine Tube (oviduct)
- Describe what happens to sperm immediately after entering the uterine tube
- what is the purpose of this?
- When do the sperm become motile again?
- What happens next?
sperm binds to epithelial cells via seminal proteins
to render them immotile and prolong their lifespan
around ovulation
they swim towards the ampulla region
What does ovulation induce in the oocyte?
completion of meiosis 1
Capacitation: Where does this usually occur?
- what happens? 5
in the uterine tube
decapacitation factors are removes
calcium and bicarbonate ions move into the sperm
this causes membrane destabilisation
the sperm detach from the oviduct epithelium and become hyperactive
they begin swimming towards the ampulla
Post Copulation: After capacitation, how has the movement of the flagellum changed?
it is moving asymmetrically at a high amplitude
Sperm reaches Oocyte: What has to happen prior to the acrosome reaction once the sperm reaches the oocyte?
there must be specific alignment of the sperm and oocyte
Sperm reaches Oocyte: Describe the composition of the Zona pellucida 3
it consists of 3 layers of glycoproteins
layer 3 expresses ZP3 receptors
this is the specific binding region
Acrosome Reaction: What is it initiated by?
- Describe what happens 7
the sperm binding to the zona pellucida
the acrosome releases hydrolytic enzymes
these digest the zona pellucida in a localised region
the sperm head penetrates the zona pellucida
this requires hyperactivity of the flagellum
the plasma membrane of the sperm fuses with the plasma membrane of the oocyte
the sperm nucleus enters the oocyte
the nuclei fuse
What does the action of sperm binding to the oocyte trigger in the oocyte?
an influx of calcium ions which indices completion of meiosis 2
Describe the events of the cortical reaction 3
- what is the purpose of this reaction?
the oocyte contains cortical granules near its membrane
their contents is released when the sperm binds to the oocyte
this causes the zona pellucida to harden
to destroy sperm receptors and prevent polyspermy
Ovulation: What is a spontaneous ovulator?
- What is an Induced ovulator?
where ovulation is independent of mating
where ovulation is stimulated by mating
Ovulation: Describe what happens at ovulation 4
the follicular wall bursts
the oocyte is released
the oocyte is carried with follicular fluid into the peritoneal cavity
the oocyte is captured by fimbria of the infundibulum
Define Fertilisation period
the period of time when oocytes are available to be fertilised by sperm
Define fertile period
the period of time when mating could result in pregnancy
Ovulation: When does a dogs oocyte get ovulated?
- How is this different from other species?
- What does this mean for the dog?
during metaphase of meiosis 1
ovulation induces completion of meiosis 1 in other species
completion of meiosis 2 and the formation of a second polar body occurs after fertilisation
State the fertilisation period for the Dog
- State their fertile period
2-5 days after ovulation
5 days before and 5 days after ovulation
What is embryonic diapause?
- Which species does this occur in?
temporary arrest of embryo development characterised by a delayed implantation in the uterus
marsupials
What is it called, before fusion of the nuclei, when the 2 pro-nuclei can both be seen in the cell?
- what is it called when the 2 nuclei fuse?
an ootid
syngamy
Embryo Development: After the nuclei fuse -
- what happens?
- what name can be given to these cells?
the zygote undergoes cleavage divisions
blastomeres
Embryo Development: What is different about cleavage divisions compared to other mitotic divisions?
- Why can blastomeres be thought of as ‘Totipotent’ until the Morula stage?
- After cleavage divisions have made 16 blastomeres, what is this 16 cell embryo called?
there is no cytoplasm synthesis so blastomere volume decreases
because each blastomere has the ability to form all cells necessary for normal embryo devleopment
a morula
Embryo Development: Describe the inner structure of the morula 3
the outer cells within the morula are more squashed than the inner cells
the outer cells form tight junctions
the inner cells form gap junctions
Embryo Development: What do the Outermost cells of the morula do?
- What is the consequence of this? 3
they pump sodium ions into the morula
this decreases the water potential inside the morula
so water diffuses into the morula by osmosis
fluid accumulates inside the morula
Embryo Development: What can be call the Morula once water influx has formed a distinct cavity inside?
a blastocyst
Blastocyst: What do the outer cells become?
- What do the inner cells become?
the trophoblast
the inner cell mass
Blastocyst: Why is pressure building inside the blastocyst? 3
because cells are still undergoing mitotic divisions
and fluid is still diffusing into the cell
and the hard zona pellucida provides a fixed volume
Blastocyst: The pressure inside the Blastocyst is high.
- what do trophoblast cells do?
- What consequence does this have?
they secrete proteolytic enzymes
this weakens the zona pellucida
it splits
the blastocyst emerges
Conceptus Progression: After fertilisation, is the embryo continually progressing towards the uterus?
yes
Conceptus Progression: Describe the progression of the conceptus in the sow and rabbit
slow and continuous
Conceptus Progression: Describe the progression in the cow, ewe and human
- What does this mean?
- How does this occur?
- Does this occur for non-fertilised oocytes too?
discontinuous progression
there is a prolonged stay in the uterine tube
anti peristaltic contractions maintain the conceptus in the uterine tube for 2-3 days
then stronger peristaltic contractions progress the conceptus forward
yes
Conceptus Progression: Describe the progression of the conceptus in the mare
- What does this mean?
- How does this work? 2
fertilised progression
only fertilised embryos pass into the uterus
the embryo secretes prostaglandins e and f
these promote embryo migration through the uterine tube and into the uterus
After Blastocyst Hatching: what do endometrial glands do?
it secretes histotroph which provides nutritional support before the placenta is established
Membrane Formation:
- What does the inner cell mass give rise to?
- what will each layer form?
the epiblast and hypoblast
the epiblast will form amniotic ectoderm so the amnion
the hypoblast will form primitive endoderm so the yolk sac
Membrane Formation: What does the hypoblast do?
it grows down and forms a cavity within the trophoblast called the yolk sac
Membrane Formation: Extraembryonic mesoderm appears
- What does it do? 3
it grows ventrally forming a sac surrounding the yolk sac
it grows dorsally forming amniotic folds
the mesoderm fuses with the trophoblast where they meet forming the chorion
Membrane Formation:
- What is the Allantois?
- Describe its growth 2
an out pouching of the hindgut
it grows as the yolk sac regresses
it fuses with the chorion where is meets forming the chorioallantoic membrane
Membrane Formation: Gastrulation
- Where does it begin?
- What happens
at the caudal end of the embryo where the node arises
cells from the epiblast migrate through the primitive streak
they differentiate into the ectoderm, mesoderm and endoderm
Establishing Pregnancy: In the absence of an Embryo, what happens? (excluding the bitch)
luteolysis is induced by prostaglandin f2 alpha
this causes progesterone to decline
the dam will return to oestrus within a few days
Establishing Pregnancy: Describe what happens in Ruminants if no embryo is present 5
oxytocin receptors are absent for most of the luteal phase
oxytocin receptors eventually appear in the endometrium
oxytocin produced from the corpus luteum binds to oxytocin receptors
this stimulates prostaglandin release
prostaglandin induces luteolysis
Establishing Pregnancy: Knowing how luteolysis is induced, what type of compound could delay luteolysis?
an oxytocin receptor antagonist
Establishing Pregnancy: Are oxytocin receptors present in the luminal epithelium throughout dioestrus? 2
no they are suppressed by progesterone
they appear by an unknown mechanism jut before luteolysis
Establishing Pregnancy: After Oxytocin binds to the Oxytocin receptor in the endometrium, what happens?
- In ruminants, how does this prostaglandin act directly on the ovary?
it stimulates pulsatile release of prostaglandin f2 alpha from the endometrium
due to a counter current system
Establishing Pregnancy: Which hormone increases during luteolysis?
- What effect does this have on luteolysis?
oestradiol
it increases oxytocin receptor transmission so speeds up luteolysis
Establishing Pregnancy: Describe the positive feedback loop during Luteolysis 2
endometrial prostaglandin stimulates the corpus luteum to release more oxytocin
oxytocin stimulate the production of more endometrial prostaglandin
Maternal Recognition: Why is maternal recognition of pregnancy required?
to avoid luteolysis and sustain the pregnancy
Maternal Recognition: What is the function of Prostaglandin in sustaining a pregnancy? 3
it maintains uterine gland secretion of histotroph
it suppresses myometrial contractions and luteolysis
it suppresses GnRH secretions to reduce follicular maturation to suppress ovulation
Maternal Recognition: What is the Embryonic Signal In Ruminants?
- Describe how this is produced 3
- How long is it expressed for?
Interferon Tau
the blastocyst starts expressing this protein during trophoblast elongation
it is expressed by trophectoderm cells
its expression is stimulated by growth factors secreted by the uterus
between days 12-24 of pregnancy
Maternal Recognition: Do all embryos secrete the same amount?
- Where does it remain after secretion?
- What is a lack of Interferon Tau associated with?
no secretion is relative to embryo size
in the lumen of the uterus where it exerts its action
embryo mortality
Maternal Recognition: Ruminants and Interferon Tau
- Where does IFT exert its action?
- What does it do? 3
on the endometrium
it suppresses oxytocin receptor expression
it stimulates protein synthesis critical for embryo growth
it has antiviral activity
Maternal Recognition: What is the conceptus signal in Pigs?
- When is this secreted?
- Is it detectable in plasma?
- What does it do?
oestradiol
just before implantation
slightly
it redirects the flow of prostaglandin away from the uterine vein
Maternal Recognition: What is the conceptus signal in horses?
- What do we know? 2
it is unknown
the embryo suppresses oxytocin receptors
no blastocyst interferons are produced
Maternal Recognition: What is the conceptus signal in primates?
- What is different about the luteolytic mechanism in primates?
- Hence, what does the conceptus signal do?
chorionic gonadotrophin
prostaglandin f2 alpha is secreted by the ovary
it acts on LH receptors on the corpus luteum to suppress prostaglandin release form the ovary
Maternal Recognition: What is the Conceptus signal in dogs?
- What does this mean?
there is no maternal recognition of pregnancy
the non-pregnant female will enter pseudopregnancy
Timing of Maternal recognition of Pregnancy:
- For which animals does it occur before implantation?
- State the day it occurs for each
cow - day 16
ewe - day 13
sow - day 12
Timing of Maternal recognition of Pregnancy:
- For which animals does it occur in Mid gestation?
rabbits and rodents
Timing of Maternal recognition of Pregnancy:
- Which species dont have maternal recognition of pregnancy?
dogs and ferrets
Timing of Maternal recognition of Pregnancy:
- When does Equine maternal recognition occur?
day 14
State the Gestation Lengths for the following species:
- Dog
- Cat
- sheep
- cow
- horse
- pig
- rabbit
63-65 days
63 days
150 days
285 days
330 days
114 days
31 days
