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MedST IB: Human Reproduction (HR) > 8.0 Coition, Fertilisation and Blastocyst Development > Flashcards

8.0 Coition, Fertilisation and Blastocyst Development Flashcards

1
Q

What are the stages of human sexual responses:

A

<b>EPOR model of sexual responses</b><br></br><br></br>Excitement → Plateau → Orgasm → Resolution

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2
Q

During erection what occurs to the pressure of the:<br></br>1) Corpora cavernosa<br></br>2) Corpus spongiosum

A

<b>1) Corpora cavernosa</b><br></br>Pressure ↑ → erection<br></br>It is surrounded by thick fibrous capsule<br></br><br></br><b>2) Corpus spongiosum</b><br></br>Pressure must remain low to maintain patency of urethra

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3
Q

What are the hemodynamic events that occur in:<br></br>1) Flaccidity<br></br>2) Tumescence<br></br>3) Erection<br></br>4) Detumescence

A

<b>1) Flaccidity</b><br></br>- Arterial input blocked by smooth muscle mounds<br></br>- Pressure in corpus cavernosum < pressure of artery<br></br><br></br><b>2) Tumescence</b><br></br>- PSNS stimulation (S2, S3, S4)<br></br>- ↑ blood flow (nNOS → NO → GC → ↑ cGMP)<br></br>- Within 30 seconds: ↑ pressure in cavernosum + engorgement<br></br><br></br><b>3) Erection</b><br></br>- Full arterial input (relaxation of smooth muscle at arterial input)<br></br>- Reduced blood flow<br></br>- ↓ venous drainage → ↑↑↑ pressure<br></br><br></br><b>4) Detumescence</b><br></br>- SNS → adrenergic tone → smooth muscle constriction<br></br>- Causes ↓ arterial flow and ↑ venous flow → ↓ pressure

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4
Q

How does viagra work?

A

Inhibits PDE5 → maintains levels of cGMP → smooth muscle relaxation

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5
Q

What muscle contracts to further increase the rigidity of the penis?

A

Ischiocavernosus

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6
Q

What is the bulbospongiosus reflex?<br></br>What nerve mediates it?

A

Pressure on glans → contraction of ischiocavernosus<br></br><br></br>Mediated by pudendal nerve (S2,3,4)

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7
Q

What are causes of erectile dysfunction?

A

<b>1) Psychogenic</b> 30-50%<br></br><b>2) Organic</b> 50-70%<br></br>- Neurogenic (MS, DM, trauma, disc lesions)<br></br>- Arteriogenic (HTN, DM, hyperlipidaemia)<br></br>- Drugs (Anti-HTN, Antidepressants)<br></br>- Endocrine (Low testosterone, high prolactin)

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8
Q

How does sperm get from testis to the epididymis

A

Via <b>vasa efferentia</b><br></br>Passive<br></br>Bulk flow<br></br>Sperm at this stage is non-motile and non-fertile

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9
Q

How does sperm move from epididymis to vas deferens?

A

Via muscular contractions<br></br><br></br>90% of fluid is absorbed → ↑ spermatocrit

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10
Q

Where do sperm mature?

A

Epididymis

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11
Q

What occurs in sperm maturation?

A

They become potentially fertile and motile<br></br>Cytoplasmic droplet is lost<br></br>Membrane lipid = more fluid<br></br>↑ surface glycoproteins + sialic acid

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12
Q

How do sperm gain the ability to move?

A

↑ cAMP content in tail/flagellum<br></br><br></br>↑ rigidity of these structures due to disulphide bonds

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13
Q

What hormone is needed for male accessory sex gland activity?

A

Androgens (5-DHT)

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14
Q

What is the function of seminal plasma/fluid?

A

1) Provides vehicle for sperm function<br></br>2) Nutritional factors<br></br><br></br><b>Not essential for sperm function</b>

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15
Q

Regarding seminal plasma/fluid, comment on the following:<br></br><br></br>Amount<br></br>Nutrition<br></br>pH<br></br>Other characteristics

A

<b>Amount:</b> 3-5ml<br></br><b>Nutrition:</b> Fructose<br></br><b>pH:</b> Alkaline (7-8)<br></br><b>Other characteristics:</b><br></br>- Antioxidants<br></br>- Prostaglandins (muscle stimulant)<br></br>- Leukocytes

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16
Q

What structures contract to cause ejaculation?

A

1) Urethra<br></br>2) Bulbospongiosus<br></br>3) Ischiocavernosus<br></br><br></br>Controlled by pudendal nerve

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17
Q

What percentage of the total ejaculate is early, mid or late?<br></br><br></br>Where does the ejaculate come from at each stage?

A

Early = 30% from prostate<br></br>Mid = 10% from vas deferens<br></br>Late = 60% from seminal vesicle

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18
Q

What are the contents of semen? Where do they come from?

A

1) Spermatozoa (vas deferens)<br></br>2) Seminal fluid (prostate and seminal vesicle)<br></br>3) Lubricant (Cowper’s glands)

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19
Q

During female arousal, what do the following cause:<br></br>1) Corpora cavernosa<br></br>2) Corpus spongiosum

A

<b>1) Corpora cavernosa</b><br></br>- Enlargement of clitoris<br></br><br></br><b>2) Corpus spongiosa</b><br></br>- Enlargement and eversion of labia minora

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20
Q

What provides lubrication to the female?

A

Vestibular glands (Bartholin’s duct + cervix)

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21
Q

What are the three aspects to the female sexual response?

A

<b>1) Transudation</b><br></br>- Lubrication of vagina + vestibule via vascular engorgement<br></br><br></br><b>2) Tenting effect</b><br></br>- Dilation of upper part of vagina caused by ↑ stimulation<br></br><br></br><b>3) Uterine elevation</b>

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22
Q

Comment on the cervical secretions and os during:<br></br>1) Oestrogen dominance<br></br>2) Progesterone dominance

A

<b>1) Oestrogen dominance</b><br></br>- Watery secretions (Spinnbarkeit)<br></br>- Os = open<br></br>- Good for sperm<br></br><br></br><b>2) Progesterone dominance</b><br></br>- Thick secretions (Ferning)<br></br>- Os = closed

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23
Q

How many sperm are inseminated?

A

350,000,000

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24
Q

Semen initially coagulates but then liquefies 20-60mins later. What causes this?

A

Activation of pro-enzymes

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25
Where does capacitation occur?
In the uterus
26
What does capacitation involve?
1) Loss of membrane cholesterol
2) Loss of glycoproteins
3) Influx of Ca²⁺ → ↑cAMP + activation of PKA
4) Mitochondrial changes
27
What can reverse capacitation?
Semen
28
An ovulated oocyte + cumulus is picked up by _________. Cilia beat in the direction from ovary to uterus. These cilia are stimulated by __________. Muscle contractions also help move the oocyte along
An ovulated oocyte + cumulus is picked up by fimbriae. Cilia beat in the direction from ovary to uterus. These cilia are stimulated by oestrogen. Muscle contractions also help move the oocyte along
29
What is Mittelschermz pain?
Pain caused by bleeding into peritoneal cavity from ovulation
30
Where does fertilisation take place?
In the ampulla region of the fallopian tube
31
What occurs to sperm at the isthmus of the fallopian tube?
They become briefly immobile (bind to oviduct epithelial cells)

Purpose =
1) Stabilizes sperm following capacitation
2) ↑ fecundity because creates a pool of sperm
32
What are the steps of fertilisation?
1) Sperm activation
2) Establishment of diploidy (prevention of polyploidy)
3) Activation of oovum
33
What causes sperm activation?
Binding to the oocyte
Induced by:
1) Progesterone
2) Binding to zona proteins (ZP1,3 and 4)
34
What occurs in sperm activation?
1) Changes in tail movement
- Ca²⁺ channels open → PKC activation
2) Acrosome reaction
35
What is required for acrosome reaction?
Phospholipase C
SNARE
36
What is the outcome of acrosome reaction?
1) Release of hyaluronidase
2) Exposure of acrosin (on inner acrosomal membrane)
37
What are zona pellucida proteins?
Large glycoproteins (glycosylation is important for sperm binding)
ZP1
ZP2
ZP3
ZP4
38
Which zona pellucida proteins induce acrosomal reaction?
ZP1

ZP3
ZP4
39
What happens on sperm binding to ZP2?
Weak binding
Allows progression through zona
40
What does sperm use for penetration?
1) Acrosome (a protease)
2) Physical movement
41
What space does sperm enter after penetration?
Pre-vitelline space
42
How long does sperm penetration take?
5-20mins
43
Where does membrane fusion (Sperm + oocyte) occur?
At the equitorial region
44
What 3 proteins are essential for binding + fusion?
1) Izumo 1 - on sperm
2) Juno - on oocyte
3) CD9 - on oocyte

Izumo1 binds to Juno. CD9 = binding partner
45
What are the steps for activation of oocyte?
Calcium waves → activation

Activation =
1) Cortical reaction (release of cortical granules)
2) Ovastacin (cleaves binding sites ZP3/4 + ZP2)
3) ZP proteins become cross linked
4) Juno is exocytosed
46
How often are the wave of calcium release?
Every 3-15 mins for 4-5 hours
47
What enzyme initiates calcium release?
PLCζ (from sperm)
48
What are the events following activation of oocyte?
1) Re-entry of meiosis
- And extrusion of second polar body

2) Pro-nucleus formation

3) Syngamy
- Pronuclear membrane breaks down → brief existence of dilpod nuclei
49
What does the oocyte contribute to offspring?
1) Membrane
2) Golgi
3) ER
4) Ribosomes
5) Pronucleus (haploid)
6) Centrosomes (meiotic spindles)
7) Mitochondria
8) Cytoplasm
50
What does the sperm contribute to offspring?
1) Pronucelus (haploid)
2) Centriole
3) Small non-coding RNA
51
What is a complete hydratiform mole?
46 XX
All genes are paternal
Snowstorm appearance on US
+++ hCG
Potentially malignant
52
Methylated genes are ________
Unmethylated genes are ________
Methylated genes are off genes
Unmethylated genes are on genes
53
What does the conflict theory state?
Paternal genes → ↑ placental growth

Maternal genes → Constrain fetal growth
54
What is a zygote?
Newly fertilised oocyte
55
What is a morula?
8-16 cell stage
All cells are totipotent (have the ability to form own individual)
56
When does compaction occur?
Morula stage
57
What processes are involved in compaction?
1) Maximizing cell adhesion
2) Creating cell polarity (initiates cell specialisation)
58
What causes formation of bastocele?
Ion gradients cause water influx
59
What do the following structures found in the blastocyst become?

1) Trophoectoderm (trophoblast)

2) Inner cell mass
Trophoectoderm (trophoblast) → placenta

Inner cell mass → fetus (+ contributes to mesoderm of placenta)
60
What is the role and location for:

1) Oct4

2) Cdx2
1) Oct4
- Promotes pluripotency
- Found in inner cell mass by blastocyst stage

2) Cdx2
- Determines trophoblast lineage
- Found in trophoblast by blastocyst stage
61
How does Hippo regulate expression of cdx2?
Yap is a transcription factor that activates cdx2

Hippo is a kinase that inactivates Yap

Hippo is found in the non-depolarised cells of the inner cell mass (hence no cdx2 in inner cell mass)
62
What mechanisms transport the zygote along the fallopian tube?
Cilia (essential)
Smooth muscle contraction (non-essential)
63
When does the conceptus enter the uterus?
3.5 days post fertilisation
64
The lumen of the fallopian tube is narrow. What can cause it to obstruct?
1) Infection (Chlamydia)
2) Scarring
65
Where does a zygote receive its nutrition?
From secretions of the oviduct cells and later from endometrial glands
66
What are the metabolic requirements for:

1) Fertilised ovum
2) 2-cell stage
3) 8-cell stage
4) Blastocyst
1) Fertilised ovum
- Pyruvate

2) 2-cell stage
- Pyruvate and lactate

3) 8-cell stage
- Glucose and essential amino acids

4) Blastocyst
- Simple sugars
67
What is blastocyst hatching?
Where does it occur?
What does it need?
Hatching = hatching from zona pellucida
Occurs in uterus
Requires proteases
68
Where does implantation occur in humans?
Fundus of uterus
Interstitial implantation (as opposed to central as seem in most animals)
69
What is placenta praevia?
Low implantation, such that the placenta covers the cervical opening
70
What hormone is dominant in the implantation window?
Progesterone (but an oestrogen burst is needed for implantation)
71
What are the changes to endometrial lining in implantation window?
1) ↓ progesterone receptors
2) Thinner mucin glycoprotein coat
3) Loss of -ve charge
4) Pinopores to absorb uterine fluid
5) Shorter microvilli
72
What are the molecular steps in blastocyst implantation?
1) ↓ glycosylation of MUC1 allows protein - protein intereaction between blastocyst and endometrium

2) LIF → has effects on trophoblast and endometrium
- Endometrium → ↑ HB-EGF receptors (these bind to HSPG on trophoblas)

3) HB-EGF - HSPG interation → ↑ integrins on both trophoblast and endometrium
73
What does LIF cause?
- Endometrium → ↑ HB-EGF receptors (these bind to HSPG on trophoblas)
74
What causes blastocyst invasion?
Matrix metalloproteinases (MMPs)
75
What is decidualization?
Transformation of endometrial cells from spindly cells to large, round (decidual) cells
76
What are the three regions of the decidua?
1) Basalis (beneath conceptus)
2) Capsularis (around conceptus)
3) Parietalis (rest of uterus)
77
What secretes hCG?
Trophoblast (STB)
78
What is the vanishing twin phenomenon?
When one twin miscarried and the other fetus resorbs them

MedST IB: Human Reproduction (HR) (13 decks)

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