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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
Q

Where does capacitation occur?

A

In the uterus

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26
Q

What does capacitation involve?

A

1) Loss of membrane cholesterol<br></br>2) Loss of glycoproteins<br></br>3) Influx of Ca²⁺ → ↑cAMP + activation of PKA<br></br>4) Mitochondrial changes

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27
Q

What can reverse capacitation?

A

Semen

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28
Q

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

A

An ovulated oocyte + cumulus is picked up by <b>fimbriae</b>. Cilia beat in the direction from ovary to uterus. These cilia are stimulated by <b>oestrogen</b>. Muscle contractions also help move the oocyte along

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29
Q

What is Mittelschermz pain?

A

Pain caused by bleeding into peritoneal cavity from ovulation

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30
Q

Where does fertilisation take place?

A

In the ampulla region of the fallopian tube

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31
Q

What occurs to sperm at the isthmus of the fallopian tube?

A

They become briefly immobile (bind to oviduct epithelial cells)<br></br><br></br>Purpose = <br></br>1) Stabilizes sperm following capacitation<br></br>2) ↑ fecundity because creates a pool of sperm

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32
Q

What are the steps of fertilisation?

A

1) Sperm activation<br></br>2) Establishment of diploidy (prevention of polyploidy)<br></br>3) Activation of oovum

33
Q

What causes sperm activation?

A

Binding to the oocyte<br></br>Induced by:<br></br>1) Progesterone<br></br>2) Binding to zona proteins (ZP1,3 and 4)

34
Q

What occurs in sperm activation?

A

<b>1) Changes in tail movement</b><br></br>- Ca²⁺ channels open → PKC activation<br></br><b>2) Acrosome reaction</b>

35
Q

What is required for acrosome reaction?

A

Phospholipase C<br></br>SNARE

36
Q

What is the outcome of acrosome reaction?

A

1) Release of hyaluronidase<br></br>2) Exposure of acrosin (on inner acrosomal membrane)

37
Q

What are zona pellucida proteins?

A

Large glycoproteins (glycosylation is important for sperm binding)<br></br>ZP1<br></br>ZP2<br></br>ZP3<br></br>ZP4

38
Q

Which zona pellucida proteins induce acrosomal reaction?

A

ZP1<br></br><br></br>ZP3<br></br>ZP4

39
Q

What happens on sperm binding to ZP2?

A

Weak binding<br></br>Allows progression through zona

40
Q

What does sperm use for penetration?

A

1) Acrosome (a protease)<br></br>2) Physical movement

41
Q

What space does sperm enter after penetration?

A

Pre-vitelline space

42
Q

How long does sperm penetration take?

A

5-20mins

43
Q

Where does membrane fusion (Sperm + oocyte) occur?

A

At the equitorial region

44
Q

What 3 proteins are essential for binding + fusion?

A

<b>1) Izumo 1</b> - on sperm<br></br><b>2) Juno</b> - on oocyte<br></br><b>3) CD9</b> - on oocyte<br></br><br></br>Izumo1 binds to Juno. CD9 = binding partner

45
Q

What are the steps for activation of oocyte?

A

Calcium waves → activation<br></br><br></br>Activation =<br></br>1) Cortical reaction (release of cortical granules)<br></br>2) Ovastacin (cleaves binding sites ZP3/4 + ZP2)<br></br>3) ZP proteins become cross linked<br></br>4) Juno is exocytosed

46
Q

How often are the wave of calcium release?

A

Every 3-15 mins for 4-5 hours

47
Q

What enzyme initiates calcium release?

A

PLCζ (from sperm)

48
Q

What are the events following activation of oocyte?

A

<b>1) Re-entry of meiosis</b><br></br>- And extrusion of second polar body<br></br><br></br><b>2) Pro-nucleus formation</b><br></br><br></br><b>3) Syngamy</b><br></br>- Pronuclear membrane breaks down → brief existence of dilpod nuclei

49
Q

What does the oocyte contribute to offspring?

A

1) Membrane<br></br>2) Golgi<br></br>3) ER<br></br>4) Ribosomes<br></br>5) Pronucleus (haploid)<br></br>6) Centrosomes (meiotic spindles)<br></br>7) Mitochondria<br></br>8) Cytoplasm

50
Q

What does the sperm contribute to offspring?

A

1) Pronucelus (haploid)<br></br>2) Centriole<br></br>3) Small non-coding RNA

51
Q

What is a complete hydratiform mole?

A

46 XX<br></br>All genes are paternal<br></br>Snowstorm appearance on US<br></br>+++ hCG<br></br>Potentially malignant

52
Q

Methylated genes are ________<br></br>Unmethylated genes are ________

A

Methylated genes are off genes<br></br>Unmethylated genes are on genes

53
Q

What does the conflict theory state?

A

Paternal genes → ↑ placental growth<br></br><br></br>Maternal genes → Constrain fetal growth

54
Q

What is a zygote?

A

Newly fertilised oocyte

55
Q

What is a morula?

A

8-16 cell stage<br></br>All cells are totipotent (have the ability to form own individual)

56
Q

When does compaction occur?

A

Morula stage

57
Q

What processes are involved in compaction?

A

1) Maximizing cell adhesion<br></br>2) Creating cell polarity (initiates cell specialisation)

58
Q

What causes formation of bastocele?

A

Ion gradients cause water influx

59
Q

What do the following structures found in the blastocyst become?<br></br><br></br>1) Trophoectoderm (trophoblast)<br></br><br></br>2) Inner cell mass

A

<b>Trophoectoderm (trophoblast)</b> → placenta<br></br><br></br><b>Inner cell mass</b> → fetus (+ contributes to mesoderm of placenta)

60
Q

What is the role and location for:<br></br><br></br>1) Oct4<br></br><br></br>2) Cdx2

A

1) Oct4<br></br>- Promotes pluripotency<br></br>- Found in inner cell mass by blastocyst stage<br></br><br></br>2) Cdx2<br></br>- Determines trophoblast lineage<br></br>- Found in trophoblast by blastocyst stage

61
Q

How does Hippo regulate expression of cdx2?

A

Yap is a transcription factor that activates cdx2<br></br><br></br>Hippo is a kinase that inactivates Yap<br></br><br></br>Hippo is found in the non-depolarised cells of the inner cell mass (hence no cdx2 in inner cell mass)

62
Q

What mechanisms transport the zygote along the fallopian tube?

A

Cilia (essential)<br></br>Smooth muscle contraction (non-essential)

63
Q

When does the conceptus enter the uterus?

A

3.5 days post fertilisation

64
Q

The lumen of the fallopian tube is narrow. What can cause it to obstruct?

A

1) Infection (Chlamydia)<br></br>2) Scarring

65
Q

Where does a zygote receive its nutrition?

A

From secretions of the oviduct cells and later from endometrial glands

66
Q

What are the metabolic requirements for:<br></br><br></br>1) Fertilised ovum<br></br>2) 2-cell stage<br></br>3) 8-cell stage<br></br>4) Blastocyst

A

<b>1) Fertilised ovum</b><br></br>- Pyruvate<br></br><br></br><b>2) 2-cell stage</b><br></br>- Pyruvate and lactate<br></br><br></br><b>3) 8-cell stage</b><br></br>- Glucose and essential amino acids<br></br><br></br><b>4) Blastocyst</b><br></br>- Simple sugars

67
Q

What is blastocyst hatching?<br></br>Where does it occur?<br></br>What does it need?

A

Hatching = hatching from zona pellucida<br></br>Occurs in uterus<br></br>Requires proteases

68
Q

Where does implantation occur in humans?

A

Fundus of uterus<br></br>Interstitial implantation (as opposed to central as seem in most animals)

69
Q

What is placenta praevia?

A

Low implantation, such that the placenta covers the cervical opening

70
Q

What hormone is dominant in the implantation window?

A

Progesterone (but an oestrogen burst is needed for implantation)

71
Q

What are the changes to endometrial lining in implantation window?

A

1) ↓ progesterone receptors<br></br>2) Thinner mucin glycoprotein coat<br></br>3) Loss of -ve charge<br></br>4) Pinopores to absorb uterine fluid<br></br>5) Shorter microvilli

72
Q

What are the molecular steps in blastocyst implantation?

A

<b>1) ↓ glycosylation of MUC1 allows protein - protein intereaction between blastocyst and endometrium</b><br></br><br></br><b>2) LIF → has effects on trophoblast and endometrium</b><br></br>- Endometrium → ↑ HB-EGF receptors (these bind to HSPG on trophoblas)<br></br><br></br><b>3) HB-EGF - HSPG interation → ↑ integrins on both trophoblast and endometrium</b>

73
Q

What does LIF cause?

A
  • Endometrium → ↑ HB-EGF receptors (these bind to HSPG on trophoblas)
74
Q

What causes blastocyst invasion?

A

Matrix metalloproteinases (MMPs)

75
Q

What is decidualization?

A

Transformation of endometrial cells from spindly cells to large, round (decidual) cells

76
Q

What are the three regions of the decidua?

A

1) Basalis (beneath conceptus)<br></br>2) Capsularis (around conceptus)<br></br>3) Parietalis (rest of uterus)

77
Q

What secretes hCG?

A

Trophoblast (STB)

78
Q

What is the vanishing twin phenomenon?

A

When one twin miscarried and the other fetus resorbs them

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

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