Fertilisation & week 1 development Flashcards
Superior
above something else towards the head
Cranial
towards the head
caudal
towards the tail
Vental
Towards the front (umbilical cord)
Dorsal
Towards the back
Transverse plain
Dividing the cranial from the caudal (cutting embryo across waist)
Sagittal section
Dividing the embryo into right and left halves
Coronal section
dividing the embryo up into ventral and dorsal (taking a slice down the “front” of the embryo)
Two techniques used to date a pregnancy
Menstrual age
Fertilisation age
How is Menstrual age used?
- Used by clinicians
Dates pregnancy from the womens first day of last menstrual period
Used as: - Cheap
- Fairly reliable
- Easy to identify
Three equal trimesters
1= 1st day of last period-12 weeks
2= 12 weeks+ 1 day to 28 weeks
3= week 28+1 to week40
How is fertilisation age used?
- Used by embryologists
More specific
Divided into 3 stages - Early development (cell division, pre- embryonic)
- Embryonic (organogenesis) period (E)
- Foetal period (F)
How common are human birth defects?
1 in 44 births in UK
Major causes of congenital malformations
Unknown (idiopathic) = 50%
Multifactorial= 25%
Major environmental= 7%
Monogenic= 8%
Chromosomal= 10%
Percentage of birth defects detected prenatal
<60%
Genetic & environmental
- Meiosis
- Mitosis
EN - Teratogens
Genetic causes of birth defects
Monogenic
- defective gene on autosome
Chromosomal
- Numerical (aneuploidy)
E.G.
Patau
Edwards
Downs
- Structural
E.G.
Cri du chat
Pallister killian syndrome
Symptoms of genetic causes
- Growth retardation
- Intellectual impairment
- Craniofacial development
- Congenital heart defects
What are teratogens?
Environmental influence that is “monster forming”
Examples of Teratogens
Infections (TORCH)
Chemicals
Physical
Maternal disease
Deficiency
Sensitivity to teratogens
Risk of congenital malformations from teratogens is at the highest when exposed between 3-5 weeks fertilisation
age
Before 3 weeks, no
placenta. So likelihood
of abnormality at this time
is very low as pregnancy
would likely just not survive
What does TORCH stand for?
Toxoplasmosis
Other (Hep B, Syphilis)
Rubella (German measles)
Cytomegalovirus (CMV)
Herpes simplex virus (HSV)
each of these diseases cross the placenta and may cause birth defects
Toxoplasmosis & congenital malformations
- Paracite
- Found in cat faeces and undercooked raw meat
- Usually asymptomatic
Congenital malformations
- Inflammation of retina and eye/ microphthalmia
- Hearing loss
- Enlarged liver spleen
- Hydrocephaly
- Microcephaly
Rubella & congenital malformations
- Infection passes over placenta in first 3 months of pregnancy
- Rates of rubella have decreased since the MMR vaccine
Congenital malformations
- Cloudy cornea
- Intellectual disability
- Microcephaly
- Heart defects
Cytomegalovirus (CMV) & congenital malformations
- Virus that crosses the placenta
- Infection via bodily fluids
- Usually asymptomatic
Congenital malformations
- Inflammation of retina/ microphthalmia
- Enlarged spleen or liver
- Mineral deposits on the brain
- Microcephaly
- Psychomotor impediments
Herpes virus & congenital malformations
Herpes simplex
- Varicella zoster virus (chicken pox)
- Most dangerous in between 13-20 weeks or just before birth to two days pp
Congenital malformations
- Segmental skinloss/ scarring
- Limb hypoplasia/ paresis
- Microcephaly
- Visual defects
Zika virus & congenital malformations
- Mosquito
- Bodily fluids (of injected person)
- Fever, rash, joint pain, red eyes
Congenital malformations
- Microcephaly
- Severe cognitive disabilities
Chemical- Thalidomide
- Developed in west germany in 1950s
- Prescribed for morning sickness
- Shortened or absent limbs
- Now used to treat leprosy and HIV
Chemical- alcohol
- Clear relationship between alcohol consumption and congenital abnormalities
Associated with:
- Prenatal and postnatal growth retardation
- Intellectual disability
- Impaired motor ability and coordination
Foetal alcohol syndrome
- smell eye openings
- Smooth philtrum
- Thin upper lip
Radiation & congenital malformations
- Causes cell death or chromosome changes
- CNS most sensitive
- Most sensitive in the first trimester
Congenital malfomations
- Microcephaly
- Mental and cognitive disabilities
- Haemopoietic malignancies and leukemia
Maternal disease & congenital malformations
- Can cause cellular structural defects and changes in cellular physiology
Congenital malformations
- Macrosomia
- Ventricular septal defects
- Spina bifida
- Renal agenesis
Folic acid deficiency & congenital malformations
- Malformations in CNS
- OTC supplements reduce risk of malformation by around 60%
Congenital malformations
- Spina bifida
- Anencephaly
What are the 4 features of male gametes
- plasma membrane
- Head (acrosome, nucleus)
- Middle piece (loaded with mitochondria)
- Tail (Flagellum)
What are the 6 features of female gametes
- Cortical granules
- Zona pellucida
- Cell membrane
- Cytoplasm
- Pronucleus
- Corona Radiata
Outline of the hormone cycle
Referred to as the HPG axis
Begins in the thalamus
Moves to pituitary and travels to the gonads (in the case of bio females, the ovaries)
Acts on gametes to begin maturation
What does the hypothalamus screte?
GnRH
What does secretion of GnRH cause?
acts on neurones in the anterior pituitary gland and causes the release of gonadotropins:
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
Formation of primary follicle
Local androgens act on the primordial follicle (diploid) to encourage development into a primary follicle (2n).
Primary follicle to late secondary follicle
Primary follicle develops into an early secondary follicle through addition of ++FSH and +LH from the anterior pituitary. FSH + LH + Cholesterol + Androgens = Oestrogen
Steps repeated for ESF to form LSF
Late secondary follicle to graafian follicle
Late Secondary follicle begins creating pools of follicular fluid, stimulated by FSH and LH, oestrogen is produced, late secondary follicle divides producing a polar body and a secondary oocyte (n) enclosed in the graafian follicle
Pools of follicular fluid coalesce and form an antrum in graafian follicle
What does oestrogen do to HPG axis?
decrease FSH and LH output until threshold oestrogen is met
What happens when threshold oestrogen is met?
graafian follicle releases Inhibin B, which decreases production of FSH and Oestrogen feeds positively on anterior pituitary to secrete huge surge of LH.
What does LH do to vessels?
acts on vessels local to graafian follicle to become leaky and as a result, the antrum swells
LH activates proteases anchoring secondary oocyte within graafian follicle
What happens to the secondary oocyte within the graafian follicle?
Pressure and lack of anchor cause eruption of secondary oocyte out of graafian follicle- OVULATION
What happens to the remainder of the graafian follicle
LH transforms it into corpus luteum, produces progesterone & oestrogen for 10 days. If no fertilisation of secondary oocyte, corpus luteum degrades and pro & oestro drop.
What happens if fertilisation occurs?
syncytiotrophoblasts of blastocyst secrete hCG which signals corpus luteum to maintain oestrogen and progesterone secretion to support the pregnancy until a placenta can take over.
Overview of fertilisation
- Fusion of male & female gametes to form zygote
- Capacitation of sperm
- Acrosome reaction
- Formation of zygote
- Fusion of pronuclei
Where does fertilisation usually occur?
- Ampulla of the uterine tube
- Fimbriae sweep oocyte (Egg) into the uterine tube
- Sperm undergo capacitation in female reproductive tract
What is a zygote?
oocyte + sperm
What happens to capacitated sperm?
- Pass through corona radiate
- Acrosome releases enzymes that allow sperm to penetrate zona pellucida
- Sperm penetration initiates cortical reaction (prevents any more sperm entering oocyte- now zygote)
- Zona pellucida becomes impenetrable= zone reaction
What happens on days 1-3 post fertilisation
0= fertilisation day
every 24 hours zygote divides by cleavage= doubles number of cells (blastomeres)
Formation of morula
Day 4
16-32 cells
Inner cell mass= embryo proper (embryoblasts)
Outer cell mass= placenta (trophoblasts)
Formation of Blastocyst
Formation of fluid filled cavity by day 5
Separates cells into a:
- Compact mass (embryoblasts)
- Thinner outer layer (trophoblasts)
Zona Pelludica jacket breaks away (shed) as teh blastocyst makes its way into the body of the uterus allowing the uterine attachment
