Embryo Implantation And Fetal Development 5.2.24 Flashcards
What are the stages in the ovarian cycle?
- Follicular phase , pre-ovulation
- Ovulation
- Luteal phase
How long is the average Ovarian cycle?
28 days
What is involved in the first stage of the Endometrial cycle?
1. Proliferative Phase
oestrogen - growth of the endometrium and myometrium , secretion of the mucus alongside the vagina and uterus
What is involved in the 2nd stage of the Endometrial cycle?
2. Secretory Phase
Oestrogen - grows the endometrium
Progesterone - softens the connective tissues in preparation for implantation and promotes secretion of nutrients ( fat and glycogen)
What is involved in the 3rd stage of the Endometrial cycle ?
3. menstrual phase
Only occurs if no fertilisation occurs
- Corpus leuteum decreases
- progesterone and oestrogen support is lost
- Uterine prostaglandins —> Vasoconstriction —> Tissue death
- Blood and endometrial debris (menses) lost through Vagina
How long can sperm survive for?
It can survive for up to 5 days but is only viable for 48 hours
What hormone does the Hypothalamus release?
GnRH
What hormone does the Anterior pituitary release?
LH/FSH
Which 2 hormones do the Ovaries release?
Oestrogen/ progesterone
What does GnRH stand for?
Gonadotropin hormone releasing hormone
What does a Rise in FSH stimulate?
Stimulates Oocyte (egg) development and follicular growth
What causes LH to spike?
Ovulation
IS ovulation a positive or negative feedback?
Positive
Is after ovulation positive or negative feedback?
Negative feedback due to progesterone
What process is Sperm is driven by to reach the oviduct?
Chemotaxis
How long after ovulation does fertilisation occur?
24 hours
what membrane do sperm penetrate?
The Corona Radiata
What do the sperm bind to after penetration?
Receptors on the Zona pellucida
What does the binding of sperm onto the receptors on Zona pellucida cause?
It causes an enzyme to be released form the acrosome that digest the Zona pellucida.
What reaction is triggered when the sperm head penetrates the ovum?
Cortical reaction
What does a cortical reaction trigger?
Inactivation of ZP3 receptor as and prevents polyspermy
when does Fusion of Nuclei occur?
Occurs within an hour triggering embryonic development
What are the 4 Stages of Ovum development?
1 - Ovum
2 - Cleavage
3 - Morula
4 - Blastocyst
What are the Stages of implantation?
- Blastocyst surface becomes sticky and adheres to endometrium
- The trophoblastic cells release protein-digesting enzymes
- Cords of trophoblastic cells go deeper into the endometrium
- The embraces of trophoblastic cells disintegrate
- Underlining endometrium produces prostaglandins that increase vascularisation and nutrients
- The embryo is implanted into the endometrium
What is the endometrium called after its been modified by prostaglandins?
Decidua
What is an ectopic pregnancy?
When implantation occurs outside of the uterus. Most typically in one of the fallopian tubes.
What is the cause for molar pregnancy?
Abnormal fertilisation
What is a molar pregnancy?
It’s where the trophoblastic tissue over grows and shows as a mass of cysts.
when there is a problem with fertilisation so the embryo and placenta don’t form correctly.
What is a molar pregnancy also known as?
Hydatiform pregnancy
What is the placenta responsible for?
Delivery of oxygen and nutrients
Removal of wastes and CO2 from the fetus
When is the developed Placenta?
What happens with the embryo when the placenta embeds itself?
Day 12 - embryo is embedded in the decidua
The placenta is well developed by 5 weeks after implantation (6 weeks of gestation)
This is when the embryonic heart starts pumping blood into the placental villi.
Fetal part of placenta starts secretion of hCG and progesterone.
Which Substances can cross the placenta barrier?
- cocaine and heroine
- Rubella virus
- Cytomegalovirus virus
- HIV
- Toxoplasma
- Treponema pallidum (syphilis)
what substances are transported From mother to fetus?
+ O2
+ water , electrolytes
+ Nutrients - carbohydrates, amino acids and lipids
+ Hormones
+ antibodies
+ Vitamins
+Iron and trace elements
+ drugs
+ toxic substances
+ viruses
what substances are transported From fetus to mother?
- CO2
- water, electrolytes
- urea, Uris acid
- Creatinine
- bilirubin
- Hormones
- red blood cells antigens
Which are the most common congenital abnormalities?
Heart
Neurotube defects
Down syndrome
Environmental factors that can cause birth defects
= thalidomide
=Radiation
=Alcohol
= Drugs
= smoking
= poisons
= infections (eg: rubella, toxoplasma Gondi, herpes)
What are some of the Genetic factors that can cause birth abnormalities?
- Chromosomal abnormalities
Eg: Down, turner, Patau syndromes - Mutant genes
Eg: achondroplasia, primordial dwarfism, fragile X syndrome and split foot anomaly
What are some Abnormalities that are visible at birth?
Spina bifid a
Cleft lip and palate
Gastroschisis/ exompholos
Anencephaly
Down syndrome
Under development of limbs
What are some of the Abnormalities invisible at birth?
Cardiac defects : tetralogy of fallout
Atresias
Rare congenital disorders eg: pain receptors
How many layers are there in the development of an embryo?
What are these layers?
3 - Ectoderm, mesoderm, endoderm
What are the Contents of the Ectoderm?
Structures that maintain contact with the outside world
- CNS and pNS
- Sensory apparatus of eye, ear and nose
- epidermis, hair and nails
- subcutaneous, mammary, pituitary glands
- enamel of the teeth
What are the Contents of the Mesoderm?
+ vertebral column
+ Dermatomes
+ Myotomes
+ urogenital structures
+ peritoneal, pleural and pericardial linings
+ Haemopoetic stem cells
What are the Contents of the endoderm?
~ GI tract
~ Epithelial linings of the respiratory tract
~ urinary bladder and urethra
~ tympanic cavity and auditory tube
~ parenchyma of thyroid, parathyroid, liver and Pancreas
What is the process of Neurulation?
The forming of the neural tubes during Fetal development
What are some of the Factors that impact the development of neural tubes and can cause defects?
- Anti-epileptic medication
- Maternal diabetes
- Hyperthermia
- High glucose + insulin
- Retinoic acid ( vitamin A metabolite)
What medicine can protect against neural tube defects?
- Folic acid supplementation can reduce the chance of defects by ~ 75% if started 2 months before conception
What is Spina bifida?
What are the different types of Spina Bifida?
Neural tube fails to close along its length
It involves the meninges, vertebrae, muscles and skin - sometimes neural structures
The spinal cord and nerves may be :
- open to the outside world - Spina bifida aperta
- covered with skin - Spina bifida occulta
- covered with just the surrounding membranes - Spina bifida cystica - meningocele or myelomeningocele
What type of Spina bifida is where the nerves are open?
Spina bifida aperta
Which type of Spina bifida are the nerves covered by skin
Spina bifida occulta
Which type of Spina bifida are the nerves covered with just the surrounding membranes ?
Spina bifida cystica, meningocele, mylomeningocele
What are the common neuro associations of Spina bifida?
Arnold chiari malformations and Hydrocephalus
How is Spina bifida detected and diagnosed?
Antenatal screening - elevated alpha fetoprotein levels
On ultrasound scan - routine scans 12 weeks and 20 weeks
What is the medical term for the Forebrain?
prosencephalon
What is the medical term for the Midbrain?
Mesencephalon
What is the medical term for the Hind brain?
Rhombencephalon
What gene controls Facial development?
Controlled by the HOX (homebox) gene
What happens in the 7th week of facial development?
The medial nasal prominences fuse to form the inter-maxillary segment
What is the resultant of the failure of fusion of the maxillary prominence and the inter-maxillary segment?
Cleft lip
What happens during during the 14th week of facial development?
The inter-maxillary process forms the philtrum of the upper lip.
What happens in the 10th week of facial development?
A fusion of the palatine shelves and primary palette to form the secondary palate.
Failure to fuse results in a cleft palate
Cleft lip is most common in?
Males
Cleft pallet is most common in ?
Females
When does the heart begin to beat?
Day 22 - 24
It can be heard at 6 weeks on ultrasound
When does blood start to flow?
Week 4
What are Common heart abnormalities?
- septal defect
- Transposition of the great arteries
- Persistent truncus arteriousus
- hypo-plastic left heart
At what stage does the embryo have Paddle- like upper limb buds?
Week 5 - 32 days
At how many weeks are Handplates formed?
Week 5 - 35 days
At how many weeks/days do Digital rays appear in hand plate ?
Week 6 - 44 days
At how many weeks is there- bend at the elbow, fingers are short and slightly webbed
Week 7 - 48 days
After how many weeks are the Fingers and toes are distinct and separated?
Week 8 - 56 days
What is the Apical Ectodermal ridge (AER) responsible for?
One of the main signaling centres during limb development
What does the AER determine?
- pattern of the limb
- Formation of early skeleton
- Muscles, tendons and vasculature
What are common Limb Development abnormalities?
~ Meromelia
~ Amelia
~ polydactyly
~ Triphalangeal thumb
~ Dysplasia’s
~ deformations due to amniotic bands
What is Meromelia?
Reduction of part of the limb
What is Amelia?
Missing limb
What is Polydactyly?
Presence of extra digits
What are Dysplasia’s?
Fusion of limb parts / disproportionate growth
