TOPIC 5 - embryology Flashcards
Acrosome reaction
Release of enzymes from the acrosome on the head of sperm that assists in penetration of the Zona Pellucida
Allantois
Waste storage organ - connected to the developing fetal bladder
Amnion
Membrane derived from epiblast that surrounds the fluid-filled amniotic cavity. Fluid cushions the fetus and assists with dilation of the cervix during labour
Anancephaly
Congenital malformation in which the anterior neuropore fails to close
- leads to failure of formation of higher brain centres: cognition (thinking), memory, speech, vision and hearing.
- cerebral hemispheres/forebrain fail to form
but A brainstem is present - basic systems so heart and lungs and some reflexes formed
Anterior neuropore
Cranial opening of the neural tube (closes by day 25)
Azoospermia
Male’s semen contains no mature spermatozoa
Bilaminar disc
Stage in week 2 of development (DAY 7)when the inner cell mass/ embryoblasts differentiate into a layer of epiblasts and hypoblasts
establishes dorsal and venteral axis of embryo
Blastocyst
Stage of embryogenesis at the time of implantation where the outer trophoblast cells from a fluid-filled sphere with a small group of embryoblast cells (ICM) at one pole
Blastomeres
Cells formed by cleavage of a fertilised ovum
Capacitation
A period of sperm conditioning in the female reproductive tract, lasting about 7 hours - secretions from female reproductive = prepares head of sperm to be able to fertilise oocyte
Caudal
Towards the tail
Chorionic cavity
Space formed between the extraembryonic mesoderm lining the cytotrophoblast and surrounding the yolk sac and embryo. Will eventually be obliterated by expansion of amniotic cavity and fusion of amnion with chorion
Chromosomal
DNA molecule with some/all genetic material of an organism
Cleavage
Division of cells in the early embryo
np change in size zygote= more cells but they are smaller
Cloacal membrane
Membrane at the caudal end formed by adhesion between epiblast and hypoblast cells. Later covers the cloaca, a chamber where the gut and urinary system drain into before the chamber is segregated
Connecting stalk
Extraembryonic mesoderm that connects the embryo to the placenta - contains the allantois and will be incorporated into the umbilical cord along with the vitelline duct and yolk sac
Corona radiata
Innermost layer of cummulus oophorus, adjacent to the zona pellucida
Cortical reaction
Occurs after fertilisation, cortical granules release calcium very quickly and make zygote impermeable to any more sperm - prevent polyspermy
Cranial
Towards the head
Cumulus oophorus
Collection of cells that surround the oocyte
Cytotrophoblast
Proliferative inner layer of the trophoblast
Definitive yolk sac
One of the three embryonic cavities formed by migration of hypoblast cells around the blastocyst cavity to form the primary yolk sac. The primary yolk sac is pinched off and degenerates. A second wave of hypoblast migration produces a new membrane and the definitive yolk sac
Dermatome
Area of the somite that forms the dermis of the skin of the back
Dextrocardia
Rare condition in which the apex of the heart points to the right
Dorsal
Towards the back
Ectoderm
The most external germ layer formed during gastrulation. Goes onto form CNS and skin
Ectopic
In an abnormal place or position
Ectopia cordis
Ventral body wall defect - heart lies outside of the thoracic cavity
lateral folds fail fuse in thoratic region
Embryoblast
Cells that form the inner cell mass, goes onto form embryo (hypoblast and epiblast cells)
Endoderm
Most internal layer of germ layers formed during gastrulation - forms most organs
Epiblast
Dorsal (top) layer of cells in the bilaminar disc during second week of development - all tissues of the embryo are derived from the epiblast
Extraembryonic mesoderm
Layer formed by the hypoblast/primary yolk sac. Surrounds the developing embryo and forms the connecting stalk. Chorionic cavity also forms from this layer.
forms day 11
Fertilisation
Fusion of male and female gametes
Gastrulation
Process that forms the three germ layers by migration of epiblast cells through the primitive streak. Formation of primitive streak = start of it
hypoblast cells soon replaced by epiblast
Gametes
Haploid cells that has undergone meiosis (sex cell)
Gametogenesis
Formation of sex cells
Gastroschisis
Ventral body wall defect caused by failure of lateral walls to form/fuse in abdominal region - intestines reside outside of the abdominal cavity
Germ layers
Three basic cell layers formed during gastrulation (endoderm, mesoderm and ectoderm)
Gestation
Process of development within the uterus
Hydatidiform mole
Trophoblast forms placental tissue but with no embryo
only presence of paternal genetic info
NB: HCG still present= + test
Hydrocephalus
Build up of cerebral spinal fluid on the brain
Hypoblast
Ventral layer of the bilaminar disc - contributes to formation of the yolk sac and extraembryonic mesoderm but not to tissues of the embryo
Inner cell mass
Cluster of cells segregated to one pole of the blastocyst and from which the embryo develops
Intermediate mesoderm
Area of mesoderm between paraxial and lateral plate mesoderm - forms much of the urogenital system: gonads, internal reproductive tracts, kidneys
Lateral plate mesoderm
lines all body cavities
Area of mesoderm that splits into parietal layer that surrounds the body wall and a visceral layer that surrounds the organs
Lithopaedian
Stone baby - foetus dies during ectopic pregnancy but can’t be absorbed by body so is calcified instead
Meiosis
Cell division to produce haploid cells
Meningeocele
Failure of the vertebral arch to form correctly, gap in vertebra (spina bifida) with meninges protruding the gap
Mesoderm
Middle germ layer formed during gastrulation. gets organised further into paraxial, intermediate and lateral plate mesoderm. Skin, blood vessels, muscle and bone
Microcephaly
Brain fails to form properly resulting in a head with a very small circumfrence
Morula
Cleavage of the developing zygote to form a ball of 16-32 cells. Inner cell mass and outer cell mass
Myelomeningeocele
Neural tube defect, failure of vertebral arches to form= gap in vertebra - protrusion of meninges and spinal cord
Myotome
Muscle forming region of a somite
Neural crest cells
Cells of the neuroepithelium that form the edges of the neural folds - migrate to form numerous different structures around the body
Migrate laterally and ventrally= dispersing widely= sometimes known 4th germ layer
Neural tube
Result of neurulation, once the neural folds fuse the tube separates from the overlying ectoderm
Neurulation
Process to form neural tube
- thickening of ectoderm overlying the notochord to form neuroectoderm and the neural plate
- elevation of neural plate to form neural folds
- neural folds fuse fro cranial to caudal end to form neural tube
- tube separates from ectoderm
Notochord
An extended column of cells in the midline that forms as the primitive streak regresses. Induces neurulation and the sclerotome to vertabrae
formed from notochordal process
Oropharyngeal membrane
Membrane formed at the cranial end of the embryonic disc by adhesion of epiblast and hypoblast cells. Goes on to cover the opening of the oral cavity and pharynx
Outer cell mass
Cells that surround the blastocyst cavity and cover the inner cell mass and that will form the trophoblast
Oligospermia
Deficiency of spermatazoa
Paraxial mesoderm
Mesoderm tissue next to the midline, responsible for forming the somites (divides into these blocks)
forms majority of skeleton, skeletal muscle and dermis of skin
Parietal mesoderm
Mesoderm that is concerned with the body wall (formed from splitting of the lateral plate mesoderm into parietal and visceral (splanchnic layers)
Posterior neuropore
Caudal opening of the neural tube. Closes by day 28
Primary yolk sac
Formed by migration of hypoblast cells around the blastocyst cavity. It is a transient structure replaced by the definitive yolk sac
Primitive streak
A groove formed on the dorsal aspect of the embryo in the epiblast. Appears at causal end of bilaminar disc and marks beginning of gastrulation. Epiblast cells migrate through the primitive streak to form the three germ layers
Pronuclei
Either of a pair of gametic nuclei after fertilisation but before fusion leads to formation of the nucleus of the zygote
Rachischisis
Failure of the posterior neuropore to close. As a result the tube does not separate from the surface ectoderm and the neural tissue is exposed to the external environment. Leads to motor and sensory deficits and an increased risk of infection and paralysis
Sacrococcygeal terratoma
Formed by excessive formation of mesoderm because of increased number of epiblast cells migrating through the primitive streak. Caused by persistent primitive streak
Sclerotome
Area of the somite that forms vertabrae
sclerotome cells surround notochord to from vertebral body + surround neural tube = from vertebral arch
Sirenomelia
Mermaid syndrome - insufficient formation of mesoderm in the caudal region due to lack of epiblast cells migrating through the primitive streak - premature regression of streak
Situs inversus
- Left and right side of body switched around
- due to problems with formation of axis
- syndrome which affects ciliary cells
- complete sinus inversus= harmless
- Partial situs inversus – some organs swapped - reversal of chambers but vessels don’t follow
Somite
Derived from paraxial mesoderm that organises to form segmental blocks either side of the neural tube. Differentiates into sclerotome, myotome and dermatome
Spina bifida
Neural tube defect that involves incomplete formation of the vertebral arches (occulta) and maybe the meninges (meningeocele) or neural tissue (mylomeningeocele)
Splanchnic (visceral) mesoderm
Mesoderm that is concerned with lining the outside of the gut and its derivitives. Formed from splitting of the lateral plate mesoderm into parietal and visceral
Syncytiotrophoblast
Outer multinucleated layer of the trophoblast that serves to invade the endometrium of the uterus
- secrete enzymes
- allow disc bind uterine linning
Teratogen
Factor that causes a birth defect,eg:
- infections
- chemical(drugs)/physical (radiaiton) damage
- deficiency
- maternal disease (diabetes)
Trisomy 21
Downs syndrome - three copies of chromosome 21 causes: intellectual retardation craniofacial abnormalities: flat nose heart defects: hole in heart
Trophoblast
Outer layer of blastocyst. Important in development of support structures for implantation of nourishment of embryo. Differentiate into cytotrophoblast and syncitiotrophoblast
Trophoblastic Lacuna
Irregular spaces within syncitiotrophoblast that merge together, maternal blood flows into the lacuna when the syncitiotrophoblasts have established a uteroplacental circulation
Ventral
Towards the front
Vitelline duct
Connection between the yolk sac and the developing midgut
Zona Pellucida
Specialised layer surrounding the plasma membrane of the ovum
Zygote
First structure formed after fertilisation by fusion of a sperm and ovum
what does TORCH stand for
all infections that may cause birth defects MUST CROSS PLACENTA - toxoplasmosis -Other (hepatitis B, Syphilis) - Rubella (German measles) - Cytomegalovirus (CMV) - Herpes simplex virus (HSV)
what is toxoplasmosis
- parasite
- found in cat faeces, raw/undercooked meat]
- carriers asymptomatic
Congenital Malformations of toxoplasmosis
- Inflammation of retina and eye/micropthalmia
- Hearing loss
- Enlarged Liver Spleen
- Hydrocephaly
- Microcephaly
Congenital Malformations of Rubella
Cloudy Cornea
Intellectual disability
Microcephaly
Heart Defects
what is Cytomegalovirus
Virus that crosses the placenta
Infection via bodily fluids
Usually asymptomatic
Congenital Malformations of Cytomegalovirus
- Inflammation of retina/micropthalmia
- Enlarged spleen or liver
- Mineral deposits on the brain- calcium deposits
- Microcephaly
- Psychomotor retardation – problems with development
what is Herpes virus
- type 2 = gentile herpes
•Passed to baby during vaginal brith
•Varicella zoster virus – Chickenpox- another strain of herpes
Congenital Malformations of herpes virus
- Segmental skinloss/ scarring
- Limb hypoplasia/paresis
- Microcephaly
- Visual defects
what is zika virus
- Mosquito
- Bodily fluids
- Fever, rash, joint pain, red eyes
Congenital Malformations of zika virus
- Microcephaly
* Severe cognitive disabilities
congenital malformations of Foetal alcohol syndrome
• Small eye openings
• Thin upper lip
Associated with:
• prenatal and postnatal growth retardation
• intellectual disability
• Impaired motor ability and coordination
physical damage: what does Radiation do to feotus
- Causes cell death or chromosome changes
* CNS most sensitive in the first trimester
Congenital Malformations of radiation
- Microcephaly
- Mental and cognitive disabilities
- Haemopoietic malignancies and leukemia
Maternal disease - Diabetes Mellitus congenital malformations
- Macrosomia- enlarged baby
- Ventricular Septal Defects- hole in heart
- Spina bifida
- Renal agenesis- absence of one or both kidneys
Amniotic cavity
small fluid filled cavity in epiblast layer
devlopes day 8
what day does the full implantation happen
day 9
- migration of hypoblast cells to from 1’ yolk sac
what day does the uteroplacental circulation happen
days 10-11
syncititrophoblasts erode walls maternal capillaries - establish uteroplacental circulation
causes small bleeding
placenta previa
abnormal implantation
placenta covering birthing canal= baby pushing down blood vessels
= ruptures
= severe bleeding
tubal implantation
- ectopic pregnancy in uterine tube
- uterine tube cannot support embryo= dies
can rupture tube = haemorrhage = severe bleeding - can make future pregnancy difficult
notochordal process
notochordal process transiently fuses with endoderm = notochordal plate
then separates from endoderm and fuses to from solid notochord
neurofibromatosis?
- genetic condition
- mutation in NF1 gene
- problems with neuro crest cells
- NF1 usually suppressor gene stops proliferation
- here NF1 ‘off’= increased cell division = benign tumours of CNS
which 2 ways does an embryo fold
1- craniocaudal folding: head to tail-‘C’ shape
2- lateral folding: 2 outer edges fuse towards midline
how does lateral folding occur
lateral edges fuse into midline:
amniotic cavity expand faster than 1’ yolk sac
amniotic cavity pushes down fusing the lateral edges
does the midgut fuse in the midline via lateral folding?
NO
gut fuses everywhere but midgut
forms belly button
gut tube continuous with yolk sac via the vitelline duct
