4 - embryology Flashcards
which 4 simples processes are involved in embryology and how do embryonic cells and mature cells differ
proliferation
movement
differentiation
apoptosis
mature cells can only show characteristics one at a time, embryonic cells can show the first 3 simultaneously
the key events that occurs in the first 2 months of development
fertilisation primplantation development implantation gastrulation neurulation
Summarise fertilisation and preimplantation development - where it happens, over how many days, what occurs on which days and what is produced (including components inside)
in fallopian tube over a period of 6 days
cleavage division to produce a ball of undifferentiated cells (morula) by day 4
morula - compaction and differentiation (inner cells differ from those on the outside)
day 5-6 forms the blastocyst.
implants into the uterus
has an inner cell mass (will form embryo), build filled blastocyst cavity and trophectoderm (will form placenta)
summarise what occurs during the implantation phase and what days
days 6-10
hatching of blastocyst to remove zona pellucida (day 6)
blastocyst beigins to implant into uterine lining (up to day 10)
inner cell mass becomes a bilayer disc:
1 - epiblast
2 - hypoblast
name places where implantation occurring could cause harm/ fatality to the mother
fallopian tube
ovary
intraperitoneal space
summarise what occurs during gastrulation and what days
days 14-18
formation of trilaminar disc from bilayer
epiblast and hypoblast form the ectoderm, mesoderm and endoderm
epiblast cells move towards centre and form a thickened primitive streak on the epiblast layer
epiblast >> mesoderm some mesoderm moves between the epiblast and hypoblast layers hypoblast cells undergo apoptosis mesoderm >> endoderm epiblast >> ectoderm
what organs will the germ layers endoderm , mesoderm and ectoderm become
endoderm - gut, liver, lungs
mesoderm - skeleton, muscle, kidney heart, blood
ectoderm - skin, nervous system
summarise what neurulation is, what occurs, what it’s under the control of and timescale
what failure can lead to
differentiation of the ectoderm to form the CNS
begins before gastrulation is complete and continues up to 4 weeks
under control of notochord in the mesoderm
- formation of neural plate
- development of neural folds
- increase in size
- neural folds meet over the neural groove and fuse to form the neural tube
anencephaly (anterior neuropore) spina bifida (posterior neuropore)
at week 3, which 2 groups of cells are outside the embryo proper
primordial germ cells in the yolk sac at the caudal end of the embryo
cardiac and vascular progenitors in the primary heart field at the cranial end of the embryo
describe the folding of the embryo into a 3d structure
folding in the antero-posteiror direction
- folds the PGCs into the hindgut
- folds the developing heart progenitors under the head of the embryo
lateral folding
- fuses the ventral midline (chest and abdomen) of the embryo
Urinary system development
Development starts at the urogenital ridge (mesoderm)
Nephric duct develops
Joins with nephrogenic cords to form pronephros, mesonephros and metanephros
pronephros - first to develop but quickly degenerates
mesonephros - temporarily functions as the kidney before degenerating
metanephros - Ureteric bud forms calyces, pelvis, ureters and collecting ducts.
Ureteric bud induces mesoderm mesenchyme differentiation to form the the rest of the kidney
kidneys migrate up as they develop. Blood supply moves with it and ureters stretch.
Defects in the urinary system development
horseshoe kidney (kidneys fuse and therefore can’t move and stay in pelvis)
pelvic kidney (retained there)
enlarged pelvis (retention of extra artery obstructs ureter)
reproductive system development
migration of primordial germ cells to genital ridge
PGCs are gamete precursors
gonads initially develop indifferent to sex
SRY determine sex
presence of SRY:
- leydig cells produce testosterone
- induces gonadal differentiation to testes
- subsequent male structures and male genitalia develop
- Wolffian / mesonephric duct remains and differentiates
- Sertoli cells produce anti-Mullerian hormone so Mullerian / paramesonephric duct disintegrates
no SRY:
- induces gonadal differentiation to ovaries
- subsequent female structures and female genitalia develop
- Wolffian / mesonephric duct disintegrates
- Mullerian / paramesonephric duct remains and differentiates
- Mullerian ducts fuse in the middle to form the uterus and vagina
Genital abnormalities:
when genetically male but have female genitalia
Androgen insensitivity syndrome - mutant androgen receptor
external genitalia looks female, testes don’t descend, internal Wolffian/mesonephric ducts are small or lacking
because AMH is normal - no female structures (vagina, uterus)
Genital abnormalities:
when genetically female but have male genitalia
(when SRY translocates onto the X chromosome)
Congenital adrenal hyperplasia
- mutation in CYP450 enzyme 21-hydroxylase so low cortisol so no negative feedback on pituitary ACTH – high — adrenals produce weak androgens e.g. androstenedione – partial virilisation of genitalia
- internally female as no SRY gene, so no testosterone means no male ducts and no AMH means they have female vagina etc…
