embryology Flashcards
what are the 4 cellular processes that are involved in embryological development
-Proliferation
-differentiation
-reorganisation
-apoptosis
The combinations of these processes give rise to all the events of embryology.
what does the Ectoderm give rise to
Ectoderm gives rise to skin and the central nervous system
what does the Mesoderm give rise to
mesoderm to muscles, blood, skeleton, heart and kidney
what does the Endoderm give rise to
endoderm to gut, lungs and liver
describe 1st step post implantation aka gastrulation (convertion of the bilayer of hypoblast and epiblast cells into a trilaminar embryo)
epiblast cells PROLIFERATE and DIFFERENTIATE into mesoderm and then MOVE into the space between the epiblast cells and the hypoblast cells. these mesoderm cells then DIFFERENTIATE further to form the endoderm cells which replace the hypoblast cells which are lost by APOPTOSIS
describe neurilation
Neurulation is the differentiation of the Ectoderm (Epiblast) to generate the central nervous system– as seen in neuro– neural plate folds and meets to form neural tube (under the control of the notocord in the mesoderm of the developing embryo)This fusion process continues during week 4 of development
what happens at the same time as neurilation
precursors of other tissues are developing within the embryo, and it is being converted from a flattened structure into a 3-dimensional embryo (during 3rd week)
what happens to the yolk sac after day 21?
After day 21, the body cavity then closes by day 28 and pinches off the yolk sac
into the umbilical cord (allantois)
when do the digits develop
fingers and toes are distinctly separated by day 56
what was the most common maldevelopment seen with thalidomide babies
maldevelopment of the upper limbs was one of the most common outcomes
how does thalidomide cause maldevelopment
it seems that it damages developing blood vessels, thus depriving the adjacent cells of nutrients and preventing their proper growth and development. the upper limb is particularly sensitive to it, and also the timing at which morning sickness occurs co-incides with development of upper limbs
what are the 3 forms of kidney during development
- Pronephros is the most immature form of kidney
- Mesonephros, an intermediate phase
- Metanephros is most developed and persists as the definitive adult kidney.
describe the formation of the kidneys
during development, the pronephros (till week 4) and mesonephros (till week 8 ish) function as kidneys until the metanephros has fully developed. kidneys arise from ureteric bud (forms collecting duct) and metanephrogenic blastema (forms nephron). initial blood supply comes from common iliac arteries but kidneys migrate upward to their normal position where they meet the adrenals and then receive blood supply from aorta via renal arteries (they can retain their old arteries as polar arteries)
what is the problem with retention of the polar renal artery
it can cause obstruction of the ureter which then enlarges
describe another kidney maldevelopment
The kidneys form separately, but may fuse to form a horseshoe kidney, the extra tissue makes it impossible to move so the joint kidney often remains in the pelvis. this may compromise kidney function.
what gives rise to the male genital ducts
mesonephric ducts
what gives rise tot he female genital ducts
paramesonephric ducts
what three sources are the gonads derived from
mesothelium
from mesonephros
what determines the development pathway the gonads take
SRY+ = male SRY- = female
describe the movement of primordial germ cells into the gonads
PGC migrate through the hind-gut and dorsal mesentery to the mesonephros and thence to the developing gonads
what do primordial germ cells differentiate into
gametes in the gonads
whats another key regulator in male gonadal development, where is it produced and whats it stimulated by
testosterone produced in testis Leydig cells and stimulated by maternal hGC
note: Testis Sertoli cells produce anti-Mullerian hormone (AMH), which causes the regression of the Mullerian (paramesonephric) ducts
describe the differences in development of the external genitalia
-same for both genders until about week 7
MALES:
-genital swellings move downwards (towards anus) to form the scrotum
-urogenital sinus closes
-phallus becomes glans penis
FEMALES:
- genital swellings move upwardswards and encase the phallus
- urogenital sinus remains open to form vaginal orifice andurethral orifice
- phallus becomes clitoris and genital fold becomes labia minora
what are the abnormalities in male and female reproductive systems development
MALES: (a) the inability to produce the appropriate hormones (testosterone and anti-Mullerian hormone (AMH) or (b) the inability of target tissues to respond to these hormones, normally the result of defects in the cognate receptors. eg Androgen Insensitivity Syndrome : There is no or limited virilisation of external genitalia (which show relatively normal female structures but no uterus/oviducts)
FEMALES: Congential Adrenal Hyperplasia (CAH), ie no negative feedback on pituitary ACTH output, leading to high ACTH due to lack of cortisol, therefore overproduction of androgens from fatal adrenals, partial virilisation (The internal systems are female, as there is no SRY )
