Embryology Flashcards
0
Q
early dev stages - implantation
A
- blastulation: blastocyte implants in the endometrium (5-8 days post fert); steroid hormone progesterone proliferates the mucosal layer to help embryo implant
- embryonic cells serete enzymes that strategically burrow into the endometrial lining to allow for implantation
1
Q
early developmental stages - cleavage
A
- after fert in fallipian, in process of moving to the uterus for implantation, the zygote undergoes rapid mitotic cell division in process called cleavage
- first cleavage makes an embryo and after more mitotic divisions still small (small and fast, no time for enlargement inbetween)
- indeterminate cleavage: cells that can still develop into complete organisms
- determinate cleavage results in cells whose fates are determined > they are committed into differentiating into a certain type of cell
- 1, 2, 3 cleavages occur at 32, 6, 72 hours after fertilization and at this point the 8 celled embryo has reached uterus
- a few divisions later embryo becomes a mass known as a morula, and then goes into the next stage callled blastulation (blastula)
- -> blastulas characterized by resence of a hollow, fluid filled cavity known as blastocoel
- mammal blastula known as blastocyte and consists of 2 cell grous: trophoblast and inner cell mass
- -> trophoblast: surround blastocoel and gives rise to placenta later
- -> inner cell mass protrudes into the blastocoel
“blasted out” cavity is a blastula
2
Q
early dev stages - gastrulation
A
- gastrulation: generation of 3 distince cell layers
- gastrula: a 2 layered cup
- inner cell layer (inside cup) is known as ENDODERM
- outer cell layer known as ECTODERM
- cavity created by the deepp invagination is known as the archenteron, which later develops into the gut
- opening of archenteron called blastopore
- in deuterostomes (humans) blastopore develops into the anus; in protostomes, it develops into the mouth
- some cells will also migrate into area between the ectoderm and endoderm generating a third cell layer known as mesoderm
Ectoderm: integument (epidermis, hair, nails, epithelium of nose mouth and anal canal)
Mesoderm: musculoskeletal system, circilatory system, excretory system, gonads, muscular and connective tissue coats of the digestive and respiratory system
Endoderm : epithelial linings of digestive and respiratory tracts and parts of the liver, pancreas, thyroid, bladder, and distal urinary and reproductive tracts
ectoderm - ‘attracto’ derm (looks)
mesoderm- ‘means’ o derm - how we get from place to place in the world and how constituents get from place to place in body -> bone, muscle, heart, blood
endoderm - “endernal” - long tube that runs through body and organs attached to it
3
Q
expertise note
A
- adrenal cortex develops from mesoderm
- adrenal medulla is derived from ectoderm (has nervous tissue)
4
Q
early dev stages - neurulation
A
- development of nervous sytem
- rod of mesoderm cells known as notochord forms along the long axis of organism (just as spinal cord runs up and down our back)
- these cells induce a group of ectodermal cells to slide inward to form neural folds which surround a neural groove
- the neural folds grow towardd one nother until they fuse into a neural tube which gives rie to the cns
- tip of each neural fold are neural crest cells -> migrate outward to from the pns including sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells
5
Q
fetal respiration
A
- theplacenta nad umbilical chord
- placenta formed from an etra enbryonic membrane called chorion which develops from trophpoblast cells
- allantois: surrounded by amnion, which is a thin, tough membrane filled with amniotic fluid that serves as a shock absorber during pregnancy and labor
- yolk sac: site of early blood vessel development
- outermost later is the chorion which completely surrounds other membranes and provies an added level of protection
- chorionic villi eventually grow into placenta and support maternal fetal gas exchange
- placentaa: where nutrient, gas, and waste exchanges occur -> simplest way to move these is throug difusion - how water, glucose, aa, and inorganic salts transferred
- oxygen gradient from moms blood to babies, and fetal blood equipped with fetal hemoglobin which has a greater affinity for oxygen than does maternal hemogloben
- placenta also does immune protection -> many foreign particles and bacteria are too large to cross the placental barrier by diffusion but virus, alcohol, and toxins are nt
6
Q
fetal circulation
A
- oxygen comes from maternal circulation and diffuses through placental vessels -> keep blood away from lungs of fetus
- foramen ovale: connects right and left atria, so that blood entering the right atrium from superior vena cva will flow into left atrium instead of right ventricle and can eventually be pumped out of the aorta into systemic circulation
- –>because of a pressure differential - pressure is higher in right side of heart than left, and this pressure differential is opposite in adults so the ovale must be closed after birth
- but valve separating right atrium and ventricle isnt closed shut, SO NOT ALL BLOOD WILL BE SENT TO LEFT ATRIA IMMEDIATELY
- ductus arteriosus: shunts leftver blood from pulmonary artery to aorta -> pressure in right fetal heart is higher than that in the left
- blood returning from the placenta via umbilical vein is rerouted to the inferior vena cava via the ductus venosus -> to prevent liver from stealingoxygen designated for the rest of the body
- umbilical arteries carry blood away from the fetus
- umbilical vein carries blood toward the fetus
- the fetus would return blood to the placenta ONLY IF all the oxygen in it were used up -> umbilical arteries carry deoxy blood
- –>only kind of blood that the fetus wants from the placenta is oxy blood, so it must be that umbilical vein carries oxy blood
7
Q
gestation
A
First trimester
- during first weeks, major organs begin to develop; heart pumps afte 22 days, eyes, gonads, limbs, and liver start to form
- end of 8 weeks, most of organs have formed, the brain is fairly developed, and enbryo referred to as a fetus
- at end of 3rd month, fetus is 9 cm long
second trimester
- tremendous amount of growth, starts to move, face human, fingers and toes elongate
- end of 6th month, fetus is 30-36 cm long
third trimester
- continued rapid growth and further brain development
- 9th month, antibodies are transported by hihgly selective active transport from the mother to the fetus for protection against foreign matter in prep for life outside womb
