Making a human

Question 1

menstrual cycle

Answer 1

menses/ menstrual stage(4-5 days : bleeding) = removal of superficial layer of endometrium
proliferative stage
secretory stage

Question 2

menses stage

Answer 2

4-5 days of bleeding, removal of the superficial layer of endometrium

Question 3

proliferative stage

Answer 3

oestrogen level increases first
(oocytes are producing oestrogen)
causes hypothalamus to produce GnRH and stimulates the LH (luteeunising) and FSH (follice stimulating hormone)
FSH ; stimulates the growth of oocytes and they increase in size, granulose layer increase and start to secrete oestrogen (positive feedback)

LH : triggers ovulation –> secretory stage in the menstrual cycle

Question 4

secretory stage

Answer 4

day 14
oocytes complete meiosis 1
oocytes are released and corpus luteam remains and it starts to release progesterone
–> leads to the thickining of the uterus wall for embryo implantation
progesterone inhibits GnRH from hypothalamus and LH / FSH from anterior pituitary (AP)

called secretory because it secretes nutrients needed for the embryo and start to produce placenta

Question 5

secretory stage cont

Answer 5

fertilisation : (7-8 days after ovulation)
embryo will move in the uterus
trophoblasts (part of the embryo) interacts with the uterus wall to start producing human chorionic gonadotropin (HCG)
–> signal the corpus luteum (cl) to continue producing progesteron, cl is maintained
=== makes sure the secretions are continued for the uterus wall to thicken, menstrual cycle stops

no fertilisation :
cl will degenerate as there is no HCG to signal it to be maintained, no progesterone to inhibit the hypothamalmus and AP so the menstrual cycle starts again

Question 6

HCG

Answer 6

human chorionic gonadotropin is a hormone produced by the trophoblasts (part of the embryo) which maintains the cl so cl can continue producing progesterone, stop the cycle and continue nourishing the uterus wall for the embryo

HCG can be used in testing (antibodies/mab/monoclonal)

Question 7

fertilisation mechanism

Answer 7

secondary oocyte released into the oviduct
sperm touches the plasma membrane of the secondary oocytes and triggers the remaining of meiosis 2
–> products : pre zygote cell and a polar body

Question 8

fertilisation day 0

Answer 8

day 0 of gestation:

prevent polyspermy
1) fast block : influx of Na+ (from oviduct), meiosis 2 is initated and polarises cell so a 2nd sperm cant enter anymore
2) slow block : Ca2+ from the ER in the oocyte cell causes cortical granules (cortical reaction!)

pronuclei (nucleus of each gamete) fuse = zygote

Question 9

cortical reaction

Answer 9

Ca2+ from the oocyte ER is released and cortical granules are removed from the cells plasma membrane. these granules contain enzymes cause the zona pellucida to harden and the sperm can no longer penetrate the cell

Question 10

polyspermy

Answer 10

when one sperm penetrates the oocyte

Question 11

cleavage

Answer 11

day 1-6:
zygote undergoes repeated mitotic divisions
= forms a ball of cells = called a morula
morula then becomes a blastocyst when cells start to differentiate
= first zone pellucida is removed “zona hatching”
next, the outside cells differeintatie into the trophoblast and be imbedded in the uterus wall
trophoblasts produce fluid, which forms a fluid-filled cavity.
blastocysts also has an inner cell mas which eventually becomes the embryo

Question 12

inner cell mass

Answer 12

totipotent : can differentiate into any cell type

Question 13

implantation

Answer 13

day 7-10
blastocysts starts implanting, trophoblasts interact with the endometrium (uterus wall)

day 12:
implantation has occurred, forms a stalk (connects developing embryo and developing placenta)
embryo has two sacs: yolk sac and the amniotic cavity
the inner mass before forms the embryonic disc

Question 14

gastrulation

Answer 14

day 12:
embryonic disc has an epiblast

primitive streak (from epiblast) which acts as the central axis and forms symmetry
epiblast cells migrate to eventually form the germ layers
gastrulation : formation of the 3 germ layers
1) ectoderm : skin, nervous system, teeth too, glands
2) mesoderm : organs, muscle and bone
3) endoderm : digestive and respiratory system

all the cells are now pluripotent, now as powerful as omnipotent cells but can still differentitate into many types

Question 15

neurulation

Answer 15

day 18:
AIM : form the neural tube (baby spinal cord and brain
triggered by the notochord made from the mesoderm that stimulates the neuroectoderm cells in the ectoderm to form the neural plate, neural plate starts to fold,
they fold until they overlap and form the neural tube
folding = determines the position of the grey and white matter

Question 16

notochord

Answer 16

structure that releases signalling moelcules to ectoderm to thicken, cells differentirate into neuroectoderm cells and form a neural plate

Question 17

organogenesis

Answer 17

week 3-8
brain = week3
heart = week 3, four chambers = week 7
kidneys = week9

week1-7 = embryo, week8 = fetus
amniotic vacity surrounds the fetus

Question 18

partuition

Answer 18

1) head starts to push against the uterus wall : stress –> uterus can no longer expand any further, a hormone “releasing hormone” is secreted from the hypothalamus in fetus brain

2)–> signal goes to pituitary gland which releases the adrenocorticotropic hormone (ACTH)
–> ACTH stimulates for adrenal cortico steroids to be produced

3) adrenal cortico sterioids goes through unbilical cord and placenta, placenta to produce more oestrogen and prostaglandin by the endometrium cells! (placenta takes over the role of the corpeus luteam and starts to produce progesterone) and inhibits progesterone

4) oestrogen and prostaglandin are responsible for muscular contraction, make the smooth muscle layer of the endometrium to contract

5) also sends sensory signals to the mothers brains, and posterior pituary gland starts to produce oxytocin

6) oxytocin + oestrogen/prostaglandin stimulates more muscluar contractions –>

dliate to 10cms

Question 19

ACTH

Answer 19

adrenocorticotropic hormone
stimulates the adrenal gland to produce adrenal coritco steroids