Embryo bullshit Flashcards
What must occur before sperm is able to fertilise egg
Capacitation
What does capacitation entail
Loss of inhibitory molecules (cholesterol, proteins, glycoproteins) from acrosome, enabling chemo/thermotaxis.
What is division of zygote called
Cleavage
What does cleavage form
Blastomeres
How does the morula transform into the blastocyst
Uterine milk enters the morula, reconfiguring the cells to form a blastocyst cavity
Two cell populations of the blastocyst
Embryoblast (inner cell mass) - forms embryo
Trophoblast - forms chorionic sac
Why does the blastocyst shed the zona pellucida
So that implantation can occur (it prevents implantation in uterine tubes)
What does the trophoblast develop into
Synctiotrophoblast - deeper into uterus
Cytotrophoblasts - closer to embryo
Function of synctiotrophoblasts and cytotrophoblasts
Secrete enzyme to burrow deeper into uterine lining
Release horomes e.g human chorionic godatropin which stops corpus luteum degenration and prevents menstruation
How does the bilaminar disc form
Embryoblast splits into
Hypoblast - primitive endoderm
Epiblast - primitive ectoderm
Cavity forms in epiblast, forming amniotic cavity
How does amnion form
Amnion (simple squamous cells) forms over epiblast, forming roof to amniotic cavity.
As embryonic disc increases in size, amnion eventually surrounds entire embryo
How does yolk sac form
During implantation, hypoblast proliferates and migrates around inside of blastocyst, forming the exocoelomic membrane.
Function of yolk sac
Nutrients for embryo for first 2-3 weeks
Source of RBC
Gives rise to primordial germ cells which become gametes
Forms part of gut
How do sinusoids form
Synctiotrophoblasts expand, creating lacunae.
Lacunae fuse to form lacunae network
Network joins up with maternal sinusoids and endometrial glands
What is the extraembryonic mesoderm
Mesoderm cells derived from yolk sac, forming a mesenchyme layer around the amnion and yolk sac
Extraembryonic coelom eventually forms in it
What does chorion consist of
Extraembryonic mesoderm
Cyto + synctiotrophoblasts
These surround the embryo
Function of chorion
Principal embryonic part of placenta Suppresses immune response -Secretes antibody production suppressing proteins -Suppresses immune response Produces human chorionic gonadotropin
How does the chorion develop
Fuses with amnion
Extraembryonic coelom now called chorionic cavity
What is the connecting stalk
Band of extraembryonic mesoderm connecting the bilaminar disc and trophoblast
What is gastrulation
Process that transforms bilaminar into trilaminar embryonic disc of three germ layers
Involves rearrangement and migration of cells from epiblast
What are the primary germ layers and what do they become
Ectoderm
Mesoderm
Endoderm
What is the first evidence of gastrulation
Formation of the primitive streak - a faint groove on the epiblast that elongates from the posterior to the anterior part of the embryo.
At the head is the primitive node
What occurs after formation of primitive streak
Epiblast cells detach and move inword below primitive streak via invagination
What are the effects of invagination
Epiblast cells displace hypoblast forming the endoderm
Cells between endoderm and epiblast become the mesoderm
Epiblast becomes ectoderm
What does the ectoderm become
All nervous tissue
Epidermis
Skeletal and connective components of head
Epithelium of oral and nasal cavities, paranasul sinuses, salivary glands, anal canal, pineal and pituitary gland, adrenal medullae
What does endoderm become
Epithelium of gastrointestinal tract and its glands
Epithelium of urinary bladder, gall bladder, liver
Epithelium of thyorid and parathyroid glands, pancreas and thymus
Gametes
What does mesoderm become
All skeletal and cardiac muscle Most smooth muscle Cartilage and bone Blood, red marrow, lymphatic tissue Kidneys and ureters Gonads
Formation of notochord
Mesodermal cells from primitive node migrate towards head end
This leaves a hollow tube of cells called the notochordal process
This eventually becomes a solid cylinder of cells called the notochord
Function of the notochord
Induction
This is the stimulation of nearby unspecialised tissue to develop into specialised tissue
e.g mesodermal tissue to form vertebral bodies
Formation of the neural plate
Ectodermal cells above notochord are induced to form the neural plate
Process of neuralation
Lateral edges of neural plate become elevated, forming the neural fold
Depressed mid region called neural groove
Folds approach and fuse to form neural tube
This occurs in the middle of the embryo and extends towards the head and tail ends
What does the neural tube become
Brain and spinal cord
Formation and function of neural crest
Formed during neuralation as ectodermal cells from tube migrate and form several layers of vells
These give rise to the PNS
Somite formation
Notochord instructs the lateral mesoderm (on either side of the neural tube) to form cuboidal structures called somites which form in parallel pairs
Function of somites
These give rise to the vertebrae and muscles in the back.
There are three regions of somites (counting from the ectodermal side): dermatome connective tissue), myotome (muscles in the back/neck) and sclerotome (vertebrae and ribs).
