Lecture 12: Embryology Flashcards
What does embryogenesis achieve
- Patterning - cells acquire identity in space in times
- Major axis are defined - anterior/posterior, dorsal (back), ventral (tummy)
- Three germ layers are defined
- Rudiments of major organs
Until what time is it called an embryo
Up to 8th week.
What are the three different germ layers and their colours
Ectoderm (blue) mesoderm (red), and endoderm (yellow)
Define pattern formation (patterning)
the developmental process by which cells acquire different identities depending on their relative spatial positions in the embryo
Ectoderm gives rise to
tissues that tend to be on the outside-> the epidermis, all nervous tissue, brain and spinal cord
Mesoderm gives rise to
internal structures/organs such as All structures in the: skeletal, muscular, cardiovascular, lymphatic system.
Endoderm gives rise to
the inside of us - gut, reproductive cells.
What are the events in the first week of development
fertilisation, cleavage of the zygote, formation of the morula and blastocyst, implantation
Describe the steps of fertilisation
sperm reach the oocyte in the uterine tube, undergo capacitation, penetrate the corona radiata and zona pellucida to fuse with the oocyte. The female pronuclei formed from meiosis II and the male pronuclei from sperm head fuse.
describe capacitation - and what is its function
the removal of cholesterol, glycoproteins and proteins from the head of the sperm by secretions in the reproductive tract that allows sperm tail to beat harder, be able to fuse with oocyte membrane and follow chemo/thermo taxic cues to egg
What is the corona radiata (crown of light)
outermost layer of somatic granulosa cells surrounding the 2ndary oocyte
How does the sperm penetrate the zona pellucida
it binds to specific ZP3 sperm receptors on the zona pellucida which triggers an acrosomal reaction. The acrosomal enzymes digest a path for the sperm through.
Directly after one sperm enters the cytoplasm of the oocyte
undergoes a series of structural changes that prevent polyspermy.
Describe the events and timing of Cleavage of the zygote and formation of morula
Rapid mitotic division that occurs post fertilisation. day one, cells divided into 2 cells called blastomeres. day 2 divided into 4 cells.
day four: loosely packed ball of cells without a cavity is formed called Morula.
Describe the events and timing the formation of the blastocyst and the most important result.
on the 5th day, cells become tightly packed together forming 1st epithelial layer through increased adhesion. Sodium pumps encourage water to flow in by osmosis forming blastocyst cavity. Two distinct cell populations arise: trophoblast and embryoblast.
What is the trophoblast and what will it form
the outer superficial layer of cells forming the spherelike wall of blastocyst. Will give rise to placenta
What is the embryoblast
Inner cell mass that will become the embryo
What processes in the first week occur in the fallopian tube
fertilisation, cleavage, morula formation
Describe process, location and timing of implantation
6th day in the uterine cavity, the Blastocyst hatches out of the zona pellucida and loosely attaches itself to the endometrium, orientating inner cell mass towards the endometrium
List the main developmental events in week 2
development of the trophoblast, embryonic disk, amnion and yolk sac
describe the development of the trophoblast and two things it does
Trophoblast cells differentiate into two different cell types syncytiotrophoblast (It secretes enzymes that enable the blastocyst to penetrate the uterine lining) and cytotrophoblast. Trophoblast also secretes human chorionic gonadotropin (hCG) that maintain the uterine lining stopping menustration.
What is the syncytiotrophoblast
contains no distinct cell boundaries located closest to the endometrium.
What is the cytotrophoblast
composed of distinct cells located between the embryoblast and syncytiotrophoblast.
what does the syncytiotrophoblast and cytotrophoblast give rise to
the extra embryonic chorion
describe development of the bilaminar embryonic disk
cells of embryoblast differentiate into hypoblast and epiblast which form a bilayered flat disc.
What are the hypoblast and epiblast
Hypoblast is primitive endoderm outside the epiblast which is primitive ectoderm.
describe development of the amniotic cavity at day 9
A small cavity forms in the epiblast which is amniotic cavity. A single layer of squamous cells forms domelike roof above epiblast cells called amnion. As embryonic disc increases and size and folds amnion will surround the entire embryo and fill with amniotic fluid.
What are the functions of amniotic fluid and where does it come from
Comes from mothers blood and foetus pee.
Serves as shock absorber, temperature regulator, prevents drying out, cells sticking to tissues it shouldn’t.
describe development of yolk sac
Formed on the 8th day by hypoblast migrating to cover the blastocyst cavity.
Function of yolk sac
provides nutrients while the placenta is being made, source of blood cells, source of primordial germ cells and later forms the gut.
Describe the development of the lacunae networks from day 9-12
Syncytiotrophoblast expands, small lacunae develop and fuse together to form lacunae networks. They fuse with maternal capilliaries called maternal sinusoids and set up a system for nutrition and waste removal.
Describe the major developmental events in week 3- 4
gastrulation, notochordal process, structures derived from three primary germ layers, neurulation and development of somites
describe gastrulation- the formation of the trilaminar disc
starts with the formation of the primitive streak, and cells from the ectoderm migrate to lie above the endoderm (e layers tightly packed) to form the third germ layer= loosely packed mesoderm
describe formation of the notochordal process at 16 days
As the primitive streak is forming mesodermal cells from the primitive node migrate towards the head end of the embryo and form a hollow tube of cells in te midline called the notochordal process.
What is function of notochordal process
Eventually form notochord- solid cylinder that induces surrounding tissue to become specialised.
How does the neural plate form
the notochord induces ectodermal cells to form tall and columnar cells that is the neural plate
The backbone of the embryo is defined by the
notochord
What is neurulation and from what days does it occur
Formation of the neural tube, day 17,19,20, 24
describe neurulation process
The neural plate thickens, lateral edges of the neural plate become more elevated and form neural folds with neural groove in the middle. The neural folds fuse together to form the neural tube.
What tissue are cells inside the neural tube made from and what will they make
ectoderm, form the spinal cord and brain (fore brain, mid brain and hind brain) at the head end.
What tissue are neural crest cells made from and what will they make
ectoderm that migrate from the tube to give rise to melanocytes, nerve cells and facial structure.
describe the development of somites (at day 17)
notochord induces lateral mesoderm either side of the notochord to form somites
What are somites and what do they give rise to (from top to bottom of somite)
to form cuboidlike structures in pairs, one on each side of the neural tube. It will differentiate into three different structures Dermatome-> connective tissue incl dermis.
Myotome -> skeletal muscle of neck, trunk, limbs.
Sclerotome-> vertebrae and ribs
List the 2 major events in week 4
Embryonic folding, formation of pharyngeal arches
Describe the process of embryonic folding
Folding in the median plane produces a head fold and a tail fold, folding in the horizontal plane results in the two lateral folds which cause the embryo to be enveloped by the amniotic cavity. Overall due to the foldings, the embryo curves into a C shape. The yolk sac defines the gut.
What causes the embryonic folding to occur
The different rates of growth of various parts of the embryo especially rapid growth of the neural tube.
Where does the mouth and anus come from
oropharyngeal membrane and cloacal membrane dissolving.
Where does the future umbilical cord come from
the yolk sac and connecting stalk come together.
describe formation of pharyngeal arches
five pairs of swellings forming on the outside of head. Inside there are pharyngeal pouches that connects to the oesophagus which will give rise to the throat. Within each arch there is (working out to in) ecto derm, mesoderm and endoderm. This will contribute to structures in the head.
How do we make a 3d embryo
embryonic folding
