Lecture 12: Embryology

Question 1

What does embryogenesis achieve

Answer 1

• 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

Question 2

Until what time is it called an embryo

Answer 2

Up to 8th week.

Question 3

What are the three different germ layers and their colours

Answer 3

Ectoderm (blue) mesoderm (red), and endoderm (yellow)

Question 4

Define pattern formation (patterning)

Answer 4

the developmental process by which cells acquire different identities depending on their relative spatial positions in the embryo

Question 5

Ectoderm gives rise to

Answer 5

tissues that tend to be on the outside-> the epidermis, all nervous tissue, brain and spinal cord

Question 6

Mesoderm gives rise to

Answer 6

internal structures/organs such as All structures in the: skeletal, muscular, cardiovascular, lymphatic system.

Question 7

Endoderm gives rise to

Answer 7

the inside of us - gut, reproductive cells.

Question 8

What are the events in the first week of development

Answer 8

fertilisation, cleavage of the zygote, formation of the morula and blastocyst, implantation

Question 9

Describe the steps of fertilisation

Answer 9

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.

Question 10

describe capacitation - and what is its function

Answer 10

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

Question 11

What is the corona radiata (crown of light)

Answer 11

outermost layer of somatic granulosa cells surrounding the 2ndary oocyte

Question 12

How does the sperm penetrate the zona pellucida

Answer 12

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.

Question 13

Directly after one sperm enters the cytoplasm of the oocyte

Answer 13

undergoes a series of structural changes that prevent polyspermy.

Question 14

Describe the events and timing of Cleavage of the zygote and formation of morula

Answer 14

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.

Question 15

Describe the events and timing the formation of the blastocyst and the most important result.

Answer 15

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.

Question 16

What is the trophoblast and what will it form

Answer 16

the outer superficial layer of cells forming the spherelike wall of blastocyst. Will give rise to placenta

Question 17

What is the embryoblast

Answer 17

Inner cell mass that will become the embryo

Question 18

What processes in the first week occur in the fallopian tube

Answer 18

fertilisation, cleavage, morula formation

Question 19

Describe process, location and timing of implantation

Answer 19

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

Question 20

List the main developmental events in week 2

Answer 20

development of the trophoblast, embryonic disk, amnion and yolk sac

Question 21

describe the development of the trophoblast and two things it does

Answer 21

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.

Question 22

What is the syncytiotrophoblast

Answer 22

contains no distinct cell boundaries located closest to the endometrium.

Question 23

What is the cytotrophoblast

Answer 23

composed of distinct cells located between the embryoblast and syncytiotrophoblast.

Question 24

what does the syncytiotrophoblast and cytotrophoblast give rise to

Answer 24

the extra embryonic chorion

Question 25

describe development of the bilaminar embryonic disk

Answer 25

cells of embryoblast differentiate into hypoblast and epiblast which form a bilayered flat disc.

Question 26

What are the hypoblast and epiblast

Answer 26

Hypoblast is primitive endoderm outside the epiblast which is primitive ectoderm.

Question 27

describe development of the amniotic cavity at day 9

Answer 27

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.

Question 28

What are the functions of amniotic fluid and where does it come from

Answer 28

Comes from mothers blood and foetus pee.

Serves as shock absorber, temperature regulator, prevents drying out, cells sticking to tissues it shouldn’t.

Question 29

describe development of yolk sac

Answer 29

Formed on the 8th day by hypoblast migrating to cover the blastocyst cavity.

Question 30

Function of yolk sac

Answer 30

provides nutrients while the placenta is being made, source of blood cells, source of primordial germ cells and later forms the gut.

Question 31

Describe the development of the lacunae networks from day 9-12

Answer 31

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.

Question 32

Describe the major developmental events in week 3- 4

Answer 32

gastrulation, notochordal process, structures derived from three primary germ layers, neurulation and development of somites

Question 33

describe gastrulation- the formation of the trilaminar disc

Answer 33

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

Question 34

describe formation of the notochordal process at 16 days

Answer 34

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.

Question 35

What is function of notochordal process

Answer 35

Eventually form notochord- solid cylinder that induces surrounding tissue to become specialised.

Question 36

How does the neural plate form

Answer 36

the notochord induces ectodermal cells to form tall and columnar cells that is the neural plate

Question 37

The backbone of the embryo is defined by the

Answer 37

notochord

Question 38

What is neurulation and from what days does it occur

Answer 38

Formation of the neural tube, day 17,19,20, 24

Question 39

describe neurulation process

Answer 39

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.

Question 40

What tissue are cells inside the neural tube made from and what will they make

Answer 40

ectoderm, form the spinal cord and brain (fore brain, mid brain and hind brain) at the head end.

Question 41

What tissue are neural crest cells made from and what will they make

Answer 41

ectoderm that migrate from the tube to give rise to melanocytes, nerve cells and facial structure.

Question 42

describe the development of somites (at day 17)

Answer 42

notochord induces lateral mesoderm either side of the notochord to form somites

Question 43

What are somites and what do they give rise to (from top to bottom of somite)

Answer 43

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

Question 44

List the 2 major events in week 4

Answer 44

Embryonic folding, formation of pharyngeal arches

Question 45

Describe the process of embryonic folding

Answer 45

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.

Question 46

What causes the embryonic folding to occur

Answer 46

The different rates of growth of various parts of the embryo especially rapid growth of the neural tube.

Question 47

Where does the mouth and anus come from

Answer 47

oropharyngeal membrane and cloacal membrane dissolving.

Question 48

Where does the future umbilical cord come from

Answer 48

the yolk sac and connecting stalk come together.

Question 49

describe formation of pharyngeal arches

Answer 49

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.

Question 50

How do we make a 3d embryo

Answer 50

embryonic folding