Lectures 10 & 11 - Embryology Flashcards
The human body develops from a single cell called a ……
Zygote
Where is the oocyte fertilized?
In the Fallopian tube
Initially the fertilized egg divides at what rate?
1 division every 24 hours
At the 16 cell stage (~3 days) the cell mass is called a ……
Morula
At 4 days the blastocyst undergoes cavitation to form a ……
Blastocoel
What are the two types of cells in a blastocyst?
- Trophoblast - outer epithelial layer;
- Inner cell mass
How many days after fertilization does the blastocoel implant into the uterine wall?
Between 5 and 10 days
What are the three types of embryonic tissue?
Ectoderm, mesoderm, endoderm
What is the process that forms the germ layers?
Gastrulation
What cell populations is the bilaminar disc made of?
The epiblast and the hypoblast.
Is the embryo a part of the epiblast or the hypoblast?
Epiblast
What does some of the epiblast and all of the hypoblast become?
Extra-embryonic tissue, such as the yolk sac (hypoblast) and amniotic membrane (rest of the epiblast that isn’t a part of the embryo)
What is the primitive streak?
A line of thickened cells n the upper surface of the bilaminar disc
How does the primitive groove form?
By invagination of the primitive streak.
What population of cells migrates into the primitive groove?
The epiblast
What is the first layer of embryonic tissue to form?
The endoderm
What is the second layer of embryonic tissue to form?
The mesoderm
How is the ectoderm formed?
It is formed from the remaining epiblast cells overlying the mesoderm.
Does the embryonic endoderm sit on top of the hypoblast?
No, it pushes it aside?
Does the embryonic mesoderm sit on top of the endoderm?
Yes
What is anterior to the primitive groove?
The primitive node
What is anterior to the primitive node?
The notocord
True or false: cells that move through different levels of the notochord have different mesoderm fates.
False: cells that move through different levels of the PRIMITIVE GROOVE have different mesoderm fates.
How does the notochord form?
The notochord forms in mesoderm by cells migrating down from the ectoderm through the primitive groove.
What are the derivatives of the ectoderm?
Nervous system and epidermis
What are the derivatives of the mesoderm?
blood, heart, kidneys, gonads, most bone, muscles, and connective tissues
What are the derivatives of the endoderm?
epithelium of gut and associated organs
What are the three basic steps of how the ectoderm gives rise to the nervous system?
- Notochord induces overlying ectoderm to form neural plate;
- Neural plate invaginates to form the neural crest.
- Neural crest folds and converges to form neural tube
What is the neural crest?
Like the crest of two waves converging, the neural crest cells are the group of cells that form the top of the neural tube.
What is derived from the neural crest?
A wide range of structures, including the structures of the face, Schwann cells, and dorsal root ganglia.
The neural tube is initially one cell thick and hollow. The rostral end starts to swell and form what?
Vesicles
The vesicles give rise to which part of the CNS?
The brainz
What are Hox genes?
Hox genes are highly conserved transcription factors responsible for rostrocaudal positioning
Fill-in the blank: __________ of genes on __________ predict expression pattern in embryo.
order; chromosome
How many Hox gene complexes are there in humans? What is their role in neural development?
4 Hox genes complexes; they define the subdivisions of the brainstem
What are some of the mesodermal derivatives?
Dermis, muscles, skeleton, urogenital tract, heart and blood vessels, wall of GIT and RT
What is the difference between mesenchyme and mesoderm?
Mesoderm: one of the three embryonic tissues
Mesenchyme: refers to shape and behavior of a cell
NOT SYNONYMOUS
What are the three subdivisions of mesoderm?
- Paraxial mesoderm (para-axial, ie medial)
- Intermediate mesoderm
- Lateral mesoderm
Name three derivative of the paraxial mesoderm.
Dermis of skin, axial skeleton, axial and limb muscles
Name three derivative of the intermediate mesoderm.
Urogenital system
Name three derivative of the lateral mesoderm.
Ventrolateral body wall, visceral pleura and peritoneum, blood vessels and blood forming tissue, heart, wall of GIT and RT
What are somitomeres?
Swellings that appear progressively along the length of the paraxial mesoderm
What happens to the 8th pair of somitomeres at the 20 somitomere stage?
The 8th pair become an independent pair of somites after which the remaining caudal somitomeres also become somites. (ie, 9th turns into a somite, the 10th and so on.)
True of false: The first 7 somitomeres never become somites.
True
Somite 8 represents what part of the adult body? What then do somitomeres 1-7 represent?
Somitomere 8 represents top of the neck, which means that somites 1-7 represent the head.
What is a somite?
A free block of mesoderm
What does each somite divide into?
A sclerotome and a dermomyotome
What does each dermomyotome divide into?
A dermotome and a myotome
What are the derivatives of the sclerotome?
Axial skeleton (except the skull), vertebrae and associated structures
What are the derivatives of the dermotome?
Dermis of skins
What are the derivatives of the myotome?
Trunk/axial muscles associated with the ribs and vertebrae
The bones of the appendicular skeleton (ie, limb) are derived from which mesoderm? (Paraxial, intermediate, or lateral)
The lateral plate/mesoderm.
What are the pharyngeal arches?
They are the evolutionary remnants of our ancestral forms that did have gills in this location, apparent at 3-4 weeks during development. They have been modified into a variety of other structures, most importantly the front gill arches have been modified into the upper and lower jaws.
What is the importance of the pharyngeal arches?
The pharyngeal arches can be modified to give rise to a whole range of structures. If there is a congenital defect in the arches early in the development it will translate into the adult, giving rise to problems of apparently unrelated structures.
When does limb development initiate?
4th-8th week
Where does the muscle of the limb comes from?
Lateral myotome of the somite
Where does the bone and connective tissue of the limb comes from?
Lateral plate mesoderm
Fill-in the blank: Limb growth is initiated by __________, then controlled by __________.
Limb growth is initiated by mesoderm, then controlled by ectoderm.
Fill-in the blank: The limb is a location where the __________ genes play a crucial role in setting this __________ information.
The limb is a location where the Hox genes play a crucial role in setting this positional information.
Limb segments are defined by combinations of Hoxd genes, which are expressed successively in the growing limb bud. What combinations form the different bones and corresponding regions of the upper limb? (Eg, scapula is formed by Hoxd 9)
Scapula: 9 Humerus: 9, 10 Forearm: 9, 10, 11 Carpus: 9, 10, 11, 12 Phalanges: 9, 10, 11, 12, 13
What is the consequence of the loss of a single Hoxd gene on the upper limb?
Loss of that particular segment. Eg, if you are a knockout Hoxd11 mouse then you won’t have a forearm, though you will still have a carpus and phalanges.
How are the hands and feet formed?
They start off as symmetrical discs and the digits are sculpted by apoptosis during development.
All the derivative of the endoderm are what type of tissue?
Epithelial.
Fill-in the blank: The __________ forms the inner lining of many organ systems, such as the __________, but the muscular wall of these organs are formed by the __________.
The endoderm forms the inner lining of many organ systems, such as the gastrointestinal tract, but the muscular wall of these organs are formed by the mesoderm.
What is the coelum?
The cavity in which the gut and viscera are going to exist.
How many weeks gestation does the coelum form?
4 weeks of age.
What shape is the embryo at ~4 weeks of age?
C-shaped tube.
The lateral mesoderm splits longitudinally to form two layers of mesoderm, an inner layer and an out layer. What are they called?
Inner: Splanchnic mesoderm
Outer: Somatic mesoderm
In conjunction with the ectoderm, what does the somatic mesoderm give rise to?
The outer layer of our body, ie the muscles that enclose the body cavity (such as the abdominal muscles.)
In conjunction with the endoderm, what does the splanchnic mesoderm give rise to?
The viscera of the body cavity
What are the derivatives of the lateral mesoderm? (4)
- Visceral pleura/peritoneum
- Blood vessels and blood forming tissues
- Heart
- Wall of gut and respiratory tracts
Fill-in the blank: the endoderm is initially continuous with the yolk sac.
the ___________ is initially continuous with the yolk sac.
Fill-in the blank (explanation of the process that forms the coelum): _____ _____ splits longitudinally so that you have two sheets of mesoderm with a space in the middle that is open to the outside world: _____ (inner) and _____ (outer) mesoderm.) These two edges start to sling inwards towards the midline and then the ______ mesoderm and the _______ come together in the midline. The ______ is initially continuous with the yolk sac so the space that becomes the lumen of the gut is eventually _____ __, with the anterior end becoming the _______ and the posterior end becoming the ______.
Lateral mesoderm splits longitudinally so that you have two sheets of mesoderm with a space in the middle that is open to the outside world: splanchnic (inner) and somatic (outer) mesoderm.) These two edges start to sling inwards towards the midline so and then the splanchnic mesoderm and the endoderm come together in the midline. The endoderm is initially continuous with the yolk sac so the space that becomes the lumen of the gut is eventually pinched off, with the anterior end becoming the foregut and the posterior end becoming the hindgut.
Prior to 3 weeks of age there is neither an oral nor an anal cavity, instead their are oral and anal pits. What are they called?
Stomadeum (oral) and proctodeum (anal)
At what age during develop (how many weeks) and where does the ectoderm meet the endorderm?
At 3 weeks the stomadeum break and the oral cavity forms.
The anus is initially sealed by the _______ membrane.
Cloacal.
What is the allantois?
A vestigial structure in humans, formed as a branch of the hindgut, which stores nitrogenous waste in other species.
What separates the allantois from the hindgut?
The urorectal septum. (Made of mesoderm)
What is the role of the urorectal septum?
It extends to divide the rectum from the urogenital tract.
What structure(s) does allantois give rise to in the adult?
The bladder and urogenital tract.
The myocardium is derived from which mesoderm?
Splanchnic lateral mesoderm
By what day do the following events occur:
Appearance of blood vessels, appearance of blood cells, heart pumping, circulating blood through vessels
17, 18, 22, 24
Formation of the heart. Fill-in the blank: Splanchnic mesoderm forms bilateral tubes that comes together in the midline, the fusion of which produces the heart.
__________ mesoderm forms __________ tubes that comes together in the ________, the fusion of which produces the heart.
The myocardium, pericardium, and endocardium are all derivative of the mesoderm whereas parts of the midline of the heart and major outflow vessels are derived from which group of cells?
Neural crest cells
Initially the heart has _ chambers. (Number)
4
Which structure divides the ventricles and the atria?
Septa
What feature of the atrial septa allows bidirectional flow between the right and left atria, and allows blood to bypass the ventricles?
The foramen ovalis
Fill-in the blank: the aortic arches develop via a process of __________ ____ of _______, and addition of new segments.
selective loss of segments
Fill-in the blank: the GI tract develops via a process of _______ _______.
Complex folding.
By week _ the body cavity is larger enough to fit the GI tract and so the gut retract back. Failure to retract is call ___________.
9; omphalocele
What is an umbilical hernia?
Retraction of the gut but failure to seal the abdominal wall.
Which part of the mesoderm is the urogenital system made of?
The intermediate mesoderm
Kidney development. Fill-in the blank: The __________ (first to appear) forms __________ and the __________ duct. The __________ degenerate but the _____________ becomes the __________ duct. Before degenerating, the __________ then induces the __________. The __________ goes on to form the adult kidneys.
The prosnephros (first to appear) forms nephrostomes and the pronephric duct. The nephrostomes degenerate but the pronephric duct becomes the mesonephric duct. Before degenerating, the mesonephros then induces the metanephros. The metanephros goes on to form the adult kidneys.
In females, what does the Mullerian duct become?
Fallopian tubes and distal vagina
All major organogenesis is complete by _ months.
3
What are teratogens? Give an example. DUring what period of pregnancy do teratogens generally have an effect?
Birth defect generating agents, eg thalidomide. They usually have an effect during the first trimester (first 3 months.)
