Embryology Flashcards
What is neurulation
Process in which the neural tube forms
When does neurulation take place
Week 3-4
What will the neural tube later become
CNS: Brain, spinal cord, meninges
As well as part of the bones that surround them
What is gastrulation and when does it take place?
Week 3
The three primary germ layers (ectoderms, mesoderm, endoderm) form and start becoming different types of tissue
What will the ectoderm differentiate into
Nervous system and skin
What will the mesoderm become
Connective tissue, bone , muscle, urogenital organs, pleura, peritoneal linings of the body cavity
What will the endoderm eventually become
Lining of the internal organs such as GIT and lining of the airways
What structure induces neurulation
Notochord
What will the notochord eventually develop into
Nucleus pulposus of the intervertebral disc
What does the neural tube come off of
Ectoderm
What happens at the end of week 3 related to neurulation
The lateral edges of the ectoderm become more elevated and will form the neural fold.
The depressed mid-region is called the neural groove.
The whole thing is referred to as the neural plate
How does neurulation advance
Both cranially and caudally
It starts from the mid-region
This means that at the end of neurulation, the cranial end will give rise to the brain
Caudally will be the spinal cord
How is the neural tube formed
Fusion of neural folds together
Starts in the middle and goes both cranially and caudally
How is a neural crest formed?
During neurulation as the neural tube forms, some of the ectodermal cells from the tube migrate form several layers of cells called the neural crest
What will the neural crest give rise to
Structures that work very closely with CNS
This includes the peripheral nervous system spinal and cranial nerves and their ganglia
Autonomic nervous system ganglia
E.g
Schwann cells, Pigment cells, adrenal medulla, bony skull, meninges, dermis
Sensory (dorsal root) ganglia
CN 5,7,9,10
What will the remaining ectoderm after neurulation become
Skin
What does the spinal cord of the neural tube become
Spine
What does the rhombencephalon of the neural tube become
Pons
Cerebellum
medulla
What does the mesencephalon of the neural tube become
Midbrain
What does the prosencephalon of the neural tube become
Cerebrum
Thalamus
Further divisions of the prosencephalon, mesencephalon and rhombencephalon
What makes up the tri laminar disc composed of?
Ectoderm
Mesoderm
Endoderm
By what week of embryonic development can the three primary brain vesicles be identified?
By the end of week 5
Embryonic development of the ventricles
Telencephalon- Lateral ventricles
Diancephalan- Third ventricle
Metencephalon- Upper part of the 4th ventricle
Myelencephalon- The lower part of the 4th ventricle
What is spina bifida?
Failure of the tube to close in the spinal cord
What is anencephalus
Failure of the tube to close in the cephalic region
What layer of the trilaminar disc are the kidneys derived?
Intermediate mesoderm.
What are the names of the 3 paired kidneys that develop in the embryo?
- Pronephros.
- Mesonephros.
- Metanephros.
What does the mesonephros form?
The mesonephric ridge and duct.
What does the mesonephric duct form in the male?
The epididymis, vas deferens, seminal vesicles and ejaculatory duct.
What does the ureteric bud form?
The ureters, collecting duct, major and minor calyces and the renal pelvis.
What does the Müllerian duct form in females?
The uterine tubes, uterus, cervix and proximal 1/3 of vagina.
What is the cloaca divided into?
- Anorectal canal.
- Urogenital sinus.
What are the 3 parts of the urogenital sinus?
- Upper part.
- Pelvic part.
- Phalic part.
What part of the urogenital sinus is the bladder formed from?
The upper part.
What does the pelvic part of the urogenital sinus form?
The prostatic and membranous urethra.
What does the phalic part of the urogenital sinus form?
The penile urethra.
What part of the trilaminar disc are the bladder and urethra formed?
The endoderm.
What layer of the trilaminar disc forms the male and female genitalia?
Intermediate mesoderm.
What is the indifferent stage?
When the Wolffian and Müllerian ducts are both present. It is impossible to tell the sex of the embryo.
When are embryos no longer indifferent?
They are indifferent until the end of the 6th week.
What causes the genital ridge to form ovarian tissue?
This happens by default due to the lack of a gonadal hormone influence. There is no Y chromosome and so no sex determining region and so no testis determining factor released.
Why does the mesonephric duct degenerate in a female?
Due to the absence of testosterone.
What does oestrogen stimulate?
The development of the female external genitalia and the differentiation of the Müllerian duct.
What does the female external genitalia develop from?
The urogenital sinus.
What does the urethral fold form in a female?
The labia minora.
What does the genital tubercle form in a female?
The clitoris.
What does the genital swelling form in a female?
The labia majora.
True or False: the ovary lies behind the broad ligament.
True.
What is the fornix?
The space between the cervix and the vagina.
What is the hymen formed from?
The urogenital sinus.
What is the primitive streak?
A depression in the epiblast.
When do leydig cells start producing testosterone?
Week 8.
What does testosterone stimulate?
Differentiation of the Wolffian duct.
Why does the Müllerian duct degenerate?
Due to inhibiting substance being released from sertoli cells.
What forms from degeneration of the Müllerian duct?
Utriculus prostaticus.
What forms the phallus?
Elongation of the genital tubercle.
What does the genital swelling form in a male?
The scrotum.
What is meckle’s diverticulum a remnant of?
The vitelline duct - connected the midgut to the yolk sac.
What is the significance of the Hilton white line?
It separates the non keratinised and keratinised epithelium in the anal canal.
When does the anal membrane rupture?
In the 7th week. This allows the upper 2/3 to be continuous with the lower 1/3 of the anal canal.
What layer of the trilaminar disc is the upper 2/3 of the anal canal derived from?
Endoderm.
What layer of the trilaminar disc is the lower 1/3 of the anal canal derived from?
Ectoderm.
What is the name of the structure that condenses in the intermediate mesoderm that gives rise to kidneys called?
Nephrogenic cords
Where does the heart tube develop from?
Splanchnic layer of the lateral plate mesoderm
What is the role of the endoderm in developing the heart tube
Secretes Vascular endothelial growth factor causing the lateral plate mesoderm to differentiate
What does the mesoderm differentiate into? heart
Angioblast
Hemocytoblast
What happens during lateral folding. heart
Through fusing 2 heart tubes become 1
2 pericardial cavities become 1
What happens to the angioblast what does it develop into? heart
Angioblast-> Endothelial lining -> Endoderm
Name the layers of the primitive heart tube, starting from the bottom
Blood flows into:
sinus venosus
primitive atria
primitive ventricle
bulbous cordis
truncus arteriosus
dorsal aortae
What does the truncus arteriosus become?
Pulmonary trunk
Aortic arch
What does the bulbus cordis become?
RV + outflow tract
What does the primitive ventricle become?
LV
What does the primitive atria become?
LA + RA
Where does blood flow from into the sinus venousos when it is a primitive heart tube?
Common cardinal vein
Umbilical vein
Vitelline veins
Stages of cardiac looping
TA + BC move down and to the right
PV moves upwards
PA moves backwards and outwards
What makes up the endocardial cushions
Neural crest cells
What the structure called when you fuse the post. and ant. endocardial cushions (heart)
Septum intermedium
What happens when the septum intermedium is formed
Forms the right AV canal and the left AV canal
Forms valves on both sides of the septum (mitral valve/tricuspid valve apparatus) and a valvular annulus
This forms cordi tendinae
What does the left hirn develop into?
Coronary sinus
What does the right common cardinal vein develop into
Superior vena cava
What happens in the elongation stage of midgut development?
Rapid elongation forms the primary intestinal loop. The proximal part of the loop forms the small intestine and the distal part forms the large intestine up to 2/3 TC.
What happens in the herniation stage of midgut development?
The rapid growth of the intestinal loop means it is pushed into the extra embryonic cavity in the umbilical cord.
What happens in the retraction stage of midgut development?
In the 10th week the herniated midgut returns into the expanded abdominal cavity. Th jejunum is first to return.
What happens in fixation of midgut organs?
This is when some regions of the gut lose their dorsal mesentery. These regions become retroperitoneal.
What happens in the rotation stage of midgut development?
The elongated intestinal loop rotates 270 degrees anticlockwise.
What connects the midgut to the yolk sac?
The Vitelline duct.
What are the 5 stages of midgut development?
- Elongation.
- Herniation.
- Rotation.
- Retraction.
- Fixation.
Easy Hores Rotate Round Fishermen
What does the ventral mesentery become?
The lesser omentum.
Blastocyst (day 4) ->
What is the low oestrogen to progesterone during pregnancy responsible for
Implantation
What develops into the placenta
Trophoblast
What does trophoblast secrete
Human chorionic gonadotropin (HCG) happens around day 8
Tell the corpus luteum to keep secreting oestrogen and progesterone. This also suppresses other follicles from maturing
What happens in the first trimester
Week 1 -13
Oestrogen + progesterone released by corpus luteum
HCG rises until it peaks before the end of the trimester and begins to degrade down.
The corpus luteum therefore shrivels and the placenta takes over
What is the most abundant type of oestrogen
estriol
Placenta and syncytiotrophoblast
Specialed trophoblast cells called the syncytiotrophoblast begin to secrete estriol and progesterone.
What is human placental lactogen (hPL)
Inhibits insulin and makes sure there is a steady flow of glucose
Does the haematocrit go up or down during pregnancy
Down
Development of the placenta
Day 7-8, the foetus implants on the endometrial wall (decidua) and the area that it implants to is the decidua basalis.
Trophoblast cells from the outer layer can snuggle deeper into the decidua basalis. the foetus assembles into two layers of cells called the cytotrophoblast and the syncytiotrophoblast.
The cytotrophoblast is an inner layer of mononucleated cells. The syncytiotrophoblast is a multinucleated outer layer.
The syncytiotrophoblast does undergo cell division and just simply dies out over time. With the number of syncytiotrophoblast cells, there is a steady flow of cytotrophoblast. The cytotrophoblast fuses with the syncytiotrophoblast forming a syncytium.
The syncytiotrophoblast gets bigger going into the decidua basalis.
Around day 14 primary villi are formed cells begin to clear out between the primary villi leaving behind empty spaces called lacunae. Arteries fuse with lacunae and become filled with oxygenated blood. Veins bring blood back to the heart
Day 17: Foetal mesoderm cells form blood vessels in villi - connect with blood vessels in the umbilical cord.
The basal plate or the decidual plate is a thick layer of the decidua basalis where the spiral arteries and veins have to pass through to get to the junctional zone
In months 4/5 decidual septa form and divide the placenta into 15-20 regions known as cotyledons
Foetal contribution to placenta
Chorionic plate
Maternal contribution to placenta
Maternal arteries
Chorionic cavity
