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Flashcards in Embryology- General and Cardio Deck (62):

Ectoderm Derivatives

Can be divided into
- Surface ectoderm (MOO DEAD PEEL)

- Neural ectoderm (COARNEE)

- Neural crest cells (PASS DR PAM the two-Faced PESO)


Neural crest cell derivatives

Pia mater, Peripheral nervous system neurons
Arachnoid mater
Schwann cells
Sympathetic chain (autonomic postganglionic neurons)

Dorsal Root ganglia
Pigment cells (melanocytes)
Adrenal Medulla chromaffin cells (vs. adrenal cortex, which is derived from mesoderm)

Facial and skull bones
Facial cartilage

Parafollicular C cells
Endocardial cushions of the heart
Spiral septum (aorticopulmonary septum)
Odontoblasts (creates dentin)


Endoderm Derivatives


Inferior 2/3 of vagina
Thymus and Thyroid

Entire gastrointestinal lumen (oral cavity through superior pectinate line)
Middle ear cavity and eustachian canal
Urethra (except distal male urethra derived from ectoderm), Urinary bladder

Bulbourethral glands (Cowper's)
Urethral glands (Littre's)
Respiratory tract
Parathyroid and Pancreas
Sublingual and submandibular glands


Lateral plate mesoderm derivatives

- Parietal serous lining of body cavities (somatic portion of lateral plate mesoderm aka Somatopleure)
- Cardiovascular system (splanchnic portion of lateral plate mesoderm aka Splanchnopleure)
- Limb buds development
- Visceral serosal linings of organs
- Dorsal mesentery (ultimately the spleen)


Notochord derivatives

Nucleus pulposus of the intervertebral discs


Paraxial mesoderm

Sclerotome, forming the cartilage and bone of the axial skeleton (including the vertebral column, sternum, and ribs)
Myotome, forming the skeletal muscles
Dermatome, forming the dermis of the dorsal skin


Intermediate mesoderm

Adrenal cortices
Superior ureters
Superior one third of the vagina
Uterus and cervix


Hypaxial Mesoderm

Differentiates into Ribs, Intercostal muscles, Oblique muscles (thoracoabdominal walls)
(part of paraxial mesoderm)


Surface Ectoderm


Mammary Glands
Oral Cavity
Olfactory Epithelium

Distal anal canal below the pectinate line
Enamel (ameloblasts are derived from surface ectoderm)
Adenohypophysis (via Rathke pouch)
Distal male urethra

Parotid salivary glands
Epidermis and accessory structures (e.g. hair, nails, sweat glands, sebaceous glands)
Ear; both the internal and external ear (not middle ear)
Lens of the eye


Neural Ectoderm


CNS neurons within the brain and spinal cord
Retina, iris, and optic nerve
Neurohypophysis (aka the posterior pituitary)
Epithalamus (aka the pineal gland)
Ependymal cells


When does Meiosis arrest in females, and when does it restart?
When does it end?

- Meiosis arrests in Prophase I at 5 months in utero
- Meiosis restarts during ovulation
- Fertilization completes meiosis


What is an ectopic pregnancy?

- A fertilized ovum fails to enter the oviduct from the ovary
- Instead lands on (any) abdominal surface

Fertilized ovum can also stay in ovary instead of going to uterus


What secretes hormones for ovum to promote/maintain pregnancy?

1. Corpus luteum- secretes PROGESTERONE until ~10 days in
- If egg is not fertilized by then, it stops and degenerates into Corpus albicans (fibrous scar tissue)

2. Trophoblasts- secrete chemical messages to avoid autoimmune rejection by mother

3. Synctiotrophoblasts secrete hCG ~9 days post-fertilization
- Signal to Corpus luteum to keep secreting PROGESTERONE (now called corpus luteum graviditatis)
NOTE: Secretion of prostaglandins at this point will result in abortion of fetus

4. Eventually, in humans, placenta will take over PROGESTERONE production


What are the parts of the bilaminar disc embryo?

- Amnion (above epiblast cells)
- Epiblast layer (top)
- Hypoblast layer (bottom)
- Yolk sac (underneath hypoblast)

- Everything is enclosed by chorionic cavity (derived from original trophoblasts)
- Smooth chorion
- Villous chorion (forms placenta)

[Note, Villi consist of: cytotrophoblasts (surround epiblasts/hypoblasts), then surrounding that are Syncytiotrophoblasts]


What germ layer forms the vasculature?

Lateral plate mesoderm


What germ layer forms the original kidneys of the body?

Intermediate mesoderm


What are the four primary body cavity membranes?

- Pleural membranes (one for each lung)
- Pericardial membrane (surrounds heart)
- Peritoneal membrane (surrounds stomach/intestine/liver, other abdominal cavity organs)


What forms the periosteal membranes

Lateral plate mesoderm


What germ layer makes the smooth muscles?

Lateral plate mesoderm


What do the sclerotomes eventually become?

Vertebrae (they resegment, then differentiate)


What does the dermatome become?

Dermis of the skin, overlying muscles


What does the myotome become?

Skeletal Muscles


What does the hypaxial mesoderm form?

- Ribs
- intercostal muscles
- oblique muscles of abdominal wall
- limbs (upper limb externally rotates, lower limb medially rotates)


Where are the four major celomic cavities?

Celom= space b/w parietal and visceral layers

- One for each lung
- One for the heart
- One for entire abdomen


What is the stromadeum?

Region that eventually forms the oral cavity (ectoderm lined with endoderm)
- Buccopharyngeal membrane covers opening to the oral cavity


What is the proctodeum?

Region that forms the cloaca (ectoderm line with endoderm)
- Eventually forms anus, vagina, urethra


What is the function of the vitelline duct?

Forms connection between yolk sac and the gut, nutritious yolk fluid can enter developing GI tract


What is the function of the vitelline veins?

Bring oxygenated blood produced by surface of the yolk sac to the forming liver/heart


What do the diverticula that bud of the primitive GI tract become?

- Liver
- Gall bladder
- Dorsal/ventral pancreas
- Caecum and appendix


What is the function of the vitelline arteries?

Return fetal blood to yolk sac
- Branch off embryonic aorta


What do the vitelline arteries become in the adult?

- Celiac artery
- Superior mesenteric artery
- Inferior mesenteric artery


What does the vitelline vein become in the adult?

The portal vein


What are the parts of a blastocyst?

- Inner cell mass/embryoblast (differentiate into primordial germ cells and somatic cells)
-> Below inner cell mass is blastocyst cavity

- Trophoblasts surround the inner cell mass = becomes nourishment structure for embryo

- Syncitotrophoblasts eventually become the placenta


What are the phases of fertilization?

Phase 1: penetration of the corona radiata

Phase 2: penetration of the zona pellucida

Phase 3: fusion of the oocyte and sperm cell membranes


Where does implantation of the blastocyst commonly occur?

The upper part of the uterus


What are the parts of an ovum undergoing ovulation/waiting to be fertilized?

- Ovum
- Zona pellucida surrounds ovum
-Cumulus oöphorous surrounds the whole thing, supporting cells are called "follicular"


What happens immediately after fertilization?

- Fertilized ovum divides to form 2- cell stage (~30 hrs post fertilization)
- Then 4-cell stage
- Then 16-cell morula (~3-4 days post fertilization)
Blastocyst forms shortly after (~4th day post fertilization, when morula begins to enter uterus)


1. When does bilaminar disc form?
2. When does trilaminar disc form?

1. During the second week (Day ~8)
2. During the third week (starting Day ~15-16)


How does trilaminar disc form?

1. Cells of the epiblast (of the bilaminar disc) begin to migrate inwards
2. Cells form a "crack and a pit"- the primitive streak and the primitive node
3. Epiblasts eat at the hypoblasts and take their place
4. Notochord forms
5. Mesoderm and Endoderm form
6. Epiblasts differentiate to form Ectoderm


How does nerulation occur?

- Once notochord forms, it signals formation of neural tube
- Center of ectoderm folds up forming two ridges (neurula formation)
- Neural plate closes over ridge (neural plate is parts of the ectoderm overlying neurula/groove)
- Before left and right ridges close completely, a population of cells dispatch from the edge --> neural crest cells
- Neural tube forms -- becomes brain/spinal cord


What is derived from the bulbus cordis?

- MAINLY: Aortic arch and the pulmonary trunk (along with truncus arteriosus)
- Aortic vestibule of left ventricle
- Conus arteriosus of right ventricle


What forms the aortic arch and pulmonary trunk?

- Truncus arteriosus (top part) and bulbus cordis (bottom part)


Sinous venosus derivatives

- Coronary sinus (left horn of sinus venosus)
- Smooth wall of right atrium


What structure later becomes the coronary sinus?

Left horn of the sinus venosus


What induces separation of truncus arteriosus into the aorta and pulmonary trunk?

Neural crest cells


What are septa?

What are ostea?

Septa are walls formed to separate chambers and vessels of the heart

Ostea are openings in the walls


How does foramen ovale form?

- Endocardial cushion migrates up to meet septum secondum and septum primum
- Foramen primum exists between endocardial cushion and septum primum

- Septum primum and endocardial cushion meet, foramen primum closes

-Septum secundum migrates towards endocardial cushion as it migrates up, BUT they do not meet (foramen ovale forms)

- Cell apoptosis occurs in fused wall of septum primum and the endocardial cushion, resulting in foramen secundum

- This is how blood can flow from right atrium to left atrium during fetal circulation


What specific structure often malfunctions in children with Down Syndrome?

Endocardial cushions, which also forms valves


How do atrial-ventricular septums form?

Endocardial cushion grows laterally to form wall


How do interventricular septums form?

-Endocardial cushion and membranous portion of interventricular septum migrates down

-Muscular portion of interventricular septum migrates up

-Aorticopulmonary septum is not yet spiraled


How do aorta and pulmonary trunk form?

- Both arise from bulbus cordis and truncus arteriosus

- The separate halves of truncus arteriosus/bulbus cordis twist and separate

- Neural crest cells facilitate separation


Types of ventricular septal defects? h

How do they arise?

1. Membranous (Most common, usually must be fixed with surgery)
--> Defect in endocardial cushion growth, does not expand all the way

2. Muscular portion (likely to spontaneously fuse, surgery not usually necessary)
--> Defect in ingrowth of muscular ventricular wall


What is the transposition of great vessels?

- Truncus arteriosus fails to spiral
- Usually due to malfunction with neural crest cells (and their messaging)
- Aorta is located above right ventricle, pulmonary trunk is located above left ventricle

-Need cardioprotective shunts to survive past utero


What is Persistent truncus arteriosus?

-Truncus arteriosus does not split properly,
so ascending aorta and pulmonary trunk are not separated
-Also occurs with VSD, so blood from both sides of heart flow through both systemic and pulmonary circulation
- There is no membranous ventricular septum, only muscular portion

- Results in CYANOSIS

- Can coexist with other neural crest migration defects!


What happens to the heart around day ~23?

Heart begins to rotate and twirl iteself upward --> "cardiac loop"
- Four chambers are in place


How does heart form?

- Smooth muscle cells differentiate, migrate from capillary bed near the pharynx
- They join together to form a tube, which later becomes the heart


How does the liver form?

- Cells from the gut differentiate into liver cells
- They migrate down underneath the heart to form the liver
- Heart and liver are connected by vitelline vein (later becomes the portal vein)

Note that the liver is formed also formed from diverticula of the gut (like most gut organs)


What structures form from the septum transversum?

- Diaphragm
- Endocardial cushions
- Fibrous pericardium (cytoskeleton of heart)
- Valves of the heart

Children with down syndrome often have defects with septum transversum (issues with valves)


What structures are within the umbilical cord?

- Vitelline duct
- Vitelline arteries
- Vitelline veins
- Umbilical arteries
- Umbilical veins


What is a remnant of the vitelline duct?

Meckel's diverticulum (appendage from intestines)


How does placental circulation work?

- Oxygen rich blood is delivered to fetus via umbilical vein

- Oxygen poor blood is returned to the placenta/mom via umbilical artery

-Chorionic villi (mainstem, then branch) take up nutrients in space between endometrium and amniochorionic membrane

-Endometrial arteries and veins allow for circulation in placenta


What do these structures in the embryo become in the adult?
1. Ductus arteriosus
2. Foramen ovale
3. Ductus venosus

1. Ligamentum arteriosum
2. Fossa ovalis
3. Ligamentum venosum