Embryology Organogenesis Flashcards
What are the derivatives of the ectoderm?
- Central nervous system
- Peripheral nervous system
- Epidermis, Hair, Nails
- Sensory epithelium (nose, ear, eye)
What are the derivatives of the mesoderm?
paraxial division: Skull, muscles, vertebrae
intermediate division: urogenital system
Lateral plate: serous membranes around organs (visceral layer) , body wall & limbs (parietal layer)
What are the derivatives of the endoderm?
Gut tube and its derivatives: glands, lungs, liver, gallbladder, pancreas
During week 3, the outer ectoderm undergoes neurulation. What are the three germ layers not our creative?
- Surface ectoderm (integumentary system)
- Neural tube (CNS)
- Neural crest cells (PNS)
What structures of the central nervous system are derived from the neural tube?
- Brain
- Spinal cord
- Posterior pituitary
Define the neural plate.
Pear-shaped thickening of ectoderm induced by the notochord and prechordal mesoderm.
(forms the CNS)
How is the neural tube formed?
The lateral edges (neural folds) of the neural plate approach each other and fuse (cranially to caudally) from a cervical region
Define neuropores. When do they close? What do they form?
- Partially incomplete fusion of the neural folds
- Day 25
- Cephalically forms the brain and the spinal cord caudally
Define neural crest.
Special Band of ectodermal cells on the neural fold that migrate into the mesoderm, proliferate, and form important structures.
Which structures are neural crest derivatives?
- Spinal ganglia
- Sensory ganglia of cranial nerves V, VII, IX, X
- Autonomic ganglia
- Adrenal medulla
- Schwann cells
- Connective tissue of the anterior part of the skull and meninges
- Melanocytes
- C cells of the thyroid gland
- conotruncal septum of the heart
- axial mesoderm becomes the notochord
- paraxial mesoderm becomes somites
- Intermediate mesoderm becomes the reproductive and urinary system
- Lateral plate music becomes splanchnic and somatic divisions
What are the paraxial mesoderm somites?
- Sclerotome (vertebrae, ribs, occipital bone)
- Somite dermatome (skin over spine in epaxial region)
- Syndetome (tendons)
- Myotome (skeletal muscle)
Which tissues are derived from the somatic lateral plate mesoderm (SoLPM)?
Connective tissue, bones and smooth muscle
Which tissues are derived from the splanchnic lateral plate mesoderm (SpLPM)?
- Connective tissue and smooth muscle associated with the visceral inner tube
- Endothelium of blood vessels arteries and veins
- cardiac muscle
How does blood vessel formation occur?
- In the extraembryonic mesoderm surrounding the yolk sac at 3 weeks, then migrates.
- Later, it forms within the lateral plate mesoderm of the embryo.
GI tract is formed due to what process?
lateral and cephalocaudal folding of the fetal trilaminar disc.
(somites grow down and pinch off gute tube and also pull the amnion around the embryo)
What causes cephalocaudal folding of the fetal trilaminar disc?
- Growth of brain ventricles
- lengthening of embryonic axis
(closes the body wall around the umbilical ring, forming the Primitive umbilical cord from the connecting stalk and the vitelline duct (yolk stalk)).
What sites in the uterus are considered normal sites for implantation?
Fundus (posterior, usually) AND body
Upon implantation what happens to the trophoblast?
It differentiates into two layers:
- the syncytiotrophoblast (outer layer)
- the cytotrophoblast (inner layer)
Define syncytiotrophoblast.
- Secretes human chorionic gonadotropin
- The outer layer which erodes endometrium and allows implantation
What does the cytotrophoblast become?
Syncytiotrophoblast
Describe how the primitive uteroplacental circulation is established.
- Syncytiotrophoblast invades endometrium
- Lacuna are formed in the uterine wall and filled with embryotroph
- Embryo invades deeper into the uterine wall and is completely embedded and covered by day 12
Define embrytroph.
Ruptured uterine capillaries and glands.
(Lacunae in the syncitiotrophoblast are filled with embryotroph, which nourishes the fetus until placenta is established)
How is the chorionic cavity formed and on what day does this occur?
Day 12
Develops within extraembryonic mesoderm (between the primitive yolk sac and the cytotrophoblast). Secondary yolk sac is pinched off from the primary yolk sac.
(the chorion surrounds the chorionic cavity. It is formed by the extra embryonic mesoderm plus two layers of trophoblast the amnion and the yolk sac)
What are the components of the chorion.
Extraembryonic mesoderm plus two layers of trophoblast (syncytiotrophoblast + cytotrophoblast)
(the amnion and yolk sac remain attached to the chorion across the chorionic cavity by the connecting stalk)
What are the functions of the placenta?
- Metabolism
- Transport of gases and nutrients
- Endocrine secretions (hCG)
When does the placenta begin forming and when is it mature?
- Week 2
- Week 20
What are the two parts of the placenta?
- Decidua: maternal portion
- Chorion: fetal portion
Name the three distinct regions of the Decidua.
- Decidua basalis
- Decidua capsularis
- Decidua parietalis
(Functional layer of the gravid endometrium)
Is the chorionic cavity located in relation to the embryo?
The chorionic cavity surrounds the embryo, amniotic cavity, and yolk sac
How is the chorion developed?
Chorionic villi (primary, secondary and tertiary); projections of the chorion into the uterine endometrium
(cover the chorion until week 8 when they are replaced by a smooth chorion)
Describe the primary villi.
Consists of syncitiotrophoblast over a core of cytotrophoblast
(week 2)
Describe secondary villi (chorionic development)
Has a core of extraembryonic mesoderm
Describe tertiary villi (chorionic development).
Core is invaded by umbilical blood vessels.
(week 3)
How is maternal and fetal blood circulation transferred?
Indirectly via diffusion across the placental membrane.
What are the three adaptations that constitute a mature placenta?
- Thin chorionic membrane (regression of cytotrophoblast)
- Large continuous intervillous space
- Extensive branching of chorionic villi
(the last two increase surface area)
In the mature uteroplacental circulation, where is maternal blood found and where is fetal blood found?
- Intervillous spaces (derived from primitive lacunae)
- Villous capillaries
What supplies the intervillous spaces (maternal blood in mature uteroplacental circulation)?
Spiral endometrial arteries
(drained by endometrial veins)
