Flashcards in 9.21.16 Embryology of Germ Layers Deck (88):
Broadly, what happens in the first week of development?
Fertilization, cleavage, implantation
From many primary ___, only one reaches full maturity. This is known as a mature ___ (Graafian) follicle.
The mature ovarian (Graafian) follicle contains ___.
What triggers ovulation?
Surge of LH production
What happens during ovulation?
The secondary oocyte is expelled, leaving a corpus luteum behind
What surrounds the secondary oocyte?
Zona pellucida and corona radiata
What does the corpus luteum do?
Secretes progesterone to prepare the uterus for implanation
What is the fusion of a male pronucleus (sperm) with a female pronucleus (ovum) to form a zygote?
What is formed during fertilization?
What are the phases of fertilization?
1. Sperm enters the oocyte by penetration of the corona radiata, zona pellucida, and oocyte membrane.
2. The zona pellucida becomes impenetrable to other sperms (zona reaction)
3. Female and male pronucleus is formed
4. Zygote is formed
What are the 3 results of fertilization?
1. Restoration of diploid number of chromosomes
2. Sex determination
3. Initiation of cleavage
What is a series of mitotic divisions that results in an increase in cells known as blastomeres?
Describe the development of a blastocyst.
1. 2 cells
2. 4 cells
3. 8 cells (all in the uterine tube)
4. 16-32 cells (morula - solid ball of blastomeres)
5. Morula enters the uterus
6. Fluid filled space appears
7. Blastocyst is formed
What are the two parts of the blastocyst?
1. Embryoblast (inner cell mass)
2. Trophoblast (outer cell mass) - surrounding layer
When does implantation occur?
Begins at the first week and is completed by the second week
Where does implantation occur?
Posterior superior wall of the uterine body as the zona pellucida disappears
Describe the process of implantation.
1. Blastocyst adheres to the endometrial epithelium.
2. Trophoblast differentiates into cytotrophoblast and syncytiotrophoblast
3. Blood filled lacunae appear in the syncytiotrophoblast, which erodes the endometrial blood vessels, establishing a uteroplacental circulation
What are the two types of abnormal implantation?
1. Ectopic pregnancy
2. Placenta previa
What is an ectopic pregnancy?
Implantation outside the uterus
What is the common type of ectopic pregnancy?
Tubal pregnancy (implantation within the ampulla)
How does a patient with ectopic pregnancy present?
Abdominal pain and missed period
What is placenta previa?
Implantation in the inferior segment of the uterus near the internal opening
How does a patient with placenta previa present?
What occurs during the second week of development?
Formation of the bilaminar germ disc; period of twos
During the second week of development, the inner cell mass differentiates into what two things?
Epiblast and hypoblast (bilaminar disc)
During the second week of development, the outer cell mass differentiates into what two things?
Cytotrophoblast (clear cell boundaries) and syncytiotrophoblast (no clear cell boundaries)
During the second week of development, two cavities form - what are they?
Amniotic cavity and yolk sac cavity
During the second week of development, the extraembryonic mesoderm splits into what two layers?
Somatic and splanchnic
What happens during the third week of development?
Trilaminar germ disc formation or gastrulation; period of 3's
What is the first event that occurs in the third week of development?
1. Primitive streak appears
2. Epiblast cells (ectoderm) migrate inward to form new cell layers (endoderm and mesoderm)
3. Gastrulation - epiblast gives rise to all three germ layers (ectoderm-endoderm-mesoderm)
What is a thickening of the epiblast cells?
What are the three germ layers?
Ectoderm, endoderm, mesoderm
What is the second event that occurs in the third week of development?
1. Primitive node forms
2. Mesenchymal cells migrate cranially until they reach the prechordal plate (oropharyngeal membrane)
3. Notochord (body axis) is formed
4. The notochord signals the ectoderm to start formation of the neural tube (neurulation)
5. The neural plate, groove, and tube form
What is a swelling at one end of the primitive streak?
What is the body axis?
What is formation of the neural tube?
What is the third event that occurs in the third week of development?
The mesoderm on each side of the notochord differentiates into three regions (paraxial, intermediate, lateral plate mesoderm)
What three regions does the mesoderm differentiate into?
1. Paraxial (somites, which are divided into sclerotome, myotome, and dermomyotome)
2. Intermediate (kidneys and gonads)
3. Lateral plate mesoderm (somatic and splanchic)
From what do neural crest cells originate?
Ectodermal cells of the neural plate
What are the two parts of the placenta?
1. Villous chorion (fetal part)
2. Decidua basalis (maternal part)
What is the maternal part of the placenta?
What is the fetal part of the placenta?
___ form as outward projections from the trophoblast.
What are the three types of chorionic villi?
1. Primary: cytotrophoblast and syncytiotrophoblast only (week 2)
2. Secondary: primary + mesenchyme core (week 3)
3. Tertiary: secondary + blood vessels (end of week 3)
What are the three types of decidua?
1. Decidua basalis
2. Decidua capsularis
3. Decidua parietalis
What type of decidua sits between the embryonic pole of the blastocyst and the myometrium?
What type of decidua covers the rest of the embryo?
What type of decidua lines the uterine cavity?
How are the fetal and maternal circulations separated?
By a thin layer of placental membrane; this is permeable to water, oxygen, nutritive substances, hormones, and noxious agents.
By the 4th month of pregnancy, the ___ regresses and the exchange from mother to fetus and fetus to mother is across the ___ (placental barrier).
Cytotrophoblast; syncytiotrophoblast and fetal endothelium
What are the fetal membranes?
Chorion, amnion, umbilical vesicle (yolk sac), and allantois
What forms an amniotic sac to enclose the embryo like a balloon?
The amnion is filled with amniotic fluid, which is produced from many sources including what four examples?
Amnion, fetal skin, kidneys, blood vessels
What are the three functions of the amniotic fluid?
1. Provide a protective buffer for the fetus
2. To allow room for fetal movements
3. To assist in the regulation of fetal body temperature
What is the ventrally endodermally lined structure connected to the midgut by the vitelline duct?
What is the small endodermally lined diverticulum off the hind gut?
What does the umbilical cord contain?
Umbilical vessels (2 arteries and left umbilical vein) and 2 ducts (allantois and vitelline duct)
The trilaminar embryonic disc becomes folded on itself forming what 4 folds?
Head fold (cranial), tail fold (caudal, 2 lateral folds
What are the 4 results of the folding of the embryo?
1. Endoderm becomes enclosed inside the embryo forming the gut-tube
2. Ectoderm covers the embryo from outside and the amniotic sac expands to surround the embryo
3. The oral membrane and the cloacal membrane become ventral
4. Pericardium and septum transversum (future diaphragm) become ventral
Monozygotic twins are formed from ___ oocyte and ___ zygote. They will have ___ chorion, ___ amnion, and ___ placenta.
1 oocyte; 1 zygote; 1 chorion; 2 amnions; 1 placenta
Dizygotic twins are formed from ___ oocyte and ___ zygote. They will have ___ chorion, ___ amnion, and ___ placenta.
2 oocytes; 2 zygotes; 2 chorions; 2 amnions; 2 placentas
What are the three layers of the epiblast?
What does the ectoderm form?
1. Epidermis, hair, nails, glands of skin
2. Brain and spinal cord
3. Neural crest and derivatives
What does the mesoderm form?
3. Intermediate mesoderm
4. Lateral plate mesoderm
What does the notochord form?
Nucleus pulposus of intervertebral discs
What does the somite form?
1. Sclerotome: vertebrae and ribs
2. Dermatome: dermis of dorsal body region
3. Myotome: trunk and limb musculature
What does the intermediate mesoderm form?
What does the lateral plate mesoderm form?
1. Somatic mesoderm
2. Splanchnic mesoderm
What does the somatic mesoderm form?
1. Parietal serosa
2. Dermis of ventral body region
3. Connective tissues of limbs (bones, joints, ligaments)
What does the splanchnic mesoderm form?
1. Walls of digestive and respiratory tracts (except epithelial lining)
2. Visceral serosa
4. Blood vessels
What does the endoderm form?
Epithelial lining and glands of digestive and respiratory tracts
What happens during gametogenesis?
The chromosome number is reduced by half and the shape of the cells is altered. Each of these cells contains a haploid number.
What are the products of gametogenesis in males and females?
Sperm (males), oocyte (female)
What are the three layers of the oocyte?
1. Corona radiata
2. Zona pellucida
3. Oocyte membrane
What are the two parts of the sperm?
Head (acrosome), tail
Where does fertilization occur?
Ampulla of the uterine tube (fallopian tube or ovoduct) - this is the widest part of the fallopian tube
What are the phases of fertilization?
1. Capacitation and acrosomal reaction
2. Penetration of three layers
3. Zona reaction
What is the acrosomal reaction?
Release of enzymes by the sperm to penetrate the oocyte
When does the zona pellucida disappar?
Re-entry into the uterus
What cues implantation?
Loss of zona pellucida
What helps the blastocyst implant?
Trophoblast (fingerlike projections)
What is HCG?
Glycoprotein produced by the syncytiotrophoblast
Low HCG may predict ___ or ___.
Spontaneous abortion or ectopic pregnancy
High HCG may predict multiple pregnancy or ___ diseases.
What is the composition of the placental barrier in early pregnancy?
Syncytiotrophoblast, Cytotrophoblast, connective tissue, fetal endothelium
What is the composition of the placental barrier in late pregnancy?
Syncytiotrophoblast and fetal endothelium
Where does exchange occur in the placenta?