Week 2: Difference between revisions
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'''Normal Implantation Sites''' - in uterine wall superior, posterior, lateral | '''Normal Implantation Sites''' - in uterine wall superior, posterior, lateral | ||
== Uterus == | |||
<gallery> | |||
Image:Uterus proliferative phase.jpg|Uterus proliferative phase | |||
Image:Uterine gland proliferative phase.jpg|Uterine gland proliferative phase | |||
Image:Uterus secretory phase.jpg|Uterus secretory phase | |||
Image:Uterine gland secretory phase.jpg|Uterine gland secretory phase | |||
</gallery> | |||
* Endometrium - 3 layers in secretory phase of menstrual cycle: compact, spongy, basal | |||
* Myometrium - muscular layer outside endometrium, contracts in parturition | |||
* Perimetrium - tunica serosa of the uterus continuous with the peritoneal wall | |||
===Endometrial Layers=== | |||
* Compact - implantation occurs in this layer, dense stromal cells, uterine gland necks, capillaries of spiral arteries | |||
* Spongy - swollen stromal cells, uterine gland bodies, spiral arteries | |||
* Basal - not lost during menstruation or childbirth, own blood supply | |||
===Decidual Reaction=== | |||
* occurs initially at site of implantation and includes both cellular and matrix changes | |||
* reaction spreads throughout entire uterus, not at cervix | |||
* deposition of fibrinoid and glycogen and epithelial plaque formation (at anchoring villi) | |||
* presence of decidual cells are indicative of pregnancy | |||
Cervix - at mouth of uterus, secretes mucus (CMP), forms a plug/barrier, mechanical and antibacterial | |||
Vascular - increased number of blood vessels | |||
===Decidua=== | |||
The endometrium becomes the decidua and forms 3 distinct anatomical regions (at approx 3 weeks) | |||
* Decidua Basalis at implantation site | |||
* Decidua Capsularis enclosing the conceptus | |||
* Decidua Parietalis the remainder of uterus | |||
** Decidua Capsularis and Parietalis fuse eventually fuse and uterine cavity is lost by 12 weeks | |||
==Week 2 Abnormalities== | ==Week 2 Abnormalities== |
Revision as of 14:48, 22 July 2010
Introduction
Key events of human development during the second week (week 2) following fertilization or Clinical week 4 (LMP).
- Week 2 Links: Lecture - Week 1 and 2 | Implantation
- Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
Timeline
Event | ||
Implantation | ||
Stage 6 | Chorionic Cavity | |
Week 2 and 3 Movies
Implantation | Mesoderm | Chorionic Cavity | Amniotic Cavity | Week 3 |
Implantation
The second week of human development is concerned with the process of implantation and the differentiation of the blastocyst into early embryonic and placental forming structures.
- implantation commences about day 6 to 7
- Adplantation - begins with initial adhesion to the uterine epithelium
- blastocyst then slows in motility, "rolls" on surface, aligns with the inner cell mass closest to the epithelium and stops
- Implantation - migration of the blastocyst into the uterine epithelium, process complete by about day 9
- coagulation plug - left where the blastocyst has entered the uterine wall day 12
Normal Implantation Sites - in uterine wall superior, posterior, lateral
Uterus
- Endometrium - 3 layers in secretory phase of menstrual cycle: compact, spongy, basal
- Myometrium - muscular layer outside endometrium, contracts in parturition
- Perimetrium - tunica serosa of the uterus continuous with the peritoneal wall
Endometrial Layers
- Compact - implantation occurs in this layer, dense stromal cells, uterine gland necks, capillaries of spiral arteries
- Spongy - swollen stromal cells, uterine gland bodies, spiral arteries
- Basal - not lost during menstruation or childbirth, own blood supply
Decidual Reaction
- occurs initially at site of implantation and includes both cellular and matrix changes
- reaction spreads throughout entire uterus, not at cervix
- deposition of fibrinoid and glycogen and epithelial plaque formation (at anchoring villi)
- presence of decidual cells are indicative of pregnancy
Cervix - at mouth of uterus, secretes mucus (CMP), forms a plug/barrier, mechanical and antibacterial Vascular - increased number of blood vessels
Decidua
The endometrium becomes the decidua and forms 3 distinct anatomical regions (at approx 3 weeks)
- Decidua Basalis at implantation site
- Decidua Capsularis enclosing the conceptus
- Decidua Parietalis the remainder of uterus
- Decidua Capsularis and Parietalis fuse eventually fuse and uterine cavity is lost by 12 weeks
Week 2 Abnormalities
Abnormal Implantation
Ectopic Pregnancy | Movie - Ectopic pregnancy ultrasound
Abnormal implantation sites or Ectopic Pregnancy occurs if implantation is in uterine tube or outside the uterus.
- sites - external surface of uterus, ovary, bowel, gastrointestinal tract, mesentry, peritoneal wall
- If not spontaneous then, embryo has to be removed surgically
Tubal pregnancy - 94% of ectopic pregnancies
- if uterine epithelium is damaged (scarring, pelvic inflammatory disease)
- if zona pellucida is lost too early, allows premature tubal implantation
- embryo may develop through early stages, can erode through the uterine horn and reattach within the peritoneal cavity
Monoygotic Twinning
Monozygotic twins (identical) produced from a single fertilization event (one fertilised egg and a single spermatazoa, form a single zygote), these twins therefore share the same genetic makeup. Occurs in approximately 3-5 per 1000 pregnancies, more commonly with aged mothers. The later the twinning event, the less common are initially separate placental membranes and finally resulting in conjoined twins.
Table based upon: Twinning. Hall JG. [1]
References
- ↑ <pubmed>12957099</pubmed>
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
- Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, May 22) Embryology Week 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_2
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G