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General embryology
Jun Zhou ( 周俊)
School of Medicine, Zhejiang University
20131223
Langman’s Medical Embryology, 9th Ed
Fertilization
14 days
Onset of last M.C.
266 days
280 days
a science which study the processes and regulations of development of human fetus.(from 1 cell (zygote) to (5-7) x1012 cells)
In general the length of pregnancy is considered to be 280 days or 40 weeks after the onset of the last menstruation, or more accurately, 266 days or 38 weeks after fertilization.
Labor
Preembryonic period: before 2 weeks
Embryonic period: 3-8 weeks
Fetal period: after 9 weeks
Total 38 weeks:
Fertilization
Definition: the process by which the male and female gametes(sperm and ovum) unite to give rise to zygoteplace: in the ampullary region of the oviduct
3) capacitation and acrosome reaction of spermatozoa: R5
• capacitation factor: secreted by epi. cells of oviduct, capacity
of releasing acrosome enzymes
4) quality and quantity of spermatozoa:
• 2-6 ml, 100,000,000/ml,
• <1.5 ml; or <10,000,000; abnormal sperm >30%; or
capacity for mobile< 70%
5) meeting of sperm and ovum within 24 hrs
Processes of fertilization:
•Phase I–penetrate the corona radiata, acrosomal release
•Phase II–ZP with receptors – zona pellucida spongy – the release of local enzymes
•Phase III–Success formation of zygote
• Entry – response1) Cortical or zona reactions -Comp
action - impermeable to more sperm
2) Oocyte finishes 2nd meiotic division
3) Female /Male pronucleus
4) Metabolic activation of the egg
• Results of fertilization– Diploid– Genetic sex– Cleavage
Cleavage •Mitosis and cytoplasmic division•Blastula - blastomeres•Morula
–inner cell mass•embryoblast
–outer cell rim•trophoblasts
•Blastocyst –Blastocoele–The cells of morula secrete fluid–Zona pellucide disappears
•Puberty – menstruation (28 days) •Hormonal regulation
–GnRH –FSH–LH
•Granulosa/theca cells–Estrogens –Progesterones
•The endometrium of the uterus is in the secretory phase
Uterus at Time of Implantation
Implantation
-Passage through the uterine tube•Day 5 –Day 11 Uterus•Orientation of implantation•Location - ant or post, fundus•Trophoblasts overlying the embryoblast pole attach to the endometrium, erosion into deep uterine vessels
Processes
zona pellucide disappear → polar trophoblast touch the endometrium→secrete enzymes →dissolve the endometrium → embedded into endometrium → coagulation plug seal the space
•Implantation site–Normal:ant or post wall of the uterus–Abnormal
–Tubal–Internal os of the cervix–Ovarian–Abdominal
•endometrium →decidua: -decidua basalis
-decidua capsularis
-decidua parietalis
•conditions: -endometrium is in secretory phase
-morula reach the cavity of uterus on time
-zona pellucide disappears in time
•Implantation - sinks deeper•The outer cell layer
–Trophoblasts•cytotrophoblasts•syncytiotrophoblasts
•Inner cell mass (embryoblast)–Fluid collection – amnion–Epiblasts & hypoblasts
Bilaminar Germ Disc
(Second week of development)
Week two – Day 9-12
•Implantation–Covered the endometrium- fibrin plug–Complete – slight bulge
•Trophoblasts–Vacuoles within syncytiotrophoblasts- fuse and form lacunar networks–Uteroplacental circ
•Extra-Embryonic Mesoderm–btwn troph & cavity–Somatic/splanchnic
Week 2 – Day 13-14
•Trophoblasts–Primary villi
•Yolk sac–Primary to seconday–Chorionic plate–Connecting stalk
End of the Week of Twos•2 major cell masses
–Trophoblasts –Inner cell mass
•Trophoblasts–Cytotrophoblasts–Syncytiotrophoblasts
•Embryonic Cavities–Amniotic cavity–Yolk sac
•Germ Disc–Epiblasts–Hypoblasts
OBJECTIVES1. The definition of Embryology
2. The major phases of fertilization and the site where fertilization typically occurs
3. Endometrial changes that enable implantation and the hormones that modulate this change
4. Normal sites of implanation and the most abnormal sites
5. Morphologic changes in the zygote that occur enroute to the uterus
6. The development roles of the inner cell mass and the outer cell mass
7. Bilaminar germ discs