Friday November 6, 2009
Dr. Yeasting
10:00-12:00
Lecture Notes
I. Amniotic State
Fetus compacts as it grows and uterus doesn’t.
Fetus is head-down
Mom’s urinary bladder is between fetus and pubis
Umbilical cord extends from the naval of the baby to the placenta
Placenta is USUALLY on POSTERIOR wall of placenta
- It makes no difference unless delivery by C-Section
Fetus rests on lumbar spine when mom lies supine
PLACENTA à area of exchange between fetus and mother
- Essential interface that creates hormones
- Contain chorionic sac and smooth chorion
- Area of branching of the umbilical chord
AMNIOCHORIONIC Membrane encapsulates fetus
- Filled with AMNIONIC FLUID
Twin Placenta of DZ twins
- Two of everything
Maternal aspect of placenta is rather rough
- Contain maternal blood and placental villi
- Superficial maternal tissue and deep fetal
- Upon birth, must make sure that placenta is completely gone
- FETUS NEEDS PLACENTA to thrive but NOT vice versa
- Growing placenta can be malignant
COTYLEDONS à Small vessels that lead into spongy area
II. Development
Time of ovulation to loss-of-function of corpus luteum define menstral cycle
- Can calculate ovulation if ovarian and uterine cycle are regular
Fertile period is day of or one or two days after ovulation
Ovulated mass is picked up by uterine (fallopian) tube
CORPUS LUTEUM is left in ovary
- Produces progesterone
- Produces Progesterone
- Changes proliferatory uterus to secretory
- Makes preparations for fertilizations
The corpus luteum is preserved by placental excretion of HUMAN CHORIONIC GONADATROPIN
ZONA PELLUCIDA à Non-cellular material around oocyte
- Oocyte and FOLLICULAR CELLS ovulated together
- Zona Pellucida contain binding site for sperm
- Limit number of sperm trying to fertilize
- Corral early cell proliferation
- Keep proliferating fetal cells from contacting maternal tissue
Follicular Cells form CORONA RADIATA
The corona radiata makes it easier for uterine tube to handle mass
The corona radiate signals sperm
- Sperm disperse corona radiate
- Sperm use ACROSOME to disperse CR
- HYALURONIDASE is used by sperm to disperse CR
- After CR gone, sperm free to interact with ZP
- Germ cells fuse and sperm enter oocyte
Fertilization causes change in oocyte
- The cortical granule reaction takes place making sperm enzymes ineffective
- Plasmalemma of oocyte pulls away from ZP
- Sperm no longer make physical contact with oocyte
CONCEPTUS à embryo proper and extra-embryonic tissue
III. Fertilization
Fertilization triggers second mitotic division
Metabolism starts
Cell division takes place as conceptus migrates down tube
First mitotic division results in two equal cells
First divisions are dividing cytosol and are accompanied by cellular shrinkage
These early divisions are contained within the zona pellucida
Some cells will end up on inside or outside of solid ball
- Figure who is whom by cell-cell interaction
- Inside and Outside cells will end up as different tissue
- If started anew, cells would rearrange themselves in and out randomly
- ZP breaks down after four or five days
- “Hatches” Cells
- Conceptus imbibes fluid and enlarges
- Further delineation between inner and outer cells
Cell divisions are synchronous up to 32 cells
- The ZP prevents cellular wandering and mom-cell contact
Conceptus and tiny empty space BLASTOCELE will enlarge together
Conceptus can contact mom after breakdown of ZP
Early in pregnancy, morphological changes will result in a flat group of epiblast and hypoblast cells called the EMBRYONIC DISK
- The amniotic cavity will arise from this disk of cells
- In the third week a thickened band of epiblast will form PRIMATIVE STREAK
- As the streak elongates it will form the PRIMITIVE NODE
- PN is at cranial end
- This allows for the identification of the craniocaudal axis
- A group hypoblasts will columnarize and become the PRECHORDAL PLATE
- This is where the head will be located
Shortly after conception the primitive streak will begin to produce mesenchyme
NOTOCHORDAL PROCESS will migrate from cranial end ans “pit”
The PRECHORDAL PLATE is an area where endoderm and ectoderm meet
- Function in the elongation of the notochord
NOTOCHORD is a rod that forms from the notochrodal process
- Notochordal process is signaled by the primitive streak
The notochord stops elongating at CLOACAL PLATE
- Site of future anus
IV. Terms (Very loose title for further information)
The is an INNER CELL MASS inside BLASTOCYST
- EMBRYOBLAST forms embryo
- EPIBLAST becomes three germ layers
- HYPOBLAST is next to cavity and will form extra-embryonic mesoderm
OUTER CELL MASS gives rise to trophoblast which will become placenta
- CYTOTROPHOBLAST retains cellularity and acts as reserve cells
- SYNCITIOTROPHOBLAST will differentiate into syncytium
Placenta is made of trophoblasic tissue
- Hormones produced syncytium
- CTP can merge and become syncytium
- Makes up CHORION or non-embryo proper
EMBRYO à First eight weeks
FETUS à eight weeks on, the time when organ systems are developing
ENDOMETRIUM à Lining of the uterus
Undergoes changes during uterine cycle which is controlled by ovarian cycle
MYOMETRIUM à Bulk of tissue in uterus
IMPLANTATION à process by which conceptus attaches to and grows in endometrium
- Implantation is an invasive process with a series of signaling interactions
V. Implantation
Conceptus invades endometrium
INTERSTITIAL IMPLANTATION à in cellular space of endometrium
DECIDUA à altered endometrial stroma
Chemical change from implantation causes the DECIDUAL RXN
- Decidual cells swell from accumulating glycogen and lipid inclusions
- Cells provide nutrient source as they are broken down by conceptus
- The ability of T-lymphocytes lose ability to recognize non-self
- Decidual cells undergo programmed cell death
Three major areas of decidua
D. BASALIS à between conceptus and myometrium
D. CAPSULARIS à In uterine cavity
- Enlarging conceptus bulges endometrium
- Capsule of expanding conceptus
D. PARIETALIS à Altered endometrium not directly related to implantation site
Decidua is the active portion of the endometrium that sheds and is replaced with normal endometrium
Cells from primary yolk sac endoderm form connective tissue layer
- Will form CONNECTING STALK between fetus and CT layer
Extra-embryonic coelum leads to the shrinkage of primary yolk sac
- Formation of secondary yolk sac
- Cells from hypoblast migrate inside primary yolk sac
- PYS provides for selective transfer of nutrients
- PYS is also the site of origin of primordial germ cells
VI. Implantation (From the zygote’s POV)
Happens at five to six days
No ZP
Conceptus has divided into embryoblast and trophoblast
Trophoblast contacts maternal tissue
- Chemical signaling and permissive invasion
- Usually part that overlies embryoblast
- This part is most sticky
Cells merge with endometrium to form STB
- Daughter cells near STB incorporated
- No mitosis in STB nuclei
- STB invades endometrial lining
No fertility if unresponsive endometrium
Conceptus follows STB which is continually forming
LACUNA à Membrane bound space in STB that will become INTERVILLOUS SPACE
- Will contain maternal blood b/c they are in maternal tissue
STB receives nutrients from mom’s endometrium
- Engulfs maternal blood vessels
Maternal blood will leak into lacunar spaces and over time circulation will begin
Shunt is opened in maternal circulation
STB will eventually form all the way around conceptus
The STB does not elaborate many antigens
CTP differentiate between lacunae and form primary villi
- STB outside with CTB core
CTB will eventually develop all the way around conceptus
Extra-embryonic mesoderm from hypoblasts will grow into villi
- Secondary villi form connective tissue core
CTB grows through STB making a “shell” upon contacting deciduum
- Decidual lymphocytes cannot recognize this foreign material
Extra-Embryonic Mesenchyme gives rise to blood vessels
- Connects with BV’s in embryo proper
- Establish preliminary fetal-placental circulation
- Completely surrounds conceptus
Maternal blood will only contact STB
Bleeding can be caused by STB contact of large artery
Villi consists of STB on outer surface
- followed by CTB à Mesenchyme à BV’s
CTB can add cells to STB
Until mid-pregnancy, materiel must diffuse through villi
- Bacteria cannot enter villi
Most of CTP is used up or degenerated by second half of pregnancy
- Diffuse through STB and fetal BV
Cotyledons form partial septa in non-vascularized space (augumented villi)
VII. Placenta
SMOOTH CHORION forms from breakdown of villi assoc. with D. Capsularis
VILLOUS CHORION is between D. Basalis villi
- Anchors placenta by interdigitation between the two membranes
Maternal blood enters placenta through SPIRAL ENDOMETRIAL ARTERIES
- Returns through ENDOMETRIAL VEINS
Maternal blood and fetal blood never contact
The nutrients and gases in maternal blood diffuse through PLACENTAL MEMBRANE
UMBILICAL VEIN carries O2 rich blood to fetus
UMBILICAL ARTERIES carry blood away to CHROIONIC ARTERY to VILLI
The placenta carries out many functions
- METABOLISM, TRANSPORT, ENDOCRINE (hCG)
The amniotic sac enlarges to form AMNIOCHORIONIC MEMBRANE with chorion
AMNION is a thin, tough membrane that surrounds the fetus and forms AMNIOTIC SAC
AMNIOTIC FLUID fills amniotic sac
- Small amount from amniotic cells
- Most from maternal tissue, fetal skin and respiratory tract, and fetal urine
Amniotic Fluid:
- Permits symmetric external growth of fetus
- Acts as a barrier against infection
- Permits normal fetal lung development
- Prevents adherence of amnion
- Cushions embryo
- Helps control fetal temperature
- Enables fetus to move freely aiding in muscular development
- Involved in fluid and electrolyte homeostasis