Advertisement Upgrade to remove ads

4 fetal membranes

chorion, amnion, yolk sac, allantois

functions of placenta

-primary site nutrient and gas exchange
-metabolism (syn of glycogen)
-endocrine secretion

5 functions of placenta and fetal membranes

-protection
-nutrition
-respiration
-excretion
-hormone production

afterbirth

expelling of placenta and fetal membranes after birth of baby

decidua

"a falling off"
-functional layer of endometrium
-part that separates from the remainder of the uterus after childbirth

3 layer of decidua

Basalis
Capsularis
parietalis

decidua basalis

part of decidua deep to the conceptus and forms the maternal part of the placenta

decidua capsularis

superficial part of decidua overlying conceptus that forms the maternal part of the placenta

decidua parietalis

all the remaining parts of the decidua

fetal part of placenta

develops from part of the chorionic sac when chorionic villi project into the intervillous space containing maternal blood

maternal part of placenta

derived from the endometrium/decidua basalis

fetomaternal junction

meeting point of fetal part/villous chorion of placnta and maternal part/decidua basalis of the placenta
-attached by the cytotrophoblastic shell(external layer of trophoblastic cells on maternal surface of placenta).
-chorionic villi anchor the chorionic sac to the decidua basalis, and endometrial arteries and veins pass freely through gaps in the shell into the intervillous space

primary chorionic villi

formed at the end of Week 2 by proliferation of cytotrophoblastic cells producing cellular extensions that grow into the syncytiotrophoblast

secondary chorionic villi

develop in Week 3 as the primary villi begin to branch and mesenchyme grows into the villi, forming a loose mesenchyme connective tissue core; villi now cover the entire surface of the chorionic sac

tertiary chorionic villi

some secondary villi differentiate into capillaries and blood cells and form tertiary villi once the vasculature is visible. The capillaries fuse to form networks and become connected with the embryonic heart; by the end of Week 3 embryonic blood flows through the tertiary villi capillaries and oxygen and nutrients begin to diffuse.

villous chorion

bushy part of the chorionic sac where chorionic villi persist (as opposed to the smooth chorion, where the villi are compressed and degenerate producing an avascular bare area). The villous chorion will form the fetal part of the placenta.

layers of placental membrane

Early/Until week 20
-Syncytiotrophoblast, -Cytotrophoblast,
- Connective Tissue of villus, -Endothelium of fetal capillaries
Late/after week 2— -Syncytiotrophoblast,
-Endothelium

metabolism products of placenta

-glycogen,
-cholesterol,
-fatty acids

mechanisms of placental transport

Diffusion,
Active Transport,
Pinocytosis

placental hormones

hCG (human chorionic gonadotropin-maintains corpus luteum)
hPL (human placental lactogen)
hCT (human chorionic thyrotropin)
hACT (human chorionic corticotropin)
prolactin
relaxin
prostaglandins
progesterone (essential for maintenance of pregnancy)
estrogen

beneficial substances that cross placenta

Nutrients—glucose, Amino Acids, Free fatty acids, vitamins
Gases—O2, CO2
Electrolytes—H2O, Na, K, Cl, Calcium Phosphate
Waste Products—CO2, urea, uric acid, bilirubin
Cells—fetal and maternal RBCs
Proteins—maternal serum
Hormones—steroids
Immunoglobins—IgG (7S class)

detrimental substances that cross placenta

Gases—CO
Viruses—Rubella (causing severe congenital anomalies), etc
Immunoglobins—IgG (anti Rh antibodies)
Drugs—most drugs, thalidomide, cocaine, alcohol, caffeine, nicotine, warfarin
Micro-organisms—Treponema Pallidum (causes syphilis), Toxoplasma Gondii (destructive changes in the brain and eyes)

substances that do not cross the placenta

Nutrients—maternally derived triglycerides, cholesterol
Hormones—All protein hormones, including insulin
Immunoglobins—IgM, IgS
Drugs—Curare, Heparin
Micro-organisms—bacteria

amnionic fluid components

H2O (99%),
CHO,
lipids,
proteins (hormones/enzymes), desquamated fetal cell,
fetal urine

production of amnionic fluid

-Initial secretion by amniotic cells;
-most fluid derived from maternal tissue fluid through diffusion across the amniochorionic membrane and later through the chorionic plate with dialysis of maternal and fetal blood.
-Fetus contributes by secreting fluid from the respiratory tract, and excreting absorbed fluid as fetal urine.

reabsorption of amnionic fluid

-Swallowed by the fetus and reabsorbed into its respiratory and GI tracts and bloodstream;
-excess fluid and waste products removed via placenta.
-During the final stages of pregnancy, the fetus swallows up to 400 mL of fluid per day

amount of amnionic fluid

At week 12—50 mL
At week 38/full term—1000 mL (gradually increases throughout pregnancy)

functions of amnioic fluid

-Permits symmetric external growth of embryo;
-acts as a barrier to infection; -permits normal lung development; -prevents adherence of the amnion to the embryo;
-cushions embryo against injury by distributing impacts received by the mother;
-helps control embryo body temperature by maintaining a constant temperature;
-enables fetus to move freely aiding in muscular development;
-involved in maintaining homeostasis of fluid and electrolytes

functions of the yolk sac

-Plays a role in the transfer of nutrients in the 2nd and 3rd weeks before uteroplacental circulation is established;
-well-vascularized extraembryonic mesoderm covering the yolk wall first develops blood in week 3 until week 6;
-becomes incorporated into the embryo as the primordial gut in week 4 with endoderm giving rise to epithelium of the respiratory and digestive tract;
-lining of the yolk sac develops primordial germ cells in week 3 which migrate to the developing sex glands and differentiate.

fate of the yolk sac

At 32 days, the yolk sac is large.
By 10 weeks, is has shrunk to about 5mm and lies in the chorionic cavity between the amnion and chorionic cavity,
-yolk stalk detaching around week 6.
-By week 20 the yolk sac is very small and will eventually be no longer visible.

Dizygotic Twins

fraternal twins that originate from two different zygotes.
There are always 2 amnions and 2 chorions, although the chorions and placentas may be fused.

Monozygotic Twins

identical twins that originate from one zygote.
-Fetal membrane formation can depend on when the twinning process occurs, but usual cases involve separation of inner cell mass into two embryoblasts during the blastocystic stage. Each embryo will have its own amnion, but share a chorion and a common placenta (although it is possible to have the same fetal membrane structure as DZ twins, especially if twinning occurs at a later stage).

umbilicial cord-Attachment

Attachment—usually near the center of the fetal surface of the membrane, although can be anywhere, epithelium is continuous with amnion adhering to the chorionic plate of the placenta
Size—1-2 cm in diameter, 30-90 cm in length

umbilicial cord-Vasculature

Vasculature—easily seen umbilical vessels branch on fetal surface to form the chorionic vessels, which enter the chorionic villi and radiate to and from the cord; two arteries and one vein surrounding by Wharton's Jelly run within the cord. Umbilical arteries carry deoxygenated blood for exchange with placenta/mother, and umbilical veins receive oxygen rich blood from placenta/mother.

four stages of labor

dilation
expulsion
placental
recovery

dilation stage

progressive dilation of cervix mediated by changes in hormones, ending with complete dilation. Lasts approximately 12 hours for first pregnancies and 7 hours for women who have already had a child

expulsion stage

Begins with a fully dilated cervix and ends with delivery of the baby, when the fetus descends through the cervix and vagina. Lasts approximately 50 minutes (first time)/20 minutes (second pregnancy on)

placental stage

Begins with birth and ends when placenta and membranes are expelled, lasting about 15 minutes. Caused by a hematoma forming deep to the placenta, separating it from the uterine wall allowing for expulsion. Pressure on the abdomen can assist the hematoma to form.

recovery stage

Post-expulsion of placenta. Lasts approximately 2 hours while contractions of uterus constrict spiral arteries to prevent excessive uterine bleeding

parturition

aka childbirth,
- process during which the fetus, placenta, and fetal membranes are expelled from the mother's reproductive tract.

hormones of parturition

Corticotropin-releasing hormone—secreted by fetus hypothalamus, stimulating... Adrenocorticotropin Hormone—from the anterior pituitary, causing secretion of...
Cortisol—from the adrenal cortex; synthesizes estrogens, stimulates contraction.
Oxytocin—stimulates peristaltic contractions of uterine smooth muscle; stimulates...
Prostaglandins—released from the decidua; stimulates myometrial contractility
Estrogens—increase myometrial contractile activity; stimulate release of Oxytocin and prostagladins

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set