Chapter 6: Fetal Membranes Flashcards
1
Q
Fetal membranes
A
Structures developed from the zygote but do not share in the formation of the embryo:
1. Chorion and placenta.
2. Amnion.
3. Umbilical cord.
4. Yolk sac.
2
Q
Chorion
A
Chorion is the wall of chorionic vesicle.
3
Q
Formation of chorion
A
- At the 12th day, extra embryonic mesoderm is formed on the inner aspect of the cytotrophoblast.
- Chorionic vesicle is formed when spaces in the extra embryonic mesoderm fuse to form extra-embryonic coelom (chorionic cavity).
4
Q
The extra-embryonic coelom is divided into
A
- Somatic mesoderm: lines cytotrophoblast and covers amniotic cavity.
- Splanchnic mesoderm: covers yolk sac.
5
Q
Layers of chorion
A
Composed of layers (external to internal):
1. Synctiotrophoblast.
2. Cytotrophoblast.
3. Extraembryonic somatic mesoderm.
6
Q
Placenta
A
Organ through which the exchange of materials occurs between maternal and fetal blood.
7
Q
Placenta shape
A
Disc shape
8
Q
Placenta weight
A
500-600 gm.
9
Q
Placenta diameter
A
15-20 cm
10
Q
Placenta thickness
A
3 cm
11
Q
Placenta site
A
Mostly in the upper segment of the posterior wall of the uterine cavity near fundus.
12
Q
Placenta surfaces
A
- Fetal surface.
- Maternal surface.
13
Q
Fetal surface
A
- Surface that faces the fetus.
- Smooth and covered with transparent amnion.
- Umbilical cord is attached near its center.
14
Q
Maternal surface
A
- Surface that lies in contact with internal surface of uterine wall.
- It shows presence of 15-20 elevations named cotyledons, separated from each other by grooves.
- Covered by thin layer of Decidua basalis.
15
Q
Formation of placenta
A
Formed by the union of two main parts:
1. Maternal part: decidual plate (basalis).
2. Fetal part: chorionic plate (frondosum).
16
Q
Structure of placenta
A
Composed of:
1. Chorionic plate.
2. Decidual plate.
3. Chorionic villi.
4. Intervillous space.
5. Placental (decidual) septa.
17
Q
Chorionic plate (external to internal)
A
- Amnion.
- Extra-embryonic somatic mesoderm
- Cytotrophoblast.
- Syncytiotrophoblast.
18
Q
Decidual plate (internal to external)
A
- Syncytiotrophoblast which lines the intervillous space.
- Cytotrophoblastic shell.
- Decidua basalis.
19
Q
Chorionic villi
A
Tertiary villi of the chorion frondosum composed of the following layers:
1. Syncytiotrophoblast (outer layer).
2. Cytotrophoblast.
3. Somatic extraembryonic mesoderm.
4. Epithelium of fetal blood vessels.
20
Q
Parts of chorionic villi
A
- Stem (anchoring) villi.
- Floating (free or absorbing) villi.
21
Q
Stem (anchoring) villi
A
Main part of the villous that extends between chorionic and decidual plates.
22
Q
Floating (free or absorbing) villi
A
Side branches from the stem villi that float in maternal blood in the intervillous spaces to allow exchange of food materials and gases between fetal and maternal blood.
23
Q
Intervillous space
A
Formed of intercommunicating spaces that separate between stem villi and extend from chorionic plate to decidual plate. Maternal arterioles and venules open into the spaces through the decidual plate.
24
Q
Placental (decidual) septa
A
- Septa that extend from decidual plate to the cavity of intervillous spaces.
- Appear during 4th to 5th months.
- Incomplete septa that do not extend to the chorionic plate.
- Each septum is composed of core Decidua basalis covered with cytotrophoblast and syncytiotrophoblast.
- Cotyledons on the maternal surface are separated by grooves that correspond to inwards extension of the placental septa.
25
Placental circulation
Circulation of blood inside the placenta composed of:
1. Maternal part (circulation of maternal blood).
2. Fetal part (inside fetal blood vessels).
26
Maternal blood (circulation of maternal blood)
1. Arterial blood flows to the intervillous space through 80-100 decidual arterioles.
2. Full term placenta contains about 150 ml of maternal blood which is changed 3-4 times/min.
3. Maternal blood flows back towards decidual plate to leave through maternal venules.
27
Fetal part (inside fetal blood vessels)
1. Umbilical arteries leave the the abdomen of the fetus through the umbilical cord.
2. They reach the fetal surface of the placenta where they branch to enter the tertiary villi inside the placenta.
3. After the exchange between fetal and maternal blood, the fetal blood is carried through left umbilical veins to the fetal heart where it is distributed to the body of fetus.
28
Placental barrier (membrane)
Membrane that separates between fetal blood (inside the tertiary villi) and maternal blood (in the intervillous spaces).
29
Early placental barrier
1. Endothelium of fetal blood vessels.
2. Somatic extraembryonic mesoderm.
3. Cytotrophoblast.
4. Syncytiotrophoblast.
30
Late placental barrier (from 4th month)
1. Endothelium of fetal blood vessels.
2. Syncytiotrophoblast.
31
Why does the placental membrane become thinner in the second half of pregnancy?
To allow rapid exchange of nutrition and gases to give adequate supply to the larger fetus.
32
Functions of placental barrier
1. Separates between fetal and maternal blood.
2. Permits gaseous, nutritive, and waste products exchange.
3. Prevents passage of bacteria and most viruses except:
- HIV.
- Poliomyelitis.
- Rubella.
- Cytomegalovirus.
- Measles.
4. Prevents passage of most toxic materials and most maternal hormones except some synthetic hormones:
- Progestin.
- Diethylstilbestrol.
33
Functions of the placenta
1. Exchange of metabolic products.
2. Exchange of gases.
3. Transmission of maternal antibodies to the fetus.
4. Endocrine function.
5. A protective role.
6. Excretory function.
34
Placenta: exchange of metabolic products
Allows transmission of nutritive substances from maternal to fetal body and in the opposite direction, waste products are transmitted from fetal to maternal blood.
35
Placenta: exchange of gases
Giving oxygen to fetus and receiving CO2 from fetal blood.
36
Placenta: transmission of maternal antibodies to the fetus
Starting from 14th week. Fetus will gain immunity since then.
37
Placenta: endocrine function
1. Progesterone hormone.
2. Estrogen hormone.
3. Human chorionic gonadotropins (HCG).
4. Somatomammotropin.
38
Endocrine: progesterone hormone
Maintains the endometrium of pregnancy.
39
Endocrine: estrogen hormone
Stimulates uterine growth and development of mammary gland.
40
Endocrine: estrogen
Stimulate uterine growth and development of mammary gland.
41
Endocrine: human chorionic gonadotropins (HCG)
Maintains corpus lutes till the 4th month. It is used to detect pregnancy.
42
Endocrine: somatotropin
Gives fetus the priority on maternal blood glucose. It also promotes breast development.
43
Placenta: protective role
Prevents passage of bacteria and most viruses from mother to fetus.
44
Placenta: excretory function
Gods rid of fetal urea and creatinine.
45
Battledore placenta
The cord is attached to the ,argon of the placenta.
46
Thinner and wider placenta
Placenta membranacea
47
Deep infiltration of the placenta to the myometrium it even covering the peritoneum is known as?
1. Placenta acccreta.
2. Placenta increta. (Myometrium)
3. Placenta percreta. (Peritoneum)
48
Amnion
Wall of amniotic cavity. After folding, the amniotic cavity surrounds the fetus.
49
When and where does the amniotic cavity appear?
At the 8th day with the embryoblast cells. It separates between the amnioblasts (adjacent to cytotrophoblast) and epiblast (adjacent to hypoblast).
50
When is the amnioectodermal junction formed?
In the third week between the ectoderm and amnion.
51
Expansion of amniotic cavity step 1
After folding, the amnioectodermal junction is shifted centrally and surrounds the primitive umbilical ring.
52
Expansion of amniotic cavity step 2
With more expansion, amnion surrounds the umbilical cord and covers the fetal surface of the placenta.
53
Expansion of amniotic cavity step 3
At the 3rd month, the amnion comes in contact with the chorion to form the amniochorion membrane with obliteration of chorionic cavity.
54
Expansion of amniotic cavity
By the end of the 3rd month, the amniochorionic membrane covered with Decidua capsularis comes in contact with Decidua Parietalis obliterating the uterine cavity.
55
Amniotic fluid
Clear, water fluid mainly composed of:
1. Water.
2. Proteins.
3. Lipids.
4. Carbohydrates.
5. Urea.
6. Phospholipids.
7. Electrolytes.
After kidney development, fetal urine is added to the amniotic fluid starting from the 5th month.
56
What is the amniotic fluid made of?
1. Partially produced by amnioblast cells.
2. Primarily it is derived maternal blood by osmosis through the amnion.
57
Volume of amniotic fluid
Reaches 1.0-1.5 liters starting from the 37th week till birth.
58
Amniotic fluid and stem cells
1. Amniotic fluid contains a considerable amount of stem cells.
2. These stem cells are pluripotent and are able to differentiate into various tissues including:
- Brain.
- Liver.
- Bone.
59
Functions of amniotic fluid: early pregnancy
1. Shock absorbent: protects the fetus against external trauma.
2. Heat insulator: constant fetal temperature.
3. Prevents adhesion: embryo to wall of uterus.
4. Prevents adhesion: fetal parts together (limb to the body).
60
Functions of amniotic fluid: late pregnancy
1. Space for fetal movement: essential for fetal muscle development.
2. Space for accumulation of urine.
3. Fetus starts to swallow the amniotic fluid (beginning of 5th month: helps fetus to learn suckling.
61
Functions of amniotic fluid: during delivery
1. Protects fetus against uterine contractions.
2. Forebag of amniotic sac helps gradual dilation of cervical canal.
3. Rupture of forebag of amniotic sac is a sign of start of labor.
4. Sterile amniotic fluid washes vagina just before the passage of the fetus.
62
Abnormalities of amniotic fluid
1. Polyhydramnios.
2. Oligohydramnios.
3. Premature rupture if amniotic sac.
63
Polyhydramnios
Increase of amniotic fluid volume.
X> 2 liters at full term.
64
Polyhydramnios causes
1. Unknown cause in 35% of cases.
2. Maternal diabetes.
3. Congenital malformation: esophageal atresia that interferes with normal fetal swallowing.
3. Congenital malformation of CNS: anencephaly.
65
Oligohydramnios
Decrease of amniotic fluid volume.
X< 400 ml at full term.
66
Oligohydramnios causes
1. Renal argenesis.
2. Obstruction of urinary tract.
67
Premature rupture of amniotic sac
1. Rupture of amniotic sac before the start of uterine contractions.
2. Most common cause of preterm labor.
68
Umbilical cord
Cord that connects between the fetus and the placenta.
69
Umbilical cord attachments
Extends between the fetal surface of the placenta and the ventral aspect of the fetal abdominal wall.
70
Umbilical cord length
50-60 cm
71
Umbilical cords structure
It contains umbilical arteries and one umbilical vein embedded in whartons jelly and covered in amnion.
72
Functions of umbilical cord
1. Contains umbilical vessels that transmit fetal blood between the fetus and the placenta.
2. It allows free mobility of the fetus.
73
Formation of primitive umbilical ring
1. Expansion of amniotic cavity leads to folding of the embryonic disc (during the 4th week) with ventral shifting of the amnioectodermal junction with subsequent formation of the primitive umbilical ring.
74
Contents of the primitive umbilical ring
1. Connecting stalk that contains allantois and umbilical vessels.
2. Vitelline duct duct and Vitelline vessels.
75
Formation of primitive umbilical cord
Expansion of the amniotic cavity leads to collecting contents of the primitive umbilical ring inside the sheath of the amnion to form the primitive cord.
76
Contents of primitive umbilical cord
1. Definitive yolk sac, Vitelline duct and Vitelline vessels.
2. Connecting stalk, remnant of allantois and umbilical vessels.
3. At the 6th week, intestinal loop herniates in the proximal part of the umbilical cord (physiological hernia).
77
Formation of definitive umbilical cord
1. Intestinal loop returns to abdominal cavity by the 3rd month.
2. Obliteration of Vitelline duct, allantois, and extra-embryonic parts of Vitelline vessels.
3. Degeneration of the right umbilical vein with persistence of the left vein.
4. Formation of Wharton’s Jelly from the mesoderm of the connecting stalk.
78
Abnormalities of umbilical
1. Short cord.
2. Long cord.
3. Congenital umbilical hernia (omphalocele).
4. Degeneration of one umbilical artery.
5. True knots.
79
Short cord
Leads to limitations of movements if the fetus and pre,acute separation of the placenta.
80
Long cord
The long cord mat encircle the neck of the fetus.
81
Congenital umbilical hernia (omphalocele)
The cord contains coils of intestine which failed to return to abdominal cavity.
82
Degeneration of one umbilical artery
With persistence of one artery.
83
Abnormal attachment
Abnormal attachment of the umbilical cord which may be attached to:
1. The margin of the placenta (battledore).
Or
2. Through membranes (velamentous).
84
True knots
1. Leads to obstruction of umbilical vessels with subsequent death of the fetus.
2. False knots are sites where umbilical vessels become tortuous, which do not interrupt blood flow.
85
Yolk sac
Sac that replaces the blastocele of the blastocyst.
86
Development it the yolk sac
Yolk sac passes through 3 stages:
1. Primary (primitive) yolk sac.
2. Secondary yolk sac.
3. Definitive yolk sac.
87
Primary (primitive) yolk sac
At the 9th day, Heuser’s membrane is developed from hypoblast cells that migrate to line the blastocele transforming it into the primary yolk sac.
88
Secondary yolk sac
It is formed on the 13th day due to the following changes:
1. New generations of the cells from the hypoblast line in the Heuser’s membrane.
2. Reduction of the size of yolk sac due to pinching off a part that is known exocoelomic cyst.
3. Formation of allantois, which is a diverticulum that extends from the caudal part of the yolk sac inside the connecting stalk.
89
Definitive yolk sac
1. During the 3rd week, the hypoblast layer is replaced by the Endodermal layer.
2. After folding (during the 4th week), the yolk sac shares in the for,axiom of the gut. The remaining part of the primitive umbilical cord is called the definitive yolk sac.
3. Definitive yolk sac is connected to the mid gut by vitello-intestinal (vitalline) duct.
90
Fate of yolk sac
Definitive yolk sac and Vitelline duct are gradually reduced in size and finally degenerate.
91
Functions of yolk sac
1. Formation of gut.
2. Formation of part of the urinary bladder.
3. Formation of primordial germ cells.
4 . Vitelline vessels.
5. Blood cells.
92
Yolk sac: formation of gut
Endodermal lining of the yolk sac shares in the formation of the mucosa of the foregut, midgut, and hindgut after the folding of the embryonic disc.
93
Formation of a part of urinary bladder
From the proximal part of the allantois.
94
Formation of the primordial germ cells
At the 2nd week, epiblast cells migrate to the wall of the caudal part of the yolk sac to form the primordial germ cells.
95
Vitelline vessels
1. Develop in the mesoderm around the Vitelline duct.
2. Intraembryonic parts of the Vitelline vessels will remain and form arteries and veins of the gut.
3. The extraembryonic parts disappear.
96
Blood cells
Develop on the mesoderm of the yolk sac in early pregnancy.
97
Allantois
A tubular extension from the caudal wall of the secondary wall of the secondary yolk sac that extends into the connecting stalk.
98
Development of allantois
During the 3rd week, allantois develops as the tubular extension from the caudal wall of secondary yolk sac into the connecting stalk. After folding, it extends from the ventral wall of the hindgut.
99
Parts of allantois
After folding, allantois tips divided into 2 parts:
1. Intraembryonic part: inside the embryo, extending from the ventral wall of the hindgut.
2. Extraembryonic part: in the primitive umbilical cord.
100
Fate of allantois: Intraembryonic part
1. Its proximal parts forms the apex of the urinary bladder.
2. Its distal part (urachus) forms the median umbilical ligament.
101
Fate of allantois: extraembryonic part
Part inside the umbilical cord. It becomes obliterated and degenerated.
102
Umbilical vessels are formed around?
Allantois.
103
Anomalies of urachus
1. Urachal fistula.
2. Umbilical polyp (urachal sinus).
3. Bladder diverticulum.
4. Urachal cyst.
104
Urachal fistula
Patency of the whole length of the urachus.
105
Umbilical polyp (urachal sinus)
Patency of the distal part of the urachus.
106
Bladder diverticulum
Patency of the proximal part of urachus that extends from the apex of the bladder.
107
Uracahal cyst
Patency of the central part of the urachus.
