1. Placenta
Hasu.chaudhari

2. Placenta is the organ that facilitates nutrient and
gas exchange between the maternal and fetal blood

3. Changes in the Trophoblast

The fetal component of the placenta is derived from the
trophoblast and extraembryonic mesoderm (chorionic plate).

The maternal component is derived from the endometrium.

By 2nd month, the trophoblast is characterised by number of
secondary and tertiary villi.

Capillary system developing in the core of villous system soon comes
in contact with capillaries of the chorionic plate and connecting stalk,
forming extraembryonic vascular system.

Maternal blood is delivered to placenta by spiral arteries in the
uterus.

5. Changes in the Trophoblast

Cytotrophoblast cells invades the terminal ends of spiral arteries,
replaces maternal endothelial cells by undergoing epithelial to
endothelial transition.

Numerous small extensions grow out from existing stem villi as free
villi into the surrounding lacunar/intervillous space.

By 4th month cytotrophoblastic cells and some connective tissue cells
disappear.

The syncytium and the endothelial wall of the blood vessel are the
only layers that separate the maternal and fetal circulations.
Preeclampsia : hypertension, proteinuria and edema during pregnancy

7. Chorion frondosum and Decidua basalis

Villi on the embryonic pole grow and expand giving rise to the
Chorion frondosum (bushy chorion).

On the aembryonic pole it degenerates by 3rd month, making the
chorion smooth, known as Chorion laeve.

This difference is also reflected in decidua, the layer of the
endometrium, which is shed during parturition.

The decidua over the chorion frondosum, the decidua basalis, have
a compact layer of large cells, decidual cells, known as decidual
plate, is tightly connected to the chorion.

The decidual layer over the abembryonic pole is the decidua
capsularis which later degenerates.

9. Chorion frondosum and Decidua basalis

Subsequently, the chorion laeve comes in contact with the
uterine wall (decidua parietalis) on the opposite side, and
the two fuse obliterating the uterine lumen.

Hence, the only portion of the chorion participating in the
exchange process is the chorion frondosum, which, together
with the decidua basalis, makes up the placenta.

Similarly, fusion of amnion and chorion to form the
amniochorionic membrane obliterates the chorionic
cavity. It is this membrane that ruptures during labor.

11. STRUCTURE OF THE PLACENTA







Fetal portion: formed by the chorion frondosum
Maternal portion: formed by the decidua basalis
On the fetal side, the placenta is bordered by the chorionic
plate.
On its maternal side, it is bordered by the decidua basalis of
which the decidual plate is most intimately incorporated
into the placenta.
In the junctional zone, trophoblast and decidual cells
intermingle.
Between the chorionic and decidual plates are the
intervillous spaces, which are filled with maternal blood.
During the 4th and 5th months, the decidua forms a number
of decidual septa, which project into intervillous spaces
but do not reach the chorionic plate. It divides placenta into
compartments known as Cotyledons.

13. Full-Term Placenta






It is discoid with a diameter of 15 to 25 cm, is
approximately 3 cm thick, and weighs about 500 to 600 g.
It is expelled approximately 30 minutes after birth of the
child.
When it is viewed from the maternal side, 15 to 20 slightly
bulging areas, the cotyledons, are clearly recognizable.
The fetal surface is covered by the chorionic plate. Large
arteries and veins, the chorionic vessels, converge toward
the umbilical cord.
The chorion, in turn, is covered by the amnion.
Attachment of the umbilical cord is usually eccentric and
occasionally even marginal.

16. Circulation of the Placenta





Cotyledons receive blood through 80 to 100 spiral arteries
and enter the intervillous spaces at more or less regular
intervals.
Pressure in these arteries forces the blood deep into the
intervillous spaces and bathes the numerous small villi of
the villous tree in oxygenated blood.
As the pressure decreases, blood flows back from the
chorionic plate toward the decidua, where it enters the
endometrial veins.
The intervillous spaces of a mature placenta contain
approximately 150 mL, replenished about 3-4 times per
minute.
Placental exchange does not take place in all villi, however,
only in those that have fetal vessels in intimate contact with
overlying syncytial membrane.

17. Circulation of the Placenta


-
Placental membrane which separates maternal and fetal
blood, is initially composed of 4 layers:
Endothelial lining of fetal vessels
Connective tissue in the villous core
Cytotrophoblastic layer
Syncytium
From 4th month on, however the placental membrane have
only 2 layers (placental barrier):
Endothelial lining of fetal vessels
Syncytium
Erythroblastosis fetalis
Fetal hydrops

18. Hydrops fetalis

19. Function of placenta




-
-
Exchange of gases
Exchange of nutrients and electrolytes
Transmission of maternal antibodies (IgG)- passive
immunity
Hormone production : by syncytial trophoblast
Progesterone: by 4th month
Estrogenic hormone (estriol) – uterine growth and
development of mammary gland
Human chorionic gonadotropin (hCG)- for first 2 months
Somatomammotropin- makes mother diabetogenic and
promotes breast development for milk production

20. Amnion and umbilical cord






The oval line of reflection between the amnion and embryonic
ectoderm is the primitive umbilical ring.
At 5th week, following structures pass through it:
Connecting stalk, containing allantois and umbilical vessels (2 arteries
and 1 vein)
Yolk stalk (vitelline duct) with vitelline vessels
Canal connecting the intraembryonic and extraembryonic cavities.
At 3rd month, amnion has expanded so that it comes in contact with
chorion, obliterating the chorionic cavity.
Yolk sac then usually shrinks and is gradually obliterated
At the end of 3rd month, allantois, vitelline duct and its vessels are
obliterated.
Now the cord contains only umbilical vessels surrounded by
Wharton’s jelly.

22. PLACENTAL CHANGES AT THE
END OF PREGNANCY

Increase in fibrous tissue in the core of villus

Thickening of basement membranes in fetal capillaries

Obliterative changes in small capillaries of villi

Deposition of fibrinoid on the surface of the villi in the
junctional zone and chorionic plate

23. Amniotic fluid






It is the clear, watery fluid filling the amniotic cavity, produced
in part by amniotic cells and derived primarily from maternal
blood.
Approximately 30 ml at 10 weeks, 450 ml at 20 weeks and
800-1000 ml at 37 weeks of gestation.
It absorbs jolt, prevents adherence of embryo to the amnion
and allows fetal movements.
Its volume is replaced every 3 hours.
From 5th month fetus swallows it own amniotic fluid, about
400 ml/day.
Fetal urine is added daily to the amniotic fluid in 5th month.

24. Twins : Dizygotic twins

25. Monozygotic twins

26. Twin defects : Conjoined twins

27. Parturition (Birth)
1.
2.
3.
Divided into three stages:
Stage 1: effacement (thinning and shortening)
and full dilatation of cervix
Stage 2 : delivery of the fetus
Stage 3 : delivery of placenta

28. Menstrual cycle






It is the cyclical changes that occurs in the uterus
(endometrium) every month.
Reproductive period – period in a woman’s life in
which she can bear children
Menstruation – monthly flow of blood from uterus
Menarche – onset of menstruation (at about 12 yrs)
Menopause – cessation of menstruation (at about 45
yrs)
Cyclical changes that takes place in the ovaries is
known as ovarian cycle.

29. Structure of uterine wall



Perimetrium – outermost layer, made up of
peritoneum
Myometrium – middle layer, made up of smooth
muscle
Endometrium – innermost layer, mucous membrane.
It is this layer which undergoes cyclical changes during
menstrual cycle

30. Structure of uterine wall

31. Constituents of endometrium



Surface covered by lining epithelium
Stroma contains numerous simple tubular glands
(uterine glands)
Spiral arteries supply the whole thickness , while
straight arteries are confined to the basal part of
endometrium

33. Phases of menstrual cycle
1.
2.
3.
4.
On the basis of changes taking place in the
endometrium it is divided into:
Postmentstrual phase
Proliferative phase
Secretory phase
Menstrual phase
Also classified as:
1.
2.
Follicular phase
Luteal phase

34. Menstrual
Post menstrual
Secretory
Proliferative

35. Phases of menstrual cycle

36. Follicular phase


It constitutes the first half of the menstrual
period.
The changes in this phase takes place under the
influence of oestrogen produced by the
developing follicle.

37. Luteal phase


It constitutes the second half of the menstrual
period.
The changes in this phase takes place under the
influence of progesterone produced by the
corpus luteum, along with oestrogen.

39. The changes during menstrual cycle are summarized as
follow:

■
■
■
-
Endometrium increases in thickness
Postmentrual phase: 0.5-1 mm
Proliferative phase: 2-3 mm
Secretory phase: 5-7 mm
Uterine gland grow in length and becomes convoluted
Lining epithelium of the glands changes
cuboidal in postmenstrual phase
columnar during proliferative phase and
apical part of cell is shed of during secretory phase
As the endometrium increases in thickness, stroma is divided into
Stratum compactum
Stratum spongiosum
Stratum basale

41. The changes during menstrual cycle are summarized as
follow:
■
■




Arteries grow in length during proliferative stage.
During secretory phase, arteries supplying the superficial 2/3rd becomes
tortous called spiral arteries and arteries to the basal 3rd remains straight.
Towards the end of secretory phase endometrium is thick, soft and
richly suppied with blood.
In the absence of pregnancy, the superficial parts of the
endometrium( stratum compactum and stratum spongiosum) are shed
off as menstrual bleeding.
Just before the onset of bleeding, there is lowering of both progesterone
and oestrogen, and it is believed that this withdrawal leads to onset of
menstual bleeding.
At the end of menstruation the endometrium that remains consists of
stratum basale and the basal portion of uterine glands.

43. Hormonal control of ovarian and menstrual cycle









Hypothalamus secretes Gonadotropin releasing hormone
Stimulates anterior pituitary to secrete gonadotropic hormones i.e.,
follicle stimulating hormone (FSH) and luteinizing hormone (LH).
In turn FSH acts on the ovary and stimulates formation and maturation
of ovarian follicles.
Maturing ovarian follicles secretes oestrogen, which causes repair and
proliferation of endometrium.
Two days before ovulation, oestrogen level rises to maximum, leading to
sudden increase on LH level (LH surge).
Ovulation takes place and corpus luteum is formed.
LH stimulates secretion of progesterone by corpus luteum.
In the absence of fertilization, granulosa cells produce inhibin, which
inhibits gonadotropin secretion from anterior pituitary.
Regresses corpus luteum, fall in oestrogen and progesterone, this
withdrawal of hormone triggers onset of menstraution.

47. Time of ovulation

In a 28 days cycle, ovulation takes place at about the
middle of the cycle.

The period between ovulation and the next menstrual
bleeding is constant at about 14 days.

One commonly used method to find out ovulation is
temperature method. At the middle of the cycle there
is sudden fall in temperature followed by rise. This rise
is believed to indicate ovulation.

49. Safe period

It is the period during one menstrual cycle in which
despite unprotected intercourse fertilization may not
occur.

Menstrual cycle : 28+2 days or 28-2 days.
Safe period calculation:
Shortest cycle minus 20 days : 26-20 = 6th day
Longest cycle minus 10 days : 30-10 = 20th day
Thus from 6th to 20th day of each cycle counting from first
day of menstrual period is considered as fertile period.


50. Development of Gastrointestinal
tract

51. General introduction




Epithelial lining is endodermal in
origin
At the mouth and anus epithelium is
ectodermal.
As a result of cephalocaudal and
lateral folding, a portion of the
endoderm-lined yolk sac cavity is
incorporated into the embryo to form
the primitive gut.
In the cephalic and caudal parts of
the embryo, the primitive gut forms a
blind-ending tube, the foregut and
hindgut, respectively. The middle
part, the midgut, remains temporally
connected to the yolk sac by means
of the vitelline duct, or yolk stalk

52. General introduction

a.
b.
c.
d.



Development of the primitive gut is divided as follow:
The pharyngeal gut, or pharynx, extends from the oropharyngeal
membrane to the respiratory diverticulum, part of foregut.
The remainder of the foregut lies caudal to the pharyngeal tube and
extends as far caudally as the liver outgrowth.
The midgut begins caudal to the liver bud and extends to the junction
of the right two-thirds and left third of the transverse colon in the
adult.
The hindgut extends from the left third of the transverse colon to the
cloacal membrane.
Endoderm forms the epithelial lining of the digestive tract and gives
rise to the specific cells (the parenchyma) of glands, such as
hepatocytes and the exocrine and endocrine cells of the pancreas.
The stroma (connective tissue) for the glands is derived from visceral
mesoderm.
Muscle, connective tissue, and peritoneal components of the wall of
the gut also are derived from visceral mesoderm.

55. DERIVATIVES OF FOREGUT
1)
Part of the floor of the mouth including the tongue.
2)
Pharynx
Various derivatives of the pharyngeal pouches and the
thyroid.
Oesophagus
Stomach
Duodenum- whole of the superior part and upper half of
descending part (upto major duodenal papilla)
Liver and extra hepatic biliary system
Pancreas
Respiratory system.
3)
4)
5)
6)
7)
8)
9)

56. DERIVATIVES OF MIDGUT
1.
2.
3.
4.
5.
6.
Duodenum- descending part distal to major
papilla, horizontal and ascending parts.
Jejunum
Ileum
Caecum and appendix
Ascending colon
Right 2/3 of the transverse colon

57. DERIVATIVES OF HIND GUT
1
2
3
4
5
Left 1/3 of the transverse colon
Descending and pelvic colon
Rectum
Upper part of anal canal
Parts of urogenital system developed from
primitive urogenital sulcus.

58. Arteries of Gut



Foregut – Coeliac artery
Midgut – Superior mesenteric artery
Hindgut – Inferior mesenteric artery
Note: The endodermal tube only gives rise to the lining
epithelium of G.I.T.
The submucous coat, muscular coat, serous coat are all
developed from splanchnopleuric layer of lateral part of
mesoderm.

59. MESENTERIES






a.
b.
Double layers of peritoneum that enclose an organ and connect it to the
body wall, such organs are called intraperitoneal.
Organs that lie against the posterior body wall and are covered by
peritoneum on their anterior surface only (e.g., the kidneys) are called
retroperitoneal.
Peritoneal ligaments are double layers of peritoneum (mesenteries)
that pass from one organ to another or from an organ to the body wall.
Caudal part of the foregut, the midgut, and a major part of the hindgut
are suspended from the abdominal wall by the dorsal mesentery.
Ventral mesentery, which exists only in the region of the terminal part
of the esophagus, the stomach, and the upper part of the duodenum, is
derived from the septum transversum.
Growth of liver in the mesenchyme of septum transversum divides the
ventral mesentery into:
Lesser omentum, extending from the lower portion of the esophagus,
the stomach, and the upper portion of the duodenum to the liver
Falciform ligament, extending from the liver to the ventral body wall

61. Derivation of individual parts of alimentary
tract
Esophagus:

At the 4th week of development a respiratroy diverticulum (lung bud)
appears at the ventral wall of foregut (between pharynx & stomach).

Separated from the foregut by tracheoesophageal septum.

Foregut then divides into dorsal portion oesophagus and ventral portion
respiratory primordium.

Muscle coat, formed by the surrounding splanchnic mesenchyme, is
straited in its upper 2/3rd (vagus) and smooth in the lower 1/3rd
(splanchnic plexus)

63. Congenital anomaly: Esophageal Atresia
with Tracheoesophageal (TE) Fistula

64. Stomach

At 4th week it appears as a fusiform dilatation.

Dorsally attached to dorsal mesogastrium.

Vertrally attached to septum transversum by ventral mesogastrium.

Liver and the diaphragm are formed in the substance of septum
transversum.

Ventral mesogastrium form lesser omentum, coronary ligament and
falciform ligament.

The dorsal mesogastrium is divided by the developing spleen to form the
gastrosplenic ligament and lienorenal ligament.

66. Stomach


It rotates around longitudinal and antero-posterior axis respectively
during development.
Undergoes differential growth resulting in alteration in its shape and
orientation.

Ventral border comes to face upward, becomes lesser curvature.

Dorsal border points downwards & to the left, becomes greater
curvature.

Rotation about the longitudinal axis pulls the dorsal mesogastrium to the
left, creating a space behind the stomach called the omental bursa
(lesser peritoneal sac).

As it rotates around anteroposterior axis, the dorsal mesogastrium bulges
down, continues to grow down and forms a double-layered sac
extending over the transverse colon and small intestinal loops like an
apron, called greater omentum.

69. Congenital anomaly: Congenital pyloric stenosis

70. Duodenum:

Derived from terminal part of foregut and cephalic part of
midgut.

Liver bud present at the Junction.

Due to the rotation of stomach, the duodenum form a Cshaped loop & rotates to the right.

Rapid growth of head of pancreas pushes duodenum to the
right side of abdominal cavity.

Its proximal part is supplied by branches from coeliac artery
and distal part by branches from superior mesenteric artery.

72. Congenital anomaly: Duodenal stenosis and Atresia

73. Jejunum and Ileum

Jejunum & ileum are derived from pre-arterial segment of mid
gut loop.

Terminal portion of the ileum is derived from the post arterial
segment proximal to the caecal bud.

74. Caecum and appendix




Caecum and appendix are derived from enlargement of caecal
bud.
Caecal bud is a diverticulum arising from the post arterial
segment of mid gut loop.
Proximal part grows rapidly to form caecum.
Distal part remains narrow and form the appendix.

75. Ascending colon

Derived from post arterial segment of mid gut loop distal to caecal bud.
Transverse colon




Right 2/3rd develops from post arterial segment of mid gut loop.
Left 1/3rd develops from hind gut.
Right 2/3rd supplied by superior mesenteric artery.
Left 1/3rd by inferior mesenteric artery.
Descending colon

Develops from hind gut

77. Rectum

Derived from the primitive rectum, i.e., the dorsal subdivision of the
cloaca

Cloaca : part of the hind gut caudal to the attachment of allantoic
diverticulum.

Cloaca is subdivided by a urorectal septum into:
Ventral part (primitive urogenital sinus)
Dorsal part (primitive rectum).
-

Cloacal membrane is divided by the urorectal septum into ventral
urogenital membrane and dorsal anal membrane.

79. Congenital anomalies: Rectal fistula: rectovesical, rectourethral,
rectovaginal, or sometime combination of more than one type.

80. Anal canal


Partly from the endoderm
of primitive rectum and
partly from ectoderm
The line of junction of
endoderm and ectoderm is
represented by anal valves
(pectinate line)
Congenital anomaly:
Imperforate anus

81. Rotation of gut






The mid gut loop after formation lies outside the abdominal
cavity.
The loop has prearterial (cephalic) segment and postarterial
(caudal) segment.
Initially the loop lies in the sagittal plane, proximal segment
being cranial and ventral to distal segment.
The loop undergoes an anticlockwise rotation by 900, so that
it lies in horizontal plane.
Now prearterial segement lies on right side and postarterial
segment on the left.
Coils of jejunum and ileum (prearterial segment), as they
return to abdominal cavity, undergoes a further anticlockwise
rotation.

82. Rotation of gut




So that coils of jejunum and ileum pass behind superior
mesenteric artery into the left half of abdominal cavity.
Finally postarterial segment returns to the abdominal cavity
undergoing anticlockwise rotation.
As a result, transverse colon lies anterior to the superior
mesenteric artery and caecum lie on right side.
Gradually caecum descends to the iliac fossa and ascending,
transverse and descending parts of colon become distinct.

85. Anomalies Associated with Malrotation: Non rotation, Volvulus,
Reverse rotation, subhepatic caecum, Omphalocele

86. Development of Liver ,pancreas and spleen







Hepatic bud or hepatic diverticulum arise from the junction
between foregut and hind gut.
Pass through the ventral mesogastrium into septum
transversum.
Elongates and divide to form pars hepatica and pars cystica.
Pars hepatica gives rise to the parenchyma of liver and bile
capillaries.
The connective tissue of liver is derived from the septum
transversum.
The gall bladder and the cystic duct are developed from the
pars cystica.
Hepatic bud proximal to the pars cystica will form the bile
duct.

88. Anomalies of liver and gall bladder



Formation of accessory
lobe and abnormal lobes.
Gall bladder may be
partially divided
Gall bladder may be
duplicated.

89. Pancreas








Two endodermal buds: dorsal and ventral buds arise from the
gut that later forms 2nd part of duodenum.
Ventral bud shifts to the left side.
The ventral bud form the uncinate process and the lower part
of head.
The dorsal bud form the upper part of head , body and tail.
The ducts of the ventral and the dorsal bud anastomose.
The duct of the dorsal bud between the anastomosis and the
duodenum – accessory pancreatic duct.
Main pancreatic duct – distally by duct of dorsal bud and
proximally by duct of ventral bud
Islets of langerhans – derived from primitive duct system.

91. Congenital anomalies in pancreas


Annular pancreas
Divided pancreas

92. Development of Spleen



Mesenchymal cells of dorsal
mesogastrium proliferate
forming the spleen.
Pass to the left side.
Dorsal mesogastrium gives rise
to gastrosplenic and linorenal
ligament.

93. Congenital Omphalocele
Herniation of abdominal viscera through the umbilical ring.
Failure of returning the bowel after physiological hernia.

94. Meckel’s (Ileal) Diverticulum
•Persistance of vitellointestinal duct: 2%; 2”; 2ft. away from antimesenteric
border of ileum.
• Ulceration, bleeding or perforation may take place.

95. Congenital anomalies of the Gut



Atresia.
Stenosis
Megacolon or
Hirschsprung’s disease.
(non development of nerve plexus
in the wall of gut).