8.placenta

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8.placenta

  1. 1. Placenta Hasu.chaudhari
  2. 2. Placenta is the organ that facilitates nutrient and gas exchange between the maternal and fetal blood
  3. 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.
  4. 4. 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
  5. 5. 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.
  6. 6. 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.
  7. 7. 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.
  8. 8. 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.
  9. 9. 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.
  10. 10. 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
  11. 11. Hydrops fetalis
  12. 12. 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
  13. 13. 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.
  14. 14. 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
  15. 15. 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.
  16. 16. Twins : Dizygotic twins
  17. 17. Monozygotic twins
  18. 18. Twin defects : Conjoined twins
  19. 19. 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
  20. 20. 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.
  21. 21. 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
  22. 22. Structure of uterine wall
  23. 23. 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
  24. 24. 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
  25. 25. Menstrual Post menstrual Secretory Proliferative
  26. 26. Phases of menstrual cycle
  27. 27. 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.
  28. 28. 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.
  29. 29. 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
  30. 30. 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.
  31. 31. 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.
  32. 32. 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.
  33. 33. 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. 
  34. 34. Development of Gastrointestinal tract
  35. 35. 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
  36. 36. 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.
  37. 37. 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)
  38. 38. 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
  39. 39. 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.
  40. 40. 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.
  41. 41. 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
  42. 42. 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)
  43. 43. Congenital anomaly: Esophageal Atresia with Tracheoesophageal (TE) Fistula
  44. 44. 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.
  45. 45. 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.
  46. 46. Congenital anomaly: Congenital pyloric stenosis
  47. 47. 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.
  48. 48. Congenital anomaly: Duodenal stenosis and Atresia
  49. 49. 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.
  50. 50. 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.
  51. 51. 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
  52. 52. 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.
  53. 53. Congenital anomalies: Rectal fistula: rectovesical, rectourethral, rectovaginal, or sometime combination of more than one type.
  54. 54. 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
  55. 55. 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.
  56. 56. 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.
  57. 57. Anomalies Associated with Malrotation: Non rotation, Volvulus, Reverse rotation, subhepatic caecum, Omphalocele
  58. 58. 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.
  59. 59. Anomalies of liver and gall bladder    Formation of accessory lobe and abnormal lobes. Gall bladder may be partially divided Gall bladder may be duplicated.
  60. 60. 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.
  61. 61. Congenital anomalies in pancreas   Annular pancreas Divided pancreas
  62. 62. 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.
  63. 63. Congenital Omphalocele Herniation of abdominal viscera through the umbilical ring. Failure of returning the bowel after physiological hernia.
  64. 64. Meckel’s (Ileal) Diverticulum •Persistance of vitellointestinal duct: 2%; 2”; 2ft. away from antimesenteric border of ileum. • Ulceration, bleeding or perforation may take place.
  65. 65. Congenital anomalies of the Gut    Atresia. Stenosis Megacolon or Hirschsprung’s disease. (non development of nerve plexus in the wall of gut).

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