Embryology ๐ถ Flashcards
what are the primary male sex organs?
the testis (2 in number).
where are the testes?
In the scrotum.
what is the function of testes?
produce sperms and secretes male sex hormone.
what are secondary male sex organs?
the epididymis, the vas deferens, the seminal vesicles, the ejaculatory ducts, the urethra and the accessory glands (seminal vesicle, prostate and bulbourethral glands).
what are male external sex organs?
(scrotum & penis; male copulatory organ).
what are female primary sex organs?
the ovaries (2 in number).
where are the ovaries?
In the pelvis
what is the function of the ovaries?
produce ova and secretes female sex hormones.
what are female secondary sex organs?
Uterine tube, uterus, and vagina
what are female external sex organs?
the vulva
what are the parts of the uterine tube?
formed of 4 parts; infundibulum, ampulla (widest part), isthmus (narrowest part) and intramural part.
The uterus
pear-shaped, lies in the pelvis, formed of 3 parts (fundus, body and cervix) and its wall consists of 3 layers (endometrium, myometrium & perimetrium).
The vagina
acts as female copulatory and birth canal, its upper end surrounds the cervix which divides it into 4 fornices (anterior, posterior, and 2 lateral).
what does a mature sperm consist of?
The mature sperm consists of:
๏ท Head:
- Contains nucleus (has the haploid number of chromosomes; 22 X or 22 Y).
- Covered by acrosome (head cap) which contains enzymes for penetration of the coverings of the ovum.
๏ท Neck.
๏ท Tail: consists of:
- Middle piece (contains mitochondrial sheath which produces energy needed for sperm motility).
- Principal piece (responsible for sperm motility).
- End piece.
what does a mature ovum consist of?
๏ Usually released from the ovary in the stage of 2ry oocyte (contains a haploid number of chromosomes; 22X).
๏ Surrounded by zona pellucida & corona radiata
what is fertilization?
it is the union of the male and female gametes to form the zygote.
Where does fertilization take place?
In the ampulla.
process of fertilization
deposition
transport of sperms
capacitation
acrosome reaction
Deposition
about 200 โ 600 million sperms are deposited in the posterior fornix of the vagina during sexual intercourse
transport of sperms
about 200 โ 300 sperms reach the fertilization site while other sperms die.
capacitation
process by which the sperm acquires the capacity to fertilize the ovum and it takes place in the femaleโs genital tract for 7 hours.
what is the mechanism of capacitation?
removal of the seminal plasma proteins from the cell membrane of the head of sperm.
acrosome reaction
process by which the sperm releases the contents of its acrosome and it takes place around the ovum.
what is the mechanism of acrosome reaction?
release of the following substances:
๏ Hyal-uronidase enzyme: penetrates the corona radiata.
๏ Trypsin-like substance: digest the zona pellucida.
๏ Zona lysine: help the sperm to penetrate the zona pellucida
what are the steps of fertilization?
1) Penetration of corona radiata: by hyal-uronidase enzyme.
(2) Penetration of zona pellucida: Trypsin-like substance digests the zona then zona lysine help the sperm to penetrate the zona.
(3) Fusion of the cell membrane of the sperm and ovum: while the head and tail enter the oocyte.
(4) Zona reaction: once the sperm penetrates the zona this reaction occurs make the zona pellucida impermeable to other sperms.
(5) Completion of the 2nd meiotic division: after entry of the sperm the oocyte completes the 2nd meiotic division to give mature ovum (female pronucleus) and 2nd polar body.
(6) Formation of male pro-nucleus: by the nucleus of the sperm.
(7) Union of the pro-nuclei: to form zygote with 46 chromosomes
what are the results of fertilization?
- The 2ry oocyte completes the 2nd meiotic division.
- Restoration of the diploid number of chromosomes.
- Determination of the sex of the embryo (if the sperm is Y male and if the sperm is X female).
- Determination of the state of health and disease of the embryo.
- The zygote starts cell division (cleavage).
what is dispermy(triploidy)?
it is the fertilization of the ovum with two sperms (69 chromosomes)
what is parthenogenesis?
it is the dividing of the ovum to form the zygote.
what is cleavage?
repeated mitotic divisions of the zygote to increase the number of cells (blastomeres).
what is the site of cleavage?
during passage of the zygote in the uterine tube towards the uterus.
what are the steps of cleavage?
- Repeated cell division: the zygote gives 2 then 4 then 8 blastomeres.
- Formation of morula: after 3 days 16 โ 32 blastomeres are formed. They are surrounded by zona pellucida which has the following functions:
๏ Keep the dividing cells together.
๏ Prevent adhesion between the dividing cells and the uterine tube. - The morula reaches the uterine cavity: about the 4th โ 5th day.
- Formation of blastula (blastocyst):
- Small cavities filled with fluid (from the uterine cavity) appear in between the dividing cells.
- The cavities fuse together to form one large cavity (Blastocele), which separates the blastomeres into 2 groups:
๏ท Trophoblast: thin outer layer which will form the fetal part of the placenta.
๏ท Inner cell mass: an inner group of cells that will give rise to the embryo.
๏ The zona pellucida degenerates and disappears.
what is implantation?
It is the embedding of the blastula in the endometrium.
when does implantation take place?
at the end of the first week up to the end of the second week
where does implantation take place?
in the endometrium of the posterior wall of the body of the uterus near the fundus.
what are the steps of implantation?
- Degeneration of the zona pellucida:
- Cause: enzymes of acrosome reaction.
- Result: exposure of the trophoblast. - Differentiation of the trophoblast into 2 layers:
Inner: cytotrophoblast.
Outer: syncytiotrophoblast - Small spaces called lacunae appear in the syncytiotrophoblast.
- The syncytiotrophoblast has the following features:
-Adhesive power: the trophoblast adheres to the endometrium.
- Histolytic power: by releasing proteolytic enzymes. - Lysis of the glands and connective tissue: forms a defect in the endometrium for implantation of the blastula.
- Lysis of the blood vessels: the blood fills the lacunae.
- After complete implantation: the defect in the endometrium is filled with fibrin clot then the epithelium regenerates.
what are the abnormal sites of implantation?
- intra-uterine (placenta praevia)
- etxra-uterine
what are the intra-uterine sites of abnormal implantation?
Implantation in the lower segment of the uterus
-praevia centralis: cover the internal os completely
-praevia lateralis: away from the internal os
-praevia marginales: cover the internal os laterally
what are extra-uterine abnormal sites of implantation?
-tubal pregnancy
-ovarian pregnancy
-abdominal (peritoneal) pregnancy
what is the site of tubal pregnancy?
the ampulla
what are the causes of tubal pregnancy?
-delay in the transport of the blastula
-early loss in zona pelucida
what are the features of tubal pregnancy?
-Signs and symptoms of pregnancy
-rupture in the uterine tube which leads to internal hemorrhageand and abdominal pain
what may be confused with tubal pregnancy?
appendicitis especially if the tubal pregnancy was in the right tube.
what causes ovarian pregnancy?
: it is either 1ry or 2ry
1ry: the fertilized ovum is directly implanted on the ovary.
2ry: rupture tubal and the blastula is re-implanted on the ovary.
what is the site of abdominal pregnancy?
on the surface of any abdominal organ.
what is the cause of abdominal pregnancy?
usually 2ry to rupture tubal pregnancy.
what are the features of abdominal pregnancy?
the placenta penetrates the wall of the organ leading
to internal hemorrhage.
what is the decidua?
It is the endometrium of pregnant uterus.
what is the structure of decidua?
The endometrium shows decidual reaction (like the secretory phase of the endometrium under the effect of progesterone hormone)
what are the parts of decidua?
decidua basalis: Between the blastula and the muscle wall of the uterus
decidua capsularis: covers the blastula
decidua paretalis: lines the rest of the uterus
what is the fate of decidua basalis?
forms the maternal part of the placenta
what is the fate of decidua paretalis and capsularis?
they fuse and degenerate
what are the changes that happen to the blastula in the second week?
During the 2nd week, the following changes occur in the blastula:
- The trophoblast differentiates into 2 layers:
๏ Syncytiotrophoblast: outer multi-nucleated layer with indistinct cell boundaries.
๏ Cytotrophoblast: inner mono-nucleated cells with clear cell boundaries.
-The embryoblast differentiates into bilaminar embryonic (germ) disc which is formed of:
๏ Epiblast: layer of tall columnar cells close to the cytotrophoblast.
๏ Hypoblast: layer of small cuboidal cells close to the blastocele.
Formation of 2 cavities:
๏ Amniotic cavity appears in the 7th or 8th day within the epiblast. Its roof is formed by amnioblasts (from the epiblasts), while its floor is formed by the epiblasts.
๏ Primary yolk sac cavity: in the 9th or 10th day the original blastocele is transformed into 1ry yolk sac. Its roof is formed by the hypoblast, while its sides and floor are formed by Hauserโs membrane (from the hypoblasts)
explain the formation of the chorionic vesicle.
๏ Extraembryonic mesoderm develops (from cytotrophoblasts) between the trophoblast (externally) and both 1ry yolk sac and amniotic cavity (internally).
๏ Multiple cavities appear in the extraembryonic mesoderm.
๏ They fuse together forming single large cavity called extraembryonic coelom (chorionic cavity) which divides the extraembryonic into:
- Somatic layer: lines the trophoblast & covers the amniotic cavity.
- Splanchnic (Visceral) layer: covering the 1ry yolk sac.
- Connecting stalk: connecting the 2 layers at the caudal end of the embryo. It is the future umbilical cord.
what is the chorion and what is the chorionic vesicle?
The trophoblast with the somatic layer of extraembryonic mesoderm is called chorion and the whole vesicle is now called the chorionic vesicle.
What are the changes during the 3rd week?
โ Changes in the structure of bilaminar embryonic plate:
๏ฒ Development of prochordal plate
๏ฒ Development of primitive streak (Groove)
๏ฒ Development of notochord
โ Formation of 3 germ layers:
๏ฒ Gastrulation
prochordal plate
Site:
โ near the cranial end in the midline
Cause:
โ elongation (in height) of the primary endoderm (hypoblast): โข It is the site of the oropharyngeal membrane
What is the site of the primitive streak?
โ Opacity formed caudally in the midline (from caudal end to middle of the embryo)
Formation of the primitive streak
โ proliferation and migration of the epiblastic cells:
โข Primitive node: the proliferation of cranial end of the primitive streak
โข Primitive pit: depression in the middle of the primitive node
What is the fate of the primitive streak?
โ Diminishes in size and becomes an insignificant structure in the sacrococcygeal region of the embryo
โ Disappears by the end of the fourth week (if it persists, it will lead to the formation of sacrococcygeal teratoma)
What is the definition of notochord?
โ The core around which the vertebral column formed
What is the source of notochord?
โ epiblast of primitive streak & nodes
What is the site of notochord?
โ in the midline between ectoderm & endoderm
What are the stages of formation of notochord?
โ Notochordal process: 17th day
โ Notochordal canal
โ Notochordal plate
โ Notochord: 20th day
What is the function of notochord?
โ Axis for the formation of the vertebral column
โ Produce intraembryonic mesoderm
โ Initiate (stimulate) neutralization (neural tube formation)
What is the fate of notochord?
โ The cranial part: some parts of bones forming skull base
โ Parts in the center of the bodies of vertebrae: Degenerate and disappear
โ Parts in the intervertebral discs: Undergo mucoid degeneration to form nucleus bulbosus.
What is the definition of gastrulation?
โ the process by which the bilaminar embryonic disc is converted into a trilaminar embryonic disc.
What is the time of gastrulation?
During the 3rd week
What are the steps of the process of gastrulation?
1) Cells from primitive streak migrate and are arranged between epiblast & hypoblast forming intraembryonic mesoderm.
2) The epiblast of primitive streak displaces the hypoblast, forming the embryonic endoderm
3) The cells remaining in the epiblast from the embryonic ectoderm
What is the first morphological sign of gastrulation?
โ The first morphologic sign of gastrulation is the formation of the primitive streak
What happens by the middle of 3rd week?
โ By the middle of the 3rd week, the intraembryonic mesoderm separates the ectoderm and endoderm everywhere except:
๏ฒ At oropharyngeal membrane cranially.
๏ฒ In median plane cranial to the
primitive node (site of notochord)
๏ฒ At the cloacal membrane caudally.
What is the origin of the intraembryonic mesoderm?
Primitive streak, Primitive node & Notochord
What are the steps of the development of the intraembryonic mesoderm?
โ A longitudinal groove appears on each side of the notochord divides the intraembryonic mesoderm into:
โข paraxial mesoderm: medial to the longitudinal groove
โข intermediate cell mass: the floor of the longitudinal groove
โข lateral plate mesoderm: lateral to the longitudinal groove
What is the definition of paraxial mesoderm?
โ the medial part of the intraembryonic mesoderm on each side of the notochord
What are the steps of the development of paraxial mesoderm?
โ The intra-embryonic mesoderm proliferates to form a thick column of paraxial mesoderm
โ At end of 3week: the paraxial mesoderm divides into segments (somites) by transverse grooves
What is the number of Somites?
โ 42 to 44 pairs of somites:
โข 4 occipital
โข 8 cervical
โข 12 thoracic 5 lumbar
โข 5 sacral
โข 8-10 coccygeal
What is the sequence of appearance of somites?
โ Appear in the craniocaudal direction
What is the fate of somites?
โ Ventromedial part (sclerotome):
โข Give axial skeleton (vertebral column& ribs
โ Dorsolateral part (dermo-myotome):
โข Dermatome: gives dermis & fascia
โข Myotome: gives skeletal muscles
What is the definition of intermediate cell mass?
โ mesoderm corresponds to the floor of the longitudinal groove
What is the fate of intermediate cell mass?
โ Kidney & Cortex of suprarenal gland
โ Testis or ovary
โ The male and female genital duct system
What is the definition of the lateral plate mesoderm?
โ mesoderm lateral to the longitudinal groove
What are the steps of the development of lateral plate mesoderm?
โ Small cavities appear in it
โ These cavities unite to form a single horse-shoe cavity (intraembryonic coelom) that divide the lateral plate mesoderm into somatic (partial), splanchnic (visceral), and intraembryonic coelom
What is the function of the somatic layer?
โ Give rise to:
โข Muscles of the chest and abdominal wall
โข Parietal layer of pericardium, pleura and peritoneum
What is the function of the splanchnic layer?
โ Give rise to:
โข Muscles of heart & Smooth muscles of the gut and bronchial tree
โข visceral layer of pericardium, pleura, and peritoneum
What is the function of the intraembryonic coelom?
give rise to:
โข pericardium, pleura and peritoneum
What are the derivatives of endoderm?
โ3 Epi + pptt + salahโ
๏ The epithelial lining of:
๏ฒ Gastrointestinal tract
๏ฒ Respiratory tract
๏ฒ Urinary tract and reproductive system
๏ Thymus& thyroid glands
๏ Parathyroid glands & pancreas
๏ Liver
What are the derivatives of mesoderm?
๏ The dermis of skin and fascia
๏ Skeletal system
๏ Muscular system (all muscles)
๏ Circulatory and lymphatic system
๏ Excretory system
๏ Reproductive system except for germ cells
๏ Suprarenal cortex
๏ The lining of the body cavity
What are the derivatives of ectoderm?
๏ Nervous system
๏ Cornea and lens of the eye
๏ Pituitary and pineal gland
๏ Epidermis & skin appendage (sweet glands& hair follicles)
๏ Epithelium of anterior part of the mouth and lower part of the anal canal
๏ Derivatives of neural crest
What is the definition of neurulation?
formation of neural tube
What are the steps of the development of the neural tube?
Neural plate: Thick epiblast above notochord
๏ฟผ๏ฟผNeural groove: Median groove at the central axis of the neural plate
๏ฟผ๏ฟผNeural fold: 2 folds on each side of the neural groove
๏ฟผ๏ฟผ๏ฟผ๏ฟผ๏ฟผ๏ฟผNeural tube:
โ Fusion of neural folds is followed by separation of the neural tube from the epiblast
โ Cranial & caudal neuropores are at first open then become closed
What is the fate of the neural tube?
โ Cranial part: become dilated to form the brain
โ Caudal part: forms the spinal cord
๏ฟผ๏ฟผ
What are the neural crest cells?
โ Neuro-ectodermal cells which separate from ectoderm during the fusion neural folds to form the neural tube
What are the derivatives of the neural crest cells?
Neuroblasts: which gives rise to all ganglia
โข Sympathetic Ganglia
โข Dorsal root ganglia
Melanocytes: pigment cells of the skin.
Spongioblasts: which gives:
โข Schwan cells
โข pia and arachnoids matter
Chromaffin cells: which gives:
โข Suprarenal medulla
โข Carotid bodies cells.
Odontoblast cells
What is the definition of folding?
โ folding of flat trilaminar embryo ventrally to form a cylindrical embryo.
What is the time of folding?
at beginning 4th week.
What are the causes of folding?
1) Rapid longitudinal growth of the central nervous system is the cause of head and tail fold.
2) Rapidly growing somites is the cause of lateral folding.
What are the results of folding?
Say Rrrโฆ.
Shape: โ embryo becomes cylindrical.
Amniotic cavity: โ enlarge at the expense of yolk sac to surround embryo completely.
Yolk sac: โ Divided into two parts:
1) Part inside the embryo form primitive gut (foregut, midgut and hindgut).
2) Part outside embryo becomes definitive yolk sac.
-The duct which connects the midgut with the definitive yolk sac called vitello-intestinal duct
Results of head folding: โ Forebrain become the most cranial structure of the embryo.
Results of tail folding: โ Cloacal membrane become the most caudal structure of the embryo & Connecting stalk is carried in the anterior surface of the embryo.
Results of lateral folding: โ the embryo becomes tubular & the Anterior abdominal wall is formed.
What is anencephaly?
- It is a serious birth defect in which a baby is born without parts of the brain and skull.
- It is a type of neural tube defect due to failure of the cranial neuropore to close
What is the definition of fetal membranes?
Structures derived from the fertilized ovum and not share information of embryo.
What are examples of fetal membranes?
1) Amnion.
2) Yolk sac.
3) Allantois.
4) Chorion.
5) Placenta.
6) Connecting stalk and umbilical cord.
What is the definition of the amnion?
a sac filled with fluid that surrounds the embryo and fetus.
What is the time of appearance of the amnion?
7th or 8th day after fertilization.
What is the definition of amniotic fluid?
fluid fills the amniotic cavity.
What is the function of amniotic fluid?
1) Allows fetal movements.
2) Allows symmetrical growth of the fetus.
3) Prevent adhesion between different parts of the fetus.
4) Control the body temperature of the fetus.
5) Barrier against infection.
6) Maintain fluid and electrolytes balance.
7) Protection against trauma and external shock.
8) During birth:
๏ฒ Dilatation of the cervix due to the bulge of the bag of water that precedes the head of the fetus in the cervical canal.
๏ฒ Fluid passes through the vagina when the bag rupture and acts as an anti-septic against infection.
What is the source of amniotic fluid?
โ Amnioblast cells. โ fetal kidneyโ Placenta.
What is the circulation of amniotic fluid?
โ Fluid accumulates in the amniotic cavity.
โ Fetus swallows fluid and some pass to lungs and absorbed by respiratory system of the fetus and digestive tracts (fetus drink 400c.c at 5th month).
What is the fate of amniotic fluid?
โ Fluid passes to fetal blood and waste products cross the placental membrane and enter maternal blood in intervillous space.
โ Excess water is excreted by the fetal kidney through the urinary tract back to the amniotic sac.
What is the composition of the amniotic fluid?
โ 99% water.
โ 1% desquamated (peeled off) epithelial cells, organic constituents.
โ Fetal excreta
Compare between oligo and polyhydramnios Acc to
Def.
Cause
Character
๏ The volume of amniotic fluid is less than 1/2 liter.
๏ Placental insufficiency ๏ Renal agenesis (absence
of one kidney)
๏ Fetal anomalies ๏ Fetal adhesions.
๏ The volume of amniotic fluid is more than 2 liters.
๏ Maternal diabetes. ๏ Fetal anomalies
๏ฒ esophageal atresia (obstruction of the esophagus).
๏ Fetal distress.
๏ Maternal distress.
๏ A true knot of umbilical due to: excessive fetal movements.
๏ Premature labor.
What is the definition of a yolk sac?
a cavity in relation to the ventral surface of the embryo.
What is the time of appearance of the yolk sac?
It begins to appear at 2nd week after fertilization โafter amniotic cavityโ
What is the fate of the yolk sac?
โ Gut formation
โ Vitellointestinal duct (obliterate but if still present will form Meckelโs diverticulum)
โ allantois
What are the functions of the yolk sac?
โ Transfer nutrients to the embryo (in the 2nd and 3rd weeks) before the function of the placenta.
โ (Haemo-poetic function) Development of blood cells and blood vessels first occurs in the extraembryonic mesoderm covering the wall of the yolk sac.
What is the definition of the chorion?
It is the wall of the chorionic sac (gestational sac).
What are the layers of the chorion?
โ Syncytiotrophoblast: outer layer.
โ Cytotrophoblast: middle layer.
โ Extraembryonic mesoderm: inner layer.
For how long do chorionic villi cover the chorionic sac?
Chorionic villi cover the chorionic sac until the beginning of the 8th week. (2nd month)
What happens as the chorionic sac grows?
As chorionic sac grows:
๏ฒ The villi associated with decidua capsularis are compressed.
๏ฒ These villi degenerates produce avascular bare area (Chorion leave).
๏ฒ Villi associated with decidua basalis increase in number, branch, and enlarge (Chorion frondosum).
What are chorionic villi? And what are they separated with?
They are projections from the chorion to increase the surface area of exchange between the fetus and the mother, They are separated by intervillous spaces containing maternal blood.
What is the definition of allantois?
Diverticulum from the caudal wall of the yolk sac into the connecting stalk.
What does the allantois divide into after folding?
- Extraembryonic part
โ Degenerates.
- Intraembryonic part
โ forms the urachus which forms:
๏ฒ The apex of the urinary bladder.
๏ฒ Median umbilical ligament: is the obliterated distal part.
From what is the umbilical cord formed?
by the elongation of the connecting stalk.
What is the length of the umbilical cord?
at birth, it is about 50 cm long (the same length as the fetus).
What are the ends of the umbilical cord?
It has 2 ends:
โ the fetal end attached to the umbilicus
โ placental end to the placenta.
What is the structure of the umbilical cord?
1) Amniotic sheath.
2) Extra embryonic mesoderm of connecting stalk become loose and gelatinous (Whartonโs jelly) and surrounded by the amnion.
3) Umbilical vessels:
๏ฒ Two umbilical arteries: carry non-oxygenated blood.
๏ฒ Left umbilical vein: carry oxygenated blood.
4) Contains loops of the small intestine (physiological umbilical hernia):
๏ฒ Exomphalos (omphalocele) results from non-reduction of the physiological umbilical hernia.
What are the changes that happen to the umbilical cord after birth?
โ Two umbilical arteries become occluded to form a medial umbilical ligament.
โ The left umbilical vein becomes occluded to form ligamentum teres of the liver.
โ The distal part of the allantois is obliterated to form a median umbilical ligament.
What are the anomalies of the umbilical cord?
- Length:
โ Long umbilical cord: may coil around the neck of the fetus (strangulation).
โ Short umbilical cord: may cause early (premature) separation of the placenta.
- Number:
Double
- Attachment:
Abnormal attachment to the placenta.
- Knots:
โ False: length of blood vessels more than umbilical cord
โ True:
โข head passes through a loop of cord, dangerous
โข true knots cause fetal death.
What are the types of chorionic villi according to structure?
โข 1) Primary chorionic villi, formed of:
Outer syncytiotrophoblast.
Inner cytotrophoblast.
โข 2) Secondary chorionic villi formed of:
Outer syncytiotrophoblast.
Inner cytotrophoblast.
extraembryonic mesoderm.
โข 3-Tertiary chorionic villi, formed of:
Outer syncytiotrophoblast
extraembryonic mesoderm.
inner cytotrophoblast.
A branch from umbilical vessels
What is the definition of the placenta?
the primary site of nutrient and gas exchange between mother and fetus.
What is the structure of the placenta?
โ Fetal part: develops from chorion frandosum.
โ Maternal part: derived from the endometrium (decidua basalis and maternal blood in intervillous space).
What are the surfaces of the placenta like?
โ Fetal surface of the placenta:
โข Smooth-shiny and covered by amnion.
โข Umbilical cord attached near its center.
โ The maternal surface of the placenta:
โข Shows cotyledons with Cobblestone appearance
produced by bulging villi.
What is the gross appearance of the placenta?
โ Shape: discoid.
โ Diameter: 15-20cm.
โ Thickness: 2-3cm.
โ Wight: 500-600gm (about 1\6 weight of fetus).
What structures could be seen by the microscope in the placenta?
1) Intervillous space
2) Placenta barrier or membrane
What are intervillous spaces?
โ Large blood-filled space results from coalescence and enlargement of lacunar networks.
โ Contain maternal blood derived from lacuna developed in syncytiotrophoblast during 2nd week of development.
What is the definition of the Placenta barrier or membrane?
the membrane separating maternal from fetal blood.
What is the structure of the placenta barrier or membrane?
Until 20 weeks
โ 4 layers:
1) Syncytiotrophoblast.
2) Cytotrophoblast.
3) Extra embryonic mesoderm.
4) Endothelium of fetal capillaries.
After 20 weeks
โ cytotrophoblast is lost so the barrier becomes 3 layers: 1) Syncytiotrophoblast.
2) Extra embryonic mesoderm
3) Endothelium of fetal capillaries.
Late in pregnancy:
โ extraembryonic mesoderm is lost, the barrier becomes formed of 2 layers:
1) Syncytiotrophoblast.
2) Enodothelium of fetal capillaries
What is the function of the placenta?
โREEM PNโ
1) Respiratory function: by simple diffusion
2) Nutritive function: by simple and selective diffusion
3) Excretory function: by simple and selective diffusion
4) Protective function
5) Metabolism
6) Endocrine function
What is the protective function of the placenta?
๏ฒ Transfer maternal antibodies as for diphtheria, smallpox, and measles.
๏ฒ Barrier against transmission of some infection from mother to fetus but some viruses as German measles and syphilis pass through placental membrane and
cause fetal infection.
What is the endocrine function of the placenta?
๏ฒ Chorionic gonadotrophin hormones (early in pregnancy)
โข Trophoblast produces chorionic gonadotropin hormone which maintains corpus luteum and stimulates corpus luteum to secret progesterone.
๏ฒ Progesterone (later in pregnancy > 4th month)
โข Trophoblast produces progesterone from the 4th month which is essential for the maintenance of pregnancy.
๏ฒ Estrogen (near labor)
โข Produced by syncytiotrophoblast which increases the sensitivity of the myometrium to oxytocin which has a role in delivery.
What are the anomalies of the placenta?
- Position:
โ Placenta previa.
โ Placenta increta & percreta: chorionic villi penetrate myometrium. - attachment of umbilical cord to the placenta.
- shape:
โ Zonary placenta: empty in middle.
โ Bipartite placenta (bilobed): with one umbilical cord.
โ Tripartite placenta: with one umbilical cord attached to it.
โ Irregular placenta.
โ Membranous placenta: thin and membranous. - number:
โ Placenta succentoriata: There is one or more small accessory placenta in addition to the main placenta which are retained in the uterus after delivery and cause postpartum hemorrhage
What is the maternal circulation in the placenta?
Maternal blood enters the intervillous spaces from the spiral arteries of the decidua and after gas exchange leaves the spaces via numerous, decidual Veins to the uterine vein.
What is the fetal circulation in the placenta?
โ The deoxygenated blood reaches the chorionic villi by two umbilical arteries.
โ Exchange of gasses, nutrients, and waste products occurs through the placental
membrane and the oxygenated blood returns to the fetus by the umbilical vein.
What is the definition of multiple pregnancies?
Delivery of more than one fetus:
โข Two fetuses (twins).
โข Three fetuses (triplets).
โข Four fetuses (quadruplets).
โข Five fetuses (quintuplets).
What is the incidence of multiple pregnancies?
โ Twins: once every 90 pregnancies.
โ Triplets: once every 8100 pregnancies.
โ Quadruplets and others are rare
What are the causes of multiple pregnancies?
โ Hereditary.
โ Medical causes: due to administration of exogenous gonadotrophin to stimulate ovulation in women with ovulatory failure and also In vitro fertilization.
Where are multiple pregnancies more common?
โข Race: most common in Negroes
โข Age: Increased maternal age
โข Parity: more common in multipara
โข Heredity: family history of multifetal gestation
โข Nutritional status: well-nourished women
โข The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium.
โข Placenta grows throughout pregnancy.
โข Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy (approximately 12โ 13 weeks).
โฆ
What are the types of multiple pregnancies?
โ Monozygotic twins. โ Dizygotic twins.
What is the definition of monozygotic (identical - true - uniovular) twins?
fertilization of one oocyte (develops from one zygote).
What is the cause of monozygotic twins?
results from splitting of the zygote at various stages of development
what are the incidences of monozygotic twins?
30% of twins
What are the characters of monozygotic twins?
โ Of the same sex, genetically identical, similar in physical character and the difference occur only by the environment.
โ Of the same fingerprint.
what are the various stages of development at which the separation may take place?
- Separation in two cell stages (up to 3 days)
- Separation in inner mass stage (between 4th & 7th day)
- Separation in the bilaminar disc (between 8th & 12th day)
What happens if separation takes place in two cell stages (up to 3 days)?
โ Two fetuses have strong resemblance as regard blood group, fingerprint, sex, the color of the eye, and hair.
โ Have 2 amnion, 2 placentas and 2 chorions.
What happens if separation takes place in the inner mass stage (between the 4th & 7th day)?
โ Results from the division of inner cell mass into 2 embryos
โ Have 2 amnion, 1 placenta, and 1 chorion
What happens if separation takes place in the bilaminar disc (between the 8th & 12th day)?
โ Cells of bilaminar disc divide into equal groups to give rise to equal embryos or unequal groups to give one large fetus and the other is small.
โ Have 1 amnion, 1 placenta, and 1 chorion.
What are the causes of conjoined monozygotic twins? (Monsters or Siamese)
the embryonic disc does not divide completely.
What are the characters of conjoined monozygotic twins?
United in Ventral:
1) Omphalopagus
2) Thoracopagus (in thoracic)
3) Cephalopagus (in the head)
4) Caudal/ ischiopagus
Lateral: Parapagus
Dorsal:
1)Craniopagus
2)Pygopagus
What is the cause of dizygotic (in identical, biovular, and fraternal) twins?
fertilization of two oocytes by different sperms to form zygotes
What is the incidence of dizygotic twins?
70% of twins.
What are the characters of dizygotic twins?
๏ฒ Same sex, or different.
๏ฒ Vary in physical appearance.
๏ฒ Each has 1 amnion, 1 chorion, 1 placenta but the chorion and placenta may be fused
