is umblical cord yolk sac

8/3/2019 is Umblical Cord Yolk Sac

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Yolk Sac


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Origin:Primary yolk sac

- Starts as vacuoles in thehypoblastic cells of theinner cell mass.

- These vacuoles coaleasetogether forming a singlecavity called primary yolksac. Its roof and side wall isformed by hypoblasts(endoderm).

Yolk Sac


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Secondary yolk sac:- Primary yolk sac is reduced in size to be transformed to theSecondary yolk sac


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After folding:The secondary yolk sac isdivided into 3 parts:

- Intraembryonic yolk sac.Part of the yolk sac will betaken inside the embryo(Foregut is made by headfold, hind gut is made by

tail fold and midgut ismade mainly by lateralfold).- Extra-embryonic yolk sac(part of the yolk sacoutside the embryo).- Vitellointestinal duct oryolk stalk connecting theintra & extraembryonic

parts of the yolk sac.


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Function & fate:1. It gives the primordial germ cells (future ova in female & future spermin male)2. The endoderm will give the mucous membrane which lines the gut &respiratory tract.

3. The splanchnopleuric primary mesoderm that surrounds the yolk sacwill give the vitelline arteries (future superior mesenteric artery) & vitellinevein (future liver sinusoids- portal & hepatic veins).


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Abnormalities1. Faecal umbilical fistula: due to persistence of the yolk stalk, so the

umbilicus will charge faces.2. Vitelline sinus: one end of the yolk stalk is opened & the other end isclosed.3. Vitelline cyst: the 2 ends of the yolk stalk are closed but still a part ofthe yolk stalk is opened between the 2 ends forming a cyst.

4. Fibrous band: obliteration of the yolk stalk occurs but it remains as aFibrous band. Intestinal obstruction may occur as a complication.


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5.Meckel' diverticulum.- It occurs due to patent intestinal end of the vitello-intestinal

duct (yolk stalk).- The rest of the duct is obliterated forming a fibrous band.

- Meckel's diverticulum is a fingerlike pouch about 3-6 cm (2inches) long that arises from the antimesentric border of the

ileum,- It is 2 feet from the iliocecal junction .

- It occurs in 2-4% of people and is 3-5 times more prevalent inmales than females.

- Sometimes it becomes inflamed and causes symptoms thatmimic appendicitis.

- It may contain gastric mucosa leads to ulcer in thisdiverticulum.


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Development& structure:- It develops as a blinddiverticulum from thecaudal part of the yolk sac(endodermal origin).- It is surrounded by

splanchnopleuric primarymesoderm. Later it isembedded in the bodystalk

Function:- The mesodermsurrounds the allantiosgive umbilical bloodvessels

Allantois


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Fate:1. The extra-

embryonic part lies

inside the umbilical

cord.

2. The intra-

embryonic partobliterates forming

the urachus in the

fetus. Later on the

urachus transformsinto ligament called

the median

umbilical ligament.


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Allantois and yolk sac

3 wks 9 wks

3 month Adult


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Abnormalities:

1. Urachal fistula:(persistence of the Allantois). Inthis defect there is a connection between the

urinary bladder & the umbilicus, so the urine will

charge from the umbilicus.2. Urachal sinus: one end of the allantois isopened & the other end is closed

3. Urachal cyst: the 2 ends of the allantois are

closed but still a part of the allantois is openedbetween the 2 ends forming a cyst.


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Umbilical cord


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Development of Umbilical cord

Early:By folding the primitive

cord is formed. It consists of:

1. Yolk stalk (vitello-intestinalduct) connecting the mid gutand the extra embryonic yolk

sac with the umbilical cord.2. Vitelline blood vessels which

are surrounded bysplanchnopleuric primarymesoderm.

3. Extra-embryonic coelomcontaining loop of herniatedmid gut.

4.Allantois (small diverticulumattached to the hind gut).


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5. Two umbilical arteries& single umbilical

vein. These vesselsoriginated frommesoderm around the

allantios(connecting stalk).

- All of these contentsare surrounded byamniotic membrane.


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Structures forming the primitive

umbilical cord (Summary)

1. Yolk stalk and the

vitelline bloodvessels.

2. Ectoderm of the

amnion.3. Body stalk.

4. Allantois.


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5. Part of extraembryonic coelom. The small intestine (midgut loop) normally

herniates in extraembryonic coelom till its disappearance at the 10th week where

the intestine is reduced back into the peritoneal cavity.

6. Umbilical blood vessels.


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Structures forming the definitive umbilical cord:

Two umbilical arteries

One umbilical vein

Mucoid connective tissue

(Whartons jelly) Allantois

Herniating loop of intestine


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Characters of thenormal umbilical cord

at birth:I. Shape:-Macroscopically:it is 50-60-cmlong, 2 cm in diameter, tortuous,has false node (due to the unequal

growth of the 2 umbilical arteries), it isattached to the center of theplacenta.-Microscopically:the definitivecord is surrounded by amniotic

membrane. It has 2 umbilicalarteries & single umbilical vein. Ithas also the allantois. All thesestructures are embedded inWharton jelly (mesoderm of body

stalk).


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III. Function:The two umbilical arteries & single umbilicalvein are responsible for the nutrition of the

embryo. The vein carries oxygen to the embryo,while the arteries carry CO2 & waste product ofthe embryo to the mother.


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Fate of the cord(Postnatal changes in theumbilical cord):1- Allantois is transformed into

the median umbilical ligament.

2- Umbilical arteries forms themedial umbilical ligaments.

3- Umbilical vein formsligamentum teres of the liver.

4- Extra-embryonic ceolomdisappears.

5- Vitalline arteries formssuperior mesenteric artery.

6- Yolk stalk disappears.


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Abnormalities of the umbilical cord:1. In length(long cordleads to strangulation of the

fetus or short cordleads to premature separation ofthe placenta).

2. Abnormality in the attachment of the placenta:a. Marginal attachment:the cord is attached

to the margin of the placenta.b. Eccentric attachment: the cord is attached

away from the center of the placenta.

c. Velamentous attachment: the cord endsbefore reaching the placenta & the umbilical

vessels reach the placenta via the amniotic

membrane.


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Long umbilical cord (Cord around neck leading tofetal strangulation.


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3. Abnormality in thenumber:double cord.4. Single umbilical artery .

5. True node . (in1 % ofpregnancies).6.Exompholos(omphalocoele)Intestine may remain

herniated in the cord, fails to

return to the fetal abdominal

cavity. So,the cord should be

ligated away from theumbilicus .7. Congenital umbilicalhernia(due to weakness of

abd.wall).


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False knot


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Thank You

is umblical cord yolk sac

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