Extra Embryonic Membranes of Mammals and Avians Flashcards
Soon after successful fertilization, the zygote undergoes cleavage or segmentation division (type of cleavage depends on the amount of yolk material) and moves along the uterine tube and enters the uterus. Movement or transport of the embryo towards the uterus is a combination of ciliary (swaying movement of the epithelial cilia of the of the endometrium) and muscular contraction of the myometrium.
Implantation/Nidation
Implantation/Nidation occurs in three stages in domestic animals: (3)
- Apposition of the blastocyst or foetal membranes to the uterine epithelium
- Adhesion
- Firm attachment or invasion of the endometrium
*Forms of Implantation
Blastocyst implants itself interstitially by passing through the uterine epithelium and becoming completely cut off from the uterine lumen. This is true in primates, guinea pigs and human.
Interstitial/Invasive Implantation
*Forms of Implantation
-blastocyst remains small and becomes lodged in the fold of the uterine lumen, where it implants itself. Example of this form of implantation are rodents.
Eccentric Implantation
*Forms of Implantation
Blastocyst elongates and enlarges until it fills a good part of the uterine cavity. This form of placentation occurs in ungulates, carnivores, swine,sheep, cattle and horse.
Centric/Superficial Implantation
*Forms of Implantation
-Blastocyst implants in the endometrium on the same side as the attachment of the mesometrium.
MesometriaL Implantation
*Forms of Implantation
-implantation occurs at a site opposite to the attachment of the mesometrium.
Anti-mesometrial Implantation
OTHER Forms of Implantation (3)
Seasonal or Obligative
Facultative or lactational
Ectopic pregnancy
Sites of abnormal implantation (3)
- Ovary
- Uterine tube
- Peritoneal cavity
*OTHER Forms of Implantation
-Implantation occurs when the probability that offsprings are born at a time of year favorable for survival .
-Mink, ferrets, roe deer, bears, badgers and seals
Seasonal or Obligative
*OTHER Forms of Implantation
-The dam ensures that it does not have to support two litters contemporaneously
-Rodents and insectivores
Facultative or lactational
*OTHER Forms of Implantation
Implantation and subsequent embryonic development in an extra-uterine location
Ectopic pregnancy
*Anong animal yarn?
When single oocyte is fertilized, the blastocyst attaches to the middle or upper third of the uterine horn adjacent to the ovulating ovary.
Cattle
*Anong animal yarn?
Whe two blastocysts are derived from one ovary, one blastocyst usually migrates to the contralateral (opposite) horn where it becomes implanted.
Sheep
*Anong animal yarn?
Blastocyst implants in either the left or right horn close to the body of the uterus.
Horse
*Anong animal yarn?
Blastocysts are evenly spaced within the uterine horns.
Polytocous (litter bearing) animals
Mechanism underlying the equal spacing of embryo is unclear although ________ produced by the developing blastocyst is considered to have an important role in embryo spacing.
estrogen
After nidation/ implantation of the embryo to the endometrium, ___ start to form.
extra embryonic membranes
tissues derived from the developing embryo that enclose and contribute to the support of the developing embryo.
Extra embryonic membranes
four EEM;
yolk sac, allantois, amnion, and chorion.
The amnion and chorion are derived from the
________ (fused mesoderm and ectoderm).
somatopleure
The allantois and yolk sac are from the
__________ (fused mesoderm and endoderm).
splanchnopleure
is small, membranous structure in egg with scant yolk material like mammals but prominent in avian species with huge amount of yolk material.
Yolk sac
Primitive hematopoiesis takes place in the ____ before the ____ and ____ eventually take over.
Yolk sac
liver
bone marrow
The remnant after birth is known as
Meckel’s diverticulum.
In avian the perimeter of the yolk sac is marked by a blood vessel called
sinus terminalis or marginal vein
is the outermost membrane surrounding the embryo in mammals, birds and reptiles (amniotes).
CHORION
Chorion develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida (in mammals), known as the ________ in other animals.
vitelline membrane
chorion produces ______, which serve to cushion and protect the embryo.
chorionic fluid
Chorion is also involved in ___ and _____ due to its vascularity.
gas and nutrient exchange
Chorion is the fetal part of the placenta the maternal component of the placenta is known as the
decidua basalis
is another membranous sac that intimately encloses the embryo when first formed. It is which serves to provide a protective environment for the developing embryo or fetus.
AMNION
In avians, chorion and amnion are paired
_________ that begin to elevate towards the head region and then progresses caudally.
chorioamniotic folds
*Amnion
The site where the folds fuse forms a scar-like thickening known as the __________ which remains throughout development in reptiles and birds.
chorioamniotic raphe
is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote’s conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.
ALLANTOIS
*Ano shape ng allantwa
in cattle, sheep and pigs
anchor shaped
*Ano shape ng allantwa
in dog, cat and horses
tube-shaped
is the connecting stalk between the fetus and the placenta.
UMBILICAL CORD
The formation, type and structure, or arrangement of the placenta is called
Placentation
2 BASIC TYPES OF PLACENTA
Choriovitelline and Chorioallantoic.
is also the yolk sac placenta, fused vascular choriovitelline membranes become attached to the endometrium
choriovitelline placenta
becomes attached to the endometrium
chorioallantoic placenta
CLASSIFICATION OF CHORIOALLANTOIC PLACENTA
- Based on gross distribution of the chorionic villi
- Based on the degree of contact between fetal and uterine mucosa
- Based on the number of tissue layers interposed between the fetal and maternal bloodstream
BASED ON GROSS DISTRIBUTION OF THE CHORIONIC VILLI (4)
- Diffuse
- Cotyledonary
- Zonary
- Discoidal
- Characterized by uniform distribution of villi on the outer surface of the chorion
- Occurs in horses and pigs
DIFFUSE
- Equidae
- Principal source of the equine chorionic gonadotrophin (formerly known as the pregnant mare serum gonadotrophin).
ENDOMETRIAL CUPS
- Chorionic villi are restricted to cotyledons
- Occurs in ruminants
- 90-100 in sheep, 70-120 in cattle
COTYLEDONARY
- Chorionic villi are confined to a girdle-like structure around the middle of the chorionic sac
- Occurs in carnivores
ZONARY
- Chorionic villi are restricted to disc-shaped areas on the chorionic sac
- Occurs in humans, monkeys and rodents
Discoidal
*BASED ON THE DEGREE OF CONTACT BETWEEN FETAL AND UTERINE
- Apposed, non-deciduate
Conjoined, deciduate
MUCOSA
*BASED ON THE DEGREE OF CONTACT BETWEEN FETAL AND UTERINE
- Loose apposition
- Separation is easily achieved at parturition without damage to maternal tissue.
- Horses, ruminants and pigs
APPOSED, NON-DECIDUATE
*BASED ON THE DEGREE OF CONTACT BETWEEN FETAL AND UTERINE
- Intimate connection is formed between maternal and embryonic tissue.
- Some maternal tissue is lost with the fetal tissue at birth.
- Humans, dogs, cats and rodents
CONJOINED, DECIDUATE
