EXTRAEMBRYONIC MEMBRANEand

PLACENTATION

Ronie G. Galia

EMBRYO

A new organism in the earliest stage of development, from the time that the fertilized embryo begins to develop a long axis up to the time that the major structures have began to develop, when it becomes a fetus.

What are Extraembryonic Membranes?

Extraembryonic membranes are membranous structures that appear in parallel with the embryo and play important roles in the embryonic development.

They form from the embryo but do not become part of the individual organism after its birth.

Extraembryonic Membranes

AMNION

The innermost membrane enclosing the developing fetus and with amniotic fluid; characteristics of reptiles, birds and mammals.The amnion is a membranous sac which surrounds and protects the embryo.The primary function of this is the protection of the embryo for its future development into a fetus and eventually an animal.

Yolk Sac

The yolk sac nourishes the developing baby (embryo) until the circulatory system has developed. Yolk is a mixture of proteins and lipoproteins.One of the extraembryonic fetal membranes

that balloons out from fetal midgut

Chorion

The outermost of the fetal membranes, composed of trophoblast lined with mesoderm; it develops villi, becomes vascularized by allantoic vessels, and forms the fetal part of the placenta.the highly vascular outer embryonic membrane that is associated with the allantois in the formation of the placenta

Allantois

A ventral outgrowth of the hindgut of the early embryo, that expands to form a large sac filled with urine-like fluid, that fuses with the chorionic to make up a major part of the placenta.The vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic

higher vertebrates (reptiles, birds and mammals)

PlacentationDuring pregnancy, placentation is the formation and growth of the placenta inside the uterus. It occurs after the implantation of the embryo into the uterine wall and involves the remodeling of blood vessels in order to supply the needed amount of blood.It transfers nutrients from maternal tissue to a growing embryo.Usually occurs in pregnant female mammals, and also occur in other animals, and eggs off poultry animals.

PLACENTA In placental mammals, the placenta forms after the

embryo implants into the wall of the uterus. The developing fetus is connected to it via an umbilical cord. Animal placentas are classified based on the number of tissues separating the maternal from the fetal blood.

An organ characteristic of true mammals during pregnancy, joining the mother and offspring, providing endocrine secretion and selective exchange of soluble blood borne substances through the apposition of uterine and tropoblastic vascularized parts.

PLACENTA

Functional PlacentationEndocrine: Hormones including gonadotropin, estrogen, and

progesterone are produced in large amounts. Excretion: Products of fetal metabolism can cross the placenta

into the maternal circulation, the placenta functioning like a kidney.

Respiration: Oxygen supplied by the mother diffuses across the

placental membrane into the fetal blood. The placenta thus serves as an efficient lung for the fetus.

Nutrition: Proteins, carbohydrates, water, fats, inorganic salts,

and vitamins can all pass in different forms from the maternal to the fetal blood.

Protection: Foreign particulate matter such as bacteria is

unable to cross the barrier unless the placenta itself becomes actively involved in the inflammatory process.Read more

Types of Placentation in Animals Based on their Attachment

ENDOTHELIOCHORIALa. The maternal vessels in the endometrium are

bared to their endothelium and these are in contact with the chorion of the fetal membranes.

b. This occurs in the bitch and queens

EPITHELIOCHORIALa. The uterine epithelium of the uterus and the

chorion are in contact in this placentation, and there is no erosion of the epithelium.

b. Characteristics of cows, sows and mares.

HAEMOCHORIALa. A type of placenta in which all maternal layers are

lost so that fetal tissue is in contact with frank maternal blood.

b. Occurs in insectivores, rodents, rabbits and most primates.

Types of Placenta According to their Morphological Structure

Diffuse Placenta

Almost the entire surface of the allantochorion is involved in formation of the placenta

Example: Pigs, and Horses

Cotyledon Placenta A type of chorioallantoic placenta in which the

villi are grouped into tufts or balls separated by regions of smooth chorion.

Example: Placenta of Ruminants(cattle, buffalo)

Zonary Placenta

The placenta takes the form of a complete or incomplete band of tissue surrounding the fetus. Seen in carnivores like dogs and cats, seals, bears, and elephants.

Other examples of animals with this type of placentation include mustelids (ferrets, skunks), bears, seals and elephants.

Discoidal Placenta

A disk-shaped placenta.A single placenta is formed and is discoid in shape. Example: Human Placenta, Rats, Monkeys

SUMMARY of ANIMAL SPECIES ACCORDING TO THEIR PLACENTAL STRUCTURE

Type of Placenta Common Examples

Diffuse, epitheliochorial Horses and pigs

Cotyledonary, epitheliochorial Ruminants (cattle, sheep, goats, deer)

Zonary, endotheliochorial Carnivores (dog, cat, ferret)

Discoid, hemochorial Humans, apes, monkeys and rodents

Types of Placenta

Non-deciduous Placenta In mammals like pig, cattle, horse and other

ruminants the chorionic villi lie on the crypts of the uterine wall apposing endometrium and do not fuse with it. During the time of parturition separation of foetus and its membranes from the uterine wall, the chorionic villi are simply drawn out from the depressions without any damage to the uterine wall and thus causing no bleeding.

Deciduous Placenta In higher eutherian mammals like dog and man,

the degree of intimacy between the maternal and foetal tissues increases. The allanto-chorionic villi become complex and penetrate deeper into the uterine tissues. The chorionic epithelium appears to lie in the connective tissue or into the maternal blood. During parturition this placenta is cast off with loss of embryonic membranes and the encapsulating maternal tissues causing extensive haemorrhage and thereby bleeding.

References• http://www.vivo.colostate.edu/hbooks/pathphys/reprod/placenta/structure.html• http://www.embryology.ch/anglais/fplacenta/type01.html• http://www.embryology.ch/anglais/fplacenta/popuppl/type/diffus.html• http://www.embryology.ch/anglais/fplacenta/popuppl/type/primate.html• http://www.embryology.ch/anglais/fplacenta/popuppl/type/cotyledonaire.html• http://www.embryology.ch/anglais/fplacenta/popuppl/type/zonaire.html• http://scienceray.com/biology/human-biology/the-importance-and-functions-of-th

e-placenta/• :

http://scienceray.com/biology/human-biology/the-importance-and-functions-of-the-placenta/#ixzz1Qb8G6Z4e

• http://images.search.yahoo.com/search/images;_ylt=A0oGdWozHglOXXwAfmVXNyoA?ei=UTF-8&p=zonary%20placenta&rd=r1&meta=vc%3Dph&fp_ip=ph&fr2=tab-web&fryfp-t-701