SEM_06_Mammalian Extraembryonic Membranes

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Questions and Answers

Which of the following extraembryonic membranes is not necessary in aquatic animals (fish and amphibians) for the development of the embryo?

Amnion

Chorion (correct)

Allantois

Yolk sac

In addition to the yolk sac, which extraembryonic membranes are necessary for the development of the embryo in reptiles and birds?

Chorion and amnion (correct)

Amnion and allantois

Chorion and allantois

Amnion and chorion

What remains the same in mammals as those that arose in reptiles and birds, even though mammals do not produce shelled eggs?

Allantois

Yolk sac

Placenta

Foetal membranes (correct)

Which group of mammals represents the most ancient mammals that continue to lay shell eggs like their reptilian ancestors?

Monotremes Signup and view all the answers

What is the role of the chorion in mammalian development?

To create multiple finger-like folds for increased surface area exchange Signup and view all the answers

Which component plays a primary role in the interaction between the uterus and the blastula for attachment?

Integrins Signup and view all the answers

What is the initial event marking the start of pregnancy in mammals?

Implantation Signup and view all the answers

In which type of implantation does the blastocyst expand before implantation and remain in the center of the uterus?

Central implantation Signup and view all the answers

What characterizes eccentric implantation in mammals?

The blastocyst is small and implants within a uterine crypt on one side of the uterus Signup and view all the answers

What is the process through which the conceptus gains control over corpus luteum function, uterine blood supply, and maternal physiology?

Maternal recognition of pregnancy Signup and view all the answers

How does embryo implantation occur in most mammals?

Apposition and attachment to the endometrium without embedding Signup and view all the answers

What is the role of integrins in embryo implantation?

To mediate the interaction between the uterus and the blastula for attachment Signup and view all the answers

What is a defining feature of interstitial implantation in mammals?

Implantation between uterine glands Signup and view all the answers

What is a key feature of human embryo implantation?

Eroding endometrium to induce decidual reaction for embedding Signup and view all the answers

What is unique about maternal recognition of pregnancy?

It involves conceptus gaining control over corpus luteum function and maternal physiology Signup and view all the answers

What is a distinguishing characteristic of mammals?

Feeding their young with milk Signup and view all the answers

Which group of mammals have a rudimentary connection between the embryo and the mother's uterus?

Marsupials Signup and view all the answers

Where do newborn marsupial embryos develop further after birth?

In a pouch Signup and view all the answers

What is the function of the allantoic placenta in placental mammals?

All of the above Signup and view all the answers

What role do the extraembryonic membranes play in prenatal survival of the mammalian embryo?

Essential for the prenatal survival of the embryo Signup and view all the answers

What do the chorion, amnion, and allantois provide to mammals?

Adaptations to terrestrial life providing protection, interchanging gases and nutrients, and handling excretion Signup and view all the answers

In what type of animals do the extraembryonic membranes form when the egg is incubated?

Birds Signup and view all the answers

What is the name of the trilaminate membrane formed in birds from the expanded yolk sac, amnion, and allantois?

'Allantochorion' Signup and view all the answers

Which group of mammals has a more elaborate and efficient connection between the embryo and the mother's uterus through an allantoic placenta?

Placental mammals Signup and view all the answers

What do placental mammals provide to their embryos through the allantoic placenta?

Nutrition, respiration, excretion, and endocrine function Signup and view all the answers

Which group of mammals includes domestic mammals and humans?

Placental mammals Signup and view all the answers

What contributes to the development of placental circulation in mammals?

The allantoic placenta Signup and view all the answers

In which type of mammals does the blastocyst enter a dormant status named diapause?

Marsupials Signup and view all the answers

What is the adaptive process in mammals that ensures optimal survival conditions to the offspring?

Embryonic diapause Signup and view all the answers

In which type of mammals is facultative diapause regulated through lactation?

Marsupials Signup and view all the answers

Which type of delayed implantation allows mammals to program the birth of their young under favorable environmental conditions?

Mandatory diapause Signup and view all the answers

What are the maternal uterine glands called that provide the embryo with energy and biochemical building blocks before implantation?

Histotrophe Signup and view all the answers

Which process rapidly becomes insufficient as the embryo grows, leading to the development of the placenta?

Histotrophe uptake Signup and view all the answers

Which type of placentas have developed specialized regions called placental areolae for ingestion of uterine secretions and cell debris?

Efficient placentas Signup and view all the answers

In which type of mammals do species with highly efficient placentas have minimal histotrophic uptake throughout most of gestation?

Primates including humans Signup and view all the answers

What is the name for the tissue created by the transformation of uterine stromal and endothelial cells during implantation?

Decidua Signup and view all the answers

What is the outer layer of the invasive trophoblast that forms an irregular invasive tissue called?

Syncytiotrophoblast Signup and view all the answers

In which type of animals does attachment and implantation occur within a few days after the blastocyst reaches the uterus?

Humans Signup and view all the answers

What is the role of the allantois in the development of mammals?

It provides oxygen and removes carbon dioxide from the embryo's blood. Signup and view all the answers

What characteristic distinguishes the placenta in domestic animals?

It is more efficient in facilitating histotrophic uptake during most of gestation. Signup and view all the answers

In which type of mammals do species with highly efficient placentas have minimal histotrophic uptake throughout most of gestation?

Monotremes (egg-laying mammals) Signup and view all the answers

What is the primary role of the amnion in reptiles, birds, and mammals?

It forms a protective fluid-filled sac around the embryo. Signup and view all the answers

What is the primary component in the interaction between the uterus and the blastula for attachment in mammals?

Trophoblast Signup and view all the answers

Which type of implantation involves the blastocyst expanding before implantation and remaining in the center of the uterus, common in domestic animals?

Central implantation Signup and view all the answers

What is the function of the chorion in mammalian development?

Increased surface area exchange Signup and view all the answers

In which type of mammals does the blastocyst implant between the uterine glands, as found in marsupials?

Marsupials Signup and view all the answers

What is the adaptive process in mammals that ensures optimal survival conditions to the offspring?

Maternal recognition of pregnancy Signup and view all the answers

What characterizes eccentric implantation in mammals?

Small blastocyst implants within a uterine crypt on one side of the uterus Signup and view all the answers

What is a key feature of human embryo implantation?

Erodes the endometrium and induces a decidual reaction for embedding of the blastocyst Signup and view all the answers

What are the maternal uterine glands called that provide the embryo with energy and biochemical building blocks before implantation?

Histotroph Signup and view all the answers

What is unique about maternal recognition of pregnancy?

Integration with maternal physiology, corpus luteum function, and uterine blood supply Signup and view all the answers

What contributes to the development of placental circulation in mammals?

Extraembryonic membrane development Signup and view all the answers

In which type of animals does attachment and implantation occur within a few days after the blastocyst reaches the uterus?

Aquatic mammals Signup and view all the answers

What remains the same in mammals as those that arose in reptiles and birds, even though mammals do not produce shelled eggs?

Extraembryonic membrane development process Signup and view all the answers

What is the role of the allantoic placenta in placental mammals?

Facilitating embryonic development and placental circulation Signup and view all the answers

Which extraembryonic membranes are adaptations to terrestrial life in mammals?

Chorion, amnion, and yolk sac Signup and view all the answers

Where do newborn marsupial embryos develop further after birth?

In a pouch Signup and view all the answers

What do the chorion, amnion, and allantois provide to mammals?

Interchanging gases and nutrients Signup and view all the answers

What characterizes eccentric implantation in mammals?

Implantation near the uterine horns Signup and view all the answers

What remains the same in mammals as those that arose in reptiles and birds, even though mammals do not produce shelled eggs?

Chorion, amnion, and allantois development Signup and view all the answers

Which type of delayed implantation allows mammals to program the birth of their young under favorable environmental conditions?

Facultative diapause Signup and view all the answers

What contributes to the development of placental circulation in mammals?

Allantoic placenta Signup and view all the answers

What is a defining feature of interstitial implantation in mammals?

Implantation within endometrial crypts Signup and view all the answers

In which type of animals do the extraembryonic membranes form when the egg is incubated?

Birds Signup and view all the answers

What is a distinguishing characteristic of placental mammals?

Highly efficient placentas Signup and view all the answers

What contributes to the prenatal survival of the mammalian embryo?

Extraembryonic membranes development Signup and view all the answers

What is the process of implantation often called?

Nidation Signup and view all the answers

Which type of implantation allows the blastocyst to expand before implantation and remain in the center of the uterus?

Eccentric implantation Signup and view all the answers

What is the name of the tissue formed by the outer layer of the invasive trophoblast in mammals?

Syncytio-trophoblast Signup and view all the answers

What is the function of the maternal uterine glands before implantation?

Provision of embryotrophe Signup and view all the answers

In which type of mammals does facultative diapause occur?

Marsupials Signup and view all the answers

Which type of mammals presents delayed implantation due to embryonic diapause?

Rodents Signup and view all the answers

What replaces histiotrophe as the embryo grows in mammals?

Haemotrophe Signup and view all the answers

'Haemotrophe' becomes the primary source of nutrients for the embryo in species with a highly efficient placenta. Which group of mammals have minimal histotrophic uptake throughout most of gestation?

Primates including humans Signup and view all the answers

What is a distinguishing characteristic of delayed implantation in some mammalian species?

Facultative diapause Signup and view all the answers

What is the primary function of the placenta in all species?

To promote selective transport of nutrients and waste products between the mother and foetus Signup and view all the answers

What is the degree of trophoblast invasion variable between, leading to varying numbers of layers of the placental barrier in different species?

The placental barrier's selective permeability Signup and view all the answers

What is the role of the close approximation of maternal and foetal vascular systems within the placenta?

To facilitate selective transport of nutrients and waste products Signup and view all the answers

What is important to recognize about the placenta's function?

There is no mixing of foetal and maternal blood within the placenta due to placental tissue interposing between the two circulations Signup and view all the answers

What is the primary function of the placental barrier?

To serve as a protective barrier against infectious agents and drugs Signup and view all the answers

What is the primary role of the allantois in placental mammals?

To fuse with the chorion and form the fetal tissues that develop into the final placenta Signup and view all the answers

Which type of placentas have developed specialized regions for ingestion of uterine secretions and cell debris?

Choriovitelline placentas Signup and view all the answers

What contributes to the development of placental circulation in mammals?

The fusion of allantois with the chorion Signup and view all the answers

Which extraembryonic membrane is an important endocrine organ that produces various hormones?

Chorion Signup and view all the answers

In which type of mammals is there substantial transfer of immunoglobulin G prior to birth?

Primates and rodents Signup and view all the answers

Which component plays a primary role in the interaction between the uterus and the blastula for attachment?

Chorion Signup and view all the answers

What is the name for the tissue formed by the outer layer of the invasive trophoblast in mammals?

Chorion Signup and view all the answers

What is a distinguishing characteristic of mammals with delayed implantation due to embryonic diapause?

Embryo entering a dormant status named diapause Signup and view all the answers

What is unique about maternal recognition of pregnancy?

Control over corpus luteum function, uterine blood supply, and maternal physiology Signup and view all the answers

What is the primary role of the amnion in reptiles, birds, and mammals?

To protect the embryo from mechanical injury and maintain a stable temperature Signup and view all the answers

What is the principal source of equine chorionic gonadotrophin (eCG) in horses?

Endometrial cups Signup and view all the answers

What are the polygonal structures, 1-2 mm in size, found on the chorionic surface of the equine placenta?

Microcotyledons Signup and view all the answers

What is the name for the brownish masses of cellular debris surrounded by mucoproteins and minerals found in the allantoic cavity of horses?

Hippomanes Signup and view all the answers

What do uterine glands in horses empty into, providing copious secretions that are absorbed by inter-microcotyledonary areas of the chorion?

Areolas Signup and view all the answers

What is the name for the epithelial elevations on the amniotic wall that can be present near the umbilical cord in horses?

Amniotic plaques Signup and view all the answers

In horses, what is the average time needed for placental expulsion after birth?

One hour Signup and view all the answers

What is one of the most common peripartum problems in mares, with an incidence in the range of 2% to 10%?

Placental expulsion delay Signup and view all the answers

In horses, what is the name for the mass of cellular debris likely originating from the foetal hindgut found floating or attached to the wall of the allantoic cavity?

Hippomanes Signup and view all the answers

What marks the start of pregnancy in horses?

Endometrial cups formation Signup and view all the answers

Which structure quickly disappears in horses after birth, allowing foals to be usually born surrounded by it and requiring their own effort to break it?

Amniotic plaques Signup and view all the answers

What ensures there is no significant loss of maternal tissue after birth in horses' placentation?

Retention of foetal membranes Signup and view all the answers

Which type of placentation is characterized by a complete or incomplete band of tissue surrounding the foetus?

Zonary placenta Signup and view all the answers

In which type of placentation are chorionic villi restricted to multiple areas of attachment, forming cotyledons and caruncles in ruminants?

Cotyledonary or multiple placentation Signup and view all the answers

Which type of placenta is the most invasive, where the trophoblast erodes the endometrium and comes in direct contact with maternal blood?

Haemochorial placenta Signup and view all the answers

Which type of embryo implantation involves the blastocyst expanding before implantation and remaining in the center of the uterus, common in domestic animals?

Central implantation Signup and view all the answers

What term is used for the tissue formed by the transformation of uterine stromal and endothelial cells during implantation?

Decidua Signup and view all the answers

In which placentation type is almost the entire surface of the allantochorion involved in the formation of the placenta, found in horses and pigs?

Diffuse placenta Signup and view all the answers

Which type of placentation involves chorionic villi eroding and fusing with the uterine mucosa, forming decidua?

Deciduate placenta Signup and view all the answers

What type of placentation is characterized by a single area of placenta being formed and being discoid in shape, found in primates and rodents?

Discoid placenta Signup and view all the answers

Which type of placentation involves chorionic villi attaching to the maternal uterine epithelium, with no maternal invasion?

Epitheliochorial placenta Signup and view all the answers

What is an example of a classification based on placental shape?

Discoid placenta Signup and view all the answers

What is a modification of epitheliochorial placenta, where trophoblast cells migrate and fuse with the maternal epithelium?

Epitheliochorial pl Signup and view all the answers

What is the primary function of the placenta in all species?

To promote selective transport of nutrients and waste products between the mother and foetus Signup and view all the answers

What constitutes the placental barrier?

Maternal tissue interposing between the foetal and maternal circulation Signup and view all the answers

What is the name for the tissue created by the transformation of uterine stromal and endothelial cells during implantation?

Decidua Signup and view all the answers

What role do the extraembryonic membranes play in prenatal survival of the mammalian embryo?

Act as a source of nutrients for the embryo Signup and view all the answers

What is the average time needed for placental expulsion after birth in horses?

48 hours Signup and view all the answers

Which structure provides temporary hormone production and secretes eCG during early pregnancy in horses?

Endometrial cups Signup and view all the answers

What marks the start of pregnancy in horses?

Implantation Signup and view all the answers

What is the name for the mass of cellular debris likely originating from the foetal hindgut found floating or attached to the wall of the allantoic cavity in horses?

Meconium cast Signup and view all the answers

What contributes to the development of placental circulation in horses?

Chorioallantoic placenta Signup and view all the answers

What ensures there is no significant loss of maternal tissue after birth in horses' placentation?

Umbilical cord segments Signup and view all the answers

Which process rapidly becomes insufficient as the embryo grows, leading to the development of the placenta in horses?

Histotrophic uptake Signup and view all the answers

What is unique about maternal recognition of pregnancy in horses?

Maternal-embryonic communication via integrins Signup and view all the answers

In horses, what is the primary role of the amnion?

"Protection and support for the developing embryo" Signup and view all the answers

Which type of placentation is characterized by the chorionic villi being restricted to multiple areas of attachment, forming cotyledons and caruncles in ruminants?

Cotyledonary placentation Signup and view all the answers

In which type of mammals is the entire surface of the allantochorion involved in the formation of the placenta?

Diffuse placenta Signup and view all the answers

Which type of placentation forms a complete or incomplete band of tissue surrounding the foetus, seen in carnivores and some other animals?

Zonary placenta Signup and view all the answers

What is the most invasive placenta, where the trophoblast erodes the endometrium and comes in direct contact with maternal blood?

Haemochorial placenta Signup and view all the answers

Which type of placentation is found in horses and pigs, involving almost the entire surface of the allantochorion in the formation of the placenta?

Diffuse placenta Signup and view all the answers

Which type of placentation is characterized by a single area of placenta being formed and being discoid in shape, found in primates and rodents?

Discoid placenta Signup and view all the answers

Which type of placentation is characterized by chorionic villi eroding and fusing with the uterine mucosa, forming decidua?

Deciduate placenta Signup and view all the answers

What type of placentation involves the chorion villi attaching to the maternal uterine epithelium, with no maternal invasion?

Epitheliochorial placenta Signup and view all the answers

What is the principal source of equine chorionic gonadotrophin (eCG) in horses?

Endometrial cups Signup and view all the answers

What are the brownish masses of cellular debris surrounded by mucoproteins and minerals found in the allantoic cavity of horses?

Allantoic calculi Signup and view all the answers

What is the name for the epithelial elevations on the amniotic wall that can be present near the umbilical cord in horses?

Amniotic plaques Signup and view all the answers

What do uterine glands, present in the maternal stroma between adjacent microcotyledons, empty their secretions into?

Crypts Signup and view all the answers

Where do newborn foals typically develop further after birth?

Surrounded by the amnion Signup and view all the answers

What is a common peripartum problem in mares, with an incidence in the range of 2% to 10%?

Retained placenta Signup and view all the answers

What is the classification of equine placenta based on its structure?

Diffuse and epitheliochorial Signup and view all the answers

What do the areolas in horses' placenta oppose to, receiving secretions from uterine glands?

Uterine glands Signup and view all the answers

What is the role of the amniotic raphe in horses' placentation?

To attach the amnion to the chorion Signup and view all the answers

What happens to the amnion after birth in horses?

It becomes free and completely detached from the chorion. Signup and view all the answers

What marks the start of pregnancy in horses?

Development of endometrial cups Signup and view all the answers

What is the primary method of energy transfer from the placenta to the fetus?

Active transport of glucose Signup and view all the answers

Which gas readily diffuses from maternal to fetal blood due to a higher partial pressure in maternal blood?

Oxygen Signup and view all the answers

Which hormone is produced by the placenta and is an important endocrine hormone in mammals?

Estrogen Signup and view all the answers

What is the primary function of the placenta in protecting the fetus?

Serving as a barrier against infectious agents and drugs Signup and view all the answers

In which type of placentas do the allantois fuse with the chorion to form the final placenta in eutherian mammals?

Chorioallantoic placentas Signup and view all the answers

What is actively transported to the fetus with higher concentrations in fetal blood?

Glucose Signup and view all the answers

What helps remove waste products such as urea, creatinine, uric acid, and bilirubin from fetal blood?

Placental exchange processes Signup and view all the answers

What is an important characteristic of gas transport across the placental barrier?

Passive diffusion of oxygen into fetal blood Signup and view all the answers

What is a characteristic of the transfer of immunoglobulins across the placenta in rodents and primates?

Substantial transfer of immunoglobulin G prior to birth Signup and view all the answers

What is the primary role of the amnion in reptiles, birds, and mammals?

Cushioning and protecting the fetus Signup and view all the answers

What is unique about the transfer of immunoglobulins across the placenta in domestic animals?

Transfer is minimal throughout gestation Signup and view all the answers

What is the primary reason why twinning is considered undesirable in cows?

Increased risk of freemartinism Signup and view all the answers

What is the most common outcome when female calves are born co-twin to a male in cattle?

Development of freemartinism Signup and view all the answers

In bovine twins, what allows hormones from the male to affect female development and leads to the mixing of haemopoietic precursor cells?

Fusion of placental blood vessels Signup and view all the answers

Which species is freemartin syndrome rarely present in, despite frequent occurrences of double or triple births?

Sheep and goats Signup and view all the answers

What is the primary type of placenta found in pigs?

Diffuse Signup and view all the answers

What is the primary type of placenta found in dogs and cats?

Zonary Signup and view all the answers

What is the characteristic of the uterine mucosa in pigs that maximizes placental exchange area?

Transversal Folds Signup and view all the answers

What characterizes the initial structure of the canine placenta?

Straight Folds Signup and view all the answers

What characterizes the allantoic vessels in the pig's placenta?

Result in avascular and necrotic parts Signup and view all the answers

What is the characteristic of the amnion in carnivores?

Separates rapidly from the chorion Signup and view all the answers

What characterizes the umbilical cord in carnivores?

Short with few twists Signup and view all the answers

Which term describes the type of placentation in horses and pigs, involving almost the entire surface of the allantochorion?

Diffuse Signup and view all the answers

What marks a distinguishing feature of the equine placenta?

Distinctly green margina haematoma Signup and view all the answers

What characterizes the transfer of immunoglobulins across the placenta in rodents and primates?

Efficient and direct transfer Signup and view all the answers

What contributes to prenatal survival of mammalian embryos via the placenta?

Minimal histotrophic uptake Signup and view all the answers

What is a defining feature of mammals with delayed implantation due to embryonic diapause?

Programmable birth under favorable environmental conditions Signup and view all the answers

In ruminants, what is the structure referred to as synepitheliochorial due to modified uterine epithelium?

The placenta Signup and view all the answers

What is the term for the small placental areas in the cotyledonary placenta of ruminants?

Placentomes Signup and view all the answers

What is the name of the oval or round thickenings in the uterine mucosa in ruminants?

Caruncles Signup and view all the answers

What characterizes implantation in pigs, involving a lengthy pre-attachment period and remodeling of the embryonic vesicle?

Filamentous sac formation Signup and view all the answers

How many piglets are typically found in a litter size of pigs?

6-12 piglets Signup and view all the answers

What characterizes the delivery of the placenta in ruminants within 12 hours of birth?

Non-deciduate placentation Signup and view all the answers

In pigs, which process occurs to form a filamentous sac during implantation?

Decidualization Signup and view all the answers

What characterizes implantation in pigs, involving a lengthy pre-attachment period and remodeling of the embryonic vesicle?

Filamentous sac formation. Signup and view all the answers

What is the term for the abnormal development of the reproductive system in female calves born co-twin to a male in cattle?

Freemartinism Signup and view all the answers

What is the most common form of intersexuality in cattle?

Freemartin syndrome Signup and view all the answers

In which species is freemartin syndrome rarely present, even in cases of double or triple births?

Both sheep and goats Signup and view all the answers

What is the main reason why twinning is considered undesirable in cattle?

High risk of perinatal mortality Signup and view all the answers

What type of placenta is characteristic of ruminants?

Epitheliochorial Signup and view all the answers

What structures form the placentome in ruminants?

Cotyledon and caruncle Signup and view all the answers

What is the term for the delivery of the placenta within 12 hours of birth in ruminants?

Non-deciduate placentation Signup and view all the answers

What characterizes implantation in pigs?

Remodeling of the embryonic vesicle Signup and view all the answers

What is the litter size range for pigs?

6-12 piglets Signup and view all the answers

What is the main source of nutrients for the embryo in species with a highly efficient placenta?

Haemotrophe Signup and view all the answers

What type of placentation is found in horses and pigs?

Zonary placentation Signup and view all the answers

In which group of mammals does facultative diapause occur?

Carnivores Signup and view all the answers

What is the term for the small placental areas in the cotyledonary placenta of ruminants?

Placentomes Signup and view all the answers

Study Notes

Mammals are a group of animals with backbones, hair or fur, warm-blooded, and feed their young with milk.
Mammals can be divided into three groups based on how their offspring develop: monotremes, marsupials, and placental mammals.
Marsupials have a rudimentary connection between the embryo and the mother's uterus through a yolk placenta.
Newborn marsupial embryos are born very immature and develop further in a pouch, where they find milk to complete their development.
Placental mammals, such as domestic mammals and humans, have a more elaborate and efficient connection between the embryo and the mother's uterus through an allantoic placenta.
The allantoic placenta provides the embryo with nutrition, respiration, excretion, and endocrine function, allowing for complete embryonic development.
Extraembryonic membranes are essential for the prenatal survival of the embryo and develop from the same germ layers as the embryo.
Extraembryonic membranes include the chorion, amnion, yolk sac, and allantois.
In mammals, the allantoic placenta gives rise to the placental circulation.
The chorion, amnion, and allantois are adaptations to terrestrial life, providing protection, interchanging gases and nutrients, and handling excretion.
In birds, the extraembryonic membranes form when the egg is incubated, and the yolk sac, amnion, and allantois expand, attaching to different layers and forming a trilaminate membrane called the allantochorion.
Mammals are a group of animals with backbones, hair or fur, warm-blooded, and feed their young with milk.
Mammals can be divided into three groups based on how their offspring develop: monotremes, marsupials, and placental mammals.
Marsupials have a rudimentary connection between the embryo and the mother's uterus through a yolk placenta.
Newborn marsupial embryos are born very immature and develop further in a pouch, where they find milk to complete their development.
Placental mammals, such as domestic mammals and humans, have a more elaborate and efficient connection between the embryo and the mother's uterus through an allantoic placenta.
The allantoic placenta provides the embryo with nutrition, respiration, excretion, and endocrine function, allowing for complete embryonic development.
Extraembryonic membranes are essential for the prenatal survival of the embryo and develop from the same germ layers as the embryo.
Extraembryonic membranes include the chorion, amnion, yolk sac, and allantois.
In mammals, the allantoic placenta gives rise to the placental circulation.
The chorion, amnion, and allantois are adaptations to terrestrial life, providing protection, interchanging gases and nutrients, and handling excretion.
In birds, the extraembryonic membranes form when the egg is incubated, and the yolk sac, amnion, and allantois expand, attaching to different layers and forming a trilaminate membrane called the allantochorion.
The placental barrier is a selective membrane that allows the transfer of nutrients, gases, waste products, antibodies, infectious agents, and hormones between the mother and fetus.
Cells do not normally cross the placental barrier, while gases do so easily due to their small molecule size.
Nutrient transport: The placenta provides energy to the fetus primarily through the transfer of glucose by facilitated diffusion.foetus receives large amounts of intact glucose but a significant amount is oxidized within the placenta to lactate. Amino acids are also actively transported to the fetus, with higher concentrations in fetal blood.
Gas transport: Oxygen readily diffuses from maternal to fetal blood due to a higher partial pressure in maternal blood. Carbon dioxide, which is produced abundantly by the fetus, diffuses from fetal blood into maternal blood.
Excretory function: The placental exchange processes help remove waste products such as urea, creatinine, uric acid, and bilirubin from fetal blood.
Protective function: The placenta serves as a protective barrier against infectious agents and drugs, but the ability of these substances to cross the placental barrier depends on their size and the specific characteristics of the placenta.
Immunoglobulin transfer: There are marked differences between species in the transfer of immunoglobulins across the placenta. In primates and rodents, there is substantial transfer of immunoglobulin G prior to birth, while in domestic animals, the neonate is essentially devoid of circulating antibodies until it absorbs them from colostrum.
Hormone production: The placenta is an important endocrine organ that produces various hormones, including steroid hormones like estrogens and progesterone, and protein hormones such as chorionic gonadotrophins.
Placental types: There are different types of placentas based on the placental membranes. In choriovitelline placentas, the yolk sac fuses broadly with the chorion to form a choriovitelline membrane, which is supported by vitelline blood vessels. In chorioallantoic placentas, the allantois fuses with the chorion, with the corionic villi of the membrane forming the fetal tissues that develop into the final placenta in eutherian mammals.
Chorioallantoic placenta: Developed with the support of the chorioallantoic membrane and allantoic vessels.
Non-deciduate placenta: Found in most domestic animals with simple chorionic villi; chorion does not fuse with the endometrium.
Deciduate placenta: In species with an invasive chorion, chorionic villi erode and fuse with the uterine mucosa, forming decidua.
Epitheliochorial placenta: Chorion villi attach to the maternal uterine epithelium, with no maternal invasion.
Synepitheliochorial placenta: A modification of epitheliochorial placenta, where trophoblast cells migrate and fuse with the maternal epithelium.
Endotheliochorial placenta: The chorion erodes the uterine epithelium and invades the maternal connective tissue.
Haemochorial placenta: The most invasive placenta, where the trophoblast erodes the endometrium and comes in direct contact with maternal blood.
Classification based on placenta shape:
- Diffuse placenta: Almost the entire surface of the allantochorion is involved in the formation of the placenta, found in horses and pigs.
- Cotyledonary or multiple placentation: Chorionic villi are restricted to multiple areas of attachment, forming cotyledons and caruncles in ruminants.
- Zonary placenta: A complete or incomplete band of tissue surrounding the foetus, seen in carnivores and some other animals.
- Discoid placenta: A single area of placenta is formed and is discoid in shape, found in primates and rodents.
Chorioallantoic placenta: Developed with the support of the chorioallantoic membrane and allantoic vessels.
Non-deciduate placenta: Found in most domestic animals with simple chorionic villi; chorion does not fuse with the endometrium.
Deciduate placenta: In species with an invasive chorion, chorionic villi erode and fuse with the uterine mucosa, forming decidua.
Epitheliochorial placenta: Chorion villi attach to the maternal uterine epithelium, with no maternal invasion.
Synepitheliochorial placenta: A modification of epitheliochorial placenta, where trophoblast cells migrate and fuse with the maternal epithelium.
Endotheliochorial placenta: The chorion erodes the uterine epithelium and invades the maternal connective tissue.
Haemochorial placenta: The most invasive placenta, where the trophoblast erodes the endometrium and comes in direct contact with maternal blood.
Classification based on placenta shape:
- Diffuse placenta: Almost the entire surface of the allantochorion is involved in the formation of the placenta, found in horses and pigs.
- Cotyledonary or multiple placentation: Chorionic villi are restricted to multiple areas of attachment, forming cotyledons and caruncles in ruminants.
- Zonary placenta: A complete or incomplete band of tissue surrounding the foetus, seen in carnivores and some other animals.
- Discoid placenta: A single area of placenta is formed and is discoid in shape, found in primates and rodents.
The placental barrier is a selective membrane that allows the transfer of nutrients, gases, waste products, antibodies, infectious agents, and hormones between the mother and fetus.
Cells do not normally cross the placental barrier, while gases do so easily due to their small molecule size.
Nutrient transport: The placenta provides energy to the fetus primarily through the transfer of glucose by facilitated diffusion.foetus receives large amounts of intact glucose but a significant amount is oxidized within the placenta to lactate. Amino acids are also actively transported to the fetus, with higher concentrations in fetal blood.
Gas transport: Oxygen readily diffuses from maternal to fetal blood due to a higher partial pressure in maternal blood. Carbon dioxide, which is produced abundantly by the fetus, diffuses from fetal blood into maternal blood.
Excretory function: The placental exchange processes help remove waste products such as urea, creatinine, uric acid, and bilirubin from fetal blood.
Protective function: The placenta serves as a protective barrier against infectious agents and drugs, but the ability of these substances to cross the placental barrier depends on their size and the specific characteristics of the placenta.
Immunoglobulin transfer: There are marked differences between species in the transfer of immunoglobulins across the placenta. In primates and rodents, there is substantial transfer of immunoglobulin G prior to birth, while in domestic animals, the neonate is essentially devoid of circulating antibodies until it absorbs them from colostrum.
Hormone production: The placenta is an important endocrine organ that produces various hormones, including steroid hormones like estrogens and progesterone, and protein hormones such as chorionic gonadotrophins.
Placental types: There are different types of placentas based on the placental membranes. In choriovitelline placentas, the yolk sac fuses broadly with the chorion to form a choriovitelline membrane, which is supported by vitelline blood vessels. In chorioallantoic placentas, the allantois fuses with the chorion, with the corionic villi of the membrane forming the fetal tissues that develop into the final placenta in eutherian mammals.
In pigs, the chorioamniotic raphe or mesoamnion persists throughout gestation, with the allantois expanding ventrally to quickly form the chorioallantoic placenta while the yolk sac shrinks towards the umbilicus.
The pig's placenta is non-invasive, epitheliochorial, and diffuse with atrophy at the peripheral tips. The allantois vessels do not expand to the tips of the chorionic sac, resulting in avascular and necrotic parts.
The uterine mucosa in pigs is provided with transversal folds, maximizing the placental exchange area with macroscopic circular folds in the chorion. The chorion has a conspicuous presence of circular areolas where uterine glands open.
Carnivores, such as dogs and cats, have a zonary placenta that forms a band around the foetus. They undergo efficient trans-uterine migration before implantation and typically have 3-8 foetuses.
The amnion in carnivores separates rapidly from the chorion, and the allantois expands dorsally to interpose itself between the amnion and the chorion. The placenta is endotheliochorial, with the foetal chorionic epithelium in contact with the endothelial cells of maternal vessels.
The initial structure of the canine placenta is in the form of straight folds, referred to as lamellae, which soon become branched and twisted, resulting in the formation of the labyrinthine placenta. The placenta is deciduate, and the marginal haematoma is a band of maternal haemorrhage at the margins of the zonary placenta, with distinctly green colouration in dogs.
The carnivore placenta is described as having an allantoic duct and four vessels (two umbilical arteries and two umbilical veins), but only the left umbilical vein enters the embryo's body. The umbilical cord is short and has few twists.
'Freemartin' is a phenomenon where a female twin is born with male hormones affecting her reproductive system due to placental circulations anastomoses.
Implantation in ruminants occurs during the peri-implantation period, involving reciprocal interactions between the elongating conceptus and endometrium.
Ruminants have an epitheliochorial placenta, but its structure is referred to as synepitheliochorial due to modified uterine epithelium.
Ruminant placenta is cotyledonary, with numerous smaller placental areas called placentomes.
Each placentome consists of a cotyledon (foetal part) and a caruncle (maternal side).
Cotyledons are made of chorion frondosum, while caruncles are oval or round thickenings in the uterine mucosa.
The placenta is delivered within 12 hours of birth, without significant loss of maternal tissue, making ruminant placentation non-deciduate.
In pigs, implantation is characterized by a lengthy pre-attachment period and remodeling of the embryonic vesicle to form a filamentous sac.
Pigs are polytocous animals giving birth to multiple offspring at the same time, with a litter size between 6 and 12 piglets.
'Freemartin' is a phenomenon where a female twin is born with male hormones affecting her reproductive system due to placental circulations anastomoses.
Implantation in ruminants occurs during the peri-implantation period, involving reciprocal interactions between the elongating conceptus and endometrium.
Ruminants have an epitheliochorial placenta, but its structure is referred to as synepitheliochorial due to modified uterine epithelium.
Ruminant placenta is cotyledonary, with numerous smaller placental areas called placentomes.
Each placentome consists of a cotyledon (foetal part) and a caruncle (maternal side).
Cotyledons are made of chorion frondosum, while caruncles are oval or round thickenings in the uterine mucosa.
The placenta is delivered within 12 hours of birth, without significant loss of maternal tissue, making ruminant placentation non-deciduate.
In pigs, implantation is characterized by a lengthy pre-attachment period and remodeling of the embryonic vesicle to form a filamentous sac.
Pigs are polytocous animals giving birth to multiple offspring at the same time, with a litter size between 6 and 12 piglets.

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Description

Explore the development and adaptive modifications of extraembryonic membranes in mammals, including the yolk sac, amnion, and allantois. Learn how these membranes continue to form despite the absence of yolk accumulation and the intrauterine mode of development.