Amniotic plaques These structures are thought to prevent the development of adhesions between the amnion and the embryo/fetus; amniotic plaques also form on the umbilical cord in some species.

After the allantois has grown into the exocoelom, it fuses with the ____ (to form ____) where the two membranes make contact with each other; this fusion allows branches of the ____ and ____ ____ (from the ____ ____ ____) to vascularize the ____.

Amnion allantoamnion Aa. and Vv. umbilicales allantoic splanchnic mesoderm amnion

In the ruminants and pig, part of the amnion also fuses to adjacent (1) to form (2). The (1) forms part of the (3) in these species, and it therefore also plays a role in (4), (5) and (6).

Chorion amniochorion placenta 4. nutrient absorption 5. respiratory gaseous exchange 6. excretion

Name the functions of the amniotic fluid (7).

1. shock-absorber and pressure equalizer 2. allows embryonal/fetal movement and changes in shape nd size to occur unhindered 3. protects the embryo/fetus against dehydration 4. prevents the development of adhesions between the embryo/fetus and the surrounding tissues 5. allows a limited uptake of fetal excreta 6. serves as a lubricant for the birth canal during parturition. 7. The intact amniotic sac serves as a hydraulic dilator of the birth canal during parturition in most species.

The allantois develops as an endodermal evagination of the ____, which grows into the ____ via the ____ ____ (see Fig. 13); it is covered by ____ ____ and accompanied by the two ___ ____.

Metenteron exocoelom umbilical cord splanchnic mesoderm Aa. umbilicales

After the allantois has expanded to completely occupy the exocoelom, its vascularized ____ ____ fuses with the non-vascularized ____ ____ of the ____ and ____. This results in the formation of a vascularized _____ and a vascularized _____.

Splanchnic mesoderm somatic mesoderm chorion amnion allanto-chorion allantoamnion

In forming the allantochorion and allantoamnion, the allantoic splanchnopleure and chorionic/amniotic somatopleure do not fuse completely. The main points of adhesion are formed by ____ ____ surrounded by ____; narrow clefts of ____ therefore persist between somatopleure and splanchnopleure.

Blood vessels mesoderm exocoelom

True or false. The allantois eventually fuses with the yolk sac.

False Narrow clefts of exocoelom persist between somatopleure and splanchnopleure.

The allantoic cavity communicates with the hindgut via the ____.

Urachus (Allantoic duct)

The proximal portion of the allantoic duct will later form the ____1____, while that portion between the bladder and the umbilicus will form the ____2____ of the __1__.

Urinary bladder median ligament bladder

The most important function of the allantois is to store ____ ____ and to prevent it from contaminating the ____ ____; it reaches the allantois via the ____ ____.

Urinary excreta amniotic fluid Urachus (allantoic duct)

The allantochorion contributes (to varying degrees) to the formation of the ____ in all the domestic species; it is thus also responsible for ____, ____ ____ ____ and ____.

Placenta nutrient absorption respiratory gaseous exchange excretion

The Aa. umbilicales that accompany the developing allantois arise caudally from the paired ____ ____; they are largely responsible for vascularizing the fetal membranes (excluding yolk sac).

Dorsal aortae

These fetal membranes are drained by two __ ____; the veins fuse (before entering or within the ____ ____, or between the ____ and ____) to form the __ ____ ____.

Vv. umbilicales umbilical cord umbilicus liver V. umbilicalis sinistra

Name the calculi that occasionally appear in the allantoic fluid of Ungulates.

Hippomanes (allantoic calculi)

Name some characteristics of Hippomanes

1. oval to disc-shaped structures 2. variable in colour 3. ranging in size from 5 to 15 cm 4. loat freely or may be attached to the allantochorion by means of a stalk 5. transverse section, they often reveal a layered appearance 6. central nucleus of cellular debris is surrounded by concentric layers of mucoprotein, calcium and phosphates.

It is thought that hippomane formation is related to the excretion of high levels of ____ metabolites by the fetal ____.

Nitrogenous kidneys

Name the outermost fetal membrane.

Chorion

The chorion consists of _____ and, since it is a major component of the ____ in all species, it plays an important role in the uptake and excretion of ____.

Somatopleure placenta metabolites

The chorionic epithelium, a single layer of ____ to ____ cells, thus acts as mediator between the embryo/ fetus and its environment.

Cuboidal columnar

The chorion acts as mediator between the embryo/ fetus and its environment. The early development of the blastocyst is thus modified in such a way that a primary chorion (i.e. the trophoblast) is already present just after the ____ stage. The continuity of the trophoblast/chorion is temporarily broken by the disappearance of the _____________, but is restored once the ____ ____ fuse dorsal to the embryo.

Morula covering layer of Rauber chorioamniotic folds

Fusing of the chorion with the highly vascular ___________ permits the umbilical vessels to vascularize the chorion's ____ ____. Areas destined to form the ____ are particularly well-vascularized and develop villi.

Allantoic splanchnic mesoderm somatic mesoderm placenta

The chorion is active _____ nutrition from an early stage, especially in the carnivores.

Histotrophic

Histotrophic nutrient sources utilized include the secretions of the ____ _____, _________ and __________.

Uterine glands desquamated uterine epithelial cells maternal red blood cells

_________, most likely originating from capillaries immediately beneath the uterine epithelium, are an important source of iron for fetal hemoglobin production.

Maternal red blood cells

The desquamated uterine epithelial cells become (1) prior to being desquamated. (1) have more than the diploid number of chromosomes, and this makes them an excellent source of (2) and other elements required for the formation of fetal (3).

1. Polyploid cells 2. amino acids 3. DNS

Name the nutrients collectively known as "uterine milk" or histotrophe.

Secretions of uterine glands desquamated uterine epithelial cells maternal red blood cells

Where a more intimate feto-maternal contact exists in the placenta, the histotrophe is gradually supplemented by the direct uptake of metabolites from the maternal circulation; these metabolites are referred to as ____.

Hemotrophe

Histotrophe and hemotrophe are collectively referred to as ____.

Embryotrophe

In the carnivores, hemotrophic nutrition involves a mass of modified ____ cells, the ____, which lies in direct contact with the maternal ____.

Chorionic syntrophoblast capillaries

The exchange of metabolites (i.e. the uptake of nutrients and oxygen, and the excretion of catabolites and carbon dioxide) is facilitated by fetal and maternal blood streams flowing in opposite directions in adjacent ____ and ____ capillaries. This arrangement ensures that there is always a ____ ____ for metabolites between the two circulations.

Chorionic uterine concentration gradient

The ____ ____ connects the embryo/fetus to its fetal membranes and thus, to its source of ____ and ____.

Umbilical cord nutrients oxygen

Apart from a short proximal portion that is covered by ____ _____, the umbilical cord is covered by a ________ of ___dermal (amniotic) origin; the epithelium is stratified only where it forms ____ ____.

Fetal skin simple squamous epithelium ecto- amniotic plaques

The umbilical cord consists of mucous connective tissue known as ____ ____.

Wharton's jelly

Name the structures the umbilical chord consists of.

Vitelline duct Aa. and Vv. vitellinae the allantoic duct Aa. and Vv. umbilicales

In what animals does the vitelline duct and vessels disappear early in development?

Ruminants and pigs

The initial communication between the endo- and exocoelom (via the umbilicus) is closed when the somatic mesoderm of the ____ ____ fuses with the splanchnic mesoderm of the ____ ____.

Body folds umbilical cord

In what species does the umbilical cord have a natural point of rupture and where is that point located?

Ungulates 1-2 cm distal to the transition from skin to amniotic epithelium This point is characterized by a sudden reduction in the dense connective tissue in the umbilical vessels' adventitia The weight of the neonate (newly born) is sufficient to break the cord.

What prevents the natural point of rupture in the umbilical chord of ungulates from hemorrhaging?

Contraction of thickened muscle fibres in the vessel walls

In _____, the umbilical cord does not have a natural point of rupture and cannot be broken by the weight of the neonate - it must be bitten through by the mother.

Carnivores

Name the 4 classification according to the Fetal Membranes forming the Pars fetalis

A. Placenta vitellina b. Placenta choriovitellina c. Placenta chorioallantoica d. Placenta chorioamniotica

There are two stages in the development of a vitelline placenta (formerly known as an omphaloplacenta). In the first, the Pars fetalis is formed by a circumscribed area of ____ ____ lying directly against the ____ at the vegetal pole; the expanding extra-embryonic mesoderm and developing vitelline circulation have not yet extended into the region. This stage is referred to as a ________.

Yolk sac trophoblast Placenta vitellina bilaminaris

During the development of a vitelline placenta. Later, once the extra-embryonic mesoderm has grown between the yolk sac and trophoblast, but before the region is vascularized, the bi-laminar vitelline placenta is converted to a __________.

Placenta vitellina trilaminaris

Placenta vitellina. In the horse, implantation commences at the ____ stage, while _____ stage(s) of vitelline placenta occur in the carnivores.

Trilaminar both

Vitelline placentae are responsible for early _____ nutrition; they are always temporary and the trilaminar stage is soon converted into a ____ placenta.

Histotrophic chorio-vitelline

The vitelline circulation has vascularized the trilaminar vitelline placenta by about the time the ____ ____ have fused and the ____ has become chorion.

Chorioamniotic folds trophoblast

____ converts the trilaminar vitelline placenta into a choriovitelline placenta.

Vascularization

A choriovitelline placenta (also formerly referred to as an omphaloplacenta) persists until its ____ layer is split into ____ and ____ layers by the expansion of the _____.

Mesodermal splanchnic somatic exocoelom

Choriovitelline placentae play a significant role in early ____ nutrition. This type of placenta occurs temporarily in the horse and carnivores, but is later replaced by a ____ placenta

Histotrophic chorioallantoic

In the horse and carnivores, the temporary __1__ placenta is eliminated by the expansion of the exocoelom. After the expanding __2__ has extended between the yolk sac and chorion, the __2__ and chorion to fuse to form __3__.

Choriovitelline allantois allantochorion

In these species, ____ and _____, the Pars fetalis of the final placenta is (effectively) entirely chorioallantoic. However, in the ____ and ____, the Pars fetalis is only partially chorioallantoic.

Horse carnivores ruminants pig

In a chorioamniotic placenta, the Pars fetalis (or part thereof) is formed by __1__. __1__ can only form where the allantois does not extend between the __2__ and __3__. In the ruminants and pig, the Pars fetalis is partially chorioamniotic.

Amniochorion amnion chorion

In an ____ placenta, there is either minimal or no loss of maternal tissue. The Pars fetalis and Pars uterina simply lie next to each other. If interdigitating villi do develop, they are simple or only slightly branched; they occur on both the Pars fetalis and Pars uterina, and interlock fairly loosely. The two placental components are thus easily separated at parturition.

Adeciduate

Name the specie(s) with adeciduate placenta.

Horse, ruminants and pig

The ____ placenta is characterized by a considerable loss of maternal tissue during placental development and at parturition. The interdigitating villi are compound and the fetomaternal contact is very firm and intimate. The Pars fetalis can only be separated from the Pars uterina once there has been some breakdown of ____ ____; parturition is thus characterized by considerable ____.

Deciduate maternal tissue hemorrhage

Name the specie(s) with deciduate placenta.

Carnivores

The area/s for hemotrophic nutrition are generally characterized by the presence of _____ (or modifications thereof) which interdigitate with ____. In this classification, adeciduate placental types are referred to by the term ____, while the term ____ is reserved for the deciduate or "true" placentae.

Chorionic villi uterine villi Semiplacenta Placenta

Name the 3 classifications of placenta according to the Area/s for Hemotrophic Nutrition.

Semiplacenta diffusa Semiplacenta cotyledonaria Placenta zonaria

A ____ ____ has villi evenly distributed over the whole Pars fetalis. This placental type occurs in the ____ and ____. However, in both species, there are areas of the chorion that have no villi at all (see 2.7.4); these placentae are thus further classified as ____ ____ ____ (a ____ ____ ____ occurs in other, non-domestic species).

Diffuse semiplacenta or Semiplacenta diffusa horse pig Semiplacenta diffusa incompleta Semiplacenta diffusa completa

A __1__ occurs in the ruminants. Hemotrophic nutrition occurs at numerous, discrete sites known as __2__. Each __2__ has a fetal and a maternal component, the __3__ and __4__ respectively.

1. cotyledonary semiplacenta or Semiplacenta cotyledonaria 2. placentome(s) 3. cotyledon 4. caruncle

The cotyledons are formed by masses of ____ ____; they develop wherever the chorionic sac makes contact with the ____.

Chorionic villi caruncles

In a __1__, the villi form a broad, transverse band around the middle of the ovoid chorionic sac; the rest of the sac remains smooth and free of villi. __1__ occur in the __2__.

Zonary placenta carnivores

Placental transport of metabolites is known to be an active/passive metabolic process?

Active

Epitheliochorial placentae occur in the what species?

Horse, ruminants and pig.

How is placental intimacy increased in Epitheliochorial placentae?

Placental intimacy may be increased by chorionic ridges that fit into corresponding uterine grooves. The epithelium covering the villi generally have microvilli that interdigitate with uterine epithelial microvilli; this further improves intimacy and increases the surface area for metabolite exchange. Intra-epithelial capillaries are present and improve placental intimacy without reducing the number of tissue layers.

In the ____ placentae uterine epithelium remains intact and the chorion simply lies against it.

Epitheliochorial

Describe Hempotrophic and Histotrophic nutrition in Epitheliochorial placentae?

Simple to compound chorionic villi are formed and are principally responsible for hemotrophic nutrition. Histotrophic nutrition usually occurs in the adjacent avillous areas, but may also involve the chorionic villi.

In the sheep and goat, the epithelium covering the tips of the uterine villi forms __1__ masses. These are masses of cells that lose their __2__ where they lie in contact with each other; they appear as large, multinucleate cytoplasmic masses with an outer plasmalemma. The presence of the __1__ masses creates the impression that the chorionic epithelium lies against uterine connective tissue between the masses. However, the uterine epithelium covering the masses remains intact, although it is extremely thinly stretched.

Symplasma plasmalemma

Endotheliochorial placentae occur in the ____.

Carnivores

In endotheliochorial placentae, the aggressive nature of the chorion results in the __1__ of uterine epithelial cells and the ___2___ penetrate into the underlying uterine connective tissue. Modified chorionic cells at the base of each villus form a fused unit or syncytium, the __3__. The __3__ surrounds the endothelium of the adjacent uterine capillaries and is responsible for __4__ nutrition. __5__ nutrition occurs at the tips of the fetal villi and in the adjacent avillous areas. Intra-epithelial capillaries are also present.

1. desquamation 2. chorionic villi 3. syntrophoblast 4. hemotrophic 5. Histotrophic

Gestational Period of the mare?

334-343 days 48-49 weeks 11 months

Gestational Period of the jenny?

360 days 52 Weeks 12 Months

A secondary ovocyte is ovulated and fertilization occurs in the ____ of the uterine tube.

Ampulla

Why does the equine embryo appear to "wander" throughout the entire uterus until day 15?

It is thought that this promotes the maternal recognition of pregnancy which apparently requires that the entire endometrium "be informed" as to the presence of the embryo.

On what day does implantation of the equine embryo occur and where?

Day 16 The embryo settles at the caudal end of one of the uterine horns. It lies with the animal pole (embryonal disc) against the antimesometrial wall, and with its longitudinal axis orientated cranio-caudally.

The vitelline/choriovitelline placenta is the primary means of __1__ nutrition until about week __2__. This prolonged period of __1__ nutrition is necessary because feto-maternal attachment takes place so late (day 16).

1. histotrophic 2. 5-6

A trilaminar vitelline placenta is established in the late blastocyst stage (about day ___) but is converted to a choriovitelline placenta by about day ___.

18 22

An arterial ring, the __1__, develops in the mesoderm around the __2__ placenta (see Fig. 18). It is formed by the two vitelline arteries; however, the __3__ artery soon disappears and only the __4__ artery remains connected to the __1__.

1. Sinus terminalis 2. chorio-vitelline 3. right 4. left

The two vitelline veins are formed by vessels that converge in the vicinity of the ____. Nutrients absorbed as ____ are transported to the embryo via the vitelline veins.

Embryo histotrophe

For about the first 4 weeks, the ____ circulation is responsible for chorionic vascularization (the area vascularized is quite small). By day 30, this function is taken over by the ____ circulation.

Vitelline umbilical (allantoic)

What is the reason that the yolk sac and vitelline circulation persist longer in the horse than they do in most other species?

The presence of the choriovitelline placenta