| Name the functions of the fetal membranes. | embryonal/fetal nutrition, excretion and protection |
| The fetal membranes develop as a covering appendage of the embryo proper and arise from the _____ parts of the blastocyst. | extra-embryonal |
| The fetal membranes comprise the following: | Yolk Sac
Amnion
Allantois
Chorion |
| The yolk sac is an ____dermally derived storage space for ____ in lower vertebrates. Although it only contains ____ in higher vertebrates, it is responsible for the formation of early ____ ____, ____ ____ and ____ ____ ____; the latter subsequently migrate to the developing gonads. In some species, it is also involved in the formation of the initial _____ and is thus partly responsible for the early absorption of nutrients. | endo-
nutrients
fluid
blood vessels
blood cells
primitive germ (reproductive) cells
placenta |
| The amnion is an ____dermal, ____-containing sac, which surrounds the ____ ____; in higher vertebrates it recreates the watery environment in which lower vertebrates develop. | ecto-
fluid
embryo proper |
| The allantois is an __1__dermal derivative, which grows into the __2__ as a storage space for __3__ ____. It is associated with the __4__ and __5__ ____ which are largely responsible for vascularizing the __6__; these vessels also play a vital role in the __6__'s respiratory function. | 1. endo-
2. exocoelom
3. urinary excreta
4. Aa. and
5. Vv. umbilicales
6. chorion |
| The allantois is an __1__dermal derivative, which grows into the __2__ as a storage space for __3__ ____. It is associated with the __4__ and __5__ ____ which are largely responsible for vascularizing the __6__; these vessels also play a vital role in the __6__'s respiratory function. | 1. endo-
2. exocoelom
3. urinary excreta
4. Aa. and
5. Vv. umbilicales
6. chorion |
| The allantois is an __1__dermal derivative, which grows into the __2__ as a storage space for __3__ ____. It is associated with the __4__ and __5__ ____ which are largely responsible for vascularizing the __6__; these vessels also play a vital role in the __6__'s respiratory function. | 1. endo-
2. exocoelom
3. urinary excreta
4. Aa. and
5. Vv. umbilicales
6. chorion |
| The chorion is the outermost, ____dermal, ____ absorbing membrane of the conceptus; it is in direct contact with the ____ and later forms an integral part of the ____. | ecto-
nutrient
endometrium
placenta |
| In contrast to the terms "embryo" and "fetus" (which refer only to the individual), the term _____ refers to the embryo or fetus together with its fetal membranes. | conceptus |
| With the development of the cylindrical body form, the dorsal part of the yolk sac is pinched-off to form the ____ ____. | primitive gut |
| In Eutheria, the yolk sac's food storage function has been lost because nutrients are available in the uterus in the form of ____ ____, ____ and ____ ____. | glandular secretions
blood
desquamated epithelium |
| In Eutheria. A vascular system, comprising the Aa. and Vv. vitellinae, thus arises early from the ____ ____ in the ____ ____ covering the yolk sac endoderm. | Area vasculosa
splanchnic mesoderm |
| The vitelline vessels then connect to the embryo's developing circulation: the Aa. vitellinae become ____ branches of the ____ ____ while the Vv. Vitellinae pass through the ____ to the ____. | ventral
dorsal aortae
liver
heart |
| In the ____ and ____ (type of animal), the yolk sac is unimportant as a fetal membrane and it undergoes early regression, especially after formation of the ____. In the ____ and ____, the yolk sac is more important as it forms part of the (temporary) initial ____; it therefore also persists for a much longer period. | ruminants and pig
allantois
horse and carnivores
placenta |
| Name the fetal membrane that is initially quite small, but enlarges progressively to accommodate the increasing volume of fluid. | amnion |
| The inner surface of the amnion can remain smooth or it may develop caseous (cheese-like) epithelial thickenings known as ____ ____. What is their function? | 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 |
