| 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 |
| At about 3 weeks, the distinctly saccular yolk sac can be identified macroscopically by its __________ and ___________. | pale yellow colour
fine parallel blood vessels |
| After the expansion of the ____, the yolk sac becomes drawn out to form a cord-like structure containing a yellowish-brown mass (see Fig. 22). The attachment of this cord-like structure to the persistent ____ ____ restricts the expansion of the midsection of the chorionic sac. | allantois
choriovitelline placenta |
| From about week 7, the ____ ____ gradually regresses and is eventually reduced to a scar by the growth of the surrounding tissue; the ____ ____ regresses simultaneously. | choriovitelline placenta
yolk sac |
| The chorioamniotic folds first appear on day ___, and the amnion and chorion are complete by day ___. | 18
21 |
| For the next 5 weeks, after the completion of the chorion and amnion on day 21, the amniotic cavity remains small and only contains about ___ ml of fluid. At parturition, the amniotic fluid volume is ____ litres. | 1
3-6 |
| From week ___, amniotic plaques begin to develop on the ____ ____. | 10
amniotic epithelium |
| Describe equine amniotic fluid. | Amniotic fluid is colourless, viscous and slightly alkaline; it consists of water (99 %) and small amounts of albumin, glucose and creatinine. It also contains some mucus, pieces of the thick epidermis which is sloughed from the fetal hooves, and traces of kidney and intestinal excreta (urea and meconium respectively). |
| Name the toughest fetal membrane. | Amnion |
| The allantois can be seen evaginating from the metenteron as early as day __. It grows rapidly between the ____ and ____ on the right side of the embryo, and then expands dorsally to form a dome over the amniotic sac which it completely encloses by day ____(see Fig. 21). | 21
amnion
chorion
28 |
| By day ___, the allentois has extended into the rest of the exocoelom and completely surrounds the ____ ____, except for the area forming the ____ ____ (see Fig. 22). | 40
yolk sac
choriovitelline placenta |
| Allantoic fluid is initially _________, but later becomes slightly ____. | clear and colourless
opaque |
| Describe Allantoic fluid. | Allantoic fluid consists of water (mainly) and small amounts of albumin, glucose, lipids, lactic acid and various phosphates. |
| At parturition, the allantoic fluid volume is ___ litres. | 8-15 |
| Describe the colour of the hippomanes that regularly occur in the allantoic fluid of equines. | Brown to olive-green |
| ____ ____ containing umbilical
Aa. and Vv. vascularises the ____ ____ of the equine amnion
and chorion. | Splanchnic mesoderm
somatic mesoderm |
| Shortly after the embryonal capsule is lost, the chorion develops an opaque, circular band known as the (1) (see Fig. 20). The (1) is about (2) wide and fully developed by day (3); it lies towards the (4), on the border between the (5) and (6) circulations (i.e. it encircles the (7)). Cells from the girdle then migrate and attach to the adjacent (8). | 1. chorionic girdle
2. 8 mm
3. 35
4. vitelline pole
5. vitelline
6. allantoic chorionic
7. choriovitelline placenta
8. uterine epithelium |
| After attacking and phagocytosing circumscribed areas of uterine epithelium and basal lamina, the girdle cells invade the ____ of the endometrium and form colonies of large, oval cells; these colonies are known as ____ (see Fig. 23). | interstitial tissue
endometrial cups |
| The endometrial cup region is visible as a roughly circular band of irregular projections on the ____ wall of the pregnant horn. The endometrial cups produce equine ____ ____ (pregnant mare serum, PMSG) from day __ to day __. | mesometrial
chorionic gonadotropin
38
120-130 |
| As soon as the endometrial cups are formed, they are surrounded, and at ___ days, invaded by ____, ____ and ____. | 60-80
lymphocytes
plasma cells
eosinophils |
| Leukocytes attack the cup cells of the chorionic girdle, which become necrotic and are eventually sloughed from the endometrium; this process is probably immunological. The sloughed cell debris either lies free in the spaces between ____ and ____, or is contained in allantochorionic pouches (see Fig. 22). | endometrium
allantochorion
allantochorionic pouches |
| The jenny only forms endometrial cups when carrying a ____ fetus and the mare, on the other hand, always forms endometrial cups, except when carrying a ____ fetus. | mule
hinny (mare x jack) |
| From day 35-40, primitive villi develop over almost the entire chorion; however, the chorion lying against the ____ and over the openings of the ____ ____ and ____ ____ never develop any villi. | cervix
uterine tubes
uterine glands |
| By day ____, the chorionic villi interdigitate with uterine villi; the contact zone between the chorionic and uterine villi is formed by interlocking ____. | 61
microvilli |
| From about day 100, the chorionic villi begin branching and adjacent villi start fusing to each other to form structures known as __1__. __1__ are completely developed over the whole chorion only by day __2__. When fully developed, each __1__ comprises a stout central stem bearing secondary and tertiary branches. Each __1__ fits into a reciprocal depression or crypt in the __3__. | 1. microcotyledons
2. 150
3. endometrium |
| The microcotyledons are involved in ____ nutrition, while the avillous areas between the microcotyledons remain involved with histotrophic____ nutrition. | hemotrophic
histotrophic |
| The uterine glands open between the microcotyledons, into the spaces between the chorionic and uterine epithelium. These spaces thus become a continuous network of __*__-filled channels or arcades involving the entire placenta (the arcades are homologous to the areolae seen in other species). No microcotyledons are formed opposite the endometrial cups, which later form cup-like indentations due to the accumulation of __*__. | histotrophe |
| The chorionic sac is initially ____ to ____. After enlarging to accommodate the expansion of the ____, it becomes more ____. It extends into and fills the body of the uterus by day __; by day __, it has extended into the smaller, non-pregnant horn and the entire endometrial surface is involved in placenta formation. The conceptus becomes ____-shaped once it occupies the entire uterus. | spherical to ovoid
allantois
fusiform
56
77
crescent |
| About __% of all pregnancies begin with twin fetuses; one fetus usually dies and is ____. In those instances where both survive, the chorionic sac of one may indent that of the other where their tips meet, or they simply push past one another. The areas of contact between the two chorionic sacs remain devoid of ____. Most twins are dizygotic (derived from separate zygotes). | 2 %
reabsorbed
villi |
| Twin chorionic sacs occasionally fuse and the formation of vascular anastomoses (fusion of blood vessels) can result in blood cell ____ (an individual having blood cells derived from a heterozygous twin, in addition to its own). However, these anastomoses form late in the pregnancy and have no detrimental effect on the development of the genital system. | chimerism |
| Because the ___ ___ extends to the chorion (choriovitelline placenta), and because the latter is some distance from the amnion, only two-thirds of the umbilical cord is covered by amniotic epithelium. | yolk sac |
| The allantoic part of the umbilical cord consists of the cord-like yolk sac surrounded by the opposing surfaces of the allantois. The funnel-shaped opening of the ____ ____ represents the point of transition between the amniotic and allantoic parts. | allantoic duc |
| The umbilical vessels (two spiralled Aa. umbilicales and two Vv. umbilicales) run in that part of the allantois, which lies against the ___ ___; they run as far as the chorio-vitelline placenta before branching into the ____. The umbilical veins fuse in the ____ part of the cord or at its junction with the ____ part. | yolk sac
allantochorion
amniotic
allantoic |
| The vitelline duct and the communication between endo- and exocoelom close early; the ____ ____, however, persists as a thin-walled passage, which remains open until birth. The cord's intervening mucous connective tissue (____ ____) soon becomes fibrous. A funnel-shaped extension of hairy skin from the abdominal wall of the fetus is seen to cover a short portion of the umbilical cord before it abruptly goes over into the smooth, thin-walled _____. | allantoic duct
Wharton's jelly
amnion |
| The umbilical cord is about ____ long at partus. | 1m |
| Classify the equine placenta. | 1. trilaminar vitelline (initially)
2. choriovitelline (later)
3. chorioallantoic (finally)
4. adeciduate
5. incompletely diffuse
6. epitheliochorial |
