|PRACTICAL 2 . THE FOETAL MEMBRANES AND PLACENTA
I. LEARNING OBJECTIVES.
To understand the external and internal gross anatomy of the pregnant uterus of the ewe.
Understanding of the arrangement of the foetal membranes-->chorion, amnion allantois and the fused membranes, chorioamnion and chorioallantois.
To identify the amniotic and allantoic cavities and fluids, observe the volume of the fluids and understand the functions.
Understand the different placental shapes and sites of attachment to the uterus: diffuse (e.g. pig,horse), cotyledonary (e.g. ruminant), zonary (e.g. carnivore).
Understanding the gross anatomy and histology of the placenta and its foetal and maternal components.
Understand the principal blood supply to, and drainage of blood and lymph from the placenta.
II. DISSECTION OF THE PREGNANT UTERUS AND FOETAL MEMBRANES OF THE SHEEP.
Examination of the external features
(i).Examine the ovary and identify ovarian follicles.
(ii). Note the immature and graafian follicles and corpora lutea. How many corpora lutea are present in each ovary? Have both ovaries been ovulated? Make free-hand sections of the ovary.
(iii).Examine the horns of the uterus for pregnancy. Is there a foetus in both horns? Is there sign of foetus absorption?.
(iv). Identify the ligaments
(v)Note size of the pregnant horn, the thickness of the uterine wall. The placentomes can be seen through it.
(vi). Locate the body of the uterus, cervix, vagina, the external genital organs and the bladder if these are still present.
Divide the uterine horns by cutting through the intercornual ligament.Divide the horns but leave the body of the uterus intact.
Open up the uterine horn very carefully, cutting through the myometrium between the placentomes. Be careful not to damage the underlying endometrium and foetal membranes. The endometrium maybe fused with the outermost foetal membrane, the chorion.
Observe the arrangement of the foetal membranes-->chorion, amnion allantois and the fused membranes, chorioamnion and chorioallantois.
Open the chorion to expose the inner membranes (allantois and amnion). Try to isolate the allantois and trace it to the umbilical cord. Note the amnion extends completely round the dorso-lateral aspects of the embryo but the allantoic cavity is restricted to the ventral part.
Open the amniotic cavity and expose the embryo.
Observe the amnion covered with small, white, oval ectodermal projections. These are amniotic plaques containing large amounts of glycogen. The allantois has white or brown allantoic calculi/hippomanes. Allantoic calculi are cellular debris derived from endodermal epithelium of the fetal gut.
Observe the structure of the umbilical cord.
III. PROSECTED SPECIMENS OF FOETAL MEMBRANES AND PLACENTA.
(i). Observe the gross anatomy of the placenta in different species-->rabbit, guinea pig, cat and dog.
(ii). Identify the foetal and maternal membranes and the structure of the foetal-maternal interface.
(iii). Identify the different placental shapes and sites of attachment to the uterus: diffuse (e.g. pig,horse), cotyledonary (e.g. ruminant), zonary (e.g. carnivore).
HISTOLOGY OF PLACENTA
(ia).Photographs of endothelial placenta of cat.
Low magnificationàdifferentiate the placental from the paraplacental zone.
The foetal membranesàchorion and allantois and the foetal blood vessels.
Structure of the placentaàthe foetal villi penetrating the maternal endometrium.
Extensive blood lacunae in the placenta.
(ib). Guinea pig haemochorial placenta 35 days.
Observe the embedded placenta in the endometrium of the uterus.
(ii). Slide. Haemochorial placenta of mouse. 15 days Haematoxylin and eosin.
Observe the structure of the placentaàembedding in the uterus.
The foetal villi penetrating the uterus
Extensive blood lacunae
The large decidual cells.
FLASCARD IN AILaboratory