Vetan Topic 3 Flashcards
referred to as the development of two (2)
or more embryos in a dam that normally gives birth to one offspring per gestation
embryonic duplication or twinning
They are twins having the same genetic composition. Derived from a single zygote that eventually divides or duplicates itself.
Free Symmetrical Monozygotic Twins/ Identical Twins
This type of twins originated from a single zygote (monozygotic) that resulted from incomplete separation of blastomeres later in embryonic development (primitive streak stage)
Conjoined or Fused Symmetrical Twins
fusion is at the sternal region of the thorax, facing
each other, often with partially fused hearts
thoracopagus twins
fusion is at the abdomen, often with partially fused
intestines
abdominopagus twins
fusion is back to back at the pelvis
or sacrum
pygopagus
fusion is in the head region
cephalopagus
twins resulting from duplication of future axial structures which may occur during the primitive streak stage
abnormal twins or monsters
two pairs/four of thoracic limbs
tetrabrachius
two faces
diprosopus
2 pairs/four pelvic limbs
tetrascelus
two tails
dicaudatus
two heads
dicephalus
consist of separate twins one is normal and the other is rudimentary that survives by being attached to the blood supply of fetal membranes
of the normal twin
free, asymmetrical twin
Mummified fetus is common in what domestic animals?
cows
type of twins occur after gastrulation when specific fields (limb field, heart field, eye field, etc.) are becoming organized.
conjoined, asymmetrical twins
an extra pelvic limb is attached to the back of the animal
notomelus twins
attached twins of unequal size (heteropagus ) and consist of one reasonably normal individual called the autosite, with an extra body part called the parasite attached to it
conjoined, asymmetrical twins
This type of twinning results when two (or more) zygotes develop separately and independently with separate fetal membranes and placenta, during the same pregnancy.
Free Symmetrical Dizygotic or Fraternal Twins
composite structure that contribute very little to the structure of embryo but form an important part of it and serve vital functions
extraembryonic (fetal) membranes
What is the first fetal membrane to be formed?
Yolk Sac
derived from inner cell mass and develops early from hypoblast and extraembryonic splanchnic mesoderm
yolk sac
In human embryos 2 – 3 weeks old, the yolk sac is the source of early nutrition but later shrinks and become non-functional as the?
Meckel’s diverticulum (outpocketing of small intestine)
By what day of incubation does the yolk sac completely encloses the yolk?
6
a short stump of splanchnopleure formed by the folding of the body and closure of the gut tube which connects the yolk sac to the embryo
yolk stalk
Amnion is absent in what animals?
fishes and amphibians
What are the five functions of amnion?
- Mechanical protection
- Allows free movement of the embryo which aids in neuromuscular development
- Antibacterial
- Allows fetal growth
- Prevents adhesion of fetal membranes
What is the outer sac that forms the outer boundary of the entire conceptus (fetus with fetal membranes)?
Chorion
a ventral diverticulum of the hindgut splanchnopleure
allantois
What are the three functions of allantois?
respiratory, excretory, digestive
a membranous structure formed by the apposition of the fetal chorioallantoic membrane ( CAM) and maternal endometrium (inner layer of the wall ) of the uterus
placenta
food of embryo is uterine milk that diffuses through the chorion and amnion
histotrophe
What are some functions of placenta?
- mediates physiological exchange between fetus and mother
- Secretes hormones like chorionic gonadotrophin
- Acts as a barrier to prevent mixing of fetal & maternal blood
placenta present in the species of horse, pig, cow and partially in goat and sheep
epitheliochorial placenta
placenta present in carnivores such as dog and cat, other canine /feline species
endochorial placenta
placenta resent in rodents, primates (monkey), human
hemochorial placenta
What are the four types of placenta according to shapes and distribution?
- Diffuse
- Cotyledonary
- Zonary -Complete or Incomplete
- Discoid –Single or Double
Villi are distributed throughout the chorionic vesicle except the undilated ends. Found in horses and pigs.
Diffuse placenta
Villi form tiny oval or round areas called cotyledons all over the external surface of the chorionic vesicle, except the undilated ends
cotyledonary
cotyledonary placenta are found in what animals?
ruminants
villi are concentrated in a wide zone that forms a belt around the chronic vesicle which can be either complete or incomplete
zonary placenta
Complete zonary placenta has a belt of villi surrounding the entire chronic vesicle which can be found in what animals?
dogs and cats
Found in bear, skunk, mink, weasel, ferret & raccoon
incomplete zonary placenta
Villi are concentrated in oval-shaped disks. Single or double. A single ______ placenta has one disk located at one end of the chorionic vesicle which are found in humans & rodents
discoid
uterine endometrium is sloughed off during
parturition
deciduate placenta
uterine endometrium remains intact during
parturition, found in horse & pig
adeciduate placenta
It is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth.
implantation
In species w/ long umbilical cords such as swine, neck or limb strangulation in varying degree may occur.
strangulation by umbilical cord
a condition characterized by parts of the amnion being attached to the embryonic structures particularly the CNS or limbs, or the distal parts of
appendages showing evidence of chorionic constriction
amniotic bands
accumulation of excessive amount of fluid in
the amnion (hydramnios) or in the allantois (hydrallantois)
hydrops of allantois or amnion
associated with some fetal malformation that interferes with its ability to swallow
hydramnios
What are the two types of implantation?
non-invasive and interstitial
trophoblasts invade & partially destroy the epithelium of the uterine endometrium.
interstitial implantation
trophoblast do not grow into the epithelium of the
uterine endometrium and can be physically separated from the latter
non-invasive implantation
