lec 20 outline and review

Lecture 20: Placentation and Recognition of Pregnancy

Reading

Chapter 13 and 14
Diagrams and pictures from lecture

Spherical, tubular, filamentous (mare remains spherical)

embryo undergoes rapid growth
Cow as an example
- Day 15, 1-2 mm in length
- Day 18-19, 10-20 cm in length

Uterine migration

cow,ewe (rare, filamentous conceptus reaches other uterine horn)
pig (day 5-12, then even spacing and fixation)
mare (day 10-16), then fixation

Gastrulation and germ layer formation

endoderm
- first forms as outgrowth of inner cell mass in blastocyst
- grows down to surround the blastocoel which then becomes the yolk sack
- gives rise to
  - Digestive , Liver, Lungs, Pancreas, Thyroid gland, Other glands
ectoderm
- cells of inner cell mass thicken and begin to multiply forming first the neural tube
- gives rise to
  - CNS, Sense organs, Mammary glands, Sweat glands, Skin, Hair, hooves
mesoderm
- separate from the ectoderm and fill space between endoderm and ectoderm
- gives rise to
  - Circulatory, Skeletal, Muscle, Reproductive tracts, Kidneys, Urinary ducts

Fetal membranes - fetal placenta

amnion
- Non-vascular, fluid filled
- Fluid produced by fetus
- Protective cushion
- Ruptures at birth (breaking of water)
yolk sac
- In birds to nourish embryo
- In mammal atrophies but source of blood cells and primordial germ cells
allantois
- Blood vessels
- Fuses with chorion
- Allantochorion
- Brings blood vessels to chorion
chorion
- Outermost membrane
- Attachment to mother

Maternal recognition of pregnancy

Luteal Regression
- luteolytic - PGF - cow, sheep, mare
- lack of CL support - human
Luteal Maintenance
- antiluteolytic - prevent effects of PGF or PGF release
- luteotrophic - enhance survival of CL, support CL
cow, ewe
- Interferons (oIFN-t, bIFN-t)
  - antiluteolytic
  - inhibits synthesis of oxytocin receptor in endometrium
    - oxytocin receptor triggers release of PGF from endometrium
  - inhibits synthesis of prostaglandin in endometrium
- critical days
  - Bovine - 16 to 17
  - Ovine - 12 to 13
pig
- Estradiol
  - antiluteolytic
  - redirect PGF secretion into the uterine lumen
  - requires 2 embryos per uterine horn
- critical days
  - 11 to 12
horse
- proteins
  - antiluteolytic
  - embryo migration must occur to expose endometrium to the antiluteolytic agents
- critical days
  - 12 to 14
primate (human)
- HCG
  - luteotrophic
- critical days
  - 8 to 12
rodents
- rodent placental lactogen
  - luteotrophic
- Estrous cycle - 4 days
- Mating induces prolactin release
  - Maintenance of CL
  - Psuedopregnancy
- Not Pregnant
  - Prolactin decreases after day 7
  - PGF increases day 11
  - Estrus by day 17
- Pregnant
  - RPL increases after day 7, h P4
  - PGF increases day 11
  - rodent placental lactogen protects CL from PGF

Implantation

time

	Attachment to Uterus (days)
Species	Beginning	Completion
pig	13	24
cow	22	40
sheep	15	28
mare	24 - 40	95 - 100
human	7 - 8	30

types
- superficial
  - Chorion lies opposed to uterine wall
  - Farm animals
- eccentric
  - Chorionic sack in a uterine fold
  - Rodent
- interstitial
  - Embryo digests part of uterine wall
  - human
degree of tissue loss at parturition
- Deciduate
  - Eccentric, interstitial
  - Rodent, human
- Indeciduate or Nondeciduate
  - Superficial
  - Farm animals

Placenta classification

shape
- cotyledonary - cow, sheep
  - Binuclear Giant Cells
    - 20% of fetal placenta
    - Secrete Placental Lactogen
      - Prolactin-like activity
      - Stimulates Milk Synthesis
      - Not Present in Pig and Mare
      - May regulate maternal metabolism to facilitate fetal growth
      - High levels in the last 1/3 of gestation.
      - High levels facilitate higher milk production.
      - Dairy cows have higher blood concentrations than beef cows
    - Secrete Pregnancy Specific Protein B
      - Function uncertain
- diffuse - horse, pig
  - Microcotelydonary
  - Endometrial Cups in Mare
    - From both trophoblast and endometrium
      5 to 10
    - Form between days 35 to 60
    - Produce equine chorionic gonadotropin (eCG, PMSG)
    - Sloughed off after day 60
- zonary - canine, feline
- discoidal - human
histology - up to 6 layers can separate maternal and fetal blood
- epitheliochorial
- syndesmochorial
- endotheliochorial
- hemochorial
- hemoendothelial
Erythroblastosis Fetalis - Human
Neonatal Isoerythrolysis - Cat adn Horse

Review Quiz and other questions below:

What type of implantation occurs in the cow and ewe?
When does implantation occur in the sow, mare, ewe, cow and woman?
Describe the 4 shape classifications of placentas.
Is more tissue lost at parturition in a deciduate or indeciduate placenta?
Describe the 5 types of placentas as classified by histology, including the number of tissue layers separating maternal and fetal blood. For each type, also give an example of a species it is present in.
How many fetuses must be present in each uterine horn of a pig to maintain pregnancy and why?
What is the major function of the amnion, yolk sac, allantois and chorion in the mammalian placenta?
What is the difference between an antiluteolytic and luteotrophic agent, and give an example of each involved in recognition of pregnancy?
T F: The uterine artery contains oxygenated blood.
Describe the mechanism of blastocyst formation.
How does the blastocyst hatch from the zona pellucida?
Describe gastrulation -specifically:
a. What are the 3 primary germ layers?
b. List one tissue that each germ layer will give rise to.
c. How does each germ layer form?
Describe the formation of the amnion.
Name the outer membrane of the placenta. What structure in the blasotcyst is this derived from?
Describe how the luteolytic substance, PGF2a, is transferred from endometrium to ovary in cattle and sheep?
What placental membrane is responsible for vascularization of the placenta?
What is the magnitude of trophoblastic elaongation in the cow between days 15 and 18 of gestation?
Describe what elongation refers to in regards to the blastocyst? What are the 3 stages the blastocyst goes through in elongation?