ANSC 331 Exam 4:Placentation and Gestation

What is gestation?

the action or process of carrying or being carried in the uterus between conception and birth

What are Monotremes

Egg laying mammals (oviparous)

- platypus, echidna

What are Marsupials?

mammals with a pouch

- viviparity = no longer lay eggs; gained the ability to produce living young

True or False: Marsupals have a very short gestation period.

True

- the offspring develops for a long time in the pouch after birth

What are Eutheria?

placental mammals

What are the two ways to classify a placenta?

1. Chorionic villus distribution (How are they distributed?)

2. Number of layers between fetal & maternal blood

What is the chorionic villus and what is its function?

The functional unit of the placenta:

- small, finger like projections on the surface of the chorion

- nutrient exchange apparatus - increase SA

- may be grouped in various arrangements

What is a placenta? What are the functions of the placenta?

Transient organ of pregnancy

- acts as a metabolic interface between mother & fetus(es)

- endocrine gland (maintains pregnancy, promote fetal & mammary gland growth, induces parturition)

Functions:

- blood supply

- nutrient transport

- elimination of waste

Describe the placentation types - by villus distribution. Which is found in which species?

Diffuse: uniform villi distribution (pig, horse)

Cotyledonary: villi located on button-like structures called cotyledons (sheep, cattle)

- placentome, fetal cotyledon, maternal carnuncle

Zonary: villi form a zone around the middle of the cenceptus (dog, cat)

- like a "belt" around the fetus

Discoid: villi form a regionalized disc (humans, primates, rodents)

What is the placentome made of? The fetal cotyledon? The maternal caruncle?

Placentome: maternal caruncle + fetal cotyledon

Fetal cotyledon: Trophectoderm origin (fetal)

Maternal caruncle: caruncular region of the uterus

Describe the placentation types - by number of layers. Which layers are found in each placenta type? Which is more invasive? Least invasive? Which is found in which species?

1. Epitheliiochorial: maternal side "epithelio" and fetal side "chorial"

- minimally invasive

- 6 layers (endometrial capillaries, interstitium, epithelium, chorionic epithelium, interstitum, capillaries)

- sows & mares

2. Synepitheliochorial: endometrial epithelium transiently erodes and regrows

- cattle & sheep

- 2nd to least invasive

- has 6 layers but the uterine epithelium temp. erodes (changes to 5 layers) and then grows back

- intermittent exposure of maternal capillaries to chorionic epithelium

3. Endotheliochorial: complete erosion of the endometrial epithelium and partial erosion of underlying interstitum

- dogs & cats

- semi-invasive plancentation

- 5 layers (endometerial capillaries, interstitium, chorionic epithelium, interstitium, capillaries)

4. Hemochorial: chorionic epithelium in direct apposition to maternal pools of blood

- humans, primates, rodents

- most invasive

- 3 layers (chorionic epithelium, interstitium, capillaries)

Describe the placentation type in pigs

Epitheliochorial:

- pigs have a folded bilayer to increase SA thereby maximizing nutrient transport

- folds get bigger as pregnancy progresses

- can "peel" placenta from the underlying endometrium

What are BNGCs? Where do they originate from? What do they secrete?

Binucleate giant cells (BNGCs) form from the chorionic (fetal origin) cells *2 of them

- migrate from chorionic epithelium & invade endometrial epithelium

- secrete placental lactogen, estrogen, and progesterone

- secrete pregnancy specific B

**Unique to ruminants, used in pregnancy test via blood sample (BioPryn)

How are nutrients transported across the placenta?

Nutrients are transported via:

- Passive transport (simple/facilitated diffusion): no energy required

- Active transport: energy required

Name the species where antibodies do and do not cross the placenta.

DO NOT:

- ruminants

- sows

- cats

- dogs

DO:

- humans

- rodents

Provide examples of what does and does not cross the placenta

DO:

- Vitamins: water soluble (B,C) & lipid soluble (A,D, E)

DO NOT:

- Lipids

- Large peptide hormones (thyroid stimulating hormone, growth hormone, insulin, and glucagon)

Describe the molecules transported across the placenta and the mechanism/functions.

Diffusion (simple):

- O2, CO2, H2O; free FA, Na, K, Cl; small viruses, drugs, pharmaceuticals & toxins

- functions: homeostasis; substrate for growth; (-) effects for fetus

Diffusion (facilitated): glucose, converted into fructose by the placenta

- functions: fetal nutrition

Active: AA; Fe, Ca, P, Zn

- functions: protein synthesis; fetal nutrition & growth

Why is hormone production by the placenta critical?

- pregnancy maintenance

- ovarian function

- fetal growth

- mammary gland development

- parturition

What is unique about the mare placenta?

The mare placenta contains endometrial cups (transient organs of trophoblast and endometrial origin

- secretes eCG

What makes eCG? what is the function of eCG?

Pregnant mare serum gonadotropin-PMSG

- maintains the CL and progesterone production

- initiates the formation of accessory CL to increase progesterone

- FSH like actions: induces superovulation (cow, sheep, rabbit)

What makes hCG? What does hCG do?

Human Chorionic Gonadotropin (hCG)

- produced by trophoblast cells of chorion

- function: provides luteotropic stimulus for the CL

What is placental lactogen? What is its function?

stimulates fetal growth (somatotrophic effects) and mammary gland development/function (lactogenic effect)

What are the primary functions of progesterone in maintaining pregnancy?

- block myometrial contractions

- stimulate endometrial gland secretion of nutrients in early pregnancy

In what species does the CL produce progesterone for the entire pregnancy?

- rabbit

- sow

In what species does the placenta take over progesterone production?

- sheep, 50 d

- cow, 6,8 month

- mare, 70 d

- human, 60-70 d