ANSC 331 exam 4 study guide questions

Define maternal recognition of pregnancy

A biochemical signal produced by the conceptus in sufficient amounts and at the correct time to prevent termination of pregnancy.

What is the goal of maternal recognition?

To prevent luteolysis so the corpus luteum continues producing progesterone and pregnancy can be maintained.

mechanism of maternal recognition in Cow/Ewe

• Signal: Interferon tau (IFNT)

• Secreted by trophoblast cells of conceptus

• Prevents oxytocin receptor expression on endometrium

• Prevents oxytocin binding

• Prevents PGF2α pulses → prevents luteolysis

mechanism of maternal recognition in Sow

• Signal: Estradiol

• Uses endocrine-exocrine theory

• Redirects PGF2α secretion into uterine lumen instead of bloodstream

• Prevents luteolysis

mechanism of maternal recognition in Mare

• Signal: 3 proteins/estrogens (?)- not exactly sure/studied

• Conceptus migrates throughout uterus (“uterine migration”)

• Migration is required to signal pregnancy recognition over entire uterus

mechanism of maternal recognition in Human

• Signal: Human chorionic gonadotropin (hCG)

• LH-like hormone

• Sustains corpus luteum

• Promotes trophoblast growth and placental development

What stimulates secretion of PGF2α during late luteal phase?

Oxytocin binding to oxytocin receptors on the endometrium stimulates PGF2α release.
(Indirectly shown because IFNT prevents OTR expression to stop PGF2α pulses.)

What does IFNT do to endometrial cells?

• Prevents oxytocin receptor expression

• Stops oxytocin binding

• Prevents PGF2α pulses

IFNT induces secretion of proteins used by what?

The conceptus/embryo uses these uterine gland secretions as nutrients.

Understand MRP in the Pig: Estradiol and endocrine-exocrine theory

Pig embryos secrete estradiol which reroutes PGF2α secretion from endocrine (bloodstream) to exocrine (uterine lumen), preventing luteolysis.

Does number of embryos matter in a pig? How many are required?

Yes — embryo number matters. Multiple embryos are required for adequate estradiol production to maintain pregnancy.
4 embryos required, 2 on each side of uterine horn
Based on pig MRP requiring sufficient estradiol from multiple embryos.

In the mare, understand uterine migration phenomenon

The equine conceptus migrates throughout the uterus repeatedly during early pregnancy to distribute pregnancy recognition signals over the entire endometrium.

In humans, what is the role of hCG?

• Sustains corpus luteum

• Promotes trophoblast growth

• Promotes placental development

Yolk Sac

• Transient membrane

• Source of some primordial germ cells

• Source of blood stem cells

• Regresses in first trimester

Amnion

• Protective sac embryo develops within

• Filled with amniotic fluid

• Allows symmetrical fetal development

• Prevents embryo from sticking to membranes

Chorion

• Outermost fetal membrane / outermost layer of placenta

• Derived from trophectoderm

• Produces MRP signal

• Attaches to uterus

• Takes up nutrients

• Eventually fuses with allantois

Allantois

• Fills with nutrients/waste from GI tract and fetal kidneys

• Provides blood supply after fusing with chorion

Allantochorion

• Fusion of allantois and chorion

• Fetal contribution to placenta

What is a placenta?

A transient organ of pregnancy that acts as the metabolic interface between mother and fetus. It is also a major endocrine gland during pregnancy.

What are the functions of the placenta?

• Maintains pregnancy

• Promotes fetal growth

• Promotes mammary gland growth

• Induces parturition

• Acts as metabolic interface for nutrient/waste exchange

• Endocrine hormone production

What are the two ways to classify a placenta?

• By villus distribution

• By number of tissue layers at maternal-fetal interface

What is a chorionic villus and what is its function?

• Small finger-like projections on surface of chorion

• Functional unit of fetal placenta

• Increases surface area for nutrient exchange

Diffuse Placenta

• Villi distributed over entire chorion

• Species: Mare, Sow

Cotyledonary placenta

• Villi grouped into cotyledons/placentomes

• Species: Ruminants (cow, ewe)

Zonary Placenta

• Villi arranged in belt/band

• Species: Dog, Cat

Discoid Placenta

• Villi in one/few disc-shaped areas

• Species: Humans, Rodents

Epitheliochorial Placenta

• 6 tissue layers remain

• Least invasive

• Species: Mare, Sow

Synepitheliochorial / Syndesmochorial Placenta

• Modified epitheliochorial

• Species: Ruminants

Endotheliochorial Placenta

• 4 layers remain

• Species: Dogs, Cats

Hemochorial Placenta

• 3 layers remain

• Most invasive

• Species: Humans, Rodents

Which is most invasive Placenta?

Hemochorial

Which is least invasive Placenta?

Epitheliochorial

How are nutrients transported across the placenta?

• Simple diffusion

• Facilitated diffusion

• Active transport

Examples of what crosses the placenta:

• Oxygen

• Carbon dioxide

• Water

• Free fatty acids

• Na, K, Cl

• Glucose

• Amino acids

• Iron, calcium, phosphorus, zinc

• Some small viruses/drugs/toxins

• Vitamins B and C easily

What does NOT cross the placenta?

• Large peptide hormones:

  • Thyroid stimulating hormone

  • Growth hormone

  • Insulin

  • Glucagon

• Antibodies in:

  • Ruminants

  • Sows

  • Cats

  • Dogs

What hormones are made by the placenta?

• Progesterone

• eCG

• hCG

• Placental lactogen

What is unique about the mare placenta?

It forms endometrial cups, transient trophoblast/endometrial structures that produce eCG.

What makes eCG?

Endometrial cups in the mare placenta

Function of eCG

Supports accessory CL formation / luteal support to maintain pregnancy.
(Associated with pregnant mare serum gonadotropin activity)

What makes hCG?

Trophoblast cells of the chorion

What does hCG do?

• Sustains corpus luteum

• Promotes trophoblast growth

• Promotes placental development

What is placental lactogen?

Placental hormone involved in:

• Stimulates fetal growth (somatotrophic effects)

• Stimulates mammary gland development (lactogenic effects)

Primary functions of progesterone in maintaining pregnancy

• Blocks myometrial contractions

• Stimulates endometrial gland secretion of nutrients in early pregnancy

What are some signs of preparation for parturition?

• Restlessness

• Solitary behavior

• Anxiety

• Udder swelling

• Vulvar dilation

• Relaxation of pelvic ligaments

At the end of pregnancy what are some things that are occurring?

• Progesterone block is removed

• Estrogen increases

• Cervical/uterine mucus production increases

• Relaxin increases

• Pelvic ligaments relax

• Myometrial contractions begin

• Fetus moves into birth canal

Understand the parturition cascade / be able to walk through it:

• Fetal/placental maturation near term initiates cascade

• Progesterone declines / progesterone block removed

• Estrogen rises

• Increased uterine/cervical mucus and lubrication

• Relaxin causes pelvic ligament relaxation

• Myometrial contractions increase

• Fetus enters birth canal

• Cervical pressure stimulates Ferguson reflex

• Oxytocin released from pituitary

• Oxytocin increases contractions

• Positive feedback continues until delivery

parturition cascade step 1

Fetal/placental maturation near term initiates cascade

parturition cascade step 2

Progesterone declines / progesterone block removed

parturition cascade step 3

Estrogen rises

parturition cascade step 4

Increased uterine/cervical mucus and lubrication

parturition cascade step 5

Relaxin causes pelvic ligament relaxation

parturition cascade step 6

Myometrial contractions increase

parturition cascade step 7

Fetus enters birth canal

parturition cascade step 8

Cervical pressure stimulates Ferguson reflex

parturition cascade step 9

Oxytocin released from pituitary

parturition cascade step 10

Oxytocin increases contractions

parturition cascade step 11

Positive feedback continues until delivery

What is relaxin and what is its role?

• Allows stretching/relaxation of pelvic ligaments

• Helps soften reproductive tract for delivery

What is the relationship between progesterone and estradiol at this time (relaxin produced)?

• Progesterone decreases

• Estradiol increases

This shift removes uterine quiescence and promotes contractions/lubrication.

What is the Ferguson reflex?

• Removal of the progesterone block → estrogen → myometrial contractions

• This pushes the fetus against the cervix

• Initiates a neuroendocrine reflex

  • stimulates the posterior pituitary to release

oxytocin.

• Oxytocin travels through the bloodstream

  • interacts with the myometrium to increase

contractions.

Stages of Parturition, Stage 1

Cervical Dilation / Preparation

• Myometrial contractions

• Cervical dilation

• Relaxation of pelvic ligaments

• Behavioral changes (restless, pacing, anxiety)

• Udder swelling / vulvar dilation

• Fetus enters birth canal

• Usually longest stage
  Typical Duration: Variable by species

Stages of Parturition, Stage 2

Fetal Expulsion

• Strong abdominal and myometrial contractions

• Placental membranes rupture

• Fluid discharge

• Delivery of fetus

• Umbilical cord broken/bitten

• Relatively rapid stage

Stages of Parturition, Stage 3

Placental Expulsion

• Expulsion of fetal membranes/placenta

• Release of chorionic villi from uterus

• Brought about by vasoconstriction of villi arteries

• Retained placenta if unsuccessful

Define the puerperium period

The physiological and anatomical changes that occur after parturition in the female reproductive tract to repair and involute uterine tissue so conception and a new pregnancy can occur.

What is the overall goal of the puerperium period in livestock species?

To return the reproductive tract to a fertile, non-pregnant state and restore ovarian function.

Why is minimizing the interval between parturition and conception important?

Because pregnancy is a key driver of livestock productivity, minimizing days open maximizes producer productivity.

What is uterine involution?

The return of the uterus back to normal size, shape, and tone postpartum.

What major changes occur in the uterus during involution?

• Uterus decreases in size

• Tissue remodeling/repair occurs

• Endometrium is repaired

• Cervix remodels and closes

• Lochia and debris are expelled

What happens to uterine size?

It dramatically decreases postpartum.

What happens to uterine tissue?

It undergoes remodeling and involution/repair.

What happens to the endometrium?

It is repaired/regenerated.

What happens to the cervix?

It remodels and returns to a rigid, closed state.

What role do myometrial contractions play immediately after parturition?

• Expel fluids/tissue debris

• Compress uterine vasculature to reduce hemorrhage

• Reduce uterine size

What is expelled from the uterus during this time?

Lochia — blood, tissue, and fetal fluids.

Why are these contractions important? (myometrial)

• Prevent hemorrhage

• Help uterine involution

• Clear uterine contents/debris

• Reduce contamination/infection risk

What key events must occur for return to fertility?

• Uterine involution

• Endometrial repair

• Cervical closure

• Resumption of ovarian activity

• Elimination/minimization of uterine contamination

How does uterine size change over time postpartum?

It progressively decreases over days/weeks postpartum.

What does this indicate about tissue remodeling?

That extensive uterine involution and repair are occurring postpartum.

How long does uterine involution take?

Species dependent

Examples:

• Mare: 21–28 d

• Beef cow: 30 d

• Dairy cow: 45–50 d

• Sow: 28–30 d

• Woman: 40–45 d

Does lactation influence return to ovarian cyclicity?

Yes — lactation can inhibit ovarian activity/postpartum cyclicity in several species.

Define Metritis

• Bacterial infection of all layers of the uterus.

• Associated with systemic illness.

• Can range from mild to fatal.

Define Endometritis

Infection of only the endometrium.
Very common postpartum, especially in cattle.

Difference Between Metritis and Endometritis

• Metritis: Entire uterine wall infected + systemic illness

• Endometritis: Endometrium only, usually localized

How do these conditions impact animal health?

• Reduced appetite

• Reduced milk yield

• Can cause systemic illness/severe disease

How do they impact fertility?

• Delay ovulation

• Reduce heat behavior

• Extend interval between ovulations

• Reduce pregnancy rates

How do they impact productivity?

• Increased days open

• Reduced reproductive efficiency

• Lower milk/meat production

• Potential culling/removal from herd

What is pyometra?

Accumulation of purulent/infected fluid (pus) within the uterus.

What is occurring within the uterus during pyometra?

Pus/infectious exudate accumulates within a closed uterus/cervix.

Why is the postpartum period high-risk for disease?

• Uterus is damaged/open after parturition

• Large bacterial contamination risk

• Tissue remodeling is occurring

• Cervix remains temporarily open

How does postpartum disease affect subsequent pregnancy success?

It significantly reduces fertility and lowers subsequent pregnancy success due to delayed cyclicity and poor uterine environment.

Define lactation

The capacity of an animal to produce milk through the mammary gland to support the development of the newborn offspring.

Why is lactation closely tied to reproduction?

Many endocrine events that drive lactation after parturition are initiated during gestation by hormones secreted by the placenta

Why is timing of lactation relative to parturition important?

Milk/colostrum must be available immediately after birth to nourish the neonate and provide immune protection.

Mammary Gland Development, Fetal Stage

• Mammogenesis begins during fetal development

• Mammary ridge develops

• Primary mammary bud forms

• Secondary mammary bud forms

• Canalization occurs

• Duct system and myoepithelial cells form

Mammary Gland Development, Prepubertal Stage

• Isometric mammary gland growth

• Grows at same rate as body

Mammary Gland Development, Pubertal Stage

• Allometric mammary gland growth

• Growth faster than rest of body

• Driven by repeated estrous cycle hormone exposure

Mammary Gland Development, Pregnancy Stage

• Major ductal and alveolar development

• Final preparation for milk production
  (Occurs under pregnancy hormone stimulation.)

What is the mammary ridge?

• Thickened epidermal tissue that gives rise to the mammary gland

• Position is species dependent

What role does mammary ridge play?

It determines location/number of mammary glands in each species.

How does mammary gland positioning differ between species?

Species vary in location and number of mammary glands along the mammary ridge.