Lecture 1-4

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Parturition

expulsion of the fetus and placenta from the uterus (“labor”).

What are the three stages of parturition?

1. Myometrial Contractions and Cervical Dilation 

2. Expulsion of the Fetus 

3. Expulsion of the Placenta

Write the steps are parturition from longest time to shortest time

Longest: Myometrial Contractions and Cervical Dilation 

Expulsion of placenta 

Shortest: Expulsion of Fetus 

Why does the expulsion of the fetus need to take the shortest amount of time?

fetal hypoxia 

Myometrial Contractions

• Only occurs after removal of progesterone block

• Stimulated by PGF2a, Oxytocin, and E2

• High E2 to P4 ration promotes contractions

• Ferguson Reflex

Ferguson Reflex 

pressure on cervix by fetus stimulates release of oxytocin which will bind to its receptors to simulate myometrial contractions. 

Draw a diagram explaining Fetal Hypothalamo-Pituitary-Adrenal Axis

1. Hypothalamus

2. CRH

3. Anterior Pituitary

4. ACTH

5. Adrenal Gland

6. Fetal Cortisol

Draw a diagram explaining how fetal coritsol induced parturition

Water Breaking 

• head and feet of fetus push on amnion/allantois, rupturing the membranes 

• Provides more lubrication

Fetal Hypoxia

• when fetus is deprived of O2 in birth canal

• stimulates fetal movement which stimulates uterine contractions

How is the placenta released?

chorionic villi are released by vasoconstriction of villi arteries

How is hemorrhaging reduced?

maternal vasoconstriction 

Dystocia

difficult birth

Why might dystocia occur?

• large fetus

• failure of cervical dilation

• abnormal presentation of the fetus

• Multiple births

What are some “solutions” to dystocia?

1. Caesarion Section

2. Symphysiotomy 

What are the three ultimate goals of pregnancy hormones?

1. Growth of endometrial epithelium - histotrophs

2. Proliferation of myometrium

3. Development of mammary glands for lactatation

What hormones is required for early embryonic development?

Progesterone

What does progesterone do in pregnancy?

• Established uterine quiescence 

• Inhibits estrogen and oxytocin receptor formation 

What are the two sources of Progesterone during pregnancy?

1. Corpus Luteum - early source of P4

2. Placenta - in some species, it takes over as primary source for P4

What hormone rises rapidly at the end of pregnancy (gets things “ramped up”)?

Estrogens

What does estrogen do in pregnancy?

• Stimulates estrogen and oxytocin receptor formation

• Participate in uterine tract motility

• Cervical Mucus

• Stimulates endometrial, myometrial, and mammary growth

Does estrogen rise rapidly at the end of pregnancy in women?

No it rises throughout the entire gestation period 

Human Chorionic Gonadotropin (hCG)

• pregnancy-specific hormone

• has strong LH activity (binds to LH receptors)

• prevents luteal regression

• what human pregnancy tests look for

Equine Chorionic Gonadotropin (eCG)

• pregnancy-specific hormones

• produced by chorion in endometrial cups

• produced at attachment

• Has LH and some FSH-like activity

• Accessory Corpora Lutea → produced P4

• Causes luteinization of ovarian follicles

Placental Lactogen

• related to growth hormones and prolactin

• assists in mammary and fetal growth

• Binds to binucleate giant cells

BioPRYN-Lab

cow pregnancy test that looks for Pregnancy Specific Protein B (PSPB).

IDEXX

cow pregnancy test that looks for other pregnancy-associated glycoproteins

Relaxin

• relaxes pelvis and cervix

• produced by either placenta or corpus luteum (depends of the species)

What are four factors that can influence fetal growth?

1. Thyroid Hormones 

2. Insulin

3. Growth Hormone

4. Alpha-Fetoprotein 

Alpha-Fetoprotein

protects female brain from defeminization

When does majority of fetal growth take place?

the last trimester

Thyroid Hormones

skeletal and muscle development

Insulin

increased energy substrate and placental growth

Growth hormone 

stimulated fetal growth

What is the main goal of MRP?

to prevent corpus luteum destruction

When does maternal recognition in farm animal occur?

Before strong attachment of the conceptus.

How does MRP work in cows and sheep?

Signal: IFN-t from conceptus

Target: Uterine endometrium

Mechanism:  inhibits estrogen and oxytocin receptor formation 

Timing: ~ day 12 (sheep); ~ day13-21 (cows)

How does MRP work in horses?

Signal: Unknown; conceptus patrols uterus multiple times a day to trigger MRP

Target: Uterine Endometrium

Mechanism: Diminishes PGF2a production 

Timing: ~ day 14-16

How does MRP work in sows?

Signal: Estrogen

Target: Uterine Endometrium

Mechanism: alters direction of PGF2a from uterine vein to uterine lumen where it is destroyed 

Timing: ~ day 8-12

How does MRP work in women?

Signal: Human Chronic Gonadotropin (hCG)

Target: Corpus Luteum

Mechanism: hCG binds to LH receptors and overrides PGF2a activity by stimulating P4 production. 

Timing: ~ day 7-8

What are the three germ layers that form and what is their function?

1. Ectoderm - mammary glands

2. Mesoderm - repro system

3. Endoderm - primordial germ cells

What are the four Placental Membranes?

1. Chorion

2. Yolk Sac

3. Amnion

4. Allantois 

Yolk Sac

• degenerates earlier in mammals 

• source of blood cells 

• source of primordial germ cells 

Amnion

• Non-vascular; fluid-filled (fluid is produced by the fetus)

• Protects the fetus by providing a cushion 

Allantois

• Fluid-filled sac that collects waste from the embryo

• Contains blood vessels connecting fetal and placental circulation

• Eventually fuses with the chorion to form the allantochorion

Chorion

• Outermost layer 

• Provides attachment to the uterus

Draw a diagram of the 4 layers of the placental membranes

yee

What is the purpose of the umbilical cord?

infiltrates the chorion to form the vascular link between mother and fetus

What is the “free-living” period?

• time before the placental membranes form

• loose attachment between mother and fetus 

What is the placenta?

endocrine organ of highly vascular contact between mother and conceptus

What are the two types of Placentation?

1. Invasive (Implantation)

2. Non-Invasive (Attachment)

What is the invasive (implantation) placentation?

• embryo invades endometrium and develops in the endometrium 

• “Interstitial”

• ex. humans

What is the non-invasive (attachment) placentation?

• chorion and endometrium make physical contact via interlocking microvilli

• “Superficial”

• ex. Farm Animals 

What are the four types of placenta?

1. Diffuse

2. Zonary

3. Cotyledonary

4. Discoid

Diffuse Placenta

• Least invasive attachment

• Chronic villi are distributed over the entire surface of the endometrium

• ex. Pigs, Horse

Zonary Placenta 

• primary region of exchange is a band near the middle of the conceptus 

• ex. dog, cat 

Cotyledonary

• Non-invasive; chronic villi restricted to cotyledons

• Cotyledons and caruncles attach, creating a placentome

Cotyledon

specialized areas on fetal placental membrane

 Caruncles 

maternal specialized regions on uterus to which cotyledons attach 

Discoid

• Primary region of exchange is a central disc

• Endometrial epithelium grows over placenta

• Bidiscoid = 2 central discs

• ex. primates, rodents

Epitheliochorial

when 6 layers are separating fetal and maternal blood (less invasive)

Hemochorial 

when 3 layers are separating fetal and maternal blood (more invasive)