Animal Reproduction Exam 3 (Rutgers)

Major sequence of events following deposition of sperm in female tract

1. immediate transport

2. cervix

3. uterus

4. oviduct

5. fertilization

immediate transport of sperm

retrograde loss, phagocytosis, entrance into cervix/uterus

15 minutes

average time between coitus and arrival of sperm in oviducts

1.5-6 days

average fertile life of sperm

8-24 hours

average fertile life of egg

sperm loss is dependent on

1. physical nature of the ejaculate

2. phagocytosis

3. contractility of reproductive tract

4. cervical secretions and the ability of sperm to navigate through two types of cervical mucus

Fallopian tube/salpinx

paired muscular tubes containing: infundibulum (fimbriae, cilia-oocyte cumulous complex 'pick-up'), ampulla, isthmus

ampulla

site of fertilization in the oviduct

site of sperm deposition: cervix

pigs, horses, camelids

site of sperm deposition: vagina

cow, sheep, rabbit, rodents, primates, dogs & cats

pig/horse ejaculate

final fraction highly viscous "rice pudding"

rodent ejaculate

coagulating protein in semen forms a vaginal plug = mating marker

phagocytosis

neutrophils (leukocytes or WBCs), during estrus, after insemination, first line responders to infections and attacks "foreign" proteins==> causes sperm loss & prevents tract infection

contractility of the reproductive tract

Estradiol (high at insemination), oxytocin (released at coitus), prostaglandins (f2a and E1) ==> causes increased motility of oviduct and uterus

Administering Phenylephrine or Ergonovine

reduces retrograde sperm loss (increased % fertilization)

Sulfomucin

high viscosity, apical barrier to sperm; eliminates non-motile sperm

Sialomucin

low viscosity, in basal areas of cervical crypts sperm enter --> reservoir = silo; sperm easily swims through

artificial insemination in uterine body vs. uterine horn

no difference in cumulative % recovered sperm

pig/camelids ejaculation

seminal fluid can induce ovulation

humans & bull ejaculation

seminal fluid has pH ~6.7-7.4; neutralizes vaginal acidity (pH~4)

AI in cervix vs. uterine horn

much more sperm recovered in cervix

intracervical insemination

used in pigs, within the cervix

transcervical insemination

used in cows, bypass the cervix

What kills sperm?

low pH, mucins, neutrophils, retrograde loss, sperm-sperm competition

What helps sperm?

seminal fluid pH, ovulation trigger, smooth muscle stimulants, sheer numbers

Chemotaxis (marine species)

resact- sea urchin peptide emitted by the egg, increases sperm motility

chemotaxis (mammals)

sperm attracted to follicular fluid, eggs & cumulous complexes, dependent on capacitation

thermotaxis

sperm can orient in the thermal gradient within the oviduct, sperm becomes hyperactive at increased temperatures (40C)

Sperm maturation

series of changes that render sperm competent to fertilize the egg, sperm ____ in the epididymis but require an extra step to fertilize the egg

Capacitation (steps)

1. epididymal- surface proteins and CHO + seminal plasma

2. ejaculated- seminal plasma coats the surface proteins + female tract

3. ______ - seminal plasma coating and some surface proteins removed

capacitation (requirements)

1. occurs in the female tract

2. NOT species specific

3. can be induced in vitro

4. reversible: _____ sperm + seminal plasma = sperm de_______

capacitation

sperm proteins removed from the sperm head

Why is capacitation important?

holds sperm in check, prevents penetration of epididymis, vaginal wall, as seminal plasma is removed, sperm gain ability to penetrate the oocyte

post-capacitation sequence of events leading to fertilization

1. hyperactive motility

2. binding to zona pellucida

3. acrosomal reaction

4. penetration of ZP

5. sperm-oocyte membrane fusion

6. sperm engulfed

7. decondensation of sperm nucleus

8. formation of mature male pronucleus

sperm hyperactivity in the oviduct

motility patterns change from linear movement to frenzied motion in the oviduct, facilitates sperm-oocyte contact, controlled molecular reaction

sperm-egg recognition

vital for fertility, blocks polyspermy; ZP3 is the main receptor

acrosomal reaction

1. sperm PM contains 2 'receptor-like' regions

2. both bind to ZP3

3. ZBR: secures sperm

4. ARPR: initiates release of acrosomal enzymes

when does the acrosomal reaction occur?

1. sperm binds to ZP

2. acrosome rxn begins enzymatic drill thru the ZP leakage of acrosomal enzymes from the sperm head

3. penetration of the ZP: loss of acrosome outer membrane

4. sperm-oocyte fusion: sperm head penetrates oocyte plasma membrane

5. cortical reaction: exocytosis of cortical granules to harden the ZP, block to polyspermy

Fusion events

1. complete penetration

2. fusion begins

3. nucleus breaks apart

zona block

coritcal reaction creates barrier at ZP level

polyspermy

fertilization of oocyte by more than one sperm, resulting in embryo death

viteline block

cortical run can alter oocyte membrane, resulting in a _______ to prevent additional sperm fusion

after sperm/oocyte fusion

sperm nucleus "decondenses" (disulfide x-links reduced, chromosomes pair)

syngamy

moment of fertilization, fusion of male and female pronuclei, zygote formed

electrical

fast block to polyspermy in non-mammalian

cortical granules

slow block to polyspermy in mammals

embryo

early stages of development; ____ of all species appear similar

fetus

unborn young still within the uterus species recognizable

conceptus

products of conception

1. embryo (during embryonic stage)

2. embryo + extraembryonic membranes

3. fetus + placenta

prior to embryo attachment

1. development within the ZP

2. 'hatching' of the blastocyst

3. extraembryonic membrane formation

4. maternal recognition of pregnancy

totipotent

ability to give rise to a complete individual

preimplantation development

steps to blastocyst 'hatching'

1. as the ____ grows and fluid accumulates, pressure rises

2. trophoblast cells begin producing enzymes, ZP weakens

3. ____ begins to contract and relax in pulses

4. ZP ruptures- embryo is free-- floating in uterine lumen

SCNT

somatic cell nuclear transfer; source of embryonic stem cells

conceptus growth

occurs in cow, pig, sheep, spherical > tubular > filamentous *mare remains spherical

four extra embryonic membranes

chorion (1), amnion (1), yolk sac(2), allantois (4)

extraembryonic membranes originate from

trophoblast, mesoderm, embryo, endoderm

yolk sac

cavity formed by the endoderm, regresses as embryo develops, contributes blood cells, primordial germ cells

mesoderm

grows and surrounds yolk sac, pushes against the trophectoderm to form amniotic folds

chorion

fusion of mesoderm and trophectoderm, forms fetal site of placental attachment

amnion

fluid-filled sac formed by the chorion, surrounds and protects embryo

allantochorion

fusion of the two membranes from the allantois & chorion, fetal contribution to the placenta

allantois

develops from the embryonic gut and collects liquid wastes

maternal recognition of pregnancy signal

usually biochemical, may also be mechanical, species-specific ==> prevents luteolysis, maintains high P4

embryonic signal in cows and sheep

interferon-tau, secreted by embryonic trophoblast cells into the uterine lumen day 13-21 of pregnancy; decreases production of OT receptors (OT cannot stimulate PGF2a synthesis); promotes protein synthesis in gonads--> promotes implantation

embryonic signal in pigs

estradiol; causes exocrine secretion of PGF2a into the uterine lumen where it is destroyed;

also need a mechanical signal, otherwise PGF2a is secreted by one of the horns and pregnancy ends

embryonic signal in horses

use mechanical signals; conceptus migrates between horns, multiple contacts with endometrium

embryonic signal in primates/women

hCG (human chorionic gonadotropin)[inhibits luteolysis, LH-like] initially secreted 8-10 d post conception by blastocyst trophectoderm; as placenta forms, chorion cells produce hCG, basis for rapid immunoassay & pregnancy diagnosis

attachment

conceptus forms a close relationship with endometrium but does NOT embed in the uterine wall; occurs in all domestic species and monkeys

implantation

conceptus embeds in uterine wall in contact with vascular and connective tissue on all sides; occurs in higher primates (chimps & man), rodents (guinea pigs, hedgehogs, rat)

delayed implantation

blastocyst floats in uterine lumen until attachment/implantation; ensures young are born at the right time (usually spring); occurs in bears, roe deer, mink, weasels, badgers, seals, sea mammals

factors involved in delayed implantation

1. light or increasing day length stimulates implantation

2. lactation delays implantation

embryo transfer

all farm animals; embryos from a donor mother can be transferred to other females for development to term; benefits: amplify number of offspring that donor females with desired traits can produce

steps in embryo transfer

1. sync of recipients with donor

2. super ovulation of donor

3. inseminate donor with semen from genetically superior bull

4. recovery & identification of viable embryos (uterine flushing)

5. transfer of viable embryos into synchronized recipients

6. pregnancy detection/ birth of calf

window of uterine receptivity

limited period of time when the uterus is able to support blastocyst attachment and implantation

preceptive

uterus unresponsive blastocysts

receptive

ovarian P4 priming followed by estrogen

nonreceptive (refractory)

high estrogen

bruce effect

hilda ____ reported that exposure of early pregnant mice to a novel male induces implantation failure (~80% of loss)

blastocyst implantation

vulnerable to excretion of estrogens by novel males

bruce effect: steps

1. inc in E2 can result in implantation failure

2. males secrete E2 in urine in response to females

3. E2 in male urine can be absorbed byVMN in females and target the uterus

4. contributing to implantation failure

placenta

temporary relationship with uterus= significant advantage to conceptus; provides: adequate nutrition, protection from environmental danger

oviparous

egg laying

eutherian mammals

subdivision of mammals with a placenta

which orders of mammals do not have a placenta?

1. marsupials (kangaroos, koalas, etc.) 2. monotremes (platypuses)

chorionic villi

finger-like projections from surface of the chorion, interact with uterine endometrium, distribution of ____ can be used to classify type of placenta

Diffuse placenta

uniform distribution of chorionic villi

found in: sow, mare

greatest surface area

cotyledonary placenta

cotyledon= placental unit of trophoblastic origin (fetal)

placentome= point of interface

chorionic villi in clumps

found in: cattle, sheep, goats (ruminants)

zonary placenta

broad band around chorion near the middle of the conceptus, bordered by pigmented ring of small hematomas (blood clots of unknown function)

found in: cats, dogs

discoid placenta

characterized by presence of 1 or 2 disk-like structures on the chorion, discs contain chorionic villi

found in: primates, rodents

least surface area

placental classification

described by the number of layers of placenta separating maternal blood from fetal blood

prefix= maternal suffix=fetal

Epthileliochorial placenta

6 layers- 3 maternal, 3 fetal

least efficient, lack of intimate relationship offset by large surface area of diffuse placenta

found in: mare & sow

LEAST invasive

syndesmochorial placenta

5 layers: 3 fetal, 2 maternal

found in: ruminants

binucleate giant cells

unique to ruminant placenta, originate from the fetal trophoblast, migrate & invade maternal endometrial epithelium, transfer molecules from fetus to mom; secrete: placental lactogen, steroids, pregnancy specific protein B

Endotheliochorial placenta

4 layers: 3 fetal, 1 maternal

fetal chorionic epithelium in contact with maternal capillary

found in: cats & dogs

Hemochorial placenta

3 layers: fetal only

fetal chorionic epithelium in direct contact with maternal blood

found in: primates

Hemoendothelial placenta

1 layer: fetal endometrium

complete erosion of maternal layers, fetal capillaries in direct contact with maternal blood

found in: rabbit, rat, guinea pigs

MOST invasive

Placental exchange

simple diffusion (water, blood gases), active transport (pumps: sodium, potassium, calcium), facilitated diffusion (glucose [fetal energy source of mostly maternal origin], amino acids)

What WILL pass the human placental exchange?

steroids, RBCs, H2O soluble vitamins, minerals, immunoglobulins (exceptions), alcohol, drugs, bacteria, viruses (measles, HIV), metals (lead, mercury)

What will NOT pass the human placental exchange?

fat soluble vitamins, lipids, maternal proteins, large peptide hormones (TSH, ACTH, GH, insulin)