Pregnancy, Development, and Lactation

What is copulation?

The mating process that occurs when the female allows breeding during heat.

Where is semen deposited during ejaculation?

In the upper portion of the vagina.

What happens to sperm once they enter the female reproductive tract?

They actively swim toward the oviducts.

What hormone helps rapidly transport sperm through the female reproductive tract?

Oxytocin.

What does oxytocin cause during sperm transport?

Contractions of the uterus and oviducts.

Why must sperm reach the oviduct before the ovum?

Sperm need time to undergo capacitation.

What is capacitation?

A series of changes sperm undergo in the female reproductive tract that increases their ability to fertilize an ovum.

What does capacitation cause to be released?

Digestive enzymes from the sperm's acrosome.

What do the enzymes from the acrosome do?

Help the sperm penetrate the layers surrounding the ovum.

How many sperm normally penetrate the ovum's cell membrane?

Only one.

What does the sperm deliver into the ovum?

Its genetic material.

What is the male pronucleus?

The nucleus of the sperm after fertilization.

What is the female pronucleus?

The nucleus of the ovum after fertilization.

What happens when the male and female pronuclei join?

They restore the diploid chromosome number and form a zygote.

What is cleavage?

Rapid cell division of the zygote without an increase in overall size.

What happens to the zygote during cleavage?

The number of cells increases while the overall size remains about the same.

What is a morula?

A solid mass of cells that resembles a raspberry.

What is a blastocyst?

A hollow ball of cells with a bump on one side that is ready to implant.

Where does the zygote move during early development?

Down toward the uterus.

What is implantation?

The process where the blastocyst attaches to the lining of the uterus.

How does the blastocyst implant?

Enzymes from the blastocyst dissolve a small pit in the uterine lining where it attaches.

What is the amnion?

The membrane that surrounds the fetus and forms the amniotic sac.

What is inside the amniotic sac?

Amniotic fluid and the fetus.

What is the allantois?

A layer surrounding the amniotic sac that forms the allantoic sac and accumulates waste.

What is the chorion?

The outer layer that covers the allantois, attaches to the uterus, and connects to the fetus through the umbilical cord.

What is a diffuse placental attachment?

Attachment spread over the entire surface of the placenta and uterine lining.

Which animals have diffuse placental attachments?

Mares and sows.

What is the advantage of diffuse attachment?

Placental separation is relatively easy.

What is a cotyledonary attachment?

Many small, separate attachment sites.

What is a cotyledon?

The attachment site on the surface of the placenta.

What is a caruncle?

The attachment site on the surface of the uterine lining.

What is a placentome?

The combined cotyledon and caruncle structure.

What is a zonary attachment?

A belt-shaped attachment that encircles the placenta.

Which animals have zonary placentas?

Dogs and cats.

What is a discoid attachment?

A single disk-shaped area where the placenta attaches to the uterus.

Which animals have discoid placentas?

Primates, rabbits, and rats.

What is gestation?

The time from fertilization of the ovum to delivery of the newborn.

What are the three trimesters of pregnancy?

First = embryonic period; second = fetal period; third = fetal growth period.

What happens during the first trimester?

The embryonic period occurs and the placenta develops.

What happens during the second trimester?

Body tissues, organs, and systems develop.

What happens during the third trimester?

The fetus primarily undergoes growth.

Average gestation length of a cat?

63 days.

Average gestation length of a dog?

63 days.

Gestation length of a cow?

280 days.

Gestation length of a horse?

336 days.

Gestation length of a goat?

151 days.

Gestation length of a pig?

115 days.

Gestation length of a rabbit?

31 days.

Gestation length of a rat?

21 days.

Gestation/incubation length of a chicken?

22 days.

What is parturition?

The birth process.

What happens to progesterone before parturition?

Progesterone levels decline.

What fetal hormones help initiate parturition?

Glucocorticoid hormones from the fetal adrenal glands.

What do fetal glucocorticoids stimulate?

An increase in estrogen and release of prostaglandin F2α.

Where is oxytocin released from?

The posterior pituitary gland.

What does oxytocin do during parturition?

Stimulates the myometrium to contract.

What happens during Stage 1 of labor?

Uterine contractions begin and the cervix gradually dilates.

What causes the cervix to dilate during Stage 1?

The myometrium contracts and presses the fetus against the cervix.

What indicates Stage 2 of labor?

Delivery of the newborn.

What causes delivery during Stage 2?

Strong uterine and abdominal muscle contractions.

What usually happens to the amniotic and allantoic sacs before delivery?

They rupture.

What indicates Stage 3 of labor?

Delivery of the placenta.

How is the placenta expelled during Stage 3?

It separates from the uterine wall and is expelled by weaker uterine contractions.

What is uterine involution?

The gradual return of the uterus to its non-pregnant size.

What happens to the endometrium during involution?

It sloughs into the uterine lumen at the sites of placental attachment.

What does the myometrium do during involution?

Continues mild contractions to move remaining uterine material through the birth canal.

How long can uterine involution take?

A few weeks to a month or more.

What are mammary glands?

Skin glands that produce colostrum and milk.

Are mammary glands present in males?

Yes, but males do not produce milk.

How many mammary glands/quarters does a cow have?

Four.

Are the cow's four quarters connected?

No. They are completely separate units.

What does each quarter have?

Its own milk-secreting system and separate teat.

What is the medial suspensory ligament made of?

Many elastic fibers.

Where is the medial suspensory ligament located?

Between the left and right halves of the udder.

What are the lateral suspensory ligaments made of?

Strong, inelastic collagen fibers.

Where are the lateral suspensory ligaments located?

They pass down and around the lateral sides of each half of the udder.

What are mammary alveoli?

Sac-like structures made of cells that secrete milk into the alveolar ducts.

What do mammary alveoli look like when arranged together?

Clusters of grapes.

Where do smaller alveolar ducts lead?

They join to form larger ducts.

Where do the largest ducts empty?

Into the gland sinus located just above the teat.

Where does milk accumulate?

In the gland and teat sinuses.

What causes mammary glands to develop?

Hormones produced at puberty.

What two hormones directly encourage mammary gland development?

Prolactin and growth hormone.

What hormones encourage development of mammary alveoli and duct systems?

Estrogen and progesterone.

What is colostrum?

A pre-milk secretion produced by the mammary glands.

What does colostrum contain large amounts of?

Proteins, lipids, amino acids, and vitamins.

What is one digestive effect of colostrum?

It acts as a laxative to help clear meconium from the newborn's intestinal tract.

What is passive immunity?

The transfer of preformed antibodies from the dam to the newborn.

Why is colostrum especially important in newborn foals?

It provides passive immunity.

What stimulates continued lactation?

Physical stimulation of the teat/nipple and regular removal of milk.

What happens if milk is not regularly removed?

Hormonal stimulation decreases and pressure in the mammary gland increases, causing lactation to gradually cease.

Where does milk initially accumulate?

In the mammary alveoli and small ducts.

What triggers milk letdown?

Physical stimulation of the nipple or teat.

What hormone causes milk letdown?

Oxytocin.

Where is oxytocin released from?

The posterior pituitary.

What does oxytocin do during milk letdown?

Causes myoepithelial cells around the alveoli and small ducts to contract.

What is the result of myoepithelial cell contraction?

Milk is pushed into the larger ducts and sinuses.