Test yourself ?s Chpt. 18 Pregnancy, Development and Lactation Flashcards Preview

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Flashcards in Test yourself ?s Chpt. 18 Pregnancy, Development and Lactation Deck (14):

Why is the timing of copulation so important? How is the precise timing accomplished?

The spermatozoa must arrive at the oviducts before the ovum does so they have time to undergo capacitation, a process that enhances their fertility.
Breeding is only allowed by the female during the estrous, or heat, period.
This helps ensure that the spermatozoa arrive at the oviducts first and have time to undergo capacitation before the ovum shows up ready to be fertilized.


Describe what happens to a zygote between fertilization and implantation.

The male and female pronuclei quickly join together to restore the diploid chromosome number and determine the unique genetic makeup of the offspring.
The zygote begins to divide rapidly by the normal process of mitosis. This rapid division is called cleavage.
Implantation is the means by which the blastocyst makes itself a home by attaching itself to the lining of the uterus (the endometrium).


Why is the placenta so important to a successful pregnancy?

It supplies oxygen and nutrients and carries wastes away must be developed. It is the life-support system.


Describe the relationship between the fetus and the amniotic and allantoic sacs of the placenta.

The layer immediately around the fetus is called the amnion.
It forms a sac around the fetus called the amniotic sac. The fetus floats in amniotic fluid inside this sac. Surrounding the amniotic sac is another layer called the allantois, which forms the fluid-filled allantoic sac. The outside of the allantoic sac is covered by the chorion, which attaches to the uterine lining. The chorion is linked to the fetus by the umbilical cord.


Describe the main structures that make up the umbilical cord and the function of each.

The umbilical cord is the link between the fetus and the nutrient and waste exchange structures of the placenta. It is a cordlike structure that contains blood vessels (the umbilical arteries and umbilical vein) and a drainage tube from the fetus' urinary bladder (the urachus).
Arteries: carry unoxygenated, waste-filled blood from fetus to placenta
Vein: carries nutrient- and oxygen-rich blood back from placenta to fetus
Urachus: tube that runs from cranial tip of fetus' urinary bladder through the umbilical cord to the allantoic sac to drain the watery fluid produced by fetus' kidneys


Which type of placental attachment to the uterus is the simplest and detaches most easily after parturition? Which is most complicated and often results in retention of the placenta?

Diffuse and Zonary attachment detach fairly easily after delivery.
Cotyledonary attachment is the most complicated type. The areas of attachment are small, separate and numerous.


What are the basic events of the three trimesters of pregnancy?

First trimester: Newly implanted zygote is getting itself organized and develops its life-supporting placenta. It is often referred to as an embryo.
Second trimester: It's now called a fetus and this period is called the fetal development period. Parts of fetus take shape and start differentiating. All body tissues, organs, and systems develop during this period.
Third trimester: Period of fetal growth. All parts of fetus grow dramatically.


Describe the three stages of labor.

First stage: Uterine contractions (muscle of the uterus = myometrium) press the membrane-covered fetus down against the cervix causing it to gradually dilate.
Second stage: Delivery of the newborn is accomplished by a combination of strong uterine and abdominal muscle contractions.
Third stage: Delivery of placenta (afterbirth). It separates from wall of uterus and is expelled by weaker uterine contractions.


Why is it important that uterine contractions continue after the fetus and placenta are delivered?

It gradually returns the uterus to its nonpregnant size through a process called involution.
The myometrium slowly continues to contract, squeezing the contents of the uterus out through the birth canal as the organ returns to its nonpregnant size. Pressure from the continued uterine contractions usually stops the bleeding relatively quickly.


Why does mastitis in one quarter of a dairy cow's udder not necessarily spread to the other three quarters?

They are completely separate units and each have their own milk-secreting systems and ducts leading down to their own teats.


Describe the suspensory apparatus of the udder.

The suspensory system consists of a slinglike arrangement of ligaments that run down the center and around the sides of the udder. The medial suspensory ligament contains many elastic fibers so that it can stretch. It passes down the center between the left and right halves of the udder. The lateral suspensory ligaments are composed largely of strong but relatively inelastic collagen fibers. They pass down and around the lateral sides of each half of the udder. The strong lateral ligaments provide firm support for the udder, and the elastic medial ligament acts as a shock absorber for the udder as the animal moves around.


Why don't the mammary glands of male animals usually develop or secrete milk?

Hormones secreted at the time of puberty stimulate the mammary glands growth and development.
The necessary hormones for mammary gland development usually don't exist in male animals.


Describe the importance of colostrum to the health of a newborn animal.

It contains larger amounts of proteins, lipids, and amino acids than milk and also contains high levels of various essential vitamins. It supplies important nutrients to the newborn and has a laxative effect that helps clear the dark, sticky meconium from the newborn's intestinal tract.
The most critical of colostrum's roles is the transfer of what is called passive immunity from the dam to the newborn. Among the proteins in colostrum are high level of immunoglobulins, also called antibodies, that are an important part of the body's defense against infection.


Describe how nursing or milking causes milk letdown and also helps sustain lactation.

The key is continued physical stimulation of the teat or nipple, combined with regular removal of milk from the gland. These activities send sensory nerve impulses to the brain. From there nerve pathways lead to the hypothalamus, which stimulates the anterior pituitary gland to continue its production of the hormones that keep lactation going.
It also causes the hypothalamus to release the hormone oxytocin from the posterior pituitary gland. The oxytocin travels to the mammary gland and causes musclelike myoepithelial cells around the alveoli and small ducts to contract. This squeezes milk down into the large ducts and sinuses, where it can be removed by nursing or milking.