20. Pregnancy, Development, and Lactation

Comprehensive vocabulary flashcards covering gamete maturation, fertilization, embryological stages, placental types, fetal circulation, gestation, parturition, and lactation.

Capacitation

The final maturation of spermatozoa that allows them to successfully penetrate the ovum wall, triggered by proteins secreted by the uterus once sperm enter the superior reproductive tract.

Acrosome

A membrane-like structure located at the superior end of the spermatozoon that degrades during capacitation, releasing withheld enzymes needed to penetrate the ovum wall.

Polyspermy Block (Cortical Reaction)

The process occurring immediately after a spermatozoon deposits its contents into the ovum, wherein the ovum degrades all surrounding sperm-binding receptors to seal off entry to other sperm.

Zygote

A single diploid cell created when the enlarged male pronucleus and female pronucleus fuse via a newly formed mitotic spindle, marking successful fertilization.

Cleavage Stage

The developmental phase immediately following fertilization where the zygote rapidly divides through mitosis without meiosis.

Morula

A developmental stage named after a mulberry, characterized by a cluster of multiplied, tiny cells within the zygote, marking the completion of the cleavage stage.

Blastocyst

A developmental structure formed when morula cells migrate toward outer walls to produce a central hollow cavity; contains the inner cell mass and outer trophoblast.

Inner Cell Mass

The internal cluster of cells within the blastocyst that will eventually differentiate and develop into the embryo.

Trophoblast

The outer cellular layer of the blastocyst that eventually develops into the placenta and the amniotic sac.

Implantation

The process by which the blastocyst attaches itself to the uterine wall, releasing hormones that maintain the hypothalamus-pituitary axis to prevent the loss of the endometrial lining.

Placenta

An organ composed of maternal and embryonic tissues that allows the exchange of nutrients and metabolic wastes between the fetal and maternal bloodstreams.

Diffuse Placenta

A placental attachment type in which attachment sites are spread evenly across the surface of the uterine lining; found in pigs, horses, and camelids.

Cotyledonary Placenta

A placental attachment type with multiple distinct attachment sites known as placentomes; found in ruminants including cattle, sheep, and goats.

Placentome

The structural unit of attachment in a cotyledonary placenta, composed of a fetal cotyledon and a maternal caruncle.

Cotyledon

The fetal portion of a placentome that embeds into the caruncles of the uterine lining to facilitate nutrient and gas exchange.

Caruncle

The maternal portion of a placentome found on the uterine lining that interlocks with the fetal cotyledon.

Zonary Placenta

A placental type where attachment points wrap around the amnion like a belt; commonly encountered in small animal clinics and present in dogs and cats.

Discoid Placenta

A placental attachment type characterized by a single, disc-shaped attachment site on the amnion; present in primates, rabbits, and rodents.

Umbilical Vein

The vessel that carries oxygenated blood from the placenta to the fetus, directed toward the fetal heart.

Umbilical Artery

The vessel that carries deoxygenated blood away from the fetal heart to the placenta for waste and gas exchange.

Portosystemic Shunt (PSS)

A fetal vascular channel that bypasses the non-functional liver to reenter systemic veins; failure to close by birth leaves toxins circulating in the body, commonly causing seizures in puppies and kittens.

Ductus Arteriosus

A fetal vessel connecting the pulmonary artery directly to the aorta to decrease blood volume reaching non-functional lungs; if it remains patent post-birth, it causes fainting episodes (syncope).

Gestation

The period of pregnancy during which the fetus develops, characterized by maternal hormonal surges, abdominal organ displacement, and up to a $40\%$ increase in maternal blood volume.

Parturition

The act of giving birth to offspring, divided into three stages: uterine/cervical contractions, delivery of the newborn, and delivery of the placenta.

Colostrum

The initial milk produced and released during lactation that is rich in nutrients and maternal antibodies, providing passive natural immunity to the newborn.

Meconium

The sticky, tar-like first feces passed by a newborn, composed of epithelial tissue, amniotic fluid, bile, and water accumulated within the intestinal tract during gestation.

Milk Let-Down

A neuroendocrine reflex stimulated by oxytocin released from the posterior pituitary, which contracts muscles to squeeze milk from teat storage regions into the teat sinuses for nursing.