Lecture 30 3/25/24 Flashcards by Danika Boltz

What are the two main roles of the placenta?

-transient organ of metabolic exchange
-transient endocrine organ

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What are the two main components of the placenta?

-fetal component derived from chorion
-maternal component derived from modifications of uterine endometrium

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What is the chorion?

outermost layer of placenta in direct contact with endometrium

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What is the allantochorion?

fusion of allantois and chorion

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What is the allantoic cavity?

fluid filled cavity containing liquid waste from the embryo that contributes to the umbilical cord

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What is the yolk sac?

transient embryonic membrane the contributes to the umbilical cord

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What is the amnion?

fluid filled inner layer that protects the embryo

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Which structures give rise to the chorion and amnion?

-trophoblast
-primitive endoderm and mesoderm

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What are the components of the blastocyst?

-inner cell mass
-trophoblast
-blastocoele

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What happens to the yolk sac as the conceptus develops?

it regresses in size

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What is the functional unit of the fetal placenta?

chorionic villus

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What is the role of the chorionic villus?

to protrude away from the chorion and interdigitate with the uterine endometrium

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What are the characteristics of diffuse placentas?

-many closely spaced villi distributed over the entire surface of the chorion
-uniform distribution
-pigs and mares

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Why is the mare unique, despite being classified as having a diffuse placenta?

the chorionic villi are concentrated in specialized microzones known as microcotyledons

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What are the characteristics of zonary placentas?

-band-like zone of chorionic villi
-prominent, broad transfer zone that allows for exchange
-pigmented zone consisting of small hematomas that allows for iron transport
-transparent zone with poor vascularity that allows for absorption of materials from uterine lumen
-dogs and cats

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What are the characteristics of cotyledonary placentas?

-numerous button-like structures called cotyledons
-placentome consists of a fetal cotyledon and a maternal cotyledon from a caruncle
-ruminants

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What are the characteristics of discoid placentas?

-form a regionalized disc
-one or two distinct adjacent discs
-primates and rodents

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What are the characteristics of an epitheliochorial placenta?

-least intimate
-both endometrial epithelium and chorionic villi epithelium are intact
-six layers of tissue
-ruminants, sows, mares

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How do ruminant epitheliochorial/syndesmochorial placentas differ?

-endometrial epithelium transiently erodes and regrows
-allows for intermittent exposure to maternal capillaries
-contain binucleate giant cells

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What are the functions of the binucleate giant cells in ruminant placentas?

-transfer complex molecules from fetal to maternal placenta
-secrete placental lactogen and pregnancy specific protein B
-site of steroidogenesis

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What are the characteristics of an endotheliochorial placenta?

-complete erosion of endometrial epithelium and underlying interstitium
-maternal capillaries are directly exposed to chorion epithelial cells
-five layers of tissue
-dogs and cats

What are the characteristics of a hemochorial placenta?

-chorionic epithelium in direct apposition to maternal pools of blood
-nutrients and gases exchanged directly from maternal blood
-three layers of tissue
-primates and rodents

Which methods of transport are utilized in placental exchange?

-simple diffusion
-facilitated transport
-active transport
-endocytosis

What is the major source of energy for the fetus?

glucose derived from maternal circulation

Which proteins are able to cross the placental barrier?

immunoglobulins

Which placenta types allow for the transfer of immunoglobulins?

-hemochorial -endotheliochorial

Which compounds must the fetus synthesize from building blocks from the dam?

-proteins -lipids

Which molecules can easily cross the placenta?

-large peptide hormones -water-soluble vitamins -nutrients -toxic substances -viruses

Why is progesterone important for early embryonic development?

-stimulates elevated secretion from endometrial glands -inhibits myometrial contractions

What are the two sources of progesterone during pregnancy?

-CL first -placenta later

When does the placenta produce estrogens?

second half of gestation

What are the characteristics of endometrial cups?

-found in mares -trophoblastic and endometrial in origin -produce equine chorionic gonadotropin/eCG -sloughed into uterine lumen after day 60 of gestation

What are the roles of equine chorionic gonadotropin?

-provides a stimulus for maintenance of the primary corpus luteum -responsible for controlling the formation and maintenance of supplementary corpora lutea

What are the characteristics of human chorionic gonadotropin?

-found in primates -originates from trophoblastic cells -secreted as soon as blastocyst hatches from zona pellucida -maintains CL -can cause ovulation in non-primate females

What are the characteristics of relaxin?

-originates from both ovary and placenta during parturition -inhibits uterine contraction -promotes rupture of fetal membranes -relaxes cervix, vagina, and pelvic ligaments

What are the roles of placental lactogen/somatomammotropin?

-lactogenic activity/promotes mammary function -somatotrophic action/promotes fetal growth

Why is the fetal hypothalamic-pituitary-adrenal axis obligatory for initiating parturition?

-fetus becomes stressed due to limited space in uterus -stress causes fetal ant. pituitary to release ACTH -ACTH stimulates fetal adrenal cortex to release corticoids -corticoids decrease progesterone and remove myometrial "progesterone block," allowing contractions -corticoids increase estrogen and lead to increased repro tract secretions to lubricate birth canal

What is the importance of pressure on the cervix due to myometrial contractions?

-activates pressure-sensitive neurons that synapse with oxytocin-producing neurons in hypothalamus -oxytocin facilitates myometrial contractility initiated by estradiol and PGF2a

What are the functions of estradiol in parturition?

-initiates secretory activity of repro tract/cervix to wash out cervical seal and lubricate birth canal -stimulates myometrial contractions

What are the functions of PGF2a in parturition?

-abolish progesterone block -stimulate myometrial contraction

What happens when the fetus becomes hypoxic in the birth canal?

-promotes fetal movement -in turn, promotes further myometrial contraction

What are the three stages of labor?

1: initiation of myometrial contractions; fetus at cervix 2: active labor, expulsion of fetus 3: expulsion of fetal membranes

What are the characteristics of parturition stage 1?

-indistinct onset -duration of 1-4 hours -myometrial contractions increase -fetus repositions

What are the clinical signs of parturition stage 1?

-sweating -urination/defecation -restlessness -Flehmen response (mares)

What are the characteristics of parturition stage 2?

-dilation of cervix -rupture of allantochorion and amnion at vulva -abdominal contractions increase to maximum rate -around 20 minutes -abnormally long stage results in dystocia/difficult birth

What are the causes of dystocia?

-excessive fetal size -failure of fetal rotation -multiple births in monotocous species

What are the characteristics of parturition stage 3?

-requires chorionic villi to become dislodged from maternal side of placenta -release is due to powerful vasoconstriction of arteries in the villi

How can pregnancy be diagnosed?

-palpation -imaging -endocrine testing

Why is it critical that the neonate ingest colostrum?

-contains high levels of immunoglobulins -immunoglobulins are absorbed in gut mucosa and establish temporary passive immunity

Which type of placenta requires neonates to ingest colostrum in order to get immunoglobulins?

epitheliochorial

How does colostrum compare to normal milk?

-twice as much dry matter -high lipid and protein -rich in vitamins -10x higher in immunoglobulins