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VMP824 Physiology/Microanatomy 2 > Lecture 30 3/25/24 > Flashcards

Lecture 30 3/25/24 Flashcards

1
Q

What are the two main roles of the placenta?

A

-transient organ of metabolic exchange
-transient endocrine organ

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2
Q

What are the two main components of the placenta?

A

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

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3
Q

What is the chorion?

A

outermost layer of placenta in direct contact with endometrium

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4
Q

What is the allantochorion?

A

fusion of allantois and chorion

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5
Q

What is the allantoic cavity?

A

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

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6
Q

What is the yolk sac?

A

transient embryonic membrane the contributes to the umbilical cord

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7
Q

What is the amnion?

A

fluid filled inner layer that protects the embryo

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8
Q

Which structures give rise to the chorion and amnion?

A

-trophoblast
-primitive endoderm and mesoderm

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9
Q

What are the components of the blastocyst?

A

-inner cell mass
-trophoblast
-blastocoele

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10
Q

What happens to the yolk sac as the conceptus develops?

A

it regresses in size

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11
Q

What is the functional unit of the fetal placenta?

A

chorionic villus

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12
Q

What is the role of the chorionic villus?

A

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

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13
Q

What are the characteristics of diffuse placentas?

A

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

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14
Q

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

A

the chorionic villi are concentrated in specialized microzones known as microcotyledons

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15
Q

What are the characteristics of zonary placentas?

A

-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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16
Q

What are the characteristics of cotyledonary placentas?

A

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

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17
Q

What are the characteristics of discoid placentas?

A

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

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18
Q

What are the characteristics of an epitheliochorial placenta?

A

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

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19
Q

How do ruminant epitheliochorial/syndesmochorial placentas differ?

A

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

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20
Q

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

A

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

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21
Q

What are the characteristics of an endotheliochorial placenta?

A

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

22
Q

What are the characteristics of a hemochorial placenta?

A

-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

23
Q

Which methods of transport are utilized in placental exchange?

A

-simple diffusion
-facilitated transport
-active transport
-endocytosis

24
Q

What is the major source of energy for the fetus?

A

glucose derived from maternal circulation

25
Q

Which proteins are able to cross the placental barrier?

A

immunoglobulins

26
Q

Which placenta types allow for the transfer of immunoglobulins?

A

-hemochorial
-endotheliochorial

27
Q

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

A

-proteins
-lipids

28
Q

Which molecules can easily cross the placenta?

A

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

29
Q

Why is progesterone important for early embryonic development?

A

-stimulates elevated secretion from endometrial glands
-inhibits myometrial contractions

30
Q

What are the two sources of progesterone during pregnancy?

A

-CL first
-placenta later

31
Q

When does the placenta produce estrogens?

A

second half of gestation

32
Q

What are the characteristics of endometrial cups?

A

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

33
Q

What are the roles of equine chorionic gonadotropin?

A

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

34
Q

What are the characteristics of human chorionic gonadotropin?

A

-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

35
Q

What are the characteristics of relaxin?

A

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

36
Q

What are the roles of placental lactogen/somatomammotropin?

A

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

37
Q

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

A

-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

38
Q

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

A

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

39
Q

What are the functions of estradiol in parturition?

A

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

40
Q

What are the functions of PGF2a in parturition?

A

-abolish progesterone block
-stimulate myometrial contraction

41
Q

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

A

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

42
Q

What are the three stages of labor?

A

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

43
Q

What are the characteristics of parturition stage 1?

A

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

44
Q

What are the clinical signs of parturition stage 1?

A

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

45
Q

What are the characteristics of parturition stage 2?

A

-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

46
Q

What are the causes of dystocia?

A

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

47
Q

What are the characteristics of parturition stage 3?

A

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

48
Q

How can pregnancy be diagnosed?

A

-palpation
-imaging
-endocrine testing

49
Q

Why is it critical that the neonate ingest colostrum?

A

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

50
Q

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

A

epitheliochorial

51
Q

How does colostrum compare to normal milk?

A

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

VMP824 Physiology/Microanatomy 2 (50 decks)

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