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REPRO > Placentation > Flashcards

Placentation Flashcards

1
Q

Which species have a luteo-placental shift?

A

Horses, sheep, humans, cows

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2
Q

What is the luteo-placental shift

A

Shift in production of progesterone from luteal to placental

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3
Q

How does the luteoplacental shift affect the use of PGF2a to terminate pregnancy?

A
  • If shift occurs, PGF2a can only be used to terminate pregnancy before the shift
  • If there is no shift, then PGF2a can always be used to terminate pregnancy
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4
Q

What is a placenta?

A

The close attaachment of foetal membranes to the uterine wall to facilitate physiological exchange of gases, nutrients and waste products

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5
Q

Name the foetal membranes

A
  • Amnion
  • Yolk sac
  • Allantois
  • Chorion
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6
Q

Describe the amnion

A
  • Innermost fluid filled membrane (reptile, bird, mammal)
  • Allows symmetrical growth and protection of the foetus
  • Temperature control and foetal movement
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7
Q

Describe the yolk sac

A
  • Surrounds yolk in reptile and bird eggs

- In higher mammals has nutritional role in early pregnancy

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8
Q

Describe the allantois

A
  • Sac from hindgut
  • Connection to foetus becomes umbilical cor
  • Collects waste products from foetus
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9
Q

Descibe the chorion

A
  • Outer membrane
  • Becomes foetal contribution to placenta
  • All placentas are chorionic at some stage of development
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10
Q

What are the layers in the submucosa of the uterine wall?

A

Perimetrium, myometrium, endometrium

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11
Q

What are the 3 stages of implantation?

A

Apposition, adhesion, firm attachment or invasion of trophoblast into uterus

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12
Q

Describe apposition

A

Blastocyst or foetal membranes become closely apposed to uterine lining (epithelium)

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13
Q

Describe adhesion

A

Complex biochemical interaction between molecules on the trophoblast and epithlium

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14
Q

Outline firm attachment or invasion of trophoblast into uterus

A

On species, can be non-invasive or invasive

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15
Q

Describe non-invasive attachment of trophoblasts to uterus

A
  • Cow, sheep
  • Blastocyst undergoes elongation, long when attaches to uterus
  • During apposition aligns with lining of uterus
  • During attachment trophoblast layer in contact with uterine epithelium
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16
Q

Describe invasive attachment of trophoblasts to uterus

A
  • Quickly after arrival of blastocyst to uterus
  • Blastocyst remains spherical
  • Invades uterine lining following apposition and attachment
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17
Q

What needs to occur to allow invasive attachment of the blastocyst?

A
  • Specific window of time

- Presence of proteoglycan MUC1 needs to be down-regulated to allow attachment

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18
Q

What are the different methods of classification of placental structure?

A
  • Foetal extraembryonic membranes
  • Source of nutrition
  • Maternal tissue shedding at birth
  • Histological structure
  • Macroscopic structure
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19
Q

What are the different types of nutrition possible in the placenta?

A
  • Haemotrophic: nutrition from circulating maternal blood

- Histotrophic: nutrition from endometrium

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20
Q

What are the different types of maternal tissue shedding at birth?

A
  • Deciduate vs non deciduate

- Deciduate: lining of uterus shed with lining of placenta at parturition

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21
Q

How can histological structure be used to calssifies placentas?

A

Different number of tissue layers interposed between maternal and foetal circulations

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22
Q

How can macroscopic anatomy of placentas be used for classification?

A
  • Nutrient exchange areas
  • Distribution of chorionic villi on chorionic sav and relationship with endometrium
  • e.g. diffuse, cotyledonary, zonary
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23
Q

What are the placental classifications based on the number of tissue layers (Grosser classification)?

A
  • Epitheliochorial
  • Endotheliochorial
  • Mesochorial
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24
Q

What are the 3 foetal layers of the placenta? (moving towards the maternal side)

A
  • Foetal blood vessel endotehlium
  • Foetal connective tissue/mesenchyme
  • Foetal trophoblast
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25
Q

What are the 3 possible maternal layers of the placenta? (moving towards the foetal side)

A
  • Maternal blood vessel endothelium
  • Maternal connective tissue/mesenchyme
  • Maternal epithelium
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26
Q

What layers are present in the epitheliochorial placenta?

A

All 3 foetal and all 3 maternal layers

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27
Q

Describe the epitheliochorial placenta

A
  • 6 layers between blood circulations
  • Present in sow and mare
  • Least invasive type of placenta
  • Chorion in contact with epithlium of maternal uterine wall
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28
Q

What layers are present in the endotheliochorial placenta?

A
  • 3 foetal

- 1 maternal (maternal blood vessel endothelium)

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29
Q

Describe the endotheliochorial placenta

A
  • Chorion in contact with endothelium of maternal blood vessel
  • 4 layers present
  • Present in bitch, queen
  • Specialised version in ruminant
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30
Q

How many layers are present in the haemochorial placenta?

A

3 - only foetal layers

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31
Q

Describe the haemochoral placenta

A
  • Endothelial cell layer around blood vessel incomplete
  • Pool of maternal blood direclty in contact with the chorion
  • Foetal layer thicker as more trophoblasts present
  • Humans, primates, mice
  • Most invasive
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32
Q

What are the classifications based on type of nutrient exchange area in the placenta?

A
  • Diffuse
  • Cotyledonary
  • Zonary
  • Discoid
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33
Q

What is the function unit of the foetal placenta?

A

The chorionic villus

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34
Q

Describe the appearance of the chorionic villus

A
  • Normally quite visible

- Interdigitation between villi of chorion and endometrium

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35
Q

Describe placentas with a diffuse nutrient exchange area

A
  • Sow and mare
  • Villi attach to crypts in endometrium
  • Mare forms micro-cotyledons
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36
Q

Describe cotyledonary nutrient exchange areas

A
  • Cow and ewe

- Cotyledons attach to caruncles to form a placentome

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37
Q

Describe zonary nutrient exchange areas

A
  • Bitch and queen

- Band around middle of foetus on chorioallantoic membrane

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38
Q

Describe discoid nutrient exchange areas

A
  • Humans and primates

- Plate shape/discoid arrangement of villi

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39
Q

Describe the placenta of the sow

A
  • Epitheliochorial
  • Diffuse
  • Non-deciduate
  • Embryotroph
  • By day 24, allantois around the periphery of the embryo
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40
Q

Describe the uterine milk in sows

A
  • Secretions important for development
  • High P4 and E2
  • Uteroferrin important for nutrition and Fe transport
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41
Q

Describe the placenta found in the ewe and cow

A
  • Synepithliochorial
  • Cotyledonary
  • Non-deciduate
42
Q

Explain synepitheliochorial placentation

A
  • Specialised epitheliochorial pacenta
  • Uninucleate trophoblast cells undergo division without cytokinesis = binucleate giant cells with small granules
  • Migrate to maternal layer, fuse with maternal cells
  • Produce hybrid cell
  • Once fused, release contents into maternal circulation
43
Q

What is contained within the granules of the binucleate cels?

A

Placental lactogen

44
Q

Describe placentomes

A
  • Foetal cotyledon + materna caruncle
  • Can be convex or concave
  • Are the exchange regions in the placenta
  • Each placentome connected to umbilicus by a chorionic stalk
45
Q

Describe a convex placentome

A
  • Found in cow

- Cotyledon sits on top of and surrounds the caruncle

46
Q

Describe a concave placentome

A
  • Sheep, goat

- Cotyledon sits within the caruncle

47
Q

Describe the placenta found in horses

A
  • Epitheliochorial, diffuse, non-deciduate
  • Forms endometrial cups
  • Microcotyledons on chorioallantoic memrbane
48
Q

What do the endometrial cups develop from?

A

Chorionic girdle cells

49
Q

Describe the microcotyledons found in equine placentas

A
  • Fit into mini-crypts in endometrium
  • Small collections of villi
  • See around week 8 gestation onwards
  • Rough appearance of inside of placenta
50
Q

Describe the formation of the chorionic girdle

A
  • Choriovitelline forms in secnd week of pregnancy
  • 4th week, chorioallantioc begins to form
  • Around 30 days have both together
  • Junction between these forms the chorionic girdle
  • Yolk sac regresses (mostly disappeared at day 50), leaves girdle
51
Q

What is the function of the chorionic girdle in horses?

A

Is what implants into the uterus (and forms endometrial cups)

52
Q

Describe teh formation of the endometrial cups

A
  • Cells from girdle invade maternal endometrium
  • Destroy epithelium
  • Bunch up and form endometrial cups
  • Secrete equine chorionic gonadotrophin (eCG)
  • LImited life span
  • Invade at day 38-40
  • Leukocytes gather around edge of cups
  • Around day 100, these invade into cups and destroy, slough from lining of uterus
53
Q

Describe the placenta in the dog

A
  • Endotheliochorial
  • Zonary
  • Deciduate
54
Q

What are the zones of the canine placenta?

A
  • Transfer zone in middle (chorionic villi)

- Pigmented zone either side of transfer zone

55
Q

What is the function of the pigmented zone?

A

Iron transfer

56
Q

Describe the human placenta

A

Haemochorial, invasive, deciduate, discoid

57
Q

Describe the decidual tissue of the human placenta

A
  • Endometrial stromal cells proliferate and enlarge to become decidual cells
  • Decidua is the maternal placenta and is shed when foetus is delivered
  • Decidual tissue important in communication between mother and foetus
  • Limits invasion of trophoblasts
58
Q

What fluid predominates in human pregnancy?

A

Amniotic, not allantoic

59
Q

What are the exchange zones in human placenta?

A
  • Pools of maternal blood in these zones

- Is area where nutrient and waste exchange takes place

60
Q

Between what structures does the umbilical cord run?

A

Placenta and foetus

61
Q

What does the umbilical vein carry?

A

From palcenta, carrying oxygenated blood

62
Q

Describe blood flow from the umbilical vein

A
  • From placenta through umbilical vein
  • Bypasses liver via ductus venosus, into cauda vena cava, into right atrium, left atrium, aorta , systemic circulation, cranial vena cava, into ventricle ductus arteriosus to bypass pulmonary and back to placenta via umbiliac arteries
63
Q

What are the umbilical arteries derived from?

A

The interna iliac arteries

64
Q

Where are the umbilical arteries located?

A

Either side of the foetal bladder

65
Q

What is the true placenta?

A

The allantochorion

66
Q

How is each piglet a separate unit in utero?

A
  • Uterine horn convoluted forming pockets, each of which contains a piglet
  • Each foetus has own foetal membranes
  • Each end of the unit is necrotic
  • Glue together towards end of pregnancy to form single tube along each horn
67
Q

How is free-martinism avoided in pigs?

A
  • Tips of each piglet unit are necrotic

- Prevents vascular anastomoses between units

68
Q

What colour is the amniotic fluid?

A

Clear

69
Q

What is the function of hormones produced by the placenta?

A

Prepare for lactation

70
Q

How long can the uterine tract of the pig get during gestation?

A

2m long

71
Q

Describe the expulsion of the placenta in the mare at birth

A
  • Foetus breaks through cervial start of placenta, descends into vagina, umbilicus goes with it
  • Placenta loosely attached to endometrium and so is pulled inside out
72
Q

What may occur if some of the placenta is retained in mares?

A
  • Bacterial proliferation

- Bacterial toxins enter blood, damage laminae of hoof wall leading to laminitis

73
Q

Differentiate between the amniotic cavity and the allantoic cavity

A
  • Amniotic cavity is between amnion and foetus

- Allantoic cavity is within the allantois

74
Q

Where does the umbilical cord arise?

A

From bilaminar omphlopleur (bounded by sinus terminalis of conceptus)

75
Q

Describe the vessels within the umbilical cord

A
  • 2 veins fuse to one vein at amnion

- 2 arteries that run into the placenta

76
Q

Where does the umbilical cord enter the foetus?

A

Via the urachus

77
Q

What happens in the umbilical cord at birth?

A
  • Umbilicus snapped, but is full of arterial blood
  • Smooth muscles very responsive to stretch
  • Contract to prevent blood loss
  • Is irreversible and cuts of blood supply so animal needs to breath for oxygen
78
Q

List the functions of the placenta:

A
  • Replaces the function of adult organs
  • Lungs: delivery of gases
  • Gut: delivery of nutrients
  • Kidney: excretion of waste products
  • Liver: storage/reservoir of energy
  • Endocrine: placental derived hormones
  • Protective: toxic substances, some immune function
79
Q

Describe placental blood flow

A

Increase in uterine and umbilical blood flow increase as gestation progresses

80
Q

Compare foetal and placental growth during gestation

A
  • Foetus grows in size
  • Placenta has some, but limited increase in weight
  • Suggests foetal growth related to increased blood flow rather than increased size of placenta
81
Q

Describe the cotyledonary microvascular density as pregnancy progresses

A
  • Increases to match foetal growth
  • Vascular density in both compartments of placentome increases
  • Dramatic increase in cotyledon, less dramatic increase on caruncular side
82
Q

Broadly, what are the transport mechanisms for nutrients and waste across the placenta?

A
  • Passive

- Active

83
Q

What affects the passive diffusion of gases, fatty acids, alcohol and drugs across the placenta?

A
  • Blood flow (volume and nature)
  • Structure (area for exchange)
  • Morphology (tissue barriers against exchange, number of layers)
  • Electrical gradient (slight, -ve charge encourages +ve charged ions)
  • Concentration gradient (maternal to foetal blood gradient for exchange)
84
Q

Compare the pH in adult and foetal blood

A

Higher [H+] hence lower pH in foetal

- 7.50 vs 7.35

85
Q

Compare partial pressure of oxygen in adult and foetal blood

A
  • Higher partial pressure of oxygen in adult
  • Aids diffusion across from adult blood to foetal blood down
    concentration gradient
  • 100 vs 25 mmHg
86
Q

Compare oxygen saturation of Hb in adult and foetal blood

A
  • Foetal Hb has higher affinity for oxygen than adult Hb

- Saturation of Hb occurs at lower partial pressures of oxygen (70% vs 95%)

87
Q

Compare partial pressure of Co2 in adult and foetal blood

A
  • Higher in foetus
  • Aids diffusion to mother for removal
  • 35 vs 50 mmHg
88
Q

Compare amount of Hb in adult and foetal blood

A
  • Higher in adult

- 15 vs 8 g/dl

89
Q

What are the different types of placental blood flow? (going from least to most efficient)

A
  • Concurrent
  • Multivillous
  • Crosscurrent
  • Countecurrent
90
Q

Describe the countercurrent blood flow found in rabbits

A
  • Blood from umbilical artery splits into network of vessels
  • Blood from mother flows into distended sinuses that fill with blood
  • Maternal blood washes against foetal tissue, blood flows are in oppposite directions to each other
  • Facilitates exchange
91
Q

Rank the types of placenta using Grosser classification from lowest to highest transfer efficiency

A
  • Epitheliochorial
  • Endotheliochorial
  • Haemochorial
  • I.e. more layers = less efficient transfer
92
Q

Describe the electrochemical gradient of the placenta

A
  • Generated by endometrium and placenta
  • May influence mineral transfer
  • Is given with respect to maternal fluid
  • Varies by species
93
Q

Explain how the concentration used for glucose transfer is established

A
  • INcreased O2 consumption later in gestation
  • Drives increased gradient to encourage further maternal glucose transfer to foetus
  • In maternal blood, higher glucose than foetus
  • Increased energy useage maintains steep gradient to facilitate transfer
94
Q

What nutrients are transferred using active transport?

A

Amino acids and glucose

95
Q

What is the active transport of nutrients across the placenta determined by?

A
  • Passive mechanisms

- density and activity of carrier molecules for amino acids and glucose

96
Q

Describe amino acid transport

A
  • Require transport from apical to basal membrane
  • 2 stages: uptake, transport into trophoblast, release into foetal circulation
  • Capacity, exhcange surface area and density increase with time to meet demands
  • Range of transporters present
97
Q

Describe placental glucose transport

A
  • Specific transproters
  • GLUT family
  • GLUT-1 primary isoform, GLUT-3 important in rats and sheep
  • High density of transporters on maternal aspect (microvillous membrane), lower density on basal membrane
  • Density on basal membrane is the rate limiting step for transport
  • IUGR can be caused by reguced glucose transport due to lack of transproters
98
Q

What is IUGR?

A

Intra-uterine growth restriction

99
Q

What are the types of anastomoses that can occur leading to Freemartinism?

A
  • Arteriovenous
  • Arterio-arterial
  • Veno-venous
100
Q

Explain how Freemartinism occurs in cattle

A
  • Anastomosis of allantoic vessels

- Usually single chorionic cavity

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