Placenta and pregnancy hormones

state 6 roles the placenta does for the embryo

1. lungs

2. gut

3. kidney

4. liver

5. endocrine

6. protective

describe the pattern of growth of the placenta

• most placental growth in the first half of pregnancy

• its efficiency increases in the last trimester as most foetal growth takes place there

what helps to mediate the efficiency of the placenta in the last trimester

• increased uterine and umbilical blood flo

how do most substances move across the placenta

• passive diffusion

State 5 factors that affect diffusion across the placenta

1. blood flow

2. structure

3. morphology

4. electrical gradient

5. concentration gradient

how does blood flow affect placental diffusion

• volume and efficiency

how does placental structure affect diffusion

• surface area

how does morphology affect placental diffusion

• tissue barriers against exchange

how does the electrical gradient affect diffusion in the placenta

• slight -ve charge encourages +ve ions

which placental histology has the:

1. least

2. middle

3. most

efficient structure for exchange of nutrients

1. epitheliochorial

2. endotheliochorial

3. haemochorial

name 2 substances that require active transport across the placenta

• amino acids

• glucose

how is the transport of amino acids and glucose determined?

• passive mechanisms

• activity of specific carrier molecules

• energy available

which glucose transporter becomes more important during gestation

• GLUT-3

what are 5 reasons the placenta produces hormones

1. stimulate ovarian/uterine function

2. maintain pregnancy

3. modulate foetal growth

4. assist in parturition

5. stimulate mammary function

which hormone is essential for gestation?

• progesterone

what produces progesterone?

• CL

• also the placenta in some species - either entirely or normally, only partly

what stimulates progesterone production

• LH

• prolactin

• oestrogens

what inhibits luteal prodcution

• PGF2a

what are 3 functiosn of progesterone

• production of histotroph, uterine milk proteins

• suppresses myometrial contractility

  • mammary gland development

what will induce an abortion?

• progesterone antagonists

which 5 species have luteal progesterone throughout gestation

• bitch

• queen

  • sow

  • rabbit

  • goat

which species have the placenta ‘take over’/support progesterone production

• human

• mare

• ewe

• cow

how does length of gestation link to placental progesterone support?

• the longer the gestation, the more likely the placenta will support/take over progesterone production

what produces oestrogens in the placenta?

• foetal cotyledone - trophoblast cells

what are 5 functions of oestrogens in pregnancy

1. stimulate placental growth

2. increase uterine blood flow

3. stimulate myometrial growth

4. prepare parturition

5. stimulate mammary development

what is prolactin produced by?

• anterior pituitary gland and placenta

what inhibits prolactin

• dopamine

what stimulates prolactin

• oestradiol

what is the function of prolactin on the CL

• stimulates progesterone

what is the function of prolactin on the mammary gland

• induces lobuloalveolar growth

• lactogenesis

besides acting on the CL and mammary gland, what other effect does prolactin have?

• stimulates maternal behaviour

what is relaxin produced by?

• placenta

• (CL)

which species produces prolactin in the CL

• sow

which species produce prolactin from the placenta?

• rabbit

• mare

• dog

• cat

what equivalent of relaxin is produced by cattle?

• relaxin like factor

do cows produce relaxin?-

• no, they produce a prolactin-like factor

what are 3 actions of relaxin

• soften connective tissue, enabling foetus growth

• relax pelvic ligaments

• parturition

what can we use relaxin for in dogs and cats?

• pregnancy test

why is relaxin used as a pregnancy test in some species

• it’s only produced by the placenta therefore has to be from a pregnant animal

what is placental lactogen

• similar to PRL

• produces BNC, modulates foetal metabolism and mammary gland development

which receptors does placental lactogen bind to?

• prolactin receptors

what is placental lactogen released into

• maternal and foetal circulation

what are 2 other placental hormones used for pregnancy diagnosis in ruminants

• pregnancy specific protein B - PSPB

• pregnancy associated glycoprotein - PAG

what are the following hormones produced by

• pregnancy specific protein B - PSPB

• pregnancy associated glycoprotein - PAG

• binucleate cells

Which hormone is which

• blue = eCG

• red = progesterone (CL then placenta, hence drop)

• pink = total oestrogens - placenta

what are endometrial cups in the mare formed from?

• invasion of foetal trophoblast cells

what do endometrial cups in the mare produce?

• equine chorionic gonadotrophin

what does eCG act like?

• FSH and LH

how does eCG initially work?

• increases progesterone from primary CL for a limited time

what does eCG induce?

• formation of accessory CL

what happens to the accessory CL formed by eCG

• loses activity and causes a decline in plasma progesterone

if progesterone is needed for pregnancy but the induced CL in mares regresses, how is the amount of progesterone needed, maintained?

• placental progesterones are produced and act locally, so don’t enter main circulation

what is the main progesterone in the mare

• 5-alpha-pregnane

what is the unique oestrogen of the mare

• foetus produced androgens - dehydroandrosterone

• which is converted by the placenta to oestrogens

outline the endocrinology of the pregnant bitch

• prolonged luteal phase, regardless of if pregnant or not

• placenta produces low amounts of steroids

• luteal P4 dependent on LH and prolactin

why is the level of progesterone higher in the non-pregnant bitch compared to the pregnant bitch

• there’s no foetus to induce parturition therefore no sudden decline in progesterone, so it lasts longer

what hormone increases at parturition

• prolactin

describe the production of progesterone in the pregnant queen

• rapid rise and diverges from non-pregnant at 21 days

• placenta produces some P4 but it’s insufficient to maintain pregnancy, therefore rapid fall before parturition

what 2 other hormones (not P4) are produced by the queen to aid with parturition

• relaxin

• prolactin

up to how long can we use PGF2a in the following species to terminate pregnancy

• cow

• up to 150 days

why can’t we use PGF2a in cows after around 150 days

• placenta takes over and produces enough progesterone itself for PGF2a to have an effect

up to how long can we use PGF2a in the following species to terminate pregnancy

• ewe

• up to 45 days

up to how long can we use PGF2a in the following species to terminate pregnancy

• sow

• throughout pregnancy

up to how long can we use PGF2a in the following species to terminate pregnancy

• mare

• up to 35 days

why can’t we use PGF2a in mares after 35 days?

• endometrial cups

up to how long can we use PGF2a in the following species to terminate pregnancy

• goat

• bitch

• queen

• throughout pregnancy

why would we not choose to use PGF2a to terminate a pregnancy in a bitch/queen after mid-pregnancy, even though we can

• causes unacceptable side effects