3. placental function and endocrinology of pregnancy

Question 1

match the placentas to the species and name the placenta type

Answer 1

left to right
- pig/horse: epitheliochorion, diffuse
- rodent/rabbit/primate: hemochorion, discoid
- dog/cat: endotheliochorion, zonary
- cow/sheep: synepitheliochorion, cotyledory

Question 2

what is the function of the placenta

Answer 2

replaces the function of the adult:
- lungs (delivery of gasses)
- gut (delivery of nutrients)
- kidney (excretion of waste products)
- liver (storage/reservoir of energy)
- endocrine (placental derived hormones)
- protective (toxic substances)

Question 3

when does the majority of placental growth occur

Answer 3

first half of pregnancy

Question 4

most of the fetal growth occurs in the last trimester. what must the placenta therefore do

Answer 4

increase efficiency with gestation to support fetal growth
- partly mediated by increased uterine and umbilical blood flow

Question 5

what factors influence the process of passive diffusion across the placenta

Answer 5

• blood flow (volume and nature)
• structure (area for exchange)
• morphology (tissue barriers against exchange)
• electrical gradient (slight -ve charge encourages =ve charged ions
• concentration gradient for exchange (maternal to fetal blood)

Question 6

describe which type of placenta has the greatest efficiency

Answer 6

• the more layers there are to go through, the less efficient

Question 7

explain active transfer across the placenta

Answer 7

some nutrients cannot get through the placenta by passive transport and need to use active transport ( amino acids and glucose)
- determined by passive mechanism plus
- activity specific carrier molecules for amino acids and glucose
- net transfer is maternal to fetal direction (works against conentration gradient, hence energy required)

Question 8

why are hormones essential for the placenta

Answer 8

• stimulate ovarian/uterine function
• maintain pregnancy
• modulate fetal growth
• assist in partuition
• stimulate mammary function (timing)

Question 9

explain progestogens in pregnancy

Answer 9

• produced by CL and in some species placenta
• stimulated by LH, prolactin and oestrogens
• luteal production inhibited by pgf2a
• stimulate production of histotroph, uterine milk proteins
• suppress myometrial contractility
• stimulate mammary gland development
• progesterone principal hormone (but are others)
• progesterone antagonists will indice abortion

Question 10

outline where prgesterone comes from during the duration of pregnancy

Answer 10

• corpus luteum is the source of progesterone for the first part of pregnancy
• in some species the placenta will produce/take over progesterone

Question 11

in which species will the placenta take over for progesterone production in pregnancy

Answer 11

• mare
• ewe
• cow
• primate

Question 12

discuss the importance of oestrogens in pregnancy

Answer 12

• distinct oestrogens produced by placenta (oestrone in ruminants, equine specific oestrogens)
• produced by fetal cotyledons (trophoblast cells)

function: growth promoters
- stimulate placental growth
- increase uterine blood flow
- stimulate myometrial growth
- preparation for parturition
- stimulate mammary development

horse churning out TONS of oestrogens mid pregnancy (no oestradiol)

Question 13

discuss the importance of prolactin in pregnancy

Answer 13

produced by the lactotrophs in the anterior pit gland and placenta
- inhibited by dopamine
- stimulated by oestradiol

function:
- on the CL in rodents and dogs, it stimulates progesterone
- on the mammary glands: induces lobuloalveolar growth (secrete milk) and lactogenesis
- stimulates maternal behavriour

Question 14

outline the importance of relaxin during pregnancy

Answer 14

• produced by the CL in some species and the placenta only (dog, cat, rabbit, mare)
• an equivalent hormone produced in cattle (relaxin like factor)

function:
- softening of tissue enabling growth of fetus
- relaxation of pelvic ligaments
- partuirition (stimulated by pgf)
- used to diagnose pregnancy in dogs and cats

Question 15

why do mares struggle to carry twins full term

Answer 15

relies on diffuse nutrient transfer and aurface area of the placentas - not enough room for 2

Question 16

what is placental lactogen, where is it produced and what is its function in pregnancy

Answer 16

• similar to prolactin (will bind to prolactin receptors)
• produced by binucleate cells and released into maternal and fetal circulation
• modulates fetal metabolism
• stimulates mammary gland development

Question 17

list some specific pregnancy hormones in ruminants and where are they produced/what can they be used for

Answer 17

• pregnancy specific protein B
• pregnancy associated glycoprotein
• produced by binucleate cels only
• only present in the pregnant animal
• can be used for pregnancy diagnosis in cattle
• only present from day 35

Question 18

which pregnancy hormones are specific to the mare and why are the relevent

Answer 18

• eCG always secreted in the first part of pregnancy

Question 19

why is progesterone low around day 200

Answer 19

produced by placenta
- different progesterones produced and they do not leave the placenta into circulation
- therefore no detection of progesterone in plasma so not shown on graph

Question 20

what are endometrial cups

Answer 20

specific to mare
- placental discrete outgrowths
- formed from invasion of fetal trophoblast cells
- appear around 40 days
- produce eCG –> fundamental in pregnancy. sole function is to produce eCG

Question 21

how does eCG increase progesterone activity in pregnancy

Answer 21

• eCG has FSH and LH like activity
• FSH stimulates follicles, LH initially increase progesterone from primary CL
• ovulate secondary/accessory CLs, egg not important but new CLs will produce progesterone then placenta produces local progesterones –> (ovulates and is pregnant then still allows more follicles to grow to turn them into more CLs to make more progesterone)
• eCg increases progesterone from primary CL for limited time
• then eCG will indice formation of accessory CL2
• but eventuallt these lose activity and plasma progesterone declines
• placental progesterones support remainder of pregnancy
• unique progestogens that act locally

Question 22

list unique progestogens and oestrogens in the mare

Answer 22

• main progestogen is 5-alpha-pregnane

oestrogens:
- fetus produces androgens (DHA)
- converted by placenta to oestrogens

Question 23

outline pregnancy endocrinology in the bitch

Answer 23

• prlonged luteal phase whether pregnant or not
• placenta produces low amounts of steroids
• luteal progesterone dependent on LH and prolactin
• CL source of progesterone throughout in bitch
• remains longer in non-pregnant animal than in pregnant

Question 24

discuss endocrinology of the pregnant queen

Answer 24

• rapid rise in progesterone and divergent from non-pregnant at 21 days
• placenta capable of producing some progesterone but
• insufficient to maintain pregnancy
• rapid fall prior to parturition
• relaxin and prolactin also produces
• rapid rise in progesterone if not pregnant after ovulation. first 20/21 days have similar profiles to pregnant/non pregnant
• progesterone decline triggers prolactin to sustain some progesterone development
• luteal phase 45 days in non-preg

Question 25

when is pgf2a definitely effective at termination of pregnancy across the species

Answer 25