3. placental function and endocrinology of pregnancy Flashcards
match the placentas to the species and name the placenta type
left to right
- pig/horse: epitheliochorion, diffuse
- rodent/rabbit/primate: hemochorion, discoid
- dog/cat: endotheliochorion, zonary
- cow/sheep: synepitheliochorion, cotyledory
what is the function of the placenta
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)
when does the majority of placental growth occur
first half of pregnancy
most of the fetal growth occurs in the last trimester. what must the placenta therefore do
increase efficiency with gestation to support fetal growth
- partly mediated by increased uterine and umbilical blood flow
what factors influence the process of passive diffusion across the placenta
- 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)
describe which type of placenta has the greatest efficiency
- the more layers there are to go through, the less efficient
explain active transfer across the placenta
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)
why are hormones essential for the placenta
- stimulate ovarian/uterine function
- maintain pregnancy
- modulate fetal growth
- assist in partuition
- stimulate mammary function (timing)
explain progestogens in pregnancy
- 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
outline where prgesterone comes from during the duration of pregnancy
- corpus luteum is the source of progesterone for the first part of pregnancy
- in some species the placenta will produce/take over progesterone
in which species will the placenta take over for progesterone production in pregnancy
- mare
- ewe
- cow
- primate
discuss the importance of oestrogens in pregnancy
- 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)
discuss the importance of prolactin in pregnancy
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
outline the importance of relaxin during pregnancy
- 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
why do mares struggle to carry twins full term
relies on diffuse nutrient transfer and aurface area of the placentas - not enough room for 2
what is placental lactogen, where is it produced and what is its function in pregnancy
- 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
list some specific pregnancy hormones in ruminants and where are they produced/what can they be used for
- 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
which pregnancy hormones are specific to the mare and why are the relevent
- eCG always secreted in the first part of pregnancy
why is progesterone low around day 200
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
what are endometrial cups
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
how does eCG increase progesterone activity in pregnancy
- 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
list unique progestogens and oestrogens in the mare
- main progestogen is 5-alpha-pregnane
oestrogens:
- fetus produces androgens (DHA)
- converted by placenta to oestrogens
outline pregnancy endocrinology in the bitch
- 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
discuss endocrinology of the pregnant queen
- 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
when is pgf2a definitely effective at termination of pregnancy across the species
