2. the corpus luteum Flashcards
what is the corpus luteum
- highly vascularised, transient endocrine gland
- solid
- progesterone production
what is luteinisation
- the formation of the CL
- process where granulosa and theca cells are transformed into luteal cells
which hormone causes ovulation and subsequent development and maintenance of the CL
LH
what is a luteotroph
a hormone that stimulates the CL
what is luteolysis
process whereby luteal tissue undergoes regression and cell death
how does the CL form
- after ovulation (follicle bursts
- basement membrane breaks down –> mixing of granulosa and theca cells
- luteinisation and migration: granulsa becomes large luteal cell, theca = small
- rapid ptoliferation and hypertrophy
- intense angiogenesis
- steroidogenesis switch and increase (oestradiol –> progesterone)
which hormones support the growth and function of the CL in different species
- LH in ruminants, sows and mares
- prolactin in rodents
- IGF-1, growth hormone and PGE2 also play a role
how does the CL produce progesterone
- both large and small luteal cells produce progesterone (but differ in their capacity and regulation)
- large luteal cells: make the majority of the progesterone
- stimulated by LH (small luteal cells only)
- key regulatory step transfers cholesterol into mitochondria (critical factor = StAR)
what are the target organs for progesterone
- uterus
- hypothalamus
- mammary
what are the function of progesterone
- progesterone is of major importance in the endocrine control of reproduction
- negative feedback of progesterone on hypothalamus
- reduces GnRH, LH and FSH pulsatility
- limits preovulatory follicle development and oestradiol production
- prevents oestrus behaviour
- prevents the LH surge
- promotes alveolar development in mammary gland prior to partuition
- growth of uterine glands and their secretions to support early embryo
- inhibits myometrial contractility
when does the CL regress and what does this process enable
- in the absence of fertilisation, luteolysis is induced
- luteolysis is the structural and functional degradation of the CL
- enables release from negative feedback on GnRH
- enables pre-ovulatory follicular development –> ovulation
- return to oestrus
what happens structurally in the regression of the CL
- reduced blood flow
- increase in macrophages and lymphocytes
- apoptosis and tissue resorption
- corpus albicans (remnant) forms
how does the CL regression functionally during lutolysis
- down regulation of steroidogenic enzymes
- rapid fall in progesterone
what is the key luteolytic hormone
prostaglandin F2alpha
in ruminants, pigs and horses which additional hormonal communication occurs during luteolysis
CL produces oxytocin
- receptors present in the uterine endometrium for oxytocin
- oxytocin binds
- PGF2a released by the uterine endometrium
- PGF2a = luteolysis
how is luteolysis initiated
- luteal cells secrete oxytocin pulses
- stimulates endometrial PGF2a
- in a positive feedback look
- endometrial oxytocin receptors increase throughout luteal phase
- until PGF2a becomes sufficient to cause luteolysis
- utero-ovarian vascular counter current system important in some speces to ensure local delivery of PGF2a (prevents from going into circ. diffuse from high concentration vessel to nearby low concentration vessel)
discuss why the CL only responds to PGF2a at certain times
- depends of PGF receptor expression
- important pharmalogical manipulation tool to manage timing of reproduction
